US20140264998A1 - Methods for manufacturing three-dimensional metamaterial devices with photovoltaic bristles - Google Patents

Abstract

Various stamping methods may reduce defects and increase throughput for manufacturing metamaterial devices. Metamaterial devices with an array of photovoltaic bristles, and/or vias, may enable each photovoltaic bristle to have a high probability of photon absorption. The high probability of photon absorption may lead to increased efficiency and more power generation from an array of photovoltaic bristles. Reduced defects in the metamaterial device may decrease manufacturing cost, increase reliability of the metamaterial device, and increase the probability of photon absorption for a metamaterial device. The increase in manufacturing throughput and reduced defects may reduce manufacturing costs to enable the embodiment metamaterial devices to reach grid parity.

Description

RELATED APPLICATIONS
• This application is a continuation-in-part of U.S. patent application Ser. No. 13/830,295, entitled “Methods for Manufacturing Three Dimensional Metamaterial Devices with Photovoltaic Bristles” filed Mar. 14, 2013, the entire contents of which are hereby incorporated by reference. This application is also related to U.S. patent application Ser. No. 13/751,914, entitled “Three-Dimensional Metamaterial Device with Photovoltaic Bristles” filed Jan. 28, 2013, the entire contents of which are hereby incorporated by reference for purposes of disclosing dimensions, materials and configurations of photovoltaic bristles that may be manufactured by the embodiment processes disclosed herein.
FIELD
• This application generally relates to photovoltaic devices, and more specifically to the methods of manufacturing photovoltaic cells featuring a large number of photovoltaic bristles.
BACKGROUND
• Solar power is a popular clean energy, but it is generally more expensive than its fossil fuel competitors (e.g., oil, coal, and natural gas) and other traditional energy sources (e.g., hydropower). Typically, solar energy is relatively expensive because traditional photovoltaic cells with a planar configuration have generally low total efficiency. Total efficiency is based upon the total power produced from a solar panel throughout the day as the sun transits across the sky. Total efficiency is different from the theoretical efficiency, which is the fraction of light energy converted to electricity by the photovoltaic cells with a zero angle of incidence (e.g., the instant when the sun is directly above the metamaterial). Thus, a high total efficiency photovoltaic cell is needed to make solar energy cost-competitive with fossil fuels and traditional energy sources.
SUMMARY
• The various embodiment methods of manufacturing and assembling may be used to produce photovoltaic cells formed from a plurality of photovoltaic bristles whose photovoltaic and conductive materials are configured to exhibit a high probability of photon absorption and internal reflection. As a result of the high probability of photon absorption and internal photon reflections, the photovoltaic cells of photovoltaic bristles exhibit high total efficiency in converting light energy into electrical energy. The high total efficiency of the embodiment photovoltaic cells may lead to increased efficiency and more power generation from the photovoltaic cell.
• In various embodiments, printing techniques may be used to ensure high throughput and low defects in manufacturing the metamaterial device. The high throughput and low defects may reduce the manufacturing cost to enable the embodiment metamaterial devices to reach grid parity. In various embodiments, arrays of cores or vias may be manufactured from an original master template. An embodiment roll-to-web system and method may create daughter templates or master webs from the original master template to protect the original master template from repeat processing, thereby reducing defects. An embodiment web-to-plate system and method may create an array of cores or vias on a substrate from the master web. The master web, or plate, may be subjected to further processing (depositing photovoltaic layers, conductive layers, etc.) to create the embodiment metamaterial device.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the features of the invention.
• FIG. 1A is a cross-sectional top view of an embodiment photovoltaic bristle.
• FIG. 1B is a cross-sectional side view of an embodiment photovoltaic bristle.
• FIG. 2A is a perspective view of an embodiment metamaterial of an array of photovoltaic bristles positioned on a flat substrate.
• FIG. 2B is a cross-sectional side view of an embodiment metamaterial array of photovoltaic bristles positioned on a flat substrate.
• FIG. 3A is a perspective view of an embodiment metamaterial with arrays of photovoltaic bristles positioned on a corrugated substrate.
• FIG. 3B is a cross-sectional side view of an embodiment metamaterial with arrays of photovoltaic bristles positioned on a corrugated substrate.
• FIG. 4A is a perspective view of an embodiment metamaterial with arrays of photovoltaic bristles positioned on alternating slanted substrate surfaces of a corrugated substrate.
• FIG. 4B is a cross-sectional side view of an embodiment metamaterial with arrays of photovoltaic bristles positioned on alternating slanted substrate surfaces of a corrugated substrate.
• FIG. 5 is an illustration of embodiments shown inFIGS. 2A,3A, and4A positioned on the slanted planes of a structure facing away or towards the equator.
• FIGS. 6A-6H are cross-sectional side views illustrating an embodiment method for forming an array of photovoltaic bristles for a metamaterial device stamping process.
• FIGS. 6I-6K are cross-sectional side views illustrating an embodiment method for forming an array of photovoltaic bristles using a molding process.
• FIGS. 7A,7B, and7C are side views of a molding process embodiment for forming a substrate and form arrays of cores on the shaped substrate.
• FIG. 8 is a process flow diagram illustrating the embodiment methods illustrated inFIGS. 6A-6K and7A-7C.
• FIGS. 9A-9J are cross-sectional side views illustrating an embodiment method a plating process to form an array of bristles for a metamaterial device.
• FIG. 10 illustrates an embodiment plating method for forming the embodiment metamaterials.
• FIGS. 11A-11L are cross-sectional side views illustrating an embodiment method for forming the embodiment metamaterial by creating vias using photolithographic and etching techniques and subsequently removing the original substrate.
• FIG. 12 is a process flow diagram illustrating the embodiment method for forming the embodiment metamaterials illustrated inFIGS. 11A-11L.
• FIGS. 13A-13L are cross-sectional side views illustrating an embodiment method for forming the embodiment metamaterial by creating vias using photolithographic and etching techniques while leaving the etched substrate intact.
• FIGS. 13M-13O are cross-sectional side views illustrating an alternative embodiment method for creating vias using lasers.
• FIG. 14 is a process flow diagram of the embodiment method illustrated inFIGS. 13A-13L.
• FIGS. 15A-15J are cross-sectional side views illustrating an embodiment method for forming the embodiment metamaterial by creating vias using a stamping method and leaving the substrate intact.
• FIGS. 15K-15M are cross-sectional side views for forming the embodiment metamaterial by molding a substrate and leaving the substrate intact.
• FIG. 16 is a process diagram of the embodiment method for forming the metamaterial illustrated inFIGS. 15A-15J.
• FIG. 17 is a cross-sectional side view of an array of photovoltaic bristles positioned on a flat substrate with current conducting traces on top of short photovoltaic bristles.
• FIG. 18 is a top view of the metamaterial ofFIG. 17.
• FIG. 19 is a cross-sectional side view of an array of photovoltaic bristles positioned on a flat substrate with current conducting traces between photovoltaic bristles.
• FIG. 20 is a top view of metamaterial ofFIG. 19.
• FIG. 21 is a cross-sectional side view of an array of photovoltaic bristles positioned on a corrugated substrate with current conducting traces between photovoltaic bristles.
• FIGS. 22A-22H are cross-sectional side views illustrating methods for adding current conducting traces to the outer conductive layer of a metamaterial.
• FIG. 23 is a process flow diagram of the embodiment method for depositing current conducting traces on the outer conductive layer of a metamaterial illustrated inFIGS. 22A-22H.
• FIGS. 24A-24J are cross-sectional side views illustrating methods for adding current conducting traces to an inner conductive layer of a metamaterial.
• FIGS. 24K-24M are cross-sectional side views of methods using a laser prior to adding current conducting traces to an inner conductive layer of a metamaterial.
• FIG. 25 is a process flow diagram of the embodiment method for depositing current conducting traces on an inner conductive layer of a metamaterial illustrated inFIGS. 24A-24J.
• FIG. 26 is a perspective view of embodiment metamaterials in a solar panel section including a corrugated base.
• FIG. 27 is a top view of a section of a solar panel with a corrugated base According to an embodiment.
• FIG. 28 is a side view of a section of a solar panel with a corrugated base according to an embodiment.
• FIG. 29 is an exploded view of a section of a solar panel with a corrugated base according to an embodiment.
• FIG. 30 is a back view of a section of a solar panel with a corrugated base according to an embodiment.
• FIG. 31 is a perspective view of a solar panel according to an embodiment.
• FIG. 32 is an exploded view of a solar panel according to an embodiment.
• FIGS. 33A-33G are cross-sectional side views illustrating an embodiment method for forming an array of photovoltaic bristles for a metamaterial device stamping process.
• FIG. 34 is a process flow diagram illustrating the embodiment method illustrated inFIGS. 33A-33G.
• FIG. 35A is a system diagram illustrating an embodiment roll-to-web system.
• FIGS. 35B-35E are logic diagrams corresponding to the roll-to-web system illustrated inFIG. 35A.
• FIG. 36A is a system diagram illustrating an embodiment web-to-plate system.
• FIGS. 36B-36E are logic diagrams corresponding to the web-to-plate system illustrated inFIG. 36A.
DETAILED DESCRIPTION
• The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” or “the” is not to be construed as limiting the element to the singular. The terms “example,” “exemplary,” or any term of the like are used herein to mean serving as an example, instance, or illustration. References to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. Any implementation described herein as an “example” is not necessarily to be construed as preferred or advantageous over another implementation.
• As used herein, the term “photovoltaic bristle” refers to a three-dimensional structure approximately cylindrical with a height approximately equal to 1-100 microns, a diameter of approximately 0.2-50 microns that includes at least one photovoltaically-active semiconductor layer sandwiched between a conductive inner layer or core and a transparent outer conductive layer (e.g., TCO and a nonconductive outerlayer). The term “bristle” is used merely because the structures have a length greater than their diameter, the structures have a generally (on average) circular cross-section, and the overall dimensions of the structures are on the dimensions of sub-microns to tens of microns. In the embodiment illustrated herein the photovoltaic bristles have an approximately cylindrical shape, by which it is meant that a substantial portion of the exterior surface of the structures have a cross-section that is approximately circular or elliptical with both radii being approximately coexistent. Due to manufacturing variability, no single photovoltaic bristle may be exactly cylindrical in profile, but when considered over a large number of photovoltaic bristles the average profile is approximately cylindrical. In another embodiment, the photovoltaic bristles may have a non-circular cross-section, such as hexagonal, octagonal, elliptical, etc. as may facilitate manufacturing.
• When the embodiment photovoltaic bristles are arranged on a substrate in an order or disordered array, the resulting structure may form a metamaterial structure. As used herein, the term “metamaterial” or “metamaterial substrate” refers to an array of photovoltaic bristles on a substrate. Metamaterials as used herein are artificial materials that are engineered with metals or polymers that are arranged in a particular structured or non-structured pattern that result in material properties (including light absorption and refraction properties) that are different from the component materials. The cumulative effect of light interacting with the array of photovoltaic bristles may be affected by controlling the shape, geometry, size, orientation, material properties, material thicknesses, and arrangement of the bristles making up the metamaterial as described herein.
• Traditional planar photovoltaic cells are flat. In traditional planar photovoltaic cells, a limited number of photons are absorbed at any given point in time. Photon absorption occurs through the thickness of the traditional planar photovoltaic cell (e.g., top-to-bottom) from the point of photon entry until the photon is converted to electrical energy. Traditional planar photovoltaic cells convert photons into electrical energy when photons interact with a photovoltaic layer. However, some photons pass through the photovoltaic layer without generating electron-hole pairs, and thus represent lost energy. While the number of photons absorbed may be increased by making the photovoltaic layer thicker, increasing the thickness increases the fraction of electron-hole pairs that recombine, converting their electrical potential into heat. Additionally, thicker photovoltaic films exhibit an exponential attenuation loss leading to a decrease in photon conversion. For this reason, traditional planar photovoltaic cells have emphasized thin photovoltaic layers, accepting the reduced photon-absorption rate in favor of increased conversion of electron-hole pairs into electrical current and reduced heating. The theoretical peak efficiency, as well as the total efficiency, of traditional planar photovoltaic cells is thus limited by the planar geometry and the un-attenuated fraction of photons that can be absorbed in a maximized optical path length through the photovoltaic layer.
• Conventional planar photovoltaic cells also suffer from low total efficiency in static deployments (i.e., without sun tracking equipment), since their instantaneous power conversion efficiency decreases significantly when the sun is not directly overhead (i.e., before and after noon). Peak efficiencies of traditional planar photovoltaic cells are affected by their orientation with respect to the sun, which may change depending on the time of day and the season. The standard test conditions for calculating peak efficiencies of solar cells are based on optimum conditions, such as testing the photovoltaic cells at solar noon or with a light source directly above the cells. If light strikes traditional photovoltaic cells at an acute angle to the surface (i.e., other than perpendicular to the surface) the instantaneous power conversion efficiency is much less than the peak efficiency. Traditional planar photovoltaic cells in the northern hemisphere are typically tilted toward the south by an angle based on the latitude in order to improve their efficiency. While such fixed angles may account for the angle of the sun at noon due to latitude, the photovoltaic cells receive sunlight at an angle during the morning and afternoon (i.e., most of the day). Thus, traditional planar photovoltaic cells actually result in a low total efficiency and low total power generation when measured beyond a single moment in time.
• The various embodiments include photovoltaic cells that exhibit metamaterial characteristics from regular or irregular arrays of photovoltaic bristles configured so the conversion of light into electricity occurs within layers of the photovoltaic bristles. Since the photovoltaic bristles extend above the surface of the substrate and are spaced apart, the arrays provide the photovoltaic cells of the various embodiments with volumetric photon absorption properties that lead to energy conversion performance that exceeds the levels achievable with traditional planar photovoltaic cells. The volumetric photon absorption properties enable the various embodiment photovoltaic cells to generate more power than traditional planar photovoltaic cells with the same footprint. Due to the small size of the photovoltaic bristles, the photovoltaically-active layers within each bristle are relatively thin, minimizing power losses due to electron-hole recombination. The thin photovoltaically-active layers help reduce attenuation losses normally present in thicker photovoltaic films because the photovoltaic bristles include a thin radial absorption depth and a relatively thicker vertical absorption depth maximizing photon absorption and power generation through the combined long circumferential absorption path length and short radial electron path length. When individual photovoltaic bristles are combined in an array on, or within, a substrate, a metamaterial structure may be formed that exhibits a high probability of photon absorption and internal reflection that leads to increased energy conversion efficiencies and power generation. Various embodiment structures also provide additional performance-enhancing benefits as will be described in more detail below.
• Further performance enhancements may be obtained by positioning the embodiment photovoltaic cells so that the photovoltaic bristles' sidewalls are at an angle to the incident photons. This can improve the probability that photons will be absorbed into the photovoltaic bristles due to wave interactions between photons and the outer conductive layer on each photovoltaic bristle. Orienting the embodiment photovoltaic bristles at an angle to the incident photons also increases the circumferential optical depth of the photovoltaic bristles exposed to the light, since in such an orientation the photons strike the sides of the bristles and not just the tops. The off-axis photon absorbing characteristics of the photovoltaic bristles also enables the embodiment photovoltaic cells to exhibit significant total energy conversion efficiency for indirect and scattered light, thereby increasing the number of photons available for absorption compared to a conventional photovoltaic cell.
• An embodiment described herein includes photovoltaic cells featuring arrays of photovoltaic bristles on roughly corrugated surfaces in order to present the bristles at an angle to incident sunlight. Further embodiments described herein include methods for manufacturing photovoltaic cells featuring arrays of photovoltaic bristles, as well as assembly of such photovoltaic cells into solar panels.
• For purposes of background on the physics and geometries that enable photovoltaic bristles to achieve significant improvements in peak power performance, an overview of embodiment photovoltaic bristles and corresponding photovoltaic cells is now presented. More details on the dimensions, materials and configurations of embodiment photovoltaic bristles are disclosed in U.S. patent application Ser. No. 13/751,914 that is incorporated by reference above.
• FIG. 1A illustrates a cross-sectional top view of one photovoltaic bristle101 andFIG. 1B illustrates a cross-sectional side view of the photovoltaic bristle101 ofFIG. 1A.FIGS. 1A and 1B illustrate the path traveled by a photon entering the side of the outer periphery of the photovoltaic bristle101. A photovoltaic bristle101 may guide an absorbedphoton112 so that it follows an internal path113 that exhibits a high probability that the photon remains within the photovoltaic bristle101 due to total internal reflection. A photovoltaic bristle may exhibit total internal reflection by controlling the thickness of thelayers103 and111 and by radially ordering the materials by indexes of refractions from a low index of refraction on the outside to a higher index of reaction in each inner layer, the photovoltaic bristle101 may refract or guidephotons112 toward the core of the photovoltaic bristle101. Since thecore106 may be highly conductive, it is also highly reflective, so that it will reflectphotons112. As illustrated, due to the large difference in index of refraction between the absorber layer and the outerconductive layer103, photons striking this boundary at an angle will be refracted inward. As a result of these reflections and refractions,photons112 may be effectively trapped within theabsorption layer111 for a longer period of time, thereby increasing the probability of interaction with the absorption layer11 causing an electron-hole pair to be formed. Increasing the probability of photon absorption may result in more electrical current being generated for the same amount of incident light energy by the embodiment photovoltaic cells than is achievable by conventional photovoltaic cells.
• It should be noted that the embodiment shown inFIGS. 2A-2B may include an inner reflector due to ametal core106. In other embodiments, a refraction layer may be applied over the core106 to achieve the same photon reflection effects. In such an embodiment, a reflective layer may be formed over the conductive core and under the absorber layer, such as a semiconductor or dielectric material layer having a lower index of refraction than the absorber layer. This refraction layer may be configured to reflect the photon at the interface between the reflection layer and the absorber layer, and not rely on reflection off of theconductive core106. For example, such a diffraction layer may be formed from an aluminum doped zinc oxide layer of about 500-1500 angstroms in thickness. Reflected photons then refract through eachlayer104,105 until they reach the outerconductive layer103, where the difference in the index of refraction between theabsorption sublayer105 and the outerconductive layer103 causes the photons to reflect back into the absorption layers of the photovoltaic bristle. The reflected photons that are not reflected inwardly at the boundary between the outerconductive layer103 and theabsorption sublayer105 may pass through the outerconductive layer103 and be reflected off of the interface between the outerconductive layer103 and air due to the difference in the index of refraction at this interface. In either manner, photons may remain within the photovoltaic bristle passing back and forth through theabsorption layer111 until they are eventually absorbed or exit the bristle.
• Each photovoltaic bristle101 is made up of a core106 that may be conductive or has a conductive outer surface, anabsorption layer111 and an outerconductive layer103, which will typically be a transparent conductive layer such as a transparent conductive oxide or transparent conductive nitride. Due to the cylindrical form of photovoltaic bristles, theabsorption layer111 surrounds thecore106, and the outerconductive layer103 surrounds theabsorption layer111. Although, twoabsorber sublayers104,105 are shown, it should be noted that theabsorption layer111 may include any number of absorber sublayers or regions of photovoltaically-active materials or combinations of photovoltaic materials. For example, theabsorption layer111 may include multiple absorber sublayers or regions that form a p-n junction, a p-i-n junction, or multi-junction regions, which have a generally circular cross-section as illustrated inFIG. 1A. If theabsorption layer111 forms a p-i-n junction with three absorber sublayers, one sublayer may be the intrinsic portion forming the p-i-n junction. If thecore106 is a semiconductor core forming a p-n junction with a single absorber sublayer, theabsorption layer111 may include only one sublayer. Regardless of the number, the absorber sublayers orregions104,105 may be made from one or more of silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, gallium arsenide, aluminum gallium arsenide, cadmium sulfide, copper indium selenide, and copper indium gallium selenide.
• The relative radial positions of the p-type, intrinsic, or n-type sublayers/regions may vary in different embodiments. For example, in one embodiment the p-type semiconductor material may be positioned radially inside the n-type semiconductor material. In another embodiment, the n-type semiconductor material may be positioned radially inside the p-type semiconductor material. In addition, multiple materials may be used to create a sequence of p-n and/or n-p junctions, or p-i-n junctions in the absorption layer. For example, the absorption layer may include an absorber sublayer of p-type cadmium telluride (CdTe) and an absorber sublayer of n-type cadmium sulfide (CdS). In an embodiment, theabsorption layer111 may be fully depleted. For example, the p-type region and the n-type region forming the sublayer orregion104 and the sublayer orregion105 may be fully depleted.
• In an example embodiment, theabsorption layer111 may include a p-type semiconductor sublayer105, such as p-type cadmium telluride, and an n-type semiconductor sublayer of a different material, such as n-type-cadmium sulfide. In another example embodiment, onesublayer104 may be a p-type region, such as p-type amorphous silicon, and anothersublayer105 may be an n-type region of the same material as thesublayer104 but doped to form an n-type semiconductor, such as n-type amorphous silicon.
• The outerconductive layer103 has a radial thickness which may be measured radially from the outer surface of theabsorption layer111 to the outer surface of the outer conductive layer103 (i.e., the outer surface of the photovoltaic bristle). In an embodiment, the outerconductive layer103 is a transparent conductive oxide (“TCO”), such as a metal oxide. In an embodiment, the outerconductive layer103 may include a dopant creating a p-type or n-type transparent conductive oxide. For example, the transparentconductive oxide layer103 may be one of intrinsic zinc oxide, indium tin oxide, and cadmium tin oxide (Cd₂SnO₄). In an embodiment, the outerconductive layer103 may include a transparent conductive nitride such as titanium nitride (TiN). In another embodiment, the outerconductive layer103 may include a buffer with or without the dopant. Some examples of an outerconductive layer103, which may be a transparent conductive oxide with a dopant, include boron-doped zinc oxide, fluorine doped zinc oxide, gallium doped zinc oxide, and aluminum doped zinc oxide. Some examples of buffers that may be added to a transparent conductive oxide include zinc stannate (Zn₂SnO₄), titanium dioxide (TiO₂), and similar materials well known in the art.
• Although not shown inFIGS. 1A-1B, the outerconductive layer103 may include any number of conductive and/or non-conductive sublayers to achieve a particular total optical thickness while simultaneously having a thin conductive sublayer. With multiple sublayers, the outerconductive layer103 may also benefit from adding flexibility to the photovoltaic bristles for a more resilient photovoltaic bristle metamaterial device. The addition of a non-conductive sublayer may have refractive properties that improve off-angle photon absorption efficiency. Analysis and observations of prototypes indicate that outer conductive layers between 500 and 15,000 angstroms result in a decrease in electrical resistance in the conductive layers from field effects at the structural discontinuities in the photovoltaic bristles. However, the outerconductive layer103 may need to be of a minimum optical thickness exceeding 500 and 15,000 angstroms a bristle to achieve the photon trapping and guiding effect shown inFIG. 1A. Thus, the outerconductive layer103 may include multiple layers to achieve the conflicting optical thickness requirement and the requirement for electrical resistivity benefits from field effects. As an example, the outerconductive layer103 may have two sublayers including a conductive sublayer such TCO and a non-conductive sublayer such as an optically transparent polymer. As another example, the non-conductive sublayer may be a bi-layer including TCO and a polymer or glass. As a further example, the outerconductive layer103 may include three sublayers where a non-conductive sublayer separates two conductive sublayers.
• In an embodiment, thecore106 may be of a variety of conductive materials and non-conductive materials. In an embodiment, thecore106 may be a solid conductive core such as a metal. For example, the solid conductive core may be gold, copper, nickel, molybdenum, iron, aluminum, or silver. In an embodiment, thecore106 may include the same material as the substrate202 (shown inFIG. 2B). For example, thecore106 and thesubstrate202 may include a polymer. In another embodiment, thecore106 may include a different material than thesubstrate202. In another embodiment, an innerconductive layer107 may surround thecore106. For example, the innerconductive layer107 may be gold, copper, nickel, molybdenum, iron, aluminum, or silver to create a conductive core. In an embodiment, thecore106 may include a polymer with an innerconductive layer107 surrounding the polymer. The innerconductive layer107 may include similar material as the outerconductive layer103. For example, the innerconductive layer107 may include a transparent conductive oxide, a transparent conductive nitride, and/or a non-conductive transparent material. The innerconductive layer107 may include multiple layers (e.g., sublayers of TCO and a non-conductive optically transparent polymer) to achieve the conflicting benefits of field effects and proper optical depth for the photovoltaic device. In an embodiment, thecore106 may include a semiconductor material. For example, thecore106 may be made from one or more of silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, gallium arsenide, aluminum gallium arsenide, cadmium sulfide, copper indium selenide, and copper indium gallium selenide.
• FIG. 1B also illustrates that photons striking the photovoltaic bristle101 will have a higher probability of absorption when they strike the sidewall of a photovoltaic bristle at a compound angle that is less than 90 degrees but more the 0 degrees to the surface, where an angle perpendicular to the sidewall surface is considered to be 0 degrees. The compound incident angle includes a vertical plane component133 (shown inFIG. 1B) and a horizontal plane component132 (shown inFIG. 1A). The horizontal plane component132 is defined by aphoton112 striking the outer surface of the bristle at a point along the perimeter of the circular cross-section plane forming an angle with the perimeter where an angle perpendicular to the perimeter is considered 0 degrees. Similarly, the vertical plane component133 is defined by thephoton112 striking the outer surface of the bristle at a point along the height forming a vertical angle with the surface where an angle perpendicular to the surface is considered 0 degrees.
• Analysis of photon absorption characteristics of the outer conductive layer have revealed that photons striking the surface of the sidewall of the photovoltaic bristle perpendicular to the horizontal component132 and the vertical component133 may result in a compound angle of 0 degrees and an increased probability of being reflected off the surface. Similarly, photons striking the surface of the sidewall of the photovoltaic bristle parallel to the vertical and the horizontal component will also have an increased probability of being reflected off the surface. However, photons striking the side surface at a compound angle between 10° and 80° have a high probability of being absorbed into the outerconductive layer203. Once absorbed, the internal refraction characteristics of theabsorber sublayers104,105 and outerconductive layer103 cause the photons to remain within the photovoltaic bristle101 for an extended time or path length. This characteristic is very different from conventional photovoltaic cells, which exhibit the maximum power conversion efficiency when the angle of incidence of photons is normal to its single planar surface.
• The difference between the incident angle corresponding to conventional photovoltaic cells and the photovoltaic bristles is illustrated by angle θ_pinFIG. 1B. The preferred incident angle for a traditional solar cell, θ_p, would form a right angle with the top of the bristle as well as the substrate of the full metamaterial device (not shown). Thus, not only does the photovoltaic bristle exhibit better absorption characteristics at off-angles (not perpendicular or parallel to the surface), the reference point for measuring an off-angle is different from that of a conventional photovoltaic cells. For a metamaterial device with photovoltaic bristles, the reference point is measured from the sidewall of a bristle in two planes, which is unachievable by a planar photovoltaic cell. Thus, due to the off-angle absorption characteristics of photovoltaic bristles, the embodiment photovoltaic cells exhibit significant power conversion efficiency across a broad range of angle of incidence. This translates to more power generation throughout the day than achievable from fixed solar panels with conventional planar solar arrays that produce their peak efficiencies (i.e., maximum power generation) when the sun is directly overhead.
• FIG. 2A illustrates a perspective view ofmetamaterial200 comprising an array ofphotovoltaic bristles201a,201b,201c,201d,201e,201f,201g,201h,201i,201j,201k,201l,201m,201n,201o,201pextending from a flat substrate202 (shown inFIG. 2B). While illustrated with twelvephotovoltaic bristles201a-201p, a metamaterial may include a larger number of photovoltaic bristles. The number ofphotovoltaic bristles201 will depend upon the dimensions and spacing of the bristles and the size of the photovoltaic cell. As with conventional photovoltaic cells, metamaterials may be assembled together in large numbers to form panels (i.e., solar panels) of a size that are suitable for a variety of installations.
• Each photovoltaic bristle201a-201pis characterized by its height “h,” which is the distance that each bristle extends from thesubstrate202.Photovoltaic bristles201a-201pare also characterized by their radius “r”. In an embodiment, allphotovoltaic bristles201a-201pwithin an array will have approximately the same height h and approximately the same radius r in order to facilitate manufacturing. However, in other embodiments,photovoltaic bristles201a-201pwithin the array may be manufactured with different heights and diameters.
• In an embodiment, the number of photovoltaic bristles in a photovoltaic cell may depend upon the substrate surface area available within the cell and the packing density or inter-bristle spacing. In an embodiment, photovoltaic bristles may be positioned on the substrate with a packing density or inter-bristle spacing that is determined based upon the bristle dimensions (i.e., h and r dimensions) as well as other parameters, and/or pattern variations. For example, a hexagonal pattern may be used rather than the trigonometric pattern shown inFIG. 2A.
• In the various embodiments, the dimensions and the inter-bristle spacing of photovoltaic bristles may be balanced against the shading of neighboring bristles. In other words, increasing the number of photovoltaic bristles on a plane may increase the surface area available for absorbing photons. However, each photovoltaic bristle casts a small shadow, so increasing the photovoltaic bristle density of a photovoltaic cell beyond a certain point may result in a significant portion of each bristle being shadowed by its neighbors. While such shadowing may not reduce the number of photons that are absorbed within the array, shadowing may decrease the number of photons that are absorbed by each photovoltaic bristle, and thus there may be a plateau in the photon absorption versus packing density of photovoltaic bristles.
• A further consideration beyond shadowing is the wave interaction effects of the array of closely packed photovoltaic bristles. The interior-bristle spacing may be adjusted to increase the probability that photons entering the array are absorbed by the photovoltaic bristles' metamaterial properties considering the bulk material properties of the layered films that makeup the array. For example, specific characteristics such as extinction coefficient or absorption path length may predict an optimal dimensional design, although one may chose to deviate from this prediction resulting in a sacrifice in performance.
• FIG. 2B is a cross-sectional side view of a section ofmetamaterial200 includingphotovoltaic bristles201m,201n,201o, and201pas illustrated inFIG. 2A. As shown inFIG. 2B the photovoltaic bristles extend from asubstrate202. In an embodiment, thecore106 may be the same material as thesubstrate202 and an innerconductive layer107 may surround thecore106. Theabsorber layer111 may surround the innerconductive layer107 and the outerconductive layer103 may surround theabsorber layer111. Theabsorber layer111 may include any number of sublayer or regions. As illustrated inFIG. 2B, theabsorber layer111 may include two sublayers orregions104,105. In an embodiment, the two absorber sublayers orregions104,105 may be any semiconductor material where one sublayer or region is doped as n-type and the other is doped as p-type.
• Themetamaterial200 may include asubstrate202 of any suitable substrate material known to one skilled in the art. For example, thesubstrate202 may be glass, doped semiconductor, diamond, metal, a polymer, ceramics, or a variety of composite materials. Thesubstrate202 material may be used elsewhere in themetamaterial200, such as a material used in any layer of aphotovoltaic bristle201m-201n. Alternatively, the material used in thesubstrate202 may be different from other materials used in the photovoltaic bristles201m-201n. In an embodiment, thecore106 and thesubstrate202 may include a common material. For example, thesubstrate202 and thecore106 may include glass, semiconductor material, a polymer, ceramics, or composites. In a further embodiment, thecore106 andsubstrate202 may include similar materials, while the innerconductive layer107 is added over thesubstrate202 and surrounding thecore106 creating a conductive core. The innerconductive layer107 may include metal such as gold, copper, nickel, molybdenum, iron, aluminum, or silver. Alternatively, the inner conductive layer may include any of the materials used for the outerconductive layer103 which may be used in combination with the previously listed metals.
• In an embodiment, the innerconductive layer107 may also be an inner refraction or reflection layer that is added on top of the core106 in order to provide an inner reflection interface for photons. In this embodiment, a layer of semi-conductive or insulator material, such as B:ZnO, Al:ZnO, ZnO, or ITO, may be applied over the metal core. This layer may be at least one-half wavelength in thickness, depending on the refractive index of the material. For example, such a layer made of Al:ZnO (AZO) may be approximately 500 to 1500 angstroms thick over which the absorber layer may be applied. Such an AZO layer has a refractive index that is lower than the absorber layer. This difference in refractive index coupled with the curvature of the interface of these two layers will reflect the photons before they reach the metal core. The reflection induced by this design may exhibit lower losses than the designs in which photons reflect from a metal surface of the core. The use of such a refraction layer may be included in any of the embodiments illustrated and described herein. For example, in the embodiments in which the center of the core is a plastic rod, a metal layer is applied over the plastic core and then the AZO is applied over the metal layer. In further embodiments, this refractive layer forming a reflecting interface may be formed using multiple layers, such as: ITO-AZO; ITO-AZO—ITO; TiO2-TiN—TiO2; ZnO-AZO—ZnO; etc. Such multiple layers may function similar to a Bragg reflector used in fiber optics.
• In ordering reason the percentage of solar photons striking photovoltaic bristles at the appropriate angle of incidence, one embodiment orients the photovoltaic bristles at an angle on a corrugated substrate. Positioning photovoltaic bristles at an angle to incident light increases the probability of off-axis photon absorption, which may reflect and propagate photons around and within the photovoltaic bristles, thereby developing an equilibrium standing wave and increasing probability of converting photon energy into electrical energy. Consequently, embodiment photovoltaic cells with such a corrugated shape may generate more electrical power than is possible from conventional photovoltaic cells.
• In addition to increasing the probability of photon absorption, embodiment corrugated photovoltaic cells provide more surfaces and more photovoltaic bristles for photon absorption within a given planar footprint than a comparable flat substrate configuration. Each corrugated photovoltaic cell may include a large number of angled surfaces with photovoltaic bristles, compared to a conventional flat substrate photovoltaic cell that has only a single flat surface or absorbing photons. The improvements from the corrugated photovoltaic cell results in an increase in optical volume enabling more photon absorption and power generation from such a metamaterial device.
• FIG. 3A is a perspective view of anembodiment metamaterial300 comprising a corrugated shaped substrate302 (shown inFIG. 3B) with arrays ofphotovoltaic bristles301 positioned on each slantedsubstrate surface308a,308b,308c,309a,309b, and309c. AlthoughFIG. 3A depicts six slanted substrate surfaces, in an embodiment, themetamaterial300 may have a larger number of slanted substrate surfaces. InFIG. 3A, each slanted substrate surface308a-308c, and309a-309cmay form an angle θ_bwith theflat foundation303 of thesubstrate302. In an embodiment angle θ_bmay be between about 30 and about 60 degrees. In further embodiments the angle θ_bmay be 30-35 degrees, 35-40 degrees, 40-45 degrees, 45-50 degrees, 50-55 degrees, and 55-60 degrees. In an embodiment, arrays ofphotovoltaic bristles301 may be oriented so that their long axis is normal to the slanted substrate surfaces308a-308cand309a-309cincluding angle θ_bto increase the probability of photon absorption and photon trapping and guiding from photons striking the sidewalls of each photovoltaic bristles301 at compound angles approximately between 10 and 80. It should be noted that each slanted substrate surface308a-308cand309a-309cmay include any number of photovoltaic bristles301 (i.e. more than the twelvephotovoltaic bristles301 shown in the figure).
• FIG. 3B is a cross-sectional side view of a section of ametamaterial300 comprising slanted substrate surfaces308aand309aat angles θ_bwith thefoundation303 and an array ofphotovoltaic bristles301 on each slanted substrate surface. As described above, each photovoltaic bristle301 may include acore106, an innerconductive layer107, and anabsorber layer111 withabsorber sublayers104,105 surrounding the inner conductive layer, and an outerconductive layer103 surrounding theabsorber layer111. In an embodiment, thecore106 may be the same material as thesubstrate302. The photovoltaic bristles301 extend from thecorrugated surface302 perpendicular to each slanted surface308,309. As illustrated in the figure, this angle enablesphotons112 traveling along the photon path113 to enter the sidewall of the photovoltaic bristle301 at a compound angle of approximately 10-80°.
• In another embodiment, photovoltaic bristles are position only on alternating slanted surfaces of the corrugated substrate, with the opposite surfaces lacking such structures. This embodiment configuration may reduce manufacturing costs while presenting photovoltaic bristles on the services most likely to receive solar radiation when deployed. Additionally, the slanted surfaces that do not include photovoltaic bristles may be coated with a reflective material (e.g., a metal) so that photons striking that surface are reflected at a desirable angle into the photovoltaic bristles on the opposite surface. Such an embodiment is illustrated inFIGS. 4A and 4B.
• FIG. 4A is a perspective view ofmetamaterial400 comprising a corrugated shaped substrate402 (shown inFIG. 4B) and arrays ofphotovoltaic bristles401 positioned at normal from the planes of alternating slanted substrate surfaces408a,408b, and408c. In an embodiment, slanted substrate surfaces409a,409b, and409cmay be without arrays ofphotovoltaic bristles401 and may be configured with a reflective surface coating, such as a metal, that may reflect photons into the photovoltaic bristles on the opposite surface is illustrated inFIG. 4B. AlthoughFIG. 4A depicts six slanted substrate surfaces, in an embodiment, themetamaterial400 may have a larger or smaller number of slanted substrate surfaces.
• FIG. 4B is a cross-sectional side view of a section ofmetamaterial400 with acorrugated substrate402 comprising slanted substrate surfaces408a,408b,409a,409bat angles1N with thefoundation403. In an embodiment, eachslanted substrate surface408a,408bmay include an array ofphotovoltaic bristles401 configured approximately normal to the slanted substrate surface. In an embodiment, slanted substrate surfaces409aand409bmay include areflective layer405. As such, thereflective layer405 may reflectphotons411 along aphoton path412 so that the reflectedphotons411′ strikes the photovoltaic bristles extending from the adjacentslanted substrate surface408bof thesubstrate402. In embodiment, a reflective layer405 (i.e., reflective film) may be any material that has high reflective characteristics to reflect photons usable for the embodied metamaterial.
• FIG. 5 illustrates an advantage of the various embodiment photovoltaic cells when installed on a typical structure502 (e.g., a house) having a roof withangled surfaces504,506. In this illustrative figuration,photovoltaic cells200 on a northern facing roof surface may have a flat profile and featurephotovoltaic bristles201 that extend perpendicular from the surface. Since this surface of theroof506 receives sunlight at an angle, the incident sunlight on this surface is preferable for increasing photon absorption on such aphotovoltaic cell200. On the southern facingroof surface504, corrugatedphotovoltaic cells300,400 may be used since the sunlight will be striking theroof surface504 at closer to a perpendicular angle of incidence. The301,304 angular orientation of the photovoltaic bristles on such corrugatedphotovoltaic cells300,400 ensures that incident sunlight strikes the photovoltaic bristles at angles of incidence that will increase photon absorption.
• Various embodiment methods of making photovoltaic bristles are now presented.
• Anembodiment method800 for manufacturing photovoltaic bristles using a press or stamping process is illustrated inFIGS. 6A-6H,7A-7C,FIG. 8. Thisembodiment method800 may enable fabricating photovoltaic bristles using low-cost substrate materials such as plastics and polymers that may be processed rapidly in large volumes. This embodiment method will be described with reference toFIGS. 6A-6H andFIG. 8 together. Although the figures illustrate and the text describes a rod imprint design, a via design may be similarly created as shown and described with reference tomethod1600. Additionally, any of a variety of raised shapes other than cylindrical rods or cones may be produced on the substrate using the embodiment methods and embodiment imprinting systems, including ridges, a mesh of interlocking ridges; hemispheres, etc.
• Inmethod800 inblock804, a plastic or polymer block or starting material may be processed in order to prepare it for a pressing or forming operation. The methods used for preparing such a polymer for pressing will depend upon the type of plastic or polymer selected. As illustrated inFIGS. 6A and 6B, in block808 a die or mold602 including a number of bristleholes604 for forming the bristle cores may be pressed into the plastic orpolymer material202 and then removed, thereby forming an array ofcores106 out of theplastic polymer202. In an embodiment,vertical stamp602 moves in a downward vertical manner into apolymer substrate202 formingcores106 and moving vertically away from thesubstrate202 and the formedcores106. Alternatively, a rolling press or rolling die may be applied to a moving sheet or tray of material similar to printing press techniques.
• When using a rolling press or rolling die a separate roll-to-web and web-to-plate sub-process may create the associated rolling stamps and the array of cores on the substrate for use inmethod800. The sub-process is discussed in depth later in this application with reference toFIGS. 33A-33G,34,35A-35E,36A-36E. Generally, a master template is created using photolithographic techniques or nanoimprint lithography. The master template imprints a pattern on a polymer sheet or a web. The sheet or web may be a base material with a thin polymer imprintable layer or coating. For example, the sheet could be glass and/or the web could be polyester. The web is then used in combination with rollers (e.g., a rolling stamp) to stamp cores on a substrate similar tosubstrate202 withcores106 illustrated inFIG. 6B.
• Inblock810, the newly formed array ofcores106 may be cured or otherwise processed in order to improve the material properties, such as to harden the material. This may involve processing with heat, ultraviolet radiation, and/or chemical vapor exposure, as would be well-known in the polymer arts and depend upon the type of material used. In an embodiment, the material processing inblock810 may be accomplished as part of the stamping operation inblock808, partly as part of the stamping operation and as a host stamping process, or entirely as a post-stamping process. For example, a rolling stamp may include an ultraviolet light that is configured so that when the rolling stamp rotates over theunformed substrate202 the ultraviolet light simultaneously cures or partially cures the newly formedcores106.
• As illustrated inFIG. 6C, inblock812, and innerconductive layer107 may be formed over thecores106. This may be accomplished by chemical vapor deposition, plasma enhanced chemical vapor deposition, physical deposition, plasma deposition, sputtering techniques, or electro-deposition techniques. The innerconductive layer107 may further be formed or thickened by electroplating processes. Multiple conductive layers may be applied as part ofblock812. In an embodiment, the inner conductive layer or layers may be one or more of copper, aluminum, gold, nickel, titanium, silver, tin, tantalum, and chromium, as well as alloys of such metals. This process forms an inner conducting core for the photovoltaic bristle.
• To form the photovoltaic portion of the photovoltaic bristles, a number of semiconductor layers may be applied to the inner conducting core using well-known semiconductor processing methods. As illustrated inFIG. 6D, inblock804, a first absorber layer of semiconductor material may be formed over the inner conductive layer. For example, thefirst absorber layer105 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. Thefirst absorber layer105 over the innerconductive layer107 by electroplating, chemical vapor deposition, atomic layer deposition, etc.
• As illustrated inFIG. 6E, in block842 a second semiconductor material layer may be formed over the first absorber layer, with the first and second absorber layers having material properties to create a p-n junction or n-p junction configured to release electrons upon absorbing a photon. Any deposition method used to add thefirst absorber layer105 may also be used to add thesecond absorber layer104. In an embodiment, the deposition method for thesecond absorber layer104 may be the same deposition method used for adding thefirst absorber layer105. In an embodiment, thesecond absorber layer104 may include a semiconductor material. For example, thesecond absorber layer104 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. In an embodiment, thesecond absorber layer104 may be an absorber sublayer or region comprising the same material as thefirst absorber layer105 with a different dopant. For example, thefirst absorber layer105 may be p-doped amorphous silicon and thesecond absorber layer104 may be n-doped amorphous silicon. In an embodiment, thesecond absorber layer104 may be an absorber sublayer comprising a different material as thefirst absorber layer105. For example, thefirst absorber layer105 may be p-doped cadmium telluride and thesecond absorber layer104 may be n-doped cadmium sulfide. Inoptional block846, additional absorber layers of semiconductor materials may be applied to form multiple p-n and/or n-p junctions (e.g., n-p-n or p-n-p junctions).
• With the photon absorber layers formed, an outer conductive layer may be formed inblock848 as illustrated inFIG. 6G. The outer conductive layer may be a transparent conducting oxide or transparent conducting nitride, as are well-known in the photovoltaic technologies. In an embodiment, the only twoabsorber layers104,105 may be applied, and thus the outerconductive layer103 is deposited (e.g., by chemical deposition or physical deposition) over thelast absorber layer104 as shown inFIG. 6F. Inoptional block852, additional outer conductive layers may be applied depending upon the configuration of the photovoltaic bristles. Although the outer conductive layer inFIG. 6G includes two layers, any number of layers may make up the outerconductive layer103.
• Corrugated photovoltaic cells may also be configured using similar processes as illustrated inFIGS. 7A-7C. For example, as illustrated in these figures, the operations of forming an array of cores in the plastic or polymer inblock808 may be accomplished by alternately pressing the material302 with dies that are oriented at the desired angle of the corrugated surfaces. For example,photovoltaic bristles106 may be formed on corrugated surfaces in the 1^storientation by pressing the material with dies702 long one angle as illustrated inFIG. 7B, followed by pressing the opposite surfaces with opposite oriented dies702 as illustrated inFIG. 7C.
• To form the embodiment illustrated inFIG. 4C in which photovoltaic bristles are formed on only alternating sides of the corrugated surface, only a single pressing step as illustrated inFIG. 7B may be a comp push. In some embodiments, in optional block854 a reflective layer may be applied to the surfaces that do not feature photovoltaic bristles. This may be accomplished using photoelectric graphic methods, such as coding the photovoltaic bristles with a photoresist that is removed from the other surfaces before a reflective layers applied.
• As illustrated inFIG. 6H, inoptional block856 but conductive traces may be added to portions of the solar cells to gather and distribute electricity from the photovoltaic bristles, thereby reducing the path length of electrons through the transparent conducting oxide layers. Finally inoptional block858, a transparent coating may be applied over the bristles in order to provide desirable strength and photon absorption c characteristics. For example, atransparent coating608 may seal each bristle in a transparent material providing stability to each bristle to prevent the bristles from breaking. Thetransparent coating608 may be conventional shatterproof material such as ethylene-vinyl acetate (EVA).
• In a further embodiment method that uses some of the same processes as inmethod800, the material forming thecores106 may be poured and formed in amold612 instead of being pressed, as illustrated inFIGS. 6I through 6K. As illustrated inFIG. 6I, instead of adie602, the same basic shape may be inverted to form amold612 onto which may be poured thematerial614 to form the cores and supporting substrate. Thismaterial614 may be a plastic or polymer, but may also be other materials, such as a metal, a ceramic paste, or a liquid glass (e.g., common glass). In this embodiment, the operations of forming the array of cores inblock808 include pouring thebase material614 into themold612, sufficiently covering the mold surface to provide asubstrate202 as shown inFIG. 6J. The material may be cured inblock810 in this state before themold612 is removed as shown inFIG. 6K. Thereafter, the operations of depositing absorber layers and outer conductive layers may be accomplished as described above with reference to blocks812-858.
• Another embodiment method for forming an array of bristles for a metamaterial device involves a plating up metal cores using a photolithographic methods to create a template on a substrate. The plating up method is illustrated inFIGS. 9A-9J andFIG. 10. In block1008 a metal layer may be deposited over a substrate. As illustrated inFIG. 9A themetal layer187 may be deposited directly may be deposited over thesubstrate202 by chemical deposition or physical deposition. In block1010 a photoresist layer over the metal layer. Thephotoresist layer189 may be deposited over themetal layer187 by chemical vapor deposition or physical deposition as shown inFIG. 9A. Thephotoresist layer189 may be a positive photoresist or a negative photoresist.
• In block1012 a mask may be applied over the photoresist. As shown inFIG. 9B, themask195 may includeholes195athrough which ultraviolet light may pass so that only the photoresist beneath the holes is exposed as shown inFIG. 9B. Inblock1014 the photoresist layer may be exposed an ultraviolet light through the mask to create exposedphotoresist portions189aas shown inFIG. 9B. When a positive photoresist is used, the exposedphotoresist portions189amatch the mask holes195a. However, if a negative photoresist is used, ultraviolet light may be able to pass through the entire mask except through solid portions of the mask which block the ultraviolet light. Regardless, after the ultraviolet light is applied to thephotoresist189 creating exposedportions189a, themask195 is removed leaving theentire photoresist layer189.
• Inblock1016 the method may include developing the photoresist layer to create a template of masked portions. A developer may be used to dissolve only the exposed portions of the photoresist. Assuming the method uses apositive photoresist189, the exposedphotoresist portions189aare removed creatingvoids189bin the photoresist layer that extend to themetal layer187 as shown inFIG. 9C. Thesevoids189aalong with the remainingphotoresist layer189 form a template over themetal layer187.
• Inblock1018 additional metal may be added to the metal layer through the photoresist layer using electroplating, chemical vapor deposition or plasma deposition methods, forming metal cores. As shown inFIG. 9D themetal cores106 may fill thevoids189bwithin thephotoresist189 by electroplating metal in thevoids189b. Metal cores may also extend above the photoresist layer. Alternatively, a second metal layer may fill thevoids189band covers the remaining portions of the photoresist layer189 (not shown). Themetal cores106 may be the same material as themetal layer187 such as gold, copper, nickel, molybdenum, iron, aluminum, or silver, or an alloy of the same.
• Inblock1020 the photoresist layer may be removed using conventional methods. As shown inFIGS. 9D and 9E, themetal cores106 may only fill thevoids189bcreated by the exposed photoresist layer through an electroplating process. When thephotoresist layer189 is removed, only the formed metal cores106 (withinvoids189b) remain. Alternatively, if a second metal layer fills thevoids189band covers thephotoresist layer189, a lift-off process known in the art may remove thephotoresist layer189 and the second metal layer leaving only themetal cores106. The resultingmetal cores106 from the lift-off process may have height greater than thevoids189b.
• In block1040 a first absorber layer (i.e., sublayer)105 may be deposited over themetal core106 formetamaterials200 illustrated inFIG. 9F. In an embodiment, thefirst absorber layer105 may include a semiconductor material. For example, thefirst absorber layer105 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. In an embodiment, thefirst absorber layer105 may be deposited over themetal core106 by electroplating, chemical vapor deposition, atomic layer deposition, etc. In an embodiment, thefirst absorber layer105 may be deposited over the innerconductive layer107 by sputtering, electron beam, pulsed laser deposition, etc.
• In block1042 asecond absorber layer104 may be deposited over thefirst absorber layer105 formetamaterial200 as illustrated inFIG. 9G. Any deposition method used with respect to thefirst absorber layer105 may also be used with thesecond absorber layer104. In an embodiment, thesecond absorber layer104 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. In an embodiment, thesecond absorber layer104 may be an absorber sublayer or region comprising the same material as thefirst absorber layer105 with a different dopant. For example, thefirst absorber layer105 may be p-doped amorphous silicon and thesecond absorber layer104 may be n-doped amorphous silicon. In an embodiment, thesecond absorber layer104 may be an absorber sublayer comprising a different material as thefirst absorber layer105. For example, thefirst absorber layer105 may be p-doped cadmium telluride and thesecond absorber layer104 may be n-doped cadmium sulfide.
• In some implementation multiple absorber layers may be applied. So, inoptional block1046 one, two or more additional absorber layers may be applied over the previous layer in a manner similar to the process steps inblocks1040 and1042. As shown inFIG. 9H, inblock1048, an outerconductive layer103 may be deposited over the last absorber layer (e.g., second absorber layer104), such as by chemical deposition or physical deposition.
• As illustrated inFIG. 9I, additional outer conductive layers may be applied inoptional block1052. In an embodiment, the outer conductive layers may comprise a transparentnon-conductive layer103a(e.g., an optical transparent polymer) and aconductive layer103b(e.g., a transparent conducting oxide). Although the outer conductive layer shown inFIG. 9I includes two layers, any number of layers may make up the outerconductive layer103. Thenon-conductive layer103aillustrated inFIG. 9I may be a conformal layer which may act as a protective coating similar to thetransparent coating608 described below. The conformalnon-conductive layer103amay be added by dip coating, chemical vapor deposition, physical deposition, and atomic layer deposition, and evaporation techniques.
• Inoptional block1056 current conducting traces may be added to themetamaterials200 and300. As explained later with reference toFIGS. 23 and 25, the current conducting traces may be added by creating a template using photolithography and depositing a highly conductive material in a selected position from the template. The current conducting trace may be deposited on the metamaterial by any known deposition method such as chemical vapor deposition, physical deposition, plating, or ink jet material deposition. The ink jet deposition methods may utilize piezoelectric ink jets to add silver or other colloidal conductive material to the desired position without damaging the metamaterial.
• Alternatively, the current conductive traces may be added by etching with laser ablation in combination with a deposition method such as ink jet. Tuned wavelength lasers may etch desired layers by controlling the laser's wavelength for different layers within the metamaterial. Once etching is complete, the method may include adding the electrical connections such as the current conducting traces at the desired positions on the metamaterial by chemical vapor deposition, physical deposition, plating or inkjet deposition.
• As a further alternative, the metamaterial may be etched using ink jet technology to apply an acid to precise locations followed by applying the conductive material using the same technology, or any other deposition method known in the art.
• Regardless of method used, the current conducting traces may allow for efficient transfer of electricity by adding a lower resistant electrical path within the metamaterials.
• In optional block1058 a transparent coating may be deposited over the bristles. As illustrated inFIG. 9J, thetransparent coating608 is different from the outerconductive layer103 and itssublayers103aand103b. Thetransparent coating608 may fully fill the voids between each bristle and extending beyond the height of each bristle. As shown, thetransparent coating608 may not be conformal thus leading to deposition methods that use liquid solutions. Thus, the method of depositingtransparent coating608 may include one or more of the following immersion coating, spray gel techniques, extrusion techniques, a spreader bar, photoresist techniques, sol gel techniques, or any other methods known in the art. Thetransparent coating608 may seal each bristle providing stability and to prevent them from breaking as well as insulate each bristle from any heat created by the metamaterial device. Observations and experimentations also indicate enhanced peak power generation as the sun translates across the sky for a metamaterial device with atransparent coating608 having a index of refraction similar to glass (e.g., around 1.5). All these benefits may add enhanced power performance and total power generation of the metamaterial device.
• A further method for forming an array of bristles formetamaterial200 includes forming bristles by etching vias in a substrate through a photolithographic template. The method includes adding an innerconductive layer107 and abase layer202bover theoriginal substrate202aand in the vias. The method then includes turning the metamaterial device over and depositingabsorber layers104,105, outerconductive layers103a,103band a transparent coating over the inner conductive layer. This via method is illustrated inFIGS. 11A-11L andFIG. 12.
• In block1210 a photoresist layer may be deposited over the substrate. Thephotoresist layer189 may be deposited over thesubstrate202aby chemical vapor deposition or physical deposition as shown inFIG. 11A. AlthoughFIGS. 11B-11D illustrates a positive photoresist, thephotoresist layer189 may be negative photoresist.
• In block1212 a mask may be deposited over the photoresist layer. Themask195 may be any suitable mask known in the art. As shown inFIG. 12B, themask195 may include mask holes195a. Alternatively, if using a negative photoresist, thepores195amay be filters for blocking ultraviolet light.
• Inblock1214 the method may include exposing an ultraviolet light to the photoresist layer through the mask. The ultraviolet light from the ultravioletlight source193 passes through the mask holes195ainto thephotoresist layer189 creating exposedportions189aof the photoresist layer as shown inFIG. 11B. The exposedphotoresist portions189amatch the mask holes195a. However, if a negative photoresist is used, ultraviolet light may be able to pass through the entire mask except through filters where at the locations of mask holes195a, which block the ultraviolet light. Regardless, after the ultraviolet light is applied to thephotoresist layer189 creating exposedportions189a, themask195 is removed leaving theentire photoresist189.
• Inblock1216 the method may include developing the photoresist layer to create a template, such as by using developer to dissolve the exposed portions of the photoresist as shown inFIG. 11C. After dissolving the required portions of the photoresist layer, the remainingphotoresist layer189 portions forms a template over thesubstrate202a.
• Inblock1218 the substrate may be etched through the template creating vias. Etching may include wet etching or dry etching Regardless of the etching technique, vias1103 are formed from within thesubstrate202a.
• Inblock1220 the photoresist layer may be removed as shown inFIGS. 11D-11E, leaving only theoriginal substrate202awith formedvias1103. Any process known in the art may remove thephotoresist layer189 from the substrate. For example, the photoresist may be removed by stripping or dissolving the remaining portion of the photoresist.
• Inblock1222 an inner conductive layer may be deposited in the vias. As shown inFIG. 11F, the innerconductive layer107 may be deposited as a layer that covers the bottoms and the sides of thevias1103 as well as covering the top of thesubstrate202a. Although the method steps do not explicitly show it, the innerconductive layer107 may include multiple layers similar to the outerconductive layer103 later described with reference toblocks1248,1450, and1452.
• As shown inFIG. 11G, inblock1224 the base layer may be deposited over the innerconductive layer107. Although thebase layer202bis a separate layer than theoriginal substrate202a, it may be the same material as theoriginal substrate202a. Alternatively, thebase layer202bmay be a different substance. It should be noted, that althoughFIG. 11G illustrates thebase layer202bcompletely fills thevias1103, the base layer may202bmay only partially fill thevias1103 and may be deposited similar to the innerconductive layer107 resulting in an unfilled void and a non-solid core.
• Inblock1226 the device may be turned over, and the substrate etched inblock1228.FIG. 11H illustrates the metamaterial device turned over (i.e., flipped 180 degrees) as well as the original substrate etched away leaving the innerconductive layer107 and thebase layer202b. A wet etching process (i.e., using acid) or a dry etching process may remove theoriginal substrate202aresulting.
• Inblock1240 the method may be depositing a first absorber layer. The first absorber layer (i.e., sublayer)105 may be deposited over the innerconductive layer107 formetamaterial200 as illustrated inFIG. 11I. In an embodiment, thefirst absorber layer105 may include a semiconductor material. For example, thefirst absorber layer105 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. In an embodiment, the manufacturing system may add thefirst absorber layer105 over themetal core106 by electroplating, chemical vapor deposition, atomic layer deposition, etc. In an embodiment, the manufacturing system may add thefirst absorber layer105 over the innerconductive layer107 by sputtering, electron beam physical deposition, pulsed laser deposition, etc.
• In block1242 a second absorber layer may be deposited over thefirst absorber layer105 formetamaterial200 as illustrated inFIG. 11I. Any deposition method used to deposit thefirst absorber layer105 may be used to deposit thesecond absorber layer104. In an embodiment, the deposition method for thesecond absorber layer104 may be the same deposition method used for adding thefirst absorber layer105. In an embodiment, thesecond absorber layer104 may include a semiconductor material. For example, thesecond absorber layer104 may include silicon, amorphous silicon, polycrystalline silicon, single crystal silicon, cadmium telluride, cadmium sulfide, gallium arsenide, copper indium selenide, and copper indium gallium selenide. In an embodiment, thesecond absorber layer104 may be an absorber sublayer or region comprising the same material as thefirst absorber layer105 with a different dopant. For example, thefirst absorber layer105 may be p-doped amorphous silicon and thesecond absorber layer104 may be n-doped amorphous silicon. In an embodiment, thesecond absorber layer104 may be an absorber sublayer comprising a different material as thefirst absorber layer105. For example, thefirst absorber layer105 may be p-doped cadmium telluride and thesecond absorber layer104 may be n-doped cadmium sulfide.
• As mentioned above, in some implementations multiple absorber layers may be applied, so inoptional block1246 such additional absorber layers may be over the previous layer in a manner similar to the process steps inblocks1240 and1242. As shown inFIG. 11J, inblock1248, an outerconductive layer103 may be deposited over the last absorber layer (e.g., second absorber layer104). Inoptional block1252, multiple outer conductive layers may be applied as illustrated inFIG. 11K. As discussed above, such outer conductive layers may be applied using chemical deposition or physical deposition.
• Inoptional block1256 current conducting traces may be deposited on themetamaterials200. As explained later with reference toFIGS. 23 and 25, the current conducting traces may be added by creating a template using photolithography and depositing a highly conductive material in a selected position from the template. The current conducting traces may be deposited on the metamaterial by any known deposition method such as chemical vapor deposition, physical deposition, plating, or ink jet material deposition. The ink jet deposition may utilize piezoelectric technology and add silver or any other colloidal material to the desired position without damaging the metamaterial. Alternatively, the current conductive traces may be added by etching with laser ablation in combination with a deposition method such as ink jet techniques. Tuned wavelength lasers may etch desired layers by controlling the laser's wavelength for different layers within the metamaterial. Once etching is complete, the method may include adding the electrical connections such as the current conducting traces at the desired positions on the metamaterial by chemical vapor deposition, physical deposition, plating or inkjet deposition. As a further alternative, the metamaterial may be etched by ink jet technology using acid followed by deposition of conductive material using the same technology or any other deposition method known in the art. Regardless of method used, the current conducting traces may allow for efficient transfer of electricity by adding a lower resistant electrical path within the metamaterials.
• As illustrated inFIG. 11L, in optional block1258 a transparent coating may be applied over the bristles. Such atransparent coating608 may be different from the outerconductive layer103 and anysublayers103aand103b. Thetransparent coating608 may fully fill the voids between each bristle and extend beyond the height of each bristle. As shown, thetransparent coating608 may not be conformal thus leading to deposition methods that use liquid solutions. Thus, the method of depositingtransparent coating608 may include using one or more of the following immersion coating, spray gel techniques, extrusion techniques, a spreader bar, photoresist techniques, sol gel techniques, or any other methods known in the art. In an embodiment, thetransparent coating608 may be a shatterproof material such as EVA. Thetransparent coating608 may seal each bristle providing stability and to prevent them from breaking as well as insulate each bristle from any heat created by the metamaterial device. Observations and experimentations also indicate enhanced peak power generation as the sun translates across the sky for a metamaterial device with atransparent coating608 having a index of refraction similar to glass (e.g., around 1.5). All these benefits may add enhanced power performance and total power generation of the metamaterial device.
• A further method for forming an array of bristles for ametamaterial200 includes forming the bristles by etching vias in a substrate through a photolithographic template. Bristles are formed within the vias by depositing an outer conductive layer, absorber layers, an inner conductive layer, an optional base layer. After forming the bristles, the metamaterial may be turned over where the original substrate is left intact serving as a protective coating and an optical enhancement for themetamaterial200. This via method is illustrated inFIGS. 13A-13L andFIG. 14. As shown inFIGS. 13A-13L and the method steps inFIG. 14, an etching technique may be used to create vias, which is particularly useful when using a glass substrate.
• In block1410 a photoresist may be deposited over the substrate. Thephotoresist layer189 may be deposited over thesubstrate202aby spin on, spray on, or other controlled flow methods know in the art as shown inFIG. 13A. AlthoughFIGS. 13B-13D illustrate a positive photoresist, thephotoresist layer189 may be negative photoresist.
• In block1412 a mask may be positioned over the photoresist layer. Themask195 may be any suitable mask known in the art. As shown inFIG. 12B, themask195 may include mask holes195a. Alternatively, if using a negative photoresist, thepores195amay be filters for blocking ultraviolet light.
• Inblock1414 the method may include exposing an ultraviolet light to the photoresist layer through the mask. Themask195 may be any suitable mask known in the art. As shown inFIG. 13B, themask195 may include mask holes195a.
• Inblock1416 the method may include developing the photoresist layer to dissolve the exposed portions of the photoresist layer. Assuming apositive photoresist layer189, the exposedportions189aare removed creatingvoids189bin the photoresist layer that extend to thesubstrate202aas shown inFIG. 13C. After dissolving the required portions of thephotoresist layer189, the remainingphotoresist layer189 forms a template over thesubstrate192.
• Inblock1418 the substrate may be etched through the template creating vias. Etching may include wet etching or dry etching Regardless of the etching technique employed,vias1103 are formed from within thesubstrate192.
• Inblock1420 the photoresist layer may be removed leaving thesubstrate192 with formedvias1103 as shown inFIGS. 13D-13E.
• Since the outside layers of the photovoltaic bristles are laid down first, conductive traces used to draw current from the photovoltaic cells may be laid down as a first step. Thus, inoptional block1421, conductive traces may be applied to the substrate. Vias for such conductive traces may be formed as part of the operations in blocks1410-1420. Alternatively, conductive traces may be applied to the substrate using dedicated photolithography steps, laser ablation steps, and deposition steps such as those described above and below. In a particular embodiment, the conductive traces may be applied using spray jet techniques. Inblock1422 an outer conductive layer may be deposited in the vias, such as by chemical vapor deposition or physical deposition. If conductive traces are prior to the outer conductive layer, the method may include depositing the outerconductive layer103 over the conductive traces as a conformal film.
• Although not shown inFIGS. 13A-13L, the metamaterial may include an outerconductive layer103 with multiple sublayers. So, inoptional block1452 another outer conductive layer may be applied over the previous layer, essentially repeatingblocks1450 and1452. As shown inFIGS. 13G-13H, in block1440 a first absorber layer may be deposited on the outer conductive layer(s), and in block1442 a second absorber layer may be deposited over the first absorber layer. The first andsecond absorber layer104,105 may be applied by chemical vapor deposition.
• Inblock1446 additional absorber layer applied over the previous layer in a manner similar to the process steps inblocks1440 and1442. Inblock1448, an innerconductive layer107 may be applied over the last absorber layer (e.g., second absorber layer105). In an embodiment, the method may include adding only twoabsorber layers104,105 and thus the innerconductive layer107 is deposited over thelast absorber layer105 by chemical deposition or physical deposition as shown inFIG. 13I. Although the method steps do not explicitly show it, the innerconductive layer107 may also include multiple layers similar to the outerconductive layer103.
• In block1424 a base layer may be deposited. As shown inFIG. 13J, thebase layer202 may be different from thesubstrate192 associated withblock1410. Thebase layer202 may be deposited over the innerconductive layer107 and serves as the actual bottom substrate of the metamaterial device once the vias are turned over. Thebase layer202 may fill thevias1103 creating bristles with solid cores. Alternatively, as shown inFIG. 13J, thebase layer202 may not fill thevias1103, creating bristles with non-solid cores. Regardless, thebase layer202 may be deposited over the innerconductive layer107 by any method known in the art.
• Inblock1426 the metamaterial may be turned over as shown inFIG. 13K, so that the bristles are turned upright presenting theoriginal substrate192 covering the outerconductive layer103 at the top and thebase layer202 at the bottom of the device. Inoptional block1460 the substrate may be further processed, such as to form an anti-reflection layer or roughouter surface192aas shown inFIG. 13L.
• In an alternative embodiment method,lasers2401 may create vias1103 out of a substrate or index matched material as illustrated inFIGS. 13M through 13O. Thelasers2401 may be controlled in terms of exposure time and energy in order to control the depth and size of the vias. After creating thevias1103, themethod1400 operations described above with references toblocks1421,1448,1452,1440,1442,1446,1442,1422,1424,1426,1458, and1460 may be followed.
• Stamps may create vias out of a substrate such as a transparent polymer. When using a polymer, a UV source may cure the stamped vias creating a more rigid structure followed by adding conductive layers, absorber layers, and a base layer. The stamping via method for forming an array of bristles for a metamaterial device is illustrated inFIGS. 15A-15J andFIG. 16.
• Inblock1608 an array of vias may be formed out of the processed polymer. As illustrated inFIGS. 15A-15B, a stamping process may be used to createvias1103 out of apolymer substrate192. Inblock1610 the formed polymer may be cured or otherwise treated to yield desired material properties. For example, such curing/treating may include heating and/or exposure to an ultravioletlight source193.
• The stamping process may include a rolling press or rolling die to createvias1103 on asubstrate192 similar toFIG. 15B. When using a rolling press or a rolling die, a roll-to-web and a web-to-plate sub-process may create the associated stamps andvias method1600. The rolling press or rolling die sub-process is described in more detail below with reference toFIGS. 33A-33G,34,35A-35E,36A-36E.
• Similar tomethod1400, themethod1600 includes laying down the outside layers of the photovoltaic bristles are laid down first, so conductive traces used to draw current from the photovoltaic cells may be laid down prior to the outerconductive layer103. Thus, inoptional block1612, conductive traces may be applied to the substrate. Vias for such conductive traces may be formed as part of the operations in blocks1608-1610. Alternatively, conductive traces may be applied to the substrate using dedicated photolithography steps, laser ablation steps, and deposition steps such as those described above and below. In particular embodiment, the method may include applying conductive traces using a spray jet techniques. Inblock1622 an outer conductive layer may be deposited in the vias. If conductive traces are added prior to the outerconductive layer103, the method may include depositing the outerconductive layer103 over the conductive traces as a conformal film. As illustrated inFIG. 15D, the outerconductive layer103 may be deposited over thepolymer192 and in thevias1103.
• Although it is not shown inFIGS. 15A-15J, multiple outerconductive layers103 or sublayers may be applied. So, inoptional block1652 additional outer conductive layers may be applied over the previous layer.
• As shown inFIGS. 15E-15F, in block1640 a first absorber layer may be applied over the outer conductive layer(s), and in block1642 a second absorber layer may be deposited over the first absorber layer. The method may deposit the first andsecond absorber layer104,105 by chemical vapor deposition. Inoptional block1646 additional absorber layers may be deposited over the other absorber layers in a manner similar to the process steps inblocks1640 and1642.
• As shown inFIG. 15G, inblock1648, an innerconductive layer107 may be applied over the last absorber layer (e.g., second absorber layer105), such as by chemical vapor deposition or physical deposition. The innerconductive layer107 may also include multiple layers similar to the outerconductive layer103 earlier described with reference toblocks1622,1650, and1652.
• As shown inFIG. 15H, in optional block1624 a base layer may be applied. Thebase layer202 may be different from thepolymer192 applied inblock1608 because thebase layer202 is deposited over the innerconductive layer107 and serves as the actual bottom substrate of the metamaterial device once turned over. Although thepolymer192 may be of the same material as thebase layer202, thepolymer192 may serve as an outer transparent coating to the metamaterial device once the metamaterial is complete. Thebase layer202 may fill thevias1103 creating bristles with solid cores. Alternatively, as shown inFIG. 15J, thebase layer202 may not fill thevias1103, creating bristles with non-solid cores. Regardless, thebase layer202 may be deposited over the innerconductive layer107 by any method known in the art.
• As shown inFIG. 15I, inblock1626 the metamaterial may be turned over for further processing. Inoptional block1660 thesubstrate192 may be processed to give it desired physical properties, such as hardening or polishing. The processing may include forming an antireflection layer or roughouter surface192aas shown inFIG. 15J.
• In a further embodiment method that uses some of the same processes as inmethod1600,material1112 in which vias1103 are poured into amold1110 instead of being pressed, as illustrated inFIGS. 15K through 15M. As illustrated inFIG. 15K, instead of a die, the same basic shape may be inverted to form amold1110 onto which may be poured thematerial1112 to form thevias1103 and supporting substrate. This material1113 may be a transparent plastic, polymer or glass that will ultimately have the desired optical properties in the finished product. In this embodiment, the operations of forming the array ofvias1103 inblock1608 include pouring thebase material1112 into themold1110, sufficiently covering the mold surface to provide asubstrate1112 as shown inFIG. 15L. The material may be cured inblock1610 in this state before themold1110 is removed as shown inFIG. 15M. Thereafter, the operations of depositing outer conductive layers, absorber layers and inner conductors may be accomplished as described above with reference to blocks1612-1626.
• As a further alternative embodiment, vias may be formed by adding an index-matched nano-imprinted layer over a substrate. The nano-imprinted layer comprises the vias formethods1200,1400,1600 and may use suitable nano-imprinting techniques known in the art. For example,methods1200,1400, and1600 may include depositing a nano-imprinted layer material with an index of refraction of 1.5 over a glass or polymer substrate.
• As mentioned with reference to block808 ofFIG. 8 forming an array of cores out of the processed polymer may include using a rolling die or rolling press. Similarly, with reference to block1608 ofFIG. 16, forming an array of vias may also include using a rolling die or rolling press. Although a rolling press may be directly applied to a substrate or a moldable layer on top of the substrate, using such a method may damage a master template having a particular pattern for creating the cores or vias. Thus, to increase yield and throughput of creating substrates with an array of cores or vias, a master template may be used to create daughter templates on a web, and each daughter template web may be applied to a substrate to create the desired core or via pattern in a surface material that will be subsequently processed to form the solar arrays. For example, a master template including cores may imprint vias on a substrate applied to a web creating a daughter template. The daughter template with vias may then be applied to a substrate to create cores on the substrate. After curing to increase material strength of the newly formed cores, the substrate may be further processed using embodiment methods such as described above with reference toFIG. 8 and blocks810-858. As an alternative example, a master template including vias may be applied to a substrate on a web to create a daughter template featuring rods that may then be applied to a substrate to imprint vias into the substrate (or a layer over a substrate). The via imprinted substrate may be further processed using embodiment methods such as described above with reference toFIG. 16 and blocks1612-1660.
• Anembodiment method3400 for manufacturing an array of cores for photovoltaic bristles using a rolling press or die is illustrated inFIGS. 33A-33G andFIG. 34. Using a rolling press or die method as described below may enable processing methods that reduce the number of defects in fabricating photovoltaic bristles by creating reusable master templates and daughter dies that can be inspected with inspection results used in a feedback control system to bypass imperfect portions.
• Referring toFIGS. 33A-33G andFIG. 34 together, inblock3402 ofmethod3400 an original master may be created to form a patterned array of bristles for the metamaterial device. Stamping processes such as nano-imprint lithography may create theoriginal master3306 withrods3308 from a flexible material as illustrated inFIGS. 33A and 33B. Any known process in the relevant art may be used to create such master templates. Companies such as EVG, Obducat, NIL Technology, Nanoex, Molecular Imprints, and S{acute over (ú)} Microtech work with nanoimprint lithography and have refined reliable nanoprint lithography techniques. As an alternative, traditional photolithography also may create the original master.
• If using nanoimprint lithography, the process may include imprinting the desired pattern onto theoriginal master3306 created out of a flexible material such as a polymer or polydimethylsiloxane (PDMS). In optional block3404 a suitable metal, such as nickel, may be electroformed over the original master to create a rigid master template or shim. Such metal plating may also be applied after the master is formed into or onto a roller as described below with reference to block3408. The rigid master template may be used to create flexible master templates such as the master webs described below. Whether created by the rigid master template or formed as the original master, flexible templates such as PDMS may be used to imprint patterns on more rigid materials.
• The master template may be formed in one piece, or a large master template may be formed from stitching together the master template inblock3406. Whether the master template is flexible or rigid, multiple masters may be stitched together as illustrated inFIG. 33C. Once the large master template is formed, inblock3408, the large master template may be wrapped around a drum roller (or formed into a roller) as illustrated inFIG. 33D. The drum roller may then be used for subsequent processing in a roll-to-web system as described below.
• The web material may be a polymer or polyester film, such a Dupont's Mylar®. By way of example, the web material may have a thickness of 25 to 250 microns, a length of 100 to 2000 feet, and a width of 0.5 to 6 feet. In block3410 a first moldable material, such as a lacquer, spin-on-glass coatings, a sol-gel, or PDMS, may be applied to a web to coat a thin layer of the material over the web. Since the web itself is flexible, a flexible material such as PDMS may be less restricting than sol-gel, spin-on-glass coatings when moving through the rollers and subsequent processing.
• Inblock3412 the first pattern from the large master template may be imprinted to the coated web to create a second imprint pattern on the web as illustrated inFIG. 33E. In this process operation, the drum roller with a rod pattern imprints vias3314binto the coated material on the web by pressing the web and the coated material against atransfer spacing roller3318. Alternatively, the drum roller with a via pattern creates a rod pattern from the coated material on the web (not shown). Inblock3414 the second imprint pattern on the web may be cured or otherwise processed to increase its material strength. An ultra violet light or a thermal mechanism for applying heat may be used to cure the second imprinted pattern. If using PDMS as a moldable material, a thermal mechanism may apply heat to cure the imprinted pattern. The result of these processor operations is a daughter die web suitable for use in subsequent operations for creating a substrate with cores (or alternatively vias) on a substrate that will eventually become solar cells. As an alternative embodiment method, the web itself may be a flexible substrate and with a cured second imprinted pattern the web substrate may be suitable for use in embodiment methods (e.g.,method800 or1600) describe herein to create metamaterial devices.
• Inblock3416 the master web may be installed on rollers in a web-to-plate process. In block3418 a moldable material may be applied to a substrate or surface on which the solar arrays will be formed. For example, the moldable material may be a polymer that can be cured (e.g., by exposing it to ultra violet radiation) after it is applied to a substrate or support surface and imprinted as described below. As another example, the moldable material may be a flexible thermally curable sol-gel that is applied to a substrate or support surface and imprinted as described below. Alternatively, the substrate itself may be a moldable material and thus the operations inblock3418 may involve creating the substrate of moldable material.
• As illustrated inFIG. 33F, the second pattern from the master web may be imprinted on the moldable material to create a third imprint pattern on or in the substrate inblock3420. In the example illustrated inFIG. 33F, a daughter die web withvias3314bwill formcores3320aof themoldable material3320 on thesubstrate3322. As described below, the process pressing the daughter die3316 into themoldable material3320 on thesubstrate3322 may be controlled so that the two surfaces come together without sliding, which could deform or fail to form the desiredcores3320a(or vias).
• Inblock3422 thecores3320a(which are the third imprinted pattern) illustrated inFIG. 33G or vias (not shown) may be cured or otherwise processed to increase their strength and rigidity before subsequent processing according to embodiment methods described above with reference toFIGS. 8 and 16. As mentioned above, such curing or processing of the cores or vias may involve exposure to ultra violet light (e.g., to increase cross linking in a polymer material) or heating (e.g., to convert sol gel into a glass or ceramic).
• FIG. 35A illustrates an embodiment roll-to-web system3500 suitable for use in the operations described above with reference to blocks3406-3414 inmethod3400. The illustration of the roll-to-web system3500 inFIG. 35A and the following description is provided as an illustrative example and is not intended to limit the scope of the claims as other roll-to-web system configurations (e.g., different roller configurations, different web paths and different sequences of operations) are possible without departing from the scope of the present invention.
• In the embodiment roll-to-web system3500 illustrated inFIG. 35A, a web material may pass through a series of rollers configured and controlled to maintain tension and orientation, apply a moldable material to the web, and imprint a first pattern from a master die on the moldable material to create a second pattern of cores or vias in the moldable material. That second pattern of cores or vias in the moldable material may be subsequently cured/processed to form the daughter die on the web.
• The roll-to-web system3500 may include an unwindroller3502 that may be driven by an unwindmotor3502aconnected to an unwindmotor controller3502bto control the rotation of the unwind roller. Anuncoated web3501amay be installed on the unwindroller3502 and be unwound throughout the roll-to-web system3500. From the unwoundroller3502, theuncoated web3501amay roll over atension sensor3312. The tension sensor may provide web-tension information to the unwindmotor controller3502bwhich may use this information as feedback along with torque sensing feedback from the unwind motor3502ato control web tension through the roll-to-web system3500.
• Theuncoated web3501amay travel over atracking roller3504, which may be adjusted by the control system to control the lateral position of the web in the system in response to signals from anedge sensor3505. By adjusting thetracking roller3504, the web's position on the rollers may also be adjusted to an optimum position/orientation to prevent skewing of the pattern on the web. For example, if the web is too far to the left side of the rollers, the tracking roller may be adjusted to move the web back toward the center of the rollers.
• Theuncoated web3501amay travel through S-wrap rollers3506, which control the velocity and tension of the web3501 as it passes through the roll-to-web system3500. The S-wrap rollers3506 may adjust the velocity of the web3501 traveling through the roll-to-web system3500 based on data from drumroller speed encoders3521. In this manner, the S-wrap rollers may serve to synchronize the speed of the web as it meets with the drum roller (which includes the master die) that imprints the pattern on the web3501. Closely controlling the relative speed of the web and the drum roller reduces the chance for defects to be printed on the daughter dies as well as the chance for damaging the master die on the drum roller.
• Theuncoated web3501amay travel between atransfer roller3507 and arubber roller3508. Thetransfer roller3507 picks up a layer ofmoldable material3509 and applies the layer to the web, while ashear roller3510 ensures the applied layer is of the desired thickness. As theuncoated web3501atravels between therubber roller3508 and thetransfer roller3507, thetransfer roller3507 collects themoldable material3509 on thetransfer roller3507. Prior to thetransfer roller3507 applying the firstmoldable material3509 to theuncoated web3501a, theshear roller3510 removes excessmoldable material3509 from thetransfer roller3507 to ensure a consistent coating on theweb3501a. Arubber roller3508, potentially made of high durometer ground rubber, may provide support to the web3501 while thetransfer roller3507 applies the firstmoldable material3509.
• After thetransfer roller3507 applies the firstmoldable material3509 to theuncoated web3501a, athickness sensor3511 may measure the thickness of the firstmoldable material3509 on thecoated web3501b. The thickness sensor may be used by a control system that may send a signal to cause theshear roller3510 shift position in order to maintain a consistent thickness and compensate for any thickness variations in theuncoated web3501a. For example, if the thickness sensor indicates the coated web's thickness is higher than a set point, control system may cause theshear roller3510 to move closer to thetransfer roller3507, thereby removing more ofmoldable material3509 from thetransfer roller3507 prior to its application to theuncoated web3501a.
• Thecoated web3501bpasses between thedrum roller3512, which includes the master template, and atransfer spacing roller3513 in order to imprint the daughter die pattern in the moldable material oncoated web3501b. The moldable material on thecoated web3501baccepts the first pattern as thecoated web3501bis pressed against thedrum roller3512 to create a second pattern in themoldable material3509. The speed of rotation of thedrum roller3512 is closely controlled by a control system so that it spins in conformity with the speed of the moving web3501 to precisely imprint the first pattern on the web. To do so, the control system may receive signals fromspeed encoders3521 coupled to the S-wrap roller(s)3506 and use this information in a closed-loop control algorithm to ensure that the surface of the drum roller matches the speed of the web3501 passing beneath or over it. Depending on the type of moldable material, the imprintedweb3501cmay be cured/processed (e.g., thermally or with ultra violet light) by acuring mechanism3514.
• The curedweb3501dmay travel over asupport roller3515 and asecond tension sensor3516 prior to being collected on awind roller3518. Thewind roller3518 may be driven by awind motor3518acontrolled by awind motor controller3518b. Thewind motor controller3518bmay adjust the wind up speed of thewind roller3518 based on the torque of thewind motor3518aand signals from thesecond tension sensor3516 to assist in maintaining proper web tension and a speed of advance.
• The roll-to-web system3500 may also include aninspection camera3519 that may scan the curedweb3501dfor defects. Images from theinspection camera3519 may be processed by a computer to identify areas of defects, which may be recorded against position on the web in a web-mapping database3520 that may be used in controlling the final printing process. As described below, a web-to-plate system3600 may access the web-mapping database3520 and adjust its system parameters (e.g., web speed, substrate linear speed, sheet gap mechanism) to avoid applying any mapped defects in theweb3501dto substrate being processed in such a system.
• The roll-to-web system may also include a moldablematerial processing system3522. The moldablematerial processing system3522 may be fluidly connected to a moldable material container that houses themoldable material3509 for thetransfer roller3507. The moldablematerial processing system3522 may recirculate themoldable material3507 through system components (filters, heat exchangers, etc) to ensure themoldable material3507 is clean and at the proper temperature for applying to theweb3501a. The moldablematerial processing system3522 may addmoldable material3509 as needed to ensure ample moldable material for the roll-to-web system3500.
• Various portions of the roll-to-web system3500 may be subject to humidity and temperature controlled to ensure that themoldable material3509 adheres to the web3501 and that themoldable material3509 accepts the desired pattern from thedrum roller3512 with minimal defects. This may be especially important if themoldable material3509 is a sol-gel or other thermally cured material.
• FIGS. 35B-35E illustrate example control systems that may be used to control various portions and components of the roll-to-web system3500 described above enable high precision printing from thedrum roller3512 to the web3501.FIG. 35B illustrates the electrical controls between thetension sensor3503, the unwindmotor3502a, and the unwindmotor controller3502b. The unwindmotor controller3502bmay utilize a PID controller system which adjust the unwindmotor3502abased on inputs from thetension sensor3503, a tension sensor set point, a torque input from the unwind motor3502a, and a torque set point. Askew actuator controller3504aillustrated inFIG. 35C may adjust the position of thetracking roller3504 based on data from theedge sensor3505 and a set point. An S-wrap motor controller3506aillustrated inFIG. 35D may control speed of the s-wrap rollers3506 and the corresponding web velocity through the roll-to-web system. The S-wrap motor controller3506acontrols S-wrap rollers3506 to synchronize the web velocity with the drum roller's rotational speed based on data from thespeed encoder3521 and a set point. Thewind motor controller3518billustrated inFIG. 35E is similar to the unwindmotor controller3502billustrated inFIG. 35B, except that thewind motor controller3518baccepts input data based on thesecond tension sensor3516, a tension set point, torque data from thewind control motor3518a, and a torque set point.
• FIG. 36A illustrates an embodiment web-to-plate system3600 that may be suitable for forming the desired pattern of cores or vias on the substrate as described above with reference to blocks3416-3422 inmethod3400. The illustration of the web-to-plate system3600 inFIG. 36A and the following description is provided as an illustrative example and is not intended to limit the scope of the claims as other web-to-plate system configurations (e.g., different roller configurations, different web paths and different sequences of operations) are possible without departing from the scope of the present invention.
• The web-to-plate system3600 may process a substrate that moves through the system on a linear drive mechanism by applying a moldable material to the surface of the substrate. As an alternative, if the substrate is the second moldable material then a moldable material does not need be added to the substrate. The moldable material applied to the substrate in this process may be different from the moldable material that is applied to the web and used to form the daughter die pattern. The web-to-plate system3600 also passes the daughter die web (which has the second template pattern as described above) through a series of rollers that control its tension and speed of advance, and presses it onto the moldable material the substrate to create a third pattern, which is the desired cores or vias. The web-to-plate system3600 has a web subsection and a plate subsection. The web subsection will be discussed first. The web-to-plate system3600 may also include a module or apparatus that cures/processes the third pattern in order to produce the substrate with a pattern of cores or vias suitable for the embodiment processes described above with reference toFIGS. 8 and 16 for applying photovoltaic materials.
• Theweb3501don the web-to-plate system3600 is weaved through various rollers to control tension and position, similar to the roll-to-web system3500. The web-to-plate system3600 may include an unwindroller3602 driven/controlled by an unwindmotor3602aconnected to an unwindmotor controller3602bconfigured to control the rotation of the unwindroller3602. The daughter dieweb3501dfrom the roll-to-web process described above may be installed on the unwindroller3602. The daughter dieweb3501dmay travel across atracking roller3603 and anedge guide sensor3604. Theedge guide sensor3604 may collect information regarding the position of theweb3501don the rollers relative to a set point and send that data to a controller of thetracking roller3603 so the position/orientation of thetracking roller3603 can be adjusted to correct the orientation of the daughter dieweb3501din the system and prevent web skewing within the rollers. The web-to-plate system3600 may include atension sensor3606 that provides data to an unwindmotor controller3602bto enable the unwindmotor controller3602bto control the unwindmotor3602ato adjust the speed of the unwindroller3606 based on tension data. The unwindmotor controller3602bmay also use torque data from the unwind motor3602a. Unlike the roll-to-web system3500, in the web-toplate system3600 thesame tension sensor3606 may also be connected to thewind motor controller3608 to enable thewind motor controller3608bto control thewind motor3608ato adjust the speed of thewind roller3608 based on the same tension data. Thetension sensor3606 may be positioned after thevelocity roller3605.
• The web-to-plate system3600 may not include S-wrap rollers to control the velocity of the web. Instead, the web-to-plate system3600 may use avelocity roller3605 to perform a similar function. Thevelocity roller3605 may be connected to a velocityroller motor controller3605a, which may adjust the velocity of the daughter dieweb3501dto match the linear speed of the substrate based on data acquired from the linear drive controller3601a. Thevelocity roller controller3605amay also adjust the speed of the web3601dbased on web-mapping data from the web-mapping database3520. For example, if there is a defect in the daughter die web, thevelocity roller3605 may increase the velocity of the daughter die web3601dat a certain point in time to ensure that the defected portions are not imprinted on thesubstrate3609a. Alternatively or in addition, the linear drive controller3601amay be controlled to pause the advance of the substrates in order to enable a portion of the daughter die web with a defect to be advanced before imprinting of the next substrate begins.
• The daughter dieweb3501bmay travel around thevelocity roller3605 past thetension sensor3606 to atransfer gap roller3607. The transfer gap roller may aid in pressing the daughter dieweb3501dagainst the substrate to imprint the second pattern into moldable material on thesubstrate3609athereby creating the third pattern of cores or vias. Once the daughter dieweb3501dimprints the second pattern on thesubstrate3609a, the daughter dieweb3501dmay be wound around thewind roller3608 and used for future processing.
• The plate subsection of the web-to-plate system3600 includes alinear drive mechanism3610 configured to control the linear motion and linear velocity of the substrate3609 through the web-to-plate system3600. Thelinear drive mechanism3610 is connected to alinear drive controller3610a, which may control the speed of the substrate3609 in the web-to-plate system3600 based on data from thesheet gap controller3611a, the web-mapping database3520, and the velocityroller motor controller3605a.
• While the preprocessedsubstrate3609ais traveling across thelinear drive mechanism3610, thesheet gap mechanism3611 may stop the preprocessedsubstrate3609aby a vertical actuation synchronized with the movement of the substrate3609 and the daughter dieweb3501dto reduce imprinting defects. For example, thesheet gap controller3611amay receive web-mapping data regarding a known defect on the daughter die web's pattern from the web-mapping database3520, and in response control thesheet gap mechanism3611 to stop thesubstrate3609afrom moving forward in the system when a defective portion of the daughter die web is present on or near thetransfer gap roller3607 to avoid printing a defect from the daughter dieweb3501don to thesubstrate3609a. As another example, thesheet gap mechanism3611 may prevent thesubstrate3609afrom moving to the secondmoldable material applicator3612, while the moldable material application is adjusted, refilled, etc. When the sheet gap mechanism is actuated a sheet gap sensor or trigger may act as an input to other controllers in the system.
• After passing thesheet gap mechanism3611, amoldable material applicator3612 may apply themoldable material3613 over the substrate to create acoated substrate3609b. Athickness sensor3614 may detect the thickness of the moldable material on thecoated substrate3609band provide feedback to themoldable material applicator3612 for adjusting the amount of moldable material applied to thesubstrate3609a. Thecoated substrate3609bcontacts the daughter dieweb3501dwith pressure applied by thetransfer gap roller3607 so that the second pattern from the daughter dieweb3501dis imprinted on thecoated substrate3609bto create an imprintedsubstrate3609c.
• Depending on the type of moldable material, the imprintedsubstrate3609cmay be cured or processed to increase its material strength, such as via thermal and/or ultra violet radiation curing in acuring mechanism3615. After curing, thefinal substrate3609dis ready for further photovoltaic processing according to an embodiment method described above with reference toFIG. 8 orFIG. 16. Further processing may include adding absorber layers, inner conductive layers, outer conductive, microtraces, etc.+
• FIGS. 36B-36E illustrate control systems that may be configured to enable high precision printing from the web to the substrate in the web-to-plate system3600.FIG. 36B illustrates electrical controls between thetension sensor3606, the unwindroller motor3602a, and the unwindmotor controller3602b. The unwindmotor controller3502bmay utilize a PID controller system that adjusts the unwindmotor3602abased on inputs from thetension sensor3606, a tension sensor set point, a torque input from the unwind motor3602a, and a torque set point. The tension input may be used as the lowest level input variable and torque from the unwind motor3602aand thewind motor3608amay be the major control variables. The unwind andwind motor controllers3602band3608b, respectively, will look for a minimum value from thetension sensor3606 to insure the web has tension. The differential between the wind/unwind torque and a respective set point may be used to determine dynamic wind or unwind force to be applied in order to maintain a desired tension. The wind and unwindcontroller3602band3608bwill evaluate the differential between the two motor systems to control the web tension. Software may run linear and non-linear proportional loop equations based on an input factor. The integral portion will smooth the interactions and the integral sample rate within a sample window. Due to the sensitive nature of the process and the time constants involved, the derivative portion may act as a dampener. Similar logic may be applied to the control of the roll-to-web system3500. Further details regarding PID logic and control loops may be found in U.S. Pat. No. 4,500,408, entitled Apparatus for and Method of Controlling Sputter Coating.
• Askew actuator controller3603aillustrated inFIG. 36C may adjust the position of thetracking roller3603 based on data from theedge sensor3604 and a set point. Avelocity controller3605amay control the speed of thevelocity roller3605 and the corresponding web velocity through the web-to-plate system3600 as illustrated inFIG. 36D. Thevelocity motor controller3605amay control thevelocity roller3605 to synchronize the web velocity with the linear drive speed controlled by thelinear drive controller3610a. Thewind motor controller3608billustrated inFIG. 36E is similar to the unwindmotor controller3602bofFIG. 36B, except that thewind motor controller3518amay accept input data based on torque data from thewind control motor3518a, and a torque set point.
• FIGS. 17-21 illustratemultiple embodiment metamaterials1700,1900,2100 with current conducting traces1701,1702,1703,1901,2101 applied to reduce electrical resistance within the metamaterials. The current conducting traces1701,1702,1703,1901,2101 provide an electrical path for flowing electrons from the outerconductive layer103 inmetamaterials200,300,400 to collector contacts on the edges of the cells. Electrons may travel from the outerconductive layer103 via the current conducting traces1701,1702,1703,1901,2101 to the outer edge of themetamaterials1700,1900,2100 where they connect to bus bars or high capacity conductors. By reducing the electrical resistance withinmetamaterials1700,1900,2100 less electrical energy will be converted to heat and more electrical power may be produced. The embodiment metamaterials1700,1900,2100 described below may include current conducting traces1701,1702,1703,1901,2101 in any combination or sub-combination.
• FIG. 17 illustrates a cross-sectional side view of ametamaterial1700, which is similar tometamaterial200 but with current conducting traces1701,1702, and1703. In an embodiment,metamaterial1700 may includecurrent conducting trace1701 on top of the outerconductive layer103 of a row of shorter photovoltaic bristles1704. AlthoughFIG. 17 shows only one row of shorterphotovoltaic bristles1704 with acurrent conducting trace1701 on the shorterphotovoltaic bristles1704, in an embodiment there may be multiple rows of shorterphotovoltaic bristles1704 with current conducting traces1701 on top.
• In an embodiment,metamaterial1700 may include current conducting traces1702,1703 in different locations than current conductingtrace1701. As with thecurrent conducting trace1701,metamaterial1700 may includecurrent conducting trace1702 on top of the outerconductive layer103 but positioned at the end of the array of photovoltaic bristles201.Metamaterial1700 may includecurrent conducting trace1703 on top of thesubstrate202 or in contact with the innerconductive layer107 to allow efficient electron flow. Electrons may flow from theabsorber sublayer105 to the outerconductive layer103 through the current conducting traces1701,1702 to the electrical destination (e.g., electrical storage, electrical converter, or motor) and the circuit is completed by connecting current conducting trace1303 to the innerconductive layer107 ormetal substrate202. Alternatively, electrons may flow from theabsorber layer105 through the innerconductive layer107 to the current conducting trace1303 and then to an electrical destination (e.g., electrical storage, power converter, etc).
• FIG. 18 illustrates the top view ofFIG. 17 ofmetamaterial1700 with current conducting traces1701,1702,1703. In an embodiment,metamaterial1700 may includecurrent conducting trace1701 on top of an array of shortenedphotovoltaic bristles1704 extending along the width of the array. Similarly, current conducting traces1702 and1703 may extend along in the same direction of the array. Connecting current conducting traces1701 and1702 to current conducting traces1703 may create a complete circuit in themetamaterial1700, thereby allowing current to flow through the array of bristles when struck by photons sufficient to generate electron movement.
• FIG. 19 illustrates a cross-sectional side view of ametamaterial1900, which is similar tometamaterial200, but with current conducting traces1901,1702,1703. In an embodiment,metamaterial1900 may includecurrent conducting trace1901 on the outerconductive layer103 between thephotovoltaic bristles201. As withFIG. 17,metamaterial1900 may include current conducting traces1702 on the outerconductive layer103 and current conducting traces1703 on thesubstrate202 and/or in contact with the innerconductive layer107. In contrast withFIG. 17,metamaterial1900 may not include a row of shorterphotovoltaic bristles1704 because current conducting traces1901 are between thephotovoltaic bristles201 on top of the outerconductive layer103. However, in an embodiment,metamaterial1900 may include a row of shorterphotovoltaic bristles1704 with acurrent conducting trace1701 on the shorterphotovoltaic bristles1704 in addition to the current conducting traces1901 positioned between photovoltaic bristles201.
• FIG. 20 illustrates the top view ofFIG. 19 of an array ofphotovoltaic bristles201 on aflat substrate202 with current conducting traces1901 positioned between photovoltaic bristles201. Similar to the current conducting traces1701,1702,1703 inFIG. 18, the current conducting traces1901,1702, and1703 extend the entire width of the array. In an embodiment, the current conducting traces1901,1702,1703 may extend in any direction. For example, the current conducting traces1901,1702, and1703 may extend diagonally, along the length, and/or along the width of themetamaterial1900.
• FIG. 21 illustrates a cross-sectional side view of a portion ofmetamaterial2100 similar tometamaterial300, but with current conducting traces2101,1702,1703.Metamaterial2100 includescurrent conducting trace2101, which may be located betweenphotovoltaic bristles301 as well as at the peak and trough of the slanted substrate surfaces308a,309a,308b,309b. In an embodiment,metamaterial2100 includes current conducting traces1702,1703 at the ends of themetamaterial2100 similar toFIGS. 17 and 19.Current conducting trace1702 may be on the outerconductive layer103 at the ends of the array of photovoltaic bristles301.Current conducting trace1703 may be on top of thesubstrate302 and/or in contact with the innerconductive layer107. In an embodiment,metamaterial2100 may include current conducting traces2101 on top of the outerconductive layer103 and betweenphotovoltaic bristles301 located on the peak and/or the trough of the slanted substrate surfaces308a,309a,308b,309b. Although it is not shown inFIG. 21, themetamaterial2100 may have current conducting traces2101 positioned on the outerconductive layer103 on top of shorterphotovoltaic bristles1704 as shown inFIG. 17. In an embodiment,metamaterial2100 may be similar tometamaterial400 as it may be withoutphotovoltaic bristles401 on slanted substrate surfaces409a,409b. For example, the metamaterial may include current conducting traces2101 betweenphotovoltaic bristles401 only on alternating slanted substrate surfaces408a,408b, etc.
• Photolithographic techniques may be used to deposit the current conducting traces1701,1702,1703,1901, and2101 ofFIGS. 17-21 onmetamaterials200,300, and400. These current conducting traces may be added to the metamaterials regardless of whether the metamaterials are created through stamping, vias, or any other technique. Although photolithographic techniques are used for adding each current conductingtrace1701,1702,1703,1901, and2101 to the metamaterial device, when addingcurrent conducting trace1703 to a metamaterial a different method may be used. Thus,FIGS. 22A-22H illustrate andFIG. 23 describes the method steps for forming current conducting traces1701,1702,1901, and2101, whileFIGS. 24A-24J illustrate andFIG. 25 describes the methods steps for formingcurrent conducting trace1703. Each method is discussed in turn.
• Current conducting traces1701,1702,1901, and2101 may be formed onmetamaterials200,300, and/or400. In block2302 a photoresist layer may be deposited over the metamaterial. As shown inFIGS. 22A and 22B, aphotoresist layer189 may be deposited over the metamaterial. In block2304 a mask may be positioned over the photoresist layer. Inblock2306 the photoresist layer may be exposed to UV light through the mask. As illustrated inFIG. 22C, exposing only a portion of thephotoresist189 to UV radiation creates an exposedportion189awithin thephotoresist layer189. Inblock2308 thephotoresist layer189 may be “developed” by exposing it to chemicals that remove the exposedportions189aleaving a protective template, and the assembly may be etched to createpores189bshown inFIG. 22D. Inoptional block2310 the substrate may be etched through the template. This step may be required when the metamaterial is formed with vias inmethods1400 or1500. When creating photovoltaic bristles using vias, the original substrate192 (shown inFIGS. 13K and 15I) may form a protective coating over the bristles. Thus, the method may include an etching step to expose the outerconductive layer103 through thesubstrate192 before depositing current conducting traces1701,1702,1901, and2101 on the outerconductive layer103 eventually followed by filling the etched void in thesubstrate192 with a transparent coating. In block2322 a current conducting trace may be deposited on the metamaterial. Current conducting traces1701,1702,1901, and2101 may be deposited on the outerconductive layer103 through photoresist template as shown inFIG. 22E. Inblock2312 the photoresist layer may be removed. As shown inFIG. 22F, when thephotoresist189 is removed, only the bristles and the current conducting trace remains. After removing the photoresist, a transparent coasting may be applied to the solar cell covering the bristles and the deposited current conducting trace.
• As an alternative to photolithographic techniques, a method for depositing the current conductive traces may include anink jet device2201 illustrated inFIGS. 22G and 22H to reduce manufacturing cost. Theink jet2201 may deposit aconductive trace1901 in desired locations (e.g., between bristles) by using colloidal material such as silver without the use of the multiple steps associated with photolithographic techniques. Thus, this alternative may include only one-step of depositing a conductive trace on the metamaterial inblock2322.
• Current conducting trace1703 may be formed by a different method as illustrated inFIGS. 24A-24J andFIG. 25. In block2502 a first photoresist layer may be deposited over the metamaterial. As shown inFIG. 24A, afirst photoresist layer189 may be deposited over and between the bristles of the metamaterial. In block2504 a first mask may be positioned over the first photoresist layer. As shown inFIG. 24B, thefirst mask195 may block UV radiation to thephotoresist189 except throughmask portion195a. This controls the UV radiation to the desired portion of thephotoresist layer189. Inblock2506 the method may include exposing a UV source to the first photoresist layer through the first mask to create an etching template. As illustrated inFIG. 24B, exposing only a portion of thephotoresist layer189 to UV radiation creates an exposedportion189awithin thephotoresist layer189. After creating the exposedportion189awithin the photoresist, the mask may be subsequently removed from the metamaterial. Inblock2508 the first photoresist layer may be developed. For a positive photoresist layer this includes removing the exposedportion189aleaving a template created by the remainingphotoresist layer189 withpores189bas shown inFIG. 24C. Inblock2510 the method may include etching the metamaterial through the etching template. As illustrated inFIG. 24D, thephotoresist template189 controls the etching process by removing only a portion of the outerconductive layer103, thefirst absorber layer105, and thesecond absorber layer104. Inblock2512 the first photoresist layer may be removed. As shown inFIG. 24E, after removing thefirst photoresist layer189, the metamaterial may include a void in the outer conductive layer and the absorber layers. In block2514 a second photoresist layer may be deposited over the metamaterial. As shown inFIG. 24F thesecond photoresist layer190 covers the bristles and the void in the metamaterial created by the etching step. In block2516 a second mask may be positioned over the second photoresist layer. As shown inFIG. 24G, asecond mask196 may block the UV radiation to thesecond photoresist layer190 except through thesecond mask portion190a. This controls the UV radiation to the desired portion of thesecond photoresist layer190. Inblock2518 the method may include exposing a UV source to the second photoresist layer through the second mask. As illustrated inFIG. 24G, exposing only a portion of thesecond photoresist layer190 to UV radiation creates a second exposedportion190awithin thesecond photoresist layer190. After creating the second exposedportion190awithin the second photoresist layer, the second mask may be subsequently removed from the metamaterial. Inblock2520 the second photoresist layer may be developed. For a positive photoresist this includes removing the second exposedportion190aleaving a template created by the remainingsecond photoresist layer190 withpores190bas shown inFIG. 24H. In block2522 a current conducting trace may be deposited on the metamaterial.Current conducting trace1703 may be deposited on the innerconductive layer107 through thesecond photoresist pore190bas shown inFIG. 24I. Inblock2524 the second photoresist layer may be removed. As shown inFIG. 24J, when thesecond photoresist layer190 is removed, only the bristles and thecurrent conducting trace1703 remains. After removing the photoresist, a transparent coasting may be applied to the metamaterial covering the bristles and the deposited current conducting trace.
• In another embodiment method that uses some of the same processes as inmethod2500, the steps for etching may include laser ablation using a wavelength-tuned laser to etch only the desired layers, as illustrated inFIGS. 24K through 24M. This may reduce the number of steps associated with the photolithographic techniques ofmethod2500 thereby reducing manufacturing cost. As illustrated, a wavelength-tunedlaser2401 may be used to etch desired exposing a desired portion of the metamaterial for a conductive trace. Since this technique provides a controlled etching alternative, it allows for any of the methods above to deposit current conducting traces at any point within the method steps.
• As an alternative embodiment to the conductive traces described above, high conductive regions may be applied to the various metamaterials though directional deposition such as solid angle physical vapor deposition or ion source deposition. The method may include preferentially coating highly conductive regions with metal while leaving other regions with minimal coating to refrain from blocking entering photons. For example, the method may include coating the area between the vias or bristles ten times as thick as the coating along the sidewalls of the vias or bristles allowing photons to pass through the sidewalls while simultaneously creating a highly conductive region to act as a conductive trace. As another example, the method may include using a thicker conductive coating only on the side of bristles or vias that will receive less exposure to photons during operation of the completed metamaterial. To accomplish the single region deposition, the method may include angling the substrate during the deposition process so that only the desired side receives the highly conductive coating. Regardless of the exact process, the conductive regions may be applied to any of the methods listed above.
• Metamaterials200,300,400,1700,1900, and2100 formed by any of the processes above may be assembled into a solar panel. As briefly described above, the corrugated shape may be incorporated into an assembled solar panel as illustrated inFIGS. 26-32. The panel assembly may include a corrugated base with panel surfaces angled at approximately 30 to 60 degrees for increasing off-axis photon absorption inmetamaterials200 with flat substrates as well as an increasing the planar bristle density without increasing shadowing, resulting in similar gains in total efficiency and power generation frommetamaterials300,400 with corrugated substrates. However, the total efficiencies gains are compounded when the panel assembly and metamaterials include a corrugated shape (e.g.,metamaterial300 in a corrugated solar panel assembly) because the assembled panel benefits from an increase in planar bristle density and off-axis photon absorption.
• FIGS. 26-32 illustrate an embodimentsolar panel3100 with acorrugated base2610. Solar panels with acorrugated base2610 may be formed by assemblingmetamaterials200,300,400,1700,1900, and/or2100 together.FIG. 26 illustrates a perspective view of a section of asolar panel2600.Solar panel section2600 may include one ormore panel surfaces2602,2604 in an alternating fashion on acorrugated base2610. In an embodiment, eachpanel surface2602,2604 may includemetamaterials200,300,400,1700,1900, and/or2100 withphotovoltaic bristles201,301,401. In an embodiment, panel surfaces2602,2604 may include the same metamaterial. For example, eachpanel surface2602,2604 may includemetamaterials200 with aflat substrate202. In an embodiment, panel surfaces2602,2604 may include different metamaterials. For example, panel surfaces2602 may includemetamaterials200 withflat substrates202 while panel surfaces2604 may includemetamaterials300 withcorrugated substrates302. In an embodiment, afirst panel surface2602 may includemetamaterials200,300,400,1700,1900, and/or2100, while asecond panel surface2604 is withoutmetamaterial200,300,400,1700,1900, and/or2100. For example,solar panel section2600 may include afirst panel surface2602 withmetamaterials300 alternating along acorrugated base2610 with asecond panel surface2604 without metamaterials. In an embodiment, asecond panel surface2604 withoutmetamaterials200,300, and/or400 may include a reflective film (i.e., a mirror). For example, the first and second panel surfaces2602,2604 may alternate along thecorrugated base2610 with afirst panel surface2602 withmetamaterials400 and asecond panel surface2604 with only a reflective film. Regardless, eachpanel surface2602,2604 rests on the front of acorrugated base2610.
• In an embodiment,fasteners2612 may be used to fasten the panel surfaces2602,2604 to thecorrugated base2610 withconnectors2608. Thesame fastener2612 may also fasten the rails2902 (shown inFIG. 29) to thecorrugated base2610 and theconnectors2608. In an embodiment,solar panel section2600 may include abuss bar2606 withconnectors2608 to connect thebuss bar2606 to eachmetamaterial200,300,400,1700,1900, and/or2100 of the panel surfaces2602,2604. In an embodiment, thebuss bar2606 may connect to thecorrugated base2610 in aslot2614 of the corrugated based2610. Theslot2614 may provide stability for thebuss bar2606 as well as allowsolar panel section2600 to rest on a flat back of thecorrugated base2610.
• FIG. 27 illustrates a top view ofsolar panel section2600. As illustrated withFIG. 26, thesolar panel section2600 may includepanel surfaces2602,2604, acorrugated base2610, abuss bar2606,fasteners2612, andconnectors2608.
• FIG. 28 illustrates a side view ofsolar panel section2600. As illustrated, theconnectors2608 may use asingle fastener2612 for each pair ofpanel surfaces2602,2604. Thefastener2612 may be any means of fastening theconnectors2608 to thecorrugated base2610 and the panel surfaces2602,2604. For example, thefasteners2612 may utilize a bolt, a joint, a rivet, screws, a pin, clips, latch, etc. In an embodiment, thefastener2612 may be metal or metalized to create an electrical pathway from themetamaterials200,300,400,1700,1900, and/or2100 ofpanel surfaces2602,2604 to theconnectors2608. As referenced inFIG. 26 thecorrugated base2610 may have aslot2614 for thebuss bar2606. Theslot2614 may allow thebuss bar2606 to connect to the backside of thecorrugated base2610 and form a flat surface (i.e. flat back) of thecorrugated base2610. The flat surface of the backside of thecorrugated base2610 may allow for a more stable assembly for the completedsolar panel2600.
• FIG. 29 illustrates an exploded view of asolar panel section2600. As illustrated,rail2902 may be secured to thecorrugated base2610 by asecuring mechanism2901. Therail2902 may be secured to thecorrugated base2610 by any means possible. For example, therail2902 may be secured to the backside of thecorrugated base2610 by a rivet, crimping, a bolt, adhesive or any other securing means. In another example, therail2902 may be secured to thecorrugated base2610 similar to afastener2612 used to fasten the panel surfaces2602,2604 to thecorrugated base2610. In an embodiment, therail2902 also may be fastened by thefastener2612 topanel surfaces2602,2604 on the backside of thecorrugated base2610 opposite theconnectors2608. In an embodiment, therail2902 may be fastened to the panel surfaces2602,2604 by any means possible including the fastening means as described with reference toFIG. 28. In an embodiment, thebuss bar2606 may be secured to thecorrugated base2610 by asecuring mechanism2901. In an embodiment, thebuss bar2606 may be attached to therail2902 with anattachment mechanism2904. Theattachment mechanism2904 may be any means of attachment. The attachment mechanism may be the same as the securingmechanisms2901, or thefasteners2612 as described above.
• In an embodiment, therails2902 and the buss bars2606 may be electrically connected to themetamaterials200,300,400,1700,1900, and/or2100 ofpanel surfaces2602,2604. In an embodiment, therails2902 may be electrically connected toconnectors2608. Theconnectors2608 may be electrically connected to the panel surfaces2602,2604 includingmetamaterials200,300,400,1700,1900, and/or2100. Themetamaterials200,300,400,1700,1900, and/or2100 may create electron movement when the photovoltaic bristles201,301,401 are struck by photons. In an embodiment, the outerconductive layer103 ofmetamaterials200,300,400 illustrated inFIGS. 2B,3B, and4B may be electrically connected toconnectors2608. In an embodiment the current conducting traces1701,1702,1703,1901, and/or2101 ofmetamaterials1700,1900,2100 as illustrated inFIGS. 17,19, and21 may be electrically connected theconnectors2608 to help reduce the electrical resistance in themetamaterial1700,1900,2100. Regardless, electron movement may create electricity to flow from themetamaterials200,300,400,1700,1900, and/or2100 within the panel surfaces2602,2604 to theconnectors2608 to therails2902 andbuss bars2606 connected to therails2902. From therails2902 andbuss bars2606, the electricity may flow toother rails2902 andbuss bars2606 in neighboringpanel sections2600 and eventually to an electrical destination (e.g. electrical storage) connected to the completedsolar panel3100.
• FIG. 30 illustrates a back view of asolar panel section2600. As discussed earlier, thebuss bar2606 of thesolar panel section2600 may have asecuring mechanism2901 to help stabilize thebuss bar2606 on the backside of thecorrugated section2600. In an embodiment, eachbuss bar2606 may have one ormore securing mechanism2901 to secure thebuss bar2606 to the back of thecorrugated base2610. Alternatively, eachbuss bar2606 may not have asecuring mechanism2901 with thecorrugated base2610 and may be secured and connected only with therails2902. AlthoughFIGS. 26-30 depict asolar panel section2600 with tworails2902 and twobuss bars2606, asolar panel section2600 may have any number ofrails2902 and buss bars2606. Some examples ofsolar panel sections2600 with a different number of rails include solar panel sections with one rail, two rails, three rails, four rails, five rails, etc. Some other examples of solar panel sections with a different number of buss bars include panel sections with one buss bar, two buss bars, three buss bars, four buss bars, five buss bars, etc.
• FIG. 31 illustrates a perspective view of asolar panel3100 with multiplesolar panel sections2600. In an embodiment, eachsolar panel section2600 may includemetamaterials200,300,400. In another embodiment, the metamaterials may include current conducting traces1701,1702,1703,1901,2101 as illustrated inmetamaterials1700,1900, or2100 ofFIGS. 17,19, and21. In an embodiment, eachsolar panel section2600 may be adjacent and combine with one or more othersolar panel sections2600. In an embodiment, thesolar panel3100 may include aframe3102 that surrounds the outer perimeter of the combinedsolar panel sections2600 within thesolar panel3100.
• FIG. 32 illustrates an exploded view of asolar panel3100. In an embodiment, thesolar panel3100 may include aframe3102, atop cover3202, and aback cover3208. In an embodiment, theframe3102 is connected withcorner brackets3206 andfasteners3204 to the corners ofsolar panel sections2600 positioned in the corners ofsolar panel3100. In an embodiment, theframe3102 forsolar panel3100 may include twoshort pieces3214a,3214band twolong pieces3216a,3216bto attach along the four sides of the assembledsolar panel sections2600. In an embodiment, thesolar panel3100 may have four or more corner brackets3206 (e.g., eight as shown) to connect the pieces of theframe3102 to the assembledsolar panel sections2600.
• In an embodiment, thetop cover3202 of thesolar panel3100 may be transparent or semitransparent. Thetop cover3202 may protect thesolar panel section3100 and their electrical and photovoltaic components. For example, thetop cover3202 may protect thesolar panel section2600 and their electrical and photovoltaic components from oxygen corrosion, wind, water, and dirt or anything else that may reduce the efficiency or life of themetamaterials200,300,400,1700,1900, and/or2100 insolar panel3100.
• In an embodiment, theback cover3208 ofsolar panel3100 may includerounded slots3212 so thatfasteners3210 may connect theback cover3208 to the assembled (i.e., combined)solar panel sections2600. Thefasteners3210 may be any type that may connect theback cover3208 to the assembledsolar panel sections2600. For example, thefasteners3210 may fasten similar to thefasteners2612 as described with reference toFIG. 28 (e.g., by bolts, screws, etc.).
• In an embodiment, theback cover3208 and thetop cover3202 may be sealed within thesolar panel3100 by theframe3102. In an embodiment, only theback cover3208 or thetop cover3202 may be sealed within thesolar panel3100 by theframe3102. Theback cover3208 and thetop cover3202 may provide structural support to thesolar panel3100 and its subparts. In addition, theback cover3208 and thetop cover3202 may protect the subparts of thesolar panel3100 from any contamination that may reduce the efficiency and life of themetamaterials200,300,400,1700,1900, and/or2100 insolar panel3100 such as wind, water, dirt or oxygen, etc.
• In another embodiment, the volumetric efficiency gains realized from the solar panel with the corrugated sections may be achieved by mounting completed solar panels in corrugated patterns with respect to each other. Thus, completed solar panels may be mounted in an array of solar panels where the surfaces of each solar panel form an angle of approximately 30 to 60 degrees with a common plane such as a base connecting the solar panels that is perpendicular to the sun. As an alternative embodiment, reflectors may replace some completed solar panels in the corrugated pattern to help maximize efficiency gain of each completed solar panel.
• The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.

Claims (6)

What is claimed is:

1. A method for manufacturing a metamaterial, comprising:

creating a daughter template on a web from an original master template; and

imprinting a pattern from the daughter template on a moldable material positioned on a substrate using a web-to-plate printing process.

2. The method ofclaim 1, wherein the pattern is an array of cores.

3. The method ofclaim 1, wherein the pattern is an array of vias.

4. A system for manufacturing a solar array, comprising:

a roll-to-web subsystem configured to transfer a first pattern from a master die to a daughter die on a web;

a daughter die; and

a web-to-plate subsystem configured to imprint the daughter die onto a substrate to generate a pattern of micron-sized structures on the substrate suitable for forming a metamaterial structure of photovoltaically active bristles.

5. The system ofclaim 4, wherein the pattern of micron-sized structures on the substrate comprises an array of cores on the substrate.

6. The system ofclaim 4, wherein the pattern of micron-sized structures on the substrate comprises an array of vias on the substrate.

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