SYSTEM AND METHOD FOR A PHOTOVOLTAIC STRUCTURE
CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Application No. 60/864,936, filed November 8, 2006, which is incorporated by reference herein for all purposes.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER
PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK. [0003] NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0004] The present invention relates generally to solar energy techniques. In particular, the present invention provides a method and resulting device fabricated from a hydrogen separation process using a co-implant to form a thin layer of single crystal material suitable for photovoltaic applications. More particularly, the present invention provides a method and resulting device for manufacturing the photovoltaic regions within the single crystal material on a substrate member. Such substrate member can be a support member, such as a low grade polysilicon plate, metal plate, glass plate, a combination of these, or the like. Merely by way of example, the invention has been applied to solar panels, commonly termed modules, but it would be recognized that the invention has a much broader range of applicability.
[0005] Consumption of energy resources continues to grow, as the population of the world increases rapidly to over six billion people. Often times, conventional energy comes from fossil fuels, including oil and coal, hydroelectric plants, nuclear sources, and others. As merely an example, further increases in oil consumption have been projected. Developing nations such as China and India account for most of the increase, although the United States remains the biggest consumer of energy resources. In the U.S., almost every aspect of our daily lives depends, in part, on oil. These aspects include driving to and from work, heating our homes, and operating large machines for construction and the like.
[0006] Oil is becoming increasingly scarce. As time further progresses, an era of "cheap" and plentiful oil is coming to an end. Oil will eventually disappear, which could possibly take us back to primitive times. Accordingly, other and alternative sources of energy have been developed. Modern day society has also relied upon other very useful sources of energy. Such other sources of energy include hydroelectric, nuclear, and the like to provide our electricity needs. Such electricity needs range from lighting our buildings and homes to operating computer systems and other equipment and the like. Most of our conventional electricity requirements for these home and business use come from turbines run on coal or other forms of fossil fuel, nuclear power generation plants, and hydroelectric plants, as well as other forms of renewable energy. A popular form of renewable energy has been solar, which is derived from our sun.
[0007] Our sun is essential for solar energy. Solar energy possesses many desired characteristics. As noted above, solar energy is renewable. Solar energy is also abundant and clean. Conventional technologies developed often capture solar energy, concentrate it, store it, and convert it into other useful forms of energy. A popular example of one of these technologies includes solar panels. Such solar panels include solar cells that are often made using silicon bearing materials, such as polysilicon or single crystal silicon. An example of such solar cells can be manufactured by various companies that span our globe. Such companies include, among others, Q Cells in Germany, Sun Power Corporation in California, Suntech of China, and Sharp in Japan.. Other companies include BP Solar and others.
[0008] Unfortunately, solar cells still have limitations although solar panels have been used successfully for certain applications. As an example, solar cells are often costly. Solar cells are often composed of silicon bearing wafer materials, which are difficult to manufacture efficiently on a large scale. Availability of solar cells made of silicon is also somewhat scarce with limited silicon manufacturing capacities. These and other limitations are described throughout the present specification, and may be described in more detail below.
[0009] From the above, it is seen that techniques for improving solar devices is highly desirable. BRIEF SUMMARY OF THE INVENTION
[0010] According to the present invention, techniques related to solar energy are provided. In particular, the present invention provides a method and resulting device fabricated from a hydrogen separation process using a co-implant to form a thin layer of single crystal material suitable for photovoltaic applications. More particularly, the present invention provides a method and resulting device for manufacturing the photovoltaic regions within the single crystal material on a substrate member. Such substrate member can be a support member, such as a low grade polysilicon plate, metal plate, glass plate, a combination of these, or the like Merely by way of example, the invention has been applied to solar panels, commonly termed modules, but it would be recognized that the invention has a much broader range of applicability.
[0011] According to an embodiment, the present invention provides a solar cell. The solar includes a supporting layer that is characterized by a first thickness. The solar cell also includes a reflective layer overlying the supporting layer. The reflective layer is characterized by a second thickness. The reflective layer is attached to the supporting layer. The solar cell additionally includes a photovoltaic layer, which includes a first side and a second side. The photovoltaic layer is characterized by a third thickness. The photovoltaic layer includes a first side and a second side. The first side is opposite from the second side. The photovoltaic layer includes a first portion and a second portion. The first portion includes a fourth thickness from the first side. The second portion includes a fifth thickness from the second side. The first side of the photovoltaic layer is attached to the reflective layer. The first portion is characterized by a predetermined polarity (e.g., p+ type doping). The fourth thickness is less than the third thickness. The fifth thickness is less than the third thickness.
[0012] According to another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a silicon layer having a surface region and a bonding region. The silicon layer is characterized by a first thickness. The surface region is characterized by a second thickness. The bonding region is characterized by a third thickness. The surface region includes n+ type material. The bonding region including p+ type material (e.g., boron doping). The solar cell structure also includes a reflective layer that includes a first side and a second side. The first side is bonded to the bonding region of the silicon layer. Additionally, the solar cell structure includes a plate supporting layer. [0013] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a single-crystal silicon layer that has a surface region and a bonding region. The silicon layer is characterized by a first thickness. The surface region is characterized by a second thickness. The bonding region is characterized by a third thickness. The surface region includes n+ type material. The bonding region includes p+ type material. The solar cell structure also includes a spin-on-glass layer, which has a first side and a second side. The first side is bonded to the bonding region of the silicon layer. The solar cell structure further includes a glass plate that is bonded to the second side of the spin-on-glass layer.
[0014] According yet another embodiment, the present invention provides a method for manufacturing a solar cell structure. The method includes a step for providing a substrate. The substrate consists essential of silicon. The substrate is characterized by a first thickness. The substrate includes a first side and a second side. The first side is opposite from the second side. The substrate includes a first portion, a second portion, and a third portion. The first portion includes a second thickness from the first side. The second portion includes a third thickness from the first side. The third thickness is greater than the second thickness. The third portion includes a fourth thickness between the second portion and the second side. The method further includes a step for doping the first portion with a predetermined polarity type. The method additionally includes a step for implanting the second portion with a hydrogen implantation to form a separation region. Additionally, the method includes a step for providing a bottom layer. The bottom layer is characterized by a fifth thickness. The bottom layer includes a third side and a fourth side. The third side is opposite from the fourth side. The method also includes a step for attaching the first side of the substrate to the third side of the bottom layer. Furthermore, the method includes a step for removing the third portion of the substrate at the separation region.
[0015] According to yet another embodiment, the present invention provides a method for fabricating a solar cell. The method includes a step for providing a single crystal silicon substrate that has a surface region. The method also includes a step for performing a first implantation process to introduce a first impurity species through the surface region and within a vicinity of a first thickness of the surface region. The method additionally includes a step for performing a second implantation process to introduce a plurality of hydrogen species at a region underlying the surface region and to define a thickness of single crystal silicon to be removed. In addition, the method includes a step for bonding the surface region of the single crystal silicon substrate to a stiffener member to form a multi-layered structure including a reflector region at an interface between the surface region and the stiffener member. Also, the method includes a step for performing a thermal treatment process on the multi-layered structure to cause separation at the region underlying the surface region of the single crystal silicon substrate and to exfoliate the thickness of single crystal silicon material, while the thickness of single crystal material remains attached to the stiffener member, to form a roughened region defining the thickness of single crystal silicon material. In addition, the method includes a step for forming one or more photovoltaic devices onto the thickness of the single crystal silicon material.
[0016] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a photovoltaic layer having a top side and a bottom side. The photovoltaic layer consisting essentially of p-type silicon material. The photovoltaic layer includes a first portion positioned between the top side and a first thickness and a second portion positioned between the bottom side and a second thickness. The first portion includes lateral patterns of p+ and n+ regions. The second portion is characterized by p+ type polarity for reducing carrier recombination. The solar cell structure additionally includes a reflective layer including a first side and a second side. The first side is coupled to the bottom side of the photovoltaic layer. The solar cell structure also includes a support layer that is coupled to the second side of the reflective layer.
[0017] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a photovoltaic layer having a top side and a bottom side. The photovoltaic layer consisting essentially of n-type silicon material. The photovoltaic layer includes a first portion positioned between the top side and a first thickness and a second portion positioned between the bottom side and a second thickness. The first portion includes lateral patterns of p+ and n+ regions. The second portion is characterized by n+ type polarity for reducing carrier recombination. The solar cell structure additionally includes a reflective layer including a first side and a second side. The first side is coupled to the bottom side of the photovoltaic layer. The solar cell structure also includes a support layer that is coupled to the second side of the reflective layer.
[0018] Many benefits are achieved by way of the present invention over conventional techniques. For example, the present technique provides an easy to use process that relies upon conventional technology such as silicon materials, although other materials can also be used. Additionally, the method provides a process that is compatible with conventional process technology without substantial modifications to conventional equipment and processes. Preferably, the invention provides for an improved solar cell, which is less costly and easy to handle. Such solar cell uses a hydrogen co-implant to form a thin layer of photovoltaic material. Since the layers are very thin, multiple layers of photovoltaic regions can be formed from a single conventional single crystal silicon or other like material wafer. In a preferred embodiment, the present thin layer removed by hydrogen implant and thermal treatment can be provided on a low grade substrate material, which will serve as a support member. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout the present specification and more particularly below.
[0019] Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 is a simplified diagram of a plurality of silicon slices from a single crystal substrate member according to an embodiment of the present invention.
[0021] Figure 2 is a simplified diagram of a multi-layered substrate according to an embodiment of the present invention.
[0022] Figure 3 is a simplified diagram of an alternative multi-layered substrate according to an alternative embodiment of the present invention.
[0023] Figure 4 is a simplified diagram of a solar cell according to an embodiment of the present invention.
[0024] Figure 5 is a simplified diagram of an alternative multi-layered substrate with opposite polarity according to an alternative embodiment of the present invention.
[0025] Figure 6 is a simplified diagram of an alternative solar cell structure with opposite polarity according to an embodiment of the present invention.
[0026] Figure 7 is a simplified diagram of a solar cell illustrating light trapping effect and photogenerated carrier collection according to an embodiment of the present invention. [0027] Figure 8 is a simplified flow diagram of a process of manufacturing a solar cell according to an embodiment of the present invention.
[0028] Figure 9 shows doping steps 802 and 803 of the flow diagram according to an embodiment of the present invention.
[0029] Figure 10 shows hydrogen implantation step 804 of the flow diagram according to an embodiment of the present invention.
[0030] Figure 11 shows gluing step 805 of the flow diagram according to an embodiment of the present invention.
[0031] Figure 12 shows detachment step 806 of the flow diagram according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] According to the present invention, techniques related to solar energy are provided. In particular, the present invention provides a method and resulting device fabricated from a hydrogen separation process using a co-implant to form a thin layer of single crystal material suitable for photovoltaic applications. More particularly, the present invention provides a method and resulting device for manufacturing the photovoltaic regions within the single crystal material on a substrate member. Such substrate member can be a support member, such as a low grade polysilicon plate, metal plate, glass plate, a combination of these, or the like. Merely by way of example, the invention has been applied to solar panels, commonly termed modules, but it would be recognized that the invention has a much broader range of applicability.
[0033] As explained above, the lack of silicon material has been a challenge in manufacturing solar panels on large scale. Over the past, various conventional techniques have been developed to produce cost-efficient solar panels. Unfortunately, conventional techniques are often inadequate in various ways. More specifically, conventional techniques often involve reducing the amount of silicon material used for manufacturing solar panels. However, solar panels that are manufactured with reduced amounts of silicon materials often fail to meet performance goals (e.g., being able to produce a desired amount of energy per unit area). [0034] Therefore, it is to be appreciated that according to various embodiments, the present invention provides a technique for manufacturing solar panels that performance substantial as same as conventional solar panels using less silicon material.
[0035] Typically, the solar cell layers in a conventional solar panels have a thickness of two hundred to three hundred microns. The thickness of conventional solar layers is related to a variety of performance metrics, such as rigidity of the solar cells, amount of energy that can be generated, etc. With conventional solar cell structure, two hundred to three hundred microns of thickness is necessary for solar panels to meet these performance metrics. At the same time, manufacturing solar cell at this thickness level means much silicon material is needed for manufacturing solar cells.
[0036] In contrast, solar cells structures according to embodiments of the present invention are manufactured using much less silicon material.
[0037] Figure 1 is a simplified diagram of a plurality of silicon slices from a single crystal substrate member according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0038] Solar cells according to embodiments of the present invention are manufactured with thin layers of silicon materials. In a specific embodiment, solar cells are manufactured with approximately two-micron thick silicon layer. As shown in Figure 1, thin slices of silicon layers (e.g., layers 105, 107, 108) are formed from a relative thick silicon wafer 101. As an example, the silicon wafer 101 has a thickness of approximately three hundred microns, which is about the thickness of the silicon layer for a conventional solar cell. In an exemplary embodiment, the silicon wafer 101 has a thickness of three hundred microns and sliced into approximately one hundred and fifty thin slices of silicon layers.
[0039] To further illustrate the cost reduction according to certain embodiments of the present invention, the following comparison is made. Assuming that a conventional solar cell is manufactured with a silicon layer of approximately three hundred microns, the amount of silicon material that is required for solar cells of according to embodiments of the present invention is approximate 1/150 of silicon material required for manufacturing the conventional solar cell. [0040] The thin slice of silicon layers as illustrated in Figure 1 are used for forming solar cell substrates. Figure 2 is a simplified diagram of a multi-layered substrate according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0041] As shown in Figure 2, a solar cell substrate 200 includes a silicon layer 201, a polar region 202, a reflective layer 205, and a support plate 207. According to certain embodiments, the silicon layer 201 essentially consists of p-type single crystal silicon material. In a specific embodiment, the silicon layer 201 is specially processed photovoltaic grade silicon that can be used for solar cell applications. While the silicon layer 201 essentially consists of p-type single crystal silicon material, it is to be understood that other types of silicon material may be used to form the silicon layer 201. For example, the silicon layer 201 may includes impurity particles. According to an alternative embodiment, the silicon layer 201 consists of essentially n-type silicon material. It is to be appreciated that, with a typical thickness ranges from two to ten microns, the silicon layer 201 is thin, which translates to less silicon material that is used for manufacturing solar cells.
[0042] According to certain embodiments, the polar region 202 is a portion of the silicon layer and consists essentially of doped silicon material. In a specific embodiment, the polar region 202 consists of single crystal silicon material that is doped with p+ type implant. For example, the polar region 202 is implanted with plus type boron at approximately 1015 dose. Depending upon application and/or processing techniques, different types of doping materials may be used, and the doping dose and concentration may vary.
[0043] In an alternative embodiment, the polar region 202 is doped by diffusion of p-type doping sources.
[0044] The polar region 202 is attached to the reflective layer 205. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics. In a specific embodiment, the reflective layer 205 also functions as a gluing layer that bonds the silicon layer 201 and the support plate 207 together. Depending upon application, various types of materials may be used forming the reflective layer 205. For example, the reflective layer 205 includes spin-on glass. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer includes dielectric material, metal material, and/or doped material, etc. [0045] The support plate 207 is bonded to the silicon layer 201 by the reflective layer 205. As thin as ten microns or less, the silicon layer 201 is extremely fragile. Without proper support, the silicon layer 201 alone is easily breakable. The support plate 207 is much thicker in comparison to the silicon layer 201. For example, the support layer 207 has a thickness ranges from two hundred to three hundred microns. Depending upon application, the support plate 207 may be fabricated using different types of material. In a specific embodiment, the support plate 207 is made of metallurgical-grade polysilicon material. Typically, metallurgical-grade polysilicon material is substantially cheaper to obtain and/or process.
[0046] Figure 3 is a simplified diagram of an alternative multi-layered substrate according to an alternative embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0047] As shown in Figure 3, a solar cell substrate 300 includes a silicon layer 301 , a polar region 302, a reflective layer 305, and a glass plate 307. According to certain embodiments, the silicon layer 301 essentially consists of p-type single crystal silicon material. In a specific embodiment, the silicon layer 301 is specially processed photovoltaic grade silicon that can be used for solar cell applications. While the silicon layer 301 essentially consists of p-type single crystal silicon material, it is to be understood that other types of silicon material may be used to form the silicon layer 301. For example, the silicon layer 301 may includes impurity particles. According to an alternative embodiment, the silicon layer 301 consists of essentially n-type silicon material. It is to be appreciated that, with a typical thickness ranges from two to ten microns, the silicon layer 301 is thin, which translates to less silicon material that is used for manufacturing solar cells.
[0048] According to certain embodiments, the polar region 302 is a portion of the silicon layer and consists essentially of doped silicon material. In a specific embodiment, the polar region 302 consists of single crystal silicon material that is doped with p+ type implant. For example, the polar region 302 is implanted with plus type boron at approximately 1015 dose. Depending upon application and/or processing techniques, different types of doping materials may be used, and the doping concentration may vary.
[0049] In an alternative embodiment, the polar region 302 is doped by diffusion of p-type doping sources. [0050] The polar region 302 is attached to the reflective layer 305. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics. In a specific embodiment, the reflective layer 305 also functions as a gluing layer that bonds the silicon layer 301 and the glass plate 307 together. Depending upon application, various types of materials may be used forming the reflective layer 305. For example, the reflective layer 305 includes spin-on glass. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer includes dielectric material, metal material, and/or doped material, etc.
[0051] The glass plate 307 is bonded to the silicon layer 301 by the reflective layer 305. As thin as ten microns or less, the silicon layer 301 is extremely fragile. Without proper support, the silicon layer 301 alone is easily breakable. The support plate 307 is much thicker in comparison to the silicon layer 301. For example, the glass layer 307 has a thickness ranges from two hundred to three hundred microns.
[0052] As an example, substrates 200 and 300 from Figures 2 and 3 respectively are partially processed substrate that are prepared for manufacturing of solar cell structures according to embodiments of the present invention. Figure 4 is a simplified diagram of a solar cell according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0053] As shown in Figure 4, a solar cell structure 400 includes a silicon layer 401, a reflective layer 405, and a support plate 407. The solar cell structure 400 additionally includes terminals 411, 412, and 413 to provide electrical connectivity to other electrical devices. As an example, the terminals are metals that are bonded to p+ and n+ regions of the silicon layer. When the solar cell structure is exposed to light, electrical energy may be obtained from the solar cell structure 400 through these terminals. According to certain embodiments, the silicon layer 401 essentially consists of p-type single crystal silicon material. In a specific embodiment, the silicon layer 401 is specially processed photovoltaic grade silicon that can be used for solar cell applications. While the silicon layer 401 essentially consists of p-type single crystal silicon material, it is to be understood that other types of silicon material may be used to form the silicon layer 401. For example, the silicon layer 401 may includes impurity particles. According to an alternative embodiment, the silicon layer 401 consists of essentially n-type silicon material. It is to be appreciated that, with a typical thickness ranges from two to ten microns, the silicon layer 401 is thin, which translates to less silicon material that is used for manufacturing solar cells.
[0054] The silicon layer 401 includes doped regions 402, 408, 409, and 410. As shown in Figure 4, regions 408, 410, and 402 are p+ type, and region 409 is n+ type. The different polarity of these region essential forms one or more p-n junctions.
[0055] According to certain embodiments, spacing, size, and arrangements of the 408 and 410 p+ regions and the 409 n+ regions can be altered to optimize collection of photo- generated carriers.
[0056] In a specific embodiment, the region 402 is a portion of the silicon layer and consists essentially of doped silicon material. In a specific embodiment, the region 402 consists of single crystal silicon material that is doped with p+ type implant. For example, the region 402 is implanted with plus type boron at approximately 1015 dose. Depending upon application and/or processing techniques, different types of doping materials may be used, and the doping concentration may vary. The doped regions 408, 409, and 410 essentially consist of doped silicon material. In certain embodiments, regions 408 and 410 are with p+ type implant. For example, the regions 408 and 410 are implanted with plus type boron at approximately 1015 dose. Depending upon application and/or processing techniques, different types of doping materials and methods (e.g. diffusion) may be used, and the doping concentration may vary.
[0057] The region 409 is doped with n+ type implant. For example, the region 408 is implanted with group V element at high concentrations. Depending upon application and/or processing techniques, different types of doping materials and doping methods (e.g. diffusion) may be used, and the doping concentration may vary.
[0058] The region 402 is attached to the reflective layer 405. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics. In a specific embodiment, the reflective layer 405 also functions as a gluing layer that bonds the silicon layer 401 and the support plate 407 together.
Depending upon application, various types of materials may be used forming the reflective layer 405. For example, the reflective layer 405 includes spin-on glass. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer includes dielectric material, metal material, and/or doped material, etc.
[0059] As an example, the layer 402 forms a polarity layer. The "polarity layer" is used to reduce carrier recombination to boost efficiency and to steer the carriers towards the top contacts.
[0060] The support plate 407 is bonded to the silicon layer 401 by the reflective layer 405. As thin as ten microns or less, the silicon layer 401 is extremely fragile. Without proper support, the silicon layer 401 alone is easily breakable. The support plate 407 is much thicker in comparison to the silicon layer 401. For example, the support layer 407 has a thickness ranges from two hundred to three hundred microns. Depending upon application, the support plate 407 may be fabricated using different types of material. In a specific embodiment, the support plate 407 is made of metallurgical-grade polysilicon material. Typically, metallurgical-grade polysilicon material is relatively cheaper to obtain and/or process. For example, low grade (i.e., low cost) polysilicon material is used to form the support plate 407. In an alternative embodiment, the support plate 407 is made of a glass plate.
[0061] It is to be understood that the present invention has a broad range of applicability. Among other things, the type of silicon used to form structures 200, 300, and 400 are p-type silicon materials. It is to be understood solar cells according to various embodiments of the present may be manufactured using n-type silicon material.
[0062] Figure 5 is a simplified diagram of a multi-layered substrate according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0063] As shown in Figure 5, a solar cell substrate 500 includes a silicon layer 501, a polar region 502, a reflective layer 505, and a support plate 507. According to certain embodiments, the silicon layer 501 essentially consists of n-type single crystal silicon material. In a specific embodiment, the silicon layer 501 is specially processed photovoltaic grade silicon that can be used for solar cell applications. While the silicon layer 501 essentially consists of n-type single crystal silicon material, it is to be understood that other types of silicon material may be used to form the silicon layer 501. For example, the silicon layer 501 may includes impurity particles. According to an alternative embodiment, the silicon layer 501 consists of essentially n-type silicon material. It is to be appreciated that, with a typical thickness ranges from two to ten microns, the silicon layer 501 is thin, which translates to less silicon material that is used for manufacturing solar cells. [0064] According to certain embodiments, the polar region 502 is a portion of the silicon layer and consists essentially of doped silicon material. In a specific embodiment, the polar region 502 consists of single crystal silicon material that is doped with n+ type implant. For example, the polar region 502 is implanted with group V elements such as phosphorous or arsenic material. Depending upon application and/or processing techniques, different types of doping materials may be used, and the doping concentration may vary.
[0065] In an alternative embodiment, the polar region 502 is doped by diffusion of n-type doping sources
[0066] The polar region 502 is attached to the reflective layer 505. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics. In a specific embodiment, the reflective layer 505 also functions as a gluing layer that bonds the silicon layer 501 and the support plate 507 together. Depending upon application, various types of materials may be used forming the reflective layer 505. For example, the reflective layer 505 includes spin-on glass. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer includes dielectric material, metal material, and/or doped material, etc.
[0067] The support plate 507 is bonded to the silicon layer 501 by the reflective layer 505. As thin as ten microns or less, the silicon layer 501 is extremely fragile. Without proper support, the silicon layer 501 alone is easily breakable. The support plate 507 is much thicker in comparison to the silicon layer 501. For example, the support layer 507 has a thickness ranges from two hundred to three hundred microns. Depending upon application, the support plate 507 may be fabricated using different types of material. In a specific embodiment, the support plate 507 is made of metallurgical- grade polysilicon material. Typically, metallurgical-grade polysilicon material is relatively cheaper to obtain and/or process. For example, low grade (i.e., low cost) polysilicon material is used to form the support plate 507. In an alternative embodiment, the support plate 507 is made of a glass plate. It is to be understood other types of stiff low cost material may be used for forming the support plate 507.
[0068] As an example, substrate 500 from Figure 5 is a processed substrate that is prepared for manufacturing of solar cell structures according to embodiments of the present invention.
[0069] Figure 6 is a simplified diagram of a solar cell according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0070] As shown in Figure 6, a solar cell structure 600 includes a silicon layer 601 , a reflective layer 605, and a support plate 607. The solar cell structure 600 additionally includes terminals 611, 612, and 613 to provide electrical connectivity to other electrical devices. As an example, the terminals are metals that are bonded to p+ and n+ regions of the silicon layer. When the solar cell structure is exposed to light, electrical energy may be obtained from the solar cell structure 600 through these terminals.
[0071] According to certain embodiments, the silicon layer 601 essentially consists of n- type single crystal silicon material. In a specific embodiment, the silicon layer 601 is specially processed photovoltaic grade silicon that can be used for solar cell applications.
While the silicon layer 601 essentially consists of n-type single crystal silicon material, it is to be understood that other types of silicon material may be used to form the silicon layer 401.
For example, the silicon layer 601 may includes impurity particles. It is to be appreciated that, with a typical thickness ranges from two to ten microns, the silicon layer 601 is thin, which translates to less silicon material that is used for manufacturing solar cells.
[0072] The silicon layer 601 includes doped regions 602, 608, 609, and 610. As shown in Figure 6, regions 608, 610, and 602 are n+ type, and region 609 is p+ type. The different polarity of these region essential forms one or more p-n junctions.
[0073] According to certain embodiments, spacing, size, and arrangements of the 608 and 610 n+ regions and the 609 p+ regions can be altered to optimize collection of photogenerated carriers.
[0074] In a specific embodiment, the region 602 is a portion of the silicon layer and consists essentially of doped silicon material. In a specific embodiment, the region 602 consists of single crystal silicon material that is doped with n+ type implant. For example, the region 602 is implanted with group V material (e.g., arsenic, phosphorous material, etc) at a predetermined concentration level. Depending upon application and/or processing techniques, different types of doping materials may be used, and the doping concentration may vary. [0075] As an example, the region 602 forms a polarity layer. The "polarity layer" is used to reduce carrier recombination to boost efficiency and to steer the carriers towards the top contacts.
[0076] The doped regions 608, 609, and 610 essentially consist of doped silicon material. In certain embodiments, regions 608 and 610 are with n+ type implant. For example, the regions 608 and 610 are implanted with group V material (e.g., arsenic, phosphorous material, etc) at a predetermined concentration level. Depending upon application and/or processing techniques, different types of doping materials and doping methods (e.g. diffusion) may be used, and the doping concentration may vary.
[0077] The region 609 is doped with p+ type implant. For example, the region 609 is implanted with boron. Depending upon application and/or processing techniques, different types of doping materials (e.g., group III material) may be used, and the doping concentration may vary.
[0078] The region 602 is attached to the reflective layer 605. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics . In a specific embodiment, the reflective layer 605 also functions as a gluing layer that bonds the silicon layer 601 and the support plate 607 together. Depending upon application, various types of materials may be used forming the reflective layer 605. For example, the reflective layer 605 includes spin-on glass. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer includes dielectric material, metal material, and/or doped material, etc.
[0079] The support plate 607 is bonded to the silicon layer 601 by the reflective layer 605. As thin as ten microns or less, the silicon layer 601 is extremely fragile. Without proper support, the silicon layer 601 alone is easily breakable. The support plate 607 is much thicker in comparison to the silicon layer 601. For example, the support layer 607 has a thickness ranges from two hundred to three hundred microns. Depending upon application, the support plate 607 may be fabricated using different types of material. In a specific embodiment, the support plate 607 is made of metallurgical-grade polysilicon material. Typically, metallurgical-grade polysilicon material is relatively cheaper to obtain and/or process. For example, low grade (i.e., low cost) polysilicon material is used to form the support plate 607. In an alternative embodiment, the support plate 607 is made of a glass plate. [0080] As illustrated above, solar cells according to embodiments of the present invention have much less silicon material when compared to conventional solar cells. It is to be appreciated that solar cells according embodiments of the present invention are capable of generating substantially the same amount of energy under similar lighting situation when compared to conventional solar cells. For example, solar cells according to the present invention benefit from, inter alia, light trapping effects.
[0081] Figure 7 is a simplified diagram illustrating the operational principle of a solar cell according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0082] As shown in Figure 7, a solar cell structure 700 includes a silicon layer 701, a reflective layer 705, and a support plate 707. The solar cell structure 700 additionally includes terminals 711, 712, and 713 to provide electrical connectivity to other electrical devices. As an example, the terminals are metals that are bonded to p+ and n+ regions of the silicon layer. When the solar cell structure is exposed to light, electrical energy may be obtained from the solar cell structure 700 through these terminals.
[0083] According to certain embodiments, the silicon layer 701 essentially consists of p- type single crystal silicon material. In a specific embodiment, the silicon layer 701 is specially processed photovoltaic grade silicon that can be used for solar cell applications. The silicon layer 701 includes doped regions 702, 708, 709, and 710. As shown in Figure 7, regions 708, 710, and 702 are p+ type, and region 709 is n+ type. The different polarity of these region essential forms one or more p-n junctions.
[0084] The region 702 is attached to the reflective layer 705. According to certain embodiments, the reflective layer consists essentially of silicon oxide type of material that exhibit reflective characteristics . In a specific embodiment, the reflective layer 705 also functions as a gluing layer that bonds the silicon layer 701 and the support plate 707 together. Depending upon application, various types of materials may be used forming the reflective layer 705.
[0085] The support plate 707 is bonded to the silicon layer 701 by the reflective layer 705. As thin as two microns or less, the silicon layer 701 is extremely fragile. Without proper support, the silicon layer 701 alone is easily breakable. The support plate 707 is much thicker in comparison to the silicon layer 701. For example, the support layer 707 has a thickness ranges from two hundred to three hundred microns.
[0086] When the solar cell structure 700 is used for generating electrical power, the silicon layer 701 of the solar cell structure 700 is exposed to light, preferably strong sun light. Typically, when photons hit the silicon layer 701, some photons are reflected, some photons pass through, and some photons are absorbed by the silicon layer 701. The photons that are reflected or passed through do not help the solar cell structure 700 produce energy. The photons that are absorbed by the silicon layer 701 produce energy by generating electron-hole pairs when photons energy is higher than the silicon band gap value. Sometimes, when a photon has an integer multiple of band gap energy, it can create more than one electron-hole pair, which translates to more energy. The electron-hole pairs generated by the absorbed photons cause electron diffusion across p-n junctions of the silicon layer 701. The electron diffusion across p-n junctions produces an electrical field across the p-n junction. By connecting external load to the terminals of the p-n junctions, electrical energy may be extracted from the solar cell structure 700.
[0087] Since only photons that are absorbed by silicon generate usable electrical energy, it is desirable for the silicon layer 701 to absorb as many photons as possible. As shown in Figure 7, a photon 752 hits the surface of the silicon layer 701 and is then reflected. Since the photon 752 is reflected, the photon 752 does not generate energy at the silicon layer 701. A photon 753 passes through the surface of the silicon layer 701 and is then absorbed by silicon. When the photon 753 is absorbed by the silicon layer 701, electron-hole pair is generated at the silicon layer 701 and energy is generated.
[0088] A photon 751 strikes the surface of silicon layer 701 and passes through. Typically, a photon 751 that passes through silicon in a conventional solar cell does not generate any usable energy for the solar cell. In comparison, the photon 751 does not simply pass through silicon. After the photon 751 passes through the polarity layer 702 and the silicon layer 701, the photon 751 is then reflected by the reflective layer 705. The reflected photon 751 may then be absorbed by the silicon layer 701, which in turn generate electrical energy from photon absorption. It is to be appreciated that the polarity layer 702 is capable of reducing carrier recombination and boosting efficiency, as the polarity layer 702 steers carriers toward the top contacts. [0089] It is to be appreciated that solar cell structures according to embodiments of the present invention are manufactured with less silicon material, and they can be manufactured efficiently. Figure 8 is a simplified flow diagram of a process of manufacturing a solar cell according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As an example, various steps as illustrated in Figure 8 may be added, removed, replaced, rearranged, repeated, overlapped, and/or partially overlapped, and should not unduly limit the scope of claims.
[0090] At step 801, a single crystal silicon substrate is provided. For example, the substrate has a surface region. Usually, a photovoltaic-grade silicon substrate is provided. Depending upon application, the single crystal silicon substrate may be p-type silicon, n-type silicon, etc. hi addition the single crystal silicon substrate may include impurity particles. The single crystal silicon substrate typically has a thickness of more than ten microns, and up to hundreds of microns. As explained above, thick layers of a silicon substrate is cut into thin slices, which are then used for forming solar cell structures.
[0091] At step 802, implantation process is performed. For example, the implantation process introduces a first impurity species through the surface region and within a vicinity of a first thickness of the surface region.
[0092] Figure 9 is a simplified diagram illustrating a process of manufacturing a solar cell according to an embodiment of the present invention. More specifically, Figure 9 illustrates a partially processed substrate that has been doped with a first impurity species. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0093] As shown in Figure 9, a substrate material 900 includes a doped layer 901 and a substrate layer 902. According to various embodiments, the doped layer 901 is doped via p+ type implantation at a specific thickness. As an example, the layer 901 is used to reduce photogenerated carrier recombination, hi a specific embodiment, the doped layer 901 is implanted by 10 keV B+ implant, at 1015 dose level. It is to be understood that other types of group III elements may be used for implantation. According to an alternative embodiment, the doped layer 901 is obtained via diffusion methods.
[0094] Now referring back to Figure 8. At step 803, the substrate material 900 is annealed. For example, the annealing process stabilizes and electrically activates the doped layer 901. In a specific embodiment, annealing is performed at 950 degrees Celsius for thirty minutes. Depending upon application, annealing parameters and methods may vary.
[0095] At step 804, a second implantation process is performed to introduce a plurality of hydrogen species at a depth underlying the surface region and to define a thickness of single crystal silicon to be removed. In a specific embodiment, hydrogen species are introduced specific for the purpose for removing a layer of silicon material.
[0096] Figure 10 is a simplified diagram illustrating a process of manufacturing a solar cell according to an embodiment of the present invention. More specifically, Figure 10 illustrates a substrate material that has been implanted with hydrogen species. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0097] As shown in Figure 10, a silicon substrate 1000 includes a doped layer 1001. According to various embodiments, hydrogen implantation to a specific thickness. For example, the region 1002 that is implanted with hydrogen species can later be separated from the region 1004. In a preferred embodiment, hydrogen species implementation is limited to region 1002, which has a thickness of approximately two microns, a desired thickness for silicon layer used in a solar cell structure according to an embodiment of the present invention. Depending upon application, hydrogen species may be implemented according to various parameters. In a specific embodiment, the implantation is performed at 200 keV with a dose range of2E16 to 4E16.
[0098] Now referring back to Figure 8. At step 805, the surface region of the single crystal silicon substrate is bonded to a stiffener member to form a multi-layered structure including a reflector region at an interface between the surface region and the stiffener member.
[0099] Figure 11 is a simplified diagram illustrating a process of manufacturing a solar cell according to an embodiment of the present invention. More specifically, Figure 11 illustrates a substrate material that has been bonded to a multi-layered structure. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0100] As seen in Figure 11, a bonded structure includes a substrate 1105 and a structure 1104. The substrate 1105 includes a region 1106 that has been implanted with hydrogen species as explained above. In addition, the substrate 1105 includes a doped layer 1107. As an example, the substrate 1105 consists essentially of p type single-crystal silicon material, and the doped layer 1107 is doped with p+ material (e.g., doped with boron, etc.). The structure 1104 includes a reflective layer 1102 and a plate 1103. According to various embodiments, the reflective layer 1102 can be used as both a gluing layer and a reflective layer. In a specific embodiment, the reflective layer 1102 is made of spin-on glass that is capable of bonding to both the substrate 1105 and the plate 1103. Merely by way of an example, the reflective layer 1102 has a different reflectivity index. It is to be understood that other types of materials may be used for forming the reflective layer 1102. According to certain embodiments, the reflective layer 1102 consists essentially of silicon oxide type of material that exhibit reflective characteristics. Depending upon application, various types of materials may be used forming the reflective layer 1102. It is to be appreciated that the present invention may be implemented in various ways. For example, the reflective layer
1102 includes dielectric material, metal material, and/or doped material, etc.
[0101] The plate 1103 is bonded to the substrate 1105 by the reflective layer 1102. The plate 1103 is to provide physical support for a solar cell structure. For example, the plate
1103 has a thickness ranges from two hundred to three hundred microns. Depending upon application, the plate 1103 may be fabricated using different types of material. In a specific embodiment, the plate 1103 is made of metallurgical-grade polysilicon material. Typically, metallurgical-grade polysilicon material is substantially cheaper to obtain and/or process. For example, low grade (i.e., low cost) polysilicon material is used to form the plate 1103. In an alternative embodiment, the plate 1103 is made of a glass plate.
[0102] Now referring back to Figure 8. At step 806, part of the substrate, which is now bonded to the multi-layered structure, is removed. According to certain embodiments, a thermal treatment process is performed on the multi-layered structure to cause separation at the region underlying the surface region of the single crystal silicon substrate and to exfoliate the thickness of single crystal silicon material, while the thickness of single crystal material remains attached to the stiffener member, to form a roughened region defining the thickness of single crystal silicon material. In a specific embodiment, the thermal treatment process (e.g., exfoliation process, etc.) is performed at approximate a range of three hundred to five hundred degrees Celsius. As an example, the removed portion of the substrate is used for manufacturing other solar cell structures. [0103] Figure 12 is a simplified diagram illustrating a process of manufacturing a solar cell according to an embodiment of the present invention. More specifically, Figure 12 illustrates partial removal of the substrate. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.
[0104] As shown in Figure 12, a substrate 1201 includes a silicon layer 1202 and a doped layer 1205. In certain embodiments, the thickness of the substrate 1201 is approximately between two to ten microns. As explained above, the thickness of the substrate 1201 is defined by the hydrogen implantation in step 804. During step 806, the plate 1204 remains bonded to the substrate 1201 by the reflective layer 1203.
[0105] Now referring back to Figure 8. One or more photovoltaic devices are formed onto the thickness of the single crystal silicon material. More specifically, additional doped regions are defined on the surface of the crystal silicon material. For example, since the doped material at the bottom of the single crystal silicon material is p+ type, n+ type doping is performed on the surface portion of the single-crystal silicon material. In addition, terminals may be formed on the single crystal silicon material to provide electrical connection.
[0106] It is to be understood that steps illustrated by Figure 8-12 merely provide a specific exemplary embodiment. In certain embodiments, n-types silicon wafers are used and the doped layer includes n+ type doping (e.g., using group V materials). There can be other variations as well.
[0107] According to an embodiment, the present invention provides a solar cell. The solar includes a supporting layer that is characterized by a first thickness. The solar cell also includes a reflective layer overlying the supporting layer. The reflective layer is characterized by a second thickness. The reflective layer is attached to the supporting layer. The solar cell additionally includes a photovoltaic layer, which includes a first side and a second side. The photovoltaic layer is characterized by a third thickness. The photovoltaic layer includes a first side and a second side. The first side is opposite from the second side. The photovoltaic layer includes a first portion and a second portion. The first portion includes a fourth thickness from the first side. The second portion includes a fifth thickness from the second side. The first side of the photovoltaic layer is attached to the reflective layer. The first portion is characterized by a predetermined polarity (e.g., p+ type doping). The fourth thickness is less than the third thickness. The fifth thickness is less than the third thickness. Merely by an example, the embodiment is illustrated according Figure 4.
[0108] According to another embodiment, the present invention provides a solar cell structure. The solar cell structures include a silicon layer having a surface region and a bonding region. The silicon layer is characterized by a first thickness. The surface region is characterized by a second thickness. The bonding region is characterized by a third thickness. The surface region includes n+ type material. The bonding region including p+ type material (e.g., boron doping). The solar cell structure also includes a reflective layer that includes a first side and a second side. The first side is bonded to the bonding region of the silicon layer. Additionally, the solar cell structure includes a supporting plate that is bonded to the second side of the reflective layer. Merely by an example, the embodiment is illustrated according to Figure 4.
[0109] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a single-crystal silicon layer that has a surface region and a bonding region. The silicon layer is characterized by a first thickness. The surface region is characterized by a second thickness. The bonding region is characterized by a third thickness. The surface region includes n+ type material. The bonding region includes p+ type material. The solar cell structure also includes a spin-on-glass layer, which has a first side and a second side. The first side is bonded to the bonding region of the silicon layer. The solar cell structure further includes a glass plate that is bonded to the second side of the spin-on-glass layer. Merely by an example, the embodiment is illustrated according to Figure 4.
[0110] According yet another embodiment, the present invention provides a method for manufacturing a solar cell structure. The method includes a step for providing a substrate. The substrate consists essential of silicon. The substrate is characterized by a first thickness. The substrate includes a first side and a second side. The first side is opposite from the second side. The substrate includes a first portion, a second portion, and a third portion. The first portion includes a second thickness from the first side. The second portion includes a third thickness from the first side. The third thickness is greater than the second thickness. The third portion includes a fourth thickness between the second portion and the second side. The method further includes a step for doping the first portion with a predetermined polarity type. The method additionally includes a step for implanting the second portion with a hydrogen implantation to form a separation region. Additionally, the method includes a step for providing a bottom layer. The bottom layer is characterized by a fifth thickness. The bottom layer includes a third side and a fourth side. The third side is opposite from the fourth side. The method also includes a step for attaching the first side of the substrate to the third side of the bottom layer. Furthermore, the method includes a step for removing the third portion of the substrate at the separation region. Merely by an example, the embodiment is illustrated according to Figure 8.
[0111] According to yet another embodiment, the present invention provides a method for fabricating a solar cell. The method includes a step for providing a single crystal silicon substrate that has a surface region. The method also includes a step for performing a first implantation process to introduce a first impurity species through the surface region and within a vicinity of a first thickness of the surface region. The method additionally includes a step for performing a second implantation process to introduce a plurality of hydrogen species at a region underlying the surface region and to define a thickness of single crystal silicon to be removed. In addition, the method includes a step for bonding the surface region of the single crystal silicon substrate to a stiffener member to form a multi-layered structure including a reflector region at an interface between the surface region and the stiffener member. Also, the method includes a step for performing a thermal treatment process on the multi-layered structure to cause separation at the region underlying the surface region of the single crystal silicon substrate and to exfoliate the thickness of single crystal silicon material, while the thickness of single crystal material remains attached to the stiffener member, to form a roughened region defining the thickness of single crystal silicon material. In addition, the method includes a step for forming one or more photovoltaic devices onto the thickness of the single crystal silicon material. Merely by an example, the embodiment is illustrated according to Figure 8.
[0112] Many benefits are achieved by way of the present invention over conventional techniques. For example, the present technique provides an easy to use process that relies upon conventional technology such as silicon materials, although other materials can also be used. Additionally, the method provides a process that is compatible with conventional process technology without substantial modifications to conventional equipment and processes. Preferably, the invention provides for an improved solar cell, which is less costly and easy to handle. Such solar cell uses a hydrogen co-implant to form a thin layer of photovoltaic material. Since the layers are very thin, multiple layers of photovoltaic regions can be formed from a single conventional single crystal silicon or other like material wafer. In a preferred embodiment, the present thin layer removed by hydrogen implant and thermal treatment can be provided on a low grade substrate material, which will serve as a support member. Depending upon the embodiment, one or more of these benefits may be achieved.
[0113] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a photovoltaic layer having a top side and a bottom side. The photovoltaic layer consisting essentially of p-type silicon material. The photovoltaic layer includes a first portion positioned between the top side and a first thickness and a second portion positioned between the bottom side and a second thickness. The first portion includes lateral patterns of p+ and n+ regions. The second portion is characterized by p+ type polarity for reducing carrier recombination. The solar cell structure additionally includes a reflective layer including a first side and a second side. The first side is coupled to the bottom side of the photovoltaic layer. The solar cell structure also includes a support layer that is coupled to the second side of the reflective layer.
[0114] According to yet another embodiment, the present invention provides a solar cell structure. The solar cell structure includes a photovoltaic layer having a top side and a bottom side. The photovoltaic layer consisting essentially of n-type silicon material. The photovoltaic layer includes a first portion positioned between the top side and a first thickness and a second portion positioned between the bottom side and a second thickness. The first portion includes lateral patterns of p+ and n+ regions. The second portion is characterized by n+ type polarity for reducing carrier recombination. The solar cell structure additionally includes a reflective layer including a first side and a second side. The first side is coupled to the bottom side of the photovoltaic layer. The solar cell structure also includes a support layer that is coupled to the second side of the reflective layer.
[0115] Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.