US20070116893A1 - Low-hydrogen photovoltaic cell - Google Patents

Abstract

A low-hydrogen photovoltaic cell is disclosed. The photovoltaic cell may contain less than 5% hydrogen. In one aspect, the photovoltaic cell may contain substantially no hydrogen, that is, the photovoltaic cell may be substantially hydrogen free. The photovoltaic cell includes a substrate and an absorber deposited on to the substrate. The absorber may typically include elements from group 11, group 12, and group 13 of the Periodic Table, for example, copper, indium, and gallium. The absorber may be treated with selenium and/or sulfur to produce a CIGS or CIGSS-type photovoltaic cell. The low-hydrogen photovoltaic cell may fabricated by a method and apparatus adapted to control metalloid vapor delivery, for example, in a low-hydrogen or hydrogen free atmosphere.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is a divisional application of co-pending application Ser. No. 11/282,934 filed on Nov. 18, 2005 [attorney docket no. 2606.002], the disclosure of which is incorporated by reference herein in its entirety.
TECHNICAL FIELD OF THE INVENTION
• The present invention relates to methods and apparatus for exposing a material or work piece to a vaporous element. Specifically, the present invention provides methods and apparatus for treating a photovoltaic precursor with a vaporous element, for example, selenium or sulfur, to produce thin film CIGS or CIGSS solar cells.
BACKGROUND OF THE INVENTION
• The limited availability of and environmental concerns about fossil fuels make them increasingly less attractive as a means to produce electricity. As a result of this trend, alternative energy sources, particularly solar energy, are becoming more popular. While solar energy is a reliable and dependable energy source, the costs associated with solar energy production have traditionally limited its availability and desirability as a substitute for fossil fuels. However, recent technological advances in solar cell manufacturing show promise to lower the cost of solar energy.
• Solar energy proponents and researchers state that higher solar cell efficiency and lower production costs are two ways to reduce the overall cost of solar energy. In particular, solar cells with absorber materials comprised of copper, indium, gallium, and selenium and/or sulfur [hereinafter Cu(In,Ga)(S,Se)₂or CIGS] show promise in higher efficiency, lower production costs, and long operational lifetimes. These absorber materials are the result of innovative thin-film manufacturing technologies that further reduce manufacturing costs by lowering raw material costs and increasing throughput and efficiencies.
• As is commonly practiced in the art, these CIGS cells are manufactured in either a one-stage thermal co-evaporation process or a two-stage process. The single stage thermal co-evaporation process consists of depositing all of the CIGS elements onto a substrate and simultaneously heating that substrate temperature to approximately 450° C. to 600° C. to allow the constituent materials to form a crystal matrix in the absorber.
• Although the one-step co-evaporation process is of interest to CIGS manufacturing, the two-step process may be more manufacturable and poses unique challenges of its own. In the first step of the two-step process, a material is deposited upon a substrate. The material deposited on the substrate is referred to as the “precursor.” The precursor may comprise one or more of copper (Cu), indium (In), gallium (Ga), and/or selenium (Se) and/or sulfur (Se). Usually the precursor is a mixture of copper, indium, and gallium. In the second step of the two-stage process of CIGS manufacturing, selenium or sulfur is introduced into the precursor by a process known in the art as “selenization.” Selenization typically includes heating the precursor in a selenium-rich (or sulfur-rich) environment until the elements react to make a crystal matrix to form the chalcopyrite CIGS material that becomes known as the “absorber.” Common sources of selenium or sulfur in CIGS manufacturing include vaporizing powdered selenium or sulfur, hydrogen selenide, hydrogen sulfide, or organic compounds of selenium or sulfur with low evaporation points. This process has been accepted by researchers in solar cell manufacturing methods as an acceptable means of introducing selenium or sulfur into the absorber material; however, this technique also poses substantial risks and costs. Further, as some researchers may blend certain elements of the one-stage and two-stage process, these challenges may apply to the one-stage process as well.
• Selenization is usually practiced by two methods. In one prior art method, selenium pellets are placed in a receptacle, or “boat,” in a chamber and then the selenium and precursor are heated to release a selenium-containing vapor which interacts with the precursor. In the other prior art method the treatment chamber is filled with selenium or sulfur vapor or with hydrogen selenide (H₂Se) or hydrogen sulfide (H₂S) gas. Sometimes a process will involve placing hydrogen (H₂) gas in the treatment chamber while heating the Se or S pellets to form H₂Se or H₂S in situ. These two methods are essentially the only methods of selenizing photovoltaic precursors.
• Due to the nature of the chemical reactions, an excess amount of Se or an over-pressure of Se is desirable during the selenization process. An excess of Se is typically necessary since the reaction of the Cu, In, Ga, and Se tends to “push” at least some of the Se out of the precursor at elevated temperature. Therefore, it is believed that, without excess Se present, any deposited Se will tend to evaporate out of the precursor matrix and not bind to the matrix as desired. Aspects of the present invention overcome this barrier by providing sufficient Se to minimize the escape of Se from, for example, the Cu—In—Ga matrix.
• With regards to thermal co-evaporation, some prior art co-evaporation processes “hint” that selenization may be used to “fix” a film that might not be quite right stoichiometrically. That is, after co-evaporation, the precursor may lack sufficient Se whereby further Se addition is required to provide the desired stoichiometric quantity of Se. This further selenization is typically practiced by one of the methods discussed above.
• Current CIGS manufacturing techniques also have serious health and environmental implications. As discussed below, various manufacturing techniques have been used to introduce selenium or sulfur into the absorber material matrix with varying success. Although some manufacturing methods are more reliable, the health or environmental concerns, especially in large-scale production volumes, make them undesirable for long-term use. More specifically, the use of the highly toxic hydrogen selenide and its derivatives is expensive because of needed safety precautions. While CIGS solar cells show great promise in solar cell manufacturing to reduce raw material costs, safe, reliable, and repeatable methods to introduce selenium or sulfur into the matrix are needed.
• Prior art also suggests that CIGS solar cells produced by selenization processes have performance problems that may be unique to the manufacturing method. Recent studies by P. K. Johnson and A. E. Delahoy showed that solar cells produced by selenization had higher defect densities, “light-inhibited” degradation of cell efficiency of up to 97%, and a 13% reduction in Voc×FF over a 30 to 45 day period. In contrast, solar cells produced by thermal co-evaporation showed lower defect densities, lower cell efficiency reduction, and less than a 2% reduction in Voc×FF over a 30 to 45 day period. The key distinguishing feature of most selenization processes and thermal co-evaporation is that selenization usually uses a hydrogen-containing species, H₂Se. Although some of the decreased product performance of selenized solar cells is due to encapsulation method of the module and migration of sodium from the soda lime substrate into the absorber matrix, a good portion of the discrepancies in cell performance have to do with manufacturing method. While the enhanced product performance factors make thermal co-evaporation more desirable, selenization process methods are more suited to manufacturing high efficiency cells on large area substrates.
• Additionally, H₂Se is incompatible with stainless steel and other metals that have the potential to replace soda lime glass as a substrate material. This distinction is increasingly important as solar cell manufacturers look to lower manufacturing costs while increasing the number of form factors available for “finished” solar cell devices. Thus, in addition to the safety and environmental concerns, a solar cell manufacturing method that comprises 1) the low hydrogen advantages of thermal co-evaporation on long term cell performance, 2) the manufacturing capability high efficiency solar cells on large area substrates, and 3) compatibility with stainless steel and other metals is also needed.
DESCRIPTION OF THE RELATED ART
• Within the art of CIGS manufacturing, the selenization process is often completed in a chamber. These chambers are either rectangular, square, or round and may or may not have shelves. An exemplary embodiment of a typical chamber is disclosed in U.S. Pat. No. 6,787,485 by Probst [herein “Probst”] and a typical selenization method is disclosed in U.S. Pat. No. 5,045,409 by Eberspacher, et al. [herein “Eberspacher”]. In particular, Probst discloses a “stack oven” with an adjustable gas atmosphere capable of operating in vacuum. Additionally, the Probst apparatus comprises heating elements and shelves that contain the process items in an arrangement that interleaves the process items and the energy sources, with at least one energy source per process item. The heating sources are arranged in a quartz glass envelope, with a liquid or gas coolant flowing through the envelope. Probst focuses on thermal uniformity of the substrates, however, unlike aspects of the present invention, Probst does not disclose 1) a high utilization rate of selenium of at least 90%, 2) a solid source of the processing vapor, 3) an enhanced means to control delivery of selenium or sulfur vapor, 4) a condenser/evaporator to deliver vapor from a solid source, 5) a vapor tight inner chamber space, nor 6) an independent thermal control of the substrates, a condenser/evaporator, and the walls of the chamber. Aspects of the present invention may provide one or more of these advantages over Probst.
• Eberspacher discloses a method to form a CIS or CIGS film without using H₂Se, which is a highly toxic gas and is thus unsuitable for large scale manufacturing because of safety concerns. In the disclosed method of Eberspacher, a mixture of copper and indium or copper, indium, and gallium are deposited on a substrate by sputtering. A selenium film is then deposited by thermal evaporation. The substrate is then heated in the presence of hydrogen, H₂Se, or H₂S to form the crystalline matrix for the solar cell absorber material. While the inventor's aim was to totally eliminate the use of H₂Se, the inventor admits in the specification that a low concentration of H₂Se is needed to improve cell performance. Eberspacher further discloses a “conventional thermal evaporation method” which takes place in an oven with a gas inlet and outlet, but, unlike aspects of the present invention, does not disclose 1) a solid source of the processing vapor, 2) a high utilization rate of selenium of at least 90%, 3) a means to control delivery of selenium or sulfur vapor, 4) a condenser/evaporator to deliver vapor from a solid source, 5) a vapor tight inner chamber space, nor 6) an independent thermal control of the substrates, a condenser/evaporator, and the walls of the chamber. Aspects of the present invention may provide one or more of these advantages over Eberspacher.
• U.S. Pat. Nos. 6,092,669 and 6,048,442 Kushiya, et al. [collectively herein “Kushiya”] discloses a method and apparatus for producing a thin-film solar cell. Specifically, Kushiya discusses processing the solar cells by heating them in an atmosphere of selenium or sulfur. According to Kushiya, the substrates are heated in an electric furnace with an undisclosed reactive gas at a temperature not higher than 600° C. Unlike aspects of the present invention, Kushiya does not disclose 1) a solid source of the processing vapor, 2) a high utilization rate of selenium of at least 90%, 3) a means to control delivery of selenium or sulfur vapor, 4) a condenser/evaporator to deliver vapor from a solid source, 5) a vapor tight inner chamber space, nor 5) an independent thermal control of the substrates, a condenser/evaporator, and the walls of the chamber. Aspects of the present invention may provide one or more of these advantages over Kushiya.
• U.S. Pat. No. 6,518,086 of Beck, et al. [herein “Beck”] discloses a two-stage process to produce a CIGS or CIGSS film on a substrate for semiconductor applications. While referencing the prior art, Beck discusses the exemplary inventions of the two best known methods of selenization: (1) vapor deposition of the constituent elements followed by heating (see U.S. Pat. No. 5,141,564 issued to Chen, et al. (herein “Chen”)) and (2) a two-stage process wherein selenium or sulfur is added to the absorber crystal matrix by heating copper indium alloys with H₂Se or Se vapor (see U.S. Pat. No. 4,798,660 issued to Ermer, et al. (herein “Ermer”) and U.S. Pat. No. 4,915,745 issued to Pollock, et al.) Beck distinguishes the first CIGS process of the Chen species as undesirable for industrial scale manufacturing because of high temperatures to form the absorber matrix. Beck further distinguishes the second selenization process of the Ermer species as undesirable because of the use of highly toxic H₂Se, low selenium utilization, and poor adhesion to molybdenum coated substrates.
• Beck discloses depositing a precursor layer of copper, indium, gallium, selenium, or sulfur in some combination to a substrate. These substrates are then heated in either an inert atmosphere comprising argon, xenon, helium, or nitrogen or under a selenium or sulfur vapor. The selenium vapor can come from evaporating selenium from a “boat” inside the chamber, H₂Se, or diethylselenide. Similar to recognized methods of selenization, Beck selenizes its precursor by heating the selenium-containing boat and precursor in the treatment chamber to produce the Se vapor and holds the boat and precursor at temperature until selenization is complete. Contrary to aspect of the present invention, Beck does not disclose 1) a high utilization rate of selenium of at least 90%, 2) a means to control delivery of selenium or sulfur vapor, 3) a condenser/evaporator to deliver vapor from a solid source, 4) a vapor tight inner chamber space, nor 5) an independent thermal control of the substrates, a condenser/evaporator, and the walls of the chamber. Aspects of the present invention may provide one or more of these advantages over Beck.
• While the disclosed prior art is not exhaustive, it is representative of what is known and practiced for selenization. In particular, in contrast with aspects of the present invention, prior art vacuum chamber apparatuses and treatment methods do not disclose 1) an independent control of substrate temperature, 2) a high utilization rate of selenium of at least 90%, 3) high throughput capability with enhanced thermal management, 4) controlled release and capture of selenium to the same place repeatedly, 5) independent control of the vapor pressure delivery of sulfur or selenium, 6) vacuum compatible selenium delivery and temperature control, 7) distinct temperature zones and valves to allow use of traditional elastomer seals and vacuum gauges, and 8) future process automation upgrade capability. Aspects of the present invention provide these other advantages and benefits not found in the prior art.
SUMMARY OF ASPECTS OF THE INVENTION
• The present invention provides methods and apparatus for treating materials with vaporous elements and compounds that enhances the versatility and adaptability of the treatment process. Though aspects of the invention may be utilized in the manufacture and processing of photovoltaic material, aspects of the invention are not limited to processing photovoltaic material, but can be applied to the treatment of any material where the control and regulation of treatment temperature impacts the cost, quality, or performance of the product produced.
• One aspect of the invention is a method for treating a work piece, for example, a CIG photovoltaic precursor, with one or more vaporous element. The method includes introducing the work piece and an element-containing material to an enclosure; heating the work piece to a first temperature; independent of the heating of the work piece, heating the element-containing material to a temperature sufficient to volatilize the element and release an element-containing vapor into the enclosure; reacting at least some of the element-containing vapor with the work piece; regulating the temperature of the element-containing material at a temperature sufficient to condense at least some of the element from the element-containing vapor on the element-containing material; and cooling the work piece to provide an element-treated work piece. In one aspect, the element comprises elemental sulfur or selenium or combinations of sulfur, selenium, tellurium, indium, gallium, or sodium. In another aspect, cooling the element-containing material may comprise cooling the element-containing material wherein substantially all of the unreacted element-containing vapor condenses on the element-containing material.
• Another aspect of the invention is an apparatus for treating a work piece with a vaporous element, the apparatus including an enclosure; means for supporting the work piece in the enclosure; means for varying the temperature of the work piece; an element-containing material in the enclosure; means for varying the temperature of the element-containing material to produce an element-containing vapor, the means for varying the temperature of the element-containing material being independent of the means for varying the temperature of the work piece; and means for exposing at least some of the work piece to the element-containing vapor. In one aspect, the enclosure comprises an inner enclosure, and wherein the apparatus further comprises an outer enclosure enclosing the inner enclosure.
• Another aspect of the invention is a method for preparing a treatment chamber for treating a work piece with a volatilizable element, the method including introducing a solid element-containing material to the treatment chamber, the treatment chamber comprising an internal cavity; heating the solid element-containing material to volatilize the element and produce an element-containing vapor in the internal cavity; regulating the temperature of a surface exposed to the internal cavity to a temperature at which the element-containing vapor condenses; and condensing at least some of the volatilized element from the element-containing vapor onto the surface. In one aspect, the method further includes regulating the temperature of the solid element-containing material to a temperature below the volatilization temperature of the element, for example, whereby at least some of the element from the element-containing vapor condenses onto the solid element-containing material.
• A still further aspect of the invention is a treatment chamber isolation apparatus, the treatment chamber having an opening, the isolation apparatus including a sealing assembly having a support structure; at least one cover plate adapted to engage the treatment chamber opening; a plurality of rods having a first end adapted to engage the support structure and a second end adapted to engage the at least one cover plate; and means for compressing the sealing assembly against the treatment chamber wherein the at least one cover plate engages the treatment chamber opening to provide at least some isolation of the treatment chamber. In one aspect, the first ends of the plurality of rods are resiliently mounted to the support structure, for example, by means of springs and/or flexures.
• Another aspect of the invention is a treatment chamber isolation apparatus, the treatment chamber having a cylindrical enclosure having an open first end, a closed second end, and an internal flange mounted between the first end and the second end, the apparatus including a sealing plate adapted to engage the internal flange; a support rod having a first end and a second end mounted to the sealing plate; a plate mounted to the second end of the support rod; and at least one actuator adapted to displace the plate whereby the sealing plate engages the internal flange of the cylindrical enclosure and substantially isolates at least part of the cylindrical enclosure. In one aspect, the treatment chamber isolation apparatus may further comprise a cylindrical extension mounted to the open first end of the cylindrical enclosure.
• Another aspect of the invention is a material delivery device including a cylindrical body having at least one outer surface; a volatilizable material applied to the at least one outer surface; means for varying the temperature of the at least one outer surface to regulate the volatilization of the volatilizable material. In one aspect, the means for varying the temperature comprises a heat exchanger having a working fluid passing through it.
• Another aspect of the invention is a method of delivering a volatile material including providing a cylindrical body having at least one outer surface; applying a volatilizable material to the at least one outer surface; and regulating the temperature of the at least one outer surface to vary the amount of material volatilized. In one aspect, applying a volatilizable material to at least one outer surface of the cylindrical body may comprise exposing the at least one outer surface to a vapor containing a volatilized material; and cooling the at least one outer surface to condense at least some of the volatilized material from the vapor on to the at least one outer surface. In one aspect, regulating the heating of the at least one surface may comprise regulating the flow and/or temperature of a coolant though a passage in the cylindrical body.
• A further aspect of the invention is a treatment chamber valve actuation device including an actuation plate; at least one actuation rod mounted to the actuation plate, the at least one actuation rod adapted to penetrate a wall of the chamber and engage a valve mechanism within the chamber; an actuator adapted to displace the actuation plate wherein the plurality of actuation rods are displaced and actuate the valve mechanism; and at least one flexible plate mounted between the actuation plate and the treatment chamber. In one aspect, the at least one flexible plate may comprise a plurality of flexures mounted between the actuation plate and the treatment furnace.
• A still further aspect of the invention is a CIGS photovoltaic cell having a low-hydrogen content or substantially no hydrogen content. In one aspect, the photovoltaic cell may comprise a substrate; and an absorber deposited on to the substrate, the absorber comprising copper, indium, gallium, and less than 5% hydrogen. In one aspect, the absorber contains less than1% hydrogen, or is even hydrogen free. In another aspect, the substrate may be a metallic substrate, for example, a steel, stainless steel, or titanium substrate.
• These and further aspects of the invention are illustrated in described with respect to the attached figures.
BRIEF DESCRIPTION OF FIGURES
• The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be readily understood from the following detailed description of aspects of the invention taken in conjunction with the accompanying figures in which:
• FIG. 1 is a schematic block diagram of a process for treating a work piece according to one aspect of the invention.
• FIG. 2 is a plot of a heating schedule for the treated work piece and the treatment material according to one aspect of the invention.
• FIG. 3 is a perspective view of a treatment furnace according to another aspect of the invention.
• FIG. 4 is a front elevation view of the furnace shown inFIG. 3.
• FIG. 5 is a right side elevation view of the furnace shown inFIG. 3.
• FIG. 6 is a left side elevation view of the furnace shown inFIG. 3.
• FIG. 7 is a rear elevation view of the furnace shown inFIG. 3.
• FIG. 8 is a top plan view of the furnace shown inFIG. 3.
• FIG. 9 is a right side elevation view of the furnace shown inFIG. 3 with the right side door removed
• FIG. 10 is a detailed side elevation view of a tube assembly as shown asDetail10 inFIG. 9.
• FIG. 11 is a detailed side elevation view of a treatment chamber isolation mechanism shown asDetail11 inFIG. 10.
• FIG. 12A is a right-hand perspective view of the treatment chamber isolation mechanism shown inFIG. 11.
• FIG. 12B is a left-hand perspective view of the treatment chamber isolation mechanism shown inFIG. 11.
• FIG. 13 is a perspective view of the valve actuating assembly shown inFIG. 9.
• FIG. 14 is a side elevation view of the valve actuating assembly shown inFIG. 9.
• FIG. 15 is a detailed side elevation view of a heat exchanger shown asDetail15 inFIG. 10.
• FIG. 16A is a perspective view of the tube and heat exchanger assembly as shown inFIG. 10.
• FIG. 16B is a detailed cross section of a conduit mounting shown inFIG. 16A.
• FIG. 17 is an exploded view of the heat exchanger shown inFIGS. 15 and 16A.
• FIG. 18A is a perspective view of a furnace assembly according to another aspect of the invention.
• FIG. 18B is a detailed view of one aspect of the furnace assembly shown inFIG. 18A.
• FIG. 19 is a left-hand perspective view of a tube furnace assembly shown inFIG. 18A.
• FIG. 20 is a front elevation view of the tube furnace shown inFIG. 18A.
• FIG. 21 is a right side elevation view of the tube furnace shown inFIG. 18A.
• FIG. 22 is a left side elevation view of the tube furnace shown inFIG. 18A.
• FIG. 23 is a cross sectional view of the tube furnace shown inFIGS. 18A-22
• FIG. 24 is a schematic block diagram of a process for charging the treatment element to the enclosure according to one aspect of the invention
• FIG. 25 is a plot of treatment element vapor pressure as a function of temperature.
• FIG. 26 is a plot of heat exchanger temperature as a function of coolant flow according to one aspect of the invention.
DETAILED DESCRIPTION OF ASPECTS OF THE INVENTION
• The present invention comprises systems, apparatus, and methods that provide improved means for fabricating photovoltaic material that overcome many of the disadvantages of prior art systems and methods. Though aspects of the invention are particularly applicable to the handling and treatment of photovoltaic materials, aspects of the invention may be applied to many different photovoltaic and non-photovoltaic materials.
• FIG. 1 is a schematic block diagram of aprocess10 for treating a material according to one aspect of the invention. The material may comprise any material that is treated with a gas or vapor, for example, an element-containing vapor. In one aspect, the material comprises a photovoltaic precursor, for example, a precursor deposited on a substrate. The treatment gas may comprise any vaporous material. However, in one aspect, the treatment vapor comprises a chalcogen-containing vapor, for example, a sulfur-, selenium-, or tellurium-containing vapor; or an indium-, gallium-, or sodium-containing vapor. Though the material being treated may comprise any material or substance, to facilitate the disclosure of the invention, in some aspects, the material being treated may be referred to as a “work piece.” However, the use of the expression “work piece” is not intended to limit the scope of the materials to which aspects of the invention may be applied.
• Process10 includes a series of steps starting withstep12 of introducing the work piece to an enclosure, for example, into a treatment oven or furnace, such as treatment furnace illustrated inFIGS. 3 through 9 orFIGS. 18A through 23, though any type of appropriate treatment furnace may be used. The work piece introduced to the enclosure may comprise any material that may be treated with a gas, for example, an element-containing vapor. According to one aspect of the invention, step12 may be practiced by simply positioning the work piece on to the bottom surface of an enclosure, on to a support structure (or “boat”), or on to a shelf positioned in an enclosure. However, as will be discussed below, step12 may be practiced by positioning one or more work pieces, for example, photovoltaic precursors deposited on substrates, into one or more individual, isolated enclosures, for example, into one or more quartz tubes. These individual, isolated enclosures permit the operator to individually regulate the treatment conditions within the individual enclosures, for example, tube, to, among other things, allow the operator to vary or control the treatment conditions within the enclosure.
• Instep14, the work piece is heated to a first temperature for treatment. One heating schedule that may be used to heat the work piece is illustrated inFIG. 2. The work piece may be heated to a first temperature to raise the work piece at least partially to treatment element temperature.FIG. 2 is aplot30 of aheating schedule curve32 for a work piece and theheating schedule curve34 and the log of thepartial pressure curve35 for a treatment element, for example, Se, according to one aspect of the invention. Theabscissa36 ofplot30 is the time of treatment, typically, in minutes; the left-hand ordinate38 ofplot30 is the temperature, typically, degrees C; and the right-hand ordinate39 is the log of the partial pressure of the treatment element. According toheating schedule32, the temperature of the work pieces may be increased from ambient temperature, T_M∞, for example, room temperature, for instance, about 20 degrees C., to a first treatment temperature, T_M1, for example, to a temperature greater than 100 degrees C. For example, when the work piece being treated is a Cu—In—Ga precursor, and treatment element is Se, temperature T_M1may be between about 100 to about 400 degrees C. This rate at which the temperature may be increased from T_M∞ and T_M1may vary. For example, when the work piece being treated is a photovoltaic precursor deposited on a substrate, a slow rise in temperature may prevent the precursor from cracking and delaminating from the substrate. The rate of temperature increase may typically be between about 5 degrees C. per minute (° C./m) to about 100 degrees C. per second (° C./s), for example, about 20° C./m. The work piece to be treated may typically be held at temperature T_M1for at least about 30 seconds to about 90 minutes, for example, at least about 30 minutes.
• After heating the work piece, the element-containing material, for example, selenium or sulfur, is heated perstep16, for example, by means of the heating schedule illustrated inFIG. 2, to release treatment-material-containing vapor into the enclosure. According to one aspect of the invention, the treatment material is heated independently of the heating of the work piece being treated. The temperature of the treatment material, for example, Se, is elevated to a temperature at or above the temperature at which treatment material vapor is released, for example, at or above the vapor temperature at the prevailing pressures.FIG. 2 also illustrates atypical heating schedule34 for heating the treatment material. The treatment material may be any material that can be volatilized upon heating, including materials having multiple elements, that is, compounds. However, to facilitate the disclosure of the invention, in the following discussion the treatment material may be referred to as “the element-containing material” or “the element containing gas or vapor.” It is to be understood that in one aspect of the invention an element-containing material or element containing gas or vapor may comprise more than one element, for example, the element-containing material may be a mixture of elements or a compound.
• With reference toFIG. 2, according to one aspect of the invention, the temperature of the treatment element, as indicated bycurve34, is increased from an initial temperature T_E0to T_E1. As shown inFIG. 2, initial temperature T_E0may typically be less than or equal to ambient temperature T_M∞. For example, as will be described more fully below in the discussion of the heat exchanger, at the start of the treatment sequence, the temperature of the treatment element may be maintained at the temperature of the heat exchanger. Therefore, in one aspect of the invention, T_E0may be less than 60 degrees C., for example, about 50 degrees C. In one aspect of the invention, the initial temperature of the treatment element, T_E0, is kept below the temperature at which the element begins to volatilize. For example, when the treatment element is Se, which begins to volatilize at about 100 degrees C., the initial treatment element temperature may be kept below 100 degrees C., for example, about 50 degrees C. The temperature T_E0may vary broadly, for example, depending upon the vapor pressure of the treatment element. For example, for materials having high vapor pressures at lower temperatures, the temperature T_E0may be less than room temperature, for example, even less than 0 degrees C. The rate of temperature increase from T_E0to T_E1may vary, but may typically be between about 5° C./m to about 100° C./s, for example, about 20° C./m. The treatment element may typically be held at temperature T_E1for at least about 30 seconds to about 90 minutes, for example, at least about 15 minutes.
• According to aspects of the present invention, the timing of the initiation of the changes in temperature shown inFIG. 2 may vary depending upon the work piece being treated, the treatment element, and the treatment device being used, among other factors. Specifically, the relative time frame and time sequences of the increases and decreases in temperature may deviate from the relative time frames shown inFIG. 2. For example, though in one aspect shown inFIG. 2, the temperature of thework piece32 may be increased before the temperature of thetreatment element34 is increased, in one aspect, the temperature of thetreatment element34 may be increased before or substantially at the same time as the temperature of thework piece32 is increased. In one aspect of the invention, the temperature of thetreatment element34 is maintained below the temperature of thework piece32.
• In one aspect, after holding the treatment element at temperature T_E1for about15 minutes, the temperature of the treatment element may be increased to a temperature T_E2, for example, for Se, T_E2may be about 100 to about 400 degrees C. The rise in temperature from T_E1to T_E2may be between about 5° C./m to about 100° C./s, for example, at least about 20° C./m. The treatment element may typically be held at temperature T_E2for at least about 30 seconds to about 90 minutes, for example, at least about 30 minutes.
• With reference again toFIG. 1, after heating the treatment element to release a treatment element-containing vapor into the enclosure perstep16, the one or more work pieces are exposed to the treatment element vapor, perstep18, whereby at least some of the work pieces are treated with the treatment element. Treating the work piece with the element-containing vapor may comprise reacting the element with the work piece or providing an overpressure of the element-containing vapor to the work piece. In one aspect, providing an overpressure comprises providing a vapor pressure of the element-containing vapor, for example, Se vapor, that is greater than the vapor pressure of the element, for example, Se, present in the work piece. This overpressure may minimize or prevent the volatilization and the net loss of element from the work piece.Step18 may simply be practiced by allowing the work pieces positioned in the enclosure to be exposed to the treatment element vapor for a predetermined time periods, for example, 5 seconds to 5 hours. The treatment time for which the work piece is exposed to the element containing vapor may typically range from about 30 seconds to about 90 minutes.
• As shown inFIG. 2, while the treatment element is held at temperature T_E2, the temperature of the work piece being treated, as indicated bycurve32, may be increased, for example, rapidly, from temperature T_M1to T_M2, for instance, to a temperature where the treatment element begins to react with the treated material, for example, at a temperature of about 400 to about 600 degrees C. Se reacts rapidly with a Cu—In—Ga matrix to form a Cu—In—Ga—Se matrix. The rise in temperature of the treated material from T_M1to T_M2may be at a rate of between about 5° C./m to about 100° C./s, for example, about 20.0° C./m. Shortly thereafter, the temperature of the treatment element, for example, Se, is increased from T_E2to T_E3to enhance the volatilization of the treatment element and release sufficient vaporous treatment element to complete the reaction. For example, for Se, the temperature T_E3may be about 200 to about 550 degrees C. The rise in temperature of the treatment element from T_E2to T_E3may be at a rate of between about 5° C./m to about 100° C./s, for example, about 20° C./m. The treated work piece may be held at temperature T_M2to provide for sufficient reaction of the treatment element with the treated work piece. This treatment time may be at least about 30 seconds to 90 minutes.
• With reference toFIG. 1, instep20, upon completion of the treatment of the work piece, the temperature of the treatment element is reduced, for example, by active cooling, for instance, by means of a cooling heat exchanger. According to one aspect of the invention, the reduction of the treatment element temperature substantially terminates the release of treatment-element-containing vapor from the treatment element, for example, the Se. The reduction of the treatment element temperature may also allow at least some of the treatment-element-containing vapor to condense onto the treatment element. In one aspect, substantially all of the treatment element vapor may condense onto the treatment element, for example, whereby the loss of treatment element to, for example, condensation onto the enclosure, is minimized. According to one aspect of the invention, due to this condensation or “recapture” of treatment element, the utilization rate of the treatment element, for example, Se or S, is very high. For example, in one aspect utilization rate is at least about 90% or more, in some instances at least about 95% or more. This temperature reduction of the treatment element is shown ascurve34 inFIG. 2.
• Again, with reference toFIG. 1, before, during, or after the practice of cooling the treatment element perstep20, the temperature of the work piece being treated may be reduced as indicated bystep22 inFIG. 1. Upon cooling, the treated work pieces may be further handled or processed as desired. The cooling of the work pieces may be practiced actively, for example, by means of a cooling heat exchanger and/or forced convection, or through unforced, natural convection and/or radiation.
• This decrease in the temperature of the treated work piece is also shown inFIG. 2. As indicated bycurve32, the temperature of the treated work piece is cooled, for example, slowly, from T_M2to about room temperature. This cooling may be practiced to prevent damage to the work piece; for example, when the work piece is a photovoltaic material, cooling is carried out relatively slowly to prevent cracking of the work piece or delamination from the substrate. The rate of cooling may range from between about 5° C./m to about 100° C./s, for example, about 5.0° C./m.
• As shown inFIG. 2, before, during, or after the treated work piece is being cooled to room temperature, the treatment element is cooled from temperature T_E3to a lower temperature percurve34, for example, to a temperature below the temperature at which the element volatilizes. When the treatment element is Se, the Se is cooled to a temperature below 100 degrees C., for example, to a temperature of about 50 degrees C. The rate of cooling may range from between about 5° C./m to about 100° C./m, for example, about 15.0° C./m. Again, the curves inFIG. 2 are representative of the invention, for example, sulfur volatilizes at a lower temperature, and tellurium volatilizes at a higher temperature.
• In one aspect of the invention, the rapid cooling of the treatment element typically causes the vaporous element to recondense upon the cooled element whereby loss of the element to condensation on the surfaces of the furnace or associated surfaces is minimized or prevented. Thus, by controlled cooling of the treatment element, more of the treatment element is retained, for example, for further treatment.
• FIG. 2 also displays a typical corresponding variation in the log of thepartial pressure curve35 of a treatment element as the temperature of thetreatment element34 varies. As shown, thepartial pressure35 tracks the changes in thetemperature34 very closely. For example, for a Se treatment element, at a temperature T_E2of the Se of about 100 to about 400 degrees C., the partial pressure of the Se is about 5.0 Torr at about 400 degrees C. Also, for a Se temperature T_E3of about 200 to about 550 degrees C., the partial pressure of the Se can be as high as about 80 Torr. Thepartial pressure curve35 is a useful parameter in controlling the operation of the cooling heat exchanger or condenser/evaporator, as will be discussed more thoroughly below.
• As shown in and described above with respect toFIG. 2, in one aspect of the invention, the temperature of a work piece to be treated and the temperature of a volatile element with which the work piece is to be treated with are independently controlled to optimize the reaction, for example, to improve reaction selectivity and/or reaction kinetics, and also to minimize the loss of treatment element, for example, sulfur or selenium. According toprocess10 shown inFIG. 1 and the heating schedules shown inFIG. 2, a work piece may be treated with treatment element in a controlled environment whereby the release of treatment element is regulated to optimize the treatment and minimize the loss of treatment element. In one aspect,method10 or sub-sequences ofmethod10 ofFIG. 1 may be practiced repeatedly. For example, steps14,16,18, and20 may be practiced at least twice, possibly three or more times, to effect the desired treatment of the work piece. Also, steps18 and20 may be practiced at least twice (possibly three or more times), for example, before proceeding withstep22, to effect the desired treatment of the work piece.
• Theprocess10 shown inFIG. 1 may also include the optional steps of charging the enclosure withtreatment element24 and cooling thetreatment element26 prior to or during theheating step14. These optional steps are shown in phantom inFIG. 1. According to one aspect of the invention, the treating element may be introduced, or “charged,”24 to the enclosure before the work piece to be treated is introduced to theenclosure12. This charging of the treatment element may be practiced by the steps illustrated inFIG. 24 and will be discussed below. The coolingstep26 may be practiced to prevent the element-containing material from volatilizing prematurely, that is, before the work piece is ready to be treated.
• The method of the invention may be practiced in any suitable enclosure that can be adapted to regulate the temperature of the work pieces and the treatment material, for example, independently regulated. One enclosure that may be used to practice aspects of the invention is illustrated inFIGS. 3 through 9 andFIGS. 18A through 23. To those of skill in the art, the term “furnace” is sometimes reserved for devices in which work pieces are heated to temperatures of at least 1200 degrees C. while the term “oven” is sometimes reserved for devices in which work pieces are heated to temperatures of between about 200 degrees C. to about 300 degrees C. However, the use of the terms “furnace” or “oven” in the following discussion is not intended to limit the scope of the invention to these temperature ranges. Aspects of the present range may be used to heat work pieces in these and other temperature ranges, for example, as low as room temperature, for example, 20 degrees C., to as high a temperature that does not impact the performance or integrity of the disclosed devices, for example, at least 2000 degrees C.
• FIG. 3 is a perspective view of atreatment furnace50 according to one aspect of the invention.Treatment furnace50 may be used to practice the invention illustrated in and described with respect toFIGS. 1 and 2.FIG. 4 is a front elevation view offurnace50 shown inFIG. 3.FIG. 5 is a right side elevation view of thefurnace50 andFIG. 6 is a left side elevation view offurnace50.FIG. 7 is a rear elevation view offurnace50 andFIG. 8 is a top plan view offurnace50 shown inFIG. 3. According to aspects of the invention, furnace50 (andfurnace200 discussed below) are specially designed to operate under a broad range of operating conditions. For example, furnace50 (and200) may be operated under a broad range of temperatures, for example, from 0 to 2000 degrees C., and a broad range of pressures, for example, super-atmospheric pressures to sub-atmospheric pressures. For instance, furnace50 (and200) may be specially designed to operate under a vacuum ranging from just below about 1 standard atmosphere to 10⁻⁶Torr.
• As shown inFIGS. 3 through 8,furnace50 includes afront door assembly52, a rightside door assembly54, a leftside door assembly56, a rear panel assembly or back58, a top60, and a bottom62.Furnace50 may be mounted on a plurality ofsupport legs64. As shown inFIGS. 3 and 4,front door assembly52 may be pivotally mounted to thefurnace50 byhinge assembly66 and may comprise aplate53 having appropriate reinforcingelements55, for example, structural tubing or angles. Reinforcingelements55 may also comprise conduits through which a heating or cooling medium may be passed to either heat orcool furnace50.Plate53 may also be heated and cooled by other means.Front door assembly52 may include valve-actuatingassembly68 mounted to plate53.Valve actuating assembly68 may be adapted to actuate one or more isolation valves mounted withinfurnace50. (SeeFIGS. 13 and 14 and their description for details of valve-actuatingassembly68.)Front door assembly52 may typically provide means for openingfurnace50 toservice furnace50 or load work pieces, for example, photovoltaic material precursors, intofurnace50 for treatment.Front door assembly52 may typically include a handle and lockingassembly57 for opening, closing, and securingfront door assembly52.
• As shown inFIGS. 3 and 5, rightside door assembly54 offurnace50 may comprise aplate57 having appropriate reinforcingelements59, for example, structural tubing or angles. Reinforcingelements59 may also comprise conduits through which a heating or cooling medium may be passed to either heat orcool furnace50.Plate57 may also be heated and cooled by other means. Though rightside door assembly54 may be rigidly mounted to furnace50 (that is, not adapted to be opened), as shown inFIG. 3, rightside door assembly54 may be removably mounted tofurnace50, for example, pivotally mounted tofurnace50 by means ofhinge assembly70. Rightside door assembly54 may be secured tofurnace50 by conventional means, for example, by means of mechanical fasteners or welding, such as, clamps72.Clamps72 may be conventional clamps adapted to secure rightside door assembly54. Rightside door assembly54 may typically provide means for openingfurnace50 for servicing, for example, servicing the work piece support structures, and related treatment devices, for example, the valves, heat exchangers, or heaters, discussed below.
• As shown inFIGS. 3 and 6, leftside door assembly56 offurnace50 may be similar in construction to rightside door assembly54 and may comprise aplate67 having appropriate reinforcingelements69, for example, structural tubing or angles. Again, reinforcingelements69 may also comprise conduits through which a heating or cooling medium may be passed to either heat orcool furnace50.Plate67 may also be heated and cooled by other means. Leftside door assembly56 may also be rigidly mounted to furnace50 (that is, not adapted to be opened). However, as shown inFIG. 6, leftside door assembly56 may be removably mounted tofurnace50, for example, pivotally mounted tofurnace50 by means ofhinge assembly80. Leftside door assembly56 may be also be secured tofurnace50 by conventional means, for example, by means of mechanical fasteners or welding, such as, clamps73.Clamps73 may be similar toclamps72 provided on the rightside door assembly54 shown inFIGS. 3 and 5. Leftside door assembly56 may typically also provide means for openingfurnace50 for servicing, for example, servicing the work piece support structures, and related treatment devices, for example, the valves and heat exchangers, discussed below.
• FIG. 7 illustrates therear panel assembly58 offurnace50 which may comprise aplate97 having appropriate reinforcingelements99, for example, structural tubing or angles. Reinforcingelements99 may also comprise conduits through which a heating or cooling medium may be passed to either heat orcool furnace50.Plate97 may also be heated and cooled by other means.Rear panel assembly58 may also be rigidly mounted tofurnace50, that is, not adapted to be opened, but may also be removable, for example, pivotally mounted tofurnace50 by means of hinge assembly. As shown inFIG. 7,rear panel assembly58 may also be secured tofurnace50 by conventional means, for example, by means of mechanical fasteners or welding.
• In aspects of the invention,furnace50 may include various access ports or openings for assorted purposes, for example, for introducing or removing process fluids (that is, liquids and/or gases), introducing or removing heating or cooling fluids, applying a vacuum, or providing pathways for wiring, cabling, or instrumentation, among other reasons. As shown inFIGS. 3 through 8, access ports or openings may be located infront door assembly52, rightside door assembly54, leftside door assembly56,rear panel assembly58, top60 or bottom62. As shown inFIG. 7, according to one aspect,rear panel assembly58 may include a plurality of access ports, including afirst row100 offlanged ports102 on the left side ofrear panel58 and asecond row104 offlanged ports106 on the right side ofrear panel58.Ports102 inrow100 andports104 inrow102 may provide ports providing power, such as toheating elements88; or for instrumentation wiring, such as to temperature or pressure sensors. As also shown inFIG. 7,rear panel58 may also include tworows108 ofports110 centrally mounted onrear panel58.Ports110 may be mounted in acommon plate112 and be mounted to plate97 ofrear panel58 by a plurality ofmechanical fasteners114, for example, bolts or screws. According to one aspect of the invention,ports110 may provide conduits for venting, purging, or introducing process or control fluids tofurnace50. For example, in one aspect,ports110 may provide cooling or heating fluid (for example, liquid or gas) to an internal component, such as, to a heat exchanger (for example,heat exchanger86 shown inFIGS. 15 and 16A).
• Thetop assembly60 offurnace50 is illustrated in the top plan view ofFIG. 8.Top assembly60 may comprise aplate117 having appropriate reinforcingelements119, for example, structural tubing or angles. Again, reinforcingelements119 may also comprise conduits through which a heating or cooling medium may be passed to either heat orcool furnace50.Plate117 may also be heated and cooled by other means.Top assembly60 may also be rigidly mounted tofurnace50, that is, not adapted to be opened, but may also be removable, for example, pivotally mounted tofurnace50 by means of a hinge assembly (not shown). As shown inFIG. 8,top assembly60 may also be secured tofurnace50 by conventional means, for example, by means of mechanical fasteners or welding. As shown inFIG. 8,top assembly60 may include a plurality of access ports, including afirst row120 offlanged ports122 on the left side oftop assembly60 and asecond row124 offlanged ports126 on the right side oftop assembly60.Ports122 inrow120 andports124 inrow122 may provide access ports for power, instrumentation, venting, purging, or process fluids, among other functions. As also shown inFIG. 8,top assembly60 may also include one or moreflanged ports130, for example, a centrally mounted port intop assembly60.Ports130 may also provide an access for ports for power, instrumentation, venting, purging, or process fluids or simply provide a access for flushing or purgingfurnace50.
• As shown inFIGS. 3 through 8, a plurality of access ports may also be located in bottom62. Similar to top60, bottom62 may include first row132 offlanged ports134 on the left side ofbottom assembly62 and asecond row136 offlanged ports138 on the right side ofbottom assembly62.Ports134 in row132 andports138 inrow136 may also provide access to the inside offurnace50 for providing purging, venting, process fluids, or instrumentation.Bottom62 may also include one or moreflanged ports140 centrally mounted inbottom62.Port140 may also provide an access for ports for power, instrumentation, venting, or process fluids or simply provide a access for flushing or purgingfurnace50.
• FIG. 9 is a right side elevation view of thefurnace50 shown inFIGS. 3 through 8 with the rightside door assembly54 and hingeassembly70 removed to reveal the internal structure offurnace50. As shown inFIG. 9,furnace50 includes at least one workpiece treatment assembly81, but typically includes a plurality of workpiece treatment assemblies81 mounted infurnace50.FIG. 10 is a detailed side elevation view of one workpiece treatment assembly81 as shown asDetail10 inFIG. 9. In one aspect of the invention, workpiece treatment assemblies81 may be mountedfront door assembly52, rightside door assembly54, leftside door assembly56,rear panel assembly58, top60, or a bottom62. For example, in one aspect, the workpiece treatment assemblies81 may be mounted as rack on a door or side offurnace50 whereby one ormore treatment assemblies81 may be manipulated or handled, for example, removed or installed, by means of a door or side offurnace50.
• As shown inFIG. 10, eachtreatment assembly81 includes a treatment chamber, container, ortube82; an isolation apparatus (or “flapper valve”)assembly84; and a material delivery (or “condenser/evaporator”)assembly86.Tubes82 are adapted to accept one ormore work pieces90, for example, a photovoltaic precursor material, to be treated. According to aspects of the invention,work piece90 is positioned intube82 and isolated from the rest offurnace50 whereby the treatment environment withintube82 can be controlled as desired, for example, at a desired temperature, pressure, and/or vapor content. The isolation oftubes82 from the rest offurnace50 minimizes the exposure of the rest offurnace50 to gases and vapors present intubes82, for example, toxic gases and vapors. According to one aspect of the invention, the use of one or more tubes orinner enclosures82 inside an outer enclosure, for example, as provided by the walls ofchamber50, isolates the hot treatment zone of the inner enclosure from the outer enclosure whereby low temperature sealing devices, for example, elastomeric seals, may be used to seal the outer enclosure from the ambient environment and minimize thermal damage to the sealing devices. It will be apparent to those of skill in the art that aspects of the invention provide enhanced functionality and enhanced throughput compared to prior art devices and methods.
• As shown inFIG. 10,furnace50 includes a plurality ofheat sources88 adapted to heat the one ormore work pieces90 intube82.Heat sources88 may be an infrared heat source, an inductive heat source, or a convective heat source. For example,heat source88 may be an infrared heating lamp.Tube82 is typically fabricated from a material that readily permits the heating ofwork piece90 by means ofheat sources88, for example, is made from a transparent or translucent material, such as, quartz, stainless steel (such as316 stainless steel) or a corrosion-resistant alloy, such as a Hastelloy® alloy.Heat sources88 may be mounted to the sides, roof, or floor offurnace50 or mounted to a perforated mounting plate (not shown) having apertures sized to receive and supportheat sources88.Tube82 may assume any appropriate cross-sectional shape, such as round, rectangular, and square, for example, depending upon the size and shape of the work piece being treated and the size and shape offurnace50. A perspective view of onetube82 that may be used in one aspect of the invention is shown inFIG. 16A. As shown inFIG. 10,tube82 may be mounted on one ormore supports92, for example, one or more bars or support tubes mounted horizontally infurnace50.Supports92 may also be fabricated from a material that readily permits the heating ofwork piece90 by means ofheat sources88, for example, is made from a transparent or translucent material, such as, glass or quartz.Tube82 may be rigidly mounted tosupports92 or may be allowed to translate onsupports92, for example, to permit ease of handling, for instance, removal, oftubes82 fromfurnace50, for instance, through openrear panel assembly58.Supports92 may be mounted to the sides, roof, or floor offurnace50 or mounted to a perforated mounting plate (not shown) having apertures sized to receive and support supports92, for example, the same mounting plate adapted to supportheat sources88. Temperature sensing devices, for example, thermocouples, may be mounted intubes82 and/or supports92.
• FIG. 11 is a detailed side elevation view of atube sealing assembly84 shown asDetail11 inFIG. 10.FIG. 12A is a right-hand perspective view oftube sealing assembly84 shown inFIG. 11.FIG. 12B is a left-hand perspective view of thetube sealing assembly84 shown inFIG. 11.
• As shown inFIGS. 11, 12A, and12B, sealingassembly84 is adapted to close or seal the end of treatment chamber or tube82 (shown in phantom). The sealingassembly84 includes a sealing or “flapper valve”assembly180 and means182 for compressing the sealingassembly180 against the treatment chamber ortube82. Though in some aspects the sealingassembly180 may provide an vapor-tight cover to the one ormore treatment chambers82, in another aspect, the engagement of sealingassembly180 may not be vapor-tight, but may simply minimize the escape of fluids (that is, gases or liquids) fromtreatment chamber82 during treatment. The sealingassembly180 includes asupport structure184, at least onecover plate186 adapted to engage the treatment chamber opening, and a plurality ofrods188. The plurality ofrods188 have afirst end190 mounted to supportstructure184, for example, resiliently mounted to supportstructure184, and asecond end195 adapted to engagecover plate186.
• Support structure184 may be any support structure adapted to support the one ormore cover plates186 and adapted to engage the means182 for compressing the sealingassembly180 against the treatment chamber ortube82 while withstanding the treatment temperatures, for example, up to 800 degrees C. In one aspect,support structure184 may be a single plate, for example, a plate having sufficient stiffness that does not require the need for additional structural support bars or ribs. In another aspect,support structure184 may comprise a plurality ofplates192, for example, a plurality of vertically or horizontally oriented plates.Plates192 may be attached by means of mechanical fasteners, welding, or by common support bars or ribs. In the aspect shown inFIG. 11,support structure184 may comprise a plurality ofhorizontal plates192 mounted to a plurality of vertical support bars194.Plates192 may be mounted tobars194 by mechanical fasteners or welding.Plates192 may include holes orslots193 through which mechanical fasteners (not shown) may adjustably engage support bars194.
• As shown inFIGS. 11 and 12A,plates192 include a plurality ofapertures197 through which the first ends190 ofrods188 pass throughplates192.Rods188 may be mounted toplates192 by conventional means, for example, by means of mechanical fasteners. As shown inFIGS. 11 and 12B, in one aspect,rods188 may mount toplates192 by means of aflexural member199 and one ormore fasteners201, for example, one or more hex nuts. (Though not shown inFIG. 12B,rod188 may be retained toflexural member199 by a second fastener, for example, a hex nut located behindflexural member199.)Flexural member199 may comprise a “flexure” as discussed below.Flexural member199 may include acircular disk section203 and anelongated stem207.Disk section203 may be sized to ensure thatdisk section203 cannot pass throughaperture197 inplate192.Stem207 may be mounted toplate192 by conventional means, for example, byclamp plate209 andfasteners216. According to one aspect of the invention, the flexibility offlexural member199 provides for at least some alignment for the positioning ofplate186 ontube enclosure82. For example,flexural member199 and pin208 may provide a parallel flexure configuration that minimizes the misalignment ofplate186 while providing at least some resiliency or compliance in the alignment of the mating structures.
• As shown inFIGS. 11, 12A, and12B,plates192 may include anextension196, for example,plates192 andextensions196 may comprise structural angles.Extension196 may be solid or include a plurality of throughholes198, for example, to facilitate assembly, to reduce the weight ofsupport structure184, or to provide a purge path to eliminate virtual leaks.Plates192,bars194, andextensions196 may be made from any metal or non-metal structural material, for example, a steel, stainless steel, titanium, nickel, or any other structural metal. In one aspect,plates192,bars194, andextensions196, may be made from stainless steel, for example,304 stainless steel.
• The one ormore cover plates186 may be metallic, but are typically made from stainless steel sheet having a thickness of from about 0.005 inches to about 0.125 inches. The size ofcover plate186 will vary depending upon the size of the treatment chamber and the treatmentchambers sealing assembly180 used to seal the treatment chamber.Cover plates186 may be about 3 inches long to about feet long and may have a width from about 1 inch to about 1 foot. Typically coverplate186 is about 2 feet long and about 2 inches in width. In one aspect of the invention,cover plate186 may engage a single or a plurality of treatment chambers, for example, 2, 3, or more treatment chambers. That is,cover plate186 may be adapted to seal a plurality of treatment chamber openings, for example, a plurality oftubes82.
• Rods188 are adapted to transmit a load fromsupport assembly184 to thecover plates186.Rods188 may have any cross section, including square or rectangular, but are typically circular in cross section and may have a diameter of between about 0.125 inches and 0.5 inches.Rods188 are typically about 0.375 inches in diameter and may be at least partially threaded.Rods188 may engageplates186 by conventional means, for example, by means of mechanical fasteners or welding. However, in one aspect, afirst end195 ofrods188 is not rigidly mounted toplates186 but may be flexibly engaged to allow for some relative displacement betweenrods188 andplates186. One means of providing this non-rigid engagement to the first end189 ofrod188 is illustrated inFIG. 12B, wherefirst end195 engagesplates186 by means ofclips200. As shown inFIG. 12B,clip200 may comprise a centralu-shaped portion219 and at least one, typically, two, cantileveredplate sections221. Cantileveredplate sections221 may comprise “flexures” as discussed below.Plate sections221 may have at least one, typically, two, holes (not shown) adapted to engage and retain thefirst end195 ofrods188, for example, by means of one ormore fasteners217, for example, hex nuts threaded torods188.Clip200 may be mounted toplate186 by mechanical fasteners or welding, for example, simple resistance welding atsection219.Clip200 is typically also made from stainless steel, for example,304 stainless steel.
• As discussed above, thesecond end190 ofrod188 is adapted to engagesupport structure180. As shown inFIG. 11 and12B,second end190 may pass through at least onehole197 inplate192 and, for example, engageflexural member199. As also shown inFIG. 11 and12B,rod188 may include a resilient mounting to plate192, for example, by means of one ormore springs204, for example, coil springs.Springs204 are preferably made from a temperature resistant material, for example, a high strength austenitic nickel-chromium-iron alloys, for instance, a Special Metals Corporation's Inconel® alloy, such as Inconel® 750 alloy, or its equivalent.Rod188 may include one or more spring capturing or retaining devices, for example, a cup-likespring retaining device206 mounted torod188. In this aspect, retainingdevice206 receivessprings204 to promote engagement betweenspring204 androd188. Retaining device may also include a sleeve223 (seeFIG. 11) though whichrod188 passes. In one aspect, the end ofsleeve223 may provide a surface against whichfastener201 capturesflexural member199 when attachingflexural member199 torod188.Plates192 may also include a recess or counter bore222 (seeFIG. 11) for receivingspring204 to facilitate assembly and ensure alignment during operation.Rods188 and retainingdevices206 may be made from any metal or non-metal structural material, for example, a steel, stainless steel, titanium, nickel, or any other structural metal. In one aspect,rods188 and retainingdevices206 may be made from stainless steel, for example,304 stainless steel.
• In one aspect, sealingassembly84 may include additional support members forrods188, for example, to positionrods188 and coverplates186 in the desired position to engagetreatment chambers82. As shown inFIG. 11, sealingassembly184 may include one or more retaining members, pins, or bars208 to supportrods188. In one aspect of the invention, bars208 may comprise “flexures” as discussed below.Bars208 may be mounted to any convenient location onsupport structure180 and engagerods188 by conventional means, for example, mechanical fasteners. In the aspect shown inFIG. 11,bars208 are mounted to extension196 (for example, to the leg of the structural angle) by means of mechanical fasteners and aclamp plate210.Bars208 may be mounted torods188 by conventional means, including welding or mechanical fasteners. As also shown, bars208 may be mounted torods188 by capture between two ormore fasteners312, for example, hex nuts, threaded torod188. It will be apparent to those of skill in the art that the threaded mounting ofbar208 torod188 vianuts312 permits the assembler to vary the position of engagement whereby the elevation of rods188 (and of plates186) may be varied as desired.
• According to aspect of the invention, the sealingassembly84 illustrated inFIGS. 11 and 12 is displaced into engagement with one or more treatment chambers ortubes82 to at least partially limit the escape of fluids fromtreatment chamber82 during treatment. The displacement of sealingassembly84 into engagement withtreatment chambers82 is effected by means of valve-actuation assembly68 (seeFIGS. 3-5 and9). Though valve-actuation assembly68 may be positioned withinfurnace50 or outside offurnace50, in the aspect shown inFIGS. 3-5, valve-actuation assembly68 is positioned outside offurnace50 and is adapted to engage sealingassembly84 by means of a plurality of rods extending through a wall offurnace50.
• FIG. 13 is a perspective view ofvalve actuation assembly68 shown inFIG. 9.FIG. 14 is a side elevation view of thevalve actuation assembly68 shown inFIG. 9. As shown,valve actuation assembly68 is mounted tofront door plate53 by means of astructural support218 and is adapted to displace at least oneactuation rod220, typically, a plurality ofrods220. In the aspect shown, sixactuation rods220 are displaced byvalve actuation assembly68.Valve actuation assembly68 includes one ormore linkage assemblies224, for example, a spherical linkage assembly, mounted to door53 and apiston assembly234 mounted tostructural support218 and tolinkage assembly224. According to the present invention,piston assembly234 displacesstructural support218 to whichrods220 are mounted to displacerods220 and sealing assembly84 (seeFIGS. 11 and 12).
• As shown inFIG. 14,linkage assembly224 includes abody228, afirst bracket230 by whichbody228 is mounted topiston assembly234 and asecond bracket232 mounted to plate233 which is mounted todoor plate53, for example, by conventional mechanical fasteners or welding. One or more pneumatic or hydraulic lines (not shown) may be provided to actuatepiston assembly234. Hydraulic orpneumatic cylinder234, for example, a short-stroke cylinder, mounted to supportstructure218.
• Support structure218 may include a variety of structural elements for transmitting the displacement provided bypiston assembly224 torods220.Piston assembly224 is mounted tomain plate236 ofsupport structure218 to which the plurality ofrods220 are mounted. Main plate oractuation plate236 may take a variety of shapes depending upon the size and number ofrods220 to whichmain plate236 is mounted. In the aspect shown inFIG. 13,main plate236 takes the general form of the letter “H” where therods220 are mounted to the uprights and thepiston assembly224 mounts to the cross beam. In one aspect, themain plate236 may be relatively stiff, for example, at least about 0.375 inches in thickness, to promote uniform displacement ofrods220, for example, to minimize misalignment ofrods220. In one aspect,main plate236 may include one or more reinforcing ribs to increase the stiffness ofplate236.
• Support structure218 may also include at least oneflexural plate238,240 mounted tomain plate236. In one aspect,plates238 and240 comprise flexures, that is, precision flexural elements that can control the accuracy of deflection, for example, parallel flexures. (See Slocum,Precision Machine Design(1992), the disclosure of which is incorporated by reference herein.)Flexural plates238 and240 not only support themain plate236 androds220, butflexural plates238 and240 may also provide at least some flexibility to supportstructure218 wherebyrods220 can be more uniformly displaced.Flexural plates238 are mounted tomain plate236 bymounts242.Mounts242 may assume a variety of shapes and sizes, but, as shown inFIGS. 13 and 14, mounts242 may comprise acenter plate244, abase plate246 mounted to the center plate, and twogussets248 mounted to the sides of the center plate.Mounts242 may be fabricated by welding or mechanical fasteners.Flexural plates238 may be mounted tomounts242 by a mountingplate250 and mechanical fasters.
• Flexural plates238 are also mounted tofurnace50, for example, to thefront door plate53, by any conventional mounting means. As shown inFIGS. 13 and 14,flexural plates238 may be mounted tofurnace50 viaflanged support252. As shown inFIG. 14,flanged support252 may include acenter web plate254 and aflange plate256. Flanged supports252 may be mounted tofurnace50 by conventional means, for example, mechanical fasteners or welding.Flexural plates238 may be mounted toflanged support252 by a mountingplate250 and mechanical fasters.
• Flexural plates240 may also be mounted tomain plate236 bymounts252, that is, structural members similar to or identical tomounts242 discussed above.Flexural plates240 may be mounted tomounts252 by a mountingplate250 and mechanical fasteners.Flexural plates240 are also mounted tofurnace50, for example, to thefront door plate53, by any conventional mounting means. As shown inFIGS. 13 and 14,flexural plates240 may be mounted tofurnace50 viaplates254. As shown inFIG. 13,plates254 may be mounted tofurnace50 by conventional means, for example, mechanical fasteners or welding.Flexural plates240 may be mounted toplates254 by a mountingplate250 and mechanical fasters.
• According to one aspect of the invention, the function ofvalve actuation assembly68 is to displace sealingassembly84 against thetreatment tubes82. This displacement of sealingassembly84 is typically effected viarods220. As shown inFIG. 14,rods220 are mounted tomain plate236.Rods220 may be mounted toplate236 by conventional mechanical fasteners, for example, as shown inFIG. 14,rods220 are mounted to plate236 by a pair ofcollars280 and281.Rod220 extends intofurnace50 throughflange282 andflanged bellows assembly284. Bellows assembly may provide some flexibility to the insertion ofrods220 intofurnace50.Bellows assembly284 includes abellows286 and twoflanged pipes287 and288.Bellows assembly284 may be a typical off-the-shelf item. According to one aspect,rods220 may be rigidly mounted toflange282, for example, by mechanical fasteners or welding, whereby the displacement ofrods220 is accompanied by the displacement, for example, compression, ofbellows286.Flanged pipe288 is mounted to aflanged nipple290 mounted tofront door plate53. The flanged connections may typically comprise “conflat” flanges, for example, conflat flanges provided by the Kurt J. Lesker Company of Clairton, Pa., or their equivalent. ISO and/or ASA flange systems may also be used. After passing throughfront door plate53,rods220 engage sealingassembly84.Rods220 may engage sealingassembly84 in any fashion effective to displace sealingassembly84. In one aspect,rods220 are mounted to supportstructure184 of sealingassembly84 by mechanical fasteners, for example, by bolts or screws, toplates192 or bars194 (seeFIGS. 11 and 12) ofsupport structure184.Rods220 may also be welded to supportstructure184.
• FIG. 15 is a detailed side elevation view of a heat exchanger or condenser/evaporator86 shown asDetail15 inFIG. 10. A perspective view ofheat exchanger86 along withtube82 is shown inFIG. 16A.FIG. 16B is a detailed cross section of the conduit mounting shown inFIG. 16A.FIG. 17 is an exploded view ofheat exchanger86 shown inFIGS. 15 and 16A. According to aspects of the invention, heat exchanger86 (and any other heat exchanger identified herein) may be a device that exchanges heat between the body of the device and a working fluid passing through the device to vary the temperature of at least one surface of the device. In one aspect of the invention, heat exchanger86 (and any other heat exchanger identified herein) may function as a “condenser,” that is a device having at least one surface upon which a volatilized material may condense upon, for example, by lowering the temperature of the surface. In one aspect of the invention, heat exchanger86 (and any other heat exchanger identified herein) may function as an “evaporator,” that is, a device having at least one surface upon which a volatilizable material is applied and from which the volatilizable material may be volatilized or “evaporated,” for example, by raising the temperature of the surface. In another aspect of the invention, heat exchanger86 (and any other heat exchanger identified herein) may function as both a “condenser” and an “evaporator,” and may be referred to as a “condovator.”
• As shown inFIGS. 15-17,tube82 comprises a maincylindrical section83, an open first end having afirst flange85, and open second end having asecond flange87.Heat exchanger86 is mounted to flange87 of the open second end oftube82 wherein a surface ofheat exchanger86 is exposed to the open end oftube82. In one aspect of theinvention heat exchanger86 may comprise a material delivery device, that is, a device for use in regulating the delivery of a vaporous material or element, for example, vaporous Se or S, totube82. As shown inFIGS. 15-17,heat exchanger86 consists of an elongatedcylindrical body150 having at least onesurface151 exposed to the open end oftube82. According to one aspect of the invention,surface151 is adapted to receive at least some volatilizable element, for example, by means of the “charging” process described below. The temperature ofsurface151 is then regulated, for example, heated or cooled, whereby the element volatilizes and the vaporous element is released intotube82 to treat work piece intube82.
• Cylindrical body150 ofheat exchanger86 may be a rectangular, square, or circular cylindrical body, or any other shaped cylindrical body adapted to be mounted to a treatment tube, such as,treatment tube82.Cylindrical body150 may include at least onefirst passage152, for example, a circular passage, extending the substantially the entire length ofbody150, and two smaller passages,154 and156, for example, also circular, and also extending substantially the entire length ofbody150. According to one aspect of the invention,passage152 is adapted to retain at least oneheating device158, for example, an infrared heat source, an inductive heat source, or a convective heat source, among other devices.Passage152 may be circular, square, rectangular, or any other shape adapted to retain aheating device158. According to one aspect,heating device158 may comprise one or more heating devices positioned along one ormore passages152.Heating device158 typically may have a power output of at least about 200 watts, typically, at least 500 watts. For instance,heating device158 may be an off-the-shelf infrared light tube.Heating device158 is typically supplied with electric power by means of a wire or cable and an appropriate electrical connector not shown (for example, throughport102 shown inFIG. 7).
• Passages154 and156 may be coolant or heating fluid flow passages, for example, passages for transmitting a working fluid, that is, a liquid or a gas, throughbody150 to heat orcool body150 andsurface151. The working fluid may be air; nitrogen; water; an inert gas, for example, helium; an oil; or an alcohol, for example, ethylene glycol; among other working fluids.Passages154 and156 are typically capped at either end byplugs160.Passages154 and156 communicate with two or more workingfluid source conduits162 and164 adapted to receive and discharge a working fluid to and from an external source.Conduits162 and164 may be positioned anywhere alongbody150, and, as shown inFIG. 16A, may be positioned in about the middle ofbody150.Conduits162 and164 may have about ¼-inch nominal diameter and be mounted inconduits111, as discussed below with respect toFIG. 16B.Conduits162 and164 typically supply working fluid toheat exchanger86 from a source outside furnace50 (also shown inFIGS. 7-9). For example, coolant flow, such as, air, may be provided toconduit162 which passes the coolant topassage156. The coolant may then flow through one or more cross passages (not shown) topassage154 and then be returned toconduit164 at a hotter temperature when cooling (or a colder temperature when heating) than the coolant introduced throughconduit162. The hotter coolant discharged throughconduit164 may be vented or passed through a heat exchanger for cooling (or heating) or to heat recovery, for example, the coolant may be cooled and reintroduced as coolant toconduit162. In one aspect, the temperature of the working fluid introduced to heat exchanger may be varied to effect the desired temperature ofsurface151. For example, the temperature ofsurface151 may be regulated by varying the temperature of the working fluid introduced toheat exchanger86 by means of an external heat exchanger (not shown).
• As shown inFIG. 15,heat exchanger86 is mounted totube82 wherebysurface151 is exposed to the inside oftube82. Sincetube82 may typically be made from a material (for example, quartz) having a different thermal expansion coefficient than the material (for example,304 stainless steel) of thebody150 ofheat exchanger86, the mounting ofheat exchanger86 to tube may make allowance for differences in thermal expansion. As shown inFIGS. 15-17, in one aspect,heat exchanger86 may be mounted totube82 by means of one or more brackets orclips166 and one or moreresilient materials168, for example, one or more coil springs or flexures. According to this aspect, theclips166 andcoil springs168 provide for a thermally expandable mounting ofheat exchanger86 totube82 while maintaining contact, for example, vapor-tight contact, betweensurface151 ofbody150 andtube82.
• FIG. 16B is a detailed cross section of the mounting ofconduits162 and164 inconduit111.Conduit111 comprises a cylindrical tube, for example, about ¾-inch nominal diameter, having an openfirst end113 and a closed second end115.Conduits162 and164 typically extend fromcylindrical body150 ofheat exchanger86 and pass throughconduit111 and through closed end115.Conduits162 and164 may have anappropriate coupling123, for example, the mail pipe coupling shown, to connect to a source of coolant, for example, air.Conduits162 and164 may be mounted to the closed end115 ofconduit111 by means of mechanical fasteners or welding.Conduits111 may be mounted tochamber50, for example, intoports110 in therear wall97 ofchamber50, by means of an appropriate mechanical fastener. For example,port110 may comprise an appropriate vacuum fitting, for example, an Ultra-Torr® vacuum fitting provided by the Swagelok Company, or its equivalent fitting. According to aspects of the invention, the mounting ofconduits162 and164 inconduit111 allows for some compliance in the mounting oftubes82 infurnace50. For example, the flexibility of the mounting ofconduits162 and164 inconduit111 permits some adjustment in the alignment ofheat exchanger86 andtube82 infurnace50.
• As shown inFIG. 17,clip166 may comprise a thin sheet metal, for example, stainless steel plate having a thickness of around 0.040 inches, bent into a U-shape. The thickness of the plate or sheet from which clip166 is made may vary from about 0.005 inches to about 0.125 inches. Though the aspect of the invention shown inFIGS. 15-17 includes a plurality ofclips166 retaining a plurality ofsprings168, aspects of the invention may include one ormore clips166 or clip-like structures having the function ofclips166 and one or more spring-like elements performing the function ofsprings168. As shown, theends167 ofclip166 may be crimped or bent to attachclip166 to the end oftube82, for example, to a flange oftube82.Clip166 may be mounted tobody150 by one ormore fasteners170, for example, screws or rivets, through one or more slottedholes172 inclip166. Slottedholes172 allowclip160 to translate with respect tobody150, for example, due to differences in thermal expansion. The mounting ofheat exchanger86 totube82 may also include two ormore springs168, for example, coil springs or Belleville springs, among others, mounted concentrically or axially with respect to each other.
• FIG. 18A is a right-hand perspective view of afurnace assembly200 according to another aspect of the invention.FIG. 18B is a detailed view of one aspect of thefurnace200 shown inFIG. 18A.FIG. 19 is a left-hand perspective view of atube furnace assembly200 shown inFIG. 18A with the extraction assembly extended according to aspects of the invention.FIG. 20 is a front elevation view of the furnace shown inFIG. 18A.FIG. 21 is a right side elevation view of the furnace shown inFIG. 18A.FIG. 22 is a left side elevation view of the furnace shown inFIG. 18A.FIG. 23 is a cross sectional view of thefurnace assembly200 shown inFIGS. 18A-22.
• As shown inFIG. 18A,furnace assembly200 includes atreatment chamber202 and a chamberisolation actuator assembly204. The contents oftreatment chamber202 are shown in phantom inFIG. 18A.Treatment chamber202 comprises acylindrical tube210 capped at adistal end211 by acover212. Though shown as a circular cylindrical tube inFIG. 18A,tube210 may comprise any cylindrical shape, for example, circular cylindrical, rectangular cylindrical, and oval cylindrical, among others. Though not shown inFIG. 18A, one or more work pieces, for example, photovoltaic precursors, may typically be positioned withintube210, for example, on a support structure or “boat.” Theproximal end213 oftube210 typically is mounted to aplate214, for example, for structural support and/or mounting to other fixtures.Treatment chamber202 may also include one ormore access ports215, such as flanged ports, for electrical power, instrumentation, or the introduction or removal (that is, purging or venting) of process fluids.
• In a fashion similar tofurnace50 shown inFIGS. 3-9, according to aspects of the invention, work pieces, for example, photovoltaic material precursors, may be treated intreatment chamber202 with vaporous elements, for example, vaporous Se or S. Furnaceassembly200 includes heating means and/or cooling means for treating work piece for example, according to predetermine temperature schedules, such as the schedule shown inFIG. 2.Furnace assembly200 may include heating means320 and cooling means322 in thedistal end211 oftube210. Heating means320 may comprise an electric heating element (for example, a concentric coil heating element) or tubing through which a working fluid, for example, heated air, water, or oil, may be passed (for example, a concentric coil tubing). Heating means320 may be mounted to the inside or outside surfaces ofcover212 ortube210 and the heating means may be energized bywire323. Cooling means322 may also comprise tubing through which a coolant is passed, for example, one or more of the coolants referenced above. The coolant tubing may be provided in concentric coil or as one or more cooling coils324 shown inFIGS. 18A and 23.
• As also shown inFIG. 18A,furnace50 may also include aheating assembly400, that is, aheating assembly400 mounted aboutcylindrical tube210. InFIG. 18A,heating assembly400 is shown in perspective cross-sectional view.Heating assembly400 may include acylindrical housing402 having afirst end404 and asecond end406. According to aspects of the invention,cylindrical housing402 comprises some form of annular heating elements, for example, infrared, conductive, or convective heating elements. In one aspect,housing402 includes at least one, but typically a plurality of sets of annular heating elements. In the aspect of the invention shown inFIG.18A housing402 comprises three sections of heating elements: afirst section401 adjacentfirst end404 ofhousing402; a secondmiddle section403; and third section405 adjacentsecond end406 ofhousing402.Sections401,402, and405 may each include a plurality ofheating elements407, for example, a plurality of resistive heating elements power and controlled by devices not shown.
• First end404 includes anannular cover plate408 having aninside diameter409 sized to accommodatetube210.Plate408 that may be mounted tohousing402 by a plurality ofmechanical fasteners410, for example, screws.Plate408 may be adapted to thermally isolate theheating assembly400 fromtube210; for example,plate408 may be made from an insulating material, such as a ceramic.First end404 may also include a sealingelement412 adapted to at least partially seal the space between the outside diameter oftube210 and insidediameter409 ofplate408.Sealing element412 may be an elastomeric sealing element or a fiberglass, such as Nextel fiberglass, or its equivalent.Second end404 may include anannular flange416 having aninside diameter418. Acover plate414 may be mounted toannular flange416 by a plurality ofmechanical fasteners420, for example, screws. In one aspect,cover plate414 includes at least one aperture through which cooling means322,heater wire323, or coolingtube324 may pass. The apertures incover plate414 may include a sealing element to minimize the escape of fluids.
• Heating assembly400 may include at least oneport422 for introducing a cooling medium to and at least oneport424 for removing a cooling medium fromheating assembly400.Port422 may comprise a radial hole incylindrical housing402 for introducing a cooling medium, for example, a gas, such as air, or a fluid, such as water, to the cavity415 betweenheating assembly400 andtube210.Port424 may be adapted to remove the medium introduced.Ports422 and424 may be equipped with appropriate fittings (not shown) to facilitate mounting conduits, such as, tubing, toports422 and424.
• According to aspects of the invention,heating assembly400 may be adapted to regulate heating oftube210 and its contents by means of individual heating zones, for example, at least two distinct heating zones. In the aspect of the invention shown inFIG. 18A,tube210 is heated by five (5) heating zones.Heating zone1 may be associated with the heating means mounted to sealingplate330, heating zone2 may be associated with theheating section410 infirst end404 ofhousing402, heating zone3 may be associated with themiddle heating section403 ofhousing402, heating zone4 may be associated with heating section405 ofsecond end406 ofhousing402, andheating zone5 may be associated with the heating means mounted to coverplate212. According to aspects of the invention, the temperature of these zones may be regulated to provide the desired treatment of the work piece introduced totube210, for example, to regulate the heating and/or cooling of a photovoltaic precursor to provide a solar cell with enhanced performance or reliability.
• The isolation oftreatment chamber200 may be effected by chamberisolation actuator assembly205 that is adapted to compress asealing plate330 against aninternal flange332 incylinder210 to isolate a volume ofcylinder210.Isolation actuator assembly205 includes at least, and typically two,cylinder actuator assemblies334, acommon mounting plate335, and acentral tube assembly336.Cylinder actuator assemblies334 may each include along stroke cylinder338 and ashort stroke cylinder340.Long stroke cylinder338 andshort stroke cylinder340 may be pneumatic or hydraulic; the fluid control lines are omitted fromFIGS. 18A and 19.Long stroke cylinders340 are mounted at a first end to mounting plate342 (seeFIG. 19), by means ofbracket344 and the second end, or working end, oflong stroke cylinder340 is mounted toshort stroke cylinder340, for example, by means of mechanical fasteners.Door342 may represent a portion of a housing into whichfurnace200 is mounted.Short stroke cylinder340 is mounted to mountingplate335 by means of mechanical fasteners.Cylinders338 and340 displaceplate335 androd346 and sealingplate330.Long stroke cylinders338 may be used for large displacements of sealingplate330, for example, during gross insertion or extraction.Short stroke cylinders340 may be used for fine displacement of sealingplate330, for example, during engagement or disengagement of sealingplate330 andinternal flange332.FIG. 19 illustrates an aspect of the invention in which long stokecylinders338 are extended. Mountingplate335, which may be displaced by one or morecylinder actuator assemblies334, is mounted to support rod ortube346.Support rod346 is mounted to sealingplate330 which is translated with the movement of mountingplate335.Support rod346 is positioned inside ofcentral tube assembly336. The displacement of sealingplate330 may also be practiced manually, for example, by means of a handle and camming mechanism. The configuration of the sealingplate330 mounted to asupport rod346,cylinders338, and ball bearings (not shown) enables a pressure gradient between thetreatment tube210 and the area disposed between214 and the back of the sealingplate330 to be about one atmosphere.
• Central tube assembly336 provides a housing that, among other things, isolates the inside oftube210 and supportsrod346.Central tube assembly336 includes aflanged nozzle348 mounted to plate342, a dual-flanged spool350, a dual flanged bellowsassembly352, and aseal plate354.Seal354 may provide a vacuum-tight sealing means between thebellows assembly352 and mountingplate335, for example, by means of one or more elastomeric o-rings355. According to one aspect of the invention,seal plate354 and o-rings355 are located at a distal location from the treatment zone intube210, that is, between sealingplate330 andcover plate212, whereby low-temperature sealing means may be used and the likelihood of thermal damage to the sealing means is minimized or prevented. This aspect of the invention further comprises an o-ring disposed betweendoor342 andplate214, which allows an additional low-temperature sealing means.Bellows assembly352 includesrods356 which retain thebellows assembly352 in the compressed state when thecylinders338 retractsupport rod346. The compression ofbellows assembly352 may be varied by means of abiasing device358, for example, a spring, a flexure, or a pneumatic cylinder.Central tube assembly336 may also include a bearing support forrod346, for example, a low-friction bearing or roller bearing (not shown) mounted withinspool350, for instance, centrally mounted withinspool350. The bearing support may supporttube346 during insertion, extraction, and operation offurnace200.
• As shown most clearly in the detail ofFIG. 18B, sealingplate330 is mounted to supportrod346 by means ofshort mounting rod358, for example, by means of welding ormechanical fastener360. As shown inFIG. 18B, sealingplate330 mates with internal annular surface orflange332 oftube210 to provide a seal fortreatment tube210. Due to the high temperatures under which treatment may be practiced, the mating surfaces of sealingplate330 andflange332 typically exhibit metal-to-metal contact with no additional sealing means there between. In one aspect, a sealing element may be provided, for example, an elasotomeric sealing element that can withstand the typical treatment temperatures expected. However, in another aspect of the invention, no elastomeric seals are needed.
• In one aspect of the invention, sealingplate330 may also include heating or cooling means and provide a surface upon which an element may be mounted and delivered totube210. For example, sealingplate330 may include an electric heating element or heating fluid coils362 similar todistal end211 oftube210. Also, sealingplate330 may includetube364 through which a working fluid can be passed. The outer surface oftube364 may provide a surface (similar tosurface151 of heat exchanger86) to which a treatment element, for example, Se, may be applied and subsequently volatilized for introducing an element-containing vapor totube210. Anelectrical conduit365 to heat the heating means or the coolingfluid tubing367 may be located withinsupport tube346. For example,support tube346 may includetube connections366 orelectrical connections368. The tubing or wiring may access the inside ofsupport tube346 through anaperture370 through plate335 (seeFIG. 19).
• According to aspects of the invention,tube furnace200 may be used to treat work pieces, for example, CIG precursors, in a fashion similar to the operation offurnace50.Tube furnace200 may first be “charged” with treatment element, for example, by introducing and heating the solid element, for example, Se, to volatilize the element, and then cooling to an internal surface offurnace200 to cause the vaporous element to condense. In one aspect, thecover plate212 at thedistal end211 oftube202 may be cooled by means of coolingtube324, which may extend insidetube210, whereby the element condenses on an external surface oftube324. As in other aspects of the invention, after charging, the work piece to be treated may be introduced tofurnace200, thefurnace200 may be closed by activatingisolation actuator assembly205 wherebyplate230 engagesflange232 to isolatetube210. The work piece to be treated and the treatment element may then be heated, for example, according to the schedule shown inFIG. 2, to treat the work piece and minimize the loss of treatment element.
• According to aspects of the present invention, work piece may be treated infurnaces50 and200 by means of the following procedures. According to aspects of the present invention, the temperatures of multiple elements offurnaces50 and200 are controlled to optimize the treatment. For example, as shown inFIG. 18A, the temperature of the sealingplate330,end plate212,tube210 may be independently controlled. With respect tofurnace200, shown inFIG. 3, the temperature of thetubes82 and the housing walls (for example,walls53 and57) may be independently controlled. The following process may be practiced for bothfurnace50 andfurnace200, but the following discussion referencesfurnace50 only to facilitate the disclosure of the invention.
• With reference toFIG. 9,furnace50 is first opened and one or more treatment elements, for example, Se, is introduced to the furnace. As noted above, it is to be understood that the expression “treatment element” is used herein to facilitate the disclosure of the invention. The treatment element may comprise a treatment compound comprising two or more elements. According to aspects of the invention, the element comprises elemental sulfur or selenium or combinations of sulfur, selenium, tellurium, indium, gallium, or sodium. The introduction of the treatment element may be practiced by means of the “charging” process described below. In the following discussion, it is assumed thatfurnace50 has been charged with Se on thesurface151 ofheat exchanger86 shown inFIG. 15.
• The work piece to be treated with, for example, Se-containing vapor, is then introduced to thetreatment tubes82, for example, through open door assembly52 (SeeFIG. 9.). One or more work pieces may be introduced totreatment tube82 on a sheet or tray to facilitate handling of the work pieces. The work piece introduced totubes82 may comprise any material, but in one aspect, the work piece comprises a photovoltaic cell precursor deposited on a substrate, such as the precursor on substrate shown inFIG. 16A. The substrate may be a metallic or non-metallic substrate, such as, a glass, a steel, a stainless steel, titanium, a ceramic, or a metal-coated plastic, such as a molybdenum-coated polyimide, among other substrate materials. In one aspect of the invention, where hydrogen may be present during treatment, stainless steel substrates are avoided due to stainless steel's susceptibility to hydrogen embrittlement that may cause instability in the resulting photovoltaic cell. The substrate may be provided as a thin substrate having a thickness of between about 5 microns and about 1 mm, for example, as a metallic foil. In the following discussion, reference will be made to workpiece90, but it will be understood that in aspects of the invention any material may correspond to workpiece90.
• In aspects of the invention, the photovoltaic cell precursor may be any precursor material that can be treated with a vaporous element or compound. In one aspect of the invention, the precursor comprises a precursor containing one or more elements from group 11 (that is, the “coinage metals”),group 12, group 13, and group 16 (that is, the “chalcogens”) of the Periodic Table (group numbering based upon IUPAC convention; the corresponding groups in the “old” convention being1B,2B,3A, and6A, respectively). For example, in one aspect, the precursor may contain one or more of copper (Cu), indium (In), gallium (Ga), selenium (Se), sulfur (S), or sodium (Na), or combinations thereof. The precursor may be a Cu—In—Ga containing material, that is, a “CIG” material; a Cu—In—Ga—Se-containing material; or a Cu—In—Ga—Se—S-containing material.
• After introducingwork piece90 to be treated intotubes82, thefront door assembly52 is closed and thefurnace50 is evacuated, for example, by applying a vacuum to one or more of the access ports, for instance a vacuum of, typically, about 10⁻³Torr gage. Thefurnace50 may then be purged with a gas, for example, a dry gas, for instance, a dry inert gas, to remove as much moisture as possible. Heat may so applied to remove moisture. The inert gas may be, for example, nitrogen, argon, or helium.
• According to one aspect of the invention, thetreatment tubes82 may be filled with a treatment gas, for example, a gas that may assist in the subsequent reaction or treatment. The treatment gas may be a forming gas, such as, hydrogen, nitrogen, or combinations thereof. A treatment gas that may also be introduced totubes82 may include oxygen, hydrogen selenide (H₂Se), hydrogen sulfide (H₂S), or an inert gas, such as argon or helium, among other treatment gases that may be used. For example, a sulfur-containing gas, such as H₂S, may be introduced totubes82 whereby the H₂S is present during the release of Se to effect a S—Se treatment, for example, to produce CIGSS. In one aspect, no forming gas may be used. The forming gas may also include hydrogen-containing gas other than H₂Se or H₂S, for example, water (H₂O) vapor, ammonia (N₂H₃), an alcohol, or a ketone. In one aspect, the hydrogen-containing gas may provide for the in-situ formation of H₂Se during treatment with a Se-containing gas. Trace amounts of hydrogen, for example, in the work piece or in the chamber, for example, provided by moisture (H₂O) in the chamber, may produce trace amounts of H₂Se formed in situ that, for example, may react with the work piece. In one aspect of the invention, little or no hydrogen is introduced to the treatment chamber. For example, only non-hydrogen-containing gases or no forming gases at all are introduced prior to or during treatment. The gas may be introduced through one or more of the ports distributed aboutfurnace50. A vacuum may also be present intubes82. After introducing the gas tofurnace50,treatment tubes82 may be closed, for example, by activatingvalve actuation assembly68 whereby sealingassembly84 engages the openings oftubes82, for example, to maintain the gas and/or vacuum withintubes82. After isolation oftubes82 by sealingassembly84, the volume between thetubes82 and the walls offurnace50 may be purged by an inert gas or vacuum to, for example, remove any excess gases or moisture.
• According to aspects of the invention, upon isolation oftubes82, the heating of thework piece90 can commence. Again, the heating ofwork piece90 may be practiced according to the heating schedule shown bycurve32 inFIG. 2 or another similar heating schedule. The heating ofwork piece90 may be practiced by energizingheating elements88. The temperature ofwork piece90 may be monitored by one or more temperature sensing devices mounted infurnace50, for example, thermocouples, resistive thermal devices (RTDs), infrared thermocouples, or a non-contact pyrometer. According to aspects of the invention, the temperature ofwork piece90 is elevated to a temperature, for example, above 500 degrees C., at which the vaporous element will react withwork piece90.
• As shown, for example, inFIG. 2, before, at about the same time, or shortly after theheating work piece90 percurve32, the temperature of the treatment element, for example, the selenium charged toheat exchanger86, is raised, for example, according tocurve34 inFIG. 2. As discussed above, the temperature of the treatment element may be regulated by controlling the energizing oflamp158 inheat exchanger86 and/or controlling the flow and/or temperature of working fluid, for example, air, throughheat exchanger86. For example, the lower the flow of coolant throughheat exchanger86, the hotter the element applied to the surface of theheat exchanger86. The temperature of the element is raised to a temperature at which the element volatilizes to form an element-containing vapor, for example, for Se, at least about 100 degrees C. However, as discussed above with respect toFIG. 2, for example, the temperature may be increased to accelerate the release of element-containing vapor. For example, Se may be elevated to temperature of 500 degrees C. or more to release sufficient Se-containing vapor to provide sufficient reaction withwork piece90. Again, according to aspects of the present invention, the temperature of the treatment element may be controlled independently of the control of the temperature ofwork piece90.
• After treatment at temperature, the treatment element and thework piece90 may be cooled to complete the treatment, cooled prior to further treatment, or cooled for further handling. In one aspect, the temperature of the element is cooled to encourage the condensation of the vaporous element back on the element. This preferred cooling may be effected by rapidly cooling the element, for example, as shown bycurve34 inFIG. 2 and/or maintaining thework piece90 and other surfaces insidefurnace50 at an elevated temperature, for example, above 170 degrees C., to discourage condensation onwork piece90 or on other surfaces withinfurnace50. The element can be cooled by de-energizing or reducing the power onlamp158 inheat exchanger86 and/or increasing the flow of coolant throughheat exchanger86. The cooling ofwork piece90 may be effected by de-energizinglamps88. Typically,work piece90 is cooled in a controlled fashion to prevent damage to workpiece90, for example, to prevent cracking or delaminating from the substrate or damage to the substrate itself. In one aspect,furnace50 and its contents, for example,work pieces90, may be rapidly cooled, for example, by forced air convective cooling. A cooling fluid my be introduced to one or more ports offurnace50, for example, toflanged port130 and vented throughflanged port140, to rapidlycool furnace50 and its contents. The cooling fluid, for example, air, may be propelled by an air mover, such as a fan or blower, and the fluid may be passed through a cooling device, for example, a cooling heat exchanger or chiller.
• In one aspect of the invention, the treatment or delivery ofwork piece90, for example, the selenization ofwork piece90, may comprise a steady-state treatment, a pulsed treatment, a cyclic treatment, a ramped treatment, a dual-source treatment, or a combination thereof. The treatment ofwork piece90 with the element-containing vapor may be practiced with an excess amount of element-containing vapor, that is, an amount greater than the stoichiometric amount typically required. In steady-state treatment, the temperature ofwork piece90 and the treatment element are elevated to treatment temperature, for example, above 400 degrees C., and maintained at the treatment temperature for the duration of treatment. In pulsed treatment, the temperature ofwork piece90 is maintained at treatment temperature and the temperature of the treatment element is varied, for example, varied rapidly during treatment. In cyclic treatment, the temperature ofwork piece90 is maintained at treatment temperature and the temperature of the treatment element is cyclically varied through, for example, a predetermined temperature cycle. In ramped treatment, the temperature ofwork piece90 is maintained at treatment temperature and the temperature of the treatment element is ramped, for example, ramped slowly to a desired temperature during treatment. In dual source treatment or delivery, a gas containing two or more elements, for example, Se and S, may be exposed towork piece90 at substantially the same time.
• Dual treatment may also comprise treatment ofwork piece90 with two or more vaporous elements or compounds provided by two or more heat exchangers (for example, condensers/evaporators). For example, two or more heat exchanges may be operated at different temperatures depending upon the volatilization temperature of the element or compound being delivered. In one aspect, two or more elements or compounds may be delivered by one heat exchanger, such asheat exchanger86 shown inFIG. 15, for example, by depositing two or more elements or compounds on thesurface151 ofheat exchanger86. The two or more elements or compounds deposited on the surface of a heat exchanger may typically have different volatilization temperatures, whereby species delivery may be varied by temperature. In another aspect, two or more elements or compounds may be delivered by two or more heat exchangers, such asheat exchanger86 shown inFIG. 15. These two or more heat exchangers adapted to deliver two or more elements or compounds to a treatment chamber may include isolation devices that limit or prevent the release of one or more vaporous elements or compounds while one or more of other vaporous elements or compounds are being released to the treatment chamber. These isolation devices may comprise seal plate or “flapper valve” type devices, for example, devices similar to the devices shown inFIGS. 11 and 12. The sequence of treatment with the two or more vaporous elements or compounds may be varied depending upon the desired treatment, for example, the delivery of the two or more vaporous elements may be provided individually or substantially simultaneously. Treatment may also be practiced repeatedly or alternated from one vaporous element to another vaporous element. In one aspect, care may be taken to avoid or prevent the condensation of one vaporous element upon another vaporous element, for example, an element having a higher condensation temperature. Again, undesirable condensation on treatment elements or compounds may be avoided by use of suitable isolation means, such as the sealing devices discussed above.
• In one aspect of the invention, dual treatment may be practiced for staged release of treatment vapors. For example, one or more heat exchangers may be used having Se and In and/or Ga compounds deposited on their outer surface. The precursor, for example, a Cu—In—Ga precursor, may first be treated with Se by raising the one or more heat exchangers to a first temperature at which Se volatilizes, but In and/or Ga compounds do not. After treatment with Se, the temperature of the one or more heat exchangers may be raised to volatilize, for example the In compound. The In compound vapor may then treat the precursor or the In compound vapor may react with the Se vapor present in the chamber to form indium selenide in situ, where the precursor may then be treated with the indium selenide vapor. A similar staged treatment may be practiced for Ga compounds, where gallium selenide may be formed in situ. Sulfur and In and/or Ga compounds may also be handled in a similar fashion to provide dual treatment with S and In and/or Ga compounds. In one aspect, this dual treatment may be an effective alternative for treating copper-rich precursors to provide effective photovoltaic materials that could not be formed otherwise. Copper-rich precursors are known to have inferior performance due to the electrical shorting effect of the excess copper compounds, for example, copper selenide. Dual treatment of copper-rich precursors according to aspects of the invention, can improve the performance of the resulting absorber.
• The treatment ofwork piece90 with the vaporous element may be practiced repeatedly, for example, three or more times, to provide the desired treatment. Upon completion of the treatment, sealingassembly84 can be disengaged fromtreatment tubes82 and the furnace purged or vented. The vented gases are typically processed to prevent release of gases to the environment.
• FIG. 24 is a schematic block diagram26 of a process for charging the treatment element to the enclosure according to one aspect of the invention. In one aspect of the invention, the “charging” of the element to the treatment chamber comprises the process of introducing the treatment element to the treatment enclosure whereby the treatment element can be subsequently released in a vaporous form to react with the work piece being treated. As shown inFIG. 24, the process of charging26 the enclosure with the treatment element may be initiated by introducing a solid treatment element to anenclosure40. For example, the treatment element may be introduced as a powder, as beads, or as an ingot. The treatment element may be introduced to the enclosure by simply placing the solid element on the bottom of the enclosure, placing a container (for example, a “boat”) containing the element into the enclosure, or placing the element on an appropriate support means, for example, a shelf or cavity, located in the enclosure. The element may also be automatically fed into the furnace, for example, by means of an automated feeder, for example, an automated wire-element feeder. As noted above, it is to be understood that the expression “treatment element” is used herein to facilitate the disclosure of the invention. The treatment element may comprise a treatment compound comprising two or more elements. According to aspects of the invention, the solid element or compound introduced to the treatment chamber may be an element ofgroup 11, 12, 13, or 16 of the Periodic Table, for example, selenium, sulfur, indium, gallium, indium selenide, indium sulfide, gallium selenide, gallium sulfide, or combinations thereof. The element or compound may also include sodium or a sodium-containing compound.
• Next, the enclosure is closed, sealed, or otherwise isolated41 to minimize or prevent the leakage of vaporous element from the enclosure. In one aspect, after isolating theenclosure41, the enclosure may be evacuated, for example, by applying a vacuum to the enclosure. In one aspect, a typical vacuum of 10⁻³Torr gage may be applied to the enclosure. The vacuum may be maintained during the charging process. When the enclosure includes an internal treatment chamber, for example, thetube82 shown inFIG. 16A,process26 may include theoptional step47 of isolating the internal treatment chamber. This isolation of the internal chamber may be practiced using a chamber isolation assembly, such as sealingassembly84 shown inFIGS. 11 and 12, for example, where a “flapper” valve isolates the internal chamber.
• As shown inFIG. 24, according toprocess26, the treating element is then heated42 to a temperature above which the element will volatilize at the prevailing pressure; for example, when the treatment element is Se, the Se is heated to a temperature of between about 100 and about 400 degrees C. The heating ofstep42 may, for example, be effected byinfrared lamps88 shown inFIG. 10,heating assembly400 shown inFIG. 18A, orheating coils320 shown inFIG. 18A. At this temperature, the Se begins to volatilize to create a selenium-containing gas into the enclosure. However, to increase the volatilization, the temperature of the element may typically be increased to a temperature greater than the initial volatilization temperature to ensure a plentiful supply of the vaporous element. For example, when Se is used, the Se is typically heated to at least about 500 degrees C. to ensure an adequate supply of Se in vaporous form.
• Prior to, during, or after the heating thetreatment element42, at least one surface inside the enclosure is cooled43 to provide a temperature less than the temperature at which the element volatilizes. For example, again, for Se, this temperature may typically be a temperature less than 100 degrees C., for example, a temperature of about 80 degrees C. or lower. In one aspect, the cooling is practiced to maintain the surface at a temperature below the vapor pressure temperature of the element, for example, Se or S. The cooling of a surface inside the enclosure is typically provided by some form of heat exchanger having a working fluid passing through it. One typical heat exchanger that may be used for aspects of this invention isheat exchanger86 shown in and described with respect toFIGS. 15-17. According to aspects of the invention shown inFIG. 24, the cooled surface of the heat exchanger provides a condensation site for thecondensation44 of the vaporous element provided byheating42. Theheating42, cooling43, and condensing44 steps of the chargingprocess26 may be practiced repeatedly (for example, three or more times) or for an extended period of time (for example, at least about 20 minutes) to provide the desired content of treatment element on a surface inside the enclosure.
• After sufficient element has been condensed upon the surface, the surface and solid element may be cooled45 (assuming that the solid element has not completely volatilized) to terminate the volatilization. In one aspect, the cooling of the surface and the treatment element is practiced rapidly, for example, at rate of at least about 10° C./min, to allow at least some of the vaporous element released instep42 to condense onto the solid element and/or surface. This recapture of the treatment element through controlled or rapid cooling of the solid element and/or surface minimizes the loss of the element to condensation on other surfaces of the enclosure and related structures. In one aspect, during cooling of the element for recapture, the temperature of the surfaces of the enclosure and of any surfaces within the enclosure may be maintained at an elevated temperature, for example, a temperature above 170 degrees C. for Se, to discourage condensation on surfaces other than the cooled surface or solid element. When cooling of theelement45 is completed, the element may be removed from theenclosure46. When an internal chamber is used,process26 may also include the step of opening the internal chamber, for example, disengaging the sealingassembly84 shown inFIGS. 11 and 12. The enclosure, and any internal treatment chambers, may be vented, for example, in preparation for subsequent treatment in the enclosure. With completion of the chargingprocess26, with treatment element provided on a surface within the enclosure, the treatment of a work piece as shown and described with respect toFIGS. 1 and 2 may commence.
• FIG. 25 is aplot300 of treatment element vapor pressure as a function of temperature for selenium, though a similar curve may be provided for other treatment elements.FIG. 26 is aplot310 of heat exchanger (for example, condenser/evaporator) temperature as a function of coolant flow according to one aspect of the invention. The curves shown inFIG. 26 were determined for one specific heat exchanger, for example, the tube type device shown inFIGS. 18A through 23. Similar curves may be provided for other heat exchangers relating coolant flow to temperature. The curves for other heat exchangers may vary depending upon the size of the heat exchanger, the type of coolant used, and the thermal characteristics of the material from which the heat exchanger is made, among other things. According to one aspect of the invention, the curves shown inFIGS. 25 and 26 may be used in conjunction with the curves shown inFIG. 2 to control the operation of a treatment furnace, for example, to control the operation offurnace50 shown inFIGS. 3-9 orfurnace200 shown inFIGS. 18-23.
• As shown inFIG. 25, thecurve302 inplot300 represents the relationship of the vapor pressure of selenium, in Torr, as shown in the log scale onordinate304 inFIG. 26, and temperature, in degrees C, shown on abscissa303. Clearly, the vapor pressure of selenium increases with temperature. Plot310 inFIG. 26 displays threecurves312,314, and316 that correspond to the relationship of the heat exchanger temperature (for example, evaporator/condenser), in degrees C, as shown onordinate318 for three furnace temperatures as a function of coolant flow, in standard cubic feet per minute (SCFM), shown on theabscissa320. In the aspect of the invention shown inFIG. 26, curves312,314, and315 correspond to representative furnace temperatures of 300 degrees C., 400 degrees C., and 500 degrees C., respectively. Again, the shape and magnitude ofcurves312,314, and318 may vary for other heat exchangers or other furnace operating temperatures.
• According to aspects of the present invention, the curves that appear inFIGS. 2, 25, and26 may be used to control the operation of a treatment furnace as follows.FIG. 2 provides one desired temperature schedule for treating a work piece, for example, a photovoltaic precursor, with a vaporous element, for example, vaporous selenium or sulfur. As discussed above, to ensure an adequate supply of vaporous element, for example, Se, to obtain the desired reaction with the work piece, for example, the precursor, the temperature of the element is increased to provide a desired partial pressure of element vapor in the treatment chamber. The desired partial pressure for one aspect of the invention is shown bycurve35 inFIG. 2. In order to obtain this element partial pressure, the temperature of the element must be regulated according to the temperature-pressure curve302 shown inFIG. 25. The temperature determined bycurve302 is then used to regulate the flow of coolant through the heat exchanger as indicated bycurves312,314, and316 inFIG. 26. The flow of coolant, for example, air, to the heat exchanger is then regulated, for example, by a control valve, to obtain the desired coolant flow. In another aspect of the invention, the temperature of the coolant, for example, air, may be varied to effect the desired element temperature. For example, the temperature of the coolant may be regulated by varying the temperature of a heat exchanger adapted to heat or cool the working fluid, for example, an external heat exchanger having a working fluid passing through it.
• For example, assuming that fromcurve35 inFIG. 2, the desired partial pressure for treating a precursor with Se at a temperature T_E3is about 1.0 Torr. FromFIG. 25,curve302, and pressure 1.0 Torr onordinate304, the desired heat exchanger temperature is about 350 degrees C. By comparing a desired heat exchanger temperature of 350 degrees C. withcurve316 inFIG. 26, a desired heat exchanger flow rate of, for example, about 14 standard cubic feet per hour (SCFH) is obtained. Therefore, to obtain the desired temperature T_E3, the flow of coolant, for example, air, through the heat exchanger is regulated to about 14 SCFH. The flow of coolant, for example, air, through a heat exchanger according to aspects of the invention may vary from about 10 SCFH to about 25 SCFM, and is typically between about 0.1 SCFM and 3 SCFM.
• This control of the operation of the coolant flow to regulate the heat exchanger may be practiced manually, but is preferably, practiced in an automated fashion, for example, by means of computer, programmable logic controller (PLC), temperature feedback loop, PID controller, or another automated controller. For example, in one aspect, the curves illustrated inFIGS. 2, 25, and26, may be programmed into a computer or PLC and operated to control the operation of, for example, an automated valve controller of a coolant flow valve.
• The methods and apparatus according to aspects of the invention described above may be used to manufacture an improved photovoltaic material, for example, a material having little or no hydrogen content. Such a material has the advantage of not being prone to the deterioration in performance that characterizes prior art materials having hydrogen. For example, as discussed above, in one aspect of the invention, a precursor may be treated with a treatment gas, such as a selenium-containing vapor, with little or no presence of hydrogen. In prior art methods, selenium is typically introduced in the form of H₂Se whereby hydrogen (H) inherently is introduced to the reaction and to the absorber matrix. According to aspects of the invention, the treatment chamber can be effectively purged of essentially all hydrogen by means of vacuum and/or non-hydrogen purge gas. As a result, the precursor, for example, the CIG precursor, can be treated with a Se— or S-containing vapor (that is, a H-free vapor) to produce an essentially H-free absorber. In one aspect of the invention, the absorber comprises a CIGS absorber having less then 5% hydrogen content, or typically less than 1% hydrogen content, or can be substantially hydrogen free. Such a low-hydrogen or hydrogen free absorber, for example, a low-H or H-free CIGS or CIGSS absorber, can provide more reliable performance without the degradation that characterizes hydrogen-containing absorbers.
• The control and operation offurnaces50 and200 may be performed manually or by means of one or more automated controllers, for example, a personal computer or PLC. These control devices may include specially designed software designed to monitor and control the operation offurnaces50 and200.Furnaces50 and200 may typically include sensors, for example, temperature sensors, pressure sensors, and flow sensors, and controllers, for example, automatic temperature, pressure, or flow controllers to regulate and control the operation offurnaces50 and200. The electrical connections associated with these sensors and controllers may pass through one or more of the many access ports associated withfurnaces50 and200.
• In one aspect of the invention, the methods and apparatuses disclosed herein may be practiced or utilized in a batch mode, for example, one or more work pieces may be treated infurnaces50 or200 and the work pieces removed for subsequent treatment of further work pieces. However, according to another aspect of the invention, the methods and apparatuses disclosed herein may be adapted for continuous treatment whereby a substantially continuous flow of work pieces may be processed according to the disclosed methods or handled by, for example, introduced and removed from, the disclosed apparatus. In one aspect, unlike the temperature variations shownFIG. 2, the treatment conditions of the continuous methods may be substantially stable as work pieces are introduced and removed from the treatment chambers.
• Aspects of the present invention provide improved means of treating work pieces, especially, improved means of treating and producing photovoltaic cells. Methods and apparatus according to aspects of the present invention can assist in reducing the production costs of photovoltaic cells whereby photovoltaic energy can be a cost effective alternative to the diminishing supply of fossil fuels.
• While several aspects of the present invention have been described and depicted herein, alternative aspects may be conceived by those skilled in the art to accomplish the same objectives. Accordingly, it is intended by the appended claims to cover all such alternative aspects that fall within the true spirit and scope of the invention.

Claims (22)

1-63. (canceled)

64. A photovoltaic cell comprising:

a substrate; and

an absorber deposited on to the substrate, the absorber comprising elements from each of group 11, group 12, and group 13 of the Periodic Table, and less than5% hydrogen.

65. The photovoltaic cell as recited inclaim 64, wherein the absorber comprises less than 1% hydrogen.

66. The photovoltaic cell as recited inclaim 65, wherein the absorber comprises substantially no hydrogen.

67. The photovoltaic cell as recited inclaim 64, wherein the absorber further comprises at least one of selenium and sulfur.

68. The photovoltaic cell as recited inclaim 64, wherein the substrate comprises a metallic substrate.

69. The photovoltaic cell as recited inclaim 64, wherein the substrate comprises at least one of steel, stainless steel, titanium, and glass.

70. The photovoltaic cell as recited inclaim 64, wherein the cell further comprises an electrical conductor mounted to the absorber.

71-74. (canceled)

75. The photovoltaic cell as recited inclaim 64, wherein the absorber comprises copper, indium, and gallium.

76. The photovoltaic cell as recited inclaim 64, wherein the substrate comprises a metallic foil.

77. The photovoltaic cell as recited inclaim 76, wherein the metallic foil has a thickness between about5 microns and about 1 mm.

78. The photovoltaic cell as recited inclaim 64, wherein the photovoltaic cell is more reliable than a photovoltaic cell containing more than about 5% hydrogen.

79. A method of fabricating a low-hydrogen containing photovoltaic cell from the substrate and absorber recited in claim1, the method comprising:

introducing the substrate and the absorber to an enclosure;

introducing an element-containing material having little or no hydrogen content to the enclosure;

heating the substrate and the absorber to a first temperature;

independent of the heating of the substrate and the absorber, heating the element-containing material to a temperature sufficient to volatilize the element and release an element-containing vapor into the enclosure;

treating the absorber with at least some of the element-containing vapor; and

cooling the substrate and the absorber to provide a low-hydrogen containing photovoltaic cell.

80. The method as recited inclaim 79, wherein the method further comprises introducing a substantially hydrogen-free treatment gas to the enclosure to provide a substantially hydrogen-free reaction atmosphere.

81. The method as recited inclaim 80, wherein the substantially hydrogen-free gas comprises at least one of oxygen, argon, helium, selenium vapor and sulfur vapor.

82. The method as recited inclaim 79, wherein the method further comprises vacuum purging the enclosure.

83. The method as recited inclaim 79, wherein the method further comprises, after reacting, regulating the temperature of the element-containing material at a temperature sufficient to condense at least some of the element from the element-containing vapor on the element-containing material.

84. The method as recited inclaim 79, wherein the element-containing material comprises one of sulfur, selenium, tellurium, indium, gallium, sodium, and combinations thereof.

85. The method as recited inclaim 79, wherein treating the absorber with at least some of the element-containing vapor comprises one of reacting the element-containing vapor with the absorber and providing an overpressure of the element-containing vapor to the absorber.

86. The method as recited inclaim 79, wherein cooling the element-containing material comprises cooling the element-containing material wherein substantially all of the unreacted element-containing vapor condenses on the element-containing material.

87. The method as recited inclaim 79, wherein the method further comprises mounting an electrical conductor to the absorber.

Images