Patent Publication Number: US-2012045533-A1

Title: Thin film buffer layer solution deposition assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application Ser. No. 61/333,241 filed May 10, 2010. All applications are fully incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to deposition systems, and more specifically, solution deposition systems for use in forming photovoltaic devices. 
     BACKGROUND OF THE INVENTION 
     Solar cells and solar modules convert sunlight into electricity. These electronic devices have been traditionally fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have been developed that can inexpensively make use of thin-film, light-absorbing semiconductor materials such as copper-indium-gallium-di-(sulfo-selenide, Cu(In, Ga)(S, Se) 2 , also termed CI(G)S(S). This class of solar cells typically has a p-type absorber layer sandwiched between a back electrode layer and an n-type junction partner layer. The back electrode layer is often Mo, while the junction partner is often CdS. A transparent conductive oxide (TCO) such as zinc oxide (ZnO x ) typically doped with aluminum is formed on the junction partner layer and is typically used as a transparent electrode. CIS-based solar cells have been demonstrated to have power conversion efficiencies exceeding 19%. 
     High throughput production methods are in development to manufacture this type of thin-film photovoltaic device. As improvements are made for high throughput production of the absorber layer in such thin-film devices, similar advances need to be made with regards the deposition or formation of the junction partner layer to prevent bottlenecking of the production process. 
     It should be understood, however, that the materials used for forming the junction partner can contain toxic material and difficulties are encountered in improving the manufacturing system. One process for forming the junction partner involves using Group II-VI compounds such as CdS. The CdS used in the formation process may create hazardous waste by-products, thus increasing processing costs. Known processes are also inefficient or unreliable in creating a system with high throughput and high yield. Some known systems either use too much starting material, much of which is wasted during production. Others use systems that may be susceptible to imperfections in the underlying substrate that may cause non-uniform deposition of the junction partner material over a wide web. Therefore, a need exists in the art for an improved junction partner deposition system. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention address at least some of the drawbacks set forth above. The present invention provides for the improved deposition system for group IIB-VIA materials. Although not limited to the following, these improved module designs are well suited for roll-to-roll, in-line processing equipment. It should be understood that at least some embodiments of the present invention may be applicable to any type of solar cell, whether they are rigid or flexible in nature or the type of material used in the absorber layer. Embodiments of the present invention may be adaptable for roll-to-roll and/or batch manufacturing processes. At least some of these and other objectives described herein will be met by various embodiments of the present invention. 
     In one embodiment of the present invention, a deposition system is provided for use with a solution and a substrate. The system comprises of a solution deposition apparatus; at least one heating chamber; at least one assembly for holding a solution over the substrate; and a substrate curling apparatus for curling at least one edge of the substrate to define a zone capable of containing a volume of the solution over the substrate. Although the term substrate is used, it should be understood that the substrate may have materials formed in it already at the time it is processed by embodiments of the current invention. Thus, the present embodiment may be depositing a buffer layer material from a solution to an exposed surface of a solar cell absorber layer of a workpiece or substrate for manufacturing of solar cells. In one embodiment, the curling apparatus is heated to assist in curving the foil. 
     In another embodiment of the present invention, a deposition system for use with a substrate, the system comprising a solution deposition apparatus; at heating chamber; and at least assembly for holding solution over the substrate to allow for a depth of at least about 0.5 microns to 10 mm. In one embodiment, the substrate comprises a magnetic component and a non-magnetic component. 
     In yet another embodiment of the present invention, a deposition system is provided for use with a solution and a substrate. The system comprises of a solution deposition apparatus; at least one heating chamber; at least one assembly for holding a solution over the substrate; and a substrate curling apparatus for curling at least one edge of the substrate to define a zone capable of containing a volume of the solution over the substrate. 
     It should be understood that any of the embodiments herein may be adapted to have one or more of the following features. In one embodiment, the assembly curls at least two edges of the substrate. Optionally, the assembly for holding solution over the substrate to allow for a depth of at least about 0.5 microns to about 10 mm. Optionally, the assembly for holding solution over the substrate to allow for a depth of at least about 1 mm to about 5 mm. Optionally, the curling apparatus curls opposing edges of the substrate. Optionally, the curling apparatus is configured to transition a planar substrate to a substrate with curls along two edges, wherein the transition occurs over a distance sufficient prevent permanent deformation of the substrate when the substrate is uncurled. Optionally, the curling apparatus is configured to transition a planar substrate to a substrate with curls along two edges over a distance of at least 4 inches. Optionally, the curling apparatus is configured to transition a planar substrate to a substrate with curls along two edges over a distance of at least 6 inches. Optionally, the curling apparatus creates curls of sufficient height to contain the volume of solution therein without allowing the solution to spill over an upper of the curl. Optionally, the assembly for holding solution further comprises of an uncurling apparatus for uncurling at least two edges of the substrate to return the substrate to a substantially planar configuration. Optionally, the curling apparatus comprise of a web guide. Optionally, the curling apparatus comprise of a shaped web guide. Optionally, the solution deposition apparatus comprises of a spray deposition system to deposit the solution over the substrate. Optionally, the solution deposition apparatus comprises of an ultrasonic spray deposition system to deposit the solution over the substrate. Optionally, the substrate comprises of a flexible material. Optionally, the substrate comprises of a metal foil. Optionally, the solution comprises a precursor for forming a junction partner for a group IB-IIIA-VIA absorber layer. Optionally, the solution comprises a precursor for forming a Group IIB-VIA junction partner. Optionally, the solution comprises a precursor for forming a junction partner selected from the group consisting of: cadmium sulfide (CdS), zinc sulfide (ZnS), zinc hydroxide, zinc selenide (ZnSe). Optionally, the solution comprises of a Group JIB ionic species is obtained from an aqueous solution of one or more of the following: sulfate, acetate, bromide, fluoride, chloride, iodide, hydroxide, nitrate, oxalate, citrate, phosphate, tungstate, or hydrates of the Group IIB species. Optionally, the solution comprises of a Group VIA ionic species is obtained from an aqueous solution of one or more of the following: oxides, halides, sulfates, nitrates, or ureates of the Group VIA species. Optionally, the solution has a pH of from about 9 to about 14. Optionally, the solution has a pH of from about 11 to about 12. Optionally, the solution has a pH of from about 12 to about 13. Optionally, the solution has a pH of from about 11 to about 13. Optionally, the assembly for holding solution is at least partially contained in the heating chamber. 
     In one embodiment of the present invention, a method is provided for depositing a buffer layer material from a solution to an exposed surface of a solar cell absorber layer disposed on a continuous flexible workpiece for manufacturing solar cells as the continuous flexible workpiece is advanced through a roll-to-roll system, comprising: advancing a section of the continuous flexible workpiece from a supply roll and having a flat shape onto a heated plate including a cavity area, wherein the cavity area of the heated plate is configured to elastically alter the section of the continuous flexible workpiece into a curved shape that conforms to the cavity area of the continuous flexible workpiece; flowing a supply solution over an exposed surface of the solar cell absorber layer of the curved-shape section of the continuous flexible workpiece, wherein the supply solution is maintained at a first temperature before flowing into the section of the continuous flexible workpiece that conforms to the cavity area of the heated plate with the curved shape and wherein the supply solution includes all the chemical components of the buffer layer material; heating, to a second temperature which is higher than the first temperature, the continuous flexible workpiece and the solar cell absorber layer using the heated plate when the section of the continuous flexible workpiece is within the cavity area and conforming to the cavity area with the curved shape, wherein the heating of the continuous flexible workpiece and the absorber layer cause the transfer of heat from the solar cell absorber layer to at least a portion of the solution that is in contact with the exposed surface of the solar cell absorber layer and to cause depositing of the buffer layer material within the solution onto the exposed surface of the solar cell absorber layer; and moving the section of the continuous flexible workpiece away from the cavity areas of the heated plate so that the section of the continuous flexible workpiece flattens. 
     A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a photovoltaic device according to one embodiment of the present invention. 
         FIG. 2  shows a processing system according to one embodiment of the present invention. 
         FIG. 3  shows a processing system according to another embodiment of the present invention. 
         FIG. 4  shows top down view of a processing system according to another embodiment of the present invention. 
         FIG. 5  shows cross-sectional view of a processing system according to one embodiment of the present invention. 
         FIG. 6  shows a processing system according to another embodiment of the present invention. 
         FIG. 7  shows a processing system according to another embodiment of the present invention. 
         FIG. 8  shows a cross-sectional view showing deposition of material embodiment of the present invention. 
         FIG. 9  shows a cross-sectional view of one embodiment of a processing system configured to curl one or more edges of a substrate. 
         FIG. 10 through 11B  show various mechanisms for use for curling one or more edges of a substrate. 
         FIGS. 12A-12C  show various configurations for a substrate with upwardly shaped edges. 
         FIGS. 13 and 14  are top down views of a processing system showing locations of the substrate shaping assemblies according to embodiments of the present invention. 
         FIGS. 15 through 19  are side views of processing systems according to various embodiments of the present invention. 
         FIG. 20  shows a top down view of one portion of a substrate according to the present invention. 
         FIGS. 21 and 22  show a cross-web view of the substrate according to embodiments of the present invention. 
         FIGS. 23A and 23B  show a cross-web view of the substrate according to embodiments of the present invention. 
         FIGS. 24 through 28  show various methods for edge sealing against the lateral edges of the substrate according to embodiments of the present invention. 
         FIGS. 29 and 30  show embodiments of the present invention with stirring mechanisms along the substrate path. 
         FIG. 31  shows one embodiment of a vacuum belt suitable for use with an embodiment of the present invention. 
         FIGS. 32A-32C  show various embodiment of a vacuum guide, bed, or belt according to embodiments of the present invention. 
         FIG. 33  shows a web path through one embodiment of processing system according to the present invention. 
         FIGS. 34 to 39  show top down schematics of various processing systems according to embodiments of the present invention. 
         FIGS. 41 to 44  show down-web cross-sectional views of portions of the curved substrate with various devices for sealing the atmosphere over the fluid on the substrate according to embodiments of the present invention. 
         FIGS. 45 to 47  show side schematic views of various processing systems according to embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. It may be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a material” may include mixtures of materials, reference to “a compound” may include multiple compounds, and the like. References cited herein are hereby incorporated by reference in their entirety, except to the extent that they conflict with teachings explicitly set forth in this specification. 
     In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings: 
     “Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, if a roller optionally contains a feature for a thermally conductive film, this means that the conductive film feature may or may not be present, and, thus, the description includes both structures wherein a roller possesses the conductive film feature and structures wherein the film feature is not present. 
     Photovoltaic Device Structure 
     Referring now to  FIG. 1 , one embodiment of such a photovoltaic device  10  will now be described. Although the present embodiment is described in the context of a thin-film group IB-IIIA-VIA device, it should be understood that other types of photovoltaic devices may also be produced using the junction partner formation techniques described herein. 
     As seen in  FIG. 1 , the structure of a photovoltaic device  10  according to the present invention includes a base substrate  12 , an optional intermediate layer  13 , a base or back electrode  14 , a p-type absorber layer  16  incorporating a film of the type described above, a n-type junction partner semiconductor thin film  18 , and a transparent electrode  20 . By way of example, the base substrate  12  may be made of a metal foil, a polymer such as polyimides (PI), polyamides, polyetheretherketone (PEEK), Polyethersulfone (PES), polyetherimide (PEI), polyethylene naphtalate (PEN), Polyester (PET), related polymers, or a metallized plastic. By way of nonlimiting example, related polymers include those with similar structural and/or functional properties and/or material attributes. The base electrode  14  is made of an electrically conductive material. By way of example, the base electrode  14  may be of a metal layer whose thickness may be selected from the range of about 0.1 micron to about 25 microns. An optional intermediate layer  13  may be incorporated between the electrode  14  and the substrate  12 . The transparent electrode  20  may include a transparent conductive layer  19  and a layer of metal (e.g., Al, Ag, Cu, or Ni) fingers  21  to reduce sheet resistance. 
     In one embodiment, the base substrate  12  may be a metal foil made of a material such as but not limited to stainless steel, copper, aluminum, nickel, molybdenum, or the like. In one embodiment, aluminum is used with a molybdenum base electrode. Aluminum and molybdenum, however, can and often do inter-diffuse into one another, especially upon heating to elevated temperatures as used for absorber growth, with deleterious electronic and/or optoelectronic effects on the device  10 . Furthermore aluminum can diffuse though molybdenum into layers beyond e.g. CIG(S). To inhibit such inter-diffusion, an intermediate, interfacial layer  13  may be incorporated between the aluminum foil substrate  12  and molybdenum base electrode  14 . The interfacial layer may be composed of any of a variety of materials, including but not limited to chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including but not limited to titanium nitride, tantalum nitride, tungsten nitride, hafnium nitride, niobium nitride, zirconium nitride, vanadium nitride, silicon nitride, or molybdenum nitride), oxynitrides (including but not limited to oxynitrides of Ti, Ta, V, W, Si, Zr, Nb, Hf, or Mo), oxides, and/or carbides. The material may be selected to be an electrically conductive material. In one embodiment, the materials selected from the aforementioned may be those that are electrically conductive diffusion barriers. The thickness of this layer can range from 10 nm to 50 nm or from 10 nm to 30 nm. Optionally, the thickness may be in the range of about 50 nm to about 1000 nm. Optionally, the thickness may be in the range of about 100 nm to about 750 nm. Optionally, the thickness may be in the range of about 100 nm to about 500 nm. Optionally, the thickness may be in the range of about 110 nm to about 300 nm. In one embodiment, the thickness of the layer  13  is at least 100 nm or more. In another embodiment, the thickness of the layer  13  is at least 150 nm or more. In one embodiment, the thickness of the layer  13  is at least 200 nm or more. Optionally, some embodiments may include another layer such as but not limited to a copper layer, a titanium layer, or other metal layer above the layer  13  and below the base electrode layer  14 . Optionally, some embodiments may include another layer such as but not limited to a copper layer, a titanium layer, an aluminum layer, or other metal layer below the layer  13  and below the base electrode layer  14 . This layer may be thicker than the layer  13 . Optionally, it may be the same thickness or thinner than the layer  13 . This layer  13  may be placed on one or optionally both sides of the aluminum foil (shown as layer  15  in phantom in  FIG. 5 ). Some embodiments may use an electrically conductive barrier on side and a non-electrically conductive barrier on the other side. Other embodiments use the same type of conductivity material on both sides. 
     If barrier layers are on both sides of the substrate  12 , it should be understood that the protective layers may be of the same material or they may optionally be different materials from the aforementioned materials. The bottom protective layer  105  may be any of the materials. Optionally, some embodiments may include another layer  107  such as but not limited to an aluminum layer above the layer  105  and below the aluminum foil  102 . This layer  107  may be thicker than the layer  103   
     In the present embodiment, the structure of the photovoltaic device  10  may include a semiconductor thin film  18  of a complementary charge type that serves as a junction partner between the compound film and the transparent conducting layer  19 . By way of example, the n-type semiconductor thin film  18  (sometimes referred to as a junction partner layer) may include inorganic materials such as cadmium sulfide (CdS), zinc sulfide (ZnS), zinc hydroxide, zinc selenide (ZnSe), n-type organic materials, or some combination of two or more of these or similar materials, or organic materials such as n-type polymers and/or small molecules. Other types of junction partner material such as poly(benzimidazobenzophenanthroline ladder) (BBL) may also be used as a junction partner material according to the present invention. Details about BBL is provided in copending U.S. patent application Ser. No. 11/409,503 filed Apr. 21, 2006, fully incorporated herein by reference for all purposes. Layers of these materials may be deposited, e.g., by chemical bath deposition (CBD) and/or chemical surface deposition (and/or related methods), to a thickness ranging from about 2 nm to about 1000 nm, more optionally from about 5 nm to about 500 nm, and most optionally from about 10 nm to about 300 nm. In some embodiments, the thickness may be in the range of about 10 to about 100 nm. In other embodiments, the thickness may be in the range of about 15 to about 80 nm. This may also configured for use in a continuous roll-to-roll and/or segmented roll-to-roll and/or a batch mode system. 
     The transparent conductive layer  19  may be inorganic, e.g., a transparent conductive oxide (TCO) such as but not limited to indium tin oxide (ITO), fluorinated indium tin oxide, zinc oxide (ZnO) or zinc oxide (ZnO x ) doped with aluminum, or a related material, which can be deposited using any of a variety of means including but not limited to sputtering, evaporation, chemical bath deposition (CBD, electroplating, sol-gel based coating, spray coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and the like. Alternatively, the transparent conductive layer may include a transparent conductive polymeric layer, e.g. a transparent layer of doped PEDOT (Poly-3,4-Ethylenedioxythiophene), carbon nanotubes or related structures, or other transparent organic materials, either singly or in combination, which can be deposited using spin, dip, or spray coating, and the like or using any of various vapor deposition techniques. Optionally, it should be understood that a non-conductive layer such as intrinsic ZnO (i-ZnO) may be used between CdS and Al-doped ZnO. Optionally, an insulating layer may be included between the layer  18  and transparent conductive layer  19 . Combinations of inorganic and organic materials can also be used to form a hybrid transparent conductive layer. Thus, the layer  19  may optionally be an organic (polymeric or a mixed polymeric-molecular) or a hybrid (organic-inorganic) material. Examples of such a transparent conductive layer are described e.g., in commonly-assigned US Patent Application Publication Number 20040187317, which is incorporated herein by reference. 
     Those of skill in the art will be able to devise variations on the above embodiments that are within the scope of these teachings. For example, it is noted that in embodiments of the present invention, portions of the IB-IIIA precursor layers (or certain sub-layers of the precursor layers or other layers in the stack) may be deposited using techniques other than microflake-based inks For example precursor layers or constituent sub-layers may be deposited using any of a variety of alternative deposition techniques including but not limited to solution-deposition of spherical nanopowder-based inks, vapor deposition techniques such as ALD, evaporation, sputtering, CVD, PVD, electroplating and the like. 
     Junction Partner Deposition System 
     Referring now to  FIG. 2 , one embodiment of a junction partner deposition system will now be described. In this embodiment of the invention, the deposition system may be a solution deposition system that occurs in an environment at atmospheric pressures. Optionally, it should be understood that the deposition system may also be used with vacuum, low vacuum, and/or sub-atmospheric pressures. Some embodiments may also use environments at pressures higher than atmospheric pressure. 
       FIG. 2  shows a system with a substrate  50  configured for use in an in-line, roll-to-roll configuration. The substrate  50  may be a coated metal, coated polymer, coated metallized polymer substrate, or any other substrate previous described herein. The coating may be a photovoltaic absorber layer such as but not limited to Cu—In—Ga—Se, Cu—In—Se, Cu—In—Ga—S, Cu—In—Ga—Se—S, other group IB-IIIA-VIA absorbers, CdTe, sulfo-salt, group IIB-VIA absorber, or other photovoltaic absorbers that use a junction partner layer. The photovoltaic absorber layer or other coating formed on the substrate  50  may be formed from one or more precursors deposited by any of a variety methods including but not limited to sputtering, electrodeposition, electroplating, solution deposition, ALD, evaporation, CVD, PVD, and/or the like. When the term substrate  50  is discussed herein, it may be a bare substrate or it may be the substrate with the coating thereon. By way of nonlimiting example, these absorber layers may also be formed on rigid substrates or flexible substrates. 
     In one embodiment, the substrate  50  is a flexible elongate substrate such as but not limited to an absorber coated metal foil. In another embodiment, the substrate  50  is a multi-layered flexible substrate such as that shown in  FIG. 1 . Optionally, there may be a carrier on which discrete or pre-cut substrates comprising the precursor layers may be placed. The carrier may then carry these discrete or pre-cut substrates through the processing station(s). As part of the initial setup, the surface of the substrate to be processed may be cleaned prior to solution deposition. 
     By way of example and not limitation, the junction partner used with the substrate  50  may be a Group IIB-VIA material. In one embodiment, the Group IIB ionic species may be comprised of one or more of the following: cadmium, mercury, zinc, cadmium, mercury or zinc which may be provided by one or more solutions of the following: sulfate, acetate, bromide, fluoride, chloride, iodide, hydroxide, nitrate, oxalate, citrate, phosphate, tungstate, hydrates or combinations thereof. The Group VIA ionic species comprises oxygen, sulfur, selenium, tellurium, polonium, or combinations thereof. The Group VIA ionic species is optionally obtained from an aqueous solution of oxides, halides, sulfates, nitrates, or ureates of the Group VIA species. The liquid coating composition optionally further comprises a solvent such as water, optionally deionized water. The liquid coating composition optionally has a pH of from about 9 to about 14, more optionally from about 10 to about 13 and most optionally from about 11 to about 12. 
     In one embodiment, a CdS layer is formed on substrate  50  by a solution deposition process. More specifically, in this embodiment, a solution containing cadmium acetate (Cd(CH.sub.3 COO).sub.2), thiourea (NH.sub.2 CSNH.sub.2), ammonium acetate (CH.sub.3 COONH.sub.4) and ammonia is prepared. In this present embodiment, the concentration of the cadmium acetate in the solution was 0.001M, the concentration of the thiourea was 0.005M, the concentration of the ammonium acetate was 0.01M and the concentration of the ammonia was 0.4M. The substrate coated in this solution to form a CdS layer on the substrate. This is purely exemplary and is non-limiting. 
     A variety of solution-based coating techniques may be used to apply the above liquids including but not limited to wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, ultrasonic spray deposition, and the like, as well as combinations of the above and/or related technologies. The surface of the substrate  50  can be modified by the addition of a wetting agent to the solution, such as but not limited to glycerine. The liquid may also be a dispersion or ink containing the aforementioned materials. Depending on such surface tension, application of the liquid onto the substrate may optionally be conducted upside down. 
     Referring still to  FIG. 2 , this embodiment shows that a spray technique is used to apply the liquid coating to the substrate  50 . In this embodiment, the solution may be a mixture of 0.005-0.01M CdSO4 solution with 2M of NH4OH to pH of about 12. Optionally, the solution may be a mixture of cadmium sulfate is between about 0.001 to about 0.008 mole/liter. Optionally, the solution may be a mixture of cadmium sulfate is between about 0.002 to about 0.005 mole/liter. Optionally, a 0.3-0.5M thiourea solution is included. Optionally, the thiourea concentration is between 0.1-0.6 mole/liter. Optionally, the thiourea concentration is between 0.2-0.5 mole/liter.  FIG. 2  shows that this embodiment uses a spraying assembly  60  configured to spray material onto the substrate  50 . By way of example and not limitation, the spray assembly  60  may use a single nozzle, two nozzles, or multiple nozzles to spray liquid across the width of the substrate  50 . One or more of the nozzles may be ultrasonic nozzles. Ultrasonic nozzles are commercially available from manufacturers such as J D Ultrasonics of the United Kingdom. Optionally, the nozzles may be dual jet nozzles that are configured for atomizing liquid across a wide web such as that available from Wilson Spray Nozzle of Singapore. There may be one or more these wide web nozzles in assembly  60 . Optionally, one or more of the nozzles may be a vortex nozzle, wherein the flow from the nozzle is such that a vortexing flow exits the nozzle to define a cone-shaped spray. Optionally, wide web and vortex nozzles may be used in combination. The spray assembly  60  may be sufficient to spray across a substrate  50  that may have a width of greater than 0.5 meters. Optionally, the spray assembly  60  may be sufficient to spray across a substrate  50  that may have a width of greater than 1.0 meters. Optionally, the spray assembly  60  may be sufficient to spray across a substrate  50  that may have a width of greater than 2.0 meters. Optionally, the spray assembly  60  may be sufficient to spray across a substrate  50  that may have a width of greater than 3.0 meters. 
     It should also be understood that the temperature of the solution or dispersion being deposited and/or that of the substrate may also be controlled. In one embodiment, the container containing this solution was put in a hot water bath kept at about 85 degree C. prior to deposition and is deposited on a substrate at a lower temperature. In some embodiments, the substrate is at ambient temperature, or heated but to a temperature less than or equal to the temperature of the solution or dispersion to be deposited. Optionally, both the solution and the substrate  50  are at substantially the same temperature. In one embodiment, neither the solution or the substrate  50  are heated and both are at ambient temperatures. In other embodiments, the substrate  50  may be heated from ambient to about 60 to about 90° C. In other embodiments, the substrate  50  may be heated from ambient to about 50 to about 90° C. In other embodiments, the substrate  50  may be heated from ambient to about 40 to about 100° C. In other embodiments, the solution or dispersion may actually be chilled or cooled to be below ambient temperature. 
     In another aspect, the amount of solution applied may be either a thin layer or it may be sufficient to create a bath of a depth of about 0.5 mm to about 5 mm in depth. Optionally, the bath may be about 0.5 microns to about 10 mm in depth. A shallow bath allows for sufficient coverage of the entire target surface of the substrate  50  while not substantially under-utilizing the raw material. The bath above the substrate  50  may be contained above the substrate  50  against a slidable seal and/or a movable seal. Optionally, the substrate  50  passes through a bath of the solution, wherein the substrate  50  may have a backside layer that can be removed. 
     Referring still to  FIG. 2 , a second deposition assembly  70  (shown in phantom) may also be used. This may be the same type of ultrasonic nozzle used in the solution deposition assembly  60 . Optionally, it may one of the other types of deposition system such as but not limited to a vortex, wide-web, or other nozzle type different from the nozzle used in the solution deposition assembly  60 . Optionally, the second deposition assembly  70  may include one or more of the following: wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, and the like, as well as combinations of the above and/or related technologies. The solution from assembly  70  may be the same as that from assembly  60  or it may be a component used in the process such as the thiourea solution or the like. 
     It should be understood that in some embodiments, there may be more than two deposition sources  60  and  70 . Some embodiments may have three or more. Each may be depositing just one component of the material in the processing solution. Some may be depositing mixtures. Some embodiments may use a combination (some sources depositing just one component, while another source depositions mixtures of one or more). It should also be understood that in some embodiments, the solutions, components, or other material from deposition sources  60  and  70  may all be at temperatures higher than that of the substrate, the same as the temperature of the substrate, or at temperatures lower than that of the substrate. Optionally, only one of the deposition sources is depositing at temperatures higher than that of the substrate. Optionally, only one of the deposition sources is depositing at temperatures the same as that of the substrate. Optionally, only one of the deposition sources is depositing at temperatures lower than that of the substrate. The sequence may also be varied such as but not limited to a cadmium salt solution first and then thiourea or other S solution later. Some embodiments may add one or more other complexing agents. The sequence may be varied with the S solution deposited first and then followed by the cadmium salt solution and any other components. Some may involve a combination of wet deposition and dry deposition processes such as a liquid S solution with cadmium salt nanoparticles added at a different station. Of course, the type of deposition may also be varied such as but not limited to slot die deposition followed by a predefined time delay of a spray deposition of another component or vice versa. Any of the multi-deposition source systems may be adapted for use with any of the embodiment of the processing system described herein. 
     As seen in  FIG. 2 , after solution deposition by assembly  60  and/or  70 , the substrate  50  enters an oven  80  for heating the solution to enable film growth or formation. In one embodiment, the over  80  is used to heat the substrate to between about 65 to about 90C. Optionally, some embodiments, may heat to higher temperatures such as about 90 to about 130C. A variety of ovens may work. In one embodiment, the oven  80  comprises of an infrared oven is used to heat the substrate  50  and the solution over the substrate  50 . Infrared ovens are available from a variety of manufacturers including Glenro Inc. of Paterson, N.J. Other embodiments may use muffles wherein the heating elements are located outside the tube furnace or muffle through which the substrate passes. The heating elements heat the muffle, which in turn heats the substrate. Some embodiments may only include heating element on one side of the oven  80  (e.g. top) or only on the other side (e.g. bottom). In one embodiment, the group IIB-VIA material over the substrate  50  may have a cured thickness of about 20 to about 100 nanometers. Optionally, the thickness may be between about 100 to about 150 nanometers. 
     After passing through the oven  80 , the substrate  50  reaches a cleaning station  90 . This cleaning system  90  may use a pressure spray of liquid such as but not limited to deionized water to remove unused or uncured solution applied to the substrate  50 . The wash off from the pressure spray is collected and the waste liquid contained or processed for proper removal. 
     Optionally, a second cleaning station  100  is included. This may be an additional washing station similar to the cleaning station  90 , it may be an air knife or other source to dry the substrate  50 , or it may be cleaning system using some other type of cleaning solution. The cleaning and/or drying may occur on only one side of the substrate  50  or it may be from the underside or other directions as indicted by stations  92  and  102  in phantom. Optionally, it may be a combined heating and air dry station to remove un-wanted material from the surface of the substrate and to prepare the substrate for the next stage of processing. In some embodiments, the heating may occur after the air drying and may use an infrared heating to increase the substrate temperature and to prepare it for the next layer to be deposited on the photovoltaic device. In one embodiment, the substrate  50  after the various processes above, is heated to about 100C or higher at 2 meters per minute to dry the web or substrate  50  and to prepare it for the next layer. 
     Referring now to  FIG. 3 , another embodiment of the present invention will now be described. This embodiment shows a junction partner deposition system  130  with a solution deposition by assembly  60  and/or  70 . The oven  80  is used to heat the solution deposited on the substrate  50  to from the assembly  60  and/or  70 . This embodiment of the junction partner deposition system includes a vacuum pull belt system  140  which will help flatten the substrate  50  during the processing. This is particularly helpful as some wider flexible substrates  50  after deposition of semiconductor or other absorber material will curl and assume non-planar configurations without force or substrate guides to help flatten the substrate  50 . Vacuum pull belt systems are available from manufacturers such as Kliklok-Woodman of Decatur Georgia. Some systems may use an articulated floating vacuum pull belt arrangement as described in U.S. Pat. No. 5,715,656 and fully incorporated herein by reference for all purposes. 
     In this embodiment, the vacuum pull belt system  140  extends outside the oven  80 . Optionally, in other embodiments, the vacuum pull belt system  140  may extend only within the boundaries of the oven  80 . As seen in  FIG. 3 , the spray of the solution may occur over the system  140  by way of the spray assembly  60  or it may occur at a location of the substrate  50  spaced away from the belt system  140  as indicated by a spray assembly located at position  70 . 
       FIG. 4  shows yet another embodiment wherein a moving seal systems  160  and  162  which may be alongside the areas where the solution is deposited on the substrate  50 .  FIG. 4  is a top down view of the substrate  50  and the seals of the systems  160  and  162  will form side walls against the substrate  50  that allows the bath to be formed over the substrate  50 . In one embodiment, the seals of the systems  160  and  162  will also keep the bath or layer of solution on only one side of the substrate  50 . The systems  160  and  162  may also be configured to have seals that move with the substrate  50 . Other embodiments may have stationary seals that allow the substrate to slide along against it. Some embodiments may also include a dip in the substrate path (see  FIG. 33 ) to help prevent the fluid or solution from flowing too far downweb or upweb. Scrubbing units  170  and  172  may also be included to clean the surface of the seal to remove and undesired build up that may prevent a good seal against the substrate  50 . Other embodiments may use the units  170  and  172  to apply sealant to help the seal against the substrate  50 . 
     Still further embodiments may use two back-to-back substrates  50  to allow for higher utilization. To avoid waste or undesired processing, two substrates may be attached together “back-to-back” to form a dual substrate having, in effect, two front sides with the back sides protected against undesired treatment. Preferably, the substrates are attached in a manner that allows them to be separated from each other after processing. By way of example the substrates may be attached with a low-strength adhesive or electrostatic film applied to the back side of one or both substrates. Alternatively, an edge where the two substrates join may be sealed, e.g., with a tape, so that reactants cannot reach the back sides during processing. The dual substrate may then be wound into a coil and coated such that both front surfaces are treated while the back surfaces are not. Processing the substrate in this fashion may reduce the waste of reactants and may increase the area of the substrate that can be processed at one time. Optionally, other embodiments may use a sacrificial backside that is removed after processing to reveal a backside that is not processed. These systems are particularly suited for a bath-type system wherein the substrate is passed through a solution that exposes both sides of the substrate. 
     Referring now to  FIG. 5 , it should be understood that the environment inside the oven may be different from the ambient atmosphere. Although some embodiments may used an ambient air environment inside the oven  180 , other embodiments may use non-air atmospheres. By way of example and non-limiting example, the atmosphere in the muffle  182  may be comprised of ammonia or ammonia based material to prevent loss of ammonia or similar material from the solution. The loss of material may create a change in pH that changes the reaction dynamics. Other embodiments may use other atmospheres that create an overpressure of the material that may be volatile and escape from the solution during processing. The material in the gas environment of muffle  182  is based on what type of reaction is occurring and what materials may be vaporized or lost during processing. 
     By way of example and not limitation, the muffle  182  may be designed with openings sized to handle foils of wide widths. In one nonlimiting example, the substrate  50  may be at least 1 meter in width. In another embodiment, the substrate  50  may be at least 2 meters in width. In another embodiment, the substrate  50  may be at least 3 meter in width. 
     In one embodiment, the openings in muffle  182  are sized so as to provide minimal clearance above the substrate to reduce the amount of gas escaping. In one embodiment, the interior height of the muffle is less than about 3 inches. In one embodiment, the interior height of the muffle is less than about 2 inches. In one embodiment, the interior height of the muffle is less than about 1 inch. In one embodiment, the interior height of the muffle is less than about 0.5 inches. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in the chamber or muffle may be at least about 10:1. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in the chamber or muffle may be greater than about 10:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the chamber or muffle may be greater than about 14:1. Although a muffle is used in this example, it should be understood that other designs using a cover over a U cross-sectional shaped web guide may also be sufficient to create the desired covered tunnel environment. In one embodiment, the height of the head space above the substrate is predetermined based on the processing gas and/or fluid used in that particular zone or area of the processing system. 
     In some embodiments herein, the muffle  182  may be multi-zoned with separate chambers in the muffle. These zones may be integrated into one structure or they may be separated detached structures each defining at least one zone. The zones may be separated from each other by a small gap, or alternately all zones may structurally be connected to each other, however they may be internally separated through use of seals or spacers. 
       FIG. 5  also shows in phantom that a second muffle  190  may be used around the inner muffler  182 . The atmosphere in outer muffle  190  may be the same as that in the inner muffle  182 . Optionally, the muffle  190  has an atmosphere different from that in the muffle  182 . In one embodiment, the muffle  190  includes an inert atmosphere such as but not limited to nitrogen, argon, or the like. The muffle  190  may be the same length as the muffle  182 . Optionally, the muffle  190  may be longer than the inner muffle  182  to prevent escape of gas into the outside environment. It would instead escape into the outer muffle  190 . Optionally, each muffle may be inert gas zones near the inlet and outlet of each muffle to help prevent escape of the interior processing gas.  FIG. 5  also shows how heater elements  192  and  194  may be located outside, above and/or below the muffle. 
     Referring now to  FIG. 6 , yet another embodiment of the present invention is shown wherein multiple spray and heating locations are shown. In this embodiment, a spray section  200  is used to deposit the solution, followed by an oven section  202  to heat the liquid. This system may be followed by spray section  204 , oven  206 , spray section  208 , and oven  210 . The spray and oven sections may be repeated as desired to create the layer on the substrate  50  of the desired thickness. In this embodiment, each spray and oven section creates about 25 to about 35 nanometer thickness of the junction partner. Other embodiments may use deposition sections that create thicker or thinner layers. Some may also use sections to deposit different materials or different components used for the junction partner. Still other embodiments may use ovens that run at different temperatures. Some may have heat in about 70 to about 90C. Optionally, others may heat higher to about 40 to about 90C. Optionally, others may heat higher to about 90 to about 130C. Optionally, others may use lower temperatures of about 55 to about 75C. The ovens may be arranged to go high heat to low heat. Optionally, they may go from low heat to high heat. Others may use a heat profile with high heat in the middle oven, but lower heat at the beginning or end ovens. This heating may be followed up by wash and dry units  90  and  100 . An oven  220  may be included to further dry the substrate and/or prepare it for the next layer of processing. Some embodiment may roll directly to the next deposition section which may be a TCO sputtering or other deposition device. The substrate  50  may also come directly from CIGS or other absorber layer deposition and processing in a complete roll-to-roll process. It should also be understood that in alternative embodiments, there may be an alternative embodiment with a delayed processing, e.g. not direct and not step repeat. In these alternative embodiments, there may be non-continuous processing of the substrate. 
     Referring now to  FIG. 7 , a still further embodiment of the present invention will now be described. This embodiment uses a frame  250  that is raised and lowered over the substrate  50 . In a step-repeat function, the substrate  50  may be advanced to place an unprocessed portion below the frame  250 . The frame  250  is lowered to contact the substrate  50  or close enough to prevent significant loss (more than 10%) of the fluid over the substrate during processing. Again, any solution deposition may be used. A variety of solution-based coating techniques may be used to apply the liquid including but not limited to wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, ultrasonic spray deposition, and the like, as well as combinations of the above and/or related technologies. The surface of the substrate  50  can be modified by the addition of a wetting agent to the solution, such as glycerine. The liquid may also be a dispersion or ink containing the aforementioned materials. Depending on such surface tension, application of the liquid onto the substrate may optionally be conducted upside down. 
     The oven  80  is heated during, before, or after deposition of fluid into the frame  250 . After processing and heating, the frame  250  is raised and the substrate  50  is advanced to place a new, untreated section below the frame  250 . Again, the oven  80  may have an ammonia or other atmosphere as described above. The frame  250  maybe filled multiple times over one section of the substrate  50  to build up the desired amount of thickness. Other embodiments may use a frame  250  that moves with the substrate to allow for a moving process where the substrate is not complete stopped. The frame  250  may be lowered down over an area of the substrate while it is outside the oven  80 . 
     Referring now to  FIG. 8 , yet another embodiment of the present invention will now be described. This embodiment shows that instead of using seals, frames or other elements to help contain a fluid over the substrate  50 , the edges  53  and  55  of a flexible substrate  50  may be curved, curled, or angled upward. This defines a cupped or bowl-type cross-sectional shape that allows fluid to be filled therebetween as indicated by line  57  shown in phantom. The depth of the fluid between the upwardly curled edges  53  and  55  may be filled to a level below the upper edges, below the upper edges, and/or optionally over the upper edges. By way of example and not limitation, the depth of fluid over the substrate  50  may be in range from about 0.1 mm to about 20 mm. Optionally, in another embodiment, the depth of fluid over the substrate  50  may be in range from about 0.5 mm to about 10 mm. In the present embodiment, a fluid deposition assembly  259  may be used to form a covering of fluid over the substrate  50 . Optionally, the assembly  259  and any other of the deposition systems such as but not limited to drip, spray, or other fluid coating devices may be mounted to move in manner such as but noted limited to that as indicated by arrows  257  to improve coverage of the fluid deposition over substrate  50 . Optionally, this may be achieved by mechanical motion laterally and/or by angulation of deposition nozzle, hose, or other deposition device/assembly. 
     It should be understood that the fluid may be deposited by any of a variety of solution deposition techniques including, but not limited to, wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, ultrasonic spray deposition, and the like, as well as combinations of the above and/or related technologies.  FIG. 8  shows one embodiment wherein the fluid is sprayed onto the substrate  50 . The fluid may being deposited may be at a temperature that is substantially the same as that of the substrate  50 . Optionally, in other embodiments, the fluid may be cooler than the substrate  50  or hotter than the substrate  50 . Some embodiments may heat the fluid so that it is warmer than the ambient temperature. Some embodiments may use an air knife to cool and/or clean the substrate prior to deposition of the fluid. 
       FIG. 9  shows that in one embodiment, the substrate  50  with or without curls  53  and  55  may be moved into a closely spaced muffle, covered oven, or other structure to minimize the amount of open space above the substrate  50 . These embodiments reduce the amount of evaporation of the fluid covering the substrate  50 . In the current embodiment, the muffle  260  is used to define the covered oven through which the substrate  50  passes. The muffle  260  is shown to have curved wall surfaces to maintain the curved configuration of the substrate  50 . Some embodiments may optionally have slots or grooves defined by guides  262  and  264  (shown in phantom). 
       FIG. 9  also shows that an optional external oven  270  may be used around the muffle  260 . This embodiment allows for convective heating to be used outside the muffle  260  to heat the muffle  260 , the substrate  50 , and the fluid over the substrate  50 . The oven  270  may be filled with the same atmosphere as that inside the muffle  260 . Optionally, the muffle  260  may be filled with an inert gas such as but not limited to nitrogen, argon, other inert gas, or other gas suitable for use with the atmosphere in the muffle  260 . The over  270  may be the same length as muffle  260 , shorter than muffle  260 , or longer than muffle  260 . 
     Referring now to  FIG. 10 , a cross-section of a guide is shown for curling the substrate  50  to have the formed edges  53  and  55 . This cross-section shows that substrate  50  may be transformed from a substantially planar configuration to one with a configuration sufficient to hold fluid therebetween. Again, guides  280  and  282  may be provided to help curl the substrate upward. The surface  281  may be a low friction surface such as but not limited to Teflon® or similar material. The surfaces of guides  280  and  282  may be similarly treated. Optionally, a low friction surface  281  may comprise of a covering, tiles, plates, or other overlayers that are placed on top of a surface that may have a higher coefficient or friction. Some embodiments may have a low friction surface along all portions of the substrate path wherein the backside of the substrate contacts or slides against any portion of the processing system. 
       FIG. 11A  shows that the surface  284  of guide  280  may be a gradually curving surface to transition the planar edge of the substrate to a curved configuration. By way of example and not limitation, the length of surface  284  as indicated by arrow  286  may be in the range from about 1 inch to about 10 inches. The greater length eases the transition from planar configuration to curved configuration. Optionally, the transition length may be in the range of about 2 to about 6 inches. Optionally, the transition length may be a percentage based on the width of the web. In one embodiment it may be between 10% to 120% of the width of the web. Optionally, in another embodiment, the transition length is selected to be between 25% to 75% of the width of the web or substrate. Optionally, some embodiments also factor the height of the bent portion into the amount of length desired for the transition. In one embodiment, the length for transition is about 8× to 24× the height of the desired bend. Optionally, the transition length is about 4× to 40× the height of the desired bend. 
       FIG. 11B  shows yet another embodiment of the invention wherein the guide  290  comprises of a plurality of discrete elements  292  that are oriented to provide the same curving the substrate  50  to achieve the same functionality as that of guide  280 . By way of example and not limitation, the discrete element  292  may be a roller, bearing, drum, or fixed roller. Other rotatable, fixed, or other shaped discrete elements may be used to guide the substrate  50 . The guides may be any of a series of smooth surfaces, angled surfaces, rounded surfaces, the like, or combinations of the foregoing to achieved the desired configuration for substrate  50 . Again, any of the surfaces of the elements in  FIGS. 11A and 11B  may also be coated or made of a low-friction material as described for surface  281 . 
     Referring now to  FIGS. 12A-12C , it should be understood that the guides herein may be configured provide a variety of different geometries.  FIG. 12A  shows that the substrate  50  may have angled but substantially straight upward extending edge  293 .  FIG. 12B  shows that the substrate  50  may have a vertical but substantially straight upward extending edge  295 .  FIG. 12C  shows that the substrate  50  may have a multi-bend upward extending edge  297 . It should be understood that other geometries of straight or curved sections may be combined in any order to create the desired cross-sectional profile for the substrate  50 . The upward extending portion of the substrate  50  may be at any angle so long as it is sufficient to contain or constrain the fluid over the substrate  50 . It should be understood that the amount of upward bending portion (on each side) may be described as a percentage of the cross-web width of the substrate such as but not limited to between 1% to 7% of the web width, with a minimum in this embodiment of at least 1 mm. Optionally, it may be between 2% to 6% of the web width, with a minimum in this embodiment of at least 2 mm. Optionally, it may be between 3% to 6% of the web width, with a minimum in this embodiment of at least 3 mm. 
       FIG. 13  shows that the guides  280  and  282  may be positioned to narrow the substrate  50  to achieve the curved configuration with the curved edges  53  and  55 . Guides  284  and  286  are similar to the guides  280  and  282 , except that the configuration is reversed to gradually uncurl the curved portions  53  and  55  and return the substrate  50  to a substantially planar configuration. By way of example and not limitation, it is desirable that the curling and uncurling occur in a manner that does not cause substantially permanent deformation that causes warping or damage to substantial portions of the substrate  50 . 
       FIG. 13  also shows that when the edges of the substrate  50  is configured to have curved portions  53  and  55 , the width  283  of the substrate  50  is less than the width  285  of the substrate  50  when planar. The movement of the substrate  50  is in the direction as indicated by arrow  294 . 
       FIG. 14  shows that a cascade of one or more guides may be used to gradually curve the substrate  50 . In this embodiment of the invention, the guides  280  and  282  are included. Additionally, a second set of guides  300  and  302  are included to further curl the substrate  50 . This decreases the width to that indicated by arrows  304 .  FIG. 14  also shows the multiple guides  306 ,  308 ,  284 , and  286  are used to uncurl, unbend, and/or uncurve a selected portion of the substrate  50 . 
     Referring now to  FIG. 15 , one embodiment of a deposition system  320  according to the present invention is shown. The deposition system  320  includes a deposition zone  322 , a heated zone  324 , a cleaning zone  326 , and a drying zone  328 . A belt system  330  is used to transport the substrate  50  through the heated zone  324 . The deposition zone  322  may be located in an unheated zone. Optionally, it may be included in the heated zone  324 . 
       FIG. 15  shows that in this embodiment an air knife or other gas source  340  may be used to clean off the surface of the substrate  50 . The air knife or cleaning mechanism  340  may also be used to cool or temperature regulate the substrate  50  before fluid is deposited onto the substrate  50 . This may be particularly useful as the belt system  330  may carry some heat from the heated zone  324 . Optionally, in other embodiments, the belt system  330  may be sized such that the system  330  is housed mainly in the heated zone  324  and does not extend into the deposition zone  322  in manner that causes the substrate  50  to be heated prior to deposition of the fluid thereon. By way of example, the substrate  50  may be moved over a low-friction surface, free spanned in the deposition zone  322 , transported by a separate conveyor system, or otherwise transported through the deposition zone  322 . Some may have sections of the processing system that are without any conveyor system while other sections are conveyored. Some embodiments are entirely without conveyors. Some systems may have the non-conveyored system with a base have a pre-defined cross-section so as to curve or bend the substrate upward when the substrate is laid on or pulled to conform to the base. 
     In the present embodiment, the deposition assembly  350  used in the deposition zone  322  may be a variety of solution deposition devices. It should be understood that the fluid may be deposited by any of a variety of solution deposition techniques including, but not limited to, wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, ultrasonic spray deposition, and the like, as well as combinations of the above and/or related technologies. In one embodiment, a ultrasonic spray system such as but not limited to the Prism Ultra-Coat system available from Ultrasonic Systems, Inc. of Haverhill, Massachusetts may be used in the deposition assembly  350 . Some embodiments may use more than one fluid deposition zone. They may use the same deposition technique or different techniques. Some embodiments may combine more than one deposition technique in the same deposition zone. It should also be understood that the fluid may be deposited at a temperature that is substantially the same as that of the substrate  50 . Optionally, in other embodiments, the fluid may be cooler than the substrate  50  or hotter than the substrate  50 . Some embodiments may heat the fluid so that it is warmer than the ambient temperature. Some embodiments may use an air knife to cool and/or clean the substrate prior to deposition of the fluid. 
     By way of example and not limitation, it should be understood that the heating zone  324  may use a variety of heating techniques. Some may use convection heating, infrared (IR) heating, or electromagnetic heating. Some embodiments may use chilled rollers or surfaces (not shown) on the underside of the substrate  50  to keep a lower portion of the substrate  50  cool while the upper portion is at a processing temperature. As seen in  FIG. 15 , there may be one or more separate zones in the heating zone  324 . This allows for different temperature profiles during processing. In one embodiment, the heating elements may be positioned to heat all components in the heating zone to the same temperature. This includes the cover over the substrate, a muffle, or other elements used inside the heating enclosure. Again, heating may occur by convection heating, infrared (IR) heating, and/or electromagnetic heating. 
     Referring still to  FIG. 15 , after the substrate  50  passes through the heating zone  324 , the cleaning zone  326  may use a combination of washing, blowing, rinsing, suction, cooling, shaping, heating, and/or other assemblies to post-treat the substrate  50  after the heating zone  324 . In the present embodiment, a water sprayer  360  is used with an air knife  362 . A second water sprayer  364  is used with a second air knife  366 . This combination is designed to remove any excess fluid that is not reacted as the substrate  50  leaves the heating zone  324 . The fluid and waste liquid being washed off will be collected by one or more liquid waste containers  370  and  372 . The waste container  370  may be viewed as the primary waste container as it will contain a more concentrated waste fluid than the waste fluid filling the waste container  372 . It should also be understood that in some embodiments, the fluid from containers  370  or  372  may be reconditioned in reservoir  373  for use again in the system. In one non-limiting example, used solution is cooled, and replenished in a solution container  373  and redirected into the deposition chamber. 
     There may be additional components such as filters on the return line  325 , filters (not shown) on the feed line  327 , or filters in fluid communication with reservoir  373  that may circulate the solution within the solution container  22  for the purpose of particle elimination, cooling, mixing etc. There may be a cooling loop with a cooling coil within the solution container  373 . A cooling liquid may be circulated through the cooling coil to lower the temperature of the bath within the solution container  373 . The temperature of the solution within the solution container  373  may be in the range of 5-40 C, preferably in the 15-20 C range. In effect the deposition section becomes a cold-wall reactor where only the wall carrying the structure to be coated with CdS is heated. 
       FIG. 15  also shows that in this embodiment of the invention, the substrate  50  is dried after passing through the cleaning zone  326 . Drying zone  328  is positioned over the substrate  50  and will cure the material on the substrate  50 . In one embodiment, the drying zone  328  uses a plurality of IR curing lamps to remove any residual moisture that may be on the substrate. Optionally, in another embodiment of the invention, heated gases may be circulated over the substrate  50  to remove any residual moisture from the substrate  50 . Some embodiment may circulate heated inert gas such as but not limited to nitrogen. Optionally, some embodiments may merely circulate heated ambient air that is drawn into the drying zone  328 . 
     It should also be understood that a variety of sensors may also be installed along the path that the substrate  50  travels through the deposition system  320 . By way of nonlimiting example, this may include a thickness sensor  380  positioned to detect the thickness of the coated substrate. Optionally, other embodiments may use an optical sensor to detect surface imperfection on the coated substrate  50 .  FIG. 15  also shows that exhausts  390 ,  392 , and  394  are positioned along the path of the substrate  50  to draw off waste gases that may be created during processing. Sensors may also be optionally present to optionally detect chemical composition either on surface and/or through depth of coating. Some embodiments may have optional sensor system to assess spatial uniformity (not just aberrations but also standard uniformity). 
     It should also be understood that some embodiments may have multiple heating zones  324 . Some embodiments may have alternating zones  322  and  324 . The zones may be combined various orders such as that shown in  FIG. 6 . Cleaning zones  326  may also be included after one or more of the heating zones  324 . 
     Referring now to  FIG. 16 , yet another embodiment of the present invention is now described. The deposition system  400  in  FIG. 16  is similar in some aspect to the system  320  shown in  FIG. 15 . By way of example and not limitation, the heating zone  324  includes additional convention chambers therein. The exhaust  394  is connected to its own chamber  410 . Deposition system  400  includes a substrate guide or contour device  420  located upstream of the heating chamber. This substrate contour device  420  will shape the edges of the substrate  50  to define an area over the substrate  50  to hold fluid thereon. A second substrate contour device  430  will uncurl the edges of the substrate  50  to return the substrate  50  to a substantially planar configuration. One other area of difference in the deposition system  400  involves the cleaning zone  326 . The cleaning zone  326  in system  400  includes a suction element  440  for removing excess fluid from the substrate  50  after processing through the heating zone  324 . This suction element  440  provides for increased control of fluid being removed from substrate  50  prior the washing and blowing elements similar to that of system  320 . 
     Optionally, it should be understood that any of the embodiments herein may be equipped with thermally conductive coverplate(s)  351  which may include a plurality of fins or other heat transfer improving shapes or features to improve the heat transfer from the convection system to the substrate  50 . The plates  351  may be made of a thermally conductive material such as but not limited to steel, aluminum, titanium, or the like. Optionally, in-line heating elements  353  may be also be included below and/or above the substrate to improve heat transfer to the substrate. They may be integrated to be part of the coverplates  351  or separate discrete elements. Some embodiment may also use free-spanning substrate  50  that is move without the use of a conveyor belt. 
       FIG. 17  shows a still further embodiment wherein a bath type deposition system  500  is used with moving seals  502  and  504 . The moving seals  502  and  504  may cover the side, top, and/or bottom surfaces of the substrate  50  as seen more clearly in  FIGS. 24-28 . The path of the substrate  50  through the system  500  may be lowered to create a bath inside the system  500  without spillage downweb or upweb. Again, any solution deposition technique may be used. A variety of solution-based coating techniques may be used to apply the liquid including but not limited to wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink jet printing, jet deposition, spray deposition, ultrasonic spray deposition, and the like, as well as combinations of the above and/or related technologies. The surface of the substrate  50  can be modified by the addition of a wetting agent to the solution, such as glycerine. The liquid may also be a dispersion or ink containing the aforementioned materials. Depending on such surface tension, application of the liquid onto the substrate may optionally be conducted upside down. Heating of the web may occur after the deposition has occurred and/or at the same time. Optionally, the solution may itself be heated to a temperature above that of the substrate. The seals which may be rubber, silicone etc., may be continually fed against the web at a speed that is substantially equal to the linear speed of the substrate. In this case there would be no relative motion between the sealing members and the substrate during processing. 
     Referring now to  FIG. 18 , this embodiment shows that the substrate  50  may be passed through a bath  550  of Group IIB-VIA-based solution as shown. The rollers  552  are positioned so as to prevent contact the coated surface  554  of the substrate  50 . Alternatively, some embodiments may allow the rollers  554  to contact the coated surface.  FIG. 18  shows that this embodiment may optionally include a stirrer  560  to keep fluid moving around the surfaces of the container.  FIG. 18  also shows that a reservoir  570  may be included to create fluid flow in the bath. Conduits  572  and  574  may be used to couple the bath  550  to the reservoir  570 . 
     Referring now to  FIG. 19 , yet another embodiment of the present invention will now be described.  FIG. 19  shows a shaped container  580  that contains a bath  582  therein. There may be movable surfaces  584  and/or  586  (shown in phantom) along the sides of the shaped container  580  to allow for deposits on those surfaces to be cleaned. Optionally, some embodiments may have normal wall surfaces, but the container  580  is frequently cleaned to remove and deposits formed thereon. Some embodiments may also be fitted with a reservoir similar to reservoir  570  to allow for constant fluid flow in the container  570  and more specifically along the walls of container  570  to minimize deposits thereon. Similar to  FIG. 18 , the rollers  588  may be configured not contact the coated surface  552  of the substrate  50 . The shaped container also prevents fluid from escaping. Heating elements may be included in the bath or outside the container  580  to heat the bath  582  therein to the desired processing temperature. Some embodiments may have the same temperature throughout the bath  582 . Optionally, other embodiments may have different heating zones that may include barriers  589  in the bath that separate different fluid zones that may have different temperatures. These embodiments may or may not use the substrate edge bending techniques previously described herein. 
       FIG. 20  shows a still further embodiment wherein an additional material  600  is coupled to the edges of the substrate  50 . This allows for the material  600  to define the curved portion that allows a bath to be defined thereon. The material  600  may be a disposable material or reusable material. This minimizes the risk that the curling may scratch or damage the coating on the substrate  50 . The material  600  may comprise of a variety of materials such as but not limited to Teflon, polymer, silicone, or other material. The material  600  may be coupled to the substrate  50  by adhesives or by heating. 
     As seen in  FIG. 21 , the material  600  may be in the form a sheet that covers the entire backside of the substrate  50  and extends beyond the edges of the substrate  50 . This may be particularly useful when the substrate  50  is a plurality of pre-formed, discrete, or pre-cut rigid substrates and the material  600  is a pliable material to allow for curving to define a zone over the substrate for holding the fluid. The material  600  may act as a carrier on which pre-formed, discrete, or pre-cut substrates may be placed. The carrier may then carry these pre-formed, discrete, or pre-cut substrates through the processing station(s). In some embodiments, the edges of the material  600  may be pre-shaped to have the upward bending configuration and not separate curling apparatus is need to help transform the material  600  from a planar configuration to one with upwardly pointing edges. 
       FIG. 22  shows that another embodiment of the invention may use the substrate  50  with strips of material  602  and  604  instead of an entire backside sheet of material  600 . The material  602  and  604  may be similar to that used for material  600 . The material  602  and  604  may be sufficiently flexible to allow the upward extending portion to be formed and allow a bath to be contained therein. This edge material may optionally be disposable so that the materials  602  and  604  may be handled more aggressively to get the desired throughput or shape. The same may also be said of material  600  in embodiments where it is designed to be disposable. 
     Referring now to  FIG. 23A , it should be understood that some embodiments may use a separate layer  610  that is attached to the backside of the substrate  50 . This provides backside protection of the substrate  50 , may also prevent unwanted formation of junction partner material on the backside, to act as a thermal mass to cool the backside, or to protect the backside during the curling or uncurling process. This backside material may be permanently attached to the substrate  50  or it may be a disposable material that is removed. Some embodiments may have the material dissolve away during processing. 
       FIG. 23B  shows that two substrates  50  and  51  may be joined together. Coating or otherwise treating both sides of one substrate can result in waste of valuable reactants or may lead to extra processing steps such as removing unwanted coatings. To avoid such waste or undesired processing, two substrates may be attached together “back-to-back” to form a dual substrate having, in effect, two front sides with the back sides protected against undesired treatment. Optionally, the substrates are attached in a manner that allows them to be separated from each other after processing. By way of example the substrates may be attached with a low-strength adhesive or electrostatic film applied to the back side of one or both substrates. Alternatively, an edge where the two substrates join may be sealed, e.g., with a tape, so that reactants cannot reach the back sides during processing. The dual substrate  50  and  51  may then be introduced into the bath and coated such that both front surfaces are treated while the back surfaces are not. Processing the substrate in this fashion may reduce the waste of reactants and may increase the area of the substrate that can be processed at one time. The substrates may be joined directly together or may have an adhesive layer  612  therebetween. 
       FIGS. 24 through 28  show some of the various types of edge seals that may be used with the substrate  50  or with substrate  50  and a disposable edge material to allow for a bath to be formed over the substrate  50 .  FIG. 24  shows that seal material  620  may be slidably or fixably attached to an upper surface  622  of the edge of the substrate  50 .  FIG. 25  shows that seal material  624  may be slidably or fixably attached to a side surface  626  of the edge of the substrate  50 . 
       FIG. 26  shows that shaped seals  630  formed against a side surface  626  and/or a bottom surface  632  of the substrate  50 . The seals  630  may be slidably or fixably attached to the substrate  50 .  FIG. 27  shows that a shaped seal  640  may be formed against a side surface  626  and/or a top surface  622  of the substrate  50 . The seals  640  may be slidably or fixably attached to the substrate  50 .  FIG. 28  shows that a shaped seal  650  may be formed against a side surface  626 , and/or a top surface  622 , and/or a bottom surface  632  of the substrate  50 . The seals  640  may be slidably or fixably attached to the various surfaces of substrate  50 . Optionally, the surfaces of shaped seal  650  engaging the surfaces of substrate  50  may be angled and not necessary parallel to the surfaces against which they engage. This may created a pinched contact if a tighter engagement is desired. 
     Referring now to  FIG. 29 , yet another embodiment of the present invention will now be described.  FIG. 29  shows a top-down view of the substrate  50  as it is being processed for formation of the junction partner layer. This embodiment has a single fluid deposition source  700  that directs fluid onto the substrate  50 . The source  700  may be oriented to direct fluid downstream. This may be as a result of a slight angle of the deposition system as seen in FIG.  3  and may help to prevent flow of fluid upstream to un-contained areas where fluid may flow off the sides of the substrate  50 . The fluid deposition source  700  may also be designed to have a reciprocating feature wherein the direction of the deposition will move through a series of angles  702  to more evenly distribute fluid over the substrate  50 . 
       FIG. 29  also shows that one or more rotational stirring elements  710  and  712  may also be included in the present invention. The stirring elements  710  and  712  may be the same or different size. They may be positioned to create gas or air flow over the bath of fluid covering substrate  50 . This may be helpful in creating convection or flow to more evenly distribute heat uniformly over the substrate  50 . Optionally, the stirring elements  710  and  712  may be fully in or at least partially stirring the fluid over the substrate  50 . They may be configured to rotate in the same or different directions. Other, non-rotation devices may also be used to create liquid flow or gas flow. 
       FIG. 30  shows a still further embodiment wherein there is more than one fluid deposition assembly  720  and  722  which are positioned at locations along the length and/or width of substrate  50 . This may achieve a desired even distribution of fluid over the substrate  50 . Some embodiments may have two or more fluid depositions assemblies. One or more the fluid deposition assembly  720  and  722  may be movable across different angles  702 , similar to that as shown in the embodiment of  FIG. 30 . For any of the embodiments herein, a static or active mixer may be used upstream of the deposition assemblies to mix the fluids together prior to deposition onto substrate  50 . 
     Referring now to  FIG. 31 , yet another aspect of the present invention will now be described.  FIG. 31  shows a conveyor belt  730  with vacuum holes  732  therein to allow for suction of a substrate  50  thereon. This is useful to facilitate transport of the substrate  50  without scratching the underside. The vacuum holes  732  in the belt are suctioned by way of a vacuum source  734 . The conveyor belt  730  may be sized to be the same as or almost the same width as the substrate  50 . Optionally, it may be wider than the substrate  50 . Optionally, belts  730  that are less wide may also be used. The thinner belts  730  may be used to suction down the substrate  50  at various strategic locations. Some embodiments may also use shaped conveyors which provide the desired contour at the edges of the substrate  50 . Such shaped conveyors may have a lip  733  (shown in phantom) that may help to maintain the contour of the substrate  50  being transported by the conveyor. In some embodiments, the conveyor may be made of a thermally conductive material such as but not limited to a metal belt of titanium, stainless steel or the like. Optionally, the conveyor may be made of a polymer or thermally insulating material. 
     Optionally as seen in  FIG. 32A , on some very low surface transport surfaces, instead of using vacuum holes on the belts, the vacuum holes  732  may optionally be formed onto the low-friction surface  738 . In one embodiment, the low-friction surface may be a Teflon® surface. Optionally, it may a surface with a static coefficient of friction between about 0.12 to about 0.20. Optionally, it may a surface with a static coefficient of friction between about 0.10 to about 0.30. This may allow the substrate to be held flat as it is pulled across the transport surface. This may be of particular use since the substrate  50  may be somewhat non-flat after processing. 
     Optionally as seen in  FIG. 32B , on some very low surface transport surfaces, instead of using vacuum holes on the belts, the vacuum channels  733  may optionally be formed onto the low-friction surface  738 . In one embodiment, the low-friction surface may be a Teflon® surface. Optionally, it may a surface with a static coefficient of friction between about 0.12 to about 0.20. Optionally, it may a surface with a static coefficient of friction between about 0.10 to about 0.30. This may allow the substrate to be held flat as it is pulled across the transport surface. This may be of particular use since the substrate  50  may be somewhat non-flat after processing. The channels  733  may be oriented cross-web as shown in  FIG. 32B , and/or optionally, oriented down web (or have both). The channels  733  can be spaced or sized so that the top surface of the web or foil remains sufficiently flat so as to be submerged or covered by the processing fluid. The channels  733  may be full length cross-web so as to keep the entire web width pulled flat against the low-friction surface of the bed. Although the channels  733  and/or the holes  732  are shown in use with a bed that has curved edges, other shapes such as but not limited to flat, convex, concave, or the like are not excluded. If the holes are not spaced correctly, the channels are made across, so all the foil sees the same gap. The suction keeps the foil flat to keep the foil flat. In some embodiments, the bed may be coated with Teflon or other low friction material. 
     Some embodiment may have a belt formed of discrete individual elements or slabs  735  with or without the lip  733  to maintain the curved shape. One nonlimiting example is seen in  FIG. 32C . Each of the elements  735  may be equipped to include force holding elements such as but not limited to vacuum and/or magnetic force to pull the substrate or web against the element  735 . Some embodiments may also include heating elements inside or on the surface of the elements  735  to provide heat to the web. The elements  735  can include any of features shown in  FIGS. 32A-32B  such as channels, holes, curved perimeters, etc. 
     Referring now to  FIG. 33 , a still further aspect of the present invention will now be described. This shows that a substrate  50  may be taken along a path that dips to allow for a bath to be created at recessed area to minimize the loss of process fluid either upstream or downstream. This dip  740  in the path may be achieved through the use of rollers or other web guiding devices to direct the substrate  50  to a lower pathway. The substrate  50  may remain at this lower level and the rise upward vertically or at an angle to rise out of the lower path. 
     Mixing 
     Referring to  FIGS. 34-39 , static and/or active mixers can be used to create laminar and/or turbulent flow in the process fluid as it lies in situ over the substrate being processed. 
     Referring to  FIG. 34 , mechanically stirring of the fluid can be achieved in one embodiment by rotational stirrers, with all the stirrers in line or staggered to mix entire web down web. With circular elements, the waves are different, depending on rpm rotation speed of the stirrer. It should be understood that in other embodiments a stirring arm using linear motion instead of circular motion can be used. Other types of mechanical motion are not excluded for use in stirring the liquid. 
     Some embodiments may use stirring by air, standing waves, and/or other methods for stirring. 
     By way of nonlimiting example, one method of stirring the processing solution involves stirring using process gas flow. In this embodiment, there is gas flow due to pressure differential in the head space above the processing solution. In one embodiment, gas flow with crossweb baffles creates high velocity regions over pre-defined areas of the foil. The narrowing created by the baffles creates high velocity regions in the low-gap areas over the processing solution. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in head space may be at least about 10:1. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 15:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 20:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 30:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 40:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 50:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 75:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the head space may be greater than about 100:1. In some embodiments, the head space may be in the range of 0.5-5 mm, optionally in the range of 1-3 mm, whereas the width of the substrate employed may be in the range of 0.3-2 m. For a 1 mm gap and 1 m wide substrate, the ratio of the wetted workpiece total front surface area to the wetted sealing member total area is about 200 cm/0.2 cm=1000. 
     Stirring by having baffles; a high velocity region in the process zone created by the baffle. 
     Stirring all over the crossweb width helps uniformity. The baffles creates mixing in the solution. In one embodiment, there are many baffles down the web. This keep as much process gas such as but not limited to ammonia. So, the baffles create more obstructions before it reaches exhaust, in addition to creating areas of high velocity. 
     Exhaust pulls the liquid off. Confined headspace opening into a big volume. A pressure reader can be used. 
     The baffles in one embodiment may be staggered cross-web. It could be evenly located across web. Going all the way across is to mitigate loss of ammonia. 
     In some embodiment, edges not getting good coverage by processing solution, so baffling or other mixing devices extending to the edges or all the way across the web can be used. This gives the ammonia longer residence in the head space before it is exhausted. In one non limiting example, the gap between top of fluid and baffle is about 5 mm. In one embodiment, the baffles are on the chamber doors associated with each chamber. 
     Other embodiments may recirculate the processing gas, an inert gas, or other gas for mixing of liquid solution. 
     Other embodiments use sonic vibration for mixing. 
     In one embodiment, vibration of any frequency can be actuated to cause mixing of fluid on the substrate. This can be by vibration of the bed, vibration of the web, contact of vibrations with the solution, contact of vibrations with the bed, contact of vibrations with the process gas above the processing solution, contact of vibrations with the process gas, etc. 
     Some embodiments tune frequency to get wave patterns across solution over the web. This can be designed to create wave only down web or only crossweb. 
     One embodiment for stirring uses the sideways flat arm to create fluid flow. Optionally, another embodiment uses anything that does not contact the web or liquid on the web to create flow or mixing. If it is non contact, vibration may be one of the candidates and can be used alone or with other contact type methods such as mechanical stirring or any of the other embodiments herein. 
     Optionally, one embodiment sets up standing waves in the processing solution on the substrate. If one has standing waves, the standing waves should be changed, else there is more solution at one spot than the other. Thus the embodiments herein will change the standing wave to move to create better uniformity. This changes the peak of the wave. 
     The stirring can be desirable to improve uniformity. The path of the fluid moves more at the areas of the baffles over the substrate which impede process gas flow. Slots may be placed in the baffles, the baffles can extend full length or only part length. Uniformity assistance is desirable, particularly in wide web where there is wide web. 
     Fluid velocity is desirable. Laminar flow and/or turbulent flow can be created. With laminar, it is more difficult to achieve mixing but is not excluded. Some embodiments may include not mixing the bottom. Optionally, some use turbulent flow or other flow that causes mixing that extends directly to the surface of the substrate. Stirring can disrupt stripes from laminar flow in some embodiments. 
     Stirring replenishes chemistry at the surface of the substrate that is being processed. In most embodiments, it is desirable to have chemistry that is refreshed. Possible that the solution is already used, since reactants are used. Some embodiments may use deeper baths or heights of liquid (more than 2 mm on a 1 m wide web) to have more processing liquid over the substrate. Optionally, some may have more than 3 mm on a 1 meter wide web. 
     Optionally, as seen in  FIG. 37 , some could have a second location  700  for injecting more process solution into the web. Optionally, some could be in different chambers or all the same chamber for multiple injection point. This can be useful if the process solution is being used/depleted. Optionally, some embodiments may want to clean the web using a first solution before adding the processing solution at the second location  701 . The first solution may be removed in one embodiment at a washing station before process solution is used at location  701 . Optionally, some do not use a washing station. Optionally, some use the processing solution (un-heated or heated to a level that does not cause reaction or grow of CdS) to clean the web before heating and/or before the second location  701  which introduces more processing solution. Thus in the example for forming CdS, the cleaning solution may be the cadmium solution, the complexing agent (ammonium hydroxide), or thiourea. Some may be single or double combinations of the components. Some may use all three components as the cleaning solution, except at a temperature below that used for processing. 
     Fresh ammonia gas or processing gas: 
     In one nonlimiting example, this could be used as a method of stirring: gas stirring by introducing ammonia. This may involve recirculating gas in the head space that is well sealed or leak free over the heating zones along the process path. 
     Thus, some embodiments add fresh processing gas, which in the case of CdS may be ammonia. This embodiment adds new gas to keep the ammonia saturated along with fresh ammonia or processing solution that may be added to the liquid. This keeps the ammonia atmosphere saturated to keep fresh ammonia solution from degrading as it is being introduced. The ammonia is a complexing solution and a change in concentration can cause too much precipitation of solid in at an undesirable rate. Some embodiments simultaneous introduce new process gas and new process solution. 
     Heating: 
     In some embodiments, the foil or substrate is heated by one more combination of heating sources such as but not limited to heating the bed, which heats the foil, and that causes evaporation. There is another heater which heats the air or gas, which may be above the cover plate of the chamber or inside the chamber. In one embodiment, the temperature set point is higher than the heated bed. 
     Optionally, some embodiments may have “stalactites” or downward protruding condensation structures  900  in the chamber as seen in  FIG. 47 . In one embodiment, these structures are staggered cross web and/or downweb: one row, another row that is offset by 50 percent or some other ratio. Optionally, the structures  900  may be a fin or vane the runs cross web or at angles to create sharp points or thin edges along which condensation may form. This allows for process gas that is condensed to return to the processing solution in the solution over the substrate. This allows the gas to return into the liquid in controlled manner and at a controlled location. It can also create stirring as the condensation droplets create stirring. Some embodiments merely keep the stalactites heated to a lower setpoint relative to the temperature of the vapor. Although active cooling is not excluded, merely keeping the temperature 5% cooler than the surround gas is sufficient in on embodiment to create condensation. Optionally, some embodiments keep the temperature 10% cooler than the surround gas. Optionally, some embodiments keep the temperature 15% cooler than the surround gas. Optionally, some embodiments keep the temperature 20% cooler than the surround gas. Optionally, some embodiments keep the temperature 25% cooler than the surround gas. Optionally, some embodiments keep the temperature 30% cooler than the surround gas. In one embodiment, the condensation is sufficient to keep active reagents reintroduced into the liquid. 
     In one embodiment, it is desirable to control the amount of ammonia or process gas in the head space. Optionally, this amount is equivalent to the vapor pressure of ammonia at the processing temperature (or concentration). The steady state can be the point where no transfer in either direction is occurring (evaporation from solution to vapor or transfer of vapor into the solution). This can be maintained for preset times such as but not limited to 4-5 minutes in the zones that are heated. 
     Ammonia evaporation will occur less where it is less heated or where there is sufficient ammonia in the atmosphere to minimize evaporation. 
     Baffle plate can be used to create circulation. This can be in the atmosphere over the fluid (such as in the muffle) and/or some embodiments may use the baffle plates in contact with the fluid over the substrate. 
     Some embodiments may use different temperature zone in the oven (ramp is from room temperature to hold at 83C, optionally about 90C, optionally about 100C, optionally about 110C, optionally about 120C). Crossweb zones and down web zones can be used. Some embodiment may have systems that are slow ramping. 
     Some embodiments keeping the solution cold to clean the web prior to heating of the web or substrate at the processing bed. 
     In some embodiments, both solutions are in there in the cleaning Optionally, some embodiments just use dilute ammonia hydroxide. 
     This embodiment uses both (inline mixer) which leads to better mixing. Optionally, some clean with one solution, get rid of it, and then introduce both solutions for processing. 
     Seals for Vapor Containment 
     Referring now to  FIGS. 40-44 , containment can be used along the perimeter of the sides of the substrate so that the loss of ammonia is minimized. At the edges of the substrate, edge seals can be used for vapor control to prevent loss out the side of the zone. 
       FIG. 40  shows a cross-sectional view showing the width of the web and that lips  800  can extend into the fluid so that a seal is created by the contact with the liquid (liquid level is indicated by the phantom line). Seals by lips  800  into the fluid do not contact the web, although in some embodiments, such contact is not excluded so long as it does not damage the web or any films formed or forming on the web. The atmosphere  802  is sealed from escaping out the sides. Some embodiments may have specific locations where gas is exhausted out. The lips  800  may extend downweb to extend the sealed zone along the entire processing zone, only along heated zones, or in other select areas. 
     Referring now to  FIG. 41 , another variation of the embodiment of  FIG. 40  shows that seals  804  may be used that seal against the edge of the substrate  50  and extend into atmosphere and close to, but not directly contacting the fluid over the substrate  50 . 
     Referring now to  FIG. 42 , another variation the seals  805  sized to extend into the fluid over the substrate  50 . This allows for the seal against the edge of the substrate at location  806  to be an optional seal. In this manner, there can be variations in the contact without causing a significant loss of seal. In this embodiment, there are at least three different vapor zones  807 ,  808 , and  809  over the fluid on substrate  50 . In one embodiment, the zones  807  and  809  are sized to be significantly smaller than that of the main zone  808 . By way of non-limiting example, the surface areas in zones  807  and  809  are together less than 10% of the total area of all three zones. Optionally, the surface areas in zones  807  and  809  are together less than 5% of the total area of all three zones. Optionally, the surface areas in zones  807  and  809  are together less than 2% of the total area of all three zones. Optionally, the surface areas in zones  807  and  809  are together less than 1% of the total area of all three zones. The material for seals can be one that does not interact with the chemistries in the fluid. Some polymeric or other materials may be coated with Teflon in one embodiment. In one embodiment, the seals  805  extend downweb along the length of the process zone. Optionally, the multiple seals  805  are used on each side to extend downweb along the length of the process zone. In some embodiments, only select portions of the process zone (such as those with areas of high evaporation) have the seals. 
     The seals  805  may be multi-component, such as that described below. Optionally, the seals  805  are fixed while the web or substrate  50  slides against it. Optionally, some embodiments may have moving seals  805  that move at the same rate or other rate relative to the substrate  50 . In some embodiments, the seals  805  create a seal at a first location (at the edge of the foil) and create a second seal at a second location (at the tip that extends into the fluid). Optionally, some embodiments only seal at the second location (in the fluid). Optionally, some seals in the second location and only partially at the first location, due to variance in the edge of foil. 
     Referring now to  FIG. 43 , some embodiments use seals up against the edge of the foil (side or top contact). This can be a moving seal that moves at the pace of the substrate. The end effector  810  can be rubber, silicone, etc., and may be continually fed against the first flexible substrate along the two long edges of the two workpieces or substrates, at a speed that is substantially equal to the linear speed of the substrate. In this case there would be no relative motion between the sealing members  810  and the substrate during processing. Optionally, the member  810  extends fully across the web in on continuous piece and it not just discrete pieces only at the ends. 
     Optionally, it is a seal with the substrate slides against the seal material  810 . Some embodiments may include an accordion structure, compliant section, or spring structure  812  that allows the seal  810  to be pressed against the edge to maintain the integrity of the seal even in location where the substrate may want to disengage. Some seals  810  may be a plurality of discrete elements so each section can press down against the substrate independently so that the contact is not lost. 
       FIG. 44  shows another embodiment wherein the spring for compliance uses an accordion edge seal for a side contact seal  820 . Rubber accordion edge seal  822  is used to laterally push the seal  820  against the side edge of the web or substrate. There is a compliant part and an actual end effector  820 . By way of example and not limitation, the end effector  820  can be a nylon based material or any sufficient to be durable and seal against the substrate. 
     This can be to reduce the amount of solution and also provide a controlled process by prevent leaks from the side of the substrate. These seals can extend along the entire length of the process zones or only in select areas. 
     Referring now to  FIG. 45 , yet another embodiment of the present invention is shown wherein rollers  830  (which rotate or are fixed) can be used to create cross-web sealing of the atmosphere over the process zones. In one embodiment, the rollers  830  can directly contact the substrate, sometimes used to create a vapor seal while also flattening the substrate, although rollers  830  not in direct contact with the substrate  50  are not excluded. Optionally, some such as roller  832  is only in contact with the fluid, but not directly with the substrate  50 . The roller in some embodiments extends beyond the cross-web width of the substrate. Optionally, some are less than the cross-web width such as but not limited to about 95%, 90% or more of the width. 
     Fluid Flow 
     Referring now to  FIG. 46 , it is desirable in some embodiments that there is flow of the fluid relative to the substrate, with relative flow of the fluid away from the deposition site. Without such flow or if the flow is at the same speed as the movement of the substrate (i.e. no relative motion between the two), then the chemistry in the fluid can be depleted without being refreshed by flow of new fluid. It can also create non-uniformities due to lack of mixing of the fluid over the substrate  50 . In some embodiments, only the bed portion or processing zone is angled. Some embodiments may angle the entire apparatus. Some may have portions at one angle and different portions at a different angle. 
     In one embodiment, the primary method for achieving the relative flow is through the tilting or angling of the bed or platform supporting the substrate. This creates an angle that through gravity, will cause a relative flow over the substrate. In one embodiment, the bed is angled to drop 1 inch every 15 yards. Optionally, the angle creates a drop of 1 inch every 12 yards. Optionally, the angle creates a drop of 1 inch every 10 yards. Optionally, the angle creates a drop of 1 inch every 7 yards. Optionally, the angle creates a drop of 1 inch every 5 yards. Optionally, the angle is between one that creates a drop of 1 inch every 15 yards to a drop of inch 1 every 5 yards. 
     Drying 
     Drying is typically at the end of the process: after liquid is removed, the web is heated. This gets the web hot enough to dry surface water, but also absorbed water, such as residual water. Temperature is at least 100C in one embodiment. The web is heated to 100C. Optionally, temperature is at least 120C in one embodiment. The web is heated to 120C. Heater is above and below to heat the web. 
     In one embodiment, IR curing lamp or IR lamps+heat the air more effectively dries the web. Getting the heat into the web can also involve using air that is dried. In some embodiment, it is better to have dried air (not ambient) or ambient controlled to always have a specific humidity or to be in a controlled atmosphere. In this manner, process variability is reduced based on the day to day changes in humidity. 
     Head Space 
     It should be understood that in some embodiments as seen in  FIG. 9 , it is desirable that a low head space is kept above the web or foil. In one embodiment, the interior head space (distance from surface of processing solution to surface of the top of the chamber) is less than about 3 inches. In one embodiment, the interior height of the head space is less than about 2 inches. In one embodiment, the interior height of the head space is less than about 1 inch. In one embodiment, the interior height of the head space is less than about 0.5 inches. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in the chamber or head space may be at least about 10:1. Although not limited to the following, the ratio of the interior width to the interior height at the narrow points in the chamber or head space may be greater than about 10:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the chamber or head space may be greater than about 14:1. Optionally in other embodiments of the invention, the ratio of the interior width to the interior height at the narrow points in the chamber or head space may be greater than about 20:1. Some may be greater than the ratios above but less than 1000:1. Although a muffle is used in this example, it should be understood that other designs using a cover over a U cross-sectional shaped web guide may also be sufficient to create the desired covered tunnel environment. In one embodiment, the height of the head space above the substrate is predetermined based on the processing gas and/or fluid used in that particular zone or area of the processing system. 
     The overall control of the processing atmosphere such as but not limited to the ammonia atmosphere is desirable to control the concentration of active agents in the processing solution. Some advantage of sealing the head space (in addition to or in place of low head space) above the solution, is that then all of the vapor trying to escape is trapped. This enables better control as there is less variability due to escaping material into the vapor. Then the system can run with less solution, since there is tighter control of the solution. There is less need to introduce more fresh solution due to loss from evaporating solution into the uncontrolled atmosphere above the foil. 
     In one embodiment, it is more keeping the head space saturated above the foil, in addition or in place of a low head space. The glass doors or chambers are to be gas tight, leak proof seals. Doors are provided for easy access, maintenance, but some embodiments may not have doors. 
     Optionally, others use rollers to curl the sides of the substrate. By way of non limiting example, it could be along the whole length, key areas, or just at the beginning when the shape. This embodiment plastically deforms the foil. Some do not. 
     While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention. For example, with any of the above embodiments, the present invention may be adapted for use with superstrate or substrate designs. The tool designs of this invention may be used for continuous, in-line processing of substrates which may be in the form of a web or in the form of large sheets such as glass sheets. The substrate may be a continuous web or sheet of a metal or an insulator comprising a precursor layer that has been reacted to form a compound film absorber layer. The present invention is not limited to deposition of junction partner material. By way of nonlimiting example, it may also be used to deposit precursor materials for photovoltaic absorber layers. Optionally, it may be used to deposit materials for use as or precursor materials that form: anti-reflective coatings on cells or modules, moisture barriers on such modules or devices, encapsulant materials, adhesive materials, conductive materials, insulating materials, and/or semiconducting material. The inclination angle of the curved edges may be in the range of 5-15 degrees. The amount of bend at the two long edges of the flexible substrate may be in the range of 2-10 mm, preferably in the range of 3-6 mm 
     Various buffer layers with various chemical compositions have been evaluated in solar cell structures. CdS, ZnS, Zn—S—OH, Zn—S—O—OH, ZnO, Zn—Mg—O, Cd—Zn—S, ZnSe, In—Se, In—Ga—Se, In—S, In—Ga—S, In—O—OH, In—S—O, In—S—OH, etc. are some of the buffer layer materials that have been reported in the literature. Buffer layers for Group IBIIIAVIA devices such as CIGS(S) solar cells may be 5-200 nm thick. 
     In one embodiment, the aqueous CdS deposition bath may be formed by mixing in water 1-50 ml of 1M cadmium salt solution, such as Cd-chloride, Cd-sulfate, Cd-acetate, or the like, 1-50 ml of 14.53 M ammonium hydroxide solution as complexing agent, and 1-50 ml of 1M thiourea as S solution. Another complexing agent solution such as 0.5M Triethanolamine (TEA) may also be added in an amount that is in the range of 1-20 ml, although some embodiments do not use more than one complexing agent. Optionally, the bath may contain (by volume) 5-15% cadmium solution, 5-15% complexing agent (ammonium hydroxide), 5-15% S solution (thiourea) and optionally 5-10% of the additional complexing agent solution (TEA), the balance being the solvent, i.e. water. Some embodiments may use more thiourea in the range of about 15-50%. 
     Homogeneous reactions within such solutions initiate once the temperature is raised, for example, to over 50 C. A bath may be stable for over 5 hours at 20C., whereas large particles may form within minutes in a bath that is heated up to 80C. The above mentioned CdS bath acts in a similar fashion. Since the solution is mostly kept at low temperature for the method of the present invention, it is possible to mix all the ingredients of the solution. In prior art techniques it is customary to mix the Cd source and the complexing agent in the solvent, then heat up the solution to 50C or higher, and then add the S source, at which time reaction and CdS formation starts. 
     For any of the embodiment herein, the substrate may be an elongate material suitable for use in a continuous, roll-to-roll process. Optionally, there may be a carrier on which discrete or pre-cut substrates comprising the precursor layers may be placed. The carrier may then carry these discrete or pre-cut substrates through the processing station(s). The carrier may be the same or a different material from the discrete, pre-cut, or individual substrate. The carrier may be sufficiently pliable to be shaped to create the zone to hold sufficient fluid on the carrier to submerge the discrete or pre-cut substrates in processing fluid. In any of these embodiments, the substrate may be moved continuously at the same or different rate, or optionally in sequential stop and go steps. 
     The heating steps and cooling steps may be repeated either for depositing thicker CdS on the same surface or for depositing CdS on surfaces of new structures introduced into the deposition section in a cyclic or continuous manner. Optionally, some embodiments may use continuous recycling of the solution between the solution container collecting used solution and the deposition section, although intermittent flow of the solution between the deposition section and the solution container may also be utilized. Once the solution is in the recirculating solution container it may be analyzed for its composition and ingredients that may be reduced due to reactions may be added to the solution. Such ingredients include but are not limited to water, ammonia, Cd salt, S source, complexing agent etc. By controlling the solution composition this way, the same solution may be used for coating a large number of structures with CdS without replacing the base solution. This reduces waste and thus cost of the process. The base solution may be occasionally replaced with a fresh one if its impurity content increases to a level that may affect the quality of the deposited CdS film. Removal of particles from the solution may be achieved through filtration using various approaches including centrifuging the solution. The CdS particles thus removed may be re-cycled later to form a Cd source for the process. 
     With regards to the type of various junction partner suitable for use with the present invention, various chemical compositions have been evaluated in solar cell structures. CdS, ZnS, Zn—S—OH, Zn—S—O—OH, ZnO, Zn—Mg—O, Cd—Zn—S, ZnSe, In—Se, In—Ga—Se, In—S, In—Ga—S, In—O—OH, In—S—O, In—S—OH, etc. are some non-limiting examples of possible materials. Such layer maybe in the thickness range of about 5-200 nm thick and may be deposited by various techniques such as evaporation, sputtering, atomic layer deposition (ALD), electrodeposition and chemical bath deposition (CBD), etc 
     In one example, a suitable solution for growing a cadmium sulfide (CdS) layer employs a chemical bath comprising cadmium (Cd) species (from a Cd salt source such as Cd-chloride, Cd-sulfate, Cd-acetate, etc.), sulfur (S) species (from a S source such as thiourea) and a complexing agent (such as ammonia, triethanolamine (TEA), diethanolamine (DEA), ethlene diamine tetra-acetic acid (EDTA), etc) that regulates the reaction rate between the Cd and S species. In one example, the deposition bath may be formed by mixing in water 1-50 ml of 1 M cadmium salt solution, such as Cd-chloride, Cd-sulfate, Cd-acetate, or the like, 1-50 ml of 14.53 M ammonium hydroxide solution as complexing agent, and 1-50 ml of 1M thiourea as S solution. Another complexing agent solution such as 0.5M Triethanolamine (TEA) may also be added in an amount that is in the range of 1-20 ml. A typical bath may contain (by volume) 5-15% cadmium solution, 5-15% complexing agent (ammonium hydroxide), 5-15% S solution (thiourea) and optionally 5-10% of the additional complexing agent solution (TEA), the balance being the solvent, i.e. water. 
     Furthermore, those of skill in the art will recognize that any of the embodiments of the present invention can be applied to almost any type of solar cell material and/or architecture. For example, the absorber layer in solar cell  10  may be an absorber layer comprised of silicon, amorphous silicon, organic oligomers or polymers (for organic solar cells), bi-layers or interpenetrating layers or inorganic and organic materials (for hybrid organic/inorganic solar cells), dye-sensitized titania nanoparticles in a liquid or gel-based electrolyte (for Graetzel cells in which an optically transparent film comprised of titanium dioxide particles a few nanometers in size is coated with a monolayer of charge transfer dye to sensitize the film for light harvesting), copper-indium-gallium-selenium (for CIGS solar cells), CdSe, CdTe, Cu(In,Ga)(S,Se) 2 , Cu(In,Ga,Al)(S,Se,Te) 2 , Cu—In, In—Ga, Cu—Ga, Cu—In—Ga, Cu—In—Ga—S, Cu—In—Ga—Se, other absorber materials, II-VI materials, IB-VI materials, CuZnTe, CuTe, ZnTe, IB-IIB-IVA-VIA absorbers, or other alloys, other absorber materials, IB-IIB-IVA-VIA absorber solar cells, other thing film solar cells, and/or combinations of the above, where the active materials are present in any of several forms including but not limited to bulk materials, micro-particles, nano-particles, or quantum dots. The CIGS cells may be formed by vacuum or non-vacuum processes. The processes may be one stage, two stage, or multi-stage CIGS processing techniques. Additionally, other possible absorber layers may be based on amorphous silicon (doped or undoped), a nanostructured layer having an inorganic porous semiconductor template with pores filled by an organic semiconductor material (see e.g., US Patent Application Publication US 2005-0121068 A1, which is incorporated herein by reference), a polymer/blend cell architecture, organic dyes, and/or C 60  molecules, and/or other small molecules, micro-crystalline silicon cell architecture, randomly placed nanorods and/or tetrapods of inorganic materials dispersed in an organic matrix, quantum dot-based cells, or combinations of the above. Many of these types of cells can be fabricated on flexible substrates. 
     Additionally, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a thickness range of about 1 nm to about 200 nm should be interpreted to include not only the explicitly recited limits of about 1 nm and about 200 nm, but also to include individual sizes such as but not limited to 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc. 
     The publications discussed or cited herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. All publications mentioned herein are incorporated herein by reference to disclose and describe the structures and/or methods in connection with which the publications are cited. For example, U.S. patent application Ser. No. 61/333,241 filed May 10, 2010 is fully incorporated herein by reference for all purposes. 
     While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A”, or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”