ANNEALING MATERIAL AND METHOD FOR ANNEALING PHOTOVOLTAIC DEVICES USING THE ANNEALING MATERIAL - Patent application

Abstract

The present invention relates to an annealing gel and a method for annealing an absorber layer using the annealing gel. A method for annealing an absorber layer includes contacting a surface of the absorber layer with an annealing material provided as a gel, the annealing material including cadmium chloride and a thickener, the gel having a viscosity of 5 millipascal-seconds or greater.

Description

[Technical field]

[0001] This disclosure relates generally to annealing materials and methods for annealing absorbent layers using annealing materials, and more particularly to methods for annealing absorbent layers using annealing materials applied as a gel. [Background technology]

[0002]

[0002] Photovoltaic devices generate power by converting light into electricity using semiconductor materials that exhibit the photovoltaic effect. Semiconductor materials can be annealed to activate dopants, recrystallize polycrystalline semiconductor materials, and increase the grain size of the semiconductor material. Cadmium chloride-based solutions can be applied to semiconductor materials, such as those containing cadmium and tellurium. However, spray application of the solution can be difficult to contain due to atomization. Furthermore, the solution may not even be conducive to application, which can lead to defect formation. Summary of the Invention [Problem to be solved by the invention]

[0003]

[0003] Therefore, a need exists for alternative annealing materials and other methods for annealing absorber layers. [Means for solving the problem]

[0004]

[0004] Embodiments provided herein relate to methods of doping photovoltaic devices with Group V dopants. These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description taken in conjunction with the drawings.

[0005]

[0005] The embodiments illustrated in the Figures are exemplary and representative in nature and are not intended to be limiting of the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following figures, in which like structure is indicated with like reference numerals and in which: [Brief description of the drawings]

[0006] [Figure 1]

[0006] FIG. 1 is a schematic diagram of a photovoltaic device according to one or more embodiments shown and described herein. [Diagram 2]

[0007] FIG. 2 illustrates a schematic diagram of a substrate according to one or more embodiments shown and described herein. [Diagram 3]

[0008] FIG. 1 illustrates a schematic diagram of a photovoltaic device according to one or more embodiments shown and described herein. [Figure 4]

[0009] FIG. 2 illustrates a schematic diagram of a partially formed photovoltaic device according to one or more embodiments shown and described herein. [Diagram 5] FIG. 2 illustrates a schematic diagram of a partially formed photovoltaic device according to one or more embodiments shown and described herein. [Figure 6]

[0010] FIG. 2 illustrates a schematic diagram of a method for implementing a solution-based method for doping an absorber layer with a Group V dopant according to one or more embodiments shown and described herein. [Figure 7] The method 260 may include a process 262 and a process 264 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007]

[0011] Described herein are embodiments of photovoltaic devices that generate electrical power from light. The photovoltaic devices generally include an absorber layer formed from a semiconductor material. The absorber layer may be subjected to one or more processing steps configured to dope the absorber layer with a Group V dopant, such as arsenic or phosphorus. Various embodiments of methods for doping the absorber layer with a Group V dopant are described in more detail herein.

[0008]

[0012] Referring now to FIG. 1, an embodiment of a photovoltaic device 100 is depicted in schematic form. The photovoltaic device 100 may be configured to receive light and convert the light into an electrical signal, e.g., photons may be absorbed from the light and converted into an electrical signal via the photovoltaic effect. Thus, the photovoltaic device 100 may define an energy face 102 configured to be exposed to a light source, e.g., the sun. The photovoltaic device 102 may also define a counter face 104 that is offset from the energy face 102. It should be noted that the term "light" may refer to various wavelengths of the electromagnetic spectrum, e.g., but not limited to, wavelengths in the ultraviolet (UV), infrared (IR), and visible portions of the electromagnetic spectrum. The photovoltaic device 100 may include multiple layers disposed between the energy face 102 and the counter face 104. As used herein, the term "layer" refers to a thickness of material provided on a surface. Each layer may cover all or any portion of the surface.

[0009]

[0013] The photovoltaic device 100 may include a substrate 110 configured to facilitate transmission of light to the photovoltaic device 100. The substrate 110 may be disposed on the energy side 102 of the photovoltaic device 100. With reference collectively to Figures 1 and 2, the substrate 110 may have a first surface 112 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 114 substantially facing the opposite side 104 of the photovoltaic device 100. One or more layers of material may be disposed between the first surface 112 and the second surface 114 of the substrate 110.

[0010]

[0014] The substrate 110 may include a transparent layer 120 having a first surface 122 substantially facing the energy surface 102 of the photovoltaic device 100 and a second surface 124 substantially facing the opposing surface 104 of the photovoltaic device 100. In some embodiments, the second surface 124 of the transparent layer 120 may form the second surface 114 of the substrate 110. The transparent layer 120 may be formed from a substantially transparent material, such as, for example, glass. Suitable glasses include soda-lime glass or any glass with reduced iron content. The transparent layer 120 may have any suitable transmittance, in some embodiments, including from about 250 nm to about 950 nm. The transparent layer 120 may have any suitable percent transmittance, including, for example, greater than about 50% in one embodiment, greater than about 60% in another embodiment, greater than about 70% in yet another embodiment, greater than about 80% in a further embodiment, or greater than about 85% in yet a further embodiment. In one embodiment, the transparent layer 120 may be formed from glass with a percent transmission of about 90%. Optionally, the substrate 110 may include a coating 126 applied to the first surface 122 of the transparent layer 120. The coating 126 may be configured to interact with light or improve the durability of the substrate 110, and may be, for example, but not limited to, an anti-reflective coating, an anti-soiling coating, or a combination thereof.

[0011]

[0015] 1, the photovoltaic device 100 can include a barrier layer 130 configured to mitigate diffusion of contaminants (e.g., sodium) from the substrate 110 that may result in degradation or delamination. The barrier layer 130 can have a first surface 132 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 134 substantially facing the opposing side 104 of the photovoltaic device 100. In some embodiments, the barrier layer 130 can be provided adjacent to the substrate 110. For example, the first surface 132 of the barrier layer 130 can be provided on the second surface 114 of the substrate 100. As used herein, the phrase "adjacent" means that two layers are disposed in contact with no intervening material between at least a portion of the layers.

[0012]

[0016] In general, the barrier layer 130 can be substantially transparent, thermally stable, with reduced pinhole count, high sodium blocking performance, and good adhesion. Alternatively or additionally, the barrier layer 130 can be configured to add color suppression to light. The barrier layer 130 can include one or more layers of suitable materials, including, but not limited to, tin oxide, silicon dioxide, aluminum doped silicon oxide, silicon oxide, silicon nitride, or aluminum oxide. The barrier layer 130 can have any suitable thickness bounded by the first surface 132 and the second surface 134, including, for example, greater than about 500 Å in one embodiment, greater than about 750 Å in another embodiment, or less than about 1200 Å in further embodiments.

[0013]

[0017] With further reference to FIG. 1 , the photovoltaic device 100 can include a transparent conductive oxide (TCO) layer 140 configured to provide an electrical contact for transporting charge carriers generated by the photovoltaic device 100. The TCO layer 140 can have a first surface 142 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 144 substantially facing the opposite side 104 of the photovoltaic device 100. In some embodiments, the TCO layer 140 can be provided adjacent to the barrier layer 130. For example, the first surface 142 of the TCO layer 140 can be provided on the second surface 134 of the barrier layer 130. In general, the TCO layer 140 can be formed from one or more layers of a substantially transparent, wide bandgap n-type semiconductor material. In particular, the wide bandgap can have a larger energy value compared to the energy of the photons of light, and can mitigate undesired absorption of light. The TCO layer 140 may include one or more layers of a suitable material, including, but not limited to, tin dioxide, doped tin dioxide (e.g., F-SnO2), indium tin oxide, or cadmium stannate.

[0014]

[0018] The photovoltaic device 100 may include a buffer layer 150 configured to provide an insulating layer between the TCO layer 140 and any adjacent semiconductor layers. The buffer layer 150 may have a first surface 152 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 154 substantially facing the opposing side 104 of the photovoltaic device 100. In some embodiments, the buffer layer 150 may be provided adjacent to the TCO layer 140. For example, the first surface 152 of the buffer layer 150 may be provided on the second surface 144 of the TCO layer 140. The buffer layer 140 may be formed of any suitable material, including, but not limited to, intrinsic tin dioxide, magnesium zinc oxide (e.g., Zn 1-x Mg x The buffer layer 150 may include a material having a higher resistivity than the TCO layer 140, including SiO2, silicon dioxide (SnO2), aluminum oxide (Al2O3), aluminum nitride (AlN), zinc tin oxide, zinc oxide, tin silicon oxide, or any combination thereof. In some embodiments, the material of the buffer layer 140 may be configured to substantially match the band gap of an adjacent semiconductor layer (e.g., absorber). The buffer layer 150 may have any suitable thickness between the first surface 152 and the second surface 154, including, for example, greater than about 100 Å in one embodiment, between about 100 Å and about 800 Å in another embodiment, or between about 150 Å and about 600 Å in further embodiments.

[0015]

[0019] Referring again to FIG. 1, the photovoltaic device 100 may include an absorber layer 160 configured to cooperate with another layer to form a pn junction within the photovoltaic device 100. Thus, absorbed photons of light can liberate electron-hole pairs, generating carrier flow and generating electrical power. The absorber layer 160 may have a first surface 162 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 164 substantially facing the opposite side 104 of the photovoltaic device 100. A thickness of the absorber layer 160 may be defined between the first surface 162 and the second surface 164. The thickness of the absorber layer 160 may be between about 0.5 μm and about 10 μm, such as between about 1 μm and about 7 μm in one embodiment, or between about 2 μm and about 5 μm in another embodiment.

[0016]

[0020] According to embodiments described herein, the absorber layer 160 may be formed from a p-type semiconductor material having an excess of positive charge carriers, i.e., holes or acceptors. The absorber layer 160 may include any suitable p-type semiconductor material, such as a Group II-VI semiconductor. Specific examples include, but are not limited to, semiconductor materials including cadmium, tellurium, selenium, or any combination thereof. Suitable examples include, but are not limited to, cadmium telluride, ternary compounds of cadmium, selenium, and tellurium (e.g., CdSe x Te 1-x ), or a quaternary compound comprising cadmium, selenium, and tellurium. In embodiments in which the absorber layer 160 comprises selenium and cadmium, the atomic percent of selenium may be greater than about 0 atomic percent and less than about 20 atomic percent. In embodiments in which the absorber layer 160 comprises tellurium and cadmium, the atomic percent of tellurium may be greater than about 30 atomic percent and less than about 50 atomic percent. It should be noted that the atomic percents described herein are representative of the entire absorber layer 160, and that the atomic percent of material at a particular location within the absorber layer 160 may vary with thickness as compared to the overall composition of the absorber layer 160. It should be noted that the concentration of tellurium, selenium, or both may vary throughout the thickness of the absorber layer 160. For example, if the absorber layer 160 comprises a ternary compound of cadmium, selenium, and tellurium (CdSe x Te 1-x ), x may vary within the absorber layer 160 with distance from the first surface 162 of the absorber layer 160. In some embodiments, the value of x may decrease within the absorber layer 160 with distance from the first surface 162 of the absorber layer 160.

[0017]

[0021] According to embodiments provided herein, the dopants in the absorber layer 160 can be activated to a desired charge carrier concentration. In some embodiments, the absorber layer 160 can be doped with a Group V dopant, such as nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), ununpentium (Uup), or combinations thereof. The total dosage of dopants in the absorber layer 160 can be controlled. In some embodiments, the atomic concentration of the Group V dopant in the central region 166 of the absorber layer 160 is about 1×10 16 cm -3 greater, for example, in one embodiment, about 1×10 17 cm -3 ~Approx. 5×10 20 cm -3 and in another embodiment, about 3×10 17 cm -3 ~Approx. 1×10 19 cm -3 or in a further embodiment, between about 5×10 17 cm -3 ~Approx. 5×10 18 cm -3 , etc. The central region 166 is 50% midway through the absorber layer 160 and is offset from each of the first and second surfaces 162, 164 of the absorber layer 160 by 25% of the thickness of the absorber layer 160. Alternatively or in addition, the concentration profile of the Group V dopant may vary through the thickness of the absorber layer 160. In particular, the amount of Group V dopant may vary with distance from the second surface 164 of the absorber layer 160.

[0018]

[0022] With further reference to FIG. 1 , a pn junction may be formed by providing an absorber layer 160 in sufficient proximity to a portion of the photovoltaic device 100 that has an excess of negative charge carriers, i.e., electrons or donors. In some embodiments, the absorber layer 160 may be provided adjacent to an n-type semiconductor material. Alternatively, one or more intervening layers may be provided between the absorber layer 160 and the n-type semiconductor material. In some embodiments, the absorber layer 160 may be provided adjacent to the buffer layer 150. For example, a first surface 162 of the absorber layer 160 may be provided on the second surface 154 of the buffer layer 150.

[0019]

[0023] 3, in some embodiments, the photovoltaic device 200 can include a window layer 170 comprising an n-type semiconductor material. Apart from the window layer 170, the photovoltaic device 200 can have a layer structure substantially similar to the photovoltaic device 100 (FIG. 1). The absorber layer 160 can be formed adjacent to the window layer 170. The window layer 170 can be a window layer 170 that is formed adjacent to the photovoltaic device 200. The window layer 170 may have a first surface 172 substantially facing the energy surface 102 and a second surface 174 substantially facing the opposite surface 104 of the photovoltaic device 200. In some embodiments, the window layer 170 may be disposed between the absorber layer 160 and the TCO layer 140. In one embodiment, the window layer 170 may be disposed between the absorber layer 160 and the buffer layer 150. The window layer 170 may comprise any suitable material including, for example, cadmium sulfide, zinc sulfide, cadmium zinc sulfide, magnesium zinc oxide, or any combination thereof.

[0020]

[0024] 1, the photovoltaic device 100 can include a back contact layer 180 configured to mitigate undesired alterations of the dopants and provide electrical contact to the absorber layer 160. The back contact layer 180 can have a first surface 182 substantially facing the energy front 102 of the photovoltaic device 100 and a second surface 184 substantially facing the opposite surface 104 of the photovoltaic device 100. A thickness of the back contact layer 180 can be defined between the first surface 182 and the second surface 184. The thickness of the back contact layer 180 can be between about 5 nm and about 200 nm, such as between about 10 nm and about 50 nm in one embodiment.

[0021]

[0025] In some embodiments, the back contact layer 180 may be provided adjacent to the absorber layer 160. For example, a first surface 182 of the back contact layer 180 may be provided on the second surface 164 of the absorber layer 160. In some embodiments, the back contact layer 180 may include binary or ternary combinations of materials from Groups I, II, VI, such as one or more layers containing zinc, copper, cadmium, and tellurium in various compositions. Further exemplary materials include, but are not limited to, zinc telluride doped with a dopant (e.g., copper telluride) or zinc telluride alloyed with copper telluride.

[0022]

[0026] The photovoltaic device 100 may include a conductive layer 190 configured to provide electrical contact with the absorber layer 160. The conductive layer 190 may have a first surface 192 substantially facing the energy side 102 of the photovoltaic device 100 and a second surface 194 substantially facing the opposite side 104 of the photovoltaic device 100. In some embodiments, the conductive layer 190 may be provided adjacent to the back contact layer 180. For example, the first surface 192 of the conductive layer 190 may be provided on the second surface 184 of the back contact layer 180. The conductive layer 190 may include any suitable conductive material, such as one or more layers of a nitrogen-containing metal, silver, nickel, copper, aluminum, titanium, palladium, chromium, molybdenum, gold, or the like. Suitable examples of nitrogen-containing metal layers may include aluminum nitride, nickel nitride, titanium nitride, tungsten nitride, selenium nitride, tantalum nitride, or vanadium nitride.

[0023]

[0027] The photovoltaic device 100 may include a back support 196 configured to cooperate with the substrate 110 to form a housing for the photovoltaic device 100. The back support 196 may be disposed on the opposite side 102 of the photovoltaic device 100. For example, the back support 196 may be formed adjacent to the conductive layer 190. The back support 196 may include any suitable material, including, for example, glass (e.g., soda-lime glass).

[0024]

[0028] 1 and 3 collectively, the fabrication of photovoltaic devices 100, 200 generally involves sequentially disposing functional layers or layer precursors into a "stack" of layers through one or more processes including, but not limited to, sputtering, spraying, evaporation, molecular beam deposition, pyrolysis, closed space sublimation (CSS), pulsed laser deposition (PLD), chemical vapor deposition (CVD), electrochemical deposition (ECD), atomic layer deposition (ALD), or vapor transport deposition (VTD). Once a layer is formed, it may be desirable to modify the physical properties of the layer through subsequent treatment processes.

[0025]

[0029] 4 and 5 collectively, a layer of annealing material 210 may be applied to the first surface 162 or the second surface 164 of the absorber layer 160 of the partially formed device. For example, the partially formed photovoltaic device 212 may include the absorber layer 160 adjacent to a layer stack 214. The layer stack 214 may include one or more of the layers of the photovoltaic device 100, 200 (FIGS. 1 and 3) disposed between the absorber layer 160 and the energy surface 102. Alternatively, the partially formed photovoltaic device 216 may include the absorber layer 160 adjacent to a layer stack 218. The layer stack 218 may include one or more of the layers of the photovoltaic device 100, 200 (FIGS. 1 and 3) between the absorber layer 160 and the opposing surface 104.

[0026]

[0030] According to embodiments provided herein, the annealing material 210 may be provided as a gel including cadmium chloride (CdCl2) and a thickening agent. The thickening agent may be configured to control the viscosity of the gel. For example, a gel formed using cadmium chloride (CdCl2) and a thickening agent may have a viscosity of about 5 millipascal seconds (mPa·s) or more, such as about 5 millipascal seconds (mPa·s) or more to about 250 millipascal seconds (mPa·s) or less in one embodiment, or about 10 millipascal seconds (mPa·s) or more to about 25 millipascal seconds (mPa·s) or less in another embodiment. Suitable thickening agents include, but are not limited to, methylcellulose, hydroxypropyl methylcellulose, corn starch, tapioca starch, guar gum, propylene glycol, or any other material with comparable alkali content.

[0027]

[0031] According to embodiments provided herein, the ratio of cadmium chloride (CdCl2) to thickener in the annealing material 210 can be 1:1 or greater, such as from about 1:1 or greater to about 160:1 or less in one embodiment, and from about 10:1 or greater to about 30:1 or less in another embodiment, based on the weight of the gel form. In other embodiments, such as, but not limited to, a thickener comprising propylene glycol, the ratio of cadmium chloride (CdCl2) to thickener in the annealing material 210 can be about 0.1:1 or greater, such as from about 0.1:1 or greater to about 2.5:1 or less in one embodiment, based on the weight of the gel form.

[0028]

[0032] 6, a system 220 for applying an annealing material 210 to a partially formed photovoltaic element 212 is depicted in schematic form. The system 220 may include a roll applicator 222 configured to apply a substantially uniform coating of gel onto the partially formed photovoltaic element 212. It is noted that while this example is provided with respect to the partially formed photovoltaic element 212, the system 220 may be used to apply gel to the partially formed photovoltaic element 216. The roll applicator 222 may include an application roller 224 for transferring the annealing material 210 to the partially formed photovoltaic element 212 as the partially formed photovoltaic element 212 is moved along a conveying direction 226. In some embodiments, the roll applicator 222 may further include a doctor roller 228 and a counter pressure roller 230. A reservoir for holding the annealing material 210 may be bounded by the doctor roller 228 and the application roller 224. The reservoir 229 may be supplied with the annealing material via a holding tank 232. For example, the holding tank 232 may cooperate with one or more pumps 234 to move the annealing material 210 through a flow path to the reservoir 229.

[0029]

[0033] The pressure, spacing, or both of the doctor roller 228 relative to the application roller 224 can control the amount of annealing material 210 transferred to the application roller 224. The surfaces of the doctor roller 228 and the application roller 224 can be smooth or rigid, and soft or hard. The surfaces of the doctor roller 228 and the application roller 224 need not be identical. For example, the doctor roller 228 can be flexible and rigid, while the application roller 224 can be hard and smooth. Alternatively, the application roller 224 can be flexible and rigid, while the doctor roller 228 can be hard and smooth. The counter pressure roller 230 can be configured to support the partially formed photovoltaic elements 212 (e.g., from the energy side 102 (FIG. 1)) and move the partially formed photovoltaic elements 212 along the direction of conveyance 226.

[0030]

[0034] According to embodiments provided herein, the roll coater 222 may be configured to recirculate the overflow of the annealing material 210 from the partially formed photovoltaic elements 212. In particular, the roll coater 222 may include a collector 236 located proximate to the partially formed photovoltaic elements 212. In some embodiments, the collector 236 is located below the application roller 224 and sized to correspond with the partially formed photovoltaic elements 212 to receive the overflow of the annealing material 210 from the ends of the partially formed photovoltaic elements 212. The overflow of the annealing material 210 captured by the collector 236 may be recirculated. For example, one or more pumps 234 may move the annealing material 210 through a flow path to a storage tank 232.

[0031]

[0035] With further reference to FIG. 6, the system 220 may include a material sensor 240 for detecting the density of the annealing material 210. In some embodiments, the material sensor 240 may directly contact the annealing material 210. For example, the material sensor 240 may be located proximate to the application roller 224, such as in the reservoir 229, or along the flow path of the annealing material 210. Alternatively or additionally, the material sensor 240 may be located at any point in the roll applicator 222, such as, but not limited to, in the flow path, the collector 236, the storage tank 232, or any combination thereof. The material sensor 240 may include any device that measures a physical quantity of the annealing material 210 and converts the detected quantity into a signal representative of the viscosity or density of the annealing material 210. It should be noted that the term "signal" may refer to a waveform (e.g., electrical, optical, magnetic, or electromagnetic) that can travel through a medium, such as DC, AC, sine wave, triangle wave, square wave, etc. Suitable examples of material sensor 240 include a viscometer, a tuning fork oscillator, a resonator, or the like.

[0032]

[0036] According to embodiments provided herein, the system 220 may include a metrology sensor 241 for detecting a thickness of the annealing material 210 applied to the partially formed photovoltaic element 212. In some embodiments, the metrology sensor 241 may be configured to measure a dimension of the annealing material 210 without changing the dimension of the annealing material. For example, the metrology sensor 241 may be disposed proximate to the roll coater 222 and configured to make a non-contact measurement of the annealing material 210 as it is applied by the roll coater 222. The metrology sensor 241 may include any device that measures a physical quantity of the annealing material 210 and converts the detected quantity into a signal indicative of a dimension of the annealing material 210. Thus, the metrology sensor may include a source and detector configured for photometry, radiometry, or the like.

[0033]

[0037] The system 220 may include a conveying system 242 configured to move the partially formed photovoltaic elements 212 along a conveying direction 226. In general, the conveying system 242 may include support elements, such as rollers, belts, or the like. Additionally, the conveying system 242 may include one or more actuators configured to control the movement of the support elements. The support elements may be configured to transmit forces from the one or more actuators to the partially formed photovoltaic elements 212. Thus, the support elements and the one or more actuators may cooperate to cause a desired movement of the partially formed photovoltaic elements 212.

[0034]

[0038] 4, 5 and 6 collectively, the system 220 may include a film induction heater 244 configured to convert the annealing material 210 from a gel to a film. The film induction heater 244 may be positioned along the direction of conveyance 226 after the roll applicator 222. The film induction heater 244 may be a relatively low temperature heater configured to heat the annealing material 210 by providing a zone or environment having a temperature of about 85° C. or higher, such as about 90° C. or higher to about 200° C. or lower in one embodiment, or about 100° C. or higher to about 150° C. or lower in another embodiment. Thus, the partially formed photovoltaic elements 212, 216 may be heated to a temperature of greater than 25° C., such as about 30° C. or higher to about 60° C. or lower in one embodiment. The film induction heater 244 may include any heating means, such as, but not limited to, radiant infrared, electricity, fuel-burned convection, forced air, or combinations thereof.

[0035]

[0039] In some embodiments, the system 220 may include a processing chamber 246 configured to provide a pressure and temperature controlled environment to facilitate annealing of the absorber layer 160 using the annealing material 210. Generally, the processing chamber 246 may be disposed along the direction of conveyance 226 after the film induction heater 244 and the roll coater 222. Note that in some embodiments, the film induction heater 244 may be omitted. In some embodiments, the processing chamber 246 may be configured to maintain a controlled pressure environment having a low vacuum pressure (between about 25 Torr and about 760 Torr), such as in one embodiment about 200 Torr to about 800 Torr. Alternatively, the processing chamber 246 may be configured to maintain a pressure greater than ambient pressure, i.e., greater than about 760 Torr. Generally, the partial pressures of the component gases of the environment may be controlled. For example, in some embodiments, the partial pressures of any inert gas and reducing gas may be controlled. As used herein, the reducing gas may be more energetically favorable for oxidation than the dopants of the absorber layer 160, i.e., the oxidation reaction of the reducing gas may have a more negative Gibbs free energy change (ΔG) than the dopants. Additionally, the processing chamber 246 may be configured to maintain an annealing temperature between about 350° C. and about 650° C.

[0036]

[0040] According to embodiments described herein, the system 220 can include one or more processors 250 communicatively connected to any of the functional components of the system 220, which are depicted diagrammatically as double arrowed lines in FIG. 6. For example, the one or more processors 250 can be communicatively connected to at least one of the roll applicator 222, the material sensor 240, the metrology sensor 241, the conveying system 242, the film induction heater 244, and the process chamber 246. As used herein, a processor can be any device capable of executing machine-readable instructions. Thus, each one or more processors 250 can be a controller, an integrated circuit, a microchip, a computer, or other computing means. The one or more processors 250 can be configured to execute logic or software and perform functions to control the functions of the system 220. Additionally, the one or more processors 250 can be communicatively connected to a memory device 252, which can store logic and / or inputs received by the one or more processors 250. The storage device 252 described herein may be RAM, ROM, flash memory, a hard drive, or any means for storing machine-readable instructions.

[0037]

[0041] Embodiments of the present disclosure may be implemented as machine-readable instructions or any generation (e.g., 1 The system 220 includes logic, including algorithms written in any programming language (e.g., GL, 2GL, 3GL, 4GL, or 5GL), such as a machine language that can be executed directly by a processor, or an assembly language, object-oriented programming (OOP), scripting language, microcode, etc. Alternatively, the logic or algorithms can be written in a hardware description language (HDL), such as logic implemented via a field programmable gate array (FPGA) configuration or an application specific integrated circuit (ASIC), and the like. Thus, the logic can be implemented in any conventional computer programming language, as a preprogrammed hardware element, or as a combination of hardware and software components. The logic can be configured such that, when executed by the one or more processors 250, the system 220 acts to automatically move the partially formed photovoltaic device 212 and control the roll applicator 222, the conveying system 242, the film induction heater 244, and the process chamber 246. In some embodiments, the one or more processors 250 can receive signals from the material sensor 240, the metrology sensor, or both. Thus, the one or more processors 250 can automatically adjust parameters of the roll coating apparatus 222, such as, but not limited to, the spacing between the application roller 224 and the doctor roller 228, the pressure between the application roller 224 and the doctor roller 228, the spacing between the application roller 224 and the partially formed photovoltaic element 212, the pressure between the application roller 224 and the partially formed photovoltaic element 212, or the speed of the partially formed photovoltaic element 212 relative to the application roller 224, to achieve a desired application amount.

[0038]

[0042] Referring now to FIG. 7, a method 260 of annealing is depicted using the annealing material 210 provided as a gel. Referring collectively to FIGS. 4, 5, 6, and 7, the method 260 may include a process 262 for contacting the absorbent layer 160 with the annealing material 210. In some embodiments, the annealing material 210 may be applied as a gel to the first surface 162 or the second surface 164 of the absorbent layer 160. In particular, the annealing material 210 may be rolled onto the absorbent layer 160 using a roll applicator 222. For example, the annealing material 210 may be directly rolled, i.e., directly contacted in one continuous layer between the application roller 224 and the absorbent layer 160. As noted above, the viscosity of the gel of the annealing material 210 may be controlled. It is believed that rolling the annealing material 210 directly onto the absorber layer 160 may reduce the sensitivity of the second surface 164 or first surface 162 of the absorber layer to atmospheric impurities as compared to spray application.

[0039]

[0043] In some embodiments, the annealing material 210 can be mixed into a solution that is converted into a gel before being rolled onto the absorber layer 160 as a gel. For example, cadmium chloride (CdCl2) and a thickener can be mixed together with water to form a solution. In some embodiments, the cadmium chloride (CdCl2) and the thickener can be mixed in dry form before adding the mixture to water to form a solution. Alternatively, the cadmium chloride (CdCl2) and the thickener can be added to the water before being mixed together to form a solution. In some embodiments, the solution of the annealing material 210 can be mixed at a mixing temperature that is higher than the application temperature of the gel of the annealing material 210, i.e., the temperature of the solution can be higher than the temperature of the gel during application. In some embodiments, the mixing temperature to the application temperature can have a ratio of at least 2:1.

[0040]

[0044] Additionally, the density of the annealing material 210 may be maintained within a desired range. Specifically, the density of the annealing material 210 may be measured using the material sensor 240. The measurements may be used to automatically determine whether the annealing material has a density within a desired range for an application. A gel may be used to determine the density of the annealing material 210. If the density is acceptable, the annealing material may be applied to the absorber layer 160. If the density is outside the desired range, the roll application of the annealing material 210 may be stopped. In some embodiments, the gel is applied only if the density is measured within the desired range. Alternatively or additionally, the amount of annealing material applied may be automatically controlled using signals provided by the material sensor 240 and the metrology sensor 241. Without being bound by theory, it is believed that application of the annealing material 210 as a gel may improve containment of cadmium chloride (CdCl2) compared to a liquid-based application. Additionally, by maintaining the density of the annealing material 210 within the desired range, the uniformity and transfer efficiency of the average application of the annealing material 210 may be improved.

[0041]

[0045] 4, 5, 6 and 7 collectively, the method 260 may include a process 264 for annealing the absorber layer 160 in the processing chamber 246. Generally, annealing involves heating the absorber layer 160 (e.g., a polycrystalline semiconductor material) for a sufficient time and at a sufficient temperature to promote recrystallization of the absorber layer 160. For example, the absorber layer 160 may be treated at a temperature between about 350° C. and about 650° C. for a period of about 5 minutes to about 60 minutes, such as, in one embodiment, at a temperature in the range of about 400° C. to about 600° C. for a period of about 10 minutes to about 55 minutes. In addition to recrystallization of the absorber layer 160, the presence of cadmium chloride (CdCl2) and the diffusion of chlorine into the absorber layer 160 may result in grain growth in the absorber layer 160, i.e., an increase in the size of the grains of the absorber layer 160.

[0042]

[0046] Optionally, the annealing material 210 can be dried into a substantially continuous film prior to annealing the absorber layer 160. For example, the annealing material 210 can be heated by a film induction heater 244 to convert it from a gel to a film. In some embodiments, a thickener can act to bind the annealing material 210 together and bond the annealing material 210 to the absorber layer 160. Thus, the film formation can further enhance containment of the cadmium chloride (CdCl2) compared to an application without a thickener, which may instead produce a more chalky cadmium chloride (CdCl2) layer. In some embodiments, the ratio of cadmium chloride (CdCl2) to thickener in the film of the annealing material 210 can be 0.1:1 or more, such as from about 1:1 or more to about 160:1 or less in one embodiment, from about 10:1 or more to about 30:1 or less in another embodiment, on a weight basis.

[0043]

[0047] Moreover, the dosage of the film of annealing material 210 can be controlled, i.e., by adjusting components of the roll coater 222 based on signals provided by the material sensor 240, the metrology sensor 241, or both. A desirable range for the dosage of the film of annealing material 210 is about 0.15 mg / cm 2 or more, for example, about 0.16 mg / cm in one embodiment 2 More than ~1.20mg / cm 2 In another embodiment, 2 More than ~about 0.5mg / cm 2 or less than about 0.175 mg / cm in further embodiments 2 More than ~0.25mg / cm 2 The following are possible:

[0044]

[0048] It should now be understood that the embodiments provided herein relate to annealing gels and methods of annealing absorber layers using annealing gels. The annealing gels can be used to improve the overall annealing process compared to alternative cadmium chloride (CdCl2) materials. For example, the annealing gels can cover about 25% more absorber surface area per unit volume of cadmium chloride (CdCl2) compared to sprayed solutions. Furthermore, the annealing gel-based methods described herein can form a substantially more uniform layer of annealing material on the surface of the absorber layer. Tests have demonstrated an improvement of about 35% in the coefficient of variation (CV) of the thickness of the layer of annealing material rolled as a gel compared to the thickness of the layer of annealing material sprayed as a solution. Moreover, using the gel-based methods described herein, the annealing material has demonstrated a greater coverage of the layer by cadmium chloride (CdCl2). In particular, surface images of the sprayed solution demonstrated less CdCl2 coverage (percent of pixels corresponding to CdCl2) displayed on a 100 μm scale than the comparative sample of roll-coated gel displayed on a 10 μm scale. Thus, the lower resolution image (100 μm scale) captured more voids per image element than the higher resolution image (10 μm scale), which corresponds to more and larger voids for the sprayed solution compared to the roll-coated gel.

[0045]

[0049] According to an embodiment of the present disclosure, a method of annealing an absorber layer may include contacting a surface of the absorber layer with an annealing material provided as a gel. The absorber layer may include cadmium and tellurium. The annealing material may include cadmium chloride and a thickener. The viscosity of the gel of the annealing material may be 5 millipascal seconds or greater. The method may include annealing the absorber layer with the annealing material in contact with the surface of the absorber layer.

[0046]

[0050] In some embodiments, the gel of the annealing material may contain cadmium chloride and a thickening agent. The viscosity of the gel of the annealing material may be 5 millipascal seconds or greater.

[0051] According to embodiments provided herein, a partially formed photovoltaic device may include an absorber layer and a film of annealing material. The absorber layer may include cadmium and tellurium. The film of annealing material may be in direct contact with a surface of the absorber layer. The application rate of the film of annealing material is 0.15 mg / cm 2 The film of annealing material may include cadmium chloride and a thickener. The ratio of cadmium chloride to thickener in the film of annealing material may be, by weight, 0.1:1 or greater.

[0047]

[0052] It should be noted that the terms "substantially" and "about" may be utilized herein to express the inherent degree of uncertainty that may result from any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to express the degree to which a quantitative representation may vary from the stated standard without resulting in a change in the basic functionality of the subject matter at issue.

[0048]

[0053] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications can be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter. [Mode of the invention] [1] 1. A method of annealing an absorber layer, comprising: contacting the surface of the absorber layer with an annealing material provided as a gel, the absorber layer comprises cadmium and tellurium; the annealing material comprises cadmium chloride and a thickener; The gel viscosity of the annealing material is 5 millipascal seconds or more; And, Annealing the absorber layer with an annealing material in contact with a surface of the absorber layer. A method comprising: [2] measuring the gel of the annealing material with the material sensor; transmitting a signal to one or more processors communicatively connected to the material sensor, where the signal is indicative of a viscosity of the gel of the annealing material; and automatically determining, with one or more processors, a density of the gel of the annealing material, where the surface of the absorber layer contacts when the viscosity of the gel of the annealing material is greater than or equal to 5 millipascal seconds; 2. The method according to claim 1, comprising: [3] 2. The method of claim 1, wherein the material sensor comprises a tuning fork oscillator. [4] 2. The method of claim 1, comprising roll-coating the surface of the absorber layer with a gel of the annealing material. [5] 5. The method of claim 4, wherein the surface of the absorbent layer is in direct contact with the application roller. [6] capturing gel overflow of annealing material from the absorbent layer; and Recirculating the gel of entrapped annealing material to the application roller. 6. The method according to claim 5, comprising: [7] 2. The method of claim 1, comprising converting the gel of annealing material into a film of annealing material by heating the gel of annealing material prior to annealing the absorber layer. [8] 8. The method according to claim 7, wherein the gel is heated to a temperature of 30°C or more and 60°C or less. [9] The application amount of the annealing material film was 0.15 mg / cm 2 The method according to claim 7,

[10] 8. The method of claim 7, wherein the ratio of cadmium chloride to thickener in the film of annealed material is 1:1 or greater by weight.

[11] mixing a solution of annealing material at a mixing temperature; converting the solution of annealing material into a gel of annealing material before the surface of the absorber layer contacts the gel of annealing material, The gel of the annealing material is at the application temperature, and The application temperature is below the mixing temperature; 2. The method according to claim 1, comprising:

[12] The ratio of cadmium chloride to thickener in the gel of the annealing material is 1:1 or more by weight. 2. The method according to claim 1.

[13] 2. The method of claim 1, comprising exposing the absorber layer to a reducing environment while annealing the absorber layer.

[14] 2. The method according to claim 1, wherein the absorber layer is annealed at a temperature between 350° C. and 650° C. for a period between 5 minutes and 60 minutes.

[15] 2. The method of claim 1, wherein the thickening agent is methylcellulose.

[16] 2. The method of claim 1, wherein the viscosity increasing agent is hydroxypropyl methylcellulose.

[17] 2. The method of claim 1, wherein the thickening agent comprises propylene glycol and the ratio of cadmium chloride to propylene glycol in the gel of the annealing material is 0.1:1 or greater by weight.

[18] 1. A gel of an annealing material comprising cadmium chloride and a thickening agent, wherein the viscosity of the gel of the annealing material is 5 millipascal seconds or greater.

[19] A partially formed photovoltaic device, comprising: an absorber layer comprising cadmium and tellurium; and a film of annealing material directly on the surface of the absorber layer, where The applied amount of the annealing material film was 0.15mg / cm 2That's all. the film of annealing material comprising cadmium chloride and a thickener; The ratio of cadmium chloride to thickener in the film of annealed material is 0.1:1 or more by weight; A photovoltaic element comprising:

[20] 3. The method of claim 1 or 2, wherein the material sensor comprises a tuning fork oscillator. [twenty one] 21. The method of any of 1, 2 and 20, comprising roll-coating a surface of the absorbent layer with a gel of the annealing material. [twenty two] 22. The method of claim 21, wherein the surface of the absorbent layer is in direct contact with the application roller. [twenty three] capturing gel overflow of annealing material from the absorbent layer; and Recirculating the gel of entrapped annealing material to the application roller. 23. The method of claim 22, comprising: [twenty four] 24. The method of any of 1, 2 and 20 to 23, comprising converting the gel of annealing material into a film of annealing material by heating the gel of annealing material prior to annealing the absorber layer. [twenty five] 25. The method of claim 24, wherein the gel is heated to a temperature of 30°C or more and 60°C or less.

[26] The applied amount of the annealing material film was 0.15mg / cm 2 26. The partially formed photovoltaic element according to any one of 1, 2, 24 and 25 or 19,

[27] 27. The method of any one of 1, 2 and 24 to 26, or 19 or 26, wherein the ratio of cadmium chloride to thickener in the film of annealed material is 1:1 or more by weight. 2. A partially formed photovoltaic device as described in claim 1.

[28] mixing the solution of annealing material at a mixing temperature; and converting the annealing material solution into an annealing material gel before the surface of the absorber layer contacts the annealing material gel, The annealing material gels at the application temperature; The application temperature is below the mixing temperature; 28. The method according to any one of 1, 2 and 20 to 27, comprising:

[29] 29. The method according to any one of 1, 2 and 20 to 28 or the gel according to 18, wherein the ratio of cadmium chloride to thickening agent in the gel of the annealing material is 1:1 or more by weight.

[30] 30. The method of any of 1, 2 and 20 to 29, comprising exposing the absorber layer to a reducing environment while annealing the absorber layer.

[31] 31. The method of any of 1, 2 and 20 to 30, wherein the absorber layer is annealed at a temperature between 350° C. and 650° C. for a period between 5 minutes and 60 minutes.

[32] 32. The method of any one of 1, 2 and 24 to 31, the partially formed photovoltaic device of any one of 19, 26 and 27 or the gel of 18 or 29, wherein the thickening agent is methylcellulose.

[33] 32. The method of any one of 1, 2 and 24 to 31, the partially formed photovoltaic device of any one of 19, 26 and 27 or the gel of 18 or 29, wherein the thickening agent is hydroxypropyl methylcellulose.

[34] 32. The method of any one of 1, 2 and 24 to 31 or the gel of 18 or 29, wherein the thickening agent comprises propylene glycol and the ratio of cadmium chloride to propylene glycol in the gel of the annealing material is 0.1:1 or more by weight.

Claims

1. 1. A method for producing an absorber layer for a photovoltaic device, comprising the steps of: providing an absorbent layer on the layer stack, wherein a first surface of the absorbent layer is adjacent to the layer stack; Preparing an annealing material comprising cadmium chloride and a thickener, The weight ratio of the cadmium chloride to the thickener in the annealing material is 0.1:1 or more and 160:1 or less; the viscosity increasing agent comprises at least one of methylcellulose, hydroxypropyl methylcellulose, or propylene glycol; and the annealing material has a viscosity in the range of 5 to 250 millipascal seconds; applying a coating of said annealing material provided as a gel to a second surface of said absorber layer, the absorber layer comprises cadmium and tellurium, and the absorber layer is doped with a Group V dopant; drying the annealing material applied to the absorber layer to form a film having a density per unit area in the range of 0.15 mg / cm 2 to 1.20 mg / cm 2 ; and treating the absorber layer by heating the absorber layer with the annealing material in contact with the second surface of the absorber layer, whereby the absorber layer recrystallizes and chlorine diffuses from the annealing material into the absorber layer. A method comprising:

2. 10. The method of claim 1, wherein treating the absorber layer comprises heating the absorber layer with the film in contact with the second surface of the absorber layer at an annealing temperature in the range of 350° C. to 650° C. for 5 minutes to 60 minutes.

3. The coating weight is 0.175 mg / cm ２ ~0.5mg / cm ２ The method of claim 1, wherein

4. measuring the viscosity of the gel of the annealing material with a material sensor; transmitting a signal to one or more processors communicatively coupled to the material sensor, wherein the signal is indicative of the viscosity of the gel of the annealing material; and automatically determining, with the one or more processors, a density of the gel of the annealing material, where the surface of the absorbent layer contacts when the viscosity of the gel of the annealing material is greater than or equal to 5 millipascal-seconds; The method of claim 1 , comprising:

5. The method of any of claims 1 to 4, wherein the gel of the annealing material has a viscosity of 10 millipascal seconds or greater.

6. contacting a second surface of the absorbent layer with an application roller; capturing overflow of the gel of the annealing material from the absorbent layer; and recirculating the gel of entrapped annealing material to the application roller. The method of claim 1 , comprising:

7. 10. The method of claim 1, wherein drying the gel of annealing material applied to the absorbent layer comprises heating the gel to a temperature of 30°C or more and 60°C or less.

8. The method of any of claims 1 to 7, comprising exposing the absorber layer to a reducing environment while annealing the absorber layer during the step of treating the absorber layer.

9. The method according to any one of claims 1 to 8, wherein the thickening agent is methylcellulose.

10. The method according to any one of claims 1 to 8, wherein the thickening agent is hydroxypropyl methylcellulose.

11. The method of any one of claims 1 to 8, wherein the thickening agent comprises propylene glycol.

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