FIELD OF INVENTION
[0002] The invention disclosed herein relates, in general, to photovoltaic devices such as solar cells. More specifically, the present invention relates to thin film solar cells.
BACKGROUND
[0003] A solar cell is a device that converts solar energy into electrical energy due to the presence of photoactive semiconductor layers. These photoactive semiconductor layers can include layers of p-doped semiconductor, i-doped semiconductor, and n-doped semiconductor. These photoactive semiconductor layers are capable of generating excitons, i.e., bound electron-hole pairs, on receiving solar energy in the form of light. These electron-hole pairs dissociate into charge carrying electrons and holes, and thereby generate electricity. An anode layer and a cathode layer are provided on sides of the photoactive layers to collect these charge carriers and utilize them in external electric circuits in the form of current.
[0004] The efficiency of a solar cell is significantly determined by its ability to capture maximum amount of incident solar light and convert this into electrical energy. One of the main ways to improve efficiency of a solar cell is to manufacture the solar cell using schemes that reduce reflection of light and/or enhance path of light through the solar cell, therefore enhancing the chances of absorption of light by the solar cell.
[0005] For crystalline silicon solar cells, the efficiency of the solar cells is generally enhanced by application of an antireflection coating and/or by texturing the surface of the crystalline silicon solar cell. A quarter wavelength antireflection coating with suitable refractive index makes use of interference effects that lead to extinction of a certain wavelength while a texture increases the chance of absorption by multiple reflections within the texture. [0006] In case of thin film solar cells, enhancing the efficiency of the solar cell is a tougher task as compared to crystalline silicon solar cells. Currently, efficiency of the thin film solar cells is enhanced by providing a random nano-texture with a texture size of around 50-200 nm on substrates or superstates of the thin film solar cells. This random nano-texture scatters the incident light, and hence, increases the optical path length of light, and this leads to more absorption of light by the semiconductor layers of the thin film solar cells.
[0007] Generally, these random nano-textures are native textures caused by specific growth conditions which is often the case for Atmospheric Pressure Chemical Vapor Deposition (APCVD) grown SnC^F or Low-Pressure Chemical Vapor Deposition (LPCVD) grown ZnO:Al. In other cases, these random nano-textures are created by a post-deposition processing step like HC1 etching of sputtered ZnO:Al.
[0008] The drawback of these random nano-textures is that the parameters of these nano-textures cannot be changed easily and independently, as they are dependent on the type of materials used and the process parameters. Also, it is not possible to independently optimize the nano-texture parameters for maximum light-trapping in a given solar cell layer stack design. [0009] Using substrates or superstrates that have an optimized periodic nano-texture can have a significant effect on the efficiency of the thin film solar cells because this periodic nano-texture enhances trapping of light by the solar cell by also using diffraction next to scattering. A periodic nano-structure can be deposited on substrates or superstrates by use of lacquers and sol-gel materials. However, the problem with these materials is that they tend to contaminate the semiconductor layers of solar cells by solvents released by these materials during manufacturing of solar cell. Another problem with the use of lacquers and sol-gel materials is that their adhesion with the Transparent Conductive Oxide (TCO) layer can be less than the adhesion between, for example, glass substrate or superstrate and the TCO layer.
[0010] In light of the above discussion, there is a need for an improvement in the current thin film solar cells in order to eliminate the drawbacks of the prior art. BRIEF DESCRIPTION OF FIGURES
[0011] The features of the present invention, which are believed to be novel, are set forth
with particularity in the appended claims. The invention may best be understood by reference to
the following description, taken in conjunction with the accompanying drawings. These
drawings and the associated description are provided to illustrate some embodiments of the
invention, and not to limit the scope of the invention.
[0012] FIG. 1 is a diagrammatic illustration of various components of an exemplary
photovoltaic device according to an embodiment of the present invention;
[0013] FIG. 2 is a flow chart describing an exemplary method of manufacturing a
photovoltaic device, in accordance with an embodiment of the present invention; and
[0014] FIG. 3 is a flow chart describing a method manufacturing a photovoltaic device, in
accordance with another embodiment of the present invention.
[0015] Those with ordinary skill in the art will appreciate that the elements in the figures are
illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the
dimensions of some of the elements in the figures may be exaggerated, relative to other
elements, in order to improve the understanding of the present invention.
[0016] There may be additional structures described in the foregoing application that are not
depicted on one of the described drawings. In the event such a structure is described, but not
depicted in a drawing, the absence of such a drawing should not be considered as an omission of
such design from the specification.
SUMMARY
[0017] The instant exemplary embodiments provide a photovoltaic device for photoelectric conversion of incident solar light.
[0018] Some embodiments of the present invention provide a method for manufacturing a photovoltaic device.
[0019] In some embodiments, a photovoltaic device for photoelectric conversion of incident solar light is provided. The photovoltaic device includes a transparent substrate having a substantially flat surface. Further, the photovoltaic device includes a layer of a viscous curable material deposited on the flat surface of the transparent substrate to form a texture on a surface of the layer of the viscous curable material. The texture is such that it enhances light trapping capability of the photovoltaic device. The photovoltaic device also includes a barrier layer deposited on the layer of the viscous curable material. The barrier layer is impermeable to one or more fluids released by the viscous curable material. Further, the photovoltaic device includes one or more semiconductor layers deposited on the barrier layer. The barrier layer prevents contamination of the one or more semiconductor layers from the one or more fluids. Finally, the photovoltaic device includes a cover substrate.
[0020] In some embodiments, a method of manufacturing a photovoltaic device is provided. The method includes providing a transparent substrate having a substantially flat surface, and depositing a layer of a viscous curable material on the flat surface of the transparent substrate to form a texture on a surface of the layer of the viscous curable material. The texture is such that it
enhances light trapping capability of the photovoltaic device. Thereafter, the method includes depositing a barrier layer on the layer of viscous curable material. The barrier layer is impermeable to one or more fluids released by the viscous curable material. Further, the method involves depositing one or more semiconductor layers on the barrier layer. The barrier layer prevents contamination of the one or more semiconductor layers from the one or more fluids. Finally, the method includes providing a cover substrate on the one or more semiconductor layers.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0021] Before describing the present invention in detail, it should be observed that the present invention utilizes a combination of method steps and apparatus components related to a method of manufacturing a photovoltaic device. Accordingly the apparatus components and the method steps have been represented where appropriate by conventional symbols in the drawings, showing only specific details that are pertinent for an understanding of the present invention so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art having the benefit of the description herein.
[0022] While the specification concludes with the claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawings, in which like reference numerals are carried forward.
[0023] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.
[0024] The terms "a" or "an", as used herein, are defined as one or more than one. The term "another", as used herein, is defined as at least a second or more. The terms "including" and/or "having" as used herein, are defined as comprising (i.e. open transition). The term "coupled" or
"operatively coupled" as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
[0025] Referring now to the drawings, there is shown in FIG. 1, a diagrammatic illustration of various components of an exemplary photovoltaic device 100 according to an embodiment of the present invention. Examples of the photovoltaic device 100 include, but are not limited to, a thin film solar cell, an organic solar cell, an amorphous silicon solar cell, a microcrystalline silicon solar cell, a micromorph silicon tandem solar cell, a Copper Indium Gallium Selenide (CIGS) solar cell, a Cadmium Telluride (CdTe) solar cell, and the like. The photovoltaic device 100 is shown to include a stack of a substrate 102, a layer 104 of a viscous curable material, a barrier layer 106, a first layer 108 of TCO, multiple semiconductor layers 110,112,114,116 and 118, a second layer 120 of TCO, a layer 122 of silver, and a layer 124 of aluminum. [0026] The substrate 102 provides strength to the photovoltaic device 100 and is used as a starting point for deposition of other layers that constitute the photovoltaic device 100. An example of a material of the substrate 102 includes, but is not limited to, glass and transparent plastics. In some exemplary embodiments, during real life applications, the photovoltaic device 100 is placed in a way that the substrate 102 is facing the sun and all the sun light falling on the photovoltaic device 100 is incident on the substrate 102. In these embodiments, the substrate 102 is made of a transparent material so that it allows maximum light to pass through itself and reach the subsequent layers. The substrate 102 includes a flat surface on which other subsequent layers can be deposited.
[0027] Moving on to the layer 104 of the viscous curable material. The layer 104 of the viscous curable material is deposited over the substrate 102. The viscous curable material should be able to retain any nano-texture embossed on it when it is cured by using mediums such as heat or light. The viscous curable material can include, but is not limited to, an ultra-violet curable material, a photo-polymer lacquer, an acrylate, and silica or silica-titania based sol-gel materials. [0028] In some embodiments, the viscous curable material is pre-cured by using light and/or heat prior to depositing the layer 104 of the viscous curable material on the flat surface of the substrate 102. Pre-curing of the viscous curable material is performed in order to minimize the out-gassing of fluids or solvents from the viscous curable material during later stages of manufacturing of the photovoltaic device 100 or during actual usage of the photovoltaic device 100. These fluids or solvents coming out of the viscous curable material have a tendency to
contaminate subsequent layers of the photovoltaic device 100 and thus, impact the overall performance of the photovoltaic device 100.
[0029] In accordance with the present invention, the layer 104 of the viscous curable material is deposited in a manner such that a texture is formed on a surface of the layer 104 of the viscous curable material. The examples of the texture include, but are not limited to, V-shaped or U-shaped features, a ID or 2D periodic grating (rectangular or sinusoidal), a blazed grating, and random pyramids. This texture is such that it that enables and enhances light trapping capability of semiconductor layers of the photovoltaic device 100. This texture helps in scattering and diffraction of the light and thus, enhances the light path through the photovoltaic device 100 and hence, enhances the chance of absorption of light by the semiconductor layers of the photovoltaic device 100.
[0030] Several methods can be used to create the texture on the layer 104 of the viscous curable material that enables light trapping. In one embodiment, the texture can be created by applying a thin layer 104 of the viscous curable material, such as a photo-polymer lacquer or a sol-gel material, onto the substrate 102 and then pressing a stamper with the nano-textured surface into this layer 104. Further, a UV curing process is applied to freeze the nano-texture on the layer 104 of the viscous curable material.
[0031] In another embodiment, the texture can be created by applying a thin layer 104 of the viscous thermally curable material, such as a photo-polymer lacquer or a sol-gel material, onto the substrate 102 and then pressing a stamper with the nano-textured surface into this layer 104. Further, heat is applied to the layer 104 in order to freeze the nano-texture on the layer 104 of the viscous curable material.
[0032] In yet another embodiment, the texture can be created by pressing the stamper against the substrate 102 while it is being heated above its deformation (glass transition) temperature (hot-embossing), followed by a rapid cooling process. Following this, the layer 104 of the viscous curable material is deposited on the substrate 102. In another embodiment, the texture can be created by use of injection molding technique. In this embodiment, an injection molding die is mounted on the surface of the substrate 102 and the texture is formed by injecting the viscous curable material in the injection molding die.
[0033] In some embodiments, after the layer 104 of the viscous curable material has been deposited over the substrate 102, annealing of the layer 104 of viscous curable material is
performed. The main purpose of annealing is to eliminate maximum amount of the fluids or solvents released by the viscous curable material and/or the substrate 102 before other layers can be deposited.
[0034] Moving on to the barrier layer 106. The barrier layer 106 is deposited on the layer 104 of the viscous curable material after the layer 104 of the viscous curable material has been deposited on the transparent substrate 102. The barrier layer 106 is impermeable to the fluids or solvents, such as volatile organic compounds like photoinitiator remains, non-reacted resins, side-reaction products or impurities, which are released by the viscous curable material during later stages of manufacturing of the photovoltaic device 100 or during actual usage of the photovoltaic device 100. The barrier layer 106 is also impermeable to contaminants that originate from substrates like sodium. Thus, the barrier layer 106 prevents the detrimental effect of the contaminants/elements, fluids or solvents released by the viscous curable material and/or the substrate (like sodium from glass) 102 on other deposited layers, such as the first layer 108 of TCO, and semiconductor layers 110, 112, 114, and 116 or on an encapsulant of the photovoltaic device 100.
[0035] The use of barrier layer 106 is important because after the texture that enables light trapping has been embossed on the layer 104 of the viscous curable material, it is annealed at higher temperatures in the range of 250-300 degrees Celsius. During this process of annealing, a lot of contaminants/elements, fluids or solvents come out from the viscous curable material and/or the substrate 102. Further, these elements, fluids or solvents have the tendency to contaminate the other deposited layers, such as semiconductor layers or the encapsulant. The barrier layer 106 prevents elements, fluids or solvents coming from the viscous curable material and/or the substrate 102 to contaminate the other deposited layers.
[0036] The barrier layer 106 can be made from a material which is optically transparent. Further, the refractive index of the barrier layer 106 generally ranges between 1.4 and 2.2. In general, the refractive index of the barrier layer 106 is dependent on the refractive index of the substrate 102 and the refractive index of TCO. Refractive index of the barrier layer 106 should lie between the refractive index of the substrate 102 and the refractive index of TCO. For example, if the substrate 102 is glass having a refractive index of 1.5 and the refractive index of TCO is 1.9, then the refractive index of the barrier layer 106 should lie between 1.5 and 1.9. Ideally, the refractive index of the barrier layer 106 should be V(nsubstrate x nTCo), where Usubstrate IS
the refractive index of the substrate 102 and n-rco is the refractive index of TCO. Therefore, in above example, the refractive index of the barrier layer 106 can be V(1.5 x 1.9), i.e. 1.69. [0037] Thickness of the barrier layer 106 can vary based on the wavelength of the light that the photovoltaic device 100 intends to trap. However, in general, the thickness of the barrier layer 106 can range between 1 nanometer and 150 nanometers. In cases where the layer thickness for the barrier layer 106 corresponds with a quarter of the wavelength of the light that needs to be trapped, the barrier layer 106 serves as antireflection layer as well. The materials that can be used for the barrier layer 106 include, but are not limited to, silicon oxides (SiOx), silicon nitrides (SiNx), AI2O3, ZnS:SiO2 and SiON. Further, the barrier layer 106 facilitates adhesion between the layer 104 of the viscous curable material and other deposited layers, such as the first layer 108 of TCO and the semiconductor layers 110,112,114,116, and 118. [0038] Moving on to the first layer 108 of TCO. The first layer 108 of TCO is deposited over the barrier layer 106. TCOs are doped metal oxides used in photovoltaic devices. Examples of TCOs include, but are not limited to, Aluminum-doped Zinc Oxide (AZO), Boron doped Zinc Oxide (BZO), Gallium doped Zinc Oxide (GZO), Fluorine doped Tin Oxide (FTO) and Indium doped Tin Oxide (ITO). TCOs have more than 80% transmittance of incident light and have conductivities higher than 10 S/cm for efficient carrier transport. The transmittance of TCOs, just as in any transparent material, is limited by light scattering at defects and grain boundaries.
[0039] Next set of layers in the stack of photovoltaic device 100 are semiconductor layers 110, 112, 114, 116, and 118. Generally, the semiconductor layers are deposited using chemical vapour deposition, sputtering, and hot wire techniques on the first layer 108 of TCO. For the purpose of this description, the semiconductor layers are shown to include a first layer of p-doped semiconductor 110, a second layer of p-doped semiconductor 112, a layer of buffer 114, a layer of i-doped semiconductor 116, and a layer of n-doped semiconductor 118. However, it will be readily apparent to those skilled in the art that the photovoltaic device 100 include or exclude one or more semiconductor layers without deviating from the scope of the invention. [0040] For the purpose of this description, the first layer of p-doped semiconductor 110 is made of uc Si:H. However, the second layer of p-doped semiconductor 112, the layer of i-doped semiconductor 116, and the layer of n-doped semiconductor 118 are made of a-Si:H.
[0041] In general, when glass is used as a superstate or substrate, the semiconductor layers are deposited in a p-i-n sequence, i.e. p-doped semiconductor, i-doped semiconductor, and n-doped semiconductor. This is because the mobility of electrons in a-Si:H is nearly twice than that of holes in aSi:H, and thus the collection rate of electrons moving from the p- to n-type contact is better as compared to holes moving from p- to n-type contact. Therefore, the p-doped semiconductor layer is placed at the top where the intensity of light is more. [0042] Following the semiconductor layers, a cover substrate is deposited. In one embodiment, the cover substrate includes the second layer 120 of TCO, the layer 122 of silver, and the layer 124 of aluminum. In other embodiments, the cover substrate can include at least one of the second layer 120 of TCO, the layer 122 of silver, and the layer 124 of the aluminum. These layers individually or in combination form the back contact of the photovoltaic device 100. In some cases, commercially available photovoltaic device 100 may have additional layers to enhance their efficiency or to improve the reliability.
[0043] All the above mentioned layers are encapsulated using an encapsulation to obtain the photovoltaic device 100.
[0044] Moving on to FIG. 2, FIG. 2 is a flow chart describing an exemplary method 200 for manufacturing the photovoltaic device 100 in accordance with an embodiment of the present invention. To describe the method 200, reference will be made to FIG. 1, although it is understood that the method 200 can be implemented to manufacture any other suitable device. Moreover, the invention is not limited to the order of in which the steps are listed in the method 200. In addition, the method 200 can contain a greater or fewer numbers of steps than those shown in FIG. 2.
[0045] The method 200 for manufacturing the photovoltaic device 100 is initiated at step 202. At step 204, the substrate 102 is provided. As described in conjunction with FIG. 1, the substrate 102 provides strength to the photovoltaic device 100 and is used as a starting point for deposition of the photovoltaic device 100. The substrate 102 is transparent in nature and can be made of materials such as glass and transparent plastic. The substrate 102 is made of a transparent material so that it can allow maximum light to pass through itself and reach the subsequent semiconductor layers. Further, the substrate 102 includes a substantially flat surface on which other layers of the photovoltaic device 100 can be deposited.
[0046] Following this, at step 206, the layer 104 of the viscous curable material is deposited on the flat surface of the substrate 102. The viscous curable material can be deposited by using a brush or roller, dispensing, slot dye coating, spin-coating, spray coating or printing. The viscous curable material can include, but is not limited to, an ultra-violet curable material, a photo-polymer lacquer, an acrylate, and a sol-gel material. The layer 104 of the viscous curable material is deposited in a manner such that a texture is formed on surface of the layer 104 of the viscous curable material. This texture is such that it that enables and enhances light trapping capability of the semiconductor layers of the photovoltaic device 100. This texture helps in scattering and diffraction of the light and thus, enhances the light path through the photovoltaic device 100 and hence, enhances the chance of absorption of light by the semiconductor layers of the photovoltaic device 100. Various methods that can be used to form the light trapping texture on the layer 104 of the viscous curable material have been described in conjunction with FIG. 1. [0047] At step 208, the barrier layer 106 is deposited on the layer 104 of the viscous curable material by, for example, physical vapor deposition, chemical vapor deposition, sputtering or plasma enhanced chemical vapor deposition. The barrier layer 106 is impermeable to the fluids or solvents released by the viscous curable material and the substrate 102 during later stages of manufacturing of the photovoltaic device 100 or during actual usage of the photovoltaic device 100. Thus, the barrier layer 106 prevents the detrimental effect of the fluids or solvents released by the viscous curable material and/or the substrate 102 on other deposited layers. [0048] The barrier layer 106 can be made from a material which is optically transparent. Further, the refractive index of the barrier layer 106 ranges between 1.4 and 2.2. Generally, the thickness of the barrier layer 106 ranges between 1 nanometer and 150 nanometers. In cases where the layer thickness for the barrier layer 106 corresponds with a quarter of the wavelength of the light that needs to be trapped, the barrier layer 106 can serve as antireflection layer as well. The materials that can be used for the barrier layer 106 include, but are not limited to, silicon oxides (SiOx), silicon nitrides (SiNx), AI2O3, ZnS:SiC>2 and SiON. Further, the barrier layer 106 facilitates adhesion between the layer 104 of the viscous curable material and other deposited layers, such as the first layer 108 of TCO and the semiconductor layers 110, 112, 114, 116, and 118.
[0049] Thereafter, at step 210, multiple semiconductor layers are deposited on the barrier layer 106. These multiple semiconductor layers can include the first layer 108 of TCO, the first
layer of p-doped semiconductor 110, the second layer of p-doped semiconductor 112, the layer of buffer 114, the layer of i-doped semiconductor 116, and the layer of n-doped semiconductor 118. As described in conjunction with FIG. 1, the semiconductor layers are deposited in a manner that they form a p-i-n structure.
[0050] Following this, at step 212, the cover substrate is provided on the multiple semiconductor layers. The cover substrate includes the second layer 120 of TCO, the layer 122 of silver, and the layer 124 of aluminum. The method 200 is terminated at step 214. [0051] FIG. 3 is a flow chart describing a method 300 for manufacturing the photovoltaic device 100, in accordance with another embodiment of the present invention. For the purpose of this description, the method 300 is explained for manufacturing of the photovoltaic device 100. To describe the method 300, reference will be made to FIG. 1, although it is understood that the method 300 can also be applied, without deviating from the scope of the invention, for manufacturing any other suitable device or system. Moreover, the invention is not limited to the order of in which the steps are listed in the method 300. In addition, the method 300 can contain a greater or fewer numbers of steps than those shown in FIG. 3.
[0052] The method for manufacturing the photovoltaic device 100 is initiated at step 302. At step 304, the substrate 102 is provided. As described in conjunction with FIG. 1, the substrate 102 provides strength to the photovoltaic device 100 and is used as a starting point for deposition of the photovoltaic device 100. The substrate 102 is transparent in nature and can be made of materials such as glass and transparent plastics. The substrate 102 is made of a transparent material so that it can allow maximum light to pass through itself and reach the subsequent semiconductor layers. Further, the substrate 102 includes a substantially flat surface on which other layers can be deposited.
[0053] Following this, at step 306, the viscous curable material is pre-cured by using light and/or heat. Pre-curing of the viscous curable material is performed in order to minimize the out-gassing of fluids or solvents from the viscous curable material during later stages of manufacturing of the photovoltaic device 100 or during actual usage of the photovoltaic device 100. These fluids or solvents coming out of the viscous curable material have a tendency to contaminate the subsequent layers and thus, impact the overall performance of the photovoltaic device 100.
[0054] Following this, at step 308, a layer 104 of pre-cured viscous curable material is deposited on the flat surface of the substrate 102. The viscous curable material can include, but is not limited to, a ultra-violet curable material, a photo-polymer lacquer, an acrylate, and a sol-gel material. The layer 104 of the viscous curable material is deposited in a manner such that a texture is formed on a surface of the layer 104 of the viscous curable material. This texture is such that it enables and enhances light trapping capability of the semiconductor layers of the photovoltaic device 100. This texture helps in scattering and diffraction of the light and thus, enhances the light path through the photovoltaic device 100 and hence, enhances the chance of absorption of light by the semiconductor layers of the photovoltaic device 100. [0055] At step 310, the layer 104 of the viscous curable material is cured/annealed by using heat and/or light. The main purpose of annealing is to eliminate maximum amount of the fluids or solvents released by the viscous curable material and/or the substrate 102 before other layers are deposited. The medium used for curing/annealing the viscous curable material is dependent on the viscous curable material. In case the viscous curable material is an ultra-violet curable material, then UV light is used as the curing/annealing medium. In another example, if the viscous curable material is an arcylate, then heat can be used as the curing/annealing medium. Curing/annealing of the layer 104 of the viscous curable material by heat is generally performed at higher temperatures in the range of 250-300 degree Celsius. Even after this process of curing/annealing, a lot of fluids or solvents come out from the viscous curable material and the substrate 102. These fluids or solvents have the tendency to contaminate the other deposited layers, such as semiconductor layers. Hence, at step 312, the barrier layer 106 is deposited on the layer 104 of the viscous curable material to prevent fluids or solvents coming from the viscous curable material and/or the substrate 102 to contaminate the other deposited layers. [0056] The barrier layer 106 is impermeable to the fluids or solvents released by the viscous curable material and the substrate 102. Thus, the barrier layer 106 prevents the detrimental effect of the fluids or solvents released by the viscous curable material and/or the substrate 102 on other deposited layers.
[0057] The barrier layer 106 can be made from a material which is optically transparent. Further, the refractive index of the barrier layer 106 ranges between 1.4 and 2.2. Generally, the thickness of the barrier layer 106 ranges between 1 nanometer and 150 nanometers. In cases where the layer thickness for the barrier layer 106 corresponds with a quarter of the wavelength
of the light that needs to be trapped, the barrier layer 106 serves as antireflection layer as well. The materials that can be used for the barrier layer 106 include, but are not limited to, silicon oxides (SiOx), silicon nitrides (SiNx), AI2O3, ZnS:Si02 and SiON. Further, the barrier layer 106 facilitates adhesion between the layer 104 of the viscous curable material and other deposited layers, such as the first layer 108 of TCO and the semiconductor layers 110, 112, 114, 116, and 118.
[0058] Thereafter, at step 314, the first layer 108 of TCO is deposited on the barrier layer 106. Thereafter, at step 316, multiple semiconductor layers are deposited on the barrier layer 106. These multiple semiconductor layers can include the first layer of p-doped semiconductor 110, the second layer of p-doped semiconductor 112, the layer of buffer 114, the layer of i-doped semiconductor 116, and the layer of n-doped semiconductor 118. As described in conjunction with FIG. 1, the semiconductor layers are deposited in a manner that they form a p-i-n structure. [0059] Following this, at step 318, the cover substrate is provided on the multiple semiconductor layers. The cover substrate includes the second layer 120 of TCO, the layer 122 of silver, and the layer 124 of aluminum. The method 300 is terminated at step 320. [0060] Various embodiments, as described above, provide a photovoltaic device, which has several advantages. One of the several advantages of some embodiments of this photovoltaic device is that it increases the efficiency of the photovoltaic device. Another advantage of this embodiment is that the semiconductor layers of the photovoltaic device are not contaminated by the fluids or solvents released by the viscous curable material and the substrate. Further, the barrier layer also provides better adhesion between the TCO layer and the substrate. [0061] While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense allowable by law. [0062] All documents referenced herein are hereby incorporated by reference.

WE CLAIMS
1. A photovoltaic device for photoelectric conversion of incident solar light, the
photovoltaic device comprising a stack of at least:
a transparent substrate having a substantially flat surface;
a layer of a viscous curable material, wherein said layer of said viscous curable material is deposited on said flat surface of said transparent substrate to form a texture on a surface of said layer of said viscous curable material, further wherein said texture enhances light trapping capability of said photovoltaic device;
a barrier layer deposited on said layer of said viscous curable material, wherein said barrier layer is impermeable to one or more fluids released by said viscous curable material;
one or more semiconductor layers deposited on said barrier layer, wherein contamination of said one or more semiconductor layers from said one or more fluids is prevented by said barrier layer; and
a cover substrate.
2. The photovoltaic device according to claim 1, wherein said barrier layer is optically transparent.
3. The photovoltaic device according to claim 1, wherein refractive index of said barrier layer ranges between 1.4 and 2.2.
4. The photovoltaic device according to claim 1, wherein said barrier layer is anti-reflective.
5. The photovoltaic device according to claim 1, wherein thickness of said barrier layer ranges between 1 nanometer and 150 nanometers.
6. The photovoltaic device according to claim 1, wherein material of said barrier layer is selected from the group comprising silicon oxides (SiOx), silicon nitrides (SiNx), A12O3, ZnS:SiO2 and SiON.
7. The photovoltaic device according to claim 1 further comprising a first layer of transparent conductive oxide, wherein said first layer of transparent conductive oxide is deposited on said barrier layer.
8. The photovoltaic device according to claim 7, wherein said barrier layer facilitates adhesion between said layer of said viscous curable material and said first layer of transparent conductive oxide.
9. The photovoltaic device according to claim 1, wherein said barrier layer facilitates
adhesion between said layer of said viscous curable material and said one or more semiconductor
layers.
10. The photovoltaic device according to claim 1, wherein said viscous curable material is
selected from the group comprising an acrylate, an ultra-violet curable material, a photo-polymer
lacquer and a sol-gel material.