JP5490031B2 - Photovoltaic device and photovoltaic module - Google Patents

Description

  The present invention relates to a photovoltaic device, a manufacturing method thereof, and a photovoltaic module, and more particularly to a photovoltaic device having a photoelectric conversion unit using a microcrystalline silicon-based thin film, a manufacturing method thereof, and a photovoltaic module.

  In a thin film solar cell, a structure is used in which incident sunlight is efficiently used by forming a texture on a transparent conductive film on a glass substrate to scatter incident light and increasing the optical path length to confine. Moreover, in the case of a stacked thin film solar cell in which a plurality of photoelectric conversion units are stacked, by controlling the wavelength of light used in each photoelectric conversion unit by providing an intermediate layer between the photoelectric conversion units, It has been practiced to improve the photoelectric conversion efficiency by balancing the current generated by the photoelectric conversion unit (see, for example, Patent Document 1).

  Furthermore, in the case of a stacked thin film solar cell, when forming a semiconductor photoelectric conversion layer using a microcrystalline silicon-based thin film used as a second cell (bottom cell) that converts light in a long wavelength region, In order to improve the photoelectric conversion efficiency by suppressing generation of defects due to unevenness, it has been proposed to use a flat light scattering film (see, for example, Patent Document 2).

JP 2003-347572 A JP 2006-128478 A

  However, when increasing the optical path length and confining light in a stacked thin-film solar cell as in the prior art, a large texture is formed on the transparent conductive film or the substrate itself, and each photoelectric conversion unit is fabricated using this as a base. ing. For this reason, there was a problem that defects in the microcrystalline photoelectric conversion unit increased.

  Further, as in the prior art, in order to realize a flat base in order to reduce defects in the microcrystalline photoelectric conversion unit, it is necessary to flatten the substrate on which the sun is incident and the transparent conductive film. Therefore, a technique has been proposed in which light is diffused by embedding a light scatterer in a transparent conductive film. However, in this case, due to the relationship between the particle size of the light scatterer and the wavelength of the light, an effective scattering effect is obtained for light of a specific wavelength, but light is emitted for light of other wavelengths. There is a problem in that sunlight is not effectively used because it is diffusely reflected not only in front of the semiconductor power generation layer (light incident direction) but also in the rear of the light incident side.

  The present invention has been made in view of the above, and can effectively use light in a wide wavelength region from a short wavelength region to a long wavelength, and a photovoltaic device excellent in photoelectric conversion efficiency and a manufacturing method thereof, The purpose is to obtain a photovoltaic module.

In order to solve the above-described problems and achieve the object, the photovoltaic device according to the present invention is composed of a light-transmitting conductive film on one surface of a light-transmitting substrate and has a root mean square roughness of 10 nm to At least one first electrode layer having a concavo-convex shape of 600 nm, a first photoelectric conversion unit having a light absorption layer made of an amorphous silicon thin film, and a second photoelectric conversion unit having a light absorption layer made of a crystalline silicon thin film. It has the laminated photoelectric conversion unit laminated | stacked one by one and the 2nd electrode layer in this order, and differs from the transparent resin layer which has translucency on the other surface of the said translucent board | substrate, and the said transparent resin layer A spherical light scatterer made of a translucent material having a refractive index and having a diameter larger than the root mean square roughness of the irregular shape of the surface of the first electrode layer and dispersedly arranged in the transparent resin layer; , Bei to give a, and the light-scattering body , Wavelength of light following equation (3) size parameter represented by α is 3 or more in the 1200nm from 900 nm, to contain a light-scattering member having a diameter of 20 or less, and wherein.

  According to the present invention, a high forward scattering effect due to the texture shape of the transparent conductive film and the light scatterer achieves good transmission scattering performance for light in a wide region from a short wavelength region to a long wavelength, and a wide wavelength region. It is possible to obtain a photovoltaic device that can effectively use the light.

FIG. 1 is a cross-sectional view schematically showing a configuration of a thin-film solar battery that is a photovoltaic device according to a first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining forward scattering of incident light by the texture structure of the transparent electrode layer of the present invention. FIGS. 3-1 is sectional drawing for demonstrating typically the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. 3-2 is sectional drawing for demonstrating typically the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. 3-3 is sectional drawing for demonstrating typically the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. FIGS. 3-4 is sectional drawing for demonstrating typically the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. FIG. 4 is a flowchart for explaining the method for manufacturing the thin-film solar cell according to the first embodiment of the present invention. FIG. 5 is a characteristic diagram showing the wavelength dependence of the haze ratio of a general substrate with a transparent conductive film for solar cells in which a transparent conductive film is formed on a glass substrate. FIG. 6 is a diagram showing a state of light scattering intensity distribution in the light scatterer when the size parameter is 1. As shown in FIG. FIG. 7 is a diagram showing a state of light scattering intensity distribution in the light scatterer when the size parameter is 3. As shown in FIG. FIG. 8 is a characteristic diagram showing an example of the haze ratio of the substrate with a transparent conductive film for solar cell according to the first embodiment when the size parameter is set to 3 for light having a wavelength of 1100 nm. FIG. 9: is sectional drawing which shows typically the structure of the thin film solar cell concerning Embodiment 2 of this invention. FIG. 10: is sectional drawing which shows typically the structure of the thin film solar cell concerning Embodiment 3 of this invention.

  Embodiments of a photovoltaic device, a manufacturing method thereof, and a photovoltaic module according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view schematically showing a configuration of a thin-film solar battery that is a photovoltaic device according to a first embodiment of the present invention. The thin film solar cell according to the first embodiment is a stacked (tandem junction) thin film solar cell in which two photoelectric conversion layers are stacked.

  As shown in FIG. 1, the thin-film solar cell according to the first embodiment has a transparent electrode layer 2 that is a first electrode layer, a first photoelectric conversion unit 7, and a second photoelectric conversion unit 8 on a translucent substrate 1. The back transparent conductive film 9 and the back electrode layer 10 as the second electrode layer are sequentially laminated. Further, as shown in FIG. 1, the thin-film solar cell according to the first embodiment includes a transparent resin layer 3 on the light incident side of the translucent substrate 1, and a light scatterer 4 disposed in the transparent resin layer 3. . In this thin film solar cell, sunlight L is incident from the transparent resin layer 3 side.

  As the translucent substrate 1, an insulating substrate having translucency is used. For such a translucent substrate 1, a material having a high transmittance is usually used, and for example, a glass substrate having a small absorption from the visible region to the near infrared region is used. As the glass substrate, an alkali-free glass substrate may be used, or an inexpensive blue plate glass substrate may be used. However, the translucent substrate 1 is not necessarily made of glass, and a substrate such as a resin can be used as long as it is an insulating substrate that transmits light.

The transparent electrode layer 2 is made of a transparent conductive film having optical transparency. The transparent electrode layer 2 is, for example, a transparent conductive material containing at least one of zinc oxide (ZnO), indium tin oxide (ITO), tin oxide (SnO ₂ ), and indium oxide (In ₂ O ₃ ). It is composed of an oxide film (TCO: Transparent Conducting Oxide) or a transparent conductive film in which these are laminated. Further, the transparent electrode layer 2 is formed by adding aluminum (Al), gallium (Ga), indium (In), boron (B), yttrium (Y), silicon (Si), zirconium (Zr), You may be comprised by the translucent film | membrane using at least 1 or more types of element selected from titanium (Ti) and fluorine (F).

  Such a transparent electrode layer 2 is formed by sputtering, electron beam deposition, atmospheric pressure chemical vapor deposition (CVD), low pressure CVD, metal organic chemical vapor deposition (MOCVD). It can be produced by various methods such as a Deposition method, a sol-gel method, a printing method, and a spray method.

  Further, the transparent electrode layer 2 has a surface texture structure in which a concavo-convex shape is formed on the surface opposite to the translucent substrate 1. This texture structure increases the optical path length by forwardly scattering light having a visible wavelength from a short wavelength region of incident sunlight, and more efficiently absorbs incident light in the first photoelectric conversion unit 7 to use light. Has a function to increase efficiency. Forward scattering means that light incident from the translucent substrate 1 is scattered in the traveling direction as shown in FIG. FIG. 2 is a schematic diagram for explaining forward scattering of incident light due to the texture structure of the transparent electrode layer 2.

  The uneven shape of the texture structure is a small uneven shape that does not deteriorate the film quality of the first photoelectric conversion unit 7 and the second photoelectric conversion unit 8. As such a shape, a shape in which triangular pyramids with a height of about 50 nm to 200 nm having a periodic structure of 100 nm to 800 nm suitable for light scattering from the short wavelength region to the visible light region are arranged is preferable. When the convex portion becomes large irregularities having a height higher than this, a defect is generated when microcrystalline silicon used in the photoelectric conversion unit is grown, and the photoelectric conversion characteristics deteriorate. This texture structure can be formed, for example, by subjecting the surface of the transparent electrode layer 2 to dry etching or wet etching.

  The first photoelectric conversion unit 7 and the second photoelectric conversion unit 8 have, for example, a pin junction, and a thin film silicon semiconductor layer as a light absorption layer (photoelectric conversion layer) that generates power by incident light and generates photovoltaic power. Is a silicon-based semiconductor photoelectric conversion unit configured by stacking one or more layers.

  The first photoelectric conversion unit 7 includes, for example, a p-type semiconductor layer 7a that is a first conductivity type semiconductor layer, a light absorption layer 7b that is an intrinsic semiconductor layer, and a second conductivity type in order from the light incident side (transparent electrode layer 2 side). Each semiconductor layer of the n-type semiconductor layer 7c which is a semiconductor layer is included. Moreover, the light absorption layer 7b which is an intrinsic semiconductor layer may exhibit weak p-type and n-type conductivity as long as the light absorption function (photoelectric conversion function) is not impaired.

  The second photoelectric conversion unit 8 includes, for example, a p-type semiconductor layer 8a that is a first conductive semiconductor layer, a light absorption layer 8b that is an intrinsic semiconductor layer, and a second layer in order from the light incident side (first photoelectric conversion unit 7 side). Each semiconductor layer is an n-type semiconductor layer 8c which is a conductive semiconductor layer. Moreover, the light absorption layer 8b which is an intrinsic semiconductor layer may show weak p-type and n-type conductivity as long as the light absorption function (photoelectric conversion function) is not impaired.

  Here, the silicon-based semiconductor photoelectric conversion unit is made of a base material mainly composed of a silicon-based semiconductor, and an acceptor or a donor suitable for each semiconductor is added to form p-type or n-type, and pin It consists of three semiconductor layers constituting the structure. As these manufacturing methods, the CVD method is common. Examples of the CVD method include atmospheric pressure CVD, reduced pressure CVD, plasma CVD, thermal CVD, hot wire CVD, and MOCVD.

  The first photoelectric conversion unit 7 can mainly perform photoelectric conversion by absorbing light in a short wavelength region. For example, the first photoelectric conversion unit 7 is a material having a large band gap, a short absorption wavelength region of sunlight, and a high open circuit amorphous silicon ( a-Si) -based materials are preferable. As such a material, amorphous silicon (a-Si), amorphous silicon carbide (a-SiC), amorphous silicon oxide (a-SiO), or the like is suitable.

  The second photoelectric conversion unit 8 can mainly absorb light in a longer wavelength region than the first photoelectric conversion unit 7 and perform photoelectric conversion. For example, the absorption wavelength region of absorbed sunlight is long and the band gap is small. The material is preferably made of a microcrystalline silicon (μc-Si) -based material. As such a material, microcrystalline silicon (μc-Si), microcrystalline silicon germanium (μc-SiGe), microcrystalline silicon tin (μc-SiSn), or the like is suitable.

The back transparent conductive film 9 is formed by any material and method similar to those of titanium oxide (TiO ₂ ) and the transparent electrode layer 2. Note that it is not always necessary to form the uneven surface by various etching.

  The back electrode layer 10 is made of a conductive film, and it is preferable that the light reflection is large and the conductivity is high. The back electrode layer 10 is made of a metal material such as silver (Ag), aluminum (Al), titanium (Ti) or palladium (Pd) having a high visible light reflectivity, an alloy thereof, or a nitride or oxide thereof. Or the like. Since the back electrode layer 10 reflects light that has not been absorbed by the photoelectric conversion unit and returns it to the photoelectric conversion unit again, it contributes to an improvement in photoelectric conversion efficiency.

  The transparent resin layer 3 is made of a light-transmitting resin that fixes the light scatterer 4, and for example, ethylene vinyl acetate is suitable.

  The light scatterer 4 is installed in the transparent resin layer 3 and scatters light in the long wavelength region in the incident sunlight to increase the optical path length, and makes the incident light more efficient in the second photoelectric conversion unit 8. It has the function of improving the light utilization efficiency. The shape of the light scatterer 4 is preferably spherical, and has a diameter suitable for forward scattering light in the long wavelength region in consideration of the Mie scattering effect, and is more than the root mean square roughness in the texture shape of the transparent electrode layer 2. Have a large diameter. The light scatterer 4 may be made of any material having a refractive index different from that of the transparent resin layer 3. For example, zinc oxide, indium oxide, titanium oxide, silicon oxide, or the like that does not absorb sunlight is used. Transparent material with can be used.

  Next, a method for manufacturing the thin-film solar cell according to the first embodiment configured as described above will be described with reference to FIGS. 3-1 to 3-4 and FIG. 3A to 3D are cross-sectional views schematically illustrating the method for manufacturing the thin-film solar cell according to the first embodiment. FIG. 4 is a flowchart for explaining the method for manufacturing the thin-film solar cell according to the first embodiment.

  First, a glass substrate is prepared as the translucent substrate 1. However, the light-transmitting substrate 1 is not necessarily a glass substrate, and a substrate such as a resin may be used as long as it is an insulating substrate that transmits light.

  Next, a transparent electrode layer 2 having a surface irregularity shape including fine irregularities as a texture structure is formed on the translucent substrate 1 by a known method (FIG. 3-1, step S110). For example, the transparent electrode layer 2 made of a zinc oxide (ZnO) film is formed on the translucent substrate 1 by a sputtering method. The transparent electrode layer 2 may be produced by other methods such as a plasma CVD method. Then, a texture structure is formed on the surface of the transparent electrode layer 2 by etching the surface of the transparent electrode layer 2. At this time, the concavo-convex shape of the texture structure is such that triangular pyramids with a height of about 50 nm to 200 nm having a periodic structure of 100 nm to 800 nm suitable for light scattering from the short wavelength region to the visible light region are arranged. Is preferred.

  Next, a first photoelectric conversion unit 7 made of amorphous silicon (a-Si) and a second photoelectric conversion unit 8 made of microcrystalline silicon (μc-Si) are formed on the transparent electrode layer 2 by a known method ( FIG. 3-2, step S120). For example, the p-type semiconductor layer 7a, the light absorption layer 7b, the n-type semiconductor layer 7c, the p-type semiconductor layer 8a, the light absorption layer 8b, and the n-type semiconductor layer 8c are made transparent in order from the transparent electrode layer 2 side by plasma CVD. On the electrode layer 2, it is laminated and formed substantially parallel to the main surface of the translucent insulating substrate 1.

Next, the back surface transparent conductive film 9 is formed on the 2nd photoelectric conversion unit 8 by a well-known method (FIG. 3-3, step S130). For example, the back transparent conductive film 9 made of a tin oxide (SnO ₂ ) film is formed on the second photoelectric conversion unit 8 by a sputtering method. Further, as a film formation method, another film formation method such as a CVD method may be used.

  Next, the back electrode layer 10 is formed on the back transparent conductive film 9 by a known method (FIG. 3-3, step S130). For example, the back electrode layer 10 made of a silver (Ag) film is formed on the back transparent conductive film 9 by a sputtering method. Further, as a film formation method, another film formation method such as a CVD method may be used.

  Next, the transparent resin layer 3 in which the light scatterers 4 are dispersedly formed is formed on the light incident side (the side opposite to the transparent electrode layer 2) of the translucent substrate 1 (FIG. 3-4, step S140). For example, ethylene vinyl acetate in which a spherical light scatterer 4 is dispersed is applied or printed on the light incident side (the side opposite to the transparent electrode layer 2) of the translucent substrate 1. By forming the transparent resin layer 3 in which the light scatterers 4 are dispersed and arranged on the outside of the translucent substrate 1 in the last step, the temperature of the manufacturing process of the thin film solar cell is not limited, and the optimum thin film solar Battery fabrication conditions can be used. In addition, there is an advantage that the range of selection of the material of the transparent resin layer 3 is widened. The thin film solar cell concerning Embodiment 1 shown in FIG. 1 is obtained by the above process.

  In the thin film solar cell according to the first embodiment as described above, the light in the long wavelength region out of the sunlight L incident on the thin film solar cell is forward scattered by the light scatterer 4 installed in the transparent resin layer 3. As a result, the optical path length increases and a good light confinement effect can be obtained. Thereby, the light in the long wavelength region is efficiently absorbed by the second photoelectric conversion unit 8, and the photoelectric conversion efficiency is improved. In the thin film solar cell according to the first embodiment, among the sunlight L incident on the thin film solar cell, light having a visible light wavelength from the short wavelength region is forward scattered by the texture structure of the transparent electrode layer 2, so that the optical path. The length increases and the first photoelectric conversion unit 7 efficiently absorbs the photoelectric conversion efficiency.

  FIG. 5 is a characteristic diagram showing the wavelength dependence of the haze ratio of a general substrate with a transparent conductive film for solar cells in which a transparent conductive film is formed on a glass substrate. FIG. 5 shows the relationship between the wavelength (nm) of incident light to the substrate with a transparent conductive film for solar cells and the haze ratio (%). The haze ratio is a numerical value represented by the following formula (1), and the higher the value, the higher the ratio of light diffusion.

  As shown in FIG. 5, the haze ratio decreases as the wavelength of incident light changes from the short wavelength region to the long wavelength region, and it can be seen that the haze rate has wavelength dependency. The diffusion of light in the substrate with a transparent conductive film for solar cells is affected by the period and size of the texture shape formed on the transparent conductive film on the substrate. In order to effectively scatter light in the long wavelength region in the substrate with a transparent conductive film for solar cells, the texture shape is desirably an uneven shape having a period or size similar to the wavelength to be scattered.

  The uneven shape size of the texture shape can be obtained by atomic force microscope (AFM) measurement, and the root mean square roughness (RMS) of the surface is preferably about 10 nm to 600 nm. As shown in FIG. 2, the RMS corresponds to the depth of the texture, and when a deep texture exceeding 600 nm exists, defects in the microcrystalline film increase. Further, if the texture depth is less than 10 nm, there is a possibility that light cannot be effectively scattered.

  For example, in Japanese Patent Application Laid-Open No. 2009-140930, after a base having large irregularities is formed, a transparent electrode layer having small irregularities on the surface is installed so as to cover the large irregularities, so that a short wavelength region to a long wavelength region can be obtained. A method of providing a function of scattering the light up to is proposed. However, when a large uneven shape is formed on the base, there is a problem that the film quality of the semiconductor layer grown on the base is deteriorated, and the open circuit voltage and the fill factor are reduced.

  In order to eliminate the adverse effect on the semiconductor layer due to such uneven shape, the surface of the transparent electrode layer as a base is smoothed by embedding a light scatterer in the transparent electrode layer, for example, as in Patent Document 2. However, a shape that can utilize the light scattering effect has been proposed. However, in order to scatter sunlight only with a light scatterer in this way, it is necessary to mix light scatterers of sizes suitable for light of various wavelengths. In this case, there is a problem that the light scattering characteristic becomes a random scattering characteristic including not only forward scattering of light but also backward scattering, and light that escapes to the outside is generated.

  However, in the thin-film solar cell according to the first embodiment, the transparent electrode has a texture structure including small irregularities that do not deteriorate the film quality of the semiconductor layer and preferentially scatters light having a visible light wavelength from a short wavelength region. The spherical light scatterer 4 that preferentially scatters light in the long wavelength region is disposed on the light incident side of the light transmissive substrate 1 with the layer 2 placed in front of the light on the light transmissive substrate 1. Install. Thereby, in the thin film solar cell concerning Embodiment 1, a high haze rate is realizable with respect to the light of the wide wavelength range from a short wavelength range to a long wavelength, without producing the above problems. Good transmission and scattering performance can be obtained.

  It is known that light scattering by a light scatterer behaves differently depending on the relationship between the wavelength of light and the size of the light scatterer. As a parameter related to the wavelength of light and the size of the light scatterer, there is a size parameter α, which is expressed by the following mathematical formula (2).

  Rayleigh scattering can be handled when the size parameter α is α << 1, Mie scattering when α˜1, and light scattering can be handled by geometric optical approximation when α >> 1. Therefore, when a light scatterer of various sizes is embedded as in Patent Document 2, Rayleigh scattering occurs due to a light scatterer with a small size, and light is scattered almost in all directions. There is a problem of returning.

  Mie scattering is a diffraction phenomenon of light by a sphere, and as the diameter of the sphere becomes larger than the wavelength of light, the forward scattering ratio increases and it becomes difficult to scatter backward. (See, for example, Hendrik Christoffel van de Hulst, “Light Scattering by Small Particles Dover Publications”, New York, (1981)).

  Thus, since Mie scattering is a diffraction phenomenon between light and a sphere, the shape of the light scatterer 4 is preferably spherical in order to obtain the effect in the thin film solar cell according to the present embodiment. Then, as shown in FIG. 5, in order to effectively scatter light having a wavelength of 900 nm or more that has a haze ratio of a common substrate with a transparent conductive film for solar cells of 10% or less, the size parameter α is approximately It is preferable to be 3 or more and 20 or less. For example, in an ethylene vinyl acetate medium, it is preferable to use a light scatterer 4 having a diameter of 1.4 μm or more and 8.6 μm or less in order to effectively scatter light having a wavelength of 900 nm.

  FIG. 6 is a diagram showing the state of the scattering intensity distribution of the light in the light scatterer 4 when the size parameter α is 1. As shown in FIG. FIG. 7 is a diagram showing a state of light scattering intensity distribution in the light scatterer 4 when the size parameter α is 3. As shown in FIG. As shown in FIG. 6, when the size parameter α is 1, light is scattered with the same intensity distribution in both the light traveling direction (θ = 0) and the incident direction (θ = 180). On the other hand, as shown in FIG. 7, when the size parameter α is 3, the scattering intensity in the light traveling direction (θ = 0) is two orders of magnitude stronger than the scattering intensity in the incident direction (θ = 180), It can be seen that the ratio of return light in the incident direction (θ = 180) is greatly reduced.

  For example, when the second photoelectric conversion unit 8 is made of microcrystalline silicon germanium (SiGe), the light scatterer 4 having a diameter of 1.8 μm or more and 12 μm or less is used to effectively scatter light up to a wavelength of 1200 nm. It is preferable. If the size parameter α exceeds 20, it becomes the above-mentioned geometric optical approximation region, so it is not necessary to make the size larger.

  FIG. 8 is a characteristic diagram showing an example of the haze ratio of the substrate with a transparent conductive film for solar cell according to the first embodiment when the size parameter α is set to 3 with respect to light having a wavelength of 1100 nm. The substrate with a transparent conductive film for a solar cell according to the first embodiment is a translucent substrate 1, a transparent electrode layer 2, and a transparent resin layer 3 among the configurations of the thin-film solar cell according to the first embodiment shown in FIG. And the light scatterer 4.

  As shown in FIG. 8, the substrate with a transparent conductive film for solar cell according to the first embodiment can realize a high haze ratio for light in a wide wavelength region from a short wavelength region to a long wavelength, and is good. Transmission performance can be obtained. And by using this board | substrate with a transparent conductive film for solar cells to comprise a thin film solar cell, the utilization efficiency of the sunlight in a thin film solar cell can be improved, and a photoelectric conversion efficiency can be improved.

  Therefore, according to the first embodiment, the high forward scattering effect by the texture shape of the transparent electrode layer 2 and the light scatterer 4 provides good transmission and scattering performance for light in a wide region from a short wavelength region to a long wavelength. Thus, a thin-film solar cell with excellent photoelectric conversion efficiency that can effectively use light in a wide wavelength region can be obtained.

Embodiment 2. FIG.
FIG. 9: is sectional drawing which shows typically the structure of the thin film solar cell concerning Embodiment 2 of this invention. In the thin film solar cell according to the second embodiment, the scatterer surface coating 5 is arranged on the surface of the light scatterer 4 in the configuration of the thin film solar cell shown in the first embodiment. In the configuration of the thin film solar cell according to the first embodiment, the light of the short wavelength region to the visible light region has a size parameter α of more than 20 with respect to the light scatterer, and the scattering and reflection characteristics on the surface of the light scatterer 4 are geometric. Optical approximation is applied. For this reason, depending on the angle, reflection occurs at the interface between the surface of the light scatterer 4 and the transparent resin layer 3, and part of the light is returned to the incident side.

  Therefore, the surface of the light scatterer 4 has a thickness of ¼ wavelength with respect to light in a short wavelength region of a wavelength of 400 nm to 500 nm that is easily reflected at the interface between the surface of the light scatterer 4 and the transparent resin layer 3. By arranging the scatterer surface coating 5 on the surface, it is possible to provide an effect of suppressing the reflection. Thereby, the light reflected back on the surface of the light scatterer 4 can be reduced, and the amount of light that can be taken into the thin film solar cell can be increased. At this time, the film thickness of the scatterer surface film 5 may be ¼ × [wavelength] ÷ [refractive index n1 of the film]. Since Mie scattering is a diffraction reaction by a sphere in a uniform medium, the scattering effect on light in the long wavelength region is not affected by the scatterer surface coating 5.

  The scatterer surface film 5 may not be a single layer film, and can be made to correspond to reflection of a wider wavelength by using a multilayer film like anti-reflection coating. As the material of the scatterer surface film 5, a material having a refractive index different from that of the light scatterer 4 can be used, for example, among zinc oxide, indium oxide, titanium oxide, and silicon oxide. Since the refractive index of the oxide changes depending on the composition of oxygen to be bonded, the surface of the oxide can be further oxidized by annealing the light scatterer 4 in an oxygen atmosphere to form the scatterer surface coating 5. Moreover, the film thickness of the scatterer surface film 5 can be controlled by the annealing time and temperature.

  When the scatterer surface film 5 is formed of a different material, for example, in order to form the scatterer surface film 5 with silicon oxide, a solution obtained by diluting silicon alkoxide (for example, tetraethoxysilane) with a solvent such as ethanol is used. After adhering to the substrate, it may be dried and sintered. In the case of this method, the film thickness of the scatterer surface film 5 can be controlled by the concentration of silicon alkoxide in the solution.

  Further, paraxylylene-based polymer (Parylene: registered trademark) is also usable because it is a substance having a refractive index of around 1.5 to 1.6 and transparent to light having a wavelength of 300 nm or more. A vapor deposition method is generally used for forming a parylene film. The dimer which is a raw material of parylene is vaporized by heating at about 150 ° C., and further heated to a high temperature of 650 ° C. to 700 ° C. to become a monomer molecule which is a precursor. The monomer molecule undergoes a polymerization reaction on the surface of the light scatterer 4 at room temperature to form a parylene film. In order to cover the surface of the light scatterer 4 that is a sphere, it is necessary to vibrate the container containing the light scatterer 4 during film formation or to stir the container by stirring it.

  According to the thin-film solar cell according to the second embodiment described above, it is favorable for light in a wide region from a short wavelength region to a long wavelength due to a high forward scattering effect by the texture shape of the transparent electrode layer 2 and the light scatterer 4. A thin-film solar cell that achieves excellent transmission and scattering performance and is excellent in photoelectric conversion efficiency that can effectively use light in a wide wavelength region.

  Moreover, according to the thin film solar cell concerning Embodiment 2, it is 1/4 wavelength with respect to the light of the short wavelength range of wavelength 400nm-500nm which is easy to reflect in the interface of the surface of the light-scattering body 4 and the transparent resin layer 3. The scatterer surface coating 5 is disposed on the surface of the light scatterer 4 so that the film thickness becomes the following thickness. As a result, an effect of suppressing reflection at the interface between the surface of the light scatterer 4 and the transparent resin layer 3 is obtained, a better transmission scattering performance is realized, and photoelectric conversion that can effectively use light in a wide wavelength region A thin film solar cell excellent in efficiency can be obtained.

Embodiment 3 FIG.
FIG. 10: is sectional drawing which shows typically the structure of the thin film solar cell concerning Embodiment 3 of this invention. The thin film solar cell according to the third embodiment has a configuration in which the surface of the transparent resin layer 3 is coated with an inorganic coating layer 11 made of an inorganic material in the configuration of the thin film solar cell according to the first embodiment. Since the surface of the transparent resin layer 3 is coated with the inorganic coating layer 11, the transparent resin layer 3 and the oxygen in the air are not in direct contact with each other, and therefore the deterioration of the transparent resin layer 3 is suppressed. Thereby, the weather resistance of the transparent resin layer 3 increases, and the long-term reliability of a thin film solar cell can be improved.

Material of the inorganic coating layer 11 is, for example alkoxysilane compound _{(R n Si (OR) 4} -n: R is an alkyl radical, n is an integer of 1 to 3) and the like are preferable. The inorganic coating layer 11 can be formed by applying such a material to the surface of the transparent resin layer 3 with a spray, a brush, a roller or the like and drying it. In the case of an alkoxylane compound, the drying process after coating can be natural drying. For this reason, it is possible to form the inorganic coating layer 11 by using an alkoxylane compound, without applying an excessive heat load to a thin film solar cell. Further, the alkoxylane compound can be dried in a shorter time by heating to about 100 ° C. to 150 ° C. that does not adversely affect the transparent resin layer 3 and the like.

  The film thickness of the inorganic coating layer 11 is preferably about 10 μm to 200 μm. When the film thickness of the inorganic coating layer 11 is thinner than 10 μm, the effect of suppressing the deterioration of the transparent resin layer 3 is lowered. Moreover, when the film thickness of the inorganic coating layer 11 is thicker than 200 micrometers, although the drying time after application | coating increases, the inhibitory effect does not change substantially.

  According to the thin film solar cell according to the third embodiment described above, it is favorable for light in a wide region from a short wavelength region to a long wavelength due to the high forward scattering effect by the texture shape of the transparent electrode layer 2 and the light scatterer 4. A thin-film solar cell that achieves excellent transmission and scattering performance and is excellent in photoelectric conversion efficiency that can effectively use light in a wide wavelength region.

  Moreover, according to the thin film solar cell concerning Embodiment 3, since the surface of the transparent resin layer 3 is coat | covered with the inorganic coating layer 11, it interrupts | blocks from oxygen in air | atmosphere, Therefore The transparent resin layer by oxygen in air | atmosphere 3 can be suppressed. Thereby, the weather resistance of the transparent resin layer 3 increases, and the thin film solar cell excellent in long-term reliability is obtained.

  In addition, although the case where the inorganic coating layer 11 was added to the structure of the thin film solar cell concerning Embodiment 2 was demonstrated in the above as an example, the inorganic coating layer 11 was added to the structure of the thin film solar cell concerning Embodiment 1. When added, the same effect as described above can be obtained.

  In addition, a plurality of thin-film solar cells having the configuration described in the above embodiment are formed on the light-transmitting substrate 1, and the adjacent thin-film solar cells are electrically connected in series or in parallel. A solar cell module having a good light confinement effect and excellent in reliability and photoelectric conversion efficiency can be realized. In this case, what is necessary is just to electrically connect one transparent electrode layer 2 and the other back surface electrode layer 10 of an adjacent thin film photovoltaic cell.

  As described above, the photovoltaic device according to the present invention is useful for realizing a photovoltaic device excellent in photoelectric conversion efficiency that can effectively use light in a wide wavelength region from a short wavelength region to a long wavelength region. is there.

DESCRIPTION OF SYMBOLS 1 Translucent board | substrate 2 Transparent electrode layer 3 Transparent resin layer 4 Light scatterer 5 Scatterer surface membrane | film | coat 7 1st photoelectric conversion unit 7a p-type semiconductor layer 7b Light absorption layer 7c n-type semiconductor layer 8 2nd photoelectric conversion unit 8a p Type semiconductor layer 8b light absorption layer 8c n type semiconductor layer 9 back transparent conductive film 10 back electrode layer 11 inorganic coating layer L sunlight

Claims (7)

A first electrode layer having a concavo-convex shape with a mean square surface roughness of 10 nm to 600 nm on the surface and a light absorption layer made of an amorphous silicon thin film on one surface of the light transmissive substrate. 1 photoelectric conversion unit and a second photoelectric conversion unit having at least one second photoelectric conversion unit having a light absorption layer made of a crystalline silicon-based thin film, and a second electrode layer in this order,
On the other surface of the translucent substrate, a transparent resin layer having translucency, and a light-transmitting material having a refractive index different from that of the transparent resin layer, the mean square of the uneven shape on the surface of the first electrode layer e Bei and a light scatterers distributed by spherical inside the transparent resin layer has a larger diameter than the surface roughness,
The light scatterer includes a light scatterer having a diameter such that the size parameter α represented by the following formula (1) is 3 or more and 20 or less when the wavelength of light is 900 nm to 1200 nm.
A photovoltaic device characterized by the above.

The light scatterer comprises at least one selected from the group consisting of zinc oxide, indium oxide, titanium oxide and silicon oxide;
The photovoltaic device according to claim 1 . The light scatterer has a light scatterer surface coating composed of one or more layers having a film thickness equal to a quarter wavelength with respect to light having a wavelength of 300 nm or more and less than 900 nm,
The photovoltaic device according to claim 1 or 2, characterized in. The light scatterer surface film is at least one selected from the group consisting of zinc oxide, indium oxide, titanium oxide, silicon oxide and parylene, and is made of a material different from the light scatterer;
The photovoltaic device according to claim 3 . The surface of the transparent resin layer is made of an inorganic material and is covered with a coating layer that blocks contact between the surface of the transparent resin layer and atmospheric oxygen,
The photovoltaic device according to any one of claims 1 to 4 , wherein: The coating layer is made of an alkoxylane compound and has a thickness of 10 μm to 200 μm.
The photovoltaic device according to claim 5 . That more than at least two of the photovoltaic device according is electrically connected to claim 1-6,
A photovoltaic module characterized by.

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