JP2011119480A - Method of manufacturing thin film solar cell - Google Patents

Abstract

A method of manufacturing a thin film solar cell having excellent photoelectric conversion efficiency is provided.
A first step of forming a transparent electrode layer made of a light-transmitting conductive material on a light-transmitting insulating substrate, and a semiconductor photoelectric conversion layer made of a semiconductor layer and performing photoelectric conversion on the transparent electrode layer are formed. A second step of forming a back side transparent electrode layer made of a translucent conductive material having a light scattering layer on the semiconductor photoelectric conversion layer, and a reflective conductive material on the back side transparent electrode layer A fourth step of forming a back-surface reflective electrode layer comprising: a light scattering layer material film including a constituent material of the light scattering layer on the semiconductor photoelectric conversion layer with a substantially uniform thickness. And a fifth step of forming the light scattering layer by aggregating the light scattering layer material film on the semiconductor photoelectric conversion layer at a temperature of 200 ° C. or lower with respect to the light scattering layer material film. And including.
[Selection] Figure 2

Description

  The present invention relates to a method for manufacturing a thin film solar cell, and more particularly to a method for manufacturing a thin film solar cell having a structure capable of reflecting or scattering light.

  In order to convert solar energy more effectively and obtain high energy conversion efficiency in a thin-film solar cell, which is a photoelectric conversion device that directly converts solar energy into electrical energy, the incident light is converted into a thin-film solar cell. It is an indispensable means to use a light confinement technique in which the optical path length is extended by repeatedly reflecting the inside to increase the utilization efficiency of incident light. As one of such light confinement techniques, a method of embedding a concavo-convex shape that scatters light or a light-scattering substance in a back-side electrode is employed (for example, see Patent Document 1).

  According to the technique of Patent Document 1, silver is used as an example of a light scattering material embedded in the back side transparent electrode. As a method for embedding the light scattering material, a silver thin film is formed by sputtering at a high substrate temperature of 300 ° C. and deposited, and the silver thin film is aggregated by thermal energy from the substrate.

Japanese Patent Laid-Open No. 5-75154 (section 5, FIG. 1)

  However, when manufacturing a thin film solar cell with high conversion efficiency, a high film forming temperature affects the film quality of other layers. For example, in an amorphous silicon solar cell, the photoelectric conversion layer is manufactured at a temperature of about 200 ° C. For this reason, when the back electrode layer is formed at a high temperature of 300 ° C. as in the technique of Patent Document 1, impurity diffusion occurs in the already formed photoelectric conversion layer, and the film quality is reduced. It has a fatal effect.

  Therefore, although the light scattering layer is formed in order to improve the photoelectric conversion efficiency which is an index of the performance of the thin film solar cell, there is a problem that the photoelectric conversion efficiency is remarkably lowered as a result.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the manufacturing method of the thin film solar cell excellent in photoelectric conversion efficiency.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a thin-film solar cell according to the present invention includes a first step of forming a transparent electrode layer made of a light-transmitting conductive material on a light-transmitting insulating substrate. And a second step of forming a semiconductor photoelectric conversion layer made of a semiconductor layer on the transparent electrode layer and performing photoelectric conversion, and a back surface side made of a translucent conductive material having a light scattering layer on the semiconductor photoelectric conversion layer A third step of forming a transparent electrode layer, and a fourth step of forming a backside reflective electrode layer made of a reflective conductive material on the backside transparent electrode layer, wherein the third step comprises the step of forming the light scattering layer. A fourth step of forming a light scattering layer material film containing a constituent material on the semiconductor photoelectric conversion layer with a substantially uniform thickness; and the light scattering layer material at a temperature of 200 ° C. or less with respect to the light scattering layer material film. The light scattering by aggregating the film on the semiconductor photoelectric conversion layer Characterized in that it comprises a and a fifth step of forming a.

  According to the present invention, the light scattering layer can be formed inside the backside transparent electrode layer without inducing the performance degradation of the thin film solar cell due to heat in the light scattering layer forming step, and good light There is an effect that a thin-film solar cell having a confinement effect and excellent in photoelectric conversion efficiency can be produced.

1-1 is sectional drawing which shows typically schematic structure of the thin film solar cell concerning Embodiment 1 of this invention. FIG. 1-2 is an enlarged cross-sectional view of the light scattering layer included in the thin-film solar cell according to the first embodiment of the present invention. FIG. 2 is a flowchart for explaining the method of manufacturing the thin-film solar cell according to the first embodiment of the present invention. FIGS. 3-1 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIGS. 3-2 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. 3-3 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. 3-4 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. 3-5 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. 3-6 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. 3-7 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 1 of this invention. FIG. 4 is a characteristic diagram showing the scattering effect of the light scattering layer in the thin-film solar cell produced by the method for producing a thin-film solar cell according to Embodiment 1 of the present invention. FIG. 5 is a characteristic diagram showing the dependence of the scattering effect on the light scattering layer on the annealing time in the thin-film solar cell produced by the method for producing a thin-film solar cell according to Embodiment 1 of the present invention. FIG. 6 is a characteristic diagram showing the dependence of the scattering effect on the light scattering layer on the annealing treatment time in the thin film solar cell produced by the method for producing a thin film solar cell according to Embodiment 1 of the present invention. FIG. 7 is a flowchart for explaining a method of manufacturing a thin-film solar cell according to the second embodiment of the present invention. FIGS. 8-1 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 2 of this invention. FIGS. 8-2 is sectional drawing for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 2 of this invention.

  Embodiments of a method for manufacturing a thin film solar cell 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. The same applies between the drawings.

Embodiment 1 FIG.
1-1 is sectional drawing which shows typically schematic structure of the thin film solar cell concerning Embodiment 1 of this invention. The thin film solar cell according to the present embodiment includes a transparent electrode layer 2 having a concavo-convex structure on the surface and serving as a first electrode layer, a semiconductor photoelectric conversion layer 3 including a semiconductor layer, and a back surface. The side transparent electrode layer 4 and the back surface reflective electrode layer 5 serving as the second electrode layer are laminated in this order.

  As the translucent insulating substrate 1, an insulating substrate having translucency is used. For such a translucent insulating substrate 1, a material having a high transmittance is usually used, and for example, a glass substrate having a small absorption from the visible 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 insulating substrate 1 is not necessarily made of glass, and a substrate made of resin or the like can be used as long as it is an insulating substrate that transmits light. In the present embodiment, white plate glass or the like is used as the translucent insulating substrate 1.

The transparent electrode layer 2 is made of a transparent conductive film and has an uneven structure. 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 has a surface uneven shape including fine unevenness, and has a function of increasing the light use efficiency in the semiconductor photoelectric conversion layer 3 by irregular reflection of light on the uneven surface. 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. In the present embodiment, a zinc oxide (ZnO) film to which aluminum (Al) is added is formed as the transparent electrode layer 2 by a sputtering method, and the texture structure on the surface is formed by wet etching.

  As the semiconductor photoelectric conversion layer 3, for example, a crystalline silicon-based semiconductor film or an amorphous silicon-based semiconductor film is used, and is composed of a semiconductor film having a pin junction (p-type-i-type-n-type) three-layer structure. In the present embodiment, the semiconductor photoelectric conversion layer 3 includes a p-type semiconductor layer 3p that is a first conductivity type semiconductor layer and an i-type semiconductor layer (intrinsic semiconductor layer) that is a second conductivity type semiconductor layer from the transparent electrode layer 2 side. 3i, a stacked film in which the n-type semiconductor layer 3n as the third conductivity type semiconductor layer is stacked is formed. For these semiconductor layers, for example, a microcrystalline silicon thin film, an amorphous silicon germanium thin film, a microcrystalline silicon germanium thin film, an amorphous silicon carbide thin film, a microcrystalline silicon carbide thin film, or the like may be used, or a laminated film of these may be used. .

Although the case where one semiconductor photoelectric conversion layer 3 is provided is shown here, the semiconductor photoelectric conversion layer 3 may be formed by stacking a plurality of semiconductor films having pin junctions. In this case, a transparent conductive film such as indium tin oxide (ITO) or zinc oxide (ZnO) between different semiconductor layers, a silicon oxide (SiO ₂ ) film whose conductivity is improved by doping impurities, A silicon compound film such as a silicon nitride (SiN) film may be inserted as an intermediate layer. Such a semiconductor photoelectric conversion layer 3 is generally deposited by using a plasma CVD method, a thermal CVD method or the like.

  The back side transparent electrode layer 4 is made of a translucent conductive material, and includes a light scattering layer 4c between the first back side transparent electrode layer 4a and the second back side transparent electrode layer 4d. The back side transparent electrode layer 4 prevents diffusion of elements from the back side reflective electrode layer 5 to the semiconductor photoelectric conversion layer 3.

The first back surface side transparent electrode layer 4a is made of a translucent conductive material, and similarly to the transparent electrode layer 2, a zinc oxide (ZnO) film added with aluminum (Al), indium tin oxide (ITO), tin oxide ( A transparent conductive oxide film (TCO) such as zinc oxide (ZnO) to which SnO ₂ ) or gallium (Ga) is added can be used. In addition, a trace amount impurity may be added in the film | membrane of the 1st back surface side transparent electrode layer 4a.

  Such a first back side transparent electrode layer 4a is produced by a known method such as sputtering, atmospheric pressure CVD, reduced pressure CVD, MOCVD, electron beam evaporation, sol-gel method, electrodeposition, spraying or the like. In particular, any method may be used as long as it does not damage the semiconductor photoelectric conversion layer 3 which is the underlayer, which causes a decrease in the performance of the thin film solar cell. In the present embodiment, as the first back-side transparent electrode layer 4a, a zinc oxide (ZnO) film to which aluminum (Al) is added is formed by a sputtering method.

  The light scattering layer 4c is sandwiched between the first back surface side transparent electrode layer 4a and the second back surface side transparent electrode layer 4d, and actively transmits light that has passed without being absorbed by the semiconductor photoelectric conversion layer 3. The light has a light scattering effect of causing light to enter the back surface reflective electrode layer 5 and efficiently making light incident on the semiconductor photoelectric conversion layer 3 again. FIG. 1-2 is an enlarged cross-sectional view of the light scattering layer 4c included in the thin-film solar cell according to the first embodiment. The shape of the light scattering layer 4c is an uneven shape such as a grain shape, a hemispherical shape, or an island shape. The light scattering layer 4c is made of, for example, silver.

The second back surface side transparent electrode layer 4d is made of a translucent conductive material, and similarly to the transparent electrode layer 2, a zinc oxide (ZnO) film added with aluminum (Al), indium tin oxide (ITO), tin oxide (SnO). ₂ ) or a transparent conductive oxide film (TCO) such as zinc oxide (ZnO) to which gallium (Ga) is added can be used. A trace amount of impurities may be added to the film of the second back surface side transparent electrode layer 4d.

  Such a second back side transparent electrode layer 4d is produced by a known method such as sputtering, atmospheric pressure CVD, reduced pressure CVD, MOCVD, electron beam evaporation, sol-gel method, electrodeposition, spraying or the like. In particular, any method may be used as long as it does not damage the semiconductor photoelectric conversion layer 3 which is the underlayer, which causes a decrease in performance of the thin film solar cell. In the present embodiment, as the first back-side transparent electrode layer 4a, a zinc oxide (ZnO) film to which aluminum (Al) is added is formed by a sputtering method.

  The back surface reflective electrode layer 5 functions as a back surface electrode and also functions as a reflective layer that reflects light that has not been absorbed by the photoelectric conversion layer and returns it to the photoelectric conversion layer, thereby contributing to improvement in photoelectric conversion efficiency. Therefore, the back surface reflective electrode layer 6 is more preferable as the light reflectance is higher and the conductivity is higher. The back reflective electrode layer 5 is at least one selected from, for example, titanium (Ti), chromium (Cr), aluminum (Al), silver (Ag), gold (Au), copper (Cu), and platinum (Pt). A layer made of a metal or an alloy thereof is used. In addition, the specific material as a metal material of these back surface reflective electrode layers is not specifically limited, It can select from a well-known material suitably and can be used. Such a back reflective electrode layer 5 is formed by sputtering, CVD, vapor deposition, coating, or the like. In the present embodiment, a silver (Ag) film formed by a sputtering method is formed as the back reflective electrode layer 5.

  As described above, in the thin-film solar cell according to the first embodiment, the light scattering layer 4c is sandwiched between the first back-side transparent electrode layer 4a and the second back-side transparent electrode layer 4d. . Thereby, in this thin film solar cell, the light that has passed without being absorbed by the semiconductor photoelectric conversion layer 3 is actively scattered and made incident on the back surface reflective electrode layer 5, and efficiently again the semiconductor photoelectric conversion layer 3. Thus, a thin film solar cell having a good light confinement effect and excellent photoelectric conversion efficiency has been realized.

  Next, a method for manufacturing the thin-film solar cell according to the present embodiment configured as described above will be described with reference to FIG. 2 and FIGS. 3-1 to 3-7. FIG. 2 is a flowchart for explaining a method of manufacturing the thin-film solar cell according to the first embodiment. FIGS. 3-1 to 3-7 are cross-sectional views for explaining the method for manufacturing the thin-film solar cell according to the first embodiment.

  First, for example, a glass substrate is prepared as the translucent insulating substrate 1. Then, the transparent electrode layer 2 is formed on one surface side of the translucent insulating substrate 1 by a known method (step S10, FIG. 3-1). For example, the transparent electrode layer 2 made of a zinc oxide (ZnO) film to which aluminum (Al) is added is formed on the translucent insulating substrate 1 by a sputtering method. Further, as a film formation method, another film formation method such as a CVD method may be used. Further, a texture structure is formed on the surface of the transparent electrode layer 2 by wet etching.

  Next, a p-type semiconductor layer 3p, an i-type semiconductor layer (intrinsic semiconductor layer) 3i, and an n-type semiconductor layer 3n are sequentially formed on the transparent electrode layer 2 by a known method (step S20, Fig. 3-2). For example, a hydrogenated amorphous silicon thin film is sequentially formed by CVD on the transparent electrode layer 2 as a p-type semiconductor layer 3p, an i-type semiconductor layer (intrinsic semiconductor layer) 3i, and an n-type semiconductor layer 3n. As the semiconductor photoelectric conversion layer 3 deposited and formed here, for example, a microcrystalline silicon thin film, an amorphous silicon germanium thin film, a microcrystalline silicon germanium thin film, an amorphous silicon carbide thin film, a microcrystalline silicon carbide thin film, or a laminated film thereof is used. Also good.

Next, the back surface side transparent electrode layer 4 is formed on the n-type semiconductor layer 3n. First, as the first back surface side transparent electrode layer 4a, a zinc oxide (ZnO) thin film to which aluminum (Al) is added is formed on the n-type semiconductor layer 3n by a sputtering method (step S30, FIG. 3-3). The first back transparent electrode 4a is made of transparent conductive material such as zinc oxide (ZnO) to which indium tin oxide (ITO), tin oxide (SnO ₂ ), or gallium (Ga) is added, as in the transparent electrode layer 2. It is possible to use a conductive oxide film (TCO). In addition to the sputtering method, the first backside transparent electrode layer 4a can be formed by atmospheric pressure CVD method, low pressure CVD method, MOCVD method, electron beam evaporation method, sol-gel method, electrodeposition method, spray method, etc. Any known method may be used as long as the method does not damage the semiconductor photoelectric conversion layer 3 as a base layer, which causes a decrease in the performance of the thin-film solar cell.

  Next, as a step before forming the light scattering layer 4c embedded in the back side transparent electrode layer 4, a light scattering layer material film containing the constituent material of the light scattering layer 4c on the first layer back side transparent electrode 4a. Then, an extremely thin silver thin film 4b having a uniform thickness is formed by, for example, a sputtering method (step S40, FIG. 3-4). Here, the reason for using the silver thin film 4b is that, when forming the light scattering layer 4c, silver is preferable as a material that has an optically high reflectance and is likely to induce an aggregating effect by thermal energy. Silver is preferable in terms of film thickness reproducibility and uniformity. Table 1 shows an example of the formation conditions (sputtering conditions) of the silver thin film 4b in the present embodiment.

  The formation of the silver thin film 4b is characterized in that the film thickness in sputtering is 80 nm or less. By setting the film thickness of the silver thin film 4b to 80 nm or less, the light scattering layer 4c having a light scattering effect can be formed by heat treatment or ultraviolet irradiation in a subsequent process. At the time of film formation, the silver thin film 4b is a continuous film.

Next, heat treatment is performed on the ultrathin silver thin film 4b having a uniform thickness so that the light scattering layer 4c having an irregular shape such as a grain shape, a hemispherical shape, or an island shape is formed on the first back transparent electrode 4a. (Step S50, FIG. 3-5). For example, by performing an annealing treatment as a heat treatment on the silver thin film 4b having a uniform thickness, the silver thin film 4b having a uniform thickness is aggregated to form an irregular shape such as a grain shape, a hemispherical shape, or an island shape. The light scattering layer 4c can be formed. The annealing of the silver thin film 4b is performed in, for example, a nitrogen (N ₂ ) atmosphere, an argon (Ar) atmosphere, an atmosphere containing argon (Ar) containing hydrogen (H ₂ ), or a non-oxidizing atmosphere such as in a vacuum. .

  The heat treatment for the silver thin film 4b is characterized in that it is performed at a temperature of 200 ° C. or less that does not have a significant adverse effect on the already formed semiconductor photoelectric conversion layer 3. Thus, after forming the thin silver thin film 4b of uniform thickness on the 1st layer back surface transparent electrode 4a, it heat-processes and forms the light-scattering layer 4c, and substrate temperature like a prior art is formed. The light scattering layer 4c can be formed without increasing the temperature to 300 ° C. That is, the light scattering layer 4c is formed on the back surface side transparent electrode layer 4 without inducing the performance degradation of the thin film solar cell due to the high heat in the manufacturing process which has been a problem in the prior art. Table 2 shows an example of preferable heat treatment conditions for the silver thin film 4b in the present embodiment.

  The heat treatment conditions that do not significantly adversely affect the semiconductor photoelectric conversion layer 3 include an annealing temperature of 150 ° C. to 200 ° C. and an annealing time of 30 minutes to 120 minutes. When the annealing temperature is too low, the silver (Ag) thin film does not sufficiently aggregate, and the ratio Td / Tt (%) of the diffuse transmittance Td to the total light transmittance Tt of the light scattering layer 4c exceeds 25%. A sufficient scattering effect cannot be obtained. If the annealing temperature is higher than 200 ° C., the semiconductor photoelectric conversion layer 3 of the thin film solar cell already formed by heat is damaged, and the photoelectric conversion efficiency is lowered. In addition, when the annealing treatment time is in a range longer than a specified time, the scattering characteristics for long-wavelength light tend to decrease as shown in FIG. 5 to be described later in the change of grains due to aggregation of silver (Ag).

  Here, the silver thin film 4b is aggregated by performing heat treatment on the silver thin film 4b, but the heat treatment method for the silver thin film 4b is not limited to this. That is, the silver thin film 4b can be formed by a method other than the annealing process as long as the effect of aggregation of the silver thin film 4b can be expressed by thermal energy without damaging the semiconductor photoelectric conversion layer 3 by heat as in the annealing process. You may heat-process with respect to.

Next, as the second back surface side transparent electrode layer 4d, a zinc oxide (ZnO) thin film to which aluminum (Al) is added is formed on the first back surface side transparent electrode layer 4a and the light scattering layer 4c by a sputtering method. (Step S60, FIGS. 3-6). The second-layer back transparent electrode 4d has a transparent conductive property such as zinc oxide (ZnO) to which indium tin oxide (ITO), tin oxide (SnO ₂ ), or gallium (Ga) is added in the same manner as the transparent electrode 2. An oxide film (TCO) can be used. In addition to the sputtering method, the second back side transparent electrode layer 4d is formed by atmospheric pressure CVD method, low pressure CVD method, MOCVD method, electron beam evaporation method, sol-gel method, electrodeposition method, spray method, etc. Any known method may be used as long as the method does not damage the semiconductor photoelectric conversion layer 3 as a base layer, which causes a decrease in the performance of the thin-film solar cell. As described above, the back side transparent electrode layer 4 in which the light scattering layer 4c is sandwiched between the first back side transparent electrode layer 4a and the second back side transparent electrode layer 4d is formed.

  Next, the back surface reflective electrode layer 5 is formed on the back surface side transparent electrode layer 4 by a well-known method (step S70, FIGS. 3-7). A back reflective electrode layer 5 made of a silver (Ag) film having a high reflectance is formed on the back transparent electrode layer 4 by a sputtering method. Further, as a film formation method, other film formation methods such as a CVD method, a vapor deposition method, and a coating method may be used. The thin film solar cell concerning this Embodiment shown in FIGS. 1-1 is obtained by the above process.

  FIG. 4 is a characteristic diagram showing the scattering effect of the light scattering layer 4c in the thin film solar cell of the example produced by the method for manufacturing the thin film solar cell according to the present embodiment described above. The heat treatment conditions are those shown in Table 2 of the implementation. In FIG. 4, the horizontal axis indicates the film thickness of the silver thin film 4b before annealing, that is, the uniform film thickness of the silver thin film 4b, and the vertical axis indicates the diffuse transmission with respect to the total light transmittance Tt of the light scattering layer 4c. The ratio Td ratio Td / Tt (%) is shown. The larger the value of Td / Tt, the greater the light scattering characteristics of the formed light scattering layer 4c. Also, the circle symbol (◯) in FIG. 4 represents Td / Tt for light having a wavelength of 600 nm. Further, the triangle symbol (black Δ) in FIG. 4 represents Td / Tt for light having a wavelength of 1000 nm.

  From FIG. 4, the value of Td / Tt is larger than 0 when the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is 85 nm or less, and the effect of scattering by the light scattering layer can be confirmed. That is, in the method for manufacturing a thin-film solar cell according to the present embodiment, in order to obtain reliable light scattering characteristics, the silver thin film 4b having a uniform thickness before annealing is applied to light having a wavelength of 600 nm or 1000 nm. The film is formed with a film thickness of 85 nm or less as a film thickness range in which the value of Td / Tt does not become zero. Furthermore, it is preferable to obtain a value of 25% or more as both Td / Tt for light having a wavelength of 600 nm and a wavelength of 1000 nm. In this case, the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is The range is from 45 nm to 60 nm.

  When the film thickness of the thin silver film 4b having a uniform thickness before the annealing process is too thin, the particle shape of the light scattering layer 4c formed after the annealing process is an example for a long wavelength light having a wavelength of 1000 nm or more. Such a state occurs that the interval between the particle shapes of the light scattering layer 4c becomes smaller or the interval becomes smaller. As a result, even if the heat treatment process is performed for a long time, the optical characteristics tend not to exhibit sufficient scattering characteristics.

  In addition, when the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is larger than 85 nm, the value of Td / Tt with respect to light having a wavelength of 600 nm and a wavelength of 1000 nm is substantially zero. That is, even if the heat treatment is performed in a state where the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is large, the heat treatment conditions for the silver thin film 4b in the present embodiment shown in Table 2 are island-like. The uneven shape is not formed, and the formation of a gap through which light is transmitted is insufficient, so that it does not function as a light scattering layer.

  Therefore, the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is preferably in the range of 85 nm or less, and 45 nm can be obtained as a Td / Tt value of 25% or more for light having a wavelength of 600 nm and a wavelength of 1000 nm. The range of ˜60 nm or less is more preferable.

  5 and 6 are characteristic diagrams showing the dependence of the scattering effect on the light scattering layer 4c on the annealing treatment time in the thin film solar cell of the example manufactured by the method for manufacturing the thin film solar cell according to the present embodiment described above. It is. FIG. 5 shows a case where the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is 50 nm, the annealing time is shown on the horizontal axis, and the total light transmittance Tt of the light scattering layer 4c is shown on the vertical axis. The ratio Td / Tt (%) of the diffuse transmittance Td is shown. FIG. 6 shows a case where the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is 30 nm, the annealing time is shown on the horizontal axis, and the total light transmittance Tt of the light scattering layer 4c is shown on the vertical axis. The ratio Td / Tt (%) of the diffuse transmittance Td is shown. Also, the circle symbol (◯) in FIGS. 5 and 6 represents Td / Tt for light having a wavelength of 600 nm. Also, the triangle symbol (black triangle) in FIGS. 5 and 6 represents Td / Tt for light having a wavelength of 1000 nm.

  FIG. 5 shows that when the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is 50 nm, the value of the scattering characteristic Td / Tt is approximately 25% or more with respect to the annealing treatment time. On the other hand, FIG. 6 shows that when the film thickness of the silver thin film 4b having a uniform thickness before the annealing treatment is 30 nm, the value of the scattering characteristics Td / Tt is less than 25% regardless of the annealing treatment time. . From these facts, it is understood that Td / Tt sufficient to show the light scattering characteristics in the light scattering layer 4c is greatly dependent on the film thickness of the silver thin film 4b before the annealing treatment.

  As described above, in the method for manufacturing the thin-film solar cell according to the first embodiment, the first backside transparent electrode layer is formed as a step of burying and forming the light scattering layer 4 c inside the backside transparent electrode layer 4. A step of forming an extremely thin silver thin film 4b having a uniform thickness on 4a, and a step of performing an annealing treatment as a heat treatment on the silver thin film 4b. Thereby, the silver thin film 4b is aggregated on the first back surface side transparent electrode layer 4a, and the light scattering layer 4c having an irregular shape such as a grain shape, a hemisphere shape or an island shape is formed on the first back surface transparent electrode 4a. Form. The formation and heat treatment of the ultrathin silver thin film 4b having a uniform thickness is performed at a temperature of 200 ° C. or less that does not adversely affect the already produced semiconductor photoelectric conversion layer 3.

  Therefore, according to the method for manufacturing the thin-film solar cell according to the first embodiment, the inside of the back-side transparent electrode layer 4 is not induced without inducing the performance degradation of the thin-film solar cell due to heat in the process of forming the light scattering layer 4c. Thus, the light scattering layer 4c can be formed, and a thin film solar cell having a good light confinement effect and excellent photoelectric conversion efficiency can be produced.

  In the above, a silver thin film is used as a material for forming the light scattering layer 4c as an example of implementation. However, it has a high optical reflectivity, and heat, laser light, electromagnetic waves such as ultraviolet rays are irradiated. Therefore, the material is not limited to silver (Ag) as long as it is a material capable of causing an aggregating action on the thin film that is the basis of the light scattering layer 4c and forming a pinhole-like hole. That is, as the material for forming the light scattering layer 4c, as in the case of silver (Ag), aluminum (Al), gold (Au), copper (Cu), etc. can be used as long as it exhibits a cohesive action by heat treatment. It is also possible to use an alloy material containing these elements. Even when such a material is used as a material for forming the light scattering layer 4c, the effect of the light scattering layer 4c due to fine unevenness can be obtained in the same manner as described above.

Embodiment 2. FIG.
In Embodiment 2, another method for manufacturing a thin-film solar cell according to Embodiment 1 will be described. Regarding the formation of the light scattering layer 4c, after the silver thin film 4b having a uniform film thickness is formed, the silver thin film 4b is selectively irradiated with light in the ultraviolet region using a UV lamp or the like. Only the silver thin film 4b can be formed as a light scattering layer having irregularities, islands, or pinholes. Thereby, as in the case of the first embodiment, it is possible to produce a structure having a function as the light scattering layer 4c.

  Since silver (Ag) absorbs light in the ultraviolet region (plasmon resonance absorption), the silver (Ag) thin film is selectively agglomerated by the irradiation of ultraviolet rays to form the light scattering layer 4c, irregularities, islands, Alternatively, a pinhole-like structure can be obtained, and in this case as well, the light scattering layer 4c having a light scattering effect can be formed in a low temperature region as in the case of annealing at 200 ° C. or lower. That is, this utilizes the plasmon absorption of silver (Ag) seen in the vicinity of a wavelength of 326 nm, and selectively gives thermal energy only to the silver thin film 4b to induce the same aggregating action. In this case, for irradiation of light in the ultraviolet region, for example, a laser such as YAG triple wave (wavelength 355 nm), excimer KrF (wavelength 248 nm), XeCl (wavelength 308 nm) can be used. A UV lamp (wavelength 254 nm or the like) using a discharge tube can also be used. In order to agglomerate a film mainly composed of silver as described above, ultraviolet rays in the wavelength range of 200 to 360 nm are effective, and the absorption effect is particularly high and more effective at wavelengths in the range of 240 to 340 nm.

  The light scattering layer 4c can be formed at room temperature by irradiating the silver thin film 4b with light in the ultraviolet region, and a temperature higher than 200 ° C. is not required in the manufacturing process. Therefore, the light scattering layer 4c can be formed without setting the substrate temperature at a high temperature such as 300 ° C. as in the prior art. That is, the light scattering layer 4c is formed on the back surface side transparent electrode layer 4 without inducing the performance degradation of the thin film solar cell due to the high heat in the manufacturing process which has been a problem in the prior art.

  Hereinafter, the manufacturing method of the thin-film solar cell according to the second embodiment will be described with reference to FIGS. 7, 3-1 to 3-4, FIG. 8-1, FIG. 8-2, FIG. To explain. FIG. 7 is a flowchart for explaining the method for manufacturing the thin-film solar cell according to the second embodiment. FIGS. 8-1 and FIGS. 8-2 are sectional drawings for demonstrating the manufacturing method of the thin film solar cell concerning Embodiment 2. FIGS.

  First, the steps (steps S10 to S40) described in the first embodiment with reference to FIGS. 3-1 to 3-4 are performed, and the transparent electrode 2 and the semiconductor photoelectric conversion are formed on the translucent insulating substrate 1. Layer 3, first backside transparent electrode layer 4 a, and silver thin film 4 b having a uniform thickness are sequentially formed.

  Next, heat treatment is performed on the ultrathin silver thin film 4b having a uniform thickness so that the light scattering layer 4c having an irregular shape such as a grain shape, a hemispherical shape, or an island shape is formed on the first back transparent electrode 4a. (Step S150, FIG. 8-1). For example, the light 7 in the ultraviolet region is irradiated using the ultraviolet irradiation device 6 to the silver thin film 4b having a uniform thickness. This makes it possible to form a layer having a non-uniform light transmission portion such as a grain shape, hemisphere, island shape, or having a large number of pinholes in a plane by using an agglomeration effect by energy at the time of plasmon resonance absorption of silver (Ag). It can be formed (FIG. 8-2). Here, since light having a low reflectance of silver (Ag) is irradiated, the light is mainly absorbed by the silver thin film 4b and used for aggregation of the silver thin film 4b. The energy of the light 7 in the ultraviolet region is not transmitted to the semiconductor photoelectric conversion layer 3 so that the semiconductor photoelectric conversion layer 3 does not reach a high temperature. Therefore, it can suppress that the semiconductor photoelectric converting layer 3 deteriorates with a heat | fever.

  Irradiation of the light 7 in the ultraviolet region to the silver thin film 4b can be performed at room temperature, and a temperature higher than 200 ° C. is not required in the manufacturing process. Therefore, the light scattering layer 4c can be formed on the back surface side transparent electrode layer 4 without inducing the performance degradation of the thin film solar cell due to high heat.

  Hereinafter, the thin film solar cell shown in FIG. 1-1 is obtained by carrying out the steps (step S60, step S70) described with reference to FIGS. 3-6 and 3-7 in the first embodiment.

  As described above, in the method for manufacturing a thin-film solar cell according to the second embodiment, the first backside transparent electrode layer is formed as a step of burying and forming the light scattering layer 4 c inside the backside transparent electrode layer 4. A step of forming an extremely thin silver thin film 4b having a uniform thickness on 4a, and a step of irradiating the silver thin film 4b with light in the ultraviolet region. Thereby, the silver thin film 4b is aggregated on the first back surface side transparent electrode layer 4a, and the light scattering layer 4c having an irregular shape such as a grain shape, a hemisphere shape or an island shape is formed on the first back surface transparent electrode 4a. Form. The ultra-thin silver thin film 4b having a uniform thickness is formed at a temperature of 200 ° C. or less that does not adversely affect the already produced semiconductor photoelectric conversion layer 3, and irradiation of light in the ultraviolet region is performed at room temperature. It does not require a temperature higher than 200 ° C.

  Therefore, according to the method for manufacturing the thin-film solar cell according to the second embodiment, as in the case of the first embodiment, without inducing the performance degradation of the thin-film solar cell due to heat in the process of forming the light scattering layer 4c. In addition, the light scattering layer 4c can be formed inside the transparent electrode layer 4 on the back side, and a thin film solar cell having a good light confinement effect and excellent in photoelectric conversion efficiency can be produced.

  As described above, the method for producing a thin film solar cell according to the present invention is useful for producing a thin film solar cell having a good light confinement effect and excellent in photoelectric conversion efficiency.

DESCRIPTION OF SYMBOLS 1 Translucent insulating substrate 2 Transparent electrode layer 3 Semiconductor photoelectric conversion layer 3p p-type semiconductor layer 3i i-type semiconductor layer (intrinsic semiconductor layer)
3n n-type semiconductor layer 4 back surface side transparent electrode layer 4a back surface side transparent electrode layer 4b silver thin film 4c light scattering layer 4d back surface side transparent electrode layer 5 back surface reflective electrode layer 6 ultraviolet irradiation device 7 light in ultraviolet region

Claims (5)

A first step of forming a transparent electrode layer made of a light-transmitting conductive material on a light-transmitting insulating substrate;
A second step of forming a semiconductor photoelectric conversion layer comprising a semiconductor layer and performing photoelectric conversion on the transparent electrode layer;
A third step of forming a back side transparent electrode layer made of a translucent conductive material having a light scattering layer on the semiconductor photoelectric conversion layer;
A fourth step of forming a backside reflective electrode layer made of a reflective conductive material on the backside transparent electrode layer;
Including
The third step includes a fourth step of forming a light scattering layer material film including a constituent material of the light scattering layer on the semiconductor photoelectric conversion layer with a substantially uniform thickness;
A fifth step of forming the light scattering layer by aggregating the light scattering layer material film on the semiconductor photoelectric conversion layer at a temperature of 200 ° C. or less with respect to the light scattering layer material film;
Including,
A method for producing a thin film solar cell. In the fifth step, the light scattering layer material film is annealed in a temperature range of 200 ° C. or lower,
The manufacturing method of the thin film solar cell of Claim 1 characterized by these. Irradiating the light scattering layer material film with ultraviolet rays in the fifth step;
The manufacturing method of the thin film solar cell of Claim 1 characterized by these. The light scattering layer material film is a film mainly composed of silver, and the light in the ultraviolet region has a wavelength of 200 to 360 nm;
The manufacturing method of the thin film solar cell of Claim 3 characterized by these. The light scattering layer material film is a silver film having a film thickness of 45 nm to 60 nm;
The manufacturing method of the thin film solar cell of Claim 1 characterized by these.

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