JP2009016556A - Light scattering film for solar battery, optical member for solar battery and solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light scattering film for a solar battery and an optical member for a solar battery, which have high optical confinement effect, and to provide a solar battery which has high conversion efficiency. <P>SOLUTION: The light scattering film 2 is the light scattering film for a solar battery formed by dispersing scattered particles having a refractive index lower than that of matrix resin in the matrix resin, and is characterized in that the average particle size of the scattered particles is 1.0 to 10.0 μm and the difference in refractive indexes between the matrix resin and scattered particles is 0.05 to 0.30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light scattering film for a solar cell, an optical member for a solar cell, and a solar cell.

In recent years, solar cells have been actively researched as an alternative energy to petroleum energy and with the increasing need for clean energy.
Examples of solar cells include single crystal silicon solar cells, polycrystalline silicon solar cells, thin film silicon solar cells, compound semiconductor solar cells, and dye-sensitized solar cells. Further, the thin film silicon solar cell includes an amorphous silicon solar cell and a microcrystalline silicon solar cell. Furthermore, there are a tandem solar cell in which an amorphous silicon solar cell and a microcrystalline silicon solar cell are stacked, and a triple solar cell in which three solar cells are stacked.
Among these, thin-film silicon solar cells have abundant constituent materials on the earth, are easy to increase in area, can be thinly formed, and consume consumption of constituent materials. It has excellent features such as few and high technical maturity.

By the way, in the thin film silicon solar cell, there is a problem that the current value to be generated cannot be increased. Generally, in a solar cell, the current generated increases with the amount of light absorption. Therefore, the current value can be increased by increasing the thickness of the i layer that contributes to light absorption in the photoelectric conversion layer.
However, when an amorphous silicon solar cell is used as a thin-film silicon solar cell, increasing the film thickness of the i layer increases the photodegradation rate, and the conversion efficiency may decrease on long-term use. Further, when a microcrystalline silicon solar cell is used as the thin-film silicon solar cell, there is a problem that if the i layer is thickened, it takes a long time to produce and the productivity is lowered.
Furthermore, even in the case of amorphous silicon solar cells and microcrystalline silicon solar cells, if the i layer is thickened, the built-in electric field is less likely to be applied. Become.

Therefore, a method of increasing the amount of light absorption in the i layer without increasing the thickness of the i layer has been studied. In Patent Document 1, a structure called “texture structure” having an uneven surface structure is provided on the light-receiving surface side of the i layer by a transparent conductive film, and incident light is scattered by this “texture structure”. A method of increasing the amount of light absorbed by the i layer by increasing the path length of light passing through the layer is disclosed.
However, when a semiconductor film is formed on the uneven surface structure having the texture structure described above, it is not patented that many defects are induced in the semiconductor film to deteriorate the output voltage and the fill factor, thereby deteriorating the conversion efficiency. It is disclosed in Document 1.

On the other hand, Patent Document 2 discloses an example in which a thin film in which insulating fine particles are dispersed in a binder is provided on the light receiving surface side of the i layer. Since the uneven surface due to the shape of the insulating fine particles is formed on the binder surface of this thin film, the incident light is scattered on the surface in the same manner as the texture structure described above, and the amount of light absorbed by the i layer is reduced. Can be increased.
However, when a semiconductor film is formed on this thin film, a defect is caused in a part of the semiconductor film due to the uneven shape of the surface, and the defect may cause a reflection loss to deteriorate the conversion efficiency.
Therefore, there is a demand for a light scattering film that does not cause defects in a semiconductor layer formed thereon and has a high light confinement effect. At the same time, an optical member having the light scattering film and a solar cell having the light scattering film or the optical member and having high conversion efficiency are required.
Japanese Patent No. 2862174 Japanese Patent No. 3706835 Y. Nasuno et al., Japanese Journal Applied Physics (Jpn. J. Appl. Phys. Lett.), 40, L303 (2001).

This invention is made | formed in view of the said situation, and aims at providing the solar cell light-scattering film | membrane and solar cell optical member with high light confinement effect, and a solar cell with high conversion efficiency.
Another object of the present invention is to provide a light scattering film for solar cells in which defects are unlikely to occur in a semiconductor layer formed thereon.

  The light scattering film for solar cells of the present invention is a light scattering film for solar cells in which scattering particles having a refractive index higher than that of the matrix resin are dispersed in a matrix resin, and the average particle size of the scattering particles is 1. It is 0.0 micrometer or more and 10.0 micrometers or less, and the refractive index difference of the said matrix resin and the said scattering particle is 0.05 or more and 0.30 or less.

  The “average particle diameter” refers to the average value of the diameters calculated based on the diameter when the scattering particles are spherical, and the short diameter when the scattering particles are spheroids.

  30 mass percent or less may be sufficient as the ratio of the said scattering particle to the light-scattering film for solar cells of this invention. Further, the film thickness of the light scattering film for solar cell of the present invention may be 1.0 μm or more.

  Moreover, the optical member for solar cells of this invention is equipped with the light-scattering film for solar cells of this invention, and the transparent base | substrate arrange | positioned at one surface of the said light-scattering film for solar cells, It is characterized by the above-mentioned.

  Furthermore, the solar cell of the present invention is a solar cell having a photoelectric conversion layer, and the solar cell light-scattering film of the present invention is disposed on at least the light incident side of the photoelectric conversion layer. Features.

According to the light scattering film for solar cell, the optical member for solar cell, and the solar cell of the present invention, the light scattering film for solar cell and the optical member for solar cell with high light confinement effect, and the solar cell with high conversion efficiency are configured. can do.
Moreover, according to the light-scattering film for solar cells and the optical member for solar cells of this invention, it can suppress that a defect arises in the semiconductor layer formed into a film on it.

Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
(First embodiment)
FIG. 1 is a schematic cross-sectional view showing an example of a solar cell according to an embodiment of the present invention.
In the solar cell 100 of this embodiment, a light scattering film (light scattering film for solar cell) 2, an upper electrode layer 3, a photoelectric conversion layer 4 and a lower electrode layer 5 are illustrated on one surface of a substrate (transparent substrate) 1. 1 are stacked in the order shown in FIG.

  The substrate 1 has a light capturing surface 1a, and one surface 2a of the light scattering film 2 is bonded to the surface 1b on the opposite side. The other surface side of the light scattering film 2 is formed as a flat surface 2b having flatness. In this way, an optical member (solar cell optical member) 10 composed of the substrate 1 and the light scattering film 2 is formed.

The photoelectric conversion layer 4 is formed by stacking a p-type thin film silicon layer 41, an i-type thin film silicon layer 42, and an n-type thin film silicon layer 43 in the order shown in FIG.
The lower electrode layer 5 is formed by laminating a lower transparent conductive electrode 51 and a metal electrode 52 in the order shown in FIG.
The structure in which the substrate 1, the upper electrode layer 3, the photoelectric conversion layer 4, and the lower electrode layer 5 are laminated in this order is referred to as “super straight type” in the following description.

  In the super straight type, light is incident on the substrate 1 from the light capturing surface 1a as shown by an arrow A in FIG. 1, and after passing through the inside of the substrate 1, is joined to the surface 1b opposite to the light capturing surface 1a. Incident on the light scattering film 2. The light incident on the light scattering film 2 passes through the light scattering film 2 and the upper electrode layer 3 and enters the photoelectric conversion layer 4. Then, a photovoltaic force is generated in the photoelectric conversion layer 4, and light is converted into electric power.

  The substrate 1 is preferably made of a transparent material. This is because if it is transparent, light is not lost in the substrate 1 and the conversion efficiency in the photoelectric conversion layer 4 can be improved. Examples of the transparent material include glass, quartz, and transparent polyimide.

The substrate 1 is preferably made of a heat resistant material. In the case where the photoelectric conversion layer 4 is formed of an amorphous silicon layer, it is preferable to have heat resistance because heat treatment is performed in the manufacturing process.
In addition, when the solar cell 100 is used outdoors, the surface of the substrate 1 may be heated by sunlight, which is advantageous when it is heat resistant.

The light scattering film 2 is configured by dispersing scattering particles having a refractive index higher than that of the matrix resin in the matrix resin.
The matrix resin and the scattering particles are preferably made of a transparent material. This is because the conversion efficiency in the photoelectric conversion layer 4 can be improved by transmitting light from the light scattering film 2 to the photoelectric conversion layer 4 without loss.

The difference in refractive index between the matrix resin and the scattering particles is preferably 0.05 or more and 0.30 or less, and more preferably 0.10 or more and 0.13 or less.
A difference in refractive index between the matrix resin and the scattering particles of less than 0.05 is not preferable because light cannot be effectively scattered. On the other hand, when the refractive index difference between the matrix resin and the scattering particles exceeds 0.30, it is not preferable because light cannot be sufficiently incident on the photoelectric conversion layer 4.
“Refractive index difference between matrix resin and scattering particles” means a refractive index difference in the ultraviolet region, visible light region, and infrared region, but in the wavelength region where the transmittance is at least 70% or more, The refractive index difference with the scattering particles may be 0.05 or more and 0.30 or less.

The light scattering film 2 preferably has a flat surface on which electrode layers and the like are laminated. That is, the surface roughness of the flat surface 2b in FIG. 1 is preferably 50 to 300 mm, more preferably 50 to 150 mm, and still more preferably 50 to 100 mm. Here, the surface roughness refers to a so-called arithmetic average roughness Ra.
If the surface roughness Ra is 300 mm or less, the upper electrode layer 3, the photoelectric conversion layer 4 and the lower electrode layer 5 formed thereon can be formed flat.
When the surface roughness Ra of the flat surface 2b exceeds 300 mm, the flatness of the upper electrode layer 3, the photoelectric conversion layer 4 and the lower electrode layer 5 laminated on the flat surface 2b cannot be increased. This is not preferable because defects in the thin film silicon layers 41 to 43 constituting the photoelectric conversion layer 4 may increase.
On the other hand, if the surface roughness Ra of the flat surface 2b is less than 50 mm, formation of a film becomes difficult and production efficiency is lowered, which is not preferable.
The surface roughness Ra can be measured, for example, with a contact-type film thickness meter (trade name “Dektak 16000” manufactured by ULVAC, Inc.).

Furthermore, the transmittance of the light scattering film 2 is preferably 70% or more, more preferably 88% or more, and still more preferably 90% or more.
When the transmittance of the light scattering film 2 is less than 70%, it is not preferable because light cannot be sufficiently incident on the photoelectric conversion layer 4 and conversion efficiency in the photoelectric conversion layer 4 cannot be improved.
The “transmittance” of the light scattering film 2 means the transmittance for light in the ultraviolet region, visible light region, and infrared region, but the transmittance must be 70% or more in all regions from ultraviolet to infrared. However, the transmittance may be 70% only in a specific part of the region, for example, a visible light region having a wavelength of 400 nm to 800 nm.
The transmittance of the light scattering film 2 can be measured, for example, by measuring the transmittance with air as a reference with a spectrometer (trade name “U4000” manufactured by Hitachi, Ltd.) and collecting the transmitted light with an integrating sphere.

In addition, the haze ratio of the light scattering film 2 is preferably 58 to 90%, and more preferably 65 to 79%.
When the haze ratio of the light-scattering film 2 is less than 58%, the light-scattering property is lowered and light cannot be effectively confined, which is not preferable. On the other hand, if the haze ratio of the light scattering film 2 exceeds 90%, the transmittance may be lowered, which is not preferable.
The “haze ratio” of the light scattering film 2 means a haze ratio with respect to light in the ultraviolet region, visible light region, and infrared region, and the haze ratio is 58 to 90 in a wavelength region where the transmittance is at least 70% or more. %.
The haze ratio of the light scattering film 2 can be measured by, for example, a haze meter (trade name “HM-150” manufactured by Murakami Color Research Co., Ltd.).

An excellent light confinement effect can be obtained when the transmittance of the light scattering film 2 is 70% or more and the haze ratio is 58 to 90%. The “light confinement effect” refers to an effect in which light incident inside the solar cell 100 is not radiated from the inside of the solar cell 100 to the outside.
As shown in FIG. 1, the solar cell 100 has a light capturing surface 1 a on one surface side, and the other surface side is constituted by a metal electrode 52. Therefore, when the light scattering film 2 is not provided in the solar cell 100, the light that has not been converted into electrical energy by the photoelectric conversion layer 4 among the light incident from the light capturing surface 1 a is reflected by the one surface 52 a of the metal electrode 52. May be released to the outside.
However, by providing the light scattering film 2 having a light confinement effect on the light capturing surface 1 a side of the photoelectric conversion layer 4, the light incident from the light capturing surface 1 a side and reflected by the one surface 52 a of the metal electrode 52 is exposed to the outside. Can be prevented.

  As a material of the matrix resin constituting the light scattering film 2, acrylic resin, silicone resin, epoxy acrylate resin, fluorene resin, or the like can be used. When the acrylic resin is halogenated, the refractive index can be further lowered. For example, a fluorinated acrylic resin can be preferably used.

Next, as the material of the scattering particles constituting the light scattering film 2, for example, acrylic particles, styrene acrylic particles and cross-linked products thereof, melamine resin particles (melamine-formalin condensate particles, benzoguanamine-melamine-formaldehyde condensate particles) ), Benzoguanamine-formaldehyde condensate particles, and silicone resin particles. PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer) Fluorine-containing polymer particles such as can be used. When an inorganic material such as TiO ₂ or SiO ₂ is added to the melamine resin, good scattering characteristics can be obtained, and such a mixture can also be preferably used.
In selecting materials for the matrix resin and the scattering particles, it is preferable to select the scattering particles so that the scattering particles have a higher refractive index than the matrix resin and have a refractive index difference in the above range.

The average particle diameter of the scattering particles is preferably 1.0 to 10.0 μm, and more preferably 1.2 to 2.0 μm.
When the average particle diameter of the scattering particles is less than 1.0 μm, it is not preferable because sufficient scattering cannot be obtained. On the other hand, when the average particle diameter of the scattering particles exceeds 10.0 μm, it is not preferable because the particle diameter is large and immediately sinks in the liquid.
The average particle diameter of the scattering particles is measured with a particle size distribution meter (trade name “SD-2000” manufactured by Sysmex Corporation). When the scattering particles are spherical, the average value of the diameters of the scattering particles When the scattering particles are spheroids, the average value of the minor axis.

  The film thickness of the light scattering film 2 is preferably 1.0 μm or more, and more preferably larger than the average particle diameter of the scattering particles to be dispersed. When applied to a thin-film silicon solar cell, the thinner the film, the better. However, when the film thickness is less than 1.0 μm, it is difficult to obtain good scattering characteristics. When the film thickness of the light scattering film 2 is smaller than the average particle diameter of the scattering particles, an uneven shape caused by the scattering particles is formed on the surface of the light scattering film 2, and the surface roughness of the flat surface 2b is set to 300 mm. It becomes difficult to make it below.

The content of the scattering particles dispersed in the matrix resin is preferably set to 30% by mass or less, more preferably 20% by mass or less as the ratio of the scattering particles in the light scattering film.
When the ratio of the scattering particles in the light scattering film exceeds 30% by mass, the scattering particles cannot be uniformly dispersed, and the characteristics such as the transmittance and haze ratio of the light scattering film 2 may vary in the plane. Since it occurs, it is not preferable.
The higher the scattering particle content, the higher the haze value and the larger the surface roughness Ra. Therefore, the content is determined based on the design haze value of the light scattering film to be created.

  The light scattering film 2 is prepared by first preparing a solution in which scattering particles are dispersed in an uncured matrix resin, and applying this solution to a spin coating method, a roll coating method, a spray method, a bar coating method, a die coating method, and a flow coating method. Alternatively, a wet process such as a dipping method is used to form a film on the substrate surface. The solution can contain additives such as an organic solvent, a dispersion aid, a leveling agent, and a coupling agent.

  The light scattering film 2 is preferably made of a heat resistant material. In the case where the photoelectric conversion layer 4 is formed of an amorphous silicon layer, heat treatment is performed in the manufacturing process, and thus heat resistance is desirable. Also, when the solar cell is used outdoors, the substrate surface may be heated by sunlight, so that it is desirable to have heat resistance. It is desirable to have a heat resistance of at least 230 to 250 ° C. for 3 hours.

The light scattering film 2 preferably has a thermal expansion coefficient close to that of Si, and is preferably less than 60 ppm / ° C.
Furthermore, it is desirable for the light scattering film 2 to have ultraviolet resistance by adding an ultraviolet absorber or including an ultraviolet absorbing functional layer. This is because when the solar cell is used outdoors, the substrate surface is exposed to ultraviolet rays by sunlight. An ultraviolet absorption functional layer may be provided outside the light scattering film 2. For example, an ultraviolet absorption functional layer may be provided between the light scattering film 2 and the substrate.

As a material of the upper electrode layer 3, a transparent conductive oxide is preferable.
For example, indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), cadmium oxide (CdO), indium cadmium oxide (CdIn ₂ O ₄ ), cadmium tin oxide (Cd ₂ SnO ₄ ), Examples include zinc tin oxide (Zn ₂ SnO ₄ ) and indium zinc oxide (In—Zn—O).
Further, impurities may be added (dope) to the transparent conductive oxide. For example, indium oxide is doped with tin (Sn), molybdenum (Mo), titanium (Ti), tin oxide is doped with antimony (Sb) and fluorine (F), zinc oxide is doped with indium, aluminum, gallium ( Ga) can be doped.
In particular, tin oxide doped with fluorine and zinc oxide doped with gallium or aluminum are preferred. Since the upper electrode layer 3 is exposed to hydrogen plasma in the next step of forming the photoelectric conversion layer 4, a material resistant to a reducing atmosphere such as F-doped SnO ₂ or Ga-doped or Al-doped ZnO is preferable. is there.

  Examples of the method for forming the upper electrode layer 3 include, but are not limited to, a sputtering method, a vapor deposition method, a CVD (Chemical Vapor Deposition) method, and a sol-gel method.

The photoelectric conversion layer 4 is formed by stacking a p-type thin film silicon layer 41, an i-type thin film silicon layer 42, and an n-type thin film silicon layer 43.
The material constituting the photoelectric conversion layer 4 may be either crystalline or amorphous silicon. Alternatively, a material containing 30% or more of silicon such as crystalline and amorphous silicon carbide or silicon germanium may be used.

  For the formation of the photoelectric conversion layer 4, a production method such as a plasma CVD method, a photo CVD method, or a hot-wire CVD method is used. In particular, it is preferable to use a plasma CVD method. This is because the plasma CVD method can form a film with good film quality with high productivity.

In the process of forming the photoelectric conversion layer 4, the p-type thin film silicon layer 41 is first formed by doping p-type dopants such as boron, gallium, and aluminum.
Examples of the raw material used for the p-type doping include a boron source such as diborane, B (CH ₃ ) ₃ , and BF ₃ , a gallium source such as trimethyl gallium and triethyl gallium, and an aluminum source such as trimethylaluminum. Examples thereof include triethylaluminum, but are not limited to these materials.

  In addition, by doping carbon when forming the p-type thin film silicon layer 41, the band gap of the p-type thin film silicon layer can be increased, and more light can be guided into the i layer. It is good also as a structure which can produce | generate a carrier. The raw material carbon source in this case can be exemplified by methane.

The i-type thin film silicon layer 42 is formed without doping with a dopant after the p-type thin film silicon layer 41 is formed.
The n-type thin film silicon layer 43 is formed by forming an i-type thin film silicon layer 42 and then doping phosphorus or the like as an n-type dopant.

The lower electrode layer 5 is formed by sequentially laminating a lower transparent conductive electrode 51 and a metal electrode 52.
Examples of the method for creating the lower electrode layer 5 include, but are not limited to, a sputtering method, a vapor deposition method, a CVD (Chemical Vapor Deposition) method, and a sol-gel method.

The material of the lower transparent conductive electrode 51 may be any material that is conductive and made of a transparent oxide.
For example, indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), cadmium oxide (CdO), indium cadmium oxide (CdIn ₂ O ₄ ), cadmium tin oxide (Cd ₂ SnO ₄ ), Examples include zinc tin oxide (Zn ₂ SnO ₄ ) and indium zinc oxide (In—Zn—O).
Further, an impurity may be added (doped) to the above oxide. For example, indium oxide is doped with tin (Sn), molybdenum (Mo), titanium (Ti), tin oxide is doped with antimony (Sb) and fluorine (F), zinc oxide is doped with indium, aluminum, gallium ( Ga) can be doped.

  The material of the metal electrode 52 is preferably a metal such as Al, Au, Ag, Cu, Pt, or Cr, and particularly preferably Al. This is because Al has specular reflectivity and can confine light in the device and can efficiently extract carriers generated in the photoelectric conversion layer 4. Moreover, the alloy containing the metal mentioned above may be sufficient.

Next, a second embodiment of the present invention will be described with reference to FIG. The difference between the solar cell 101 of the present embodiment and the solar cell 100 of the first embodiment described above is that the lower photoelectric conversion layer 6 is laminated between the photoelectric conversion layer 4 and the lower electrode layer 5. .
In addition, about the structure similar to the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

(Second Embodiment)
FIG. 2 is a schematic cross-sectional view showing the solar cell 101 of the present embodiment.
In the solar cell 101 of the present embodiment, a light scattering film 2, an upper electrode layer 3, a photoelectric conversion layer 4, a lower photoelectric conversion layer 6, and a lower electrode layer 5 are laminated on a substrate 1 in the order shown in FIG. It is configured.

The lower photoelectric conversion layer 6 laminated between the photoelectric conversion layer 4 and the lower electrode layer 5 has a p-type thin film silicon layer 61, an i-type thin film silicon layer 62, and an n-type thin film silicon layer 63 in the order shown in FIG. It is formed by stacking.
As described above, the structure in which the substrate 1, the light scattering film 2, the upper electrode layer 3, the photoelectric conversion layer 4, the lower photoelectric conversion layer 6, and the lower electrode layer 5 are stacked is referred to as “tandem type” in the following description. Called.

  In the tandem type, light enters the substrate 1 from the light capturing surface 1a of the substrate 1 and passes through the inside of the substrate 1 and then joins to the surface 1b opposite to the light capturing surface 1a, as in the first embodiment. The incident light enters the light scattering film 2. The incident light passes through the light scattering film 2 and the upper electrode layer 3 and enters the photoelectric conversion layer 4 and the lower photoelectric conversion layer 6. Light is converted into electric power by generating a photovoltaic force in the photoelectric conversion layer 4 and the lower photoelectric conversion layer 6.

As shown in FIG. 2, the tandem type has a structure in which two photoelectric conversion layers of a photoelectric conversion layer 4 and a lower photoelectric conversion layer 6 are connected in series. Since it has two photoelectric conversion layers, it can make a photovoltaic power larger than the solar cell which has only one photoelectric conversion layer.
In the tandem type, when a solar cell element having a large band gap is installed on the light incident side, light can be used more effectively, so that the photoelectric conversion layer 4 is an amorphous silicon solar cell and the lower photoelectric conversion layer 6 is a microcrystal. A silicon solar cell or a silicon germanium solar cell is preferred.

Next, a third embodiment of the present invention will be described with reference to FIG. The difference between the solar cell 102 of the present embodiment and the solar cell 100 of the first embodiment described above is that the light scattering film and the substrate are stacked apart.
In addition, about the structure similar to the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

(Third embodiment)
FIG. 3 is a schematic cross-sectional view showing the solar cell 102 of the present embodiment.
The solar cell 102 of the present embodiment is configured by laminating the lower electrode layer 5, the photoelectric conversion layer 4, the upper electrode layer 3, and the light scattering film 2 on the substrate 11 in the order shown in FIG. The light scattering film 2 is laminated so as to be spaced apart.
Furthermore, one surface of the upper electrode layer 3 is bonded to the flat surface 2b of the light scattering film 2 in the same manner as the solar cell 100 of the first embodiment. Therefore, the flatness of the upper electrode layer 3, the photoelectric conversion layer 4, and the lower electrode layer 5 is ensured.
A light capturing surface 2 a is provided on the other surface side of the flat surface 2 b of the light scattering film 2 so that light can be captured inside the solar cell 102.
In the following description, the structure in which the light scattering film and the substrate are stacked apart as described above is referred to as a “substrate type”.

  In the substrate type, light is incident on the light scattering film 2 from the light capturing surface 2a as indicated by an arrow A in FIG. The incident light passes through the inside of the light scattering film 2 and then enters the upper electrode layer 3 bonded to the flat surface 2b opposite to the light capturing surface 2a. The light further passes through the upper electrode layer 3 and enters the photoelectric conversion layer 4. Then, a photovoltaic force is generated in the photoelectric conversion layer 4, and light is converted into electric power.

  Therefore, in the case of the substrate type, no light enters from the substrate 11, and therefore the substrate 11 may be formed of an opaque material. That is, as a material for forming the substrate 11, a transparent material such as glass, quartz, and transparent polyimide can be used as in the substrate 1 in the first embodiment, but in addition to this, an opaque polyimide, A stainless steel plate or the like can also be used.

  According to the light scattering film 2 of the present invention described above, since scattering particles having a refractive index higher than that of the matrix resin are dispersed in the matrix resin, light is effectively scattered. In addition, since the average particle diameter of the scattering particles is 1.0 μm or more and 10.0 μm or less and the refractive index difference between the matrix resin and the scattering particles is 0.05 or more and 0.30 or less, it is high in the light scattering film 2. A transmittance and a high haze ratio can be realized at the same time. Therefore, by applying to a solar cell, the light confinement effect can be improved and the conversion efficiency of the solar cell can be improved.

  In addition, since the ratio of the scattering particles in the light scattering film 2 is 30 mass percent or less, the surface on which the semiconductor layers and the like are stacked can be formed flat, and defects are less likely to occur in the formed semiconductor layer. . Therefore, by applying to a solar cell, it is possible to configure a solar cell with good conversion efficiency without deterioration of output voltage and curve factor due to defects in the semiconductor film.

  Furthermore, since the film thickness of the light scattering film is 1.0 μm or more, it constitutes a light scattering film in which the laminated surface of a semiconductor or the like is formed flat while having a thickness sufficiently applicable to a thin film silicon solar cell. be able to.

  Furthermore, according to the optical member 10 of the present invention, the optical member 10 includes the light scattering film 2 and the transparent substrate 1 disposed on one surface of the light scattering film 2. The confinement effect can be improved and the conversion efficiency of the solar cell can be improved.

  In addition, since the light scattering film 2 or the optical member 10 is disposed at least on the light capturing side of the photoelectric conversion layer 4, the solar cell of the present invention has a high light confinement effect and a high conversion efficiency. Can do.

  Hereinafter, the present invention will be described more specifically based on examples. However, the present invention is not limited only to these examples.

Example 1
First, 5 parts by mass of melamine / formaldehyde condensation particles (trade name “Eposter S12” manufactured by Nippon Shokubai Co., Ltd.), 20 parts by mass of alkali-soluble acrylic resin, and polyfunctional acrylic monomer (manufactured by Toagosei Co., Ltd.) , Trade name “Aronix M-400”), 10 parts by weight, photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name “Irgacure 907”), 0.5 part by weight, and organic solvent (propylene glycol monomethyl ether) A coating solution for forming a light scattering film was prepared by sufficiently mixing 120 parts by mass of acetate).
Melamine / formaldehyde condensation particles having an average particle diameter of 1 to 2 μm were used.

Next, a predetermined amount of the above coating solution was dropped onto a Corning 1737 glass substrate, and this glass substrate was rotated at a rotation speed of 800 rpm for 5 seconds to form a coating film. After drying this coating film, baking is performed at 230 ° C. for 60 minutes to form a 2.5 μm thick light scattering film on a Corning 1737 glass substrate, and an optical member composed of the glass substrate and the light scattering film is produced. did.
The surface of the produced light scattering film was extremely flat, and the surface roughness Ra was 230 mm. The haze value of the light scattering film was 58.2%.

Next, a ZnO: Ga (Ga: 5 wt%) ceramic target was sputtered using a DC magnetron sputtering apparatus, and a gallium-doped zinc oxide transparent conductive film was formed to a thickness of 200 nm on the light scattering film to form an upper electrode layer. .
Next, using a plasma CVD apparatus, a p-type amorphous silicon carbide layer having a thickness of 20 nm, an i-type amorphous silicon layer having a thickness of 300 nm, and an n-type amorphous silicon layer having a thickness of 25 nm are formed on the gallium-doped zinc oxide transparent conductive film. Were formed in this order to form a photoelectric conversion layer.
Subsequently, using a DC magnetron sputtering apparatus, a ZnO: Ga (Ga: 5 wt%) ceramic target was sputtered to form a gallium-doped zinc oxide transparent conductive film having a thickness of 15 nm to form a lower transparent electrode.
Finally, a metal electrode made of aluminum having a film thickness of 100 nm is formed on the n-type amorphous silicon layer by a vacuum deposition apparatus, and a lower electrode made of a lower transparent electrode and a metal electrode is formed. A solar cell sample was prepared.

(Example 2)
First, in the coating liquid material used in Example 1, the content of melamine / formaldehyde condensation particles was 10 parts by mass, and further 2 parts by mass of colloidal silica (trade name “PMA-ST” manufactured by Nissan Chemical Co., Ltd.) was added. Except for this, a coating solution for forming a light scattering film was prepared in the same manner as in Example 1.

Next, a light scattering film having a thickness of 2.5 μm was formed by the same method as in Example 1, and an optical member composed of a glass substrate and a light scattering film was produced.
The surface of the produced light scattering film was extremely flat, and the surface roughness Ra was 200 mm. The haze value of this light scattering film was 71.2%.

  Furthermore, the upper electrode layer, the photoelectric conversion layer, the lower electrode composed of the lower transparent electrode and the metal electrode were sequentially laminated in the same manner as in Example 1 to produce a super straight type solar cell sample.

(Example 3)
First, 10 parts by mass of melamine / silica composite particles (manufactured by Nissan Chemical Industries, trade name “Optobeads”), 20 parts by mass of alkali-soluble acrylic resin, and polyfunctional acrylic monomer (manufactured by Toagosei Co., Ltd.) 10 parts by mass of trade name “Aronix M-400”, 0.5 parts by mass of photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name “Irgacure 907”), and colloidal silica (manufactured by Nissan Chemical Co., Ltd.) 2 parts by mass of the name “PMA-ST”) and 120 parts by mass of an organic solvent (propylene glycol monomethyl ether acetate) were sufficiently mixed to prepare a coating solution for forming a light scattering film.
The melamine / silica composite particles used had an average particle size of 2.0 μm.

Next, a light scattering film having a thickness of 3.0 μm was formed in the same manner as in Example 1, and an optical member composed of a glass substrate and a light scattering film was produced.
The surface of the produced light scattering film was extremely flat, and the surface roughness Ra was 215 mm. Further, the haze value of this light scattering film was 80.5%.

  Furthermore, the upper electrode layer, the photoelectric conversion layer, the lower electrode composed of the lower transparent electrode and the metal electrode were sequentially laminated in the same manner as in Example 1 to produce a super straight type solar cell sample.

(Comparative Example 1)
An Asahi-Type-U substrate (manufactured by Asahi Glass Co., Ltd.) having a haze ratio of 10% was prepared and set at a predetermined position in the chamber of the DC magnetron sputtering apparatus. Using this DC magnetron sputtering apparatus, a ZnO: Ga (Ga: 5 wt%) ceramic target is sputtered, a 200 nm gallium-doped zinc oxide transparent conductive film is formed on an Asahi-Type-U substrate, and an upper electrode layer is formed. did.
Next, using a plasma CVD apparatus, a p-type amorphous silicon carbide layer having a thickness of 20 nm, an i-type amorphous silicon layer having a thickness of 300 nm, and an n-type amorphous silicon layer having a thickness of 25 nm are formed on the gallium-doped zinc oxide transparent conductive film. Were formed in this order to form a photoelectric conversion layer.
Subsequently, using a DC magnetron sputtering apparatus, a ZnO: Ga (Ga: 5 wt%) ceramic target was sputtered to form a gallium-doped zinc oxide transparent conductive film having a thickness of 15 nm to form a lower transparent electrode.
Finally, a metal electrode made of aluminum having a film thickness of 100 nm is formed on the n-type amorphous silicon layer by a vacuum deposition apparatus, and a lower electrode made of a lower transparent electrode and a metal electrode is formed. A solar cell sample was prepared.

The characteristic measurement experiment of the solar cell sample produced in Examples 1-3 and Comparative Example 1 was conducted.
In a 25 ° C. atmosphere, a solar simulator creates AM1.5, 100 mW / cm ² simulated sunlight and irradiates the solar cell sample with four characteristics: open-circuit voltage, fill factor, short-circuit current, and conversion efficiency. Was measured.
The characteristics of the light scattering films of Examples 1 to 3 and Comparative Example 1 are shown together in Table 1, and the characteristics of the solar cells of Examples 1 to 3 and Comparative Example 1 are shown in Table 2 and FIG. Here, the transmittance is represented by an average value of transmittance measured values (measured with air as a reference) using an integrating sphere at wavelengths of 400 nm to 800 nm.
As can be seen from Table 2 and FIG. 4, the open-circuit voltage, the fill factor, the short-circuit current, and the conversion efficiency of the solar cell samples of Examples 1 to 3 are higher than those of the solar cell sample of Comparative Example 1 and have excellent power generation. It can be seen that the characteristics are shown.

It is a figure which shows an example of the solar cell which is embodiment of this invention. It is a figure which shows an example of the solar cell which is embodiment of this invention. It is a figure which shows an example of the solar cell which is embodiment of this invention. It is the graph showing the relationship between the haze rate of the light-scattering film of the Example of this invention, and an open circuit voltage, a fill factor, a short circuit current, and conversion efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate (transparent substrate), 1a ... Light extraction surface, 2 ... Light scattering film (light scattering film for solar cell), 2a ... Light extraction surface, 2b ... Flat surface, 3 ... Upper electrode layer, 4 ... Photoelectric conversion layer DESCRIPTION OF SYMBOLS 10 ... Optical member (optical member for solar cells), 41 ... p-type thin film silicon layer, 42 ... i-type thin film silicon layer, 43 ... n-type thin film silicon layer, 5 ... lower electrode layer, 51 ... lower transparent conductive electrode, 52 ... Metal electrode, 6 ... Lower photoelectric conversion layer, 61 ... P-type thin film silicon layer, 62 ... i-type thin film silicon layer, 63 ... N-type thin film silicon layer, 100, 101, 102 ... Solar cell

Claims (5)

A light scattering film for solar cells in which scattering particles having a refractive index higher than that of the matrix resin are dispersed in the matrix resin,
The average particle diameter of the scattering particles is 1.0 μm or more and 10.0 μm or less, and the refractive index difference between the matrix resin and the scattering particles is 0.05 or more and 0.30 or less. Light scattering film.   2. The solar cell light scattering film according to claim 1, wherein a ratio of the scattering particles in the solar cell light scattering film is 30 mass percent or less.   3. The solar cell light scattering film according to claim 1, wherein the solar cell light scattering film has a thickness of 1.0 μm or more. 4. The light-scattering film for solar cells according to any one of claims 1 to 3,
A transparent substrate disposed on one surface of the solar cell light scattering film;
An optical member for solar cells, comprising: A solar cell having a photoelectric conversion layer,
The solar cell light-scattering film of any one of Claim 1 to 3 is arrange | positioned at the surface at the side into which light injects at least of the said photoelectric converting layer, The solar cell characterized by the above-mentioned.

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