JP2009016553A - 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, which is free from a defect arising in a semiconductor layer formed thereupon and has high optical confinement effect, and to provide an optical member for a solar battery and a solar battery. <P>SOLUTION: The light scattering film 2 for a solar battery has a flat surface 2b formed by dispersing scattered particles having a refractive index lower than that of matrix resin in the matrix resin, the light scattering film 2 for a solar battery is characterized in that the transmissivity of the light scattering film 2 is ≥70% and the haze rate thereof is 57 to 90%. <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.

However, the thin film silicon solar cell has a problem that the generated current value cannot be increased. In general, in a solar cell, the value of a current generated with the amount of light absorption can be increased. Therefore, it is necessary to increase 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 decreases rather than considering long-term use. When a microcrystalline silicon solar cell is used as a thin-film silicon solar cell, increasing the thickness of the i layer requires a longer production time and lowers productivity.
Furthermore, in both amorphous silicon and microcrystalline silicon solar cells, increasing the thickness of the i layer makes it difficult to apply a built-in electric field, so the output voltage and curve factor deteriorate and conversion efficiency cannot be improved. It was.

  Therefore, a method for increasing the amount of light absorbed 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, as described in Non-Patent Document 1, this uneven surface structure of “texture structure” induces many defects in the semiconductor film and deteriorates the output voltage and the fill factor when the semiconductor film is formed thereon. In some cases, the conversion efficiency deteriorated.

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 this thin film forms an uneven shape on the binder surface due to the shape of the insulating fine particles, it scatters incident light on the surface like the “texture structure” and increases the amount of light absorbed by the i layer. Can be made. 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 causes a reflection loss to deteriorate the conversion efficiency.
Therefore, a light scattering film having a high light confinement effect without causing defects in the semiconductor layer formed thereon is desired. 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).

  An object of the present invention is to provide a solar cell light-scattering film and a solar cell optical member having a high light confinement effect without causing defects in a semiconductor layer formed thereon, and a solar cell having high conversion efficiency. And

In order to achieve the above object, the present invention employs the following configuration. That is,
The light scattering film for solar cells of the present invention is a light scattering film having a flat surface in which scattering particles having a refractive index lower than that of the matrix resin are dispersed in a matrix resin, and the transmittance of the light scattering film Is 70% or more, and the haze ratio is 57 to 90%.

  In the light scattering film for solar cell of the present invention, the flat surface preferably has a surface roughness of 50 to 300 mm.

  In the light scattering film for a solar cell of the present invention, the difference in refractive index between the matrix resin and the scattering particles is preferably 0.05 to 0.30.

  An optical member for a solar cell according to the present invention comprises the light scattering film for a solar cell described above and a transparent substrate disposed on the surface opposite to the flat surface of the light scattering film for the solar cell. And

  The solar cell for the solar cell of the present invention is a solar cell comprising a photoelectric conversion layer, wherein the light scattering film for solar cell described above is provided at least on the light capturing side of the photoelectric conversion layer. Features.

  According to the above configuration, it is possible to provide a solar cell light scattering film and a solar cell optical member having a high light confinement effect without causing defects in a semiconductor layer formed thereon, and a solar cell having high conversion efficiency. Can do.

Hereinafter, modes for carrying out the present invention will be described.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing an example of a solar cell according to an embodiment of the present invention.
A light scattering film (solar cell light scattering film) 2, an upper electrode layer 3, a photoelectric conversion layer 4, and a lower electrode layer 5 are laminated in this order on a substrate (transparent substrate) 1 to constitute a solar cell 100. .
The substrate 1 has a light capturing surface 1a, and one surface 2a of the light scattering film 2 is bonded to the opposite surface 1b. The other surface side of the light scattering film 2 is flat and has a flat surface 2b. 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 this order. The lower electrode layer 5 is formed by laminating a lower transparent conductive electrode 51 and a metal electrode 52 in this order.
A 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 “super straight type” structure, light is incident on the substrate 1 from the light capturing surface 1 a and passes through the inside of the substrate 1, as indicated by an arrow A in FIG. It is configured to be incident on the light scattering film 2 bonded to the surface 1b opposite to 1a. Further, the light passes through the light scattering film 2 and the upper electrode layer 3 and enters the photoelectric conversion layer 4. Photoelectric power is generated in the photoelectric conversion layer 4 so that 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, heat treatment is performed in the manufacturing process, and thus heat resistance is desirable.
In addition, when the solar cell is used outdoors, the substrate surface may be heated by sunlight, so that it is desirable to be heat resistant.

The light scattering film 2 is configured by dispersing scattering particles in a 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 refractive index difference between the matrix resin and the scattering particles is preferably 0.05 to 0.30, more preferably 0.10 to 0.25, and still more preferably 0.12 to 0.20.
When the refractive index difference between the matrix resin and the scattering particles is less than 0.05, it is not preferable because light cannot be effectively scattered, and the refractive index difference between the matrix resin and the scattering particles exceeds 0.30. In such a case, it is not preferable because light cannot be sufficiently incident on the photoelectric conversion layer 4.
The refractive index difference between the matrix resin and the scattering particles indicates the refractive index difference in the ultraviolet region, visible light region, and infrared region, but the refraction between the matrix resin and the scattering particles is at least in the wavelength region where the transmittance is 70% or more. The rate difference may be 0.05 to 0.30.

The light scattering film 2 is preferably a film having a flat surface 2b, and the surface roughness of the flat surface 2b is preferably 50 to 300 mm, more preferably 50 to 150 mm, and more preferably 50 to 100 mm. Further preferred. 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.
When the surface roughness Ra of the flat surface 2b is less than 50 mm, it is not preferable because it becomes difficult to form a light scattering film and the production efficiency is lowered.
The surface roughness Ra can be measured, for example, with a contact-type film thickness meter (trade name “Dektak 16000” manufactured by ULVAC, Inc.).

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 indicates the transmittance for light in the ultraviolet region, visible light region, and infrared region, but the transmittance does not have to be 70% or more in all regions from ultraviolet to infrared. The transmittance may be 70% in a specific part of the region, for example, only in the visible light region.
The transmittance of the light scattering film 2 can be measured, for example, by measuring the transmittance using air as a reference with a spectroscopic measurement device (trade name “U4000” manufactured by Hitachi, Ltd.) and collecting the transmitted light with an integrating sphere.

The light scattering film 2 is preferably a film having a haze ratio of 57 to 90%, more preferably 65 to 79%.
When the haze ratio of the light scattering film 2 is less than 57%, it is not preferable because the light scattering property is lowered and the light cannot be effectively confined. When the haze ratio of the light scattering film 2 exceeds 90% This is not preferable because the transmittance may be lowered.
The haze ratio of the light scattering film 2 indicates the haze ratio for light in the ultraviolet region, visible light region, and infrared region, and if the haze rate is 57 to 90% in the wavelength region where the transmittance is at least 70% or more. Good.
The haze ratio of the light scattering film 2 can be measured, for example, with a haze meter (trade name “HM-150” manufactured by Murakami Color Research Co., Ltd.).

When the transmittance of the light scattering film 2 is 70% or more and the haze ratio is 57 to 90%, an excellent light confinement effect is exhibited. 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, either a thermosetting resin or a photocurable resin may be used.
The thermosetting resin used for the matrix resin is preferably a cardo resin, a melamine resin, an epoxy resin, an acrylic resin, or the like. Further, as the photocurable resin, a type in which a thermosetting resin such as the cardo resin or epoxy resin is modified to add a double bond is desirable.
The matrix resin preferably has a refractive index in the range of 1.51 to 1.68.
For example, the refractive index of a thermosetting cardo resin is about 1.62, and the refractive index of a cardo resin modified with an acrylic monomer is about 1.58.

  When the light scattering film 2 is formed by patterning, it is preferable to use a photocurable resin as the matrix resin. If a photosensitive resin composition obtained by adding an acrylic monomer, a photopolymerization initiator, or the like to a photocurable resin is used, the light scattering film 2 can be formed by patterning by a photolithography method or the like.

Alternatively, an inorganic compound may be dispersed in the matrix resin as an auxiliary material. By dispersing the inorganic compound in the matrix resin, the refractive index of the matrix resin can be further increased and the refractive index difference from the scattering particles can be further increased. Also, the transmittance can be increased. If the inorganic compound is added too much, the transmittance of the light-scattering film 2 decreases, so the amount of the inorganic compound is preferably 10% by mass or less. As the inorganic compound, it is preferable to use fine particles having an average particle size on the order of several nm. Examples of the inorganic compound include TiO ₂ and SnO ₂ .
For example, when a thermosetting cardo resin is used as the matrix resin and TiO ₂ is dispersed as the auxiliary material, the concentration of TiO ₂ is preferably about 2.5% by mass. The refractive index of the cardo resin containing about 10% TiO ₂ is about 1.64.

Next, as the material of the scattering particles constituting the light scattering film 2, an inorganic compound or a resin is preferable. The scattering particles preferably have a refractive index of about 1.40 to 1.50.
As the inorganic compound used for the scattering particles, inorganic oxides such as silica and hollow fillers such as airgel (porous silica and the like) are preferable.
As the resin used for the scattering particles, acrylic resin (refractive index 1.51), halogenated acrylate, etc. are preferable. In particular, fluorinated acrylate is preferable because the refractive index is as small as 1.45 (halogen lamp D line 589 nm). .

  Further, the scattering particles may be composed of two or more kinds of particles of different kinds. For example, in the matrix resin, scattering particles made of fluorinated acrylate and scattering particles made of a hollow filler may be mixed.

In order to improve the dispersibility with respect to the matrix resin, an appropriate treatment may be performed on the surface of the scattering particles.
For example, the surface is coated with SiO ₂ , ZrO ₂ , Al ₂ O ₃ , ZnO, a transparent resin, a coupling agent, a surfactant, or the like, or an alcohol, an amine, or an organic acid is used. Thus, the dispersibility of the scattering particles with respect to the matrix resin can be improved by chemically treating the surface.

As described above, for the scattering particles, a material having a refractive index lower than that of the matrix resin may be selected.
Table 1 shows an example of the combination of the matrix resin and the scattering particles, and shows the refractive index of the matrix resin and the scattering particles and the difference in refractive index between the matrix resin and the scattering particles. This combination is merely an example, and the present invention is not limited to this combination.

The average particle diameter of the scattering particles is preferably 1.0 to 10.0 μm, more preferably 1.0 to 3.0 μm, and still more preferably 1.2 to 1.45 μm.
When the average particle size of the scattering particles is less than 1.0 μm, it is not preferable because sufficient scattering cannot be obtained, and when the average particle size of the scattering particles exceeds 10.0 μm, the particle size is large and the liquid is immediately Since it sinks in, it is not preferable.
The average particle diameter of the scattering particles is measured with a particle size distribution analyzer SD-2000 (manufactured by Sysmex Corporation). When the scattering particles are spherical, the average particle diameter is the scattering particle diameter. When the particles are spheroids, the average value of the minor axis.

  More preferably, the scattering particles are a mixture of two types of scattering particles having different average particle diameters. This is because by mixing two types of scattering particles having different average particle diameters, light on the long wavelength side can be scattered more and the amount of power generation can be increased in the photoelectric conversion layer 4. For example, it is preferable to use a mixture of scattering particles having an average particle diameter of 1.0 to 1.9 μm and scattering particles having an average particle diameter of 1.5 to 1.9 μm.

  The film thickness of the light scattering film 2 is preferably larger than the average particle diameter of the scattering particles. When the film thickness of the light scattering film 2 is smaller than the average particle diameter of the scattering particles, an uneven shape due to the scattering particles is formed on the surface of the light scattering film 2, and the surface roughness of the flat surface 2b is 300 mm or less. This is because it becomes difficult to do.

The content of scattering particles dispersed in the matrix resin is preferably 30% by mass or less.
When the content of the scattering particles dispersed in the matrix resin exceeds 30% by mass, the scattering particles cannot be uniformly dispersed, and characteristics such as transmittance and haze ratio of the light scattering film 2 may vary in the plane. Is not preferable.

  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 be heat resistant. 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 can be set as the structure which can produce | generate a carrier. In this case, methane can be cited as the carbon source of the raw material.

The i-type thin film silicon layer 42 is formed without doping with the 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 said metal may be sufficient.

(Embodiment 2)
FIG. 2 is a schematic cross-sectional view showing another example of a solar cell that is an embodiment of the present invention.
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 sequentially stacked on the substrate 1 to constitute a solar cell 101.
The substrate 1 has a light capturing surface 1a, and one surface 2a of the light scattering film 2 is bonded to the opposite surface 1b. The other surface side of the light scattering film 2 is flat and has a flat surface 2b. In this way, the 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 this order.
The lower photoelectric conversion layer 6 is formed by stacking 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 this order. The lower electrode layer 5 is formed by laminating a lower transparent conductive electrode 51 and a metal electrode 52 in this order.
A structure in which the substrate 1, the upper electrode layer 3, the photoelectric conversion layer 4, the lower photoelectric conversion layer 6, and the lower electrode layer 5 are laminated in this order is referred to as a “tandem type”.
In addition, about the member same as Embodiment 1, the same code | symbol is attached | subjected and shown.

  In the “tandem type” structure, light is incident on the substrate 1 from the light capturing surface 1 a and passes through the inside of the substrate 1, as indicated by an arrow A in FIG. It is configured to be incident on the light scattering film 2 bonded to the surface 1b opposite to 1a. Further, the 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. Photoelectric power is generated in the photoelectric conversion layer 4 and the lower photoelectric conversion layer 6 so that light is converted into electric power.

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

(Embodiment 3)
FIG. 3 is a schematic cross-sectional view showing still another example of the solar cell according to the embodiment of the present invention.
A lower electrode layer 5, a photoelectric conversion layer 4, an upper electrode layer 3, and a light scattering film 2 are sequentially laminated on a substrate 11 to constitute a solar cell 102.
A lower electrode layer 5 is provided on the substrate 11. The lower electrode layer 5 is formed by laminating a metal electrode 52 and a lower transparent conductive electrode 51 in this order.
On the lower transparent conductive electrode 51, the photoelectric conversion layer 4 is provided.
The photoelectric conversion layer 4 is formed by laminating an n-type thin film silicon layer 43, an i-type thin film silicon layer 42, and a p-type thin film silicon layer 41 in this order.
An upper electrode layer 3 is provided on the photoelectric conversion layer 4.
Furthermore, one surface of the upper electrode layer 3 is bonded to the flat surface 2 b of the light scattering film 2. Therefore, the upper electrode layer 3, the photoelectric conversion layer 4, and the lower electrode layer 5 are configured to ensure flatness.
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 addition, a structure in which the upper electrode layer 3, the photoelectric conversion layer 4, the lower electrode layer 5, and the substrate 11 are stacked in this order is referred to as a “substrate type”.
In addition, about the member same as Embodiment 1, it attaches and shows the same code | symbol.

  In the “substrate type” structure, light is incident on the light scattering film 2 from the light capturing surface 2 a and passes through the light scattering film 2 as indicated by an arrow A in FIG. In this configuration, the light is incident on the upper electrode layer 3 bonded to the flat surface 2b opposite to the light capturing surface 2a. Further, the light passes through the upper electrode layer 3 and enters the photoelectric conversion layer 4. Photoelectric power is generated in the photoelectric conversion layer 4 so that light is converted into electric power.

The substrate 11 may be an opaque material. This is because in the “substrate type” structure, light is incident from the surface opposite to the substrate 11, that is, the light capturing surface 2 a of the light scattering film 2, and is photoelectrically converted in the photoelectric conversion layer 4 to generate photovoltaic power. For example, transparent materials such as glass, quartz, and transparent polyimide can be used, but opaque polyimide, stainless steel thin plate, and the like can also be used.
Hereinafter, the effects of the present invention will be described.

  The light scattering film of the present invention can be a film that effectively scatters light in a solar cell because scattering particles having a refractive index lower than that of the matrix resin are dispersed in the matrix resin.

  Since the light scattering film of the present invention has a flat surface, the semiconductor layer deposited thereon does not cause defects. Therefore, many defects are not induced in the semiconductor film to deteriorate the output voltage and the fill factor, and the conversion efficiency is not deteriorated.

  Since the light scattering film of the present invention has a flat surface with a surface roughness of 50 to 300 mm, it does not cause defects in the semiconductor layer formed thereon, and induces many defects in the semiconductor film to produce an output voltage. It does not worsen the conversion factor.

  The light scattering film of the present invention has a transmittance of 70% or more and a haze ratio of 57 to 90%, so that the light confinement effect can be improved and the conversion efficiency of the solar cell can be improved. it can.

  Since the light scattering film of the present invention has a refractive index difference between the matrix resin and the scattering particles of 0.05 to 0.30 (preferably 0.12 to 0.20), the light confinement effect is improved. And the conversion efficiency of the solar cell can be improved.

  Since the optical member of the present invention comprises the light scattering film described above and a transparent substrate disposed on the surface opposite to the flat surface of the light scattering film, a semiconductor film is formed on the light scattering film. Does not cause defects in the layer. Furthermore, since it also has the effect of improving the light confinement effect, the conversion efficiency of the solar cell can be improved.

The solar cell of the present invention is a solar cell comprising a photoelectric conversion layer, and the light scattering film described above is provided at least on the light capturing side of the photoelectric conversion layer. It can be set as the equipped solar cell. Furthermore, the light confinement effect is enhanced, and a solar cell with high conversion efficiency can be obtained.
Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.

Example 1
First, 10 parts by mass of fluorinated acrylic particles, 20 parts by mass of alkali-soluble fluorene resin, 10 parts by mass of a polyfunctional acrylic monomer (manufactured by Toagosei Co., Ltd., trade name “Aronix M-400”), 0.5 parts by mass of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name “Irgacure 907”) and 120 parts by mass of an organic solvent (propylene glycol monomethyl ether acetate) are mixed to form a light scattering film 2 The coating solution for forming was prepared.
The fluorinated acrylic particles having an average particle size of 1.6 μm were used.

Next, a predetermined amount of 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 2.0 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 light scattering film was extremely flat, and the surface roughness Ra was 150 mm. The haze value of the light scattering film was 57.3%.

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 with 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 produced.

(Example 2)
First, a coating solution for forming a light scattering film was prepared in the same manner as in Example 1 except that 2 parts by mass of inactive titanium oxide having an average particle diameter of 10 nm as an inorganic compound was added to the material used in Example 1. did.
The fluorinated acrylic particles having an average particle size of 1.9 μm were used.

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 light scattering film was extremely flat, and the surface roughness Ra was 105 mm. Further, the haze value of this light scattering film was 70.5%.

  Further, an upper electrode layer, a photoelectric conversion layer, a lower electrode composed of a lower transparent electrode and a 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 the fluorinated acrylic particles used in Examples 1 and 2, 25 parts by mass of a fluorene resin having a glycidyl group, 5 parts by mass of trimellitic acid which is a polyvalent carboxylic acid, and Example 2 2 parts by mass of the titanium oxide used in Example 1 and 120 parts by mass of the organic solvent used in Examples 1 and 2 were mixed to prepare a coating solution for forming a light scattering film.
The fluorinated acrylic particles having an average particle size of 1.9 μm were used.

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 light scattering film was extremely flat, and the surface roughness Ra was 98 mm. Further, the haze value of this light scattering film was 79.3%. These results are also shown in Table 2.

  Further, an upper electrode layer, a photoelectric conversion layer, a lower electrode composed of a lower transparent electrode and a 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 with 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 produced.

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 2, and the characteristics of the solar cells of Examples 1 to 3 and Comparative Example 1 are shown in Table 3 and FIG. Here, the transmittance is expressed as 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 3 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 | membrane of Examples 1-3 and the comparative example 1, 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

Claims (5)

A light scattering film having a flat surface in which scattering particles having a refractive index lower than that of the matrix resin are dispersed in the matrix resin,
The light scattering film for solar cells, wherein the light scattering film has a transmittance of 70% or more and a haze ratio of 57 to 90%.   The light scattering film for a solar cell according to claim 1, wherein the flat surface has a surface roughness of 50 to 300 mm.   3. The solar cell light-scattering film according to claim 1, wherein the refractive index difference between the matrix resin and the scattering particles is 0.05 to 0.30. 4.   It consists of the light-scattering film for solar cells of any one of Claims 1-3, and the transparent base | substrate arrange | positioned on the surface on the opposite side to the said flat surface of the said light-scattering film for solar cells, An optical member for a solar cell. A solar cell comprising a photoelectric conversion layer,
A solar cell comprising the light scattering film for a solar cell according to any one of claims 1 to 3 on at least a light capturing side of the photoelectric conversion layer.

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