JPH04107882A - Solar cell - Google Patents

Abstract

PURPOSE:To scatter incident light and more effectively use the light by sandwiching small mass at a boundary between a protecting film and a transpar ent electrode or a collecting electrode. CONSTITUTION:A reflecting conductive layer 202 made of Ag is formed by sputtering method on a stainless steel base 201 which is previously polished, and a ZnO layer as a buffer layer 203 is formed by the sputtering method on the reflecting conductive layer 202 so as to smooth the surface of a substrate 101. A PIN type amorphous silicon solar cell photoelectric transfer layer 102 is formed by RFCVD method on the substrate 101 formed by such method, and a transparent electrode 103 and a collecting electrode 104 are formed on the layer 102 by heat deposition. When attaching an ethylene fluoride copolymer film to the solar cell, glass head 105 are sandwiched between the adhering planes. The average grain diameter of the glass head 105 is within the range of 0.2-3mum and the glass sphere works well for the short-circuit current. As a result, the transfer efficiency is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solar cell, and more specifically to a solar cell that improves conversion efficiency by scattering incident light.

[Prior art] In a solar cell using a light-reflecting substrate, the light-reflecting surface is formed as a rough surface with unevenness to increase the optical path length in the photoelectric conversion layer, especially for long-wavelength light with a small absorption coefficient. For example, a method of increasing photoelectric conversion efficiency by
, No. 126,150 (Applicant RCA) No. 7 Column 3
This is suggested in lines 8 to 8, and is also described in Japanese Patent Application Laid-open No. 152276/1983 (Ongdai).

Further, in Japanese Patent Application Laid-Open No. 59-104185 (Exxon Research and Engineering Company), the optical effects of a roughened substrate are detailed.

These prior art techniques have made it possible to absorb and utilize more light incident on solar cells, and as a result, it has become possible to improve the output characteristics of solar cells.

However, the above-mentioned prior art still leaves unsatisfactory points.

That is, when forming an uneven structure on the surface of a light-reflective substrate and effectively utilizing long-wavelength light by the light confinement effect by diffusely reflecting the light that reaches the substrate, the uneven structure on the surface of the light-reflective substrate is used. The larger the height difference between
As a result, there is a drawback that the solar cell may malfunction.

On the other hand, even if a transparent conductive film is provided between the substrate and the photoelectric conversion layer to prevent malfunctions due to short circuits, if the transparent conductive film is thick enough to prevent short circuits, the series resistance will increase. There was a problem in that this caused an increase in the solar cell characteristics and deteriorated the characteristics of the solar cell.

[Problem to be solved by the invention]

The present invention has been made in view of the above points, and provides a solar cell with improved output characteristics by scattering incident light and making more effective use of long wavelength light with a small absorption coefficient. The purpose is to provide a method that does not reduce yield.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention includes a photoelectric conversion layer, a transparent electrode, and, if necessary, a current collecting electrode, on a light reflective substrate.
and a transparent protective film in the above order, the solar cell is configured such that a small lump is sandwiched between the transparent protective film and the transparent electrode or the current collecting electrode, and the small lump is The lumps have an average particle size of 0.2 to 3 μm, for example.
It is made of resin or glass.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 is a schematic diagram showing a conventional PIN type amorphous silicon solar cell to which the present invention can be applied, and FIG. 1 is a schematic diagram showing the concept of applying the present invention to the same solar cell.

In Fig. 2, 201 is the base of the solar cell, and its material is a flexible plate made of molybdenum, tungsten, titanium, cobalt, chromium, iron, copper, tantalum, niobium, zirconium, aluminum metal, or an alloy thereof. body,
A film body is mentioned. Among these, stainless steel, nickel-chromium alloys, and nickel, tantalum, niobium, zirconium, titanium metals and/or alloys are particularly preferred from the viewpoint of corrosion resistance. It is also possible to use films or sheets in which these metals and/or alloys are laminated onto synthetic resins such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyamide. be.

Further, the thickness of the base body 201 is determined according to solar cell manufacturing,
As long as it has the strength required for actual use, it is desirable to be as thin as possible in consideration of cost, storage space, etc. Specifically, the thickness is preferably 0.01 mm to 5 mm, more preferably 0.02 mm to 2 mm, and optimally 0.05 mm to 1 mm. However, when using a thin plate of metal, etc., the thickness should be relatively Even if it is made thinner, the desired strength can be easily obtained.

A reflective conductive layer 202 is provided on the base 201 . Examples of the material for the reflective conductive layer 202 that can be applied to the present invention include metals with high optical reflectivity such as gold, silver, copper, and aluminum.

Further, by increasing the thickness of the reflective conductive layer, it is also possible to create a structure in which the base body 201 is omitted.

In addition, for the purpose of preventing mutual diffusion of constituent elements between the base material and the functional deposited film constituting the photoelectric conversion layer of the large VA battery described later, and as a B barrier layer for short termination prevention, etc. It is also possible to provide a light-transmitting and conductive metal oxide, fluoride, nitride, or the like on the surface of the reflective conductive layer 202 as the buffer layer 203 .

Suitable materials for the buffer layer 203 include ZnO, MgFz, and the like.

In addition, the reflection of light on the surface of the reflective conductive layer 202 is diffused, which increases the optical path length of long-wavelength light in the photoelectric conversion layer, and as a result improves the conversion efficiency of large V:J batteries. It is also possible to provide an uneven structure on the surface in order to make the surface smoother. As will become clear in the experimental examples below, in general, the more conspicuous the uneven structure, the better the utilization of light, but on the other hand, short circuits in the photoelectric conversion layer are more likely to occur, and as a result, the yield of solar cells is reduced. There was a situation that caused it to decline. However, in the case of the solar cell of the present invention, light can be used effectively even if the uneven structure does not cause short circuit of the large VijMi pond. In this case, the uneven shape of the surface of the reflective conductive layer 202 is spherical, conical, pyramidal, etc., and the center line average roughness (Ra) is 10 μm or less, preferably 5 μm or less, and the maximum height ( ) is 0.5 μm or less, preferably 0.3 μm or less.

Further, the uneven shape of the surface of the reflective conductive layer 202 can be controlled by changing conditions such as the substrate temperature when forming the reflective conductive layer 202 or the buffer layer 203. It is generally known that the higher the substrate temperature during formation of the uneven structure, the coarser the grain boundaries of the metal forming the uneven structure.

A p-type (n-type) semiconductor layer 204 (
206), an n-type semiconductor layer 205, and an n-type (p-type) semiconductor layer 206 (204), which form a photoelectric conversion layer 102 shown in FIG. 1, which will be described later.

N-type semiconductor layer 205 suitably used in solar cells
The semiconductor material constituting is a-Si:H,a
-Si:F, a-5i:H:Fa-3iC:l(
, a-SiC:F, a:sic:H:F, a-5iGe
:H, a-5iGe:F.

a-3iGe:H:F, polycrystalline 1 (Si:H1), polycrystalline Si:F, polycrystalline Si:H:F, etc., so-called group II and group II alloy semiconductor materials, as well as It-Vl group and m -v
Examples include so-called compound semiconductor materials of the group.

P-type semiconductor layer (204 or 206) and n-type semiconductor layer (
206 or 204), the semiconductor material constituting the n-type semiconductor layer described above has a valence electron side m
obtained by doping with an agent.

As a means for forming the photoelectric conversion layer, that is, a functional deposited film, microwave plasma CVD method, RF plasma CVD method, sputtering method, reactive sputtering method, ion blasting method, photo CVD method, thermal CVD method, MOC
Means for realizing a method used for forming a so-called functional deposit 81I film, such as a VD method, an MBE method, and an HR-CVD method, can be mentioned, and an appropriate method can be selected to produce a desired solar cell. Ru.

In a solar cell, a transparent electrode 207 is formed on the photoelectric conversion layer 102 made of the p-type, i-type, and n-type semiconductor layers. It is desirable that the light transmittance be high in order to efficiently absorb light within the semiconductor layer, and furthermore, the sheet resistance value should be 100Ω or less so that it does not become a resistance component to the output of the solar cell electrically. Materials with such characteristics include SnO2 and Ins On.

ZnO, CdO, Cds S n O4, IT.

Metal oxides such as (I ni Os +Snow),
Examples include metal thin films made of extremely thin, translucent metals such as Au, Al, and Cu. As a method for producing these, a resistance heating evaporation method, an electron beam heating evaporation method, a sputtering method, a spray method, etc. can be used, and the method is appropriately selected depending on the need.

The current collecting electrode 208 is provided on the transparent electrode 207 for the purpose of reducing the surface resistance value of the transparent electrode 207. The electrode material is Ag + Cr + N 1 .

Examples include thin films of metals such as AI, Ag, Au, Ti, Pt, Cu, Mo, and W, or alloys thereof.

These thin films can be used in a stacked manner.

Further, the shape and area of the semiconductor layer are appropriately designed so that a sufficient amount of light incident on the semiconductor layer is ensured. For example, it is desirable that the shape spreads uniformly over the light-receiving surface of the solar cell, and that its area is preferably 15% or less, more preferably 10% or less of the light-receiving area.

The base body 201, the reflective conductive layer 202, and the buffer layer 20 are collectively referred to as a substrate 101 as shown in FIG.

In the present invention, functional deposited films such as p-type, i-type, and n-type semiconductor layers constituting the photoelectric conversion layer 102 formed on the substrate 101 may be Si, Ge, etc., regardless of whether they are amorphous or crystalline.
, C, etc., so-called group III semiconductor thin films, 5iGe, SiC, 5
So-called group II alloy semiconductor thin films such as iSn, GaAs, Ga
P.

So-called m-v group compound semiconductor thin films such as GaSb, InP, and InAs, and Zn5e and ZnS.

So-called II such as ZnTe, CdS, CdSe, CdTe, etc.
-Vl group compound semiconductor thin films and the like.

Furthermore, the functional deposited film can control valence electrons and forbidden band width. Specifically, when forming the functional deposited film, a raw material compound containing an element that becomes a valence electron control agent or a forbidden band width control agent is used alone or mixed with the raw material gas for forming the deposited film or the diluent gas. Control can be achieved by introducing the film into the film forming space.

In the present invention, the structure is similar to the structure of the conventional solar cell shown in FIG. 2 described above, that is, as shown in FIG.
, and a current collecting electrode 104 are laminated, and a protective film 106 is further laminated thereon, and a small lump 10 is formed between the transparent electrode 103 or the current collecting electrode 104 and the protective film 106.
5 are sandwiched together to form a solar cell.

The properties of the protective film 106 suitably used in the solar cell of the present invention are at least translucency and preferably flexibility. It must have high durability against stress. Materials for protective films with such properties include polyvinylidene fluoride (VDF), tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-6-fluoropropylene copolymer (FEP), and tetrafluoroethylene copolymer (FEP). ethylene-perfluoroalkyl vinyl ether copolymer (PFA),
Examples include polychlorotrifluoroethylene (CTFE). The material for the protective film is appropriately selected from among these materials in consideration of the desired usage and structure of the solar cell. Generally, it is desirable for the protective film 106 to have a large refractive index in order to effectively scatter light. However, when filling the bonding surface of the protective film with an adhesive as described later, after the adhesive has hardened, In order to effectively scatter light, it is desirable that the material has a refractive index as different as possible from the refractive index. Therefore, in such cases, a material having the lowest possible refractive index may be selected.

The small lump 1 preferably used in the solar cell of the present invention
The material of 05 is desirably one that has appropriate hardness, has no risk of damaging the transparent conductive layer 103 or current collecting electrode 104, and is transparent. Examples of such materials include glass materials such as quartz glass and soda glass, silicone resins, and plastic materials such as the above-mentioned fluororesin. Similar to the material of the protective film 106 described above, when the bonding surface is filled with adhesive, it is desirable that the material has a refractive index as different as possible from the refractive index of the adhesive.

Further, the small lump 105 may be made of a mixture of two or more types of materials.

It is desirable that the shape of the small lump 105 is spherical in terms of ease of handling and maintenance of uniformity, but other shapes may be used as long as these requirements are met6. The average particle size of the small lumps 105 is appropriately determined depending on the material of the protective film used, etc., but in order to effectively utilize the incident light, the average particle size is between 0.2 μm and 3 μm. It is desirable that there be.

Examples of methods for dispersing the small lumps 105 include a method of spraying together with gas using a nozzle or the like, a method of spraying together with an organic solvent such as alcohol or acetone, and then drying.

In addition, it is desirable that the distribution of the nodules 105 be uniform in order to reduce variations in the solar cell characteristics, and the density is determined by the average distance of the other nodules that are closest to a given nozzle. The average size of the nodules divided by 1 to 1
It is preferably 0, more preferably 1 to 7.

The method of pasting the protective film 106 is as follows: First, the small lumps 105 are spread on the bonding surface using the method described above, and then the film is placed on the bonding surface, and while being pressed with a roller or the like, the periphery of the bonding surface is, for example, heat-sealed. Bye. Preferably, these films are applied and the periphery is adhesively sealed after the blobs have been sprinkled onto the adhesive surface in a vacuum apparatus in order to more completely evacuate the adhesive surface.

Furthermore, when filling the bonding surfaces of these films with an adhesive, the small lumps may be mixed in the adhesive in advance. Adhesives suitable for use in this case include:
Examples include ethylene-vinyl acetate copolymer (EVA), silicone resin, etc., and those having a different refractive index with respect to the protective film 106 and the resin or glass lumps 105 are appropriately selected and used.

The present invention will be further explained below using experimental examples conducted by the inventors in completing the present invention.

(Experiment Example 1) In this experiment, the configuration of the solar cell is almost the same as that shown in Figures 1 and 2, so the reference numbers in the same figure will be cited for explanation. A reflective conductive layer 202 made of Ag is formed on a substrate 201 made of stainless steel by sputtering, and a buffer layer 203 of ZnO is formed on the F layer.
The layer was formed by sputtering under conditions such that the surface of the substrate 101 was smooth. A PIN type amorphous silicon solar cell photoelectric conversion layer 102 is formed on the substrate 101 obtained in this manner by the usual RFCVD method, and the transparent electrode 103 and the current collecting electrode 104 are respectively formed thereon by the heating lid 1 method. Formed. ITO was used as the material for the transparent electrode tLi 103, and Ag was used as the material for the current collecting electrode 105.

The following experiment was conducted using the solar cell produced in this way.

When attaching a film of tetrafluoroethylene copolymer to the above solar cell, a solar cell (A) (comparative field) in which nothing is sandwiched between the bonding surfaces and a glass bulb with a diameter of 0.1 μm to 10 μm is sandwiched. Solar cells (B1 to B15) (products of the present invention) were produced and their output characteristics were measured. The measurement results of the short-circuit current and conversion efficiency of the solar cells (B1 to B15) are shown in FIG. 6, with the value of the solar cell (A) set to 1. Note that the measurement was performed using a solar simulator (YSS-150 manufactured by Sanno Denso, AMl, 5,100 mW/cm'').

As is clear from these measurement results, the solar cell of the present invention is particularly excellent in short final current when the average particle size of the glass spheres is in the range of 0.2 to 3 μm, and as a result, the conversion efficiency is high. It can be seen that there has been a significant improvement.

(Experimental Example 2) Solar cells (Al to A8) were prepared using the substrates used in Experimental Example 1, on which uneven structures of various degrees were formed on the surface by adjusting the substrate temperature at the time of forming the reflective conductive layer 202. FIG. 7 shows the results of fabricating the device and examining its characteristics and yield rate. As is clear from this figure, in the conventional method of scattering incident light by forming an uneven structure on the substrate surface, the conversion efficiency can be improved by increasing the degree of the uneven structure on the substrate surface. However, at the same time, the uneven structure causes an increase in short circuits, which leads to a decrease in yield and an increase in the manufacturing cost of solar cells.

(Examples) Specific examples of the solar cell of the present invention will be shown below, but the present invention is not limited to these examples in any way.

(Example 1) FIG. 3 is a schematic diagram conceptually showing the cross-sectional structure of the solar cell of this example. In this example, a PIN type amorphous silicon solar cell photoelectric conversion layer 302 is formed on a substrate 301 having a reflective smooth surface, and a transparent electrode 3
03. Using a current collecting electrode 304 formed one after another, a polychlorotrifluoroethylene film 30. with a silicone resin sphere 305 of 0.6 μm in diameter (7) interposed thereon.
6 was attached by a heat fusion method.

AML of 5,100% was added to the solar cell thus prepared.
The short-circuit current, conversion efficiency, and yield rate measured by irradiating light of "mW/cm" from the direction of arrow A in the figure are each 1, assuming that the value of the solar cell manufactured without the silicone resin sphere 305 is 1. t) at .20, 1.18 and 1.0.

(Example 2) FIG. 4 is a schematic diagram conceptually showing the cross-sectional structure of the solar cell of this example. In this example, a PIN-type amorphous silicon solar cell photoelectric conversion layer 402 is formed on a substrate 401 having a reflective smooth surface, and a transparent electrode 4 is formed on it.
03. Using a current collector electrode 404 formed in sequence, a glass bulb 405 with a diameter of 2.2 μm is interposed thereon, and a polyvinylidene fluoride film is pasted in a vacuum apparatus by heat fusion method without drawing a vacuum. I attached it.

AML of 5.100 was applied to the solar cell thus prepared.
The short-circuit current, conversion efficiency, and yield rate measured by irradiating light of "mW/cm" from the direction of arrow A in the figure are each 1, assuming that the value of the solar cell manufactured without the glass bulb 405 is 1. .22, 1.21 and 1.0.

(Example 3) FIG. 5 is a schematic diagram conceptually showing the cross-sectional structure of the solar cell of this example. In this example, a PIN type amorphous silicon solar cell photoelectric conversion layer 502 is formed on a substrate 501 having an uneven structure on the surface, and a transparent electrode 502 is formed on the PIN type amorphous silicon solar cell photoelectric conversion layer 502.
03. Using a current collector electrode 504 formed in sequence, a glass bulb 505 with a diameter of 1.2 μm and an ethylene-vinyl acetate copolymer 508 as an adhesive are interposed thereon to form a mixture of tetrafluoroethylene and hexafluoropropylene. A copolymer film 506 was adhered.

AML of 5,100% was added to the solar cell thus prepared.
The short circuit current, conversion efficiency, and yield rate measured by irradiating light of mW/cm' from the direction of arrow A in the figure are 1.1, respectively, assuming that the value of the solar cell manufactured without the glass bulb 505 is 1. 15, 1.16 and 1.0.

[Effects of the Invention] The present invention provides a solar cell in which a photoelectric conversion layer, a transparent electrode, if necessary a current collecting electrode, and a transparent protective film are provided on a substrate in this order. By sandwiching the small lump at the boundary with the transparent electrode or the current collecting electrode, it has become possible to scatter the incident light and use it more effectively. As a result, the output characteristics are thicker, especially in the region of light rays on the long wavelength side. (Now available.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of the solar cell of the present invention, FIG. 2 is a schematic diagram showing the general structure of a PIN type amorphous silicon solar cell applicable to the solar cell of the present invention,
3 is a schematic diagram showing the cross-sectional structure of the solar cell of Example 1, FIG. 4 is a schematic diagram showing the cross-sectional structure of the solar cell of Example 2, and FIG. 5 is a schematic diagram showing the cross-sectional structure of the solar cell of Example 3. Figure 6, which is a schematic diagram showing the cross-sectional structure of a battery, shows the output characteristics of solar cells (B1 to B15) in which glass bulbs with a diameter of 0.1 μm to 10 μm are sandwiched between the bonded surface of a protective film. The graph shown in FIG. 7 shows the value of the solar cell (A) without sandwiching as 1. The graph shown in FIG.
8) is a graph showing the relationship between the degree of unevenness, conversion efficiency, and yield. 101.301, 401, 501--Substrate, 102.
302,402,502...Photoelectric conversion layer 105.30
5,405.505...small lump, 106.306.40
6,506--Protective film 201--Substrate,
202...Reflective conductive layer, 203-...Buffer layer, 204.206...P-type semiconductor layer or n-type semiconductor layer 2
05--i-type semiconductor layer, A-light irradiation direction. Patent applicant Canon Co., Ltd. Representative Patent attorney Tadashi Wakabu

Claims (1)

[Scope of Claims] 1. A solar cell in which a photoelectric conversion layer, a transparent electrode, if necessary a current collecting electrode, and a transparent protective film are provided in the above order on a light reflective substrate, wherein the transparent A solar cell characterized in that a small lump is sandwiched between a photoprotective film and the transparent electrode or current collecting electrode. 2. The small lumps are made of resin or glass, and the average particle size is 0.2.
2. The solar cell according to claim 1, which has a thickness of 3 μm.