JPH05145096A - Transmission type solar cell - Google Patents

Abstract

PURPOSE:To improve the transmittance of a transmission solar cell without sacrificing a solar cell formation area by a method wherein the constitution of a rear electrode is formed into a multilayer structure, which is obtained by laminating in order an inorganic compound film, a metal film and an inorganic compound film and consists of the three layers. CONSTITUTION:When a rear electrode is formed into a three-layer structure of an inorganic compound film 4, a metal film 5 and an inorganic compound film 6, the spectral reflectivity of light, which is reflected in a photoactive layer by the rear electrode and returns, is changed by the constitutions of the respective film thicknesses of the three layers of the films 4, 5 and 6. The spectral transmittance of light, which is reflected from the rear electrode to the photoactive layer, and the spectral transmittance of light, which is transmitted to the side of the atmosphere through the rear electrode, are specified by limiting the film thickness of each layer of this rear electrode in a specified range. The wavelength of the light at the minimum point of reflection is decided by the film thickness of the film 4 and the wavelength of the light at the maximum point of reflection and the reflectivity of the light are decided by the film thickness of the film 6. It is desirable that the film thickness of the film 4 is 600 to 800Angstrom or 1500 to 2000Angstrom from the viewpoint of a conversion efficiency, and is 1500 to 2000Angstrom from the viewpoint of a transmittance. Accordingly, it is desirable that it is finally 1500 to 2000Angstrom .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive solar cell having a structure capable of transmitting a part of incident light.

[0002]

2. Description of the Related Art A solar cell using an amorphous alloy containing silicon and optionally carbon, nitrogen, germanium, boron, phosphorus and hydrogen (hereinafter referred to as amorphous silicon) in a photoactive layer is known. , Low cost compared with crystalline solar cells, easy junction formation, high degree of freedom in device structure, etc. have been promoted development, and calculator of small area device, Applications for wristwatches have been announced.

Conventionally, the development of the small-area device has been the mainstream, so that the performance other than the output characteristics has not been considered so much, but in recent years, the light transmissivity has been aimed at for application to construction, automobiles and the like. The development of solar cells has started. Examples of these are JP-A-62-71.
No. 70, a composite of a metal and a metal oxide as the second electrode layer, and Japanese Utility Model Laid-Open No. 63-1.
Japanese Patent No. 78356 discloses a structure in which a solar cell non-forming region is provided on a solar cell forming surface to transmit incident light. In addition, JP-A-2-12285
There is also reported an example in which a transparent conductive thin film similar to that used for the first electrode layer is used for the second electrode layer as shown in Japanese Patent Laid-Open Publication No. 2003-242242.

On the other hand, in an attempt to produce a highly efficient solar cell using a transmissive solar cell, there is an example in which the transmissive solar cell is used as a top cell of a four-terminal two-layer tandem structure solar cell. About Kim W. Mitchell, "T
oward High Efficiency ThinFilm Power Modules ", Opto
electronics Device and Technologies, vol.5, No.2, pp2
Details are disclosed in 75 (hereinafter referred to as reference (1)).

[0005]

Each of the above methods has various problems, and in any case, the disclosed method cannot sufficiently achieve the desired effect. For example, in the structure disclosed in Japanese Patent Laid-Open No. 62-7170, the optimization of the film thickness composition of the back electrode is incomplete, so that the transmittance of visible light is improved.
There is a problem in that visible light having a wavelength range of 600 nm or less, which is an effective wavelength range for power generation, is transmitted to the outside again from the second electrode without being used, resulting in a decrease in power generation output.

Further, as shown in Japanese Utility Model Application Laid-Open No. 63-178356, in the case of the structure in which the non-formed region is provided in the solar cell, the effective power generation efficiency of the substrate is reduced because the area of the power generation region is narrowed. There was a problem that reduced the.

Further, as shown in JP-A-2-312285 or Reference (1), when a transparent conductive thin film is used as the second electrode layer, it is compared with the case where a metal electrode is used. Then, although the transmittance of the solar cell as a whole is improved, in addition to the drawback that the power generation output is reduced for the same reason as in the first example, in order to sufficiently reduce the resistance of the second electrode layer, the transparent conductive layer is used. There is also a problem that the efficiency (throughput) of producing a solar cell is significantly reduced because the film thickness of the conductive thin film has to be 1 μm or more.

[0008]

The present invention has been made to solve the above problems, and a first electrode layer (hereinafter referred to as a transparent conductive film) formed of a transparent conductive thin film on a transparent insulating substrate. And a photoactive layer that generates a photoelectromotive force by light irradiation,
A transmissive solar cell comprising a second electrode layer (hereinafter, referred to as a back electrode) formed of a conductive thin film capable of transmitting light, wherein the photoactive layer is made of amorphous silicon, and the back electrode Is a multilayer structure composed of three layers in which an inorganic compound film, a metal film, and an inorganic compound film are sequentially laminated, and preferably the inorganic compound film in contact with the photoactive layer has a thickness of 1500 Å or more, Within the range of 2000Å or less,
In the range of 100 Å or more and 200 Å or less of the metal film,
The thickness of the inorganic compound film on the side not in contact with the photoactive layer is 40
The present invention provides a transparent solar cell characterized by being designed in a range of 0 Å or more.

Solar Cell Handbook (Institute of Electrical Engineers, 198)
As is clear from 5 years, Corona Inc., etc., the collection efficiency of an amorphous silicon solar cell is a curve having a peak near 550 nm as shown in FIG. The collection efficiency sharply decreases on the short wavelength side and the long wavelength side, and becomes 550
When the collection efficiency at the peak wavelength near nm is 1, the collection efficiency for wavelengths of about 400 nm or less and 640 nm or more is 0.5 or less. Therefore, in order to ensure sufficient conversion efficiency even though it is a transmissive solar cell,
Of the light that enters the battery, it is desirable that the light of 400 to 640 nm is reflected from the back electrode into the photoactive layer as much as possible and used for power generation.

On the other hand, the sensitivity (visual sensitivity) of the human eye is shown in FIG.
As shown in (1), it is almost impossible to detect on the short wavelength side near 400 nm, while it is possible to detect up to about 750 nm on the long wavelength side. Therefore, of the light transmitted through the amorphous silicon layer, the light in the wavelength range in which the collection efficiency of amorphous silicon is sufficiently large is reflected again in the amorphous silicon layer to contribute to power generation, while If there is a back electrode that allows light in the long wavelength range that cannot be absorbed by silicon to be transmitted to the atmosphere side, a transmissive solar cell having higher transmittance can be manufactured. The back electrode according to the present invention fulfills such requirements.

The structure of the transparent solar cell according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a transparent solar cell according to the present invention. In the figure, 1 indicates a transparent insulating substrate made of a glass substrate or the like. Reference numeral 2 denotes a transparent conductive film, and 3 denotes a photoactive layer that generates a photoelectromotive force by light irradiation. 4 is the inorganic compound film corresponding to the first layer of the back electrode, and 5 is the second layer.
A metal film corresponding to a layer is shown, and 6 is an inorganic compound film corresponding to a third layer. That is, the back electrode has a three-layer structure of inorganic compound film 4 / metal film 5 / inorganic compound film 6.

With such a film structure, the spectral reflectance of the light reflected back into the photoactive layer by the back electrode changes depending on the thickness of each of the three layers. By limiting the film thickness of each layer of the back electrode to a specific range, it is possible to specify the spectral transmittance of the light reflected from the back electrode to the photoactive layer and the light transmitted to the atmosphere side through the back electrode. Means.

The use of the back electrode according to the present invention makes it possible to improve the transmittance without sacrificing the solar cell formation area. Therefore, the second example in "Problems to be solved by the invention" (Actual Development Sho 63) It is not necessary to consider problems such as No. 178356). In addition, the first example (Japanese Patent Laid-Open No. 62-
No. 7170) and a third example (JP-A-2-312285).
In the present invention, the problems such as (No.) are solved because the sunlight spectrum is effectively used for power generation while ensuring the transmittance.

Further, the decrease in the throughput in the production is very fast because the resistance value of the entire back electrode layer can be reduced by the metal film in the electrode layer in the case of the constitution of the present invention. Throughput can be obtained. As described above, according to the method of the present invention, all the problems described in the conventional art can be solved.

The object of the present invention is to devise the structure of the back electrode so as to have a sufficient reflectance to the photoactive layer in the wavelength region where the collection efficiency of photoelectric conversion is high, and the wavelength region where the collection efficiency is low. On the contrary, in order to realize a structure in which the reflectance decreases and the amount of light passing through the back electrode increases, the maximum and minimum values of the reflectance and A detailed study was carried out on how the wavelength of the light changes.

First, the results obtained by numerical calculation of changes in these values due to the film thickness configuration of the back electrode will be described. Amorphous silicon was used as the photoactive layer for the optical constants for executing this numerical calculation, indium oxide was used for the inorganic compound films 4 and 6 and silver was used for the metal film 5 for the back electrode. The optical constants of these materials were obtained by spectroscopic measurement. However, the content of the present invention is not limited to the calculation example in which the substance forming the back electrode is specified in this way.

First, the effect of changing the film thickness of the inorganic compound film (hereinafter referred to as the inorganic compound film 4) on the side in contact with the photoactive layer will be described. FIG. 4 shows the relationship between the spectral reflectance in the visible region reflected in the photoactive layer and the minimum wavelength of the reflectance and the film thickness of the inorganic compound film 4. Here, the thickness of the metal film is 150Å, and the inorganic compound film (hereinafter,
The film thickness of the inorganic compound film 6) was 600 Å.

As is apparent from FIG. 4, the wavelength distribution of light reflected in the photoactive layer changes depending on the thickness of the inorganic compound film 4. When the first appearing minimum point (this is referred to as the first minimum point) moves to the long wavelength side as the thickness of the inorganic compound film 4 increases, the next minimum point (this becomes the second minimum point). ) Appears on the short wavelength side. The second minimum point also moves to the long wavelength side due to the increase in the thickness of the inorganic compound film 4, and when the thickness of the inorganic compound film 4 becomes about 1600Å, the higher minimum point (this is the third minimum point). ) Appears, and this also moves to the longer wavelength side as the film thickness increases. This is indicated by a dotted line in FIG.

When the thickness of the inorganic compound film 4 is 800 Å or more, the reflectance of the back electrode is 8 in the wavelength range of 1.5 μm or more.
Since it becomes 0% or more, and this tails toward the visible light side, the first minimum point disappears. The thickness of the inorganic compound film 4 also affects the reflectance into the photoactive layer at the minimum point wavelength, and this effect will be described later.

Next, FIG. 5 shows the result of conducting the same examination by changing the film thickness of the inorganic compound film 6. In FIG. 5, the thickness of the metal film 5 is 150Å and the thickness of the inorganic compound film 4 is 15
The calculation results for the case of 00Å are shown.
As is clear from FIG. 5, even if the film thickness of the inorganic compound film 6 is changed, the minimum point wavelength (min.2) on the long wavelength side hardly moves. Also, the minimum point (min.1) on the short wavelength side is from 0Å to 300Å
It moves to the long wavelength side over time, but becomes 0 again at 400 Å
It returns to almost the same wavelength as Å, and it does not change when the film thickness is higher than that.

Considering the variation of the film thickness and the like, it can be said that the thickness of the inorganic compound film 6 is preferably 400 Å or more. FIG. 6 shows the calculation results of the reflectance R to the photoactive layer when the thickness of the inorganic compound film 6 was changed to 400 Å, 800 Å, and 1200 Å.

Finally, the same examination was conducted on the metal film 5 with the film thicknesses of the inorganic compound film 4 and the inorganic compound film 6 set to 1500Å and 600Å, respectively. First, as a result of examining the electric resistance of the back electrode having such a structure, it was found that the film thickness of the metal film needs to be 100 Å or more from the viewpoint of ensuring effective conductivity as an electrode. On the other hand, from the viewpoint of transmittance, as shown in FIG.
It can be seen that at 0 Å or more, the reflectance at the minimum point sharply increases and sufficient transparency cannot be secured. Therefore, the effective film thickness range is 100 to 200Å.
As is clear from this, the minimum point wavelength hardly changes in this range.

In summary of FIGS. 4, 5 and 6, the minimum wavelength of reflection is determined by the thickness of the inorganic compound film 4, and the maximum wavelength of reflection and its reflectance are determined by the thickness of the inorganic compound film 6. It turns out that it will be decided. On the other hand, according to the results of FIG. 7, the movement of the reflection minimum point due to the change of the metal film thickness is slight in the range of the metal film thickness of 100 Å or more, but when the metal film thickness is 200 Å or more, sufficient transmission It turns out that it is not possible to secure the sex.

On the basis of the above examination results, the inorganic compound film 4
Several kinds of solar cells were made while changing the film thickness of the, and the power generation characteristics and the visible light transmission characteristics were investigated, and the electrode configuration was finally optimized from the viewpoint of the cell performance. For solar cells, a tin oxide layer of 5000 Å is deposited on a glass substrate by atmospheric pressure CVD,
A p-type amorphous silicon layer 200Å doped with boron, an i-type amorphous silicon layer 3500Å which is not doped with boron, and an n-type amorphous silicon layer 500Å doped with phosphorus are formed by plasma CVD. To
Further, a back electrode made of indium oxide, silver, and indium oxide is sequentially laminated by a sputtering method.

Table 1 shows the wavelength of the minimum reflection point, power generation characteristics (open circuit voltage V _OC , short circuit current J _SC , filter factor FF, conversion efficiency η) and transmittance of a solar cell having various back electrodes.
Shown in. Among these results, a sample using a 2000 Å silver electrode that does not transmit any light as the back electrode (No. 13)
The power generation characteristics and the light transmission characteristics (No. 1) of the sample without the back electrode are also shown for comparison. In the table, the film thickness of the back electrode is expressed as follows: inorganic compound film 4 (Å) / metal film 5 (Å) / inorganic compound film 6 (Å).

[0026]

[Table 1]

In order to understand the above results, the reflectance (which cannot be measured) from the back electrode to the photoactive layer, which directly affects the conversion efficiency and the transmittance of the solar cell, was calculated. The results are shown in Figures 8, 9, 10, and 11. The results of Samples 2, 3, and 4 are regions corresponding to the region A in FIG. 4 when the thickness of the inorganic compound film 4 is 400 Å or less. In this region, as the thickness of the inorganic compound film 4 increases, the conversion efficiency increases, but the transmittance of the battery decreases. It can be easily understood from FIG. 8 that this is because when the thickness of the inorganic compound film 4 increases, the wavelength of the minimum point moves to the long wavelength side and the reflectance at the minimum point sharply increases. it can.

The thickness of the inorganic compound film 4 is 600Å and 8
At 00Å (Samples 5 and 6 are examples of this, and
This corresponds to the area) As shown in FIG. 9, the second minimum point appears in the ultraviolet region. When the film thickness of the inorganic compound film 4 is 600Å, the conversion efficiency is improved because the maximum of reflection is in the wavelength range of 400 to 500 nm, but the second film is increased as the film thickness of the inorganic compound film 4 increases. Since the minimum point of is also moved to the long wavelength side, the efficiency decreases again. Since the reflectance at the first minimum point is high in this region, the transmittance of the battery is
It is even lower than 4.

As shown in Samples 7, 8 and 9, when the thickness of the inorganic compound film 4 is 1200 Å or more (C, D and E in FIG. 4).
(Corresponding to the area), the reflectance at the minimum point is 1 due to the increase in film thickness.
It becomes 0% or less, which contributes to the improvement of the transmittance of the battery. In particular, when the film thickness of the inorganic compound film 4 became 1500 Å or more as shown in Samples 8 and 9, the third minimum point appeared and the wavelength range of 400 to 500 nm became the reflection maximum area and appeared near 650 nm or 750 nm. It can be seen from FIG. 10 that the reflectance due to the second minimum point becomes 10% or less.
I understand more. As a result, both conversion efficiency and battery transmittance
Particularly favorable characteristics are exhibited.

However, the thickness of the inorganic compound film 4 is 2000
When it exceeds Å (Samples 10 and 11), the third minimum point moves to the visible region as shown in FIG. 11, so that the conversion efficiency decreases.

When the results are rearranged according to the wavelength of the minimum reflectance point, in Samples 8, 9 and 10 in which the conversion efficiency and the transmittance are excellent, the wavelength of the minimum point is 400 nm or less or 640 nm or more. It can be seen that it exists in. That is, it is understood that the wavelength region of 400 to 640 nm is a region where the collection efficiency of the photoactive layer is high, and the photoelectric conversion current can be increased by reflecting the incident light of this wavelength region on the back electrode and reusing it. In other words, it is safe to assume that the conversion efficiency reflects whether or not the light in this wavelength range is fully utilized.

On the other hand, in order to improve the transmittance of the battery, the wavelength through which light is transmitted (referred to as a window) is set to a region of 640 nm or more where the collection efficiency of the photoactive layer is lowered, and the back electrode of the window is It is important that the reflectance is low. Therefore, although the local minimum point of reflection is used as the window, when the thickness of the inorganic compound film 4 is set to 400 to 800 Å and the first local minimum point is moved to this region, it is also clear from FIGS. As the reflectance of the back surface electrode increases,
As a result, there arises a disadvantage that the transmittance of the battery is reduced. That is, using the first local minimum as the window is not a suitable choice.

On the other hand, the thickness of the inorganic compound film 4 is set to 1
If you increase it to more than 500Å and use the second minimum point as a window, the situation will be very different. As is clear from FIG. 10, the reflectance of the back surface electrode at the second minimum point is an extremely low value, and it can be said that using the second minimum point for the window is a very preferable selection. It is possible to perform the same study on higher-order minimum points, but it is necessary to further increase the film thickness of the inorganic compound film 4 in order to use the higher-order minimum points for the window, and it is necessary to form the back electrode. The disadvantage occurs that the membrane time increases.

In other words, the thickness of the inorganic compound film 4 on the back electrode is preferably 600 Å or more and 800 Å or less, or 1500 Å or more and 2000 Å or less from the viewpoint of conversion efficiency. However, from the viewpoint of transmittance, only 1,500 Å or more and 2,000 Å or less is a preferable range, and finally 1500 Å or more and 2,000 Å or less is a preferable range as a common portion of both.

Using FIG. 2, the relationship between the wavelength of 640 nm, which is the boundary line for using the minimum point of reflection as a window, and the collection efficiency of the photoactive layer is determined. This wavelength is the peak of the collection efficiency of amorphous silicon. It can be seen that when 1 is set to 1, it corresponds to a wavelength of about 0.5. If the film thickness range of the inorganic compound film 4 is calculated based on this numerical value (0.5), the optimum film thickness configuration can be determined for any material system. As a result of performing calculations based on this idea also in this example, it was found that the lower limit of the film thickness of the inorganic compound film 4 was 1500Å.

[0036]

EXAMPLE Sample 8 in Table 1 is shown as an example of the transmission type back electrode according to the present invention, Comparative Example 1 (Sample 2) is shown as a structure conforming to the first example of the prior art, and Example 3 of the prior art is shown. As a configuration, Comparative Example 2 (Same 12), Comparative Example 3 (Same 13) as an example of an opaque silver electrode, and Comparative Example 4 (Same 1) as an example when the back electrode was not prepared were selected. The conversion efficiency and the transmittance were compared and examined. Table 2 shows the comparison result of the conversion efficiency, and FIGS. 12 and 13 show the comparison result of the transmittance. The method for producing these solar cells is as described in Table 1. Also, the film thickness composition of the back electrode is expressed as in indium oxide 4 (Å) / silver 5 (Å) / indium oxide 6 (Å) as in Table 1.

[0037]

[Table 2]

The open-circuit voltage V _OC of each of the four types of solar cells is 0.83 to 0.84 V, and the fill factor FF is 0.
No difference between 64-0.65 and the structure of the back electrode is observed. From this, it can be seen that the back electrode according to the present invention does not affect the physical properties of the amorphous silicon that is the photoactive layer. On the other hand, the short-circuit current J _SC, which is proportional to the amount of absorbed light, is 15.2 mA in this example, which is almost equivalent to that of the opaque solar cell of Comparative Example 3, while Comparative Examples 1, 2 Then, it can be seen that it is reduced by about 15%.

As is clear from FIGS. 12 and 13, there is no significant difference in transmittance between the example and the comparative examples 1, 2 and 4. The reason why the light transmittance is improved in the back electrode of Comparative Example 2 is that indium oxide functions as an antireflection film of amorphous silicon which is a photoactive layer.
That is, the transmittance of this example is a value close to the upper limit for an amorphous silicon solar cell.

From the examination of the above examples, according to the present invention, it is possible to improve the transmittance of the solar cell without losing the output of the solar cell. It can be seen that the output also drops.
That is, it is most effective to use the configuration of the back electrode according to the present invention in order to significantly increase the transmittance of the solar cell while sufficiently ensuring the light reflection from the back electrode to the photoactive layer. Is understood.

The photoactive layer of the present invention comprises an amorphous layer containing silicon as a main component or an amorphous alloy layer further containing at least one of carbon, nitrogen, germanium, boron, phosphorus and hydrogen. Any thing can be used. In the embodiment, the photoactive layer has a structure of p-type amorphous silicon doped with boron / i-type amorphous silicon undoped / n-type amorphous silicon doped with phosphorus. However, the transparent solar cell of the present invention is not limited to this configuration,
A conventionally known structure, for example, a structure in which the p-type amorphous silicon layer is replaced with a p-type amorphous silicon carbide layer or a p-type microcrystalline silicon layer, or a plurality of p-i-n It is also possible to use a tandem cell structure in which units are stacked.

It is needless to say that the film thickness of the amorphous silicon layer shown in the embodiments can be changed to a film thickness that can achieve the required transmittance and conversion efficiency. For example, by making the thickness of the amorphous silicon layer smaller than that of this embodiment, the transmittance can be improved even if the output is sacrificed to some extent. In such a configuration, the amorphous silicon layer cannot completely absorb the incident light in one pass, so that the reflection effect by the back electrode should work more effectively.

The configuration of the film thickness of the back electrode is not limited to the example shown in the embodiment. Further, as the metal layer 5, at least one of silver, gold, copper, platinum, palladium, chromium, aluminum, nickel and molybdenum can be used. In addition, various transparent conductive films (indium, tin,
It is also possible to use a conductive oxide film containing at least one of zinc, cadmium, vanadium and titanium). Further, as a method of integration when producing a large-area solar cell, various conventionally known methods can be used.

[0044]

EFFECTS OF THE INVENTION With the use of the transmissive solar cell of the present invention, compared with some conventionally proposed transmissive solar cells,
It is possible to improve the transmittance and reduce the manufacturing cost without deteriorating the characteristics of the solar cell. Further, in the back electrode according to the present invention, by adopting a film having a low internal stress as the inorganic compound film 6, it is possible to expect an effect of improving the long-term improvement in device reliability even when applied to a solar cell. ..

Further, in the embodiment, the solar cell in which the photoactive layer is composed of an amorphous silicon film has been described. However, when the photoactive layer is composed of a material such as amorphous silicon carbide or copper indium selenium. Needless to say, the method of limiting the film thickness of the inorganic compound film 4 by the same method is effective.

For a solar cell made of amorphous silicon carbide, for example, first, data of wavelength distribution of its refractive index and attenuation constant is obtained, and then it is determined by multiple reflection with the back electrode based on the data. The reflectance wavelength distribution in the photoactive layer is obtained by numerical calculation. At that time, as described above, the minimum value of the reflectance of the back electrode may be determined with a wavelength of 0.5 when the maximum value of the assumed collection efficiency of the solar cell is set to 1.

That is, for the amorphous silicon carbide solar cell, the wavelength at which the collection efficiency is 50% of the maximum value is 315n from the wavelength dependence curve of the collection efficiency shown in FIG.
Since it can be seen that m and 560 nm, the film thickness configuration of the back electrode may be determined so that the wavelength of the minimum reflectance value is 315 nm or less or 560 nm or more. In this case, since a region having higher visibility than the amorphous silicon solar cell penetrates from the back electrode to the atmosphere side, the solar cell having a higher transmittance than the case where the present invention is applied to the amorphous silicon solar cell. Is obtained.

Further, although the back electrode is in contact with the atmosphere in the present invention, the back surface of the solar cell is sealed with a transparent resin such as ethylene vinyl acetate or polyvinyl butyral or glass to form a transmissive solar cell. Also in this case, the method of the present invention can be easily applied by substituting the optical constant of the transparent material for sealing in the calculation of the back electrode film thickness distribution and performing exactly the same calculation.

Further, according to the present invention, since the transparent conductive film is inserted between the amorphous silicon and the metal film, the adhesion strength between the silicon layer and the metal electrode is improved by setting appropriate film forming conditions. The effect of doing can be expected.

When the solar cell uses a transparent conductive film such as tin oxide or indium oxide as the first electrode layer, this film has excellent heat ray reflection performance for infrared rays of 1 μm or more. Therefore, for example, even when the solar cell of the present invention is installed on the sunroof portion of an automobile, it is possible to avoid an increase in indoor temperature due to transmitted light.

By using the back electrode according to the present invention, the transmittance can be improved without sacrificing the solar cell formation area. Therefore, it is necessary to consider the problem as in the second example of the related art. Disappear. Furthermore, when the transparent solar cell of the present invention is applied as a top cell of a four-terminal two-layer tandem solar cell, as compared with the case of using the back electrode composed of one transparent conductive film layer described in the prior art, It can be expected that the power generation efficiency of the top cell will be greatly improved.

On the other hand, a solar cell using copper indium selenium as the photoactive layer has a peak of collection efficiency in a long wavelength region of 700 nm or more. Therefore, in order to improve the conversion efficiency of the bottom cell, the transmittance of the top cell is It is necessary to secure enough in this wavelength range.

When the three-layer electrode of the present invention is used, it is possible to design the minimum value of reflection to be around 700 nm, so that the short wavelength light amount reflected in the top cell is maximized and the length passed to the bottom cell is increased. It is also possible to maximize the amount of wavelength light, and it is expected that the conversion efficiency of the tandem solar cell will be greatly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a transparent solar cell according to the present invention.

FIG. 2 is a graph showing a wavelength distribution of collection efficiency of an amorphous silicon solar cell and an amorphous silicon carbide solar cell.

FIG. 3 is a graph showing wavelength dependence of luminosity.

FIG. 4 is a graph showing the dependency of the minimum reflection point on the thickness of the inorganic compound film 4.

FIG. 5 is a graph showing the film thickness dependence of the inorganic compound film 6 at the minimum reflection point.

FIG. 6 is a graph showing the spectral reflectance R into the photoactive layer of the back electrode when the thickness of the inorganic compound film 6 is changed.

FIG. 7 is a graph showing the dependence of the minimum reflection point on the thickness of the metal film.

FIG. 8 is a graph showing the spectral reflectance from the back electrode to the photoactive layer in a solar cell having various back electrodes.

FIG. 9 is a graph showing the spectral reflectance from the back electrode to the photoactive layer in a solar cell having various back electrodes.

FIG. 10 is a graph showing the spectral reflectance from the back electrode to the photoactive layer in the solar cell having various back electrodes.

FIG. 11 is a graph showing the spectral reflectance from the back electrode to the photoactive layer in a solar cell having various back electrodes.

FIG. 12 is a graph showing the spectral transmittance of various solar cells.

FIG. 13 is a graph showing the spectral transmittance of various solar cells.

[Explanation of symbols]

 1 transparent insulating substrate 2 transparent conductive film 3 photoactive layer 4 inorganic compound film 5 metal film 6 inorganic compound film

Claims (7)

[Claims] 1. A first electrode layer comprising a transparent conductive thin film on a transparent insulating substrate, a photoactive layer generating a photoelectromotive force by light irradiation, and a conductive thin film capable of transmitting light. In the transmissive solar cell formed by depositing the second electrode layer, the structure of the second electrode layer capable of transmitting light is
A transmissive solar cell having a multilayer film structure including three layers in which an inorganic compound film, a metal film, and an inorganic compound film are sequentially stacked. 2. The photoactive layer comprises amorphous silicon, and
2. The transparent solar cell according to claim 1, wherein the thickness of the inorganic compound film in contact with the photoactive layer among the three thin films constituting the electrode layer is 1500 Å or more and 2000 Å or less. 3. The film thickness of the metal film in the second electrode layer is 1
The transparent solar cell according to claim 2, wherein the inorganic compound film on the side not in contact with the photoactive layer has a film thickness of 400 Å or more, which is 00 Å or more and 200 Å or less. 4. The photoactive layer comprises an amorphous layer containing silicon as a main component or an amorphous alloy layer further containing at least one of carbon, nitrogen, germanium, boron, phosphorus and hydrogen. The transparent solar cell according to any one of claims 1 to 3, which is characterized in that. 5. A metal thin film in which the metal film of the second electrode layer contains as a main component at least one metal selected from the group consisting of silver, gold, copper, platinum, palladium, chromium, aluminum, nickel and molybdenum. The transparent solar cell according to any one of claims 1 to 4, wherein 6. The transparent solar cell according to claim 1, wherein the inorganic compound film of the second electrode layer is a transparent conductive metal oxide film. 7. The transparent conductive metal oxide film according to claim 6, wherein the transparent conductive metal oxide film contains at least one of indium, tin, zinc, cadmium, vanadium and titanium as a main metal component thereof. Solar cells.