JPH0786625A - Solar cell - Google Patents

Abstract

PURPOSE:To provide a solar cell, in which a heavy metal such as Cd, Se, etc., is not dispersed into air even at the time of a fire and which has high safety, by forming a low melting-point glass layer to the layer of either section on the outside of a plurality of compound semiconductor layers in the solar cell, in which a plurality of the compound semiconductor layers are laminated. CONSTITUTION:The upper section of the substrate 1 of soda lime glass is coated with low melting-point glass 2, and a transparent conductive film 3 such as ZnO is formed onto the low melting-point glass 2 through a sputtering method. A CdS film 4 is evaporated onto the transparent conductive film 3 as an N-type window layer. A CuInSe2, film 5 as an optical absorbing layer is formed onto the CdS film 4, and an Au film is shaped onto the film 5 as a rear electrode layer 6. A low melting-point glass film 7 is sputtered and deposited onto the rear electrode film 6 in 10mum under the same film formation conditions as the low melting-point glass 2, and the film 7 is housed in a metallic frame. A PbO-B2O3-SiO2-Al2O3 group is used as the low melting-point glass.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solar cell using a compound semiconductor such as CdS / CuInSe) ₂ system containing a heavy metal such as Cd or Se.

[0002]

_2. Description of the Related Art A solar cell using a laminated film of a CdS film and a chalcopyrite type compound thin film such as CuInSe ₂ has been well known. The conversion efficiency of this type of compound thin film solar cell is as high as about 15% despite the thin film system. Also, this type of solar cell does not have the problem of photodegradation unlike the amorphous silicon type, and is expected as the next generation power solar cell of the currently used crystalline silicon type solar cells [Katsuya Kushiya, Japan Bulletin of the Japan Institute of Metals, Volume 30, pp930-935 (1991)].

[0003]

However, this solar cell contains heavy metals such as Cd and Se, and there is a possibility that heavy metal elements such as Cd and Se may be scattered in the air in the case of a fire or the like. There is a problem in the effect on.

In order to solve the above conventional problems, the present invention aims to provide a solar cell using a highly safe compound semiconductor in which heavy metals such as Cd and Se do not scatter in the air even in the case of a fire or the like. And

[0005]

In order to achieve the above object, the solar cell of the present invention is a solar cell in which a plurality of compound semiconductor layers are laminated, and any one of the outer sides of the plurality of compound semiconductor layers is provided. A low melting point glass layer is formed on a part of the layers.

In the above structure, the low melting point glass layer is preferably formed over the entire surface of the compound semiconductor layer. In the above structure, the low melting point glass layer may be formed on a part of the surface of the compound semiconductor layer.

Further, in the above structure, it is preferable that the low-melting-point glass layers are formed on both lower and upper outer surfaces of the compound semiconductor layers. That is, a plurality of compound semiconductor layers may be sandwiched between the low melting point glass layers.

In the above structure, the softening temperature of the low melting point glass is preferably 500 ° C. or lower. In the above structure, the low melting point glass layer has a thickness of 0.
It is preferably in the range of 1 to 10 μm.

[0009] In the above configuration, the low-melting glass, with at least one selected from _{PbO-B 2 O 3 -SiO 2} -Al 2 O 3 based glass and ZnO-B ₂ O ₃ -SiO ₂ based glass Preferably there is.

In the above structure, it is preferable that the low melting point glass layer is formed by a dry deposition method. Further, in the above structure, the dry deposition method is preferably a sputtering method.

In the above structure, it is preferable that the low melting point glass layer is formed on the surface of the soda-lime glass substrate, and the compound semiconductor is laminated thereon. Further, in the above structure, the compound semiconductor is preferably a chalcopyrite type compound semiconductor.

Further, in the above structure, it is preferable that the laminated film of the compound semiconductor contains at least one element selected from Cd, S, and Se. In the above structure, the compound semiconductor layer is made of Cu (In, Ga) (S
e, S) ₂ layer and at least one layer selected from CdS layers.

[0013]

According to the above-mentioned constitution of the present invention, a low melting point glass layer is formed in a layer outside any of the plurality of compound semiconductor layers in a solar cell in which a plurality of compound semiconductor layers are laminated. By doing so, even in case of fire etc. Cd and S
It is possible to obtain a highly safe solar cell in which heavy metals such as e do not scatter in the air. That is, in the solar cell of the present invention, even when the solar cell is heated in the air due to a fire or the like, the compound semiconductor used is thermally decomposed to generate Cd or Se.
Before releasing such substances, the coexisting low melting point glass softens and covers the semiconductor laminated film, and Cd, Se and the like are not scattered in the air. Further, the reason why the compound semiconductor laminated film is used in the present invention is that the photoelectric conversion efficiency is high and the durability is excellent.

According to the preferable example in which the low-melting-point glass layer is formed over the entire surface of the compound semiconductor layer, the low-melting-point glass is efficiently softened when exposed to high temperature due to a fire or the like. Covering the laminated film, Cd
Do not scatter Se or Se into the air.

Further, in the above description, according to the example in which the low melting point glass layer may be formed on a part of the surface of the compound semiconductor layer, when the high melting point glass layer is exposed to a high temperature, the low melting point glass layer softens and flows to form a film. Since it spreads over the whole, Cd, Se, etc. can be sealed.

Further, in the above description, the low melting point glass layers are formed on both lower and upper outer sides of the plurality of compound semiconductor layers, that is, the plurality of compound semiconductor layers are sandwiched by the low melting point glass layers. According to the preferable example of Cd, when exposed to high temperature, Cd is most efficiently
And Se can be sealed.

Further, according to the preferable example that the softening temperature of the low-melting glass is 500 ° C. or less, it exists stably up to the softening temperature, and is rapidly softened at the softening temperature or higher to efficiently increase Cd and Cd. Se and the like can be sealed. That is, when the low-melting glass is softened below the thermal decomposition temperature of a compound such as Cd or Se, it can be sealed before Cd, Se, etc. scatter.

Further, in the above, the thickness of the low melting point glass layer
Is in the range of 0.1 to 10 μm.
Is sufficient to seal Cd, Se, etc. at high temperature.
It In the above, as the low melting point glass, PbO is used.
-B₂O₃-SiO₂-Al₂O₃System, ZnO-B₂O
₃-SiO₂System, PbO-B₂O₃-ZnO system, PbO
-B₂O₃-SiO₂System can be used, and
Kuni PbO-B₂O ₃-SiO₂-Al₂O₃System Gala
And ZnO-B₂O₃-SiO₂Choose from system glasses
At least one of them is suitable for sealing Cd, Se, etc.
Good

In the above description, the low melting point glass layer may be formed by any method, and it is particularly preferable that the low melting point glass layer is formed by a dry deposition method because it can be formed without degrading the compound semiconductor. In this case, the sputtering method is suitable.

According to the preferable example in which the low melting point glass layer is formed on the surface of the soda-lime glass substrate and the compound semiconductor is laminated thereon, the soda-lime glass substrate and the low-melting point glass layer are formed. It is preferable because it has excellent adhesion.

According to the preferable example in which the compound semiconductor is a chalcopyrite type compound semiconductor, a solar cell having high photoelectric conversion efficiency and less problem of photodegradation can be formed.

Further, according to the preferable example in which the compound semiconductor laminated film contains at least one element selected from Cd, S, and Se, the photoelectric conversion efficiency is also high and the problem of photodegradation is also caused. Fewer solar cells can be formed.

In the above structure, the compound semiconductor layer is a Cu (In, Ga) (Se, S) ₂ layer and CdS.
According to the preferable example including at least one layer selected from the layers, it is possible to form a solar cell having high photoelectric conversion efficiency and less problems of photodegradation.

[0024]

The present invention will be described in more detail with reference to the following examples. First, CdS, CuInS ₂ , CuInSe ₂
The change when heated in air was examined by thermogravimetric analysis (TG). FIG. 1 shows a thermogravimetric curve when heated in air of CdS. The weight of CdS starts to increase at around 600 ° C, and the weight decreases at around 800 ° C. The weight increase from 600 ° C. is due to the formation of sulfate (SO ₄ ), and the weight decrease is due to the scattering of sulfur oxide due to the decomposition of the formed sulfate. At this time, it is considered that part of Cd is also scattered.

In FIG. 2, CuInS₂When heated in air
The thermogravimetric curve of CuInS ₂Is around 500 ° C
The weight starts to increase, and the weight decreases from around 600 ° C.
Weight increase from 500 ° C is due to sulfate (SO_Four) By the formation of
And the weight loss is due to the decomposition of the sulfates formed.
This is due to the scattering of sulfur oxides. At this time Cu and I
It is considered that n is also partly scattered.

FIG. 3 shows a thermogravimetric curve of CuInSe ₂ when heated in air. CuInSe ₂ is 500 ° C
Weight decreases from the vicinity. This weight reduction is due to CuInSe ₂
This is due to the scattering of selenium oxide due to the thermal decomposition in the air. At this time, it is considered that Cu and In are partly scattered.

Thus, CdS, CuInS ₂ and Cu
From the analysis result of the thermal decomposition process of InSe ₂ , all of these compounds are stable at 500 ° C. or lower, and decompose at temperatures higher than 500 ° C. 500 ℃ as low melting point glass
It is desirable that the compound semiconductor is sufficiently softened below to seal these compound semiconductors.

Next, specific examples of the present invention will be described. (Embodiment 1) FIG. 4 is a sectional view of a super straight solar cell according to an embodiment of the present invention. In FIG. 4, a low melting glass 2 is coated on a substrate 1 of soda-lime glass. The thermal expansion coefficient of this substrate is CuInS
87 × 10 ⁻⁷ / ° C., which is about the same as e ₂ , is preferable. As a component of the low-melting glass _{PbO-B 2 O 3 -SiO 2} -Al 2 O
_{It is a 3} series. A high frequency magnetron sputtering method was used for coating. The target using 5 inches × 15 inches _{PbO-B 2 O 3 -SiO 2} -Al 2 O 3 based glass area, and sputtering was carried out at room temperature in an Ar atmosphere at 8 × 10 ^-3 Torr. The applied power was 1 KW, and the distance between the substrate glass and the target was 10 cm. The deposition rate at this time was about 0.1 μm / min, and sputtering was performed for 10 minutes to form the low melting point glass layer 2 having a film thickness of 1 μm. A transparent conductive film 3 made of ZnO or the like was formed thereon by a sputtering method. A CdS film 4 was vapor-deposited thereon as an n-type window layer. Furthermore, a CuInSe ₂ film 5 serving as a light absorption layer is formed on top of it.
Was formed, and an Au film was formed thereon as the back electrode layer 6. The ZnO film has a thickness of 1.0 μm, the CdS film has a thickness of 0.2 μm, and the CuInSe _{2 has} a thickness of 2.0 μm.
The film thickness was 0.1 μm. A low melting point glass film 7 was sputter-deposited on the back electrode film 6 under the same film forming conditions as the low melting point glass 2 by 10 μm and housed in a metal frame. Here, the film thickness of the low-melting-point glass layer 2 on the glass substrate is appropriately in the range of 0.1 to 2 μm in order to alleviate the stress caused by the difference in the coefficient of thermal expansion from that of the substrate glass. As the film thickness of the low melting point glass layer 7 of
2-10μ to cover CdS and CuInSe ₂ film sufficiently
A range of m is suitable.

In the case of the super straight type, ZnO, C
Since the dS and CuInSe ₂ films are formed at a temperature of 300 ° C. or lower, there is no problem even if a substrate coated with low melting point glass is used. The characteristics of the low melting point glass used this time are strain point: 361 ° C., annealing point: 370 ° C., transition point: 366.
C., yield point: 389.degree. C., softening point: 440.degree.

Even if the building in which this solar cell panel is installed is heated and the solar cell is heated, CdS or Cu
Below the thermal decomposition temperature of the compound semiconductor containing a heavy metal such as InSe ₂ , the low melting point glass layers 2 and 7 are softened and the compound semiconductor layer is sealed. Moreover, the softened low-melting-point glass is very active and chemically reacts with the compound semiconductor to form C.
Heavy metals such as d and Se are taken into the glass.
Therefore, Cd, Se, etc. do not scatter and the safety is high.

In order to confirm the safety of this solar cell,
It is heated in a mixed gas atmosphere of 80% N ₂ gas and 20% O ₂ gas up to 850 ° C. which is the maximum temperature in a normal fire,
Absorb the generated gas in nitric acid solution and use it for ICP
Analysis by (Inductive Coupled Plasma) mass spectrometry revealed that heavy metals such as Cd and Se were hardly detected.

(Embodiment 2) FIG. 5 also shows a sectional view of a substrate type solar cell which is an embodiment of the present invention.
In FIG. 5, the substrate 11 on which the compound semiconductor thin film is formed is soda lime glass. Mo is formed as the lower electrode 12 on the substrate by a sputtering method, and Cu (In _0.8
The light absorption layer 13 of Ga _0.2 ) Se ₂ was formed by a four-source vapor deposition method. A CdS layer 14 was formed thereon by a solution deposition method, and a ZnO / ITO transparent conductive layer 15 was further formed thereon. A Ni / Al film was vapor-deposited as a collector electrode 16 on a part thereof. Mo, Cu (In _0.8 Ga _0.2 ) Se ₂ , C
The film thickness of each of the dS, ZnO / ITO, and Ni / Al films is
It is 1.0, 3.0, 0.05, 1.0, 2.0 μm. ZnO—B ₂ O ₃ —SiO ₂ was formed on the transparent conductive film 15 or the current collecting electrode 16 under the same film forming conditions as in Example 1 above.
The low melting point glass layer 17 of the system was formed. The film thickness of the low melting point glass layer is 10 μm. It was covered with protective glass, and EVA (ethylene vinyl acetate) was filled in the gap with the low-melting glass.

Even in the case of this type of solar cell, even if the building in which the solar cell panel is installed is heated and the solar cell is heated, the thermal decomposition of the compound semiconductor containing heavy metals such as CdS and CuInSe _{2 is performed.} Low melting point glass layer 1 below temperature
7 softens and seals the compound semiconductor layer. Moreover, the softened low-melting-point glass is very active and chemically reacts with the compound semiconductor to take in heavy metals such as Cd and Se into the glass. Therefore, Cd, Se, etc. do not scatter and the safety is high.

In order to confirm the safety of this solar cell,
It is heated in a mixed gas atmosphere of 80% N ₂ gas and 20% O ₂ gas up to 850 ° C. which is the maximum temperature in a normal fire,
The generated gas was absorbed in a nitric acid solution and analyzed by ICP mass spectrometry, but heavy metals such as Cd and Se were hardly detected.

As the window layer, a (Cd, Zn) S film, a light
CuIn (Se, S) as the absorption layer ₂Or Cu (I
n, Ga) (Se, S)₂Even if a film is used, there is Cd as well.
Heavy metals such as Se and Se were not detected.

(Example 3) Efficient analysis of sunlight spectrum
As a solar cell that absorbs and obtains high conversion efficiency, it absorbs light.
Tandem stacking two solar cells with different wavelength range
There are shape configurations. Low melting glass is applied to this tandem configuration.
An example of application will be described below. Figure 6 shows CdS / CdT
e Solar cells and CdS / CuInSe₂Using a solar cell
1 shows the configuration of a tandem solar cell. Where Cd
Te and CuInSe₂The light absorption edge wavelength of the film is about
0.85 μm and 1.2 μm. Therefore, the solar power
The light of wavelength 0.85 μm or less out of the spectrum is thicker than CdTe.
In the positive battery, the light of wavelength 0.85-1.2 μm is CuInS
e₂Absorbed by solar cells. Fabrication of tandem solar cells
An example is given below. Corning 70 on substrate 18
59 glass was used. A transparent conductive film 19 is formed on this glass.
Then, the ITO / ZnO film is formed by the same sputtering method as in the first embodiment.
Formed. The window layer CdS film 2 is formed on the ITO / ZnO film.
0 and the light absorption layer CdTe film 21 are formed by the hot wall deposition method.
(Cover the space from the evaporation source to the substrate with a cylinder, and
It is formed by a method of vapor deposition while heating. CdTe
SnO as a transparent conductive film 22 on the film₂The film is sputtered
To form a CdTe solar cell. Of each membrane
The film thickness is ITO: 0.2 μm, ZnO: 0.8 μm, C
dS: 0.3 μm, CdTe: 5 μm, SnO₂: 1.
It is 0 μm. This SnO₂PbO-B on the film₂O₃−
SiO₂-Al₂O₃System low melting point glass film 23
Room temperature, vacuum degree 2 × 10^-FiveTorr, filament electric
Electron beam evaporation under conditions of current 0.3A and acceleration voltage 10KV
It was formed by wearing. The current value and accelerating voltage are the chamber of the device
Size or distance between filament and evaporation source or evaporation
It depends on the size of the source. The deposition rate of the formed film is
0.05 μm / min and the film thickness is about 2 μm.
It was PbO-B₂O₃-SiO₂-Al₂O₃Low melting point
ZnO films 3 and C were formed on the glass film in the same manner as in Example 1.
dS film 4, CuInSe₂Film 5 and Au film 6 are deposited and
-Perfect type CuInSe₂Making solar cells
It was Further, on the back electrode film 6 of Au, the same as in Example 1 was applied.
PbO-B with a film thickness of 10 μm under the conditions ₂O₃-SiO₂-A
l₂O₃A low melting point glass 7 was formed.

Even in the case of this type of solar cell, even if the building in which the solar cell panel is installed is heated and the solar cell is heated, a compound semiconductor containing a heavy metal such as CdS, CdTe and CuInSe ₂ is used. Below the thermal decomposition temperature, the two low melting point glass layers 7 and 23 are softened and the compound semiconductor layer is sealed. Therefore, Cd, Se, Te, etc. do not scatter and the safety is high.

In order to confirm the safety of this solar cell,
It is heated in a mixed gas atmosphere of 80% N ₂ gas and 20% O ₂ gas up to 850 ° C. which is the maximum temperature in a normal fire,
The generated gas was absorbed in a nitric acid solution and analyzed by ICP mass spectrometry, but heavy metals such as Cd, Se and Te were hardly detected.

[0039]

As described above, according to the present invention, there is provided a solar cell in which a plurality of compound semiconductor layers are laminated, and a low melting point glass layer is formed on any part of the outside of the plurality of compound semiconductor layers. By forming the, it is possible to obtain a highly safe solar cell in which heavy metals such as Cd and Se do not scatter in the air even in the case of a fire or the like. Further, the solar cell of the present invention, despite using the compound semiconductor, has no scattering of heavy metals in the case of a fire, which was a problem in the prior art, has high photoelectric conversion efficiency, and is extremely safe. It is a thing.

[Brief description of drawings]

FIG. 1 is a thermogravimetric curve of CdS when heated in air.

FIG. 2 is a thermogravimetric curve of CuInS ₂ when heated in air.

FIG. 3 is a thermogravimetric curve of CuInSe ₂ when heated in air.

FIG. 4 is a cross-sectional view of a super straight type CdS / CuInSe ₂ solar cell which is an embodiment of the present invention.

FIG. 5 is a substrate type Cd which is an embodiment of the present invention.
S / Cu (In, Ga) Se 2 cross-sectional view of a solar cell.

FIG. 6 is a tandem CdS / C that is an embodiment of the present invention.
dTe // CdS / CuInSe sectional view of a _two solar cells.

[Explanation of symbols]

 1 Substrate 2 Low Melting Glass 3 Transparent Conductive Film 4 CdS Film 5 Light Absorbing Layer 6 Back Electrode 7 Low Melting Glass 11 Substrate 12 Back Electrode 13 Light Absorbing Layer 14 CdS Film 15 Transparent Electrode 16 Low Melting Glass 17 Protective Glass 18 Substrate 19 Transparent Conductive film 20 CdS film 21 CdTe film (light absorption layer) 22 Transparent conductive film 23 Low melting point glass

Front page continued (72) Inventor Shoji Terauchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Takuyuki Negami 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Naoki Ohara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (13)

[Claims] 1. A solar cell in which a plurality of compound semiconductor layers are laminated, wherein a low melting point glass layer is formed on a layer at any part outside the plurality of compound semiconductor layers. . 2. The solar cell according to claim 1, wherein the low melting point glass layer is formed over the entire surface of the compound semiconductor layer. 3. The solar cell according to claim 1, wherein the low melting point glass layer is formed on a part of the surface of the compound semiconductor layer. 4. The solar cell according to claim 1, wherein the low-melting-point glass layers are formed on both lower and upper surfaces of a plurality of compound semiconductor layers. 5. The solar cell according to claim 1, wherein the low melting point glass has a softening temperature of 500 ° C. or less. 6. The low melting point glass layer has a thickness of 0.1 to 10
The solar cell according to claim 1, which is in the range of μm. 7. The low melting glass is PbO—B ₂ O ₃ —S.
iO ₂ -Al ₂ O ₃ based glass and ZnO-B ₂ O ₃ -
The solar cell according to claim 1, which is at least one selected from SiO ₂ based glasses. 8. The solar cell according to claim 1, wherein the low melting point glass layer is formed by a dry deposition method. 9. The solar cell according to claim 8, wherein the dry deposition method is a sputtering method. 10. The solar cell according to claim 1, wherein the low melting point glass layer is formed on the surface of the soda-lime glass substrate, and the compound semiconductor is laminated thereon. 11. The solar cell according to claim 1, wherein the compound semiconductor is a chalcopyrite type compound semiconductor. 12. A compound semiconductor layered film containing Cd,
The solar cell according to claim 1, comprising at least one element selected from S and Se. 13. The compound semiconductor layer comprises Cu (In, G
The solar cell according to claim 1, comprising a) at least one layer selected from a (Se, S) ₂ layer and a CdS layer.