JP3535774B2 - Solar cell - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solar cell formed by using a solar cell element containing cadmium sulfide (hereinafter referred to as CdS).

[0002]

2. Description of the Related Art In recent years, there have been striking mass productions of semiconductor devices and electronic equipments. "Is called" heavy metal component ") and it is the time when we must consider the environmental pollution. For such semiconductors, Si, Ge, Se alone, or SiG
e, GaP, GaAs, InP, InSb, CdAs,
There are various materials such as binary semiconductors such as SiN, Ta ₂ O ₃ and ZrO _3, and ternary semiconductors such as CdGeAs ₂ and SiGeB. In addition, examples of devices using these semiconductors include transistors, integrated semiconductors such as LSI and VLSI, and photoelectric conversion devices. Moreover, there are many applications of the photoelectric conversion element, such as a light modulation element, an optical sensor, an optical waveguide, a light emitting element, and a solar cell.

As a solar cell element which is one of these photoelectric conversion elements, a silicon solar cell element and a compound semiconductor solar cell element have been put into practical use. In the case of silicon solar cell elements, there is no concern about environmental pollution due to Si itself used as the main material, but when lead solder, which is considered to require environmental pollution countermeasures, is often used as the conductive material in these elements. There is.

Further, the compound semiconductor solar cell element is
n ₂ O ₃ , SnO ₂ , SbO _3, etc. are used as transparent conductive films, CdS, ZnS, GaAs etc. are used as n-type semiconductors, and CdTe, CuInSe as P-type semiconductors,
CuInS, GaAs, etc. are used. As described above, a material containing many kinds of heavy metal components such as single crystal, polycrystal, amorphous silicon, II-VI group or III-V group compound semiconductor, or organic semiconductor is used for the solar cell element.

Currently, these solar cell elements are, for example,
As a variety of optical sensors, they are increasingly used in electronic device products such as watches, calculators, and road signs. Cd and T contained in the elements used for these
Heavy metal components such as e, Se, Ga, As, Pb, and In are extremely small amounts when viewed from the total weight of the device. In addition, since these devices are rarely used in one place, no special measures against environmental pollution are taken.

On the other hand, the solar cell uses the inexhaustible energy of sunlight, and unlike fossil fuel-based power generation, it is a clean energy source that does not cause depletion of fossil fuel or generation of harmful gas during combustion. Was noticed,
It is widely used as a large outdoor power supply for homes and electric power, and the power supply is also becoming larger. Since a large number of solar cell elements are used in these large-sized power supply devices and the amount of heavy metal components used is large, it is important to consider measures against the environmental pollution problem caused by these.

[0007] Among the problems of concern due to these heavy metal components, for solar cells that have passed their useful lives or become unnecessary, environmental pollution can be avoided by recovering them and detoxifying them. Conceivable. However, when these solar cell power supply devices are damaged due to aged deterioration, an accident such as an earthquake or storm, and the like, the solar cell elements in the power supply device may be exposed to rainwater. Particularly, when acid rain contacts the solar cell element, it is considered that the heavy metal component contained in the solar cell element is eluted into the rainwater. In such a case, there is a concern that heavy metal components may soak into the surrounding soil such as a house where the power supply device is installed, thereby causing environmental pollution. This problem, like CdS / CdTe-based or CdS / CuInSe-based solar cell elements,
This is particularly important in the case of a solar cell using an element containing CdS which is particularly easily eluted in an acidic or neutral aqueous solution such as rainwater.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to provide these solar cells as a preemptive measure against the environmental pollution problem described above using a solar cell element containing CdS which is particularly liable to be eluted in rainwater. When the solar cell is damaged due to an accident such as an accident and exposed to rainwater such as acid rain, etc., the elution of the Cd compound from the solar cell element into the rainwater is prevented,
It is to prevent environmental pollution.

[0009]

The solar cell of the present invention comprises C
Solar cell element containing dS and the solar cell element
A backing plate and an outer frame surrounding the solid base material ,
In the area inside the solar cell that is isolated from the solar cell element,
It is characterized in that it is arranged so that a part of it is exposed . As the solid base material, at least one material selected from the group consisting of metal oxides, metal hydroxides and metal carbonates can be widely used. Particularly, as the solid base material, it is preferable to use at least one material selected from the group consisting of alkaline earth metals, alkaline earth metal oxides, alkaline earth metal hydroxides and alkaline earth metal carbonates. . Further, the solar cell of the present invention is preferably one in which the solid base material is provided separately from the solar cell element such as being fixed to the inner surface of the back plate . According to these aspects of the present invention, when the solar cell is damaged and the solar cell element containing CdS is exposed to rainwater or the like, the elution of the Cd compound into rainwater or the like is prevented, and the Cd compound contaminates soil or the like. Can be effectively prevented.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As a typical example of a solar cell containing CdS, CdS is used as an n-type semiconductor and Cd is used as a P-type semiconductor.
There is a CdS / CdTe-based solar cell that uses Te, and this solar cell includes cadmium telluride (CdT) in addition to CdS.
e) is included, and cadmium chloride (CdCl ₂ ) is usually used as a treating agent for enhancing the semiconductor characteristics of CdTe or CdS. These solar cells and each solar cell element housed in the solar cell are usually sufficiently liquid-tightly sealed, but when the seal part is damaged and rainwater penetrates from the damaged part and touches the solar cell element. , C such as CdS existing in the solar cell element in the invading rainwater
The d compound may elute. The Cd compound eluted in the rainwater may diffuse according to the concentration gradient with the rainwater outside the solar cell element and be released to the outside of the solar cell. Therefore, in order to prevent the Cd compound from flowing out of the solar cell, it is necessary to reduce the amount of the Cd compound dissolved in the rainwater that has entered the damaged solar cell as much as possible.

Among the above Cd compounds, the solubility of CdS in a neutral aqueous solution is extremely high at 2 × 10 ⁸ gr / dm ³ at room temperature, and it is more easily dissolved in an acidic aqueous solution.
CdCl ₂ has the property of being easily dissolved in a neutral or acidic aqueous solution next to CdS, and CdTe has a lower solubility in a neutral aqueous solution than the above two, but its solubility in an acidic aqueous solution is I can't ignore it. The present invention focuses on the fact that each of the above Cd compounds including CdS has a property that the solubility in an alkaline aqueous solution is so small that it can be almost ignored, and by providing a solid base material inside a solar cell, The solid base material is brought into contact with rainwater that enters the solar cell to change the rainwater into an alkaline state, preventing elution of these Cd compounds into rainwater,
It is possible to suppress the diffusion of the d compound to the outside of the solar cell.

The solid base material in the present invention has the property of increasing the pH value of the aqueous solution when these materials or the reaction product of these materials and water are dissolved in a neutral or acidic aqueous solution. Any of these materials can be used. As the solid base material, for example, among metal oxides, metal hydroxides and metal carbonates,
A wide variety of materials having the above properties can be used. However, when the alkaline substance comes into contact with the semiconductor in the solar cell element using CdS, it may diffuse inside the semiconductor and deteriorate semiconductor characteristics such as photoelectric conversion efficiency. As the solid base material capable of preventing this deterioration, it is particularly preferable to use a material which has a relatively large ionic radius of the metal element constituting the material, is non-deliquescent, and has a small vapor pressure at room temperature and atmospheric pressure.

Preferred solid base materials satisfying the above conditions are alkaline earth metals, alkaline earth metal oxides,
Alkaline earth metal hydroxides and alkaline earth metal carbonates can be used. In addition to the above, for example, aluminum metal, aluminum alloy, and iron,
Oxides, hydroxides, carbonates, borax, and the like of metals such as copper, vanadium, chromium, and molybdenum also have properties similar to those of the above materials, and can be used as preferable solid base materials. When these solid base materials are installed in a solar cell, they do not necessarily have to be isolated from the solar cell element, and even if they are installed in direct contact with the solar cell element, the characteristics of the solar cell are not impaired. Absent.

On the other hand, materials such as alkali metal oxides, alkali metal hydroxides and alkali metal carbonates have relatively small ionic radii of the constituent metal elements, but p such as rainwater.
There is an advantage that the effect of increasing the H value is great. Therefore, these materials are preferably used as solid base materials in a state where they are placed in a solar cell in a state where they are isolated from a portion that does not directly contact the solar cell element, in a state where the influence on the above semiconductor characteristics is eliminated. You can

[0015]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 A solar cell module using a CdS / CdTe solar cell element was manufactured using aluminum (Al) as a solid base material. The schematic cross section of the produced solar cell module is shown in FIG. First, a transparent glass substrate 1 (100 × 100 × 100 × 100) having a transparent electrode 2 made of tin oxide (conductivity: about 10 Ω / cm ² , light transmittance: 98%).
5 on 100mm, 1.2mm thick borosilicate glass plate)
A CdS layer 3 having a thickness of 00Å was formed by thermally decomposing cadmium diethyldithiocarbamate at a temperature of 350 ° C. for 1 minute. Then, the CdTe layer 4 was formed to a thickness of 3000 Å by the proximity sublimation method. Then add 2 copper powders
A carbon paste containing 0 ppm was applied onto the CdTe layer 4 and baked at 150 ° C. for 30 minutes to form a carbon electrode 5. Next, a part of the surface of the carbon electrode 5 and CdS
A silver paste was applied to the exposed part of the layer 3 and sintered to form a + side silver electrode 6 and a − side silver electrode 7 as lead electrodes, respectively, to fabricate a solar cell element.

Next, a solar cell module was produced using the above solar cell element. First, after connecting the lead wires 15 to the + side silver electrode 6 and the − side silver electrode 7 of the solar cell element 14 produced as described above, the entire outer periphery of the solar cell element 14 excluding the glass substrate 1 portion is removed. , And sealed with glass glaze 8. The connected lead wire 15 was connected to the module terminal 13 provided on the back plate 11. On the back surface of the back plate 11, a glass paste containing Al powder having a particle size of 10 μm was applied and dried to form the solid base material layer 9. Further, an aluminum plate which also functions as a solid base material was used as the outer frame 10 and the back plate 11, and a sealing material 12 made of silicon rubber was used for packaging to manufacture a solar cell module.

Reference Example 1 An Al powder having a particle size of 10 μm was used as a solid base material, and a glass paste containing this powder was prepared.
+ Side silver electrode 6 of solar cell element 14 produced in the same manner as
The solid base material layer 9 was formed by applying it over the exposed surface of the carbon electrode 5 and drying it. Thereby, the Al powder was brought into direct contact with both electrodes 5 and 6. Using the solar cell element thus manufactured, a solar cell module was manufactured in the same manner as in Example 1.

Example 2 A solid base material layer 9 is formed by using Mg.Al alloy powder (3: 7 alloy), which is an alloy containing an alkaline earth metal, as a solid base material, and an alloy having the same composition as the solid base material layer 9. A solar cell module was produced in the same manner as in Example 1 except that the plate was used as the back plate 11.

Reference Example 2 Reference is made except that the solid base material layer 9 is formed using Mg.Al powder (3: 7 alloy) having a particle diameter of 10 μm, which is an alloy containing an alkaline earth metal, as the solid base material. A solar cell module was produced in the same manner as in Example 1 .

Comparative Example 1 A solar cell module was produced in the same manner as in Example 1 except that the solid base material layer 9 was not provided and stainless steel plates were used for the outer frame 10 and the back plate 11.

Example 1 thus produced and
2. On the solar cell modules of Reference Examples 1 and 2 and Comparative Example 1, steel balls (diameter 3.
8 cm, 227 ± 2 g) was dropped to break the glass substrate 1. Then, p the destroyed solar cell module
After soaking in a hydrochloric acid aqueous solution of H = 4.8 for 1 day, the amount of Cd contained in the soaked solution was quantified by chemical analysis. As a result, in the case of Example 1 and Reference Example 1 ,
Cd less than 7 ppm in the solution was found in Example 2 and Reference Example.
In the case of 2 , only 5.0 ppm of Cd was detected, while in the case of Comparative Example 1, 1800 was found in the solution.
ppm Cd was detected. From this, it was found that by using Al metal or Mg.Al alloy as the solid base material, a remarkable effect of preventing the elution of the Cd compound according to the present invention can be obtained.

Next, in order to investigate the influence of the alkaline earth metal and Al metal as the solid base material on the semiconductor element, each of the above solar cell modules was stored in a thermostat at 80 ° C. for 50 days, and the photoelectric conversion efficiency was increased. I examined the change of. As a result, 4.8% in the case of Example 1 , 5.0% in the cases of Reference Examples 1 and 2 , 4.9% in the case of Example 2 , and 4. The characteristics deteriorated by 6%, and all showed almost the same characteristics. From these facts, even when the alkaline earth metal or Al metal is used as the solid base material and is directly contacted with the solar cell element and disposed in the solar cell, it is disposed separately from the solar cell element. Like the case, according to the present invention without adversely affecting the any cell characteristics same
It was found that such a Cd compound elution preventing effect can be obtained.

Example 3 Calcium oxide powder, which is an alkaline earth metal oxide, was used as a solid base material, and 100 wt% of this powder was mixed with 10 w% of Teflon powder to give a thickness of 1 mm and a size of 75.
The solid base material layer 9 was formed by molding into a 75 mm plate. This plate was attached to the back plate 11, and the outer frame 10 and the back plate 11 were made of stainless steel, in the same manner as in Example 1,
A solar cell module was produced.

Example 4 A solar cell module was produced in the same manner as in Example 3 except that magnesium oxide powder which was an alkaline earth metal oxide was used as the solid base material.

For each of the solar cell modules of Examples 3 and 4 , a Cd elution experiment and a characteristic deterioration test were conducted under the same conditions as in Example 1. As a result, the Cd elution amount was 5.3 ppm in Example 3 and 4.5 p in Example 4 .
It showed a very low value of pm. From this, it was found that by using the alkaline earth metal oxide as the solid base material, the remarkable effect of preventing the elution of the Cd compound according to the present invention can be obtained.

Reference Example 3 A solar cell module was produced in the same manner as in Reference Example 1 , except that calcium oxide powder having a particle size of 10 μm was used as the solid base material.

Reference Example 4 A solar cell module was produced in the same manner as in Reference Example 1 except that magnesium oxide powder having a particle size of 10 μm was used as the solid base material.

Next, the above Examples 3 and 4 and Reference
Each of the solar cell modules of Consideration Examples 3 and 4 was stored in an 80 ° C. constant temperature bath for 50 days, and changes in photoelectric conversion efficiency were examined.
As a result, in Examples 3 and 4 , 4.8%, Reference Example
In the cases of 3 and 4, the deterioration of the characteristics was 4.9%, and the characteristics were almost the same as those of Comparative Example 1 in which the solid base material was not used. From these facts, even when an alkaline earth metal oxide as a solid base material is placed in contact with a solar cell element in a solar cell, no matter what kind of cell similar Cd compound elution preventing effect when the present invention without adversely affecting the properties to be obtained has been found.

Example 5 A solar cell module was produced in the same manner as in Example 3 except that lithium oxide powder which was an alkali metal oxide was used as the solid base material.

Example 6 A solar cell module was produced in the same manner as in Example 3 except that sodium oxide powder which was an alkali metal oxide was used as the solid base material.

Reference Example 5 A solar cell module was prepared in the same manner as in Reference Example 1 except that lithium oxide powder having a particle size of 10 μm was used as the solid base material.

Reference Example 6 A solar cell module was produced in the same manner as in Reference Example 1 except that sodium oxide powder having a particle size of 10 μm was used as the solid base material.

Example 7 A solar cell module was produced in the same manner as in Example 3 except that sodium carbonate powder which was an alkali metal carbonate was used as the solid base material.

Reference Example 7 A solar cell module was produced in the same manner as in Reference Example 1 except that sodium carbonate powder having a particle size of 10 μm was used as the solid base material.

Next, with respect to the solar cell modules of Examples 5 to 7 and Reference Examples 5 to 7 , Cd elution test and characteristic deterioration test were conducted in the same manner as in Example 1. As a result, regarding the elution amount of Cd, Example 5 and Reference Example 5
5.4 ppm in the case of Example 6 , 6.1 ppm in the case of Example 6 and Reference Example 6 , and 5.8 ppm in the case of Example 7 and Reference Example 7 , both showing low values, It showed almost the same effect. Regarding the deterioration of photoelectric conversion efficiency, 5.8% in Example 5 and 5.3 in Example 6.
%, In Example 7 , it was 4.2%, showing almost the same effect as in Example 1.

However, in the case of Reference Example 5 , 40.2%,
In the case of Reference Example 6 , 35.3%, in the case of Reference Example 7 , 3%
A large deterioration of the photoelectric conversion efficiency of 7.9% was shown. This is because the alkali metal, lithium or sodium, became monovalent ions, and the radius of these ions was small, so that they diffused into the CdTe electrode through the silver electrode and the carbon electrode during the storage period of the solar cell. It is presumed that it had a bad influence on. From these facts, when an alkali metal oxide, an alkali metal hydroxide or an alkali metal carbonate is used as a solid base material, it is not directly contacted with the semiconductor layer or the electrode of the solar cell element but in an isolated state. It has been found preferable to install it in the solar cell module.

Example 8 A solar cell module was produced in the same manner as in Example 3 except that calcium carbonate powder which was an alkaline earth metal carbonate was used as the solid base material.

Reference Example 8 A solar cell module was produced in the same manner as in Reference Example 1 except that calcium carbonate powder having a particle size of 10 μm was used as the solid base material.

As with Example 1, the solar cell modules of Example 8 and Reference Example 8 were subjected to a Cd elution test and a characteristic deterioration test. As a result, Example 8 and Reference Example
In the case of 8 , the elution amount of Cd remained at 4.8 ppm. In Example 8 , the characteristic deterioration of photoelectric conversion efficiency was 6.2.
%, And Reference Example 8 showed 6.7%, showing almost the same effect as that of Example 1. From these facts, when an alkaline earth metal carbonate as a solid base material is placed in contact with a solar cell element in a solar cell, no matter what, as in the case where it is placed separately from the solar cell element. the same Cd compound elution preventing effect when the present invention is obtained without adversely affecting the battery characteristics was found.

Example 9 A solar cell module was produced in the same manner as in Example 3 except that potassium carbonate powder which was an alkali metal carbonate was used as the solid base material.

Reference Example 9 A solar cell module was produced in the same manner as in Reference Example 1 except that potassium carbonate powder having a particle size of 10 μm was used as the solid base material.

The solar cell modules of Example 9 and Reference Example 9 were subjected to the Cd elution test and the characteristic deterioration test in the same manner as in Example 1. As a result, the amount of Cd eluted was found in Example 9.
In each of Reference Example 9 and Example 9 , the concentration was suppressed to 4.1 ppm.
And showed almost the same effect. On the other hand, regarding the photoelectric conversion efficiency, in Example 9 , the characteristic deterioration was only 5.7%.
Reference Example 9 showed a deterioration of 37.9%. It is considered that this is because the potassium became a monovalent ion and the ionic radius of the potassium was small, and thus diffused into the CdTe electrode through the silver electrode and the carbon electrode during the storage period of the solar cell, which adversely affected the semiconductor characteristics. .

Example 10 A solar cell module was produced in the same manner as in Example 3 except that barium carbonate powder which was an alkaline earth metal carbonate was used as the solid base material.

Reference Example 10 A solar cell module was produced in the same manner as in Reference Example 1 except that barium carbonate powder having a particle size of 10 μm was used as the solid base material.

Example 11 A solar cell module was produced in the same manner as in Example 3 except that magnesium carbonate powder which was an alkaline earth metal carbonate was used as the solid base material.

Reference Example 11 A solar cell module was produced in the same manner as in Reference Example 1 except that magnesium carbonate powder having a particle size of 10 μm was used as the solid base material.

Examples 10 and 11 and Reference Example 10
The solar cell modules 11 and 11 were subjected to the Cd elution test and the characteristic deterioration test in the same manner as in Example 1. As a result, in the case of Example 10 and Reference Example 10 , the elution amount of Cd was suppressed to 4.3 ppm, and in the case of Example 11 and Reference Example 11 , it was suppressed to 3.9 ppm, and the characteristic deterioration in photoelectric conversion efficiency did not occur. In Example 10 , it was 5.0%, in Reference example 10 , it was 4.8%, in Example 11 , it was 4.8%, and in Reference example 11 , it was 4.3%, all showing almost the same effect as Example 1. It was From these facts, even when alkaline earth metal carbonates such as barium carbonate and magnesium carbonate as solid base materials were placed in contact with the solar cell element in the solar cell, they were placed separately from the solar cell element. Like the case, according to the present invention without adversely affecting the any cell characteristics
It has been found that similar Cd elution preventing effect is obtained.

Example 12 Example 12 was repeated except that copper carbonate powder was used as the solid base material.
A solar cell module was produced in the same manner as in 3 .

Reference Example 12 A solar cell module was produced in the same manner as in Reference Example 1 except that copper carbonate powder having a particle size of 10 μm was used as the solid base material.

Example 13 Example 13 except that iron carbonate powder was used as the solid base material.
A solar cell module was produced in the same manner as in 3 .

Reference Example 13 A solar cell module was produced in the same manner as in Reference Example 1 except that iron carbonate powder having a particle size of 10 μm was used as the solid base material.

Example 14 Example 14 except that borax powder was used as the solid base material.
A solar cell module was produced in the same manner as in 3 .

Reference Example 14 A solar cell module was produced in the same manner as in Reference Example 1 except that borax powder having a particle size of 10 μm was used as the solid base material.

Examples 12-14 and Reference Examples 12-14
For the solar cell module of C, as in Example 1, C
The dissolution test of d and the characteristic deterioration test were performed. As a result, Cd
With respect to the elution amount of 5.7 ppm in the case of Example 12 and Reference Example 12 , 6.1 ppm in the case of Example 13 and Reference Example 13, and 3.8 ppm in the case of Example 14 and Reference Example 14. It was suppressed. In addition, characteristic deterioration in photoelectric conversion efficiency was 4.6% in Example 12 , and Reference Example 1
2 , 4.6% in Example 13 , 6.1% in Example 13 , Reference Example 13
In Example 14 was 4.2%, and in Example 14 was 4.0%, showing almost the same effect as Example 1, and in Reference Example 14 was 12.2%.
%, Which showed a rather large storage deterioration. This is presumed to be that sodium in borax had some influence on the storage characteristics.

By the above series of examples and reference examples ,
When a specific metal compound such as alkaline earth metal, alkaline earth metal oxide, alkaline earth metal hydroxide, alkaline earth metal carbonate, and iron carbonate or copper carbonate is used as a solid base material, even when allowed to placed in contact with the solar cell element, the onset that is arranged to isolate the solar cell elements
Like the bright, with little effect on the battery characteristics, C
It was found that the effect of preventing the elution of the d compound can be obtained. Borax also showed relatively good results close to this. On the other hand, when an alkali metal oxide, an alkali metal hydroxide, or an alkali metal carbonate is used as the solid base material, by arranging the metal base separately from the solar cell element, the battery characteristics are hardly affected. , Cd according to the invention
It was found that an elution preventing effect can be obtained.

[0057]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, in a photoelectric conversion element provided with CdS, a solid base material is reduced in the module inside a portion isolated from the photoelectric conversion element.
Both of them have a structure in which they are exposed so that even if these elements are damaged and exposed to rainwater, the Cd metal existing inside the elements can be prevented from escaping into the rainwater. A conversion element could be obtained.

[Brief description of drawings]

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

[Explanation of symbols]

1 glass substrate 2 transparent electrode 3 CdS layer 4 CdTe layer 5 carbon electrodes 6 + side silver electrode 7-side silver electrode 8 glass glaze 9 Solid base material layer 10 outer frame 11 Back plate 12 Seal material 13 module terminals 14 Solar cell element 15 lead wire

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-92064 (JP, A) JP-A-8-195498 (JP, A) JP-A-5-299686 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (5)

(57) [Claims] 1. A solar cell element containing cadmium sulfide.
And a back plate and an outer frame surrounding the solar cell element , and a solid base material is provided inside the solar cell element.
A solar cell , wherein at least a part of the solar cell is disposed in a part isolated from the child . 2. A solid base material fixed to the inner surface of the back plate.
The solar cell according to claim 1, which is provided. 3. The solid base material is at least one material selected from the group consisting of metal oxides, metal hydroxides and metal carbonates, or
The solar cell according to 2 . 4. The solid base material is at least one material selected from the group consisting of alkaline earth metals, alkaline earth metal oxides, alkaline earth metal hydroxides and alkaline earth metal carbonates. Claim 1 or
Or the solar cell described in 2 . 5. The solid base material, according to claim 1 or 2, characterized in that at least one material selected from the group consisting of aluminum metal and aluminum alloys
The solar cell according to.