JPH0936402A - Thin film solar cell with conversion efficiency improvement treatment and thin film solar cell array with conversion efficiency improvement means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the conversion efficiency of thin film solar cell and thin film solar cell array using a simple pre-processing or conversion efficiency enhancing means, e.g. means for irradiating light or applying a bias voltage. SOLUTION: Conversion efficiency of a thin film solar cell 1 is enhanced by subjecting the thin film solar cell 1 comprising a first p-type multielement compound semiconductor layer 4 serving as a light absorption layer, a second n-type metal oxide compound semiconductor layer 6 serving as a window layer, and an interface layer 5 of mixed crystal compound containing sulfur, ZnSe, etc., selected from II-VI compound to a simple pre-processing, e.g. irradiation with light or application of a forward bias voltage. Conversion efficiency of a thin film solar cell array is enhanced by additionally providing means for enhancing the conversion efficiency by irradiating light or applying a forward bias voltage.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heterojunction thin film solar cell using a multi-element compound semiconductor thin film as a light absorbing layer,
In particular, as a light absorption layer, a Cu-III-VI ₂ group chalcopyrite semiconductor such as copper indium diselenide (CIS), copper indium gallium diselenide (CIGS) or copper indium gallium sulfuride indium gallium (CIGSS) is used. A light absorption layer of a V-shaped semiconductor and an n-type semiconductor transparent conductive film as a window layer are used, and an interface layer (or a buffer layer) is transparent and has high resistance at the interface between the light absorption layer and the window layer. −
The present invention relates to a thin film solar cell in which a group VI compound semiconductor thin film is formed on a light absorbing layer of the p-type semiconductor, a thin film solar cell in which a plurality of the thin film solar cells are connected in series or in parallel, and a thin film solar cell array.

[0002]

2. Description of the Prior Art Thin-film solar cells of the above type are considered to be widely applicable and are described in U.S. Pat. No. 4,335,226 (Michelsen et al., Issued June 15, 1982) and have high conversion. It is disclosed that a cadmium sulfide (CdS) layer, which is a II-VI group compound semiconductor thin film, is grown on a light absorption layer made of CIS to provide an efficient thin film solar cell.

[0003]

Regarding the light irradiation effect, in a II-VI group compound semiconductor thin film, a report on a CIGS thin film solar cell having a pn heterojunction using ZnSe as an interface layer (or buffer layer). (For example,
Japanese Journal of Applied Physics 33, No12 (199
4), Kushiya and others). Here, in the case where the output characteristics of the thin-film solar cell are improved by the light irradiation as described above, it is stated that there is a problem in the pn heterojunction interface, and by improving the pn heterojunction interface. , Concluded that it is important to fabricate thin-film solar cells that do not exhibit such light irradiation effects.

In the last few years, the conversion efficiency of CIS type thin film solar cells has been greatly improved. In addition, attempts have been made to actively eliminate harmful substances such as cadmium from thin-film solar cells of this material type in principle, and have been implemented. However, attempts to produce thin film solar cells with high conversion efficiency using CIS-based thin film solar cells that do not contain harmful substances such as cadmium have been unsuccessful because the heterojunction interface was not successfully controlled.

Further, since the interface layer may be as thin as 50 nm or less, it is difficult to evaluate a single film, and at the same time, such evaluation has little meaning. Therefore, as a method of judging the quality of this interface layer, a thin film solar cell in which this layer is formed on a p-type semiconductor thin film which is a light absorption layer is produced, and the output characteristics of this thin film solar cell are measured and evaluated. Is generally done.

Further, in order to improve the quality of the interface layer itself and to optimize the interface state when the interface layer is formed on the p-type semiconductor thin film light absorption layer, development of a method for producing the interface layer itself, It is necessary to understand the characteristics and effects of the interface between the thin film light absorption layer and the interface layer or the interface between the window layer and the interface layer, and such thin film solar cells have a complicated laminated structure. In order to extract and optimize only the layers, it is necessary to stably and uniformly produce each layer other than the interface layer constituting the solar cell.

However, development of a thin-film solar cell manufacturing technique for stable, reproducible and uniform production, design and optimization of the structure of a thin film solar cell in a complicated stack, analysis or grasp of characteristics and effects of junction interface state However, there is a problem in that a large amount of development items, development costs, and time are required to solve the above problems.

An object of the present invention is to use a pretreatment process for improving the conversion efficiency such as light irradiation or applying a bias voltage and a conversion efficiency improving means, to obtain the same degree as that of a CIS type thin film solar cell containing cadmium. It is intended to provide a cadmium-free heterojunction thin-film solar cell that achieves the above conversion efficiency and a thin-film solar cell module in which a plurality of thin-film solar cells are connected in series or in parallel.

Another object of the present invention is C which can be applied to mass production with excellent economical efficiency, reproducibility and yield.
It is to provide an IS-based thin-film solar cell and a high conversion efficiency CIS-based thin-film solar cell module.

Another object of the present invention is to provide a high open circuit voltage.
A thin-film solar cell having (V _OC ).

[0011]

In order to solve the above problems, the present invention provides a metal back electrode layer, and a p-type conductivity type on the back electrode layer, which serves as a light absorbing layer. A first multi-component compound semiconductor thin film and a first multi-component compound semiconductor thin film having a conductivity type opposite to that of the first conductivity type on the first multi-component compound semiconductor thin film, and having a wide forbidden band serving as a window layer and having transparency and conductivity. Two
And a structure having mainly a II-VI group compound semiconductor thin film having a high resistance and grown at an interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film. A thin-film solar cell made of, which is characterized by being subjected to pretreatment for improving conversion efficiency.

Further, the present invention is characterized in that the pretreatment for improving the conversion efficiency is performed by irradiating light under a solar simulator (a device for producing artificial light corresponding to sunlight on the ground surface).

Further, according to the present invention, the pretreatment for improving the conversion efficiency is carried out under a solar simulator (a device for producing artificial light corresponding to sunlight on the surface of the earth) for an irradiation time of 1 hour or more and an air mass (AM). 1.5, irradiation intensity 100mW / cm
It is characterized by irradiating artificial light of ² .

Further, the present invention is characterized in that the pretreatment for improving the conversion efficiency applies a forward bias voltage of 1 V or less while exceeding the open circuit voltage of the thin film solar cell in a dark state where no light is applied. To do.

Further, in the present invention, the pretreatment for improving the conversion efficiency is performed in a dark state in which a forward bias voltage of 1 V or less is applied and light is not applied while exceeding the open circuit voltage of the thin film solar cell.
Characterized by adding more than 15 minutes.

Furthermore, the present invention is characterized in that the transparent and conductive second metal oxide semiconductor thin film having a conductivity type opposite to the first conductivity type and serving as the window layer is made of zinc oxide. And

Further, the present invention is mainly composed of a II-VI group compound semiconductor thin film (interface) which is transparent and has high resistance grown at the interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film. The layer or the buffer layer) is made of cadmium sulfide, zinc selenide or a zinc mixed crystal compound containing oxygen, sulfur and a hydroxyl group.

Further, the present invention is characterized in that the first multi-element compound semiconductor thin film is made of one of the copper-III-VI ₂ group chalcopyrite compound semiconductors.

Furthermore, the present invention is characterized in that the first multi-component compound semiconductor thin film serving as the light absorption layer is made of copper indium diselenide, copper indium gallium diselenide, or copper selenide indium gallium. To do.

Furthermore, the present invention provides a metal back electrode layer, a first multi-component compound semiconductor thin film having a p-type conductivity type on the back electrode layer and serving as a light absorbing layer, and the first thin film. A second metal oxide semiconductor thin film having a conductivity type opposite to the first conductivity type on the multi-element compound semiconductor thin film, the second metal oxide semiconductor thin film having a wide forbidden band and being transparent and serving as a window layer; A thin film solar cell or a thin film solar cell comprising a structure having a transparent and high-resistance mainly II-VI group compound semiconductor thin film grown at the interface between the multicomponent compound semiconductor thin film and the second metal oxide semiconductor thin film A thin film solar cell array (or panel) having a structure in which a plurality of thin film solar cells are connected in series or in parallel, wherein an array (or panel) conversion efficiency improving means is added to the thin film solar cell.

Further, according to the present invention, the conversion efficiency improving means applies a forward bias voltage of approximately 1 V or less to the light while exceeding the open-circuit voltage generated depending on the number of the thin film solar cells connected in series or in parallel. It is characterized by adding more than 15 minutes in the dark state.

Further, the present invention is characterized in that the conversion efficiency improving means has an automatic starting means for starting at least 15 minutes before the sunrise time of the sun or the time when the sunlight reaches a predetermined illuminance.

Furthermore, the present invention is characterized in that the conversion efficiency improving means is a means for irradiating artificial light having an air mass (AM) of 1.5 and an irradiation intensity of 100 mW / cm ² for an irradiation time of 1 hour or more.

Further, the present invention is characterized in that the conversion efficiency improving means has an automatic starting means for starting at least one hour before the sunrise time of the sun or the time when the sunlight reaches a predetermined illuminance.

Further, the present invention is characterized in that a secondary battery for storing electric power generated by the thin film solar cell is used as a power source of the conversion efficiency improving means.

[0026]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows an example of the structure of the thin film solar cell of the present invention. The thin film solar cell 1 is formed on a glass substrate 2 having a thickness of 1 to 3 mm. The back surface electrode 3 is a metal such as molybdenum or titanium having a thickness of 1 to 2 microns formed on the glass substrate. First serving as light absorption layer 4
Is a thin film of a Cu-III-VI ₂ group chalcopyrite structure having a p-type conductivity and having a thickness of 1 to 3 μm, for example, a multi-element compound semiconductor thin film such as CIS, CIGS or CIGSS. On this thin film, mainly high resistance as described below
The II-VI group compound semiconductor thin film 5 is formed as an interface layer (or a buffer layer). A second metal oxide semiconductor made of zinc oxide having an n-type conductivity and a wide bandgap, is transparent, and is conductive and has a thickness of 0.5 to 3 μm. A thin film is formed. The upper electrode or scribe line 7 is optionally produced on the exposed surface of n-type zinc oxide.

In the thin-film solar cell of the present invention, the first semiconductor thin film having a p-type Cu-III-VI ₂ group chalcopyrite structure which is a light absorption layer and the n-type _second semiconductor which is a window layer. At the interface with the transparent conductive film, a zinc compound, that is, "zinc mixed crystal compound thin film containing sulfur", "ZnSe thin film", etc., from the II-VI group compound semiconductor is used as an interface layer in the light absorption layer. Defects (or recombination levels) occur at the interface during the formation on a certain p-type first semiconductor thin film, and these defects (or recombination levels) lower the open circuit voltage and conversion efficiency of the thin film solar cell. It is presumed that this is affecting. Therefore, it is necessary to eliminate this defect (or recombination level).

By previously applying light irradiation or forward bias voltage to the thin film solar cell of the present invention, electrons which are minority carriers are generated, and these electrons exist near the junction interface between the light absorption layer and the interface layer. The number of defects (or recombination levels) is greatly reduced or eliminated by entering and filling in the defects (or recombination levels). as a result,
The conversion efficiency equivalent to that of a thin-film solar cell using an interface in which defects (or recombination levels) are unlikely to have a significant adverse effect on electrical properties, that is, an interface with a small number of defects (or recombination levels) Found to get.

Next, the characteristics of the thin film solar cell (open voltage V _OC , bending factor FF and conversion efficiency E _F ) when light irradiation and forward bias voltage are applied to the thin film solar cell will be described.

The sulfur-containing zinc mixed crystal compound semiconductor thin film interface layer (or buffer layer) was applied to a CIS type thin film solar cell (see FIG. 1) prepared by a solution growth method under a solar simulator with an air mass (AM) of 1.5 and an irradiation intensity of 100 m.
After irradiating artificial light of W / cm ² for a certain period of time, under the solar simulator, air mass (AM) 1.5, irradiation intensity
Figure 2 shows the output characteristics when measured by irradiating 100 mW / cm ² artificial light. As a result, the output characteristics such as the open-circuit voltage V _OC and the bending factor FF of the CIS thin-film solar cell are greatly improved by the light irradiation effect, and as a result, the light irradiation time is 60
In a minute, a high conversion efficiency E _{F of} about 12% can be obtained.

ZnSe interface layer (or buffer layer)
CIGS thin film solar cell with a solar simulator under air mass (AM) 1.5, irradiation intensity 100mW / cm
After irradiation the ^second artificial light, shown Eamasu (AM) 1.5 Under solar simulator, the output characteristic when measured by light irradiation to artificial light irradiation intensity 100 mW / cm ² in FIG. Than this, the output characteristics such as the open circuit voltage V _OC and song factor FF of the thin film solar cell by the light irradiation effect is greatly improved, as a result, achieve high conversion efficiency E _F of about 12% at the light irradiation time 60 minutes To be

Similarly, after applying a forward bias voltage of 0.5 V to a CIGS thin film solar cell having a ZnSe interface layer (or a buffer layer) in a dark state without irradiating light, air mass (AM) 1.5 under a solar simulator,
FIG. 4 shows the output characteristics when measured by irradiating artificial light with an irradiation intensity of 100 mW / cm ² . From this, the conversion efficiency E _F of the thin film solar cell by the application of the bias voltage is increased with the application time, a high conversion efficiency which the application time exceeds 11% for 30 minutes to 60 minutes is obtained.

As described above, according to the present invention, the thin film solar cell 1 is previously irradiated with the artificial light source 52 as shown in FIG. 5, or the thin film solar cell 1 is provided with the secondary battery as shown in FIG. (Or DC power supply) 62 is used to apply a forward bias voltage to a pretreatment step for improving the conversion efficiency or a conversion efficiency improving means to add a defect (or a defect) near the junction interface between the light absorption layer and the interface layer. The conversion efficiency of a thin-film solar cell having a certain amount of recombination levels) is improved, and the conversion efficiency equivalent to that of a thin-film solar cell using an interface with a small number of defects (or recombination levels) can be obtained. .

The effect of the pretreatment step for improving the conversion efficiency or the addition of the conversion efficiency improving means is that the light absorbing layer p
Of the II-VI group compound semiconductor as an interface layer at the interface between the first semiconductor thin film having a Cu-III-VI ₂ chalcopyrite structure and the n-type second semiconductor transparent conductive film that is the window layer ,
In particular, a zinc compound, that is, a "zinc mixed crystal compound thin film containing sulfur", a "ZnSe thin film", or the like is a p-type Cu-I that is a light absorption layer.
II-VI ₂ Remarkably appears in a thin film solar cell having a structure formed on a first semiconductor thin film having a chalcopyrite structure.

In the case of light irradiation in the pretreatment step for improving the conversion efficiency or the addition of the conversion efficiency improving means,
Normal artificial light, air mass (AM) 1.5, irradiation intensity 10
It is preferable to irradiate with a light amount of 0 mW / cm ² for about 30 to 60 minutes, preferably 60 minutes. Similarly, in the case of applying a forward bias voltage, 0.5-1.0V, preferably 0.5V
It is preferable to leave it in the dark for 15 minutes while applying.

The thin-film solar cell of the present invention has an air mass (AM) of 1.5 and an irradiation intensity of 10 under a solar simulator.
Artificial light of 0 mW / cm ² is applied for 1 hour or longer, or 1 V or less in the dark state where forward bias voltage of 1 V or less is not applied.
When the output characteristics of the solar cell are measured by irradiating artificial light with an air mass (AM) of 1.5 and an irradiation intensity of 100 mW / cm ² for 1 hour or more under a solar simulator after applying for 5 minutes or more, the output is mainly open. The conversion efficiency E _F is greatly improved by improving the voltage V _OC and the bending factor FF.

In the above embodiments, the effect of light irradiation or the application of forward bias voltage is used independently as the pretreatment step or the conversion efficiency improving means for improving the conversion efficiency, but as another method. By combining the light irradiation and the application of the forward bias voltage, the output characteristics of the solar cell can be improved.

Further, the thin film solar cell using the effect for improving the conversion efficiency is a light quantity measuring sensor utilizing the characteristic that this property reversibly appears and light receiving switching utilizing the change in the current or voltage due to the light irradiation. Application as a device element is also possible.

Next, as another embodiment, a solar cell array or panel in which conversion efficiency improving means is added to a solar cell module in which a plurality of thin film solar cells of the present invention shown in FIG. 1 are connected in series or in parallel. Will be described with reference to FIG. 7. As described above, the unit device including the thin film solar cell includes the first semiconductor thin film having the p-type Cu-III-VI ₂ group chalcopyrite structure which is the light absorption layer and the n-type first semiconductor thin film which is the window layer layer. As the interface layer at the interface with the semiconductor transparent conductive film of No. 3, from among II-VI group compound semiconductors, particularly zinc compounds, that is, "zinc mixed crystal compound thin film containing sulfur", "Zn
A defect (or recombination level) is generated at the interface in the process of forming a “Se thin film” or the like on the p-type first semiconductor thin film that is the light absorption layer, and this defect (or recombination level) is a thin film solar. It is presumed that the open circuit voltage and conversion efficiency of the battery are affected, and light irradiation or forward bias voltage is applied to the thin film solar cell in advance to generate electrons which are minority carriers, and the electrons absorb the light. The number of defects (or recombination levels) is greatly reduced or eliminated by entering and filling the defects (or recombination levels) existing near the junction interface between the layer and the interface layer, and the conversion efficiency of the thin film solar cell In this embodiment, the method for improving the conversion efficiency of the unit element is applied to the thin-film solar cell module, since the above can be improved.

The unit element includes a metal back electrode layer, a first multi-component compound semiconductor thin film having a p-type conductivity type on the back electrode layer and serving as a light absorbing layer, and the first multi-component. A second metal oxide semiconductor thin film having a conductivity type opposite to the first conductivity type on the compound semiconductor thin film, serving as a window layer, having a wide bandgap, being transparent and having conductivity; A thin-film solar cell having a structure mainly including a II-VI group compound semiconductor thin film which is transparent and has high resistance grown at an interface between a multi-component compound semiconductor thin film and a second metal oxide semiconductor thin film 1
The thin film solar cell array or panel 51 is formed by connecting a plurality of these in series (or in parallel).

In this embodiment, a conversion efficiency improving means 72 is added to the thin film solar cell array or panel 71, and the conversion efficiency improving means 72 stores secondary electricity generated by daytime sunlight. Battery 721 and a predetermined time (time required to improve conversion efficiency, that is, time required to significantly reduce or eliminate the number of defects (or recombination levels)) by generating an ON signal at sunrise time of the sun , For example, 15 minutes or more), or a timer that generates an off signal after a predetermined time (same as the predetermined time) before the power generation start time of the thin-film solar cell module, and an off signal after the predetermined time. 722 and this timer 72
A switch 723 that is turned on or off by a two on or off signal, and a voltage adjustment circuit 724 that adjusts the output voltage of the secondary battery 721 to a desired voltage.

Next, the operation of the thin film solar cell module will be described. At the sunrise time of the sun or the desired power generation start time, the timer 722 generates an ON signal, the switch 723 is turned on, and the output voltage from the secondary battery 721 is adjusted by the voltage adjustment circuit 724 to a voltage (eg , 1 V or less) (in the case of series connection, the voltage is adjusted to an integral multiple (the number of connected unit elements) and applied to the thin-film solar cell array or panel 71. After the same), the switch 723 is turned off by the generation of the off signal of the timer 722, and the voltage application is stopped. At that point, the individual thin film solar cells 1 of the thin film solar cell array or panel 71
Has significantly reduced or eliminated the number of defects (or recombination levels) and has the highest conversion efficiency.

As another embodiment of the conversion efficiency improving means, there is a method of irradiating artificial light. In this case, the secondary battery is used as a power source for this light source, and an air mass (AM) 1.5 is supplied from the artificial light source. Then, the artificial light having an irradiation intensity of 100 mW / cm ² is irradiated with light for 1 hour or more using the same timer as in the above-described embodiment, whereby the same state as in the above-described embodiment is obtained.

Further, as another embodiment of the conversion efficiency improving means, there is a method of irradiating sunlight, and when the irradiation amount of sunlight is small, a method of using a condensing device such as a flannel lens or a concave mirror is used. There is also.

[0046]

As described above, according to the present invention, the problems related to the harmfulness of cadmium in the conventional CIS type thin film solar cell containing cadmium sulfide as its constituent material are solved, and the conversion is simple and inexpensive. It becomes possible to obtain a thin film solar cell or a thin film solar cell array (or panel) with high conversion efficiency by adding a pretreatment step for improving efficiency or a conversion efficiency improving means, and a thin film solar cell or thin film solar cell array (or The yield at the time of manufacturing a panel) is also improved, and as a result, the cost of the thin film solar cell itself can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a thin film solar cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing the effect of light irradiation on the characteristics of a CIS-based thin film solar cell having a sulfur-containing zinc mixed crystal compound semiconductor thin film interface layer.

FIG. 3 is a diagram showing the effect of light irradiation on the characteristics of a CIGS thin film solar cell having a ZnSe interface layer.

FIG. 4 is a diagram showing the effect of bias voltage application on the characteristics of a CIGS thin film solar cell having a ZnSe interface layer.

FIG. 5 is a schematic configuration diagram of a thin-film solar cell irradiated with artificial light as a pretreatment for improving conversion efficiency according to the first embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a thin film solar cell to which a bias voltage is applied as a pretreatment for improving the conversion efficiency in the first embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a solar cell array or panel to which a bias voltage applying unit is added as a conversion efficiency improving unit according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Thin Film Solar Cell 2 Substrate 3 Back Electrode 4 Light Absorption Layer (p-type Semiconductor) 5 Interface Layer (or Buffer Layer) 6 Window Layer (n-type Semiconductor) 7 Top Electrode or Scribing Line

Claims (15)

[Claims] 1. A metal back electrode layer, a first multi-component compound semiconductor thin film having a p-type conductivity type on the back electrode layer and serving as a light absorption layer, and the first multi-component compound semiconductor thin film. A second conductive type having a conductivity type opposite to that of the first conductive type and serving as a window layer having a wide forbidden band and being transparent and conductive.
And a structure having mainly a II-VI group compound semiconductor thin film having a high resistance and grown at an interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film. A thin film solar cell comprising: a thin film solar cell characterized by having been subjected to pretreatment for improving conversion efficiency. 2. The thin film sun according to claim 1, wherein the pretreatment for improving the conversion efficiency is performed by irradiating light under a solar simulator (a device for producing artificial light corresponding to sunlight on the surface of the earth). battery. 3. The pretreatment for improving the conversion efficiency is carried out under a solar simulator (a device for producing artificial light corresponding to sunlight on the ground surface) for an irradiation time of 1 hour or more, an air mass (AM) 1.5, and an irradiation intensity. The thin film solar cell according to claim 2, which is irradiated with artificial light of 100 mW / cm ² . 4. The pretreatment for improving the conversion efficiency is characterized by applying a forward bias voltage of 1 V or less while exceeding the open circuit voltage of the thin film solar cell in a dark state where no light is applied. The thin film solar cell described. 5. The pretreatment for improving the conversion efficiency is characterized by applying a forward bias voltage of 1 V or less and applying a forward bias voltage of 1 V or less for 15 minutes or more in a dark state where no light is applied to the thin film solar cell. The thin film solar cell according to claim 4. 6. The transparent and conductive second metal oxide semiconductor thin film, which has a conductivity type opposite to that of the first conductivity type and serves as a window layer, is made of zinc oxide. The thin film solar cell according to 1, 2, or 4. 7. A mainly II-VI compound semiconductor thin film (interfacial layer or buffer layer) grown at the interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film and having high resistance. 5.) The thin film solar cell according to claim 1, 2 or 4, wherein c) comprises cadmium sulfide, zinc selenide, or a zinc mixed crystal compound containing oxygen, sulfur and a hydroxyl group. 8. The first multi-component compound semiconductor thin film is copper-III.
The thin film solar cell according to claim 1, 2 or 4, which is made of one of -VI ₂ group chalcopyrite compound semiconductors. 9. The first multi-element compound semiconductor thin film used as the light absorption layer is made of copper indium diselenide, copper indium gallium diselenide, or copper indium disulphide / gallium indium gallium.
The thin film solar cell described. 10. A metal back electrode layer, and a first p-type conductive type on the back electrode layer and serving as a light absorbing layer.
And a second multi-element compound semiconductor thin film having a conductivity type opposite to the first conductivity type on the first multi-component compound semiconductor thin film, having a wide forbidden band serving as a window layer, being transparent, and having conductivity. And a structure having mainly a II-VI group compound semiconductor thin film having a high resistance and grown at an interface between the first multi-component compound semiconductor thin film and the second metal oxide semiconductor thin film. Or a thin film solar cell having a structure in which a plurality of thin film solar cells are connected in series or in parallel, wherein a conversion efficiency improving means is added to the thin film solar cell. 11. A dark state in which the conversion efficiency improving means exceeds an open circuit voltage generated according to several thin film solar cells connected in series or in parallel and is not exposed to a forward bias voltage of about 1 V or less in light. The thin film solar cell array according to claim 10, wherein the heating time is 15 minutes or more. 12. The conversion efficiency improving means has an automatic starting means for starting at least 15 minutes before the sunrise time of the sun or the time when the sunlight reaches a predetermined illuminance. Thin film solar cell array. 13. The conversion efficiency improving means applies artificial light having an air mass (AM) of 1.5 and an irradiation intensity of 100 mW / cm ² for an irradiation time of 1
The thin film solar cell array according to claim 10, wherein the thin film solar cell array is irradiated with light for a time or more. 14. The conversion efficiency improving means has an automatic starting means for starting at least one hour before the sunrise time of the sun or the time when the sunlight reaches a predetermined illuminance. Thin film solar cell array. 15. A power source for the conversion efficiency improving means,
The thin film solar cell array according to claim 10, wherein a secondary battery that stores electric power generated by the thin film solar cell is used.