Thin film solar cell and manufacturing method of thin film solar cell

Abstract

To provide a thin film solar cell capable of repairing radiation damage, and a manufacturing method of the thin film solar cell.SOLUTION: A p-type light absorption layer of a thin film solar cell comprises a first region and a second region which are obtained by equally dividing the p-type light absorption layer into two. The p-type light absorption layer contains Cu as a group I element and contains Ga and In as group III elements. An average value of a ratio C1 in atomic numbers of Cu and the group III element in the first region is lower than an average value of the ratio C1 in the second region. An average value of a ratio G1 in atomic numbers of Ga and the group III elements in the first region is lower than an average value of the ratio G1 in the second region, and the average value of the ratio G1 in the p-type light absorption layer is 0.2 or more and 0.4 or less. An absolute value of a change rate of the ratio G1 from a first electrode side to a second electrode side becomes maximum in the first region and in the first region, the ratio G1 in the p-type light absorption layer tends to decrease from the first electrode layer side to the second electrode layer side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a thin-film solar cell and a method for manufacturing a thin-film solar cell. [Background technology]

[0002] Thin-film solar cells are one type of solar cell. Thin-film solar cells include CIS-based thin-film solar cells that use a group I-III-VI2 compound with a chalcopyrite structure containing Cu, In, Ga, Se, and S as a p-type light absorbing layer. As shown in Non-Patent Document 1, academic research on CIS-based thin-film solar cells is actively conducted. In addition, Patent Document 1 describes an atomic profile of a p-type light absorbing layer aimed at improving the photoelectric conversion efficiency of CIS-based thin-film solar cells. Thin-film solar cells are sometimes used in outer space, and Non-Patent Document 2 describes thin-film solar cells applied in outer space. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6297038 [Non-patent literature]

[0004] [Non-Patent Document 1] Physica Status Solidi. Rapid Research Letters, 2019, Vol.13, pp.1900415 [Non-Patent Document 2] Advanced Energy Materials, 2022, Vol.12, Issue 29, pp.2200125 Summary of the Invention [Problem to be solved by the invention]

[0005] Strong radiation exists in space, and thin-film solar cells placed in space are exposed to strong radiation. Radiation causes defects in the light absorption layer in thin-film solar cells, degrading their performance.

[0006] Therefore, an object of the present invention is to provide a thin-film solar cell that can withstand radiation and has a long life, and a method for manufacturing the thin-film solar cell. [Means for solving the problem]

[0007] A thin-film solar cell according to an embodiment of the present disclosure includes a substrate, a first electrode layer provided on the substrate, a p-type light absorbing layer provided on the first electrode layer and containing a I-III-VI2 group compound, and an n-type second electrode layer provided on the p-type light absorbing layer, the p-type light absorbing layer having a first region on the second electrode layer side when the p-type light absorbing layer is divided into two equal parts in the depth direction of the p-type light absorbing layer, and a second region other than the first region. The p-type light absorbing layer includes Cu as a group I element and Ga and In as group III elements, and the average atomic ratio of Cu to group III elements in the first region is lower than the average atomic ratio of Cu to group III elements in the second region. The average atomic ratio of Ga to group III elements in the first region is lower than the average atomic ratio of Ga to group III elements in the second region, and the average atomic ratio of Ga to group III elements in the p-type light absorbing layer is 0.2 or more and 0.4 or less. In the p-type light absorbing layer, the absolute value of the rate of change of the atomic number ratio of Ga to the group III element from the first electrode layer side to the second electrode layer side is maximum in the first region, and the atomic number ratio of Ga to the group III element in the p-type light absorbing layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region.

[0008] A method for manufacturing a thin-film solar cell according to one embodiment of the present disclosure includes a first step of providing a first electrode layer on a substrate, a second step of providing a p-type light absorbing layer containing a group I-III-VI2 compound on the first electrode layer, and a third step of providing an n-type second electrode layer on the p-type light absorbing layer, wherein the p-type light absorbing layer has a first region on the second electrode layer side when the p-type light absorbing layer is divided into two equal parts in a depth direction of the p-type light absorbing layer, and a second region other than the first region, the p-type light absorbing layer contains Cu as a group I element and Ga and In as group III elements, and the second step is a step of providing an n-type second electrode layer on the first region such that an average ratio of the atomic numbers of Cu and the group III elements in the first region is greater than or equal to an average ratio of the atomic numbers of Cu and the group III elements in the second region. the average atomic ratio of Ga to group III elements in the first region is lower than the average atomic ratio of Ga to group III elements in the second region, the average atomic ratio of Ga to group III elements in the p-type light absorbing layer is 0.2 or more and 0.4 or less, the absolute value of the rate of change of the atomic ratio of Ga to group III elements from the first electrode layer side to the second electrode layer side in the p-type light absorbing layer is maximum in the first region, and the atomic ratio of Ga to group III elements in the p-type light absorbing layer has a decreasing tendency from the first electrode layer side to the second electrode layer side in the first region. Effect of the Invention

[0009] According to the present invention, it is possible to provide a thin-film solar cell which can withstand radiation and has a long life, and a method for manufacturing the thin-film solar cell. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of a thin-film solar cell according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram showing a Cu profile in the p-type absorber layer according to the embodiment. [Diagram 3] FIG. 4 is a diagram showing a Ga profile in a p-type absorber layer according to the embodiment. [Figure 4] FIG. 11 is a diagram showing another example of a Ga profile in the p-type absorber layer according to the embodiment. [Diagram 5]FIG. 11 is a diagram showing another example of a Ga profile in the p-type absorber layer according to the embodiment. [Figure 6A] 1A to 1C are cross-sectional views illustrating an example of a method for manufacturing a thin-film solar cell according to an embodiment of the present invention. [Figure 6B] 1A to 1C are cross-sectional views illustrating an example of a method for manufacturing a thin-film solar cell according to an embodiment of the present invention. [Figure 6C] 1A to 1C are cross-sectional views illustrating an example of a method for manufacturing a thin-film solar cell according to an embodiment of the present invention. [Figure 6D] 1A to 1C are cross-sectional views illustrating an example of a method for manufacturing a thin-film solar cell according to an embodiment of the present invention. [Figure 6E] 1A to 1C are cross-sectional views illustrating an example of a method for manufacturing a thin-film solar cell according to an embodiment of the present invention. [Figure 7A] 4A to 4C are diagrams illustrating the recovery effect of the thin-film solar cell according to the embodiment. [Figure 7B] 4A to 4C are diagrams illustrating the recovery effect of the thin-film solar cell according to the embodiment. [Figure 7C] 4A to 4C are diagrams illustrating the recovery effect of the thin-film solar cell according to the embodiment. [Figure 7D] 4A to 4C are diagrams illustrating the recovery effect of the thin-film solar cell according to the embodiment. [Figure 8] FIG. 11 is a diagram comparing the recovery effect of the thin-film solar cell according to the present embodiment with other thin-film solar cells. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to the accompanying drawings, in which like reference numerals denote like or similar structures.

[0012] 1 shows a cross-sectional view of a thin-film solar cell 100 according to this embodiment. The thin-film solar cell 100 has a substrate 101, a first electrode layer 102, a p-type light absorbing layer 103, an electron transport layer 104, a second electrode layer 105, and a grid electrode 106. The thin-film solar cell 100 receives light from the grid electrode 106 side and generates electricity.

[0013] The substrate 101 may be, for example, a glass substrate such as soda lime glass or low-alkali glass, a metal substrate such as a stainless steel plate, or a polyimide resin substrate. The first electrode layer 102 may be, for example, a metal conductive layer disposed on the substrate 101 and made of a metal such as Mo, Cr, or Ti. The thickness of the first electrode layer 102 may be, for example, 200 to 800 nm.

[0014] The p-type light absorbing layer 103 is disposed on the first electrode layer 102, for example, and is made of a group I-III-VI2 compound. The p-type light absorbing layer 103 contains Cu as a group I element, Ga and In as group III elements, and Se and S as group VI elements. The thickness of the p-type light absorbing layer 103 can be, for example, 1 to 3 μm.

[0015] The p-type light absorbing layer 103 has a first region R1 on the second electrode layer 105 side when the p-type light absorbing layer 103 is divided into two equal parts, and a second region R2 on the first electrode layer 102 side, different from the first region. The first region R1 also has a third region R3 on the second electrode layer 105 side when the first region R1 is divided into two equal parts, and a fourth region R4 on the second region R2 or first electrode layer 102 side, different from the third region, with respect to the depth direction of the p-type light absorbing layer 103.

[0016] The electron transport layer 104 is disposed on the p-type light absorbing layer 103, and is made of, for example, Zn(O,S,OH) x The electron transport layer 104 can be formed to a thickness of, for example, 20 to 150 nm. The electron transport layer 104 can be formed using a thin film of a II-VI group compound semiconductor such as CdS, ZnS, or ZnO, or a mixed crystal thereof such as Zn(O,S). x Specific examples include In2O3, In2S3, and In(O, S, OH). x The insulating layer 11 may also be formed from an In-based compound semiconductor thin film such as those mentioned above.

[0017] The second electrode layer 105 is disposed on the electron transport layer 104, and may be made of, for example, ZnO:B, which has n-type conductivity, a wide band gap, is transparent, and has a low resistance. The second electrode layer 105 may be formed as a transparent conductive film having a thickness of, for example, 0.1 to 1.5 μm. The second electrode layer 105 may also be formed of a transparent conductive film made of ZnO:Al, ZnO:Ga, and ITO.

[0018] The grid electrode 106 is, for example, an electrode disposed on the second electrode layer 105 to extract electricity from the second electrode layer 105. The grid electrode 106 is made of a conductive material, and for example, a metal material, an alloy material, or a transparent conductive material can be used.

[0019] <Example> Next, the atomic number ratio (C1) between Cu and group III elements and the atomic number ratio (G1) between Ga and group III elements in the p-type light absorbing layer 103 of the thin-film solar cell 100 according to this embodiment will be described. The inventors manufactured three thin-film solar cells 100 according to this embodiment (A to C), and will describe the ratios C1 and G1 measured for the three examples with reference to Figs. 2 to 5. The atomic number is measured, for example, by measuring a cross section of the light absorbing layer by energy dispersive X-ray spectroscopy using a scanning electron microscope.

[0020] Fig. 2 shows an example of the atomic ratio C1 between Cu and group III elements in the p-type light absorbing layer 103 in Example A of the thin-film solar cell 100. The horizontal axis in Fig. 2 is the depth from the surface of the p-type light absorbing layer 103 on the second electrode layer 105 side. The horizontal axis is also used in Figs. 3 to 5. The atomic ratio C1 between Cu and group III elements is calculated as the ratio of (number of Cu atoms) / (number of group III elements). The group III elements are, for example, In and Ga.

[0021] The ratio C1 of the entire p-type light absorbing layer 103 is lower than 1.0. In the example of FIG. 2, the average value of the ratio C1 of the entire layer is 0.91. If the ratio C1 is 1.0 or more, the photoelectric conversion efficiency may decrease. On the other hand, it is preferable that the ratio C1 is larger than 0.80 from the viewpoint of forming a p-type light absorbing layer with an appropriate carrier concentration.

[0022] Furthermore, in the p-type light absorbing layer 103, the average value of the ratio C1 in the first region R1 is lower than the average value of the ratio C1 in the second region R2. In the example of Fig. 2, the average value of the ratio C1 in the first region R1 is 0.89, and the average value of the ratio C1 in the second region R2 is 0.94.

[0023] In this way, by lowering the ratio C1 on the surface on the second electrode layer 105 side, the thin-film solar cell 100 can repair damage caused by radiation.

[0024] Specifically, radiation is known to cause defects in Cu in the crystal structure of the p-type light absorbing layer 103. One type of defect is an antisite defect that is generated when In or Ga, a group III element, is placed in a Cu vacancy caused by radiation. The antisite defect significantly deteriorates the electrical characteristics. The antisite defect is passivated by being modified by other Cu vacancies, and in this case, the deterioration of the electrical characteristics is reduced. It is also known that the Cu vacancies can transition in the p-type light absorbing layer even with relatively weak external energy such as light irradiation or heating. By using this transition to promote the modification of the antisite defect by the Cu vacancy, the thin-film solar cell 100 can self-repair even if it is damaged, and as a result, the damage caused by radiation can be repaired.

[0025] In the p-type light absorbing layer 103, by lowering the atomic ratio of Cu to group III elements on the surface on the second electrode layer 105 side, it is possible to increase the number of Cu vacancies that bring about defect repair, thereby enabling sufficient self-repair and enabling the thin-film solar cell 100 to repair damage caused by radiation.

[0026] 3 to 5 show examples of the atomic ratio G1 between Ga and group III elements in the p-type absorber layer 103 in Examples A to C. The atomic ratio G1 between Ga and group III elements is calculated as the ratio of (number of Ga atoms) / (number of group III elements).

[0027] In the p-type light absorbing layer 103, the average value of the ratio G1 in the first region R1 is lower than the average value of the ratio G1 in the second region R2. In the example of FIG. 3, the average value of the ratio G1 in the first region R1 in Example A is 0.13, and the average value of the ratio G1 in the second region is 0.45. In the example of FIG. 4, the average value of the ratio G1 in the first region R1 in Example B is 0.15, and the average value of the ratio G1 in the second region is 0.42. In the example of FIG. 5, the average value of the ratio G1 in the first region R1 in Example C is 0.09, and the average value of the ratio G1 in the second region is 0.48.

[0028] In the p-type light absorbing layer 103, the average value of the ratio G1 in the p-type light absorbing layer 103 is 0.2 or more and 0.4 or less. Figures 3, 4, and 5 show a case where the average value of the ratio G1 in the entire p-type light absorbing layer 103 is 0.29. By setting the average value of the ratio G1 to be 0.2 or more and 0.4 or less, the photoelectric conversion efficiency can be increased.

[0029] In the p-type light absorbing layer 103, the absolute value of the rate of change of the ratio G1 from the first electrode layer 102 side to the second electrode layer 105 side is maximum in the first region R1. In the example of FIG. 3, the absolute value of the rate of change of the ratio G1 is maximum 74.6% in the first region R1. In the example of FIG. 4, the absolute value of the rate of change of the ratio G1 is maximum 52.7% in the first region R1. In the example of FIG. 5, the absolute value of the rate of change of the ratio G1 is maximum 70.4% in the first region R1. More specifically, the absolute value of the rate of change of the ratio G1 is maximum in the fourth region R4 in the first region R1 in all of FIGS. 3 to 5.

[0030] In this manner, by making the position where the absolute value of the rate of change of the ratio G1 is maximum be in the first region R1, which is the region on the second electrode layer 105 side, it is possible to promote the movement of electrons to the surface on the second electrode layer 105 side by utilizing the band gradient of the conduction band of the p-type light absorbing layer 103.

[0031] In the first region R1, the ratio G1 in the p-type light absorbing layer 103 tends to decrease from the first electrode layer 102 side to the second electrode layer 105 side. This tendency is commonly shown in each of FIGS.

[0032] In the p-type light absorbing layer 103, the ratio G1 in the third region R3 is preferably 0.15 or less. More preferably, the ratio G1 is, for example, 0.13 or less. In the example of FIG. 3, the maximum value of the ratio G1 in the third region R3 is 0.10. In the example of FIG. 4, the maximum value of the ratio G1 in the third region R3 is 0.13. In the example of FIG. 5, the maximum value of the ratio G1 in the third region R3 is 0.06. In addition, in the first region R1, in a region at a depth of 300 nm from the surface on the second electrode layer 105 side, the ratio G1 is 0.1 or less.

[0033] In this way, by adjusting the ratio G1 in the entire p-type light absorbing layer 103 and the ratio G1 on the surface on the second electrode layer 105 side, the thin-film solar cell 100 can repair damage caused by radiation. Among the above-mentioned antisite defects, the antisite defect in which Ga is arranged in a Cu vacancy is characterized by being difficult to self-repair by light irradiation or heating. By lowering the ratio of the number of atoms of Ga and group III elements on the surface on the second electrode layer 105 side as in the p-type light absorbing layer 103, it is possible to reduce Ga, which causes defects that are difficult to self-repair, and thus suppress the occurrence of defects, and the thin-film solar cell 100 can repair damage caused by radiation.

[0034] Finally, the p-type light absorbing layer 103 contains S as a group VI element. More specifically, S may be contained in the first region R1. This allows the band gap of the p-type light absorbing layer 103 to be adjusted and the photoelectric conversion efficiency to be increased. In particular, by containing S in the first region R1 in which the ratio of Ga is reduced, it is possible to increase the photoelectric conversion efficiency while making it possible to repair damage caused by radiation.

[0035] <Manufacturing method> Next, a method for manufacturing the thin-film solar cell 100 will be described with reference to FIGS. 6A to 6E.

[0036] First, as shown in Fig. 6A, a first electrode layer 102 is formed on a substrate 101. The thickness of the first electrode layer 102 may be, for example, 200 to 800 nm. The first electrode layer 102 is formed by DC sputtering using Mo as a material, for example. The deposition conditions for the DC sputtering method are deposition pressure: 0.5 to 2.5 Pa, applied power: 1.0 to 3.0 W / cm 2 It is also possible to use the following.

[0037] Next, as shown in FIG. 6B, a p-type light absorbing layer 103 containing a Group I-III-VI2 compound is formed on the first electrode layer 102.

[0038] Examples of methods for forming the p-type light absorbing layer 13 include (1) a method of forming a metal precursor film of group I elements and group III elements, and forming a compound of the metal precursor film and a group VI element, and (2) a method of forming a film of group I elements, group III elements, and group VI elements by a vapor deposition method.

[0039] First, a case where the p-type light absorbing layer 103 is formed by using the method (1) will be described. In the method (1), a precursor film containing Ga and Cu is formed on the first electrode layer 102, then a precursor film containing In is formed, and then a precursor film containing Ga and Cu and a compound of the precursor film containing In and a group VI element (Se and S) are formed. As for Cu, which is a group I element, as described above, a precursor film containing a mixed crystal of Ga and Cu may be formed, or a precursor film containing Cu may be laminated on a precursor film containing Ga. The Cu concentration on the surface of the precursor film is controlled by using the Se-S concentration in the reaction gas.

[0040] Each precursor film can be formed by using a known film formation technique such as a sputtering method, etc. In this manner, the p-type light absorbing layer 103 having the atomic profile described with reference to FIGS.

[0041] In addition, the ratio G1 of the number of Ga atoms to the number of Group III elements on the surface can be reduced by shortening the heat treatment time for forming a compound with the Group VI element or by adding an alkaline compound (e.g., by adding it to the precursor film or diffusing it from the substrate).

[0042] The atomic ratio C1 of Cu to group III elements in the entire p-type light absorbing layer 103 can be adjusted by controlling the atomic numbers of Cu and group III elements in the precursor films to be laminated, for example, by changing the film thickness ratio of the Cu—Ga precursor film to the In precursor film or the film thickness ratio of the Cu—Ga precursor film to the Cu precursor film.

[0043] Next, a case where the p-type light absorbing layer 103 is formed by the method (2) will be described. In the method (2), when I, III, and VI elements are evaporated on the first electrode layer 102 as evaporation sources, Ga is evaporated before In is evaporated as the evaporation source of the III element, thereby forming a semiconductor layer having a chalcopyrite structure, and the p-type light absorbing layer 103 is formed. In this manner, the p-type light absorbing layer 103 having the atomic profile described with reference to Figs. 2 to 5 may be formed. In addition, the ratio G1 of the number of atoms of Ga and the III element on the surface can be reduced by shortening the heat treatment time for evaporating the VI element and adding an alkali compound (evaporation using an alkali compound as an evaporation source, diffusion of an alkali metal from the substrate).

[0044] Cu, which is a group I element, may be further deposited as a deposition film containing Cu and Ga or In, or as a deposition source containing Cu and S or Se, to form a p-type light absorbing layer.

[0045] Se or S, which is a Group VI element, may be deposited as a Se film, an S film, or a film containing Se and S.

[0046] For example, the p-type light absorbing layer 103 is formed on the first electrode layer 102 by first evaporating Ga and Se, or Ga, In and Se, then evaporating Cu, Se and S, and finally evaporating In, Se and S. A compound of Cu, Se or S, and In and Ga is formed by the heat generated when each element is evaporated. After each element is evaporated, a heat treatment may be performed to form a compound of Cu, Se or S, and In and Ga. For the evaporation, a method such as a multi-source simultaneous evaporation method may be used.

[0047] Alternatively, on the first electrode layer 102, first, Cu and Ga (or a CuGa compound) may be evaporated, then Cu and In (or a CuIn compound), and then Se, S and In (or an InSeS compound) may be evaporated to form the p-type light absorbing layer 103. A compound of Cu, Se or S, and In and Ga may be formed by the heat generated when In (Se, S) is evaporated. Alternatively, after In (Se, S) is evaporated, a heat treatment may be performed to form a compound of Cu, Se or S, and In and Ga.

[0048] Alternatively, on the first electrode layer 102, first, Cu and Ga (or a CuGa compound) may be evaporated, then Cu and In (or a CuIn compound), and then Se and S (or a SeS compound) may be evaporated to form the p-type light absorbing layer 103. A compound of Cu, Se or S, and In and Ga may be formed by the heat generated when Se-S is evaporated. Alternatively, after the evaporation of Se-S, a heat treatment may be performed to form a compound of Cu, Se or S, and In and Ga. This concludes the description of the process of forming the p-type light absorbing layer 103 using method (2).

[0049] Next, as shown in FIG. 6C, an electron transport layer 104 is formed on the p-type light absorbing layer 103. The electron transport layer 104 can be formed by a solution growth method, an MOCVD method, an ALD method, a vapor deposition method, or a sputtering method. Next, as shown in FIG. 6D, a second electrode layer 105 is formed on the electron transport layer 104. The second electrode layer 105 may be formed by a sputtering method or an MOCVD method. Next, as shown in FIG. 6E, a grid electrode 106 is formed on the second electrode layer 105. The grid electrode 106 may be formed by, for example, a vapor deposition method or by printing a paste-like conductive material on the second electrode layer 105.

[0050] <Self-repair effect> 7A to 7D, the self-repair effect of the thin-film solar cell 100 will be described. In FIG. 7A to FIG. 7D, the retention rate of the photoelectric conversion efficiency of the thin-film solar cell 100 (FIG. 7A), the open-circuit voltage V oc(FIG. 7B), the short-circuit current density J of the thin-film solar cell 100 sc 7A to 7D are average values ​​of data from a plurality of thin-film solar cells 100 including the thin-film solar cells 100 of Examples A, B, and C.

[0051] The horizontal axis of FIG. 7A to FIG. 7D is the proton fluence, which indicates the number of particles of the proton beam per unit area. In FIG. 7A to FIG. 7D, the respective storage ratios in the case of irradiation with a 300 keV proton beam are indicated by solid lines, and the respective storage ratios in the case of irradiation with a 3 MeV proton beam are indicated by dashed lines. The storage ratio is the ratio of the value after irradiation to the value before irradiation. In addition, in the example of FIG. 7A to FIG. 7D, the respective storage ratios are shown in the case where light irradiation (Light Soaking: LS) ​​and heat light soaking (Heat Light Soaking: HLS) are performed for self-repair of the thin-film solar cell 100 after irradiation. The light irradiation or heat light irradiation promotes the movement of Cu defects in the p-type light absorbing layer 103, modifies the antisite defects, and recovers the performance of the thin-film solar cell 100. In addition, for comparison, the respective storage ratios in the case where light irradiation or heat light irradiation is not performed are shown.

[0052] As shown in Figures 7A to 7D in common, even if the thin-film solar cell 100 is irradiated with a proton beam and its performance is degraded, for example, as shown in the case of no repair, each characteristic is largely restored by light irradiation or thermal light irradiation. Such characteristic recovery is believed to be due to the fact that the p-type light absorbing layer 103 has the atomic profile described with reference to Figures 2 to 5.

[0053] 7A to 7D, the thermal irradiation was performed by irradiating light for one hour at a temperature of 150° C. This corresponds to approximately 16 to 69 days at a temperature of 60° C. Therefore, the thin-film solar cell 100 can perform sufficient self-repair even in an actual space environment.

[0054] FIG. 8 shows the storage rate of photoelectric conversion efficiency when the thin-film solar cell 100 according to this embodiment and other thin-film solar cells are irradiated with a proton beam of 300 keV and self-repaired by thermal irradiation. The data of the thin-film solar cell 100 in FIG. 8 is an average value of data from a plurality of thin-film solar cells 100 including the thin-film solar cells 100 of Examples A, B, and C. FIG. 8 shows the storage rate RF1 of the photoelectric conversion efficiency of the thin-film solar cell 100, the storage rate RF2 of the photoelectric conversion efficiency of the thin-film solar cell described in Non-Patent Document 1, and the storage rate RF3 of the photoelectric conversion efficiency of the thin-film solar cell (GaAs-based) described in Non-Patent Document 2. It is shown that the thin-film solar cell 100 has a higher self-repair effect than other thin-film solar cells.

[0055] In a typical thin-film solar cell arranged in outer space, in order to suppress deterioration of the cell performance, a protective means such as a cover glass that protects the light absorption layer of the thin-film solar cell is attached to the thin-film solar cell by an adhesive. However, the cover glass and adhesive for space use are very expensive, and the use of the cover glass and adhesive increases the weight of the entire power generation device, which is not preferable. Therefore, by enabling the thin-film solar cell itself to sufficiently self-repair as in the thin-film solar cell 100, it becomes unnecessary to use the cover glass and adhesive. This makes it possible to reduce the weight of the battery module including the thin-film solar cell 100, and it is possible to reduce the cost of launching and the cost due to the number of parts. Furthermore, since the thin-film solar cell 100 can self-repair damage caused by radiation, it can be used as a long-life battery in outer space or the atmosphere above the stratosphere. In addition, since the thin-film solar cell 100 has radiation resistance, it can be used as a battery with a longer life than conventional thin-film solar cells even in a radiation environment. It can also be used as a battery with a longer life in the troposphere, where the amount of radiation is less than in outer space. For example, it can be attached to the surfaces (roofs, windows, walls, etc.) of buildings, moving objects, aircraft, etc., and used as a long-life power generation device.

[0056] The thin-film solar cell 100 according to this embodiment has been described above. The thin-film solar cell 100 includes a substrate 101, a first electrode layer 102 provided on the substrate 101, a p-type light absorbing layer 103 provided on the first electrode layer 102 and containing a I-III-VI2 group compound, and an n-type second electrode layer 105 provided on the p-type light absorbing layer 103. The p-type light absorbing layer 103 has a first region R1 on the second electrode layer 105 side when the p-type light absorbing layer 103 is divided into two equal parts in the depth direction of the p-type light absorbing layer 103, and a second region R2 other than the first region R1. The p-type light absorbing layer 103 includes Cu as a group I element and Ga and In as group III elements, and the average value of the ratio of the number of atoms of Cu and group III elements in the first region R1 is lower than the average value of the ratio of the number of atoms of Cu and group III elements in the second region R2. The average atomic ratio of Ga to group III elements in the first region R1 is lower than the average atomic ratio of Ga to group III elements in the second region R2, and the average atomic ratio of Ga to group III elements in the p-type light absorbing layer 103 is 0.2 or more and 0.4 or less. In the p-type light absorbing layer 103, the absolute value of the rate of change of the atomic ratio of Ga to group III elements from the first electrode layer 102 side to the second electrode layer 105 side is maximum in the first region R1, and the atomic ratio of Ga to group III elements in the p-type light absorbing layer tends to decrease from the first electrode layer 102 side to the second electrode layer 105 side in the first region R1.

[0057] In the p-type light absorbing layer 103, the amount of Cu vacancies that repair defects caused by radiation can be increased on the second electrode layer 105 side, so that the thin-film solar cell 100 can repair damage caused by radiation. In addition, by lowering the ratio of the number of atoms of Ga and group III elements on the surface on the second electrode layer 105 side, the amount of Ga that causes defects that are difficult to repair can be reduced, so that the generation of defects can be suppressed and the thin-film solar cell 100 can easily repair damage caused by radiation. By making the position where the absolute value of the rate of change of the ratio of the number of atoms of Ga and group III elements is maximum in the first region R1, it is possible to promote electron migration to the surface on the second electrode layer 105 side using the band gradient of the conduction band of the p-type light absorbing layer 103, and to improve the electrical characteristics. These factors enable the thin-film solar cell 100 to repair damage caused by radiation.

[0058] The p-type light absorbing layer 103 may contain S as a group VI element, which can adjust the band gap of the p-type light absorbing layer 103 and increase the photoelectric conversion efficiency. In particular, when S is contained in the first region R1 in which the ratio of Ga is reduced, the photoelectric conversion efficiency can be increased while making it possible to repair damage caused by radiation.

[0059] The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangements, materials, conditions, shapes, sizes, etc., are not limited to those shown as examples and can be changed as appropriate. In addition, configurations shown in different embodiments can be partially substituted or combined with each other. [Explanation of symbols]

[0060] 100... thin-film solar cell, 101... substrate, 102... first electrode layer, 103... p-type light absorbing layer, 104... electron transport layer, 104, 105... second electrode layer, 106... grid electrode

Claims

1. A substrate; A first electrode layer provided on the substrate; I-III-VI are provided on the first electrode layer. ２ a p-type light absorbing layer including a group compound; an n-type second electrode layer provided on the p-type light absorbing layer; the p-type light absorbing layer has a first region on the second electrode layer side when the p-type light absorbing layer is divided into two equal parts in a depth direction of the p-type light absorbing layer, and a second region other than the first region, The p-type light absorbing layer is Contains Cu as a Group I element, Group III elements include Ga and In, an average ratio of the number of atoms of Cu to the group III element in the first region is lower than an average ratio of the number of atoms of Cu to the group III element in the second region; an average ratio of the number of atoms of Ga to the group III element in the first region is lower than an average ratio of the number of atoms of Ga to the group III element in the second region; an average ratio of the number of atoms of Ga to the number of group III elements in the p-type light absorbing layer is 0.2 or more and 0.4 or less; in the p-type light absorbing layer, an absolute value of a rate of change in the ratio of the number of atoms of Ga to the group III element from the first electrode layer side to the second electrode layer side is maximum in the first region, a ratio of the number of Ga atoms to the number of Group III elements in the p-type light absorbing layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region.

2. The thin-film solar cell according to claim 1 , the first region includes a third region on the second electrode layer side when the first region is divided into two equal parts in the depth direction, and a fourth region other than the third region, A thin-film solar cell, wherein the ratio of the number of atoms of Ga to the number of atoms of a group III element in the third region is 0.15 or less.

3. The thin-film solar cell according to claim 2, The absolute value of the rate of change is maximum in the fourth region.

4. The thin-film solar cell according to claim 1 , The thin-film solar cell, wherein the p-type light absorbing layer contains S as a Group VI element.

5. The thin-film solar cell according to claim 4, The thin-film solar cell, wherein the S is included in the first region.

6. A first step of providing a first electrode layer on a substrate; I-III-VI on the first electrode layer ２ a second step of providing a p-type light absorbing layer including an aromatic compound; and a third step of providing an n-type second electrode layer on the p-type light absorbing layer, the p-type light absorbing layer has a first region on the second electrode layer side when the p-type light absorbing layer is divided into two equal parts in a depth direction of the p-type light absorbing layer, and a second region other than the first region, The p-type light absorbing layer is Contains Cu as a Group I element, Group III elements include Ga and In, The second step comprises: an average ratio of the number of atoms of Cu to the group III element in the first region is lower than an average ratio of the number of atoms of Cu to the group III element in the second region; an average ratio of the number of atoms of Ga to the group III element in the first region is lower than an average ratio of the number of atoms of Ga to the group III element in the second region; an average ratio of the number of atoms of Ga to the number of group III elements in the p-type light absorbing layer is 0.2 or more and 0.4 or less; in the p-type light absorbing layer, an absolute value of a rate of change in the ratio of the number of atoms of Ga to the group III element from the first electrode layer side to the second electrode layer side is maximum in the first region, a p-type light absorbing layer having a p-type conductivity type that is greater than or equal to the first electrode layer side and greater than or equal to the second electrode layer side, the p-type light absorbing layer having a p-type conductivity type that is greater than or equal to the first electrode layer side, the p-type light absorbing layer having a p-type conductivity type that is ...

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