Photoelectric conversion element, photovoltaic module, flying object and method for manufacturing photoelectric conversion element

Abstract

The present invention provides a photoelectric conversion element which is capable of maintaining the performance related to photoelectric conversion even in a low-temperature environment. This photoelectric conversion element (10) comprises a photoelectric conversion layer (26) that contains a selenium compound, a first electrode layer (22) that contains Mo, and a first buffer layer (27) that is disposed between the first electrode layer (22) and the photoelectric conversion layer (26). If y is a real number satisfying 0 ≤ y < 1, the first buffer layer (27) has a compound layer that contains A(Sy, Se 1-y)2. The element A is at least one of Nb and Ta.

Description

Photoelectric conversion element, photovoltaic module, flying object, and method for manufacturing photoelectric conversion element

[0001] The present invention relates to a photoelectric conversion element, a photovoltaic module, a flying object, and a method for manufacturing a photoelectric conversion element.

[0002] Photoelectric conversion elements that convert light energy into electrical energy are known. One such photoelectric conversion element includes a so-called CIS-based or CIGS-based photoelectric conversion layer (light absorption layer).

[0003] The CIS-based or CIGS-based photoelectric conversion layer includes a sulfide-based compound semiconductor. The photoelectric conversion layer including the sulfide-based compound semiconductor is formed by depositing a precursor film made of Group I elements (e.g., Cu) and Group III elements (e.g., In and Ga), and then heat-treating the precursor film in a sulfur atmosphere (sulfurization of the precursor film).

[0004] Patent Document 1 below discloses an electrode for a photoelectric conversion element. The electrode for a photoelectric conversion element includes a molybdenum layer and a sulfuration-resistant layer formed on the molybdenum layer. The sulfuration-resistant layer contains one or more elements selected from the group consisting of Nb, Ti, Ta, Au, V, Mn, and W.

[0005] Patent Document 1 describes that if a molybdenum sulfide layer is formed on the electrode during sulfurization of the precursor film, the series resistance increases, causing a decrease in the conversion efficiency of the photoelectric conversion element. In Patent Document 1, a sulfuration-resistant layer is provided between the photoelectric conversion layer and the electrode layer to prevent sulfurization of molybdenum in the electrode layer.

[0006] JP 2014-049572 A

[0007] The invention described in Patent Document 1 is directed to suppressing an increase in sheet resistance that accompanies sulfurization of molybdenum in an electrode layer. Example 1 of Patent Document 1 shows the results of an experiment in which an electrode including a substrate, a molybdenum electrode layer, and a sulfurized sulfuration-resistant layer was formed and the sheet resistance of the electrode was measured.

[0008] However, Patent Document 1 does not conduct any experiments on a photoelectric conversion element in which a photoelectric conversion layer is formed on a sulfur-resistant layer, and therefore does not suggest anything about the performance of a photoelectric conversion element including a photoelectric conversion layer.

[0009] The inventors of the present application have considered the use of a photoelectric conversion element in a low-temperature environment. When a photoelectric conversion element is used, for example, at a high altitude on Earth, the photoelectric conversion element is placed in a low-temperature environment.

[0010] Therefore, a photoelectric conversion element that can maintain its photoelectric conversion performance even in a low-temperature environment is desired.

[0011] A photoelectric conversion element according to one embodiment includes a photoelectric conversion layer containing a selenium compound, a first electrode layer containing Mo, and a first buffer layer between the first electrode layer and the photoelectric conversion layer. When y is a real number that satisfies "0≦y<1," the first buffer layer has a conductivity of A(S ｙ , Se １－ｙ ) ２ The element A is at least one of Nb and Ta.

[0012] A photovoltaic module according to one aspect includes the above-described photoelectric conversion element.

[0013] A flying object according to one embodiment includes the photovoltaic module described above.

[0014] A method for manufacturing a photoelectric conversion element according to one embodiment includes the steps of forming a layer containing Mo on a substrate, forming a layer containing element A, which is at least one of Nb and Ta, on the layer containing Mo, forming a precursor film on the layer containing element A, and a chalcogenization step of forming a photoelectric conversion layer containing a selenium compound by selenizing the precursor film or by selenizing and sulfurizing the precursor film. The chalcogenization step is performed by forming a photoelectric conversion layer containing a selenium compound by selenizing the precursor film or by selenizing and sulfurizing the precursor film. ｙ , Se １－ｙ ) ２ The process is carried out so as to form a compound layer containing the compound.

[0015] FIG. 1 is a schematic plan view of a photoelectric conversion element according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the photoelectric conversion element taken along line 2A-2A in FIG. 1. FIG. 3 is a schematic cross-sectional view of a photoelectric conversion element according to the second embodiment. FIG. 4 is a schematic cross-sectional view of a photoelectric conversion element according to the third embodiment. FIG. 5 is a diagram for explaining a step in a method for manufacturing a photoelectric conversion element. FIG. 6 is a graph showing the temperature dependence of each characteristic of the photoelectric conversion elements in the examples and the reference example. FIG. 7 is a diagram showing the temperature dependence of the current-voltage characteristics of the photoelectric conversion element in Example 1. FIG. 8 is a diagram showing the temperature dependence of the current-voltage characteristics of the photoelectric conversion element in the reference example. FIG. 9 is a schematic plan view of a photovoltaic module including a photoelectric conversion element. FIG. 10 is a schematic perspective view of a flying object including a photovoltaic module.

[0016] Hereinafter, embodiments will be described with reference to the drawings. In the following drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and the ratios of the dimensions may differ from those of the actual parts.

[0017] [First Embodiment] Fig. 1 is a schematic plan view of a photoelectric conversion element according to one embodiment, and Fig. 2 is a schematic cross-sectional view of the photoelectric conversion element taken along line 2A-2A in Fig. 1.

[0018] The photoelectric conversion element 10 according to this embodiment may be a thin-film type photoelectric conversion element, and preferably is a photovoltaic element that converts light energy into electrical energy.

[0019] The photoelectric conversion element 10 has a substrate 20 that serves as a base on which each film is formed. The substrate 20 may be made of, for example, glass, ceramics, resin, or metal. The substrate 20 may be a flexible substrate. The shape and dimensions of the substrate 20 are determined appropriately depending on the size of the photoelectric conversion element 10, etc.

[0020] When a metal substrate is used as the substrate 20, the substrate 20 is formed of, for example, titanium (Ti), stainless steel (SUS), copper, aluminum, or an alloy thereof. Alternatively, the substrate 20 may have a layered structure in which a plurality of metal base materials are stacked, and for example, a stainless steel layer, a titanium layer, a molybdenum layer, or a molybdenum-sodium layer may be formed on the surface of the substrate.

[0021] The photoelectric conversion element 10 may have a first electrode layer 22, a first buffer layer 27 on the first electrode layer 22, a photoelectric conversion layer 26 on the first buffer layer 27, a second buffer layer 28 on the photoelectric conversion layer 26, and a second electrode layer 24 on the second buffer layer 28.

[0022] The photoelectric conversion layer 26 is provided between the first electrode layer 22 and the second electrode layer 24. The photoelectric conversion layer 26 is a layer that contributes to the mutual conversion between light energy and electrical energy. In a photovoltaic element that converts light energy into electrical energy, the photoelectric conversion layer 26 is sometimes called a light absorption layer.

[0023] The first electrode layer 22 and the second electrode layer 24 are adjacent to the photoelectric conversion layer 26. In this specification, the term "adjacent" means not only that both layers are in direct contact with each other, but also that both layers are close to each other via another layer.

[0024] The second electrode layer 24 may be composed of a transparent electrode layer. When the second electrode layer 24 is composed of a transparent electrode layer, light incident on the photoelectric conversion layer 26 or emitted from the photoelectric conversion layer 26 passes through the second electrode layer 24.

[0025] When the second electrode layer 24 is a transparent electrode layer, the first electrode layer 22 may be an opaque electrode layer or a transparent electrode layer. The first electrode layer 22 is a layer mainly containing molybdenum (Mo). The thickness of the first electrode layer 22 may be, for example, 50 nm to 1500 nm.

[0026] As a preferred example, the second electrode layer 24 may be formed of an n-type semiconductor, more specifically, a material having n-type conductivity and relatively low resistance. The second electrode layer 24 can function both as an n-type semiconductor and a transparent electrode layer. The second electrode layer 24 includes, for example, a metal oxide doped with a Group III element (B, Al, Ga, or In). Here, the "group" of an element in this specification is based on the short periodic table (the same applies hereinafter).

[0027] Examples of metal oxides that form the second electrode layer 24 include ZnO and SnO. ２ The second electrode layer 24 is made of, for example, indium tin oxide (In ２ O ３ : Sn), indium titanium oxide (In ２ O ３ :Ti), indium zinc oxide (In ２ O ３ :Zn), tin-zinc-doped indium oxide (In ２ O ３ : Sn, Zn), tungsten-doped indium oxide (In ２ O ３ :W), hydrogen-doped indium oxide (In ２ O ３ :H), indium gallium zinc oxide (InGaZnO ４ ), zinc tin oxide (ZnO:Sn), fluorine-doped tin oxide (SnO ２ :F), gallium-doped zinc oxide (ZnO:Ga), boron-doped zinc oxide (ZnO:B), aluminum-doped zinc oxide (ZnO:Al), and the like can be selected.

[0028] Although not particularly limited, the thickness of the second electrode layer 24 may be, for example, 500 nm to 2500 nm.

[0029] The photoelectric conversion layer 26 may include, for example, a p-type semiconductor. In a specific example, the photoelectric conversion layer 26 may function as, for example, a polycrystalline or microcrystalline p-type compound semiconductor layer.

[0030] The photoelectric conversion layer 26 is a layer containing a selenium compound. The selenium compound is a I-III-VI selenium compound having a chalcopyrite structure.２ The photoelectric conversion layer 26 may be a group compound semiconductor. Here, the group I element may be selected from copper (Cu), silver (Ag), gold (Au), etc. The group III element may be selected from indium (In), gallium (Ga), aluminum (Al), etc. The photoelectric conversion layer 26 contains selenium (Se) as a group VI element. Furthermore, the photoelectric conversion layer 26 may contain sulfur (S), tellurium (Te), etc. as a group VI element in addition to selenium (Se).

[0031] The composition of the selenium compound constituting the photoelectric conversion layer 26 is Cu(In,Ga)(S ｘ , Se １－ｘ ) ２ The selenium compound according to this composition may contain at least one of indium and gallium. Here, the symbol x in the composition is a real number that satisfies "0≦x<1" (the same applies hereinafter).

[0032] The first buffer layer 27 is provided between the first electrode layer 22 and the photoelectric conversion layer 26. The first buffer layer is mainly composed of A(S ｙ , Se １－ｙ ) ２ Here, y is a real number that satisfies "0≦y<1" (the same applies hereinafter). The element A is at least one of Nb and Ta. Therefore, the compound layer that constitutes the first buffer layer 27 may contain niobium selenide, niobium sulfoselenide, tantalum selenide, and / or tantalum sulfoselenide.

[0033] In the first buffer layer 27, the upper limit of the thickness of the region containing the element A at the highest ratio among elements other than S and Se may be, for example, less than 100 nm, preferably less than 50 nm, more preferably less than 30 nm, even more preferably less than 15 nm, and most preferably 12 nm or less.

[0034] In the first buffer layer 27, the lower limit of the thickness of the region containing the element A at the highest ratio among elements other than S and Se may be, for example, 1 nm or more, preferably 3 nm or more, and more preferably 5 nm or more.

[0035] In the first buffer layer 27, the thickness of the region containing the element A at the highest ratio among elements other than S and Se may be within a range that arbitrarily combines the above upper limit and lower limit values. The upper limit and lower limit values ​​may be appropriately selected so as to optimize the characteristics of the photoelectric conversion element 10. From the viewpoint of suppressing peeling of the photoelectric conversion layer 26, it is preferable that the film thickness of the first buffer layer 27 be as small as possible.

[0036] As will be described later, A(S ｙ , Se １－ｙ ) ２ The compound layer containing A(S) in the first buffer layer 27 is formed by forming a layer containing element A on the Mo layer constituting the first electrode layer 22, forming a precursor film on the layer containing element A, and then selenizing or selenizing and sulfurizing the precursor film. ｙ , Se １－ｙ ) ２ The thickness of the compound layer containing element A may increase by about 1.0 to 3.0 times due to selenization or selenization and sulfurization. Therefore, the thickness of the region in first buffer layer 27 that contains the element A at the highest ratio among elements other than S and Se is considered to be about 1.0 to 3.0 times the thickness of the layer containing element A formed on the Mo layer during manufacturing.

[0037] The first buffer layer 27 is substantially A(S ｙ , Se １－ｙ ) ２ Alternatively, the first buffer layer 27 may be made of a compound layer containing A(S ｙ , Se １－ｙ ) ２ Alternatively, the compound layer may include another layer different from the compound layer containing the compound.

[0038] The second buffer layer 28 may be a semiconductor material having the same conductivity type as the second electrode layer 24, or may be a semiconductor material having a different conductivity type. The second buffer layer 28 may be made of a material having a higher electrical resistance than the second electrode layer 24.

[0039] The second buffer layer 28 is formed on the photoelectric conversion layer 26. Although not particularly limited, the thickness of the second buffer layer 28 may be, for example, 10 nm to 100 nm.

[0040] The second buffer layer 28 can be made of a compound selected from compounds containing zinc (Zn), cadmium (Cd), and indium (In). Examples of compounds containing zinc include ZnO, ZnS, and Zn(OH). ２ , or mixed crystals thereof such as Zn(O,S) and Zn(O,S,OH), as well as ZnMgO and ZnSnO. Compounds containing cadmium include, for example, CdS, CdO, or mixed crystals thereof such as Cd(O,S) and Cd(O,S,OH). Compounds containing indium include, for example, In ２ S ３ , In ２ O ３ or a mixed crystal thereof, In ２ (O, S) ３ , In ２ (O, S, OH) ３ There is In ２ O ３ , In ２ S ３ , In(OH) ｘ The second buffer layer may have a laminated structure of these compounds.

[0041] The second buffer layer 28 has the effect of improving characteristics such as photoelectric conversion efficiency, but it can be omitted. When the second buffer layer 28 is omitted, the second electrode layer 24 is formed directly on the photoelectric conversion layer 26.

[0042] The photoelectric conversion element 10 may include a collecting electrode 30 on the second electrode layer 24. The collecting electrode 30 collects charge carriers from the second electrode layer 24 and is made of a conductive material. The collecting electrode 30 may be in direct contact with the second electrode layer 24. From the viewpoint of improving power generation efficiency, it is preferable that the area of ​​the collecting electrode 30 is as small as possible.

[0043] The collecting electrode 30 may have a plurality of substantially linear first portions 31 and second portions 32 connected to the first portions 31. The first portions 31 may also be referred to as "fingers." The second portions 32 may also be referred to as "bus bars."

[0044] The first portions 31 are arranged at intervals from one another. The plurality of linear first portions 31 are connected to the second portions 32. The first portions 31 serve to conduct electricity generated in the photoelectric conversion layer 26 to the second portions 32.

[0045] A plurality of first portions 31 of the collecting electrode 30 may be arranged side by side in the first direction (Y direction in the figure). The plurality of linear first portions 31 may be connected to the same second portion 32.

[0046] The second portion 32 of the collecting electrode 30 may extend in a first direction (Y direction in the figure). The second portion 32 may be connected to the first portion 31 at an end of the first portion 31. In this case, the multiple first portions 31 may extend from the second portion 32 along a second direction (X direction in the figure).

[0047] The second portions 32 of the collecting electrodes 30 may extend in the first direction (the Y direction in the figure) substantially from near one end to near the other end of the photoelectric conversion element 10. The width of the second portions 32 of the collecting electrodes 30 (the width in the X direction in the figure) may be larger than the width of each of the first portions 31 (the width in the Y direction in the figure).

[0048] The collecting electrode 30 (first portion 31 and second portion 32) may be made of a material having higher conductivity than the material constituting the second electrode layer 24. The material constituting the collecting electrode 30 is, for example, indium tin oxide (In ２ O ３ : Sn), indium titanium oxide (In ２ O ３ :Ti), indium zinc oxide (In ２ O ３ :Zn), tin-zinc-doped indium oxide (In ２ O ３ : Sn, Zn), tungsten-doped indium oxide (In ２ O ３ :W), hydrogen-doped indium oxide (In２ O ３ :H), indium gallium zinc oxide (InGaZnO ４ ), zinc tin oxide (ZnO:Sn), fluorine-doped tin oxide (SnO ２ The material can be selected from at least one of aluminum-doped zinc oxide (ZnO:Al), boron-doped zinc oxide (ZnO:B), gallium-doped zinc oxide (ZnO:Ga), Ni, Ti, Cr, Mo, Al, Ag, and Cu, or a compound containing one or more of these. The current collecting electrode 30 may be formed from an alloy or a laminate formed from a combination of the above-mentioned materials.

[0049] The photoelectric conversion element 10 may include a wiring 50 joined to the collecting electrode 30. The wiring 50 may be joined to the second portion 32 of the collecting electrode 30. The wiring 50 may be, for example, an interconnector for electrically connecting the photoelectric conversion element 10 to the outside, and / or a connector for connecting to a bypass diode that electrically bypasses a cell that cannot perform photoelectric conversion.

[0050] In the above-described embodiment, the photoelectric conversion element 10 includes the collecting electrodes 30 and the wiring 50. However, the collecting electrodes 30 and the wiring 50 are not essential components, and the photoelectric conversion element 10 does not necessarily have to include the collecting electrodes 30 and the wiring 50.

[0051] For example, the photoelectric conversion element 10 may have an integrated structure in which a plurality of photoelectric conversion cells are integrated with each other. In this case, it is sufficient that one or each of the plurality of photoelectric conversion cells has the first electrode layer 22 and the first buffer layer 27 described above.

[0052] The photoelectric conversion element 10 may also be a so-called tandem-type photoelectric conversion element having a structure in which two photoelectric conversion cells are stacked on top of each other. In this case, it is sufficient that one or both of the two photoelectric conversion cells have the first electrode layer 22 and the first buffer layer 27 described above.

[0053] Second Embodiment A photoelectric conversion module according to a second embodiment will be described below with reference to Fig. 3. Fig. 3 is a schematic cross-sectional view of a photoelectric conversion element according to the second embodiment. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. Please note that the description of the same components as those in the first embodiment may be omitted.

[0054] The configuration of the photovoltaic conversion module 10 in the second embodiment is the same as that in the first embodiment, except for the structure of the first buffer layer 27. In the second embodiment, the first buffer layer 27 contains A(S ｙ , Se １－ｙ ) ２ and a compound layer 27a containing Mo(S) as a main component and an element A added thereto. ｚ , Se １－ｚ ) ２ and a layer 27b containing Mo(S ｚ , Se １－ｚ ) ２ The layer 27 b containing is provided between the compound layer 27 a and the first electrode layer 22 .

[0055] Here, y is a real number that satisfies "0≦y<1" (the same applies hereinafter). z is a real number that satisfies "0≦y<1" (the same applies hereinafter). Furthermore, the element A is at least one of Nb and Ta, as in the first embodiment.

[0056] In the first buffer layer 27, the upper limit of the thickness of the region (compound layer 27a) containing the element A at the highest ratio among elements excluding S and Se may be, for example, less than 100 nm, preferably less than 50 nm, more preferably less than 30 nm, even more preferably less than 15 nm, and most preferably 12 nm or less.

[0057] In the first buffer layer 27, the lower limit of the thickness of the region (compound layer 27a) containing the element A at the highest ratio among elements other than S and Se may be, for example, 1 nm or more, preferably 3 nm or more, and more preferably 5 nm or more.

[0058] In the first buffer layer 27, the thickness of the region containing the element A at the highest ratio among elements other than S and Se may be within a range that arbitrarily combines the above upper limit and lower limit values. The upper limit and lower limit values ​​may be appropriately selected so as to optimize the characteristics of the photoelectric conversion element 10.

[0059] [Third Embodiment] A photoelectric conversion module according to a third embodiment will be described below with reference to Fig. 4. Fig. 4 is a schematic cross-sectional view of a photoelectric conversion element according to the second embodiment. In the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. Please note that the description of the same components as those in the first embodiment may be omitted.

[0060] The configuration of the photovoltaic conversion module 10 in the third embodiment is the same as that in the first embodiment, except for the structure of the first buffer layer 27. In the third embodiment, the first buffer layer 27 contains A(S ｙ , Se １－ｙ ) ２ and a layer 27c containing element A as a main component. The layer 27c containing element A is provided between the compound layer 27a and the first electrode layer 22. Here, y is a real number that satisfies "0≦y<1" (the same applies hereinafter). The element A is at least one of Nb and Ta, as in the first embodiment.

[0061] In the first buffer layer 27, the upper limit of the thickness of the region (compound layer 27a) containing the element A at the highest ratio among elements excluding S and Se may be, for example, less than 100 nm, preferably less than 50 nm, more preferably less than 30 nm, even more preferably less than 15 nm, and most preferably 12 nm or less.

[0062] In the first buffer layer 27, the lower limit of the thickness of the region (compound layer 27a) containing the element A at the highest ratio among elements other than S and Se may be, for example, 1 nm or more, preferably 3 nm or more, and more preferably 5 nm or more.

[0063] In the first buffer layer 27, the thickness of the region containing the element A at the highest ratio among elements other than S and Se may be within a range that arbitrarily combines the above upper limit and lower limit values. The upper limit and lower limit values ​​may be appropriately selected so as to optimize the characteristics of the photoelectric conversion element 10.

[0064] [Method for manufacturing photoelectric conversion element] Next, a method for manufacturing a photoelectric conversion element according to the first, second and third embodiments will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining one step in the method for manufacturing a photoelectric conversion element. Fig. 5 shows a state in which a precursor film, which will be described later, has been formed.

[0065] First, a layer containing Mo is formed on the substrate 20. The layer containing Mo is formed on the surface of the substrate 20 by, for example, a sputtering method. The sputtering method may be a direct current (DC) sputtering method or a radio frequency (RF) sputtering method. Alternatively, the layer containing Mo may be formed by a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method, or the like instead of the sputtering method. The layer containing Mo is formed as a material constituting the first electrode layer 22.

[0066] Next, a layer 27p containing element A, i.e., at least one of Nb and Ta, is formed on the layer containing Mo. The layer 27p containing element A is formed by, for example, a sputtering method, which is physical vapor deposition (PVD). The sputtering method may be a direct current (DC) sputtering method or a radio frequency (RF) sputtering method. The physical vapor deposition (PVD) may be, for example, an electron beam evaporation method or a pulsed laser method. Alternatively, the layer 27p containing element A may be formed by a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method, or the like.

[0067] The layer 27p containing element A is formed to a thickness of, for example, less than 50 nm, preferably less than 30 nm, more preferably less than 15 nm, and even more preferably 12 nm or less. The layer 27p containing element A is formed to a thickness of, for example, 1 nm or more, preferably 3 nm or more, and more preferably 5 nm or more. The thickness of the layer 27p containing element A may be within a range that arbitrarily combines the above upper and lower limits. The film thickness of the layer 27p containing element A may be appropriately selected so as to optimize the characteristics of the photoelectric conversion element 10 after manufacture. From the viewpoint of suppressing peeling of the photoelectric conversion layer 26 after the chalcogenization step described below, it is preferable that the film thickness of the layer 27p containing element A be as small as possible.

[0068] Next, a precursor film 26p is formed on the layer 27p containing element A. The precursor film 26p is a precursor for forming the photoelectric conversion layer 26.

[0069] The precursor film 26p may be a stack including a film 26p1 containing a group III element and a film 26p2 containing a group I element. Specifically, the film 26p1 containing a group III element may be formed on the layer 27p containing element A, and then the film 26p2 containing a group I element may be formed on the film 26p1 containing a group III element.

[0070] The material constituting the film 26p2 containing a group I element can be selected from, for example, Ag, Cu, Au, etc. The material constituting the film 26p1 containing a group III element can be selected from, for example, indium, gallium, aluminum, etc. Furthermore, the precursor film 26p may additionally contain an alkali metal such as Li, Na, K, Rb, or Cs.

[0071] The precursor film 26p can be formed by, for example, physical vapor deposition (PVD). Examples of physical vapor deposition (PVD) include sputtering and evaporation. Evaporation is a method of forming a film using atoms or the like that are vaporized by heating an evaporation source. Note that FIG. 5 shows a state after the formation of the precursor film 26p is completed and before the start of the selenization step described below.

[0072] Next, the precursor film 26p is selenized, or the precursor film 26p is selenized and sulfurized to form the photoelectric conversion layer 26 containing a selenium compound (chalcogenization step).

[0073] In the chalcogenization step, for example, selenization is first performed by vapor-phase selenization. The selenization is performed by heating the precursor film 26p in an atmosphere of a selenium source gas (e.g., hydrogen selenide or selenium vapor) containing selenium as a Group VI element source. Although not particularly limited, the selenization is preferably performed at a temperature in the range of 300° C. to 600° C. in a heating furnace.

[0074] As a result, the precursor film 26p is converted into a selenium compound containing a group I element, a group III element, and selenium. Note that selenization may be performed by a method other than vapor-phase selenization. For example, selenization can also be performed by solid-phase selenization, vapor deposition, ink application, and / or electrodeposition.

[0075] Next, the selenium compound containing Group I elements, Group III elements, and selenium is sulfurized. The sulfurization is performed by heating the selenium compound in an atmosphere of a sulfur-containing sulfur source gas (e.g., hydrogen sulfide or sulfur vapor). As a result, the selenium compound before sulfurization is converted into a selenium compound containing Group I elements, Group III elements, selenium, and sulfur. The sulfur source gas serves to substitute sulfur for selenium in crystals composed of Group I elements, Group III elements, and selenium, for example, chalcopyrite crystals.

[0076] Although not particularly limited, the sulfurization is preferably carried out in a heating furnace at a temperature in the range of 450° C. to 650° C., for example.

[0077] In the above embodiment, the precursor film 26p is selenized and sulfurized. Alternatively, the precursor film 26p may be only selenized without sulfurizing it.

[0078] By the above-mentioned selenization or selenization and sulfurization, the precursor film 26p is converted into the above-mentioned photoelectric conversion layer 26. By the above-mentioned selenization or selenization and sulfurization, A(S ｙ , Se１－ｙ ) ２ The compound layer containing the compound is formed together with the formation of the selenium compound that constitutes the photoelectric conversion layer 26. Here, y is a real number that satisfies "0≦y<1".

[0079] A (S ｙ , Se １－ｙ ) ２ The compound layer containing A(S) is formed by selenizing or selenizing and sulfurizing at least a part of the layer 27p containing the element A. Therefore, the element A contains at least one element of Nb and Ta. ｙ , Se １－ｙ ) ２ The compound layer containing is a component of the first buffer layer 27 described in the first, second, and third embodiments. Here, when only selenization is performed, y may be 0. On the other hand, when selenization and sulfurization are performed, y may be in a range that satisfies "0<y<1."

[0080] In the chalcogenization step, substantially the entire layer 27p containing element A is selenized or selenized and sulfurized, and the layer containing Mo for forming the first electrode layer 22 does not need to be substantially selenized or selenized and sulfurized. In this case, the first buffer layer 27 is formed by selenizing the Mo-containing layer 27p containing element A(S ｙ , Se １－ｙ ) ２ This provides the first buffer layer 27 described in the first embodiment.

[0081] Alternatively, in the chalcogenization step, substantially the entire layer 27p containing element A and a portion of the surface side of the layer containing Mo for forming the first electrode layer 22 may be selenized or selenized and sulfurized. In this case, the first buffer layer 27 may be formed of A(S ｙ , Se １－ｙ ) ２ and a compound layer 27a containing Mo(S ｚ , Se １－ｚ ) ２ and a layer 27b containing the element A. Here, z is a real number that satisfies "0≦z<1." ｚ , Se １－ｚ ) ２The layer 27b containing Mo is formed by selenizing or selenizing and sulfurizing a part of the surface side of the layer containing Mo, and doping the upper layer with the element A. Therefore, the Mo(S ｚ , Se １－ｚ ) ２ The layer 27b containing A(S ｙ , Se １－ｙ ) ２ and the first electrode layer 22. In this manner, the first buffer layer 27 described in the second embodiment is obtained.

[0082] Alternatively, in the chalcogenization step, a portion of the front surface side of the layer 27p containing element A may be selenized or selenized and sulfurized, and a portion of the back surface side of the layer 27p containing element A may not be substantially selenized or selenized and sulfurized. In this case, the first buffer layer 27 may be formed by selenizing the first buffer layer 27 with A(S ｙ , Se １－ｙ ) ２ The layer 27c containing the element A has a compound layer 27a containing A(S ｙ , Se １－ｙ ) ２ and the first electrode layer 22. In this manner, the first buffer layer 27 described in the third embodiment is obtained.

[0083] Next, a second buffer layer 28 is formed on the photoelectric conversion layer 26 formed in the chalcogenization step, if necessary. The second buffer layer 28 can be formed by a method such as CBD (chemical bath deposition), sputtering, CVD, or ALD. The materials constituting the second buffer layer are as described above. If the second buffer layer 28 is not required, it need not be formed.

[0084] Next, the second electrode layer 24 is formed on the photoelectric conversion layer 26 or the second buffer layer 28. The second electrode layer 24 is formed by a method such as sputtering, CVD, or ALD. The material constituting the second electrode layer 24 is as described above.

[0085] Next, if necessary, the collecting electrode 30 (first portion 31 and second portion 32) may be formed, and the wiring 50 may be formed. By the above process, the photoelectric conversion element described in the first embodiment, the second embodiment, and the third embodiment can be obtained.

[0086] Hereinafter, as a reference example, a case will be described in which a layer 27p containing at least one element A of Nb and Ta is not formed on a layer containing Mo in the manufacturing process of a photoelectric conversion element. In this case, the precursor film 26p is formed directly on the layer containing Mo. In the reference example, in the step of selenizing or selenizing and sulfurizing the precursor film 26p, a part of the surface side of the layer containing Mo is selenized or selenized and sulfurized. Therefore, the first buffer layer 27 is substantially composed of Mo(S ｙ , Se １－ｙ ) ２ That is, the photoelectric conversion layer 26 is formed of Mo(S ｙ , Se １－ｙ ) ２ come into contact with.

[0087] Hereinafter, an image of the band structure at the interface between the photoelectric conversion layer 26 and the first buffer layer 27 will be described, although it is only a guess, for the photoelectric conversion elements 10 according to the first, second, and third embodiments and the photoelectric conversion element according to the reference example. In the first, second, and third embodiments, the CIGS-based photoelectric conversion layer 26 and the A(S ｙ , Se １－ｙ ) ２ There is a layer interface (A=Nb or Ta).

[0088] A (S ｙ , Se １－ｙ ) ２ is expected to be a metallic layer. ｙ , Se １－ｙ ) ２ The layer is thought to form a metal-semiconductor junction, including an ohmic junction, by junctioning with the photoelectric conversion layer (p-type semiconductor) containing a selenium compound, and therefore it is presumed that the carrier mobility characteristics can be maintained even in a low-temperature environment.

[0089] Next, as the reference example described above, the first buffer layer is made of Mo(S ｙ , Se １－ｙ ) ２ Let us consider the case where the Mo(S ｙ , Se １－ｙ ) ２ is known as a semiconductor, and a band structure with a Schottky barrier is formed when it is bonded to a photoelectric conversion layer (p-type semiconductor) containing a selenium compound. Therefore, it is presumed that the carrier mobility is reduced by the Schottky barrier at low temperatures.

[0090] From the above considerations, it is inferred that the photoelectric conversion element 10 according to the first, second and third embodiments can maintain its photoelectric conversion performance even in low temperature environments, compared to the above-mentioned reference examples.

[0091] Example 1 Next, a photoelectric conversion element according to Example 1 will be described. In the photoelectric conversion element according to Example 1, a first electrode layer 22, a first buffer layer 27, a photoelectric conversion layer 26, a second buffer layer 28, and a second electrode layer 24 are stacked in this order on a MoNa layer on a titanium substrate. The first electrode layer 22 is made of molybdenum. The first buffer layer 27 is made of Nb(S ｙ , Se １－ｙ ) ２ The first buffer layer 27 includes a compound layer made of Nb(S ｙ , Se １－ｙ ) ２ and a compound layer 27a containing Mo(S) as a main component and Nb added thereto. ｚ , Se １－ｚ ) ２ and a layer 27b containing Cu(In,Ga)(S) (the aspect described in the second embodiment). ｘ , Se １－ｘ ) ２ The second buffer layer 28 is made of CdS. The second electrode layer 24 is made of In ２ O ３ It is formed by

[0092] In manufacturing the photoelectric conversion element, a Mo layer was formed as the first electrode layer 22 on the MoNa layer on the titanium substrate, a Nb layer was formed on the Mo layer, and a predetermined precursor film (Cu(In,Ga) film) was formed on the Nb layer. The thickness of the formed Nb layer was 9 nm.

[0093] Then, the precursor film and the Nb layer were selenized and sulfurized as described above to form a first buffer layer 27 and a photoelectric conversion layer 26. Next, a second buffer layer 28 and a second electrode layer 24 were formed in this order on the photoelectric conversion layer 26.

[0094] [Reference Example] The photoelectric conversion element according to the reference example was manufactured in the same manner as in Example 1, except that the Nb layer was not formed. Therefore, as described above, in the reference example, when the precursor film was selenized and sulfurized, Mo(S) was formed as the first buffer layer 27 under the photoelectric conversion layer 26. ｙ , Se １－ｙ ) ２ A layer is formed.

[0095] [Measurement of characteristics of photoelectric conversion element] For the photoelectric conversion elements according to Example 1 and Reference Example, the photoelectric conversion efficiency (η), photoelectric conversion efficiency ratio (η / η ＿ＳＴＤ ), open circuit voltage ratio (Voc / Voc ＿ＳＴＤ ), fill factor ratio (FF / FF ＿ＳＴＤ ), series resistance ratio (Rs / Rs ＿ＳＴＤ These measurements were performed using a solar simulator at 1000 W / m ２ 6 is a graph showing the temperature dependence of each characteristic of the photoelectric conversion elements in Example 1 and Reference Example.

[0096] In FIG. 6, η ＿ＳＴＤ , Voc ＿ＳＴＤ , F.F. ＿ＳＴＤ and Rs. ＿ＳＴＤ and η / η respectively mean the photoelectric conversion efficiency, open circuit voltage, fill factor, and series resistance of the photoelectric conversion element at a temperature of 25° C. Therefore, the photoelectric conversion efficiency ratio (η / η ＿ＳＴＤ ), open circuit voltage ratio (Voc / Voc ＿ＳＴＤ ), fill factor ratio (FF / FF ＿ＳＴＤ ) and series resistance ratio (Rs / Rs＿ＳＴＤ ) correspond to the values ​​obtained by dividing the photoelectric conversion efficiency, open circuit voltage, fill factor, and series resistance at each temperature by the photoelectric conversion efficiency, open circuit voltage, fill factor, and series resistance at 25°C, respectively.

[0097] The photoelectric conversion efficiency (η) in Example 1 increases with decreasing temperature. The photoelectric conversion efficiency in the Reference Example increases with decreasing temperature in the range of 25°C to -80°C. However, in the Reference Example, the rate of increase in photoelectric conversion efficiency with decreasing temperature is low in the range of -30°C to -80°C (see also the graph of photoelectric conversion efficiency ratio). Furthermore, in the Reference Example, the photoelectric conversion efficiency does not increase at temperatures below -80°C. As a result, the photoelectric conversion efficiency in Example 1 is higher than that in the Reference Example at temperatures below -90°C.

[0098] The fill factor ratio (FF / FF) in Example 1 ＿ＳＴＤ ) increases with decreasing temperature. On the other hand, the fill factor ratio in the Reference Example decreases with decreasing temperature below approximately −30° C. to −60° C. It is believed that the fill factor in the Reference Example becomes lower at temperatures below −90° C. than the fill factor at 25° C.

[0099] The series resistance ratio (Rs / Rs ＿ＳＴＤ ) slightly decreases with decreasing temperature. On the other hand, the series resistance ratio in the Reference Example increases sharply with decreasing temperature at temperatures of -30°C to -40°C or lower. The series resistance ratio in Example 1 is significantly smaller than that in the Reference Example at temperatures of -30°C to -40°C or lower. Therefore, it is considered that the photoelectric conversion element according to Example 1 may be more effective in terms of photoelectric conversion than the photoelectric conversion element according to the Reference Example at temperatures lower than -30°C to -40°C.

[0100] From the results shown in Figure 6, it is thought that the photoelectric conversion element of Example 1 may be more significant in terms of photoelectric conversion than the photoelectric conversion element of the reference example at temperatures lower than -30°C to -40°C.

[0101] The temperature dependence of the current-voltage characteristics of the photoelectric conversion elements according to Example 1 and Reference Example was measured. The measurement was carried out using a solar simulator at 1000 W / m ２ The measurements were carried out under conditions in which sunlight or simulated sunlight was irradiated onto the photoelectric conversion element. FIG. 7 is a graph showing the temperature dependence of the current-voltage characteristics of the photoelectric conversion element in Example 1. FIG. 8 is a graph showing the temperature dependence of the current-voltage characteristics of the photoelectric conversion element in Reference Example. In FIG. 7, the multiple lines in the graph represent, from left to right, the current-voltage characteristics at 60°C, 25°C, 10°C, -10°C, -30°C, -60°C, -80°C, -100°C, and -120°C. In FIG. 8, the multiple lines in the graph represent, from left to right, the current-voltage characteristics at 120°C, 80°C, 60°C, 25°C, 10°C, 0°C, -10°C, -30°C, -60°C, -80°C, -100°C, and -120°C.

[0102] 7, in the photoelectric conversion element according to Example 1, the current decreases in an upwardly convex curve as the voltage increases at any temperature in the range of 60° C. to −120° C. In this way, the photoelectric conversion element according to Example 1 exhibits normal current-voltage characteristics in the temperature range of 60° C. to −120° C.

[0103] 8, in the photoelectric conversion element according to the reference example, the current decreases in an upwardly convex curve as the voltage increases in the temperature range of 120°C to -10°C. However, in the photoelectric conversion element according to the reference example, one or two inflection points are observed in the current-voltage curve as the voltage increases in the temperature range of -30°C to -120°C. Thus, the photoelectric conversion element according to the reference example exhibits abnormal current-voltage characteristics in the temperature range of -30°C to -120°C.

[0104] The measurement results of the current-voltage characteristics show that the photoelectric conversion element according to Example 1 has the potential to maintain its photoelectric conversion performance even in a low-temperature environment.

[0105] [Photovoltaic Module] Next, a photovoltaic module including a photovoltaic conversion element will be described. Fig. 9 is a schematic plan view of a photovoltaic module including a photovoltaic conversion element. A photovoltaic module 300 may include one or more photovoltaic conversion elements 10. Note that Fig. 9 shows a photovoltaic conversion module 300 including a plurality of photovoltaic conversion elements 10. The one or more photovoltaic conversion elements 10 may be sealed with, for example, a sealing material.

[0106] When the photoelectric conversion module 300 includes a plurality of photoelectric conversion elements 10, the plurality of photoelectric conversion elements 10 may be arranged in at least one direction, preferably in a lattice pattern. In this case, the plurality of photoelectric conversion elements 10 may be electrically connected to each other in series and / or parallel.

[0107] In the example shown in Fig. 9, the photoelectric conversion elements 10 are arranged so as to partially overlap each other. Among the photoelectric conversion elements 10 arranged in one direction, adjacent photoelectric conversion elements 10 partially overlap each other. Specifically, as shown in Fig. 9, a certain photoelectric conversion element 10 may be arranged so as to cover the second portion 32 of the collecting electrode 30 of the adjacent photoelectric conversion element 10. Instead of the embodiment shown in Fig. 9, adjacent photoelectric conversion elements 10 may be arranged with a gap between them. The wiring 50 described above may electrically connect adjacent photoelectric conversion elements 10 to each other.

[0108] [Flying Object] Next, a flying object equipped with a photovoltaic module will be described. Fig. 10 is a schematic perspective view of a flying object equipped with a photovoltaic module. The flying object 900 may have a base 910 and wing portions 920.

[0109] The wing portion 920 may include the photovoltaic module 300 described above. Preferably, the wing portion 920 includes a plurality of photovoltaic modules 300. Because the flying object 900 is exposed to a low-temperature environment during operation, it is desirable to use a photovoltaic module 300 including the photoelectric conversion element 10 described above. The flying object 900 is not particularly limited in flight altitude during operation. The flying object 900 may fly in the stratosphere, for example. In this case, the flying object 900 may be exposed to a temperature environment of -70°C to -100°C.

[0110] 10 , the flying object 900 has wings 920. Alternatively, the flying object 900 may not have wings 920. The flying object 900 may have a shape similar to that of an airship or a balloon, for example. Even in this case, the flying object 900 may include one or more photovoltaic modules 300. Here, the photovoltaic modules 300 may generate electricity using sunlight or light other than sunlight.

[0111] As described above, the contents of the present invention have been disclosed through the embodiments, but the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. Therefore, the technical scope of the present invention is defined only by the inventive features of the claims that can be reasonably understood from the above description.

[0112] This application claims priority based on Japanese Patent Application No. 2023-059625, filed on March 31, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A photoelectric conversion layer containing a selenium compound, A first electrode layer containing Mo, A first buffer layer is provided between the first electrode layer and the photoelectric conversion layer, When y is a real number satisfying "0 ≤ y < 1", the first buffer layer is A(S ｙ , Se １－ｙ ) ２ Having a compound layer containing, A photoelectric element in which element A is at least one of Nb and Ta.

2. The photoelectric conversion element according to claim 1, wherein in the first buffer layer, the thickness of the region containing the largest proportion of element A among elements other than S and Se is less than 100 nm.

3. The photoelectric conversion element according to claim 1, wherein in the first buffer layer, the thickness of the region containing the element A among the elements excluding S and Se is 1 nm or more and 12 nm or less.

4. The selenium compound is I-III-VI ２ The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is a compound semiconductor.

5. The first buffer layer is substantially A(S ｙ , Se １－ｙ ) ２ A photoelectric conversion element according to claim 1, comprising the compound layer containing the above.

6. When z is a real number satisfying "0 ≤ z < 1", the first buffer layer has a layer containing Mo(S ｚ , Se １－ｚ ) ２ between the compound layer and the first electrode layer. The photoelectric conversion element according to claim 1.

7. The photoelectric conversion element according to claim 1, wherein the first buffer layer has a layer containing element A between the compound layer and the first electrode layer.

8. A photovoltaic power generation module comprising a photoelectric conversion element according to any one of claims 1 to 7.

9. A flying object equipped with the light-power generation module described in claim 8.

10. The steps include forming a layer containing Mo on a substrate, The step of forming a layer containing at least one of element A, Nb and Ta, on the layer containing Mo, The steps include forming a precursor film on a layer containing the element A, The method comprises a chalcogenization step of forming a photoelectric conversion layer containing a selenium compound by selenization of the precursor film or by selenization and sulfurization of the precursor film, The chalcogenization step is performed when y is a real number satisfying "0 ≤ y < 1", A(S ｙ , Se １－ｙ ) ２ A method for manufacturing a photoelectric conversion element, wherein a compound layer containing the compound is formed.

11. The method for manufacturing a photoelectric conversion element according to claim 10, wherein the layer containing element A is formed to a thickness of less than 50 nm.

12. The method for manufacturing a photoelectric conversion element according to claim 10, wherein the layer containing element A is formed to a thickness of 1 nm or more and 12 nm or less.

13. The method for manufacturing a photoelectric conversion element according to claim 10, wherein the precursor film is a laminate comprising a film containing a group III element and a film containing a group I element.

14. The method for manufacturing a photoelectric conversion element according to claim 10, wherein the chalcogenization step includes substantially selenizing or selenizing and sulfurizing the layer containing Mo, and substantially selenizing or selenizing and sulfurizing the entire layer containing element A.

15. The method for manufacturing a photoelectric element according to claim 10, wherein the chalcogenization step includes selenizing or selenizing and sulfidating substantially the entire layer containing element A and a portion of the surface side of the layer containing Mo.

16. The method for manufacturing a photoelectric element according to claim 10, wherein the chalcogenization step includes selenizing or selenizing and sulfurizing a portion of the surface side of the layer containing element A.