Photoelectric conversion element

Abstract

A photoelectric conversion element (10) has a photoelectric conversion layer (26) containing a chalcogen compound semiconductor. When the thickness at a point corresponding to 1 / 4 of the thickness of the photoelectric conversion layer (26) from one interface of the photoelectric conversion layer (26) in the thickness direction is defined as a first depth (D1) and the thickness at a point corresponding to 3 / 4 of the thickness of the photoelectric conversion layer (26) from the interface is defined as a third depth (D3), the content ratio of one element among alkali metal elements in the photoelectric conversion layer (26) at the first depth (D1) is 2.5 times or more than the content ratio of said element at the third depth (D3).

Description

Photoelectric conversion element

[0001] This invention relates to a photoelectric conversion element.

[0002] A photoelectric conversion element that converts light energy into electrical energy is known (see Patent Document 1 below). The photoelectric conversion element described in Patent Document 1 has a so-called CIS-type or CIGS-type photoelectric conversion layer. The CIS-type or CIGS-type photoelectric conversion layer has a chalcopyrite structure I-III-VI ２ It has a group compound semiconductor. Such CIS-based or CIGS-based photoelectric conversion layers are formed by first depositing a precursor film made of group I (such as Cu) and group III (such as In or Ga), and then selenizing and / or sulfidizing the precursor film.

[0003] Japanese Patent Publication No. 2020-181922 Japanese Patent Publication No. 2020-200208

[0004] The inventors of this application have found that alkali metal elements leach out of the photoelectric conversion layer during its formation. If the ratio of alkali metal elements in the photoelectric conversion layer is low, the photoelectric conversion efficiency of the photoelectric conversion element may decrease.

[0005] Therefore, there is a need for a photoelectric conversion element that can suppress the decrease in photoelectric conversion efficiency or improve the photoelectric conversion efficiency.

[0006] A photoelectric conversion element according to one embodiment has a photoelectric conversion layer containing a chalcogen compound semiconductor. When a point corresponding to 1 / 4 of the thickness of the photoelectric conversion layer from one interface in the thickness direction of the photoelectric conversion layer is defined as the first depth, and a point corresponding to 3 / 4 of the thickness of the photoelectric conversion layer from the interface is defined as the third depth, the content ratio of one of the alkali metal elements in the photoelectric conversion layer at the first depth is 2.5 times or more the content ratio of that element at the third depth.

[0007] FIG. 1 is a schematic plan view of a photoelectric conversion device according to an embodiment. FIG. 2 is a schematic cross-sectional view of the photoelectric conversion device taken along line 2A-2A of FIG. 1. FIG. 3 is an example of a graph showing the content ratio of one of the alkali metal elements in the photoelectric conversion layer. FIG. 4 is a diagram showing a flowchart of a method for manufacturing a photoelectric conversion device according to an embodiment. FIG. 5 is a schematic cross-sectional view for explaining one step in the method for manufacturing a photoelectric conversion device according to an embodiment. FIG. 6 is a graph for explaining the concentration of the alkali metal element in the glass substrate. FIG. 7 is a schematic view for explaining the step following FIG. 5. FIG. 8 is a schematic view for explaining the step following FIG. 7. FIG. 9 is a schematic view for explaining the step following FIG. 8. FIG. 10 is a schematic view for explaining the step following FIG. 9. FIG. 11 is a graph showing the content ratio of gallium element in the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1. FIG. 12 is a graph showing the content ratio of sulfur element in the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1. FIG. 13 is a graph showing the content ratio of potassium element in the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1. FIG. 14 is a graph showing the results of PL (photoluminescence) evaluation in Experimental Example 2 and Reference Example 2. FIG. 15 is a graph showing the results of the current-voltage characteristics (IV characteristics) of the photoelectric conversion device according to Experimental Example 第二の実施形態に係る光電変換素子の製造方法のフローチャートを示す図である。図5は、第二の実施形態に係る光電変換素子の製造方法における一ステップを説明するための模式的断面図である。図6は、ガラス基板中のアルカリ金属元素の濃度を説明するためのグラフである。図7は、図5に続くステップを説明するための模式図である。図8は、図7に続くステップを説明するための模式図である。図9は、図8に続くステップを説明するための模式図である。図10は、図9に続くステップを説明するための模式図である。図11は、実験例1及び参考例1における光電変換層26のガリウム元素の含有比率を示すグラフである。図12は、実験例1及び参考例1における光電変換層26の硫黄元素の含有比率を示すグラフである。図13は、実験例1及び参考例1における光電変換層26のカリウム元素の含有比率を示すグラフである。図14は、実験例2と参考例2におけるPL(フォトルミネッセンス)評価の結果を示すグラフである。図15は、実験例2と参考例2に係る光電変換素子の電流-電圧特性(IV特性)の結果を示すグラフである。図16は、第二の実施形態に係る光電変換モジュールの模式的平面図である。図17は、光電変換モジュールを備えた人工衛星の模式的斜視図である。

[0008] 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 respective dimensions may be different from the actual ones.

[0009] [Photoelectric conversion device] FIG. 1 is a schematic plan view of a photoelectric conversion device according to an embodiment. FIG. 2 is a schematic cross-sectional view of the photoelectric conversion device taken along line 2A-2A of FIG. 1.

[0010] The photoelectric conversion element 10 according to this embodiment may be a thin-film type photoelectric conversion element. Preferably, the photoelectric conversion element 10 is a solar cell element that converts light energy into electrical energy.

[0011] The photoelectric conversion element 10 has a glass substrate 20 that serves as a base for forming each film. The glass substrate 20 is a substrate on which a first electrode layer 22, a photoelectric conversion layer 26, and a second electrode layer 24, which will be described later, are formed. The shape and dimensions of the glass substrate 20 are appropriately determined according to the size of the photoelectric conversion element 10 and the like.

[0012] The glass substrate 20 may be a substrate having an ion exchange layer 20a in which at least a part of the alkali metal ions is replaced with another alkali metal ion (see also FIG. 5). Preferably, the glass substrate 20 may be a substrate having an ion exchange layer 20a in which at least a part of the alkali metal ions (excluding potassium ions) is replaced with potassium ions. More preferably, the ion exchange layer 20a may be a layer in which at least a part of the lithium ions and / or sodium ions in the glass material, for example, is replaced with potassium ions.

[0013] The ion exchange layer 20a may be formed near the surface of the glass substrate 20 on the side where the photoelectric conversion layer 26, which will be described later, is formed. However, the ion exchange layer may also be formed near both surfaces of the glass substrate 20.

[0014] The thickness of the ion exchange layer 20a may be defined by the range in which the concentration of the introduced alkali metal ions decreases to 5% of the maximum concentration from the surface of the glass substrate 20 (the surface into which the alkali metal ions are introduced) (corresponding to the range D in FIG. 6).

[0015] The thickness of the ion exchange layer 20a may be, for example, 5 μm or more, preferably 8 μm or more, more preferably 10 μm or more. The upper limit value of the thickness of the ion exchange layer 20a is not particularly limited and may be, for example, 200 μm or less.

[0016] Preferably, at least a part of the depth position of the ion exchange layer may have the maximum ratio of potassium element among all alkali metal elements. The ratio of potassium element among all alkali metal elements is defined by "(amount of potassium element) / (total amount of all alkali metal elements)" at a certain depth of the glass substrate.

[0017] The glass substrate 20 may be so-called chemically strengthened glass. Chemically strengthened glass has a so-called compressive stress layer formed by substituting (ion-exchanging) alkali metal ions. In this case, the ion exchange layer 20a described above may correspond to the compressive stress layer of the chemically strengthened glass. The compressive stress layer of the chemically strengthened glass is formed by substituting at least a part of lithium ions and / or sodium ions in, for example, sodium and / or lithium-containing glass with potassium ions.

[0018] The photoelectric conversion element 10 may include at least a first electrode layer 22, a second electrode layer 24, and a photoelectric conversion layer 26 provided between the first electrode layer 22 and the second electrode layer 24. Specifically, the photoelectric conversion element 10 has a structure in which the first electrode layer 22, the photoelectric conversion layer 26, and the second electrode layer 24 are laminated in this order on the glass substrate 20.

[0019] The photoelectric conversion element 10 may have an underlayer 21 between the glass substrate 20 and the first electrode layer 22. The underlayer 21 is not essential and may not be provided. The underlayer 21 is, for example, SiO ２ 、SiO ｘ MoSi ２ MoSi ｘ SiN, SiNx, Al ２ O ３ Al ｘ O ｙ Ti, TiO ２ TiO ｘ TiN, and TiNx, and may contain a material having at least one selected from the group consisting of. Here, positive real numbers x and y may be appropriately selected.

[0020] The thickness of the underlayer 21 may be, for example, in the range of 0.5 to 100 nm, preferably 1 to 50 nm, and more preferably 2 to 30 nm.

[0021] The photoelectric conversion layer 26 is a layer that contributes to the interconversion of light energy and electrical energy. In solar cell elements that convert light energy into electrical energy, the photoelectric conversion layer 26 is sometimes called a light absorption layer.

[0022] 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, but also that both layers are in close proximity to each other through another layer.

[0023] The first electrode layer 22 is provided between the photoelectric conversion layer 26 and the glass substrate 20. The second electrode layer 24 is located on the opposite side of the photoelectric conversion layer 26 from the glass substrate 20. Therefore, the first electrode layer 22 is located on the opposite side of the photoelectric conversion layer 26 from the second electrode layer 24.

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

[0025] When the second electrode layer 24 is composed of a transparent electrode layer, the first electrode layer 22 may be composed of an opaque electrode layer or a transparent electrode layer. The first electrode layer 22 may be made of a metal such as molybdenum, titanium, or chromium. The thickness of the first electrode layer 22 may be, for example, 50 nm to 1500 nm, preferably 50 nm to 1200 nm, more preferably 50 nm to 800 nm, and even more preferably 50 nm to 500 nm.

[0026] In this embodiment, 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 serve the functions of both an n-type semiconductor and a transparent electrode layer. The second electrode layer 24 comprises, for example, a metal oxide to which a group III element (B, Al, Ga, or In) is added as a dopant. Here, the description of "group" of elements in this specification is based on the short-period periodic table (the same applies hereinafter).

[0027] Examples of metal oxides that constitute the second electrode layer 24 include ZnO or SnO ２ For example, the second electrode layer 24 is made of 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 Options include ZnO:F), gallium-doped zinc oxide (ZnO:Ga), boron-doped zinc oxide (ZnO:B), and aluminum-doped zinc oxide (ZnO:Al).

[0028] While not particularly limited, the thickness of the second electrode layer 24 may be, for example, 0.5 μm to 2.5 μm.

[0029] The photoelectric conversion layer 26 may, for example, include 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] In this embodiment, the photoelectric conversion layer 26 contains at least a group I element and a group III element. Specifically, the photoelectric conversion layer 26 may contain a chalcogen compound semiconductor containing at least a group I element and a group III element. The chalcogen compound semiconductor is a compound containing at least one chalcogen element. The chalcogen compound includes, for example, sulfides, selenides, and / or tellurides.

[0031] Specifically, the photoelectric conversion layer 26 has a chalcopyrite structure I-III-VI ２ The photoelectric conversion layer 26 may include a group compound semiconductor layer. Here, the group I element can be selected from copper (Cu), silver (Ag), gold (Au), etc. The group III element can be selected from indium (In), gallium (Ga), aluminum (Al), etc. In addition, the photoelectric conversion layer 26 may include tellurium (Te) as a group VI element, in addition to selenium (Se) and sulfur (S).

[0032] Instead, the photoelectric conversion layer 26 is a CZTS-based chalcogen compound containing Cu, Zn, Sn, S, or Se. ２ -(II-IV)-VI ４ It may contain a group compound semiconductor layer. A typical example of a CZTS-based chalcogen compound semiconductor is Cu ２ ZnSnSe ４ ,Cd ２ ZnSn(S,Se) ４ Examples include those using compounds such as the following.

[0033] The photoelectric conversion layer 26 contains alkali metal elements such as Li, Na, K, Rb, and Cs. Preferably, the photoelectric conversion layer 26 contains potassium.

[0034] The content ratio and / or content of alkali metal elements in the photoelectric conversion layer 26 in this embodiment will be explained with reference to Figure 3. Figure 3 is an example of a graph showing the content ratio of one of the alkali metal elements in the photoelectric conversion layer. The horizontal axis in Figure 3 represents the normalized depth of the photoelectric conversion layer 26. "0" on the horizontal axis in Figure 3 represents the interface of the photoelectric conversion layer 26 on the first electrode layer 24 side. "1" on the horizontal axis in Figure 3 represents the interface of the photoelectric conversion layer 26 closer to the glass substrate 20. The vertical axis in Figure 3 represents the content ratio (atomic %) of one of the alkali metal elements in the photoelectric conversion layer 26. More specifically, Figure 3 shows the content ratio of one type of alkali metal element introduced into the glass substrate 20 by ion exchange from among multiple alkali metal elements. Note that Figure 3 shows a typical example of the content ratio of alkali metal elements introduced into the glass substrate 20 by ion exchange.

[0035] In this specification, the interface of the photoelectric conversion layer 26 on the first electrode layer 24 side and the interface of the photoelectric conversion layer 26 on the glass substrate 20 side may be defined by the position where the content ratio of the main elements constituting the photoelectric conversion layer 26, such as In, Ga, Al, Se, S, Cu, Zn, or Sn, reaches a maximum value. For example, in Experimental Example 1 and Reference Example 1 described later, the interface of the photoelectric conversion layer 26 on the first electrode layer 24 side may be defined, for example, by the maximum value of the content ratio of element S in the thickness direction. Similarly, in Experimental Example 1 and Reference Example 1 described later, the interface of the photoelectric conversion layer 26 on the glass substrate 20 side may be defined, for example, by the maximum value of the content ratio of element Ga in the thickness direction.

[0036] As shown in Figure 3, the content ratio of alkali metal elements in the photoelectric conversion layer 26 generally increases from the interface on the first electrode layer 24 side toward the interface on the glass substrate 20 side.

[0037] Here, the photoelectric conversion layer 26 is divided into a first region 26a and a second region 26b, starting from one interface in the thickness direction of the photoelectric conversion layer. In this case, the first region 26a and the second region 26b are divided such that they have equal thickness in the thickness direction (see Figure 3). Here, the one interface in the thickness direction of the photoelectric conversion layer may be the interface of the photoelectric conversion layer 26 that is closer to the glass substrate 20. That is, the first region 26a is located closer to the glass substrate 20 than the second region 26b.

[0038] Furthermore, the point corresponding to 1 / 4 of the thickness of the photoelectric conversion layer 26 from one interface in the thickness direction of the photoelectric conversion layer 26 is defined as the "first depth D1". The point corresponding to 1 / 2 of the thickness of the photoelectric conversion layer 26 from one interface in the thickness direction of the photoelectric conversion layer 26 is defined as the "second depth D2". Furthermore, the point corresponding to 3 / 4 of the thickness of the photoelectric conversion layer 26 from one interface in the thickness direction of the photoelectric conversion layer 26 is defined as the "third depth D3". Here, the above interface in the thickness direction of the photoelectric conversion layer may be the interface of the photoelectric conversion layer 26 that is closer to the glass substrate 20. That is, the first depth D1, second depth D2, and third depth D3 are arranged in this order from the side closest to the glass substrate 20. The second depth D2 is located at the center of the photoelectric conversion layer 26 in the thickness direction and corresponds to the boundary between the first region 26a and the second region 26b.

[0039] In this embodiment, the content ratio of one of the alkali metal elements in the photoelectric conversion layer 26 at the first depth D1 may be preferably 2.5 times or more, more preferably 3.0 times or more, more preferably 3.5 times or more, and most preferably 4.0 times or more, the content ratio of that element at the third depth D3.

[0040] As a result, one of the alkali metal elements is present in large quantities in at least a portion of the photoelectric conversion layer 26. More specifically, one of the alkali metal elements is present in large quantities in the region closer to the glass substrate 20, i.e., the first region 26a. The alkali metal element present in the photoelectric conversion layer 26 in this ratio may be Li, Na, K, Rb, or Cs, and is preferably K (potassium).

[0041] By including one of the alkali metal elements in high concentrations in at least a portion of the photoelectric conversion layer 26, it becomes possible to suppress the decrease in photoelectric conversion efficiency or to improve the photoelectric conversion efficiency.

[0042] From the above viewpoint, it is more preferable that the content ratio of one of the alkali metal elements in the photoelectric conversion layer 26 at the first depth D1 is, for example, six times or more, or eight times or more, the content ratio of that element at the third depth D3.

[0043] Furthermore, although not particularly limited, the content ratio of one of the alkali metal elements in the photoelectric conversion layer 26 at the first depth D1 may be, for example, 20 times or less, 18 times or less, or 15 times or less than the content ratio of that element at the third depth D3.

[0044] The content ratio of one alkali metal element in the photoelectric conversion layer 26 at the second depth D2 may be greater than the content ratio of that element at the third depth D3. Also, the content ratio of one alkali metal element in the photoelectric conversion layer 26 at the second depth D2 may be less than the content ratio of that element at the first depth D1. Here, one of the alkali metal elements may be Li, Na, K, Rb, or Cs, and is preferably K (potassium element).

[0045] The content ratio of one alkali metal element in the photoelectric conversion layer 26 at the first depth D1 may be, for example, 1.5 times or more, preferably 2.0 times or more, more preferably 2.5 times or more, and most preferably 3.0 times or more, than the content ratio of that element at the second depth D2. Here, the one alkali metal element may be Li, Na, K, Rb, or Cs, and preferably K (potassium element).

[0046] The content ratio of one alkali metal element in the photoelectric conversion layer 26 at the first depth D1 may be, for example, 1.5 to 20 times, preferably 2.0 to 20 times, more preferably 2.5 to 18 times, and most preferably 3.0 to 18 times, the content ratio of that element at the second depth D2. Here, the one alkali metal element may be Li, Na, K, Rb, or Cs, and preferably K (potassium element).

[0047] The amount of substance (in moles) of one of the alkali metal elements in the first region 26a may be greater than the amount of substance of that element in the second region 26b. Here, the amount of substance of an element in the first region 26a or the second region 26b refers to the total amount contained in each region of the first region 26a or the second region 26b. The amount of substance of an element in the first region 26a or the second region 26b is determined by the total amount of substance (in moles) in each region 26a and 26b.

[0048] Furthermore, the amount of substance of one of the alkali metal elements in the first region 26a may be, for example, three times or more, preferably four times or more, and more preferably five times or more, the amount of substance of that element in the second region 26b. As a result, one of the alkali metal elements is contained in large quantities in the first region 26a of the photoelectric conversion layer 26. By containing large quantities of one of the alkali metal elements in the first region 26a of the photoelectric conversion layer 26, it becomes possible to suppress a decrease in photoelectric conversion efficiency or to improve photoelectric conversion efficiency. Here, one of the alkali metal elements may be Li, Na, K, Rb, or Cs, and is preferably K (potassium element).

[0049] While not particularly limited, the amount of substance of one of the alkali metal elements in the first region 26a may be, for example, 20 times or less, 18 times or less, or 15 times or less, the amount of substance of that element in the second region 26b. When the content ratio of alkali metal elements is below this upper limit, peeling of the photoelectric conversion layer 26 is easily suppressed, and / or the photoelectric conversion efficiency is easily improved.

[0050] If the glass substrate 20 does not have an ion exchange layer in which at least some of the alkali metal ions are replaced with other alkali metal ions, then in the manufacturing process of the photoelectric conversion element described later, the alkali metal element (typically potassium) in the precursor film 26a (photoelectric conversion layer) may be replaced with alkali metal ions in the glass substrate 20 during heating. This can lead to a decrease in the amount of one of the alkali metal ions (e.g., potassium) in the photoelectric conversion layer after manufacturing, which can result in a decrease in the photoelectric conversion efficiency of the photoelectric conversion element.

[0051] In this embodiment, the glass substrate 20 has an ion exchange layer 20a in which at least a portion of alkali metal ions are replaced with other alkali metal ions. That is, the ion exchange layer 20a of the glass substrate 20 contains alkali metal elements introduced by ion exchange. In this case, when the precursor film 26a and the glass substrate 20 are heated, the alkali metal elements introduced into the glass substrate 20 by ion exchange can move into the precursor film 26a (photoelectric conversion layer 26). As a result, the content ratio of alkali metal elements (alkali metal elements introduced by ion exchange) in the region of the photoelectric conversion layer 26 closest to the glass substrate 20, i.e., in the first region 26a, becomes greater than the content ratio of alkali metal elements (alkali metal elements introduced into the glass substrate 20) in the second region 26b. More specifically, the relationship between the content ratios of alkali metal elements in the photoelectric conversion layer 26 at the first depth D1, the second depth D2, and the third depth D3 can be obtained.

[0052] The amount of alkali metal elements (alkali metal elements introduced by ion exchange) that move from the glass substrate 20 to the photoelectric conversion layer 26 can be adjusted by the amount of alkali metal elements introduced into the glass substrate by ion exchange, and by the manufacturing conditions of the photoelectric conversion layer 26, such as the heating temperature. Through this adjustment, a photoelectric conversion layer 26 having the alkali metal element distribution described above can be obtained (see Figure 3).

[0053] As a result of obtaining a photoelectric conversion layer 26 that contains sufficient alkali metal elements in this way, it is possible to suppress the decrease in the photoelectric conversion efficiency of the photoelectric conversion element 10 or to improve the photoelectric conversion efficiency.

[0054] More preferably, the distribution of alkali metal elements in the photoelectric conversion layer 26 described above using Figure 3 may be a distribution of potassium elements. In other words, the "one of the alkali metal ions" mentioned above in terms of content ratio and content may be potassium elements. In this case, it is preferable that the glass substrate 20 has an ion exchange layer 20a in which at least a portion of the alkali metal ions (excluding potassium ions) are replaced with potassium ions.

[0055] The thickness of the photoelectric conversion layer 26 may be, for example, in the range of 0.5 μm to 5.0 μm, preferably in the range of 1.0 μm to 3.0 μm.

[0056] The photoelectric conversion element 10 may have a first buffer layer 27 between the photoelectric conversion layer 26 and the first electrode layer 22. In this case, the first buffer layer 27 may be a semiconductor material having the same conductivity type as the first electrode layer 22, or it may be a semiconductor material having a different conductivity type. The first buffer layer 27 may be made of a material with higher electrical resistance than the first electrode layer 22.

[0057] The first buffer layer 27 is not particularly limited, but may be, for example, a layer containing a chalcogenide compound of a transition metal element having a layered structure. Specifically, the first buffer layer 27 may be composed of a compound consisting of a transition metal material such as Mo, W, Ti, V, Cr, Nb, Ta and a chalcogen element such as O, S, Se. For example, the first buffer layer 27 may be Mo(Se,S) ２ Layer, Mose ２ Layer or MOS ２ It may be a layer or the like. The first buffer layer 27 can be formed on the surface of the first electrode layer 22 when the precursor layer used as a precursor for the photoelectric conversion layer 26 is chalcogenized to form the photoelectric conversion layer 26.

[0058] The photoelectric conversion element 10 may have a second buffer layer 28 between the photoelectric conversion layer 26 and the second electrode layer 24. In this case, the second buffer layer 28 may be a semiconductor material having the same conductivity type as the second electrode layer 24, or it may be a semiconductor material having a different conductivity type. The second buffer layer 28 may be made of a material with higher electrical resistance than the second electrode layer 24.

[0059] The second buffer layer 28 is formed on the photoelectric conversion layer 26. The thickness of the second buffer layer 28 may be, for example, 10 nm to 100 nm, although this is not particularly limited.

[0060] The second buffer layer 28 can be selected from compounds containing zinc (Zn), cadmium (Cd), and indium (In). Examples of zinc-containing compounds include ZnO, ZnS, and Zn(OH). ２ These include Zn(O,S), Zn(O,S,OH), and even ZnMgO and ZnSnO. Examples of cadmium-containing compounds include CdS, CdO, or their mixed crystals Cd(O,S) and Cd(O,S,OH). Examples of indium-containing compounds include In ２ S ３ In ２ O ３ , or these mixed crystals In ２ (O, S) ３ In ２ (O, S, OH) ３ Yes, ２ O ３ In ２ S ３ In (OH) ｘ These can be used. Furthermore, the second buffer layer 28 may have a layered structure of these compounds.

[0061] The second buffer layer 28 has the effect of improving characteristics such as photoelectric conversion efficiency, but it can be omitted. If the second buffer layer 28 is omitted, the second electrode layer 24 is formed directly on the photoelectric conversion layer 26.

[0062] It should be noted that the stacked structure of the photoelectric conversion element 10 is not limited to the above-described embodiment and can take various forms. For example, the photoelectric conversion element 10 may have a configuration in which both an n-type semiconductor and a p-type semiconductor are sandwiched between a first electrode layer and a second electrode layer. In this case, the second electrode layer does not have to be made of an n-type semiconductor. Furthermore, the photoelectric conversion element 10 is not limited to a p-n coupled structure, but may also have a p-i-n coupled structure that includes an intrinsic semiconductor layer (i-type semiconductor) between the n-type semiconductor and the p-type semiconductor.

[0063] The photoelectric conversion element 10 may include a current collector electrode 30 adjacent to the second electrode layer 24. The current collector electrode 30 collects charge carriers from the second electrode layer 24 and is made of a conductive material. The current collector 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 current collector electrode 30 be as small as possible.

[0064] The current collector 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 are sometimes referred to as "finger". The second portions 32 are sometimes referred to as "busbars".

[0065] The first parts 31 are arranged at intervals from one another. Multiple linear first parts 31 are connected to the second part 32. The first parts 31 are responsible for guiding the electricity generated in the photoelectric conversion layer 26 to the second part 32.

[0066] The photoelectric conversion element 10 may include wiring 50 connected to the current collector electrode 30. The wiring 50 may be connected to a second portion 32 of the current collector electrode 30. The wiring 50 may include, for example, an interconnector 52 for electrically connecting to the outside of the photoelectric conversion element 10, and / or a connector 54 for connecting to a bypass diode that electrically bypasses cells that cannot be photoelectrically converted.

[0067] The current collector electrode 30, wiring 50, interconnector 52 and / or connector 54 are not mandatory and may not be provided.

[0068] [Method for Manufacturing a Photoelectric Conversion Element] Next, a method for manufacturing a photoelectric conversion element according to one embodiment will be described using Figures 4 to 10. Figure 4 is a flowchart showing the method for manufacturing a photoelectric conversion element according to one embodiment. Figure 5 is a schematic cross-sectional view illustrating one step in the method for manufacturing a photoelectric conversion element according to one embodiment. Figure 6 is a graph illustrating the concentration of alkali metal elements in a glass substrate. Figure 7 is a schematic diagram illustrating the step following Figure 5. Figure 8 is a schematic diagram illustrating the step following Figure 7. Figure 9 is a schematic diagram illustrating the step following Figure 8. Figure 10 is a schematic diagram illustrating the step following Figure 9.

[0069] The method for manufacturing a photoelectric conversion element according to this embodiment may include the steps of: preparing a glass substrate S1; forming a base layer S2; forming a first electrode layer S3; forming a precursor film S4; heating the precursor film S5; forming a second buffer layer S6; forming a second electrode layer S7; and forming a current collector electrode S8. Here, the steps of forming the base layer S2, forming the first electrode layer S3, forming the second buffer layer S6, forming the second electrode layer S7, and forming the current collector electrode S8 are not essential and may be omitted if unnecessary.

[0070] First, step S1 is performed to prepare the glass substrate, as shown in Figure 5. The shape and dimensions of the glass substrate 20 are appropriately determined according to the size of the photoelectric conversion element 10 to be manufactured.

[0071] The glass substrate 20 may be a substrate having an ion exchange layer 20a in which at least a portion of alkali metal ions are replaced with potassium ions (see Figure 4). Preferably, the glass substrate 20 may be a substrate having an ion exchange layer 20a in which at least a portion of alkali metal ions (excluding potassium ions) are replaced with potassium ions. More preferably, the ion exchange layer 20a may be, for example, a layer in which at least a portion of lithium ions and / or sodium ions in the glass material are replaced with potassium ions.

[0072] The ion exchange layer 20a may be formed near at least one surface of the glass substrate 20. The ion exchange layer 20a may also be formed near both sides of the glass substrate 20.

[0073] The thickness of the ion exchange layer 20a may be defined by the range in which the concentration of introduced alkali metal ions reaches 5% of the maximum concentration from the surface of the glass substrate 20 (the surface into which the alkali metal elements are introduced) (corresponding to range D in Figure 6). The horizontal axis in Figure 6 indicates the position (depth) in the thickness direction of the glass substrate 20. The vertical axis in Figure 6 indicates the concentration of alkali metal elements in the glass substrate 20. Therefore, Figure 6 shows the relationship between the concentration of alkali metal elements in the glass substrate 20 and the depth of the glass substrate 20.

[0074] The alkali metal element concentrations shown in Figure 6 are illustrative. Figure 6 illustrates, for example, the concentrations of alkali metal elements in a glass substrate having an ion exchange layer 20a in which at least some of the sodium ions in the glass material are replaced with potassium ions. As shown in Figure 6, the concentration of potassium element (alkali metal element introduced by ion exchange) in the glass substrate 20 is substantially maximum at the surface of the glass substrate 20 (position "0" on the horizontal axis) and decreases as the depth of the glass substrate 20 increases. On the other hand, the concentration of sodium element in the glass substrate 20 is low at the surface of the glass substrate 20 (position "0" on the horizontal axis) and increases as the depth of the glass substrate 20 increases.

[0075] Such a concentration distribution of alkali metal elements can be achieved by a process that replaces alkali metal ions in the glass material with potassium ions. Ion exchange of alkali metal ions in the glass material can be carried out by methods such as immersion ion exchange or electric field application ion exchange. Immersion ion exchange and electric field application ion exchange are known, for example, as methods for manufacturing chemically strengthened glass (see Patent Document 2 mentioned above). For example, by contacting a glass material containing sodium and / or lithium elements with a solution containing potassium ions, at least a portion of the sodium and / or lithium elements in the glass material can be replaced with potassium elements.

[0076] The glass substrate 20 to be prepared may be chemically strengthened glass. Chemically strengthened glass has a so-called compressive stress layer formed by replacing (ion-exchange) alkali metal ions in the glass material. In this case, the ion-exchange layer 20a may correspond to the compressive stress layer of the chemically strengthened glass (see Patent Document 2).

[0077] The thickness of the ion exchange layer 20a may be, for example, 5 μm or more, preferably 8 μm or more, and more preferably 10 μm or more. The upper limit of the thickness of the ion exchange layer 20a is not particularly limited and may be, for example, 200 μm or less. It is thought that the greater the thickness of the ion exchange layer 20a, the greater the amount of alkali metal elements in the glass substrate 20, and therefore the deficiency of alkali metal elements in the precursor film 26a, which will be described later, can be suppressed.

[0078] When potassium is introduced by ion exchange, at the maximum concentration of potassium in the ion exchange layer 20a, the ratio (molar ratio) of potassium to sodium may be, for example, 100-50:0-50, preferably 100-80:0-20, and more preferably 100-90:0-10.

[0079] Preferably, the ratio (molar ratio) of potassium element to all alkali metal elements may be maximized at at least a portion of the depth of the ion exchange layer 20a. In this case, the amount of potassium element in the ion exchange layer 20a can be increased.

[0080] Next, as shown in Figure 7, step S2 is performed to form the base layer 21 and step S3 is performed to form the first electrode layer 22. The base layer 21 is formed on the glass substrate 20. The base layer 21 can be formed, for example, by sputtering.

[0081] The base layer 21 is, for example, SiO ２ SiO ｘ MoSi ２ MoSi ｘ , SiN, SiNx, Al ２ O ３ Al ｘ O ｙ , Ti, TiO ２ , TiOｘ The material may include at least one selected from the group including TiN and TiNx. Here, the positive real numbers x and y can be selected as appropriate. These materials can function to adjust the amount of alkali metal element migration in the heating step described later. The thickness of the base layer 21 may be set as appropriate to adjust the amount of alkali metal element migration in the heating step described later. The thickness of the base layer 21 may be, for example, in the range of 0.5 to 100 nm, preferably 1 to 50 nm, and more preferably 2 to 30 nm.

[0082] The first electrode layer 22 is formed on the glass substrate 20 or the underlayer 21. If the underlayer 21 is provided, the first electrode layer 22 is formed on the underlayer 21. If the underlayer 21 is not provided, the first electrode layer 22 is formed on the surface of the glass substrate 20.

[0083] The thickness of the first electrode layer 22 may be, for example, 50 nm to 1500 nm, preferably 50 nm to 1200 nm, more preferably 50 nm to 800 nm, and even more preferably 50 nm to 500 nm. In the heating step described later, it is preferable that the first electrode layer 22 is not too thick, in order to effectively move the alkali metal elements (alkali metal elements introduced by ion exchange) in the glass substrate 20 into the photoelectric conversion layer 26.

[0084] The first electrode layer 22 is formed by depositing the material constituting the first electrode layer 22 onto the surface of the glass substrate 20 or the underlayer 21, for example, by sputtering. The material constituting the first electrode layer 22 is as described above. The sputtering method may be direct current (DC) sputtering or radio frequency (RF) sputtering. Alternatively, the first electrode layer 22 may be formed using methods such as CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition) instead of sputtering.

[0085] The base layer 21 and / or the first electrode layer 22 are preferably formed on the surface side of the glass substrate 20 where the ion exchange layer 20a is formed.

[0086] Next, as shown in Figure 8, step S4 is performed to form a precursor film 26a on the glass substrate 20. The precursor film 26a is formed on the glass substrate 20, more specifically on the first electrode layer 22.

[0087] The precursor film 26a can be formed, for example, by physical vapor deposition (PVD). Examples of physical vapor deposition (PVD) methods include sputtering and vapor deposition. Vapor deposition is a method of forming a film using atoms that have been heated to create a gas phase from a deposition source.

[0088] When forming a CIS-based photoelectric conversion layer 26, step S4, which involves forming a precursor film 26a, includes forming a film of at least a group I element and a group III element. That is, the precursor film 26a may contain a group I element and a group III element. For example, the precursor film 26a may be formed as a laminate of a film containing a group III element and a film containing a group I element. The group I element can be selected from, for example, Ag, Cu, Au, etc. The group III element can be selected from, for example, indium, gallium, aluminum, etc. Furthermore, it is preferable that the precursor film 26a additionally contains alkali metal elements such as Li, Na, K, Rb, Cs, preferably potassium.

[0089] Furthermore, the precursor film 26a may additionally contain tellurium as a group VI element, in addition to selenium and sulfur.

[0090] As an example, the precursor film 26a may be formed as a laminate of a film containing a group I element and a group III element, and a film containing a group III element. In this case, it is preferable that one of the films constituting the laminate contains an alkali metal element, preferably potassium.

[0091] Furthermore, as shown in Figure 8, the precursor film 26a may include a first film 26b containing group I and group III elements, a second film 26c containing group I and group III elements, and a third film 26c containing group III elements. In this case, it is preferable that at least one of the first film 26b and the second film 26c contains an alkali metal element, preferably potassium.

[0092] On the other hand, when forming a CZTS-based photoelectric conversion layer 26, the precursor layer 26a is formed by depositing at least Cu, Zn, and Sn elements, or by depositing at least Cu, Zn, Sn, Se, and S elements. Preferably, potassium elements may be deposited additionally. The precursor layer 26a may be formed as a thin film of, for example, Cu-Zn-Sn or Cu-Zn-Sn-Se-S. This thin film may contain alkali metal elements, preferably potassium elements.

[0093] Next, as shown in Figure 9, step S5 is performed to heat the glass substrate 20 and the precursor film 26a.

[0094] The inventors of the present invention have found that the following advantages can be obtained in step S5, which involves heating the glass substrate 20 and the precursor film 26a. If the glass substrate 20 does not have an ion exchange layer in which at least some of the alkali metal ions are replaced with other alkali metal elements, then in step S5, the alkali metal elements in the precursor film 26a may be replaced by alkali metal ions (other alkali metal elements) in the glass substrate 20 during heating. This can lead to a decrease in the amount of alkali metal elements contained in the photoelectric conversion layer 26 after heating, which can result in a decrease in the photoelectric conversion efficiency of the photoelectric conversion element.

[0095] In this embodiment, the glass substrate 20 has an ion exchange layer 20a in which at least a portion of alkali metal ions are replaced with other alkali metal elements. That is, the ion exchange layer 20a of the glass substrate 20 contains alkali metal elements introduced by ion exchange. Preferably, the alkali metal element introduced into the glass substrate 20 by ion exchange is potassium. When the precursor film 26a and the glass substrate 20 are heated, the alkali metal elements introduced by ion exchange can move from the glass substrate 20 to the precursor film 26a.

[0096] Here, by adjusting the amount of alkali metal elements that move from the glass substrate 20 to the precursor film 26a, the distribution of alkali metal element content ratios in the photoelectric conversion layer 26 as described above can be obtained (see Figure 3).

[0097] From the viewpoint of moving alkali metal elements in the ion exchange layer 20a of the glass substrate 20 toward the precursor film 26a (photoelectric conversion layer 26), it is considered that a higher heating temperature is preferable in heating step S5. In heating step S5, the glass substrate 20 and the precursor film 26a may be heated, preferably at 250°C or higher, more preferably at 350°C or higher, and more preferably at 450°C or higher.

[0098] From the viewpoint of suppressing a decrease in the photoelectric conversion efficiency of the manufactured photoelectric conversion element 10, it is preferable that in step S5, the amount of alkali metal elements in the film corresponding to the precursor film 26a after heating (photoelectric conversion layer 26) is the same as or greater than the amount of alkali metal elements in the precursor film 26a before heating. In order to increase the amount of alkali metal elements in the precursor film 26a after heating, the concentration of alkali metal elements in the ion exchange layer 20a of the glass substrate 20 can be increased, or the heating temperature and heating time of the glass substrate 20 and the precursor film 26a can be adjusted.

[0099] In heating step S5, the concentration of alkali metal elements in the film corresponding to the precursor film 26a after heating (photoelectric conversion layer 26) can be set to twice or more the concentration of alkali metal elements in the precursor film 26a before heating. Furthermore, in heating step S5, the concentration of alkali metal elements in the film corresponding to the precursor film 26a after heating (photoelectric conversion layer 26) can be set to three times or more the concentration of alkali metal elements in the precursor film 26a before heating. The concentration of alkali metal elements in the photoelectric conversion layer 26 after heating may be, for example, 30 times or less, 20 times or less, or 10 times or less the concentration of alkali metal elements in the precursor film 26a before heating.

[0100] In this embodiment, step S5, which involves heating the glass substrate 20 and the precursor film 26a, also includes chalcogenization of the material constituting the precursor film 26a. Chalcogenization may include at least one, preferably both, of selenization and sulfidation.

[0101] The precursor film 26a is chalcogenized to form a chalcogen compound semiconductor. As a result, a photoelectric conversion layer 26 containing the chalcogen compound semiconductor is formed on the glass substrate 20.

[0102] When forming a CIS-based photoelectric conversion layer 26, the chalcogenization treatment of the precursor film 26a involves heating the precursor film 26a, which contains at least group I and group III elements, and the glass substrate 20 in an atmosphere containing group VI elements. This chalcogenizes the precursor film 26a, forming the photoelectric conversion layer 26.

[0103] In the chalcogenization process, for example, selenization is first performed by a gas-phase selenization method. Selenization is carried out by heating the precursor layer 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, selenization is preferably carried out in a heating furnace at a temperature in the range of, for example, 250°C to 650°C, preferably 350°C to 650°C, and more preferably 450°C to 650°C.

[0104] As a result, the precursor film is converted into a compound (photoelectric conversion layer 26) containing a group I element, a group III element, and selenium. Note that the compound (photoelectric conversion layer 26) containing a group I element, a group III element, and selenium may be formed by methods other than the gas-phase selenization method. For example, such a compound can also be formed by solid-phase selenization, vapor deposition, ink coating, electrodeposition, etc.

[0105] Next, a compound containing a Group I element, a Group III element, and selenium is sulfurized. The sulfurization is carried out by heating the selenized precursor film and the glass substrate 20 in an atmosphere of a sulfur-containing sulfur source gas (e.g., hydrogen sulfide or sulfur vapor). As a result, the photoelectric conversion layer 26 is converted into a semiconductor compound containing a Group I element, a Group III element, and selenium and sulfur as Group VI elements. The sulfur source gas plays a role in substituting selenium with sulfur in crystals composed of Group I elements, Group III elements, and selenium, such as chalcopyrite crystals, on the surface of the photoelectric conversion layer 26.

[0106] The sulfidation is preferably carried out, for example, in a heating furnace at a temperature within the range of 450°C to 650°C.

[0107] Through the chalcogenization described above, the precursor film 26a is converted into the photoelectric conversion layer 26. In addition, along with the chalcogenization, a first buffer layer 27 is formed between the first electrode layer 22 and the photoelectric conversion layer 26. This buffer layer 27 contains a compound made of transition metal materials such as Mo, W, Ti, V, Cr, Nb, and Ta that constitute the first electrode layer 22, and chalcogen elements such as O, S, and Se.

[0108] On the other hand, when forming a CZTS-based photoelectric conversion layer 26, the chalcogenization treatment of the precursor layer 26a involves sulfidating and selenizing the precursor layer 26a containing Cu, Zn, and Sn, and the glass substrate 20 in a hydrogen sulfide atmosphere and a hydrogen selenide atmosphere at a temperature within the range of 450°C to 650°C. This process results in Cu ２ ZnSn(S,Se) ４ A CZTS-based photoelectric conversion layer 26 having the above properties can be formed. Furthermore, the above sulfidation and selenization process forms a first buffer layer 27 between the first electrode layer 22 and the photoelectric conversion layer 26.

[0109] The heating in step S5, which involves heating the glass substrate 20 and the precursor film 26a, may be equivalent to the heating performed in the chalcogenization (selenization and / or sulfidation) described above.

[0110] In the above embodiment, both selenization and sulfidation are performed when the precursor film 26a is converted into the photoelectric conversion layer 26. However, the precursor film can be converted into the photoelectric conversion layer 26 by any chalcogenization treatment.

[0111] Next, as shown in Figure 10, step S6 is performed to form the second buffer layer 28 and step S7 is performed to form the second electrode layer 24. The second buffer layer 28 is formed by depositing a film on the photoelectric conversion layer 26 using methods such as CBD (chemical bath deposition), sputtering, CVD, or ALD. The materials constituting the second buffer layer 28 are as described above.

[0112] The second electrode layer 24 is formed on the second buffer layer 28 by methods such as sputtering, CVD, or ALD. Alternatively, if the second buffer layer 28 is not formed, the second electrode layer 24 is formed directly on the photoelectric conversion layer 26. The material constituting the second electrode layer 24 is as described above.

[0113] Next, step S8 is performed to form the current collector electrode 30. The current collector electrode 30 is formed on the second electrode layer 24. The current collector electrode 30 can be formed by applying printing processes such as sputtering, CVD, ALD, AD, vapor deposition, inkjet, or screen printing.

[0114] The current collector electrode 30 may include a plurality of linear first portions 31 and a second portion 32 connected to the plurality of first portions 31. Wiring 50 is connected to the current collector electrode 30 as needed. Here, the current collector electrode 30 and wiring 50 are not essential and may not be formed if they are not needed.

[0115] [Experimental Example 1] Next, Experimental Example 1 will be described. First, an aluminosilicate glass containing an ion exchange layer in which at least a portion of sodium ions are replaced with potassium ions was prepared as the glass substrate 20. Specifically, the glass substrate 20 is chemically strengthened aluminosilicate glass. Chemically strengthened aluminosilicate glass is formed by bringing a solution of molten potassium ions into contact with aluminosilicate glass at a high temperature.

[0116] After cleaning the glass substrate 20, a base layer 21 and a first electrode layer 22 were deposited on the glass substrate 20 by sputtering. The material constituting the base layer 21 is SiO ２ The material constituting the first electrode layer 22 was molybdenum.

[0117] Next, a precursor film 26a was deposited on the first electrode layer 22 by sputtering. The precursor film 26a was formed by a laminate of a CuGaK film 26b, a CuGa film 26c, and an In film 26d. The amount of potassium element in the precursor film 26a was 0.013 μmol / cm³. ２ That was the case.

[0118] Next, the photoelectric conversion layer 26 was obtained by reacting the glass substrate 20 and the precursor film 26a with hydrogen selenide and hydrogen sulfide at a high temperature of 500°C or higher (chalcogenization) (heating step S5). The photoelectric conversion layer 26 is mainly composed of Cu(In,Ga)(Se,S) ２ It was formed by [something].

[0119] ICP analysis was performed on samples up to the photoelectric conversion layer 26. Specifically, the prepared samples were immersed in a mixed acid of hydrochloric acid and nitric acid to completely dissolve the first electrode layer 22 and the photoelectric conversion layer 26 in the acid. After diluting this acid solution with ultrapure water, ICP analysis was performed to quantitatively measure the sodium and potassium concentrations.

[0120] [Reference Example 1] Next, Reference Example 1 will be described. In Reference Example 1, an aluminosilicate glass without an ion exchange layer, in which at least a portion of the alkali metal ions (excluding potassium ions) were replaced with potassium ions, was prepared as the glass substrate 20. Except that the glass substrate 20 did not contain an ion exchange layer, the underlayer 21, the first electrode layer 22, and the photoelectric conversion layer 26 were formed on the glass substrate 20 under the same conditions as in Experimental Example 1.

[0121] Furthermore, the potassium concentration was quantitatively measured by performing ICP analysis on the sample up to the photoelectric conversion layer 26 using the same procedure as in Experimental Example 1. In Experimental Example 1 and Reference Example 1, the concentration of potassium element in the precursor film 26a before chalcogenization was 0.013 μmol / cm³. ２ It is to that extent.

[0122] In Reference Example 1, the potassium concentration after chalcogenization was 0.007 μmol / cm³. ２ The concentration has decreased from the concentration before chalcogenization. Therefore, it is thought that the potassium element contained in the precursor film has moved into the glass substrate 20.

[0123] In Experimental Example 1, the potassium concentration after chalcogenization was 0.047 μmol / cm³. ２The concentration has increased significantly from the concentration before chalcogenization. Therefore, it is considered that the potassium element in the ion exchange layer 20a of the glass substrate 20 has moved toward the precursor film 26a (photoelectric conversion layer 26).

[0124] Thus, if the glass substrate 20 has an ion exchange layer 20a in which at least a portion of alkali metal ions are replaced with potassium ions, the potassium elements in the ion exchange layer 20a can suppress a deficiency of potassium elements in the precursor film 26a (photoelectric conversion layer 26) or increase the amount of potassium elements in the precursor film 26a (photoelectric conversion layer 26).

[0125] In Experimental Example 1, the concentration of potassium element in the photoelectric conversion layer 26 after heating (after chalcogenization) is two to three times or more the concentration of potassium element in the precursor film 26a before heating.

[0126] Furthermore, the content ratios and / or contents of gallium, sulfur, and potassium elements in the photoelectric conversion layer 26 were measured for Experimental Example 1 and Reference Example 1. The content ratios and / or contents of each element were quantitatively measured by glow discharge emission spectrometry (GD-OES). Glow discharge emission spectrometry was performed using a GD-Profiler 2 (manufactured by Horiba, Ltd.) by argon ion sputtering under the conditions of a discharge gas pressure of 160 Pa, a discharge power of 30 W, and an anode diameter of 4 mm.

[0127] Figure 11 is a graph showing the gallium element content ratio of the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1. Figure 12 is a graph showing the sulfur element content ratio of the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1. Figure 13 is a graph showing the potassium element content ratio of the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1.

[0128] In Figures 11 to 13, the horizontal axis represents the normalized depth of the photoelectric conversion layer 26. In Figures 11 to 13, "0" on the horizontal axis represents the surface of the photoelectric conversion layer 26 on the first electrode layer 24 side. In Figures 11 to 13, "1" on the horizontal axis represents the interface of the photoelectric conversion layer 26 on the glass substrate 20 side. In Figures 11 and 12, the vertical axes represent the content ratios of gallium and sulfur elements in the photoelectric conversion layer 26, respectively. In Figure 13, the vertical axis represents the content ratio (atomic %) of potassium element in the photoelectric conversion layer 26.

[0129] As shown in Figures 11 and 12, the content ratio of gallium and sulfur elements in the photoelectric conversion layer 26 in Experimental Example 1 and Reference Example 1 varies depending on the position in the thickness direction. The maximum value of the sulfur element content ratio defines the interface of the photoelectric conversion layer 26 on the first electrode layer 24 side and the interface of the photoelectric conversion layer 26 on the glass substrate 20 side. In this case, the maximum value of the gallium element content ratio coincides with the interface of the photoelectric conversion layer 26 on the glass substrate 20 side.

[0130] Furthermore, as shown in Figures 11 and 12, the distribution of the gallium and sulfur content ratios in the photoelectric conversion layer 26 is almost the same in Experimental Example 1 and Reference Example 1.

[0131] As shown in Figure 13, the potassium content ratio in the photoelectric conversion layer 26 in Experimental Example 1 generally increases from the interface on the first electrode layer 24 side toward the interface on the glass substrate 20 side. In Experimental Example 1, the amount of potassium in the first region 26a is greater than the amount of potassium in the second region 26b.

[0132] As shown in Figure 13, in Experimental Example 1, the potassium content ratio in the photoelectric conversion layer 26 at the first depth D1 is approximately 10 times that of the potassium content ratio at the third depth D3. Also in Experimental Example 1, the potassium content ratio in the photoelectric conversion layer 26 at the first depth D1 is approximately 5 times that of the potassium content ratio at the second depth D2.

[0133] More specifically, in Experimental Example 1, the distribution of potassium element content in the thickness direction is as already explained using Figure 3. This distribution of potassium element content is thought to be obtained because potassium element migrated from the glass substrate 20 to the photoelectric conversion layer 26.

[0134] On the other hand, in Reference Example 1, the potassium content ratio in the photoelectric conversion layer 26 generally increases gradually from the surface on the first electrode layer 24 side toward the surface on the glass substrate 20 side near the interface on the glass substrate side. However, in Reference Example 1, the potassium content ratio in the photoelectric conversion layer 26 at the first depth D1 is approximately the same as the potassium content ratio in the photoelectric conversion layer 26 at the third depth D3. Furthermore, in Reference Example 1, the potassium content ratio in the photoelectric conversion layer 26 at the first depth D1 is approximately the same as the potassium content ratio in the photoelectric conversion layer 26 at the second depth D2. This is thought to be because a glass substrate without an ion exchange layer was used in Reference Example 1.

[0135] From the above results, it is considered that the alkali metal element (potassium in Experimental Example 1) forcibly introduced by ion exchange moves from the glass substrate 20 into the photoelectric conversion layer 26 upon heating. Therefore, if the alkali metal element introduced by ion exchange is an alkali metal element other than potassium, it is considered that the alkali metal element other than potassium (the alkali metal element forcibly introduced by ion exchange) may be included in the photoelectric conversion layer 26 in a distribution similar to the distribution shown in Figure 3.

[0136] [Experimental Example 2] Next, Experimental Example 2 will be described. First, an aluminosilicate glass containing an ion exchange layer 20a in which at least a portion of sodium ions are replaced with potassium ions was prepared as a glass substrate 20. Specifically, the glass substrate 20 is chemically strengthened aluminosilicate glass. Chemically strengthened aluminosilicate glass is formed by contacting aluminosilicate glass with a high-temperature potassium ion molten salt solution. After cleaning the glass substrate 20, a base layer 21 and a first electrode layer 22 were deposited on the glass substrate 20 by sputtering. The material constituting the base layer 21 is SiO ２ The material constituting the first electrode layer 22 was molybdenum.

[0137] Next, a precursor film 26a was deposited on the first electrode layer 22 by sputtering. The precursor film 26a was formed by a laminate of a CuGaK film 26b, a CuGa film 26c, and an In film 26d. The amount of potassium element in the precursor film 26a was 0.013 μmol / cm³. ２ That was the case.

[0138] Next, the photoelectric conversion layer 26 was obtained by reacting the glass substrate 20 and the precursor film 26a with hydrogen selenide and hydrogen sulfide at a high temperature of 500°C or higher (chalcogenization) (heating step S5). The photoelectric conversion layer 26 is mainly composed of Cu(In,Ga)(Se,S) ２ It was formed by [something].

[0139] PL evaluation was performed on samples in which the photoelectric conversion layer 26 had been formed. In the PL evaluation, light was irradiated onto the photoelectric conversion layer 26, and the light (emission spectrum) generated when excited electrons returned to the ground state was observed.

[0140] After performing a PL evaluation, a cadmium sulfide layer was deposited on the surface of the photoelectric conversion layer 26 as a second buffer layer 28 by immersion. Furthermore, indium tin oxide was deposited on the second buffer layer 28 as a second electrode layer 24 by sputtering. The current-voltage characteristics of the photoelectric conversion element thus obtained were measured. In measuring the current-voltage characteristics, a simulated sunlight irradiation device (Wacom Denso Co., Ltd.'s solar simulator (model number: WXS-350S-L2MS)) was used as the light source, and the light intensity was 1 sun (AM 1.5G, 100 mW / cm²). ２ The device was adjusted to JIS C8912 Class A. A 1-sun light was shone onto the photoelectric conversion element, and the output current was measured while varying the bias voltage.

[0141] [Reference Example 2] Next, Reference Example 2 will be described. In Reference Example 2, an aluminosilicate glass without an ion exchange layer, in which at least a portion of the alkali metal ions were replaced with other alkali metal ions, was prepared as the glass substrate 20. Except that the glass substrate 20 did not contain an ion exchange layer 20a, the underlayer 21, the first electrode layer 22, and the photoelectric conversion layer 26 were formed on the glass substrate 20 under the same conditions as in Experimental Example 2. PL evaluation was performed on the sample in which the photoelectric conversion layer 26 had been formed using the same procedure as in Experimental Example 2.

[0142] After performing the PL evaluation, the second buffer layer 28 and the second electrode layer 24 were deposited using the same procedure and materials as in Experimental Example 2. The current-voltage characteristics of the resulting photoelectric conversion element were measured in the same manner as in Experimental Example 2.

[0143] Figure 14 is a graph showing the results of the PL (photoluminescence) evaluation in Experimental Example 2 and Reference Example 2. In Figure 14, the horizontal axis represents the wavelength of light, and the vertical axis represents the intensity of the emission spectrum.

[0144] The intensity of the emission spectrum in Experimental Example 2 is higher than that of Reference Example 2. This suggests that the photoelectric conversion layer 26 in Experimental Example 2 has fewer non-luminescent recombination centers. Therefore, it can be concluded that the photoelectric conversion layer 26 in Experimental Example 2 is likely to be more suitable as a light absorption layer.

[0145] Figure 15 is a graph showing the current-voltage characteristics (IV characteristics) of the photoelectric conversion elements for Experimental Example 2 and Reference Example 2. In Figure 15, the horizontal axis represents the voltage value and the vertical axis represents the current value. Referring to Figure 15, the current-voltage curve of the photoelectric conversion element for Experimental Example 2 is generally higher than the current-voltage curve of the photoelectric conversion element for Reference Example 2. Therefore, it can be seen that the output of the photoelectric conversion element for Experimental Example 2 is higher and the current-voltage characteristics are better.

[0146] [Photoelectric Conversion Module] Next, a photoelectric conversion module according to one embodiment will be described with reference to Figure 16. Figure 16 is a schematic plan view of the photoelectric conversion module according to one embodiment.

[0147] The photoelectric conversion module 100 may include one or more photoelectric conversion elements 10. Figure 17 shows a photoelectric conversion module 100 that includes multiple photoelectric conversion elements 10. One or more photoelectric conversion elements 10 may be sealed, for example, with a sealing material. The configuration of each photoelectric conversion element 10 is as described in the above embodiments.

[0148] When the photoelectric conversion module 100 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 grid pattern. In this case, the plurality of photoelectric conversion elements 10 may be electrically connected to each other in series and / or in parallel.

[0149] In the example shown in Figure 16, adjacent photoelectric conversion elements 10 arranged in one direction partially overlap each other. Specifically, as shown in Figure 16, one photoelectric conversion element 10 is positioned to cover a portion of another adjacent photoelectric conversion element 10.

[0150] Adjacent photoelectric conversion elements 10 may be electrically connected to each other by a connector (interconnector 52). In this case, the connector may extend across adjacent photoelectric conversion elements 10.

[0151] Instead of the configuration shown in Figure 16, adjacent photoelectric conversion elements 10 may be arranged with a gap between them.

[0152] [Artificial Satellite and Paddle for Artificial Satellite] Next, an artificial satellite equipped with a photoelectric conversion module and a paddle for an artificial satellite will be described. Figure 17 is a schematic perspective view of an artificial satellite equipped with a photoelectric conversion module. The artificial satellite 900 may have a base 910 and a paddle 920. The base 910 may be equipped with equipment not shown that is necessary for controlling the artificial satellite 900. An antenna 940 may be attached to the base 910.

[0153] The paddle 920 may be equipped with the aforementioned photoelectric conversion module 100. The paddle 920 equipped with the photoelectric conversion module 100 can be used as a power source to operate various devices provided on the base 910. In this way, the photoelectric conversion module 100 can be applied to paddles for artificial satellites.

[0154] The paddle 920 may have a connecting portion 922 and a hinge portion 924. The connecting portion 922 corresponds to the part that connects the paddle 920 to the base portion 910.

[0155] The hinge portion 924 extends along one direction, allowing the paddle 920 to be folded around the hinge portion 924 as an axis of rotation. Each paddle 920 may have at least one, preferably more than one, hinge portion 924. This allows the paddle 920 equipped with the photoelectric conversion module 100 to be foldable into a small size. At the time of launch of the satellite 900, the paddle 920 may be in a folded state. The paddle 920 should be unfolded when generating electricity by receiving sunlight.

[0156] Instead of the structure shown in Figure 17, the paddle 920 may have a cylindrical shape formed by winding. This allows the paddle 920 to take on a substantially flat unfolded state due to the rotation of the wound portion. During the launch of the satellite 900, the paddle 920 may maintain a generally cylindrical shape. When generating electricity by receiving sunlight, the paddle 920 should unfold to a substantially flat state.

[0157] As described above, the scope of the present invention has been disclosed through embodiments, but the descriptions and drawings that constitute part of this disclosure should not be understood as limiting the invention. Various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art from this disclosure. Therefore, the technical scope of the present invention is defined solely by the inventive features relating to the claims that are reasonable from the above description.

[0158] This application claims priority under Japanese Patent Application No. 2024-192201, filed on 31 October 2024, the entire contents of said patent application are incorporated herein by reference.

Claims

1. A photoelectric element having a photoelectric conversion layer containing a chalcogen compound semiconductor, wherein when a point corresponding to 1 / 4 of the thickness of the photoelectric conversion layer from one interface in the thickness direction of the photoelectric conversion layer is defined as the first depth, and a point corresponding to 3 / 4 of the thickness of the photoelectric conversion layer from the interface is defined as the third depth, the content ratio of one alkali metal element in the photoelectric conversion layer at the first depth is 2.5 times or more the content ratio of that element at the third depth.

2. The photoelectric conversion element according to claim 1, wherein the content ratio of the element at the first depth is 3.0 times or more, 3.5 times or more, or 4.0 times or more than the content ratio of the element at the third depth.

3. The photoelectric conversion element according to claim 1 or 2, wherein the content ratio of the element at the first depth is 20 times or less the content ratio of the element at the third depth.

4. The photoelectric conversion element according to any one of claims 1 to 3, wherein when the photoelectric conversion layer is divided into a first region and a second region with equal thickness, starting from one interface in the thickness direction of the photoelectric conversion layer, the amount of substance of the element in the first region is three times or more the amount of substance of the element in the second region.

5. The photoelectric conversion element according to any one of claims 1 to 4, wherein when a point corresponding to half the thickness of the photoelectric conversion layer from one interface in the thickness direction of the photoelectric conversion layer is defined as the second depth, the content ratio of the element in the photoelectric conversion layer at the second depth is greater than the content ratio of the element at the third depth and less than the content ratio of the element at the first depth.

6. The photoelectric conversion element according to any one of claims 1 to 5, wherein the element is potassium.

7. A photoelectric conversion element according to any one of claims 1 to 6, comprising a glass substrate on which the photoelectric conversion layer is formed.

8. The photoelectric conversion element according to claim 7, wherein the one interface is the interface of the photoelectric conversion layer that is closer to the glass substrate.

9. The photoelectric conversion element according to claim 7 or 8, wherein the glass substrate has an ion exchange layer in which at least a portion of alkali metal ions are replaced with other alkali metal ions.

10. The photoelectric element according to claim 9, wherein the ion exchange layer is a layer in which at least a portion of lithium ions and / or sodium ions are replaced with potassium ions.

11. The photoelectric conversion element according to any one of claims 7 to 10, wherein the glass substrate is chemically strengthened glass.

12. A photoelectric conversion element according to any one of claims 7 to 11, comprising a first electrode layer between the glass substrate and the photoelectric conversion layer, wherein the thickness of the first electrode layer is in the range of 50 nm to 1500 nm.

13. The photoelectric conversion element according to any one of claims 1 to 12, wherein the thickness of the photoelectric conversion layer is 0.5 μm or more and 5.0 μm or less.

14. A solar cell module comprising a photoelectric conversion element according to any one of claims 1 to 13.

15. A paddle comprising the solar cell module according to claim 14.

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