Perovskite compounds and photoelectric conversion elements

Abstract

To provide a perovskite-type compound having high heat resistance.SOLUTION: A perovskite-type compound has a composition formula represented by A(Pb1-xSnx)I3-yBry. An element A is one or more elements selected from a group consisting of Li, Na, K, Rb and Cs. x and y in the formula belong to any of the following ranges (1) to (6): (1) 0.0≤x<0.0125 and 1.6≤y≤3.0, (2) 0.0125≤x<0.1 and 1.1≤y≤3.0, (3) 0.1≤x<0.3 and 0.8≤y≤3.0, (4) 0.3≤x<0.5 and 0.8≤y≤3.0, (5) 0.5≤x<0.7 and 0.8≤y≤2.8, and (6) 0.7≤x≤0.8 and 0.8≤y≤1.8.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to perovskite-type compounds and photoelectric conversion elements. [Background technology]

[0002] In recent years, photoelectric conversion elements (e.g., perovskite solar cells) containing compounds with a perovskite structure (perovskite-type compounds) have attracted attention as one of the next-generation solar cells. As an example, a perovskite solar cell has a so-called nip-type stacked structure in which an electron transport layer made of an n-type semiconductor, a perovskite layer (light absorption layer), and a hole transport layer made of a p-type semiconductor are arranged in that order from the light-receiving surface. As another example, a perovskite solar cell has a so-called pin-type stacked structure in which a hole transport layer made of a p-type semiconductor, a perovskite layer, and an electron transport layer made of an n-type semiconductor are arranged in that order from the light-receiving surface.

[0003] The perovskite layer contains compounds having a perovskite-type crystal structure. Compounds having a perovskite-type crystal structure are represented by the general formula AB-X3.

[0004] It is known that a wide variety of elements or molecules can be used as elements or molecules A, B, and X that constitute perovskite-type compounds (Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Liang, J., et al., J. Am. Chem. Soc. 139, 14009-14012 (2017) [Non-Patent Document 2] Fang, Z., et al., Nano Energy 61, 389-396 (2019) [Non-Patent Document 3] Wang, Z., et al., Adv. Sci. 2019, 6, 1801704

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, many of the perovskite-type compounds applied to photoelectric conversion elements are known to have problems from the perspective of heat resistance. In particular, in an environment where it can be exposed to high temperatures, for example, when used in outer space such as an artificial satellite, a perovskite-type compound that can withstand a higher temperature than when used on the ground is required.

[0007] From such a perspective, a perovskite-type compound and a photoelectric conversion element having high heat resistance are desired.

Means for Solving the Problems

[0008] The perovskite-type compound according to one aspect has a composition formula represented by A(Pb 1-x Sn x )I 3-y Br y . Element A is one or more elements selected from the group consisting of Li, Na, K, Rb, and Cs. x and y in the composition formula belong to any one of the following ranges (1) to (6): (1) 0.0 ≦ x < 0.0125 and 1.6 ≦ y ≦ 3.0 (2) 0.0125 ≦ x < 0.1 and 1.1 ≦ y ≦ 3.0 (3) 0.1 ≦ x < 0.3 and 0.4 ≦ y ≦ 3.0 (4) 0.3 ≦ x < 0.5 and 0.4 ≦ y ≦ 3.0 (5) 0.5 ≦ x < 0.7 and 0.4 ≦ y ≦ 2.8 (6) 0.7 ≦ x ≦ 0.9 and 0.4 ≦ y ≦ 1.8.

[0009] The photoelectric conversion element according to one aspect has a light absorption layer containing the above perovskite-type compound.

Effects of the Invention

[0010] This provides a photoelectric conversion element containing a perovskite layer with high heat resistance. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a cross-sectional view in the thickness direction showing an example of a photoelectric conversion element according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view in the thickness direction showing another example of a photoelectric conversion element according to one embodiment. [Figure 3] Figure 3 is a diagram showing the band gap of a perovskite compound having the compositional formula Cs(Pb1-xSnx)I3-yBry. [Figure 4] Figure 4 shows the Tauc plots of the extinction coefficients for several perovskite-type compounds. [Figure 5] Figure 5 is a graph showing the results of X-ray diffraction experiments on several perovskite-type compounds. [Figure 6] Figure 6 is a plot showing experimental results of heat resistance for several perovskite-type compounds. [Modes for carrying out the invention]

[0012] The embodiments will be described below with reference to the drawings. In the following drawings, identical or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the proportions of the dimensions, etc., may differ from those of reality.

[0013] Figure 1 is a cross-sectional view in the thickness direction showing an example of a photoelectric conversion element according to one embodiment. The photoelectric conversion element shown in Figure 1 may be a perovskite-type solar cell equipped with a light-absorbing layer containing a compound having a perovskite structure. The photoelectric conversion element shown in Figure 1 is a so-called single-junction type photoelectric conversion element.

[0014] The photoelectric conversion element 10 may have a substrate 11, a first conductive layer 12, an electron transport layer 13, a light absorption layer 14, a hole transport layer 15, a second conductive layer 16, and a third conductive layer 17. The first conductive layer 12 is provided on the substrate 11. The electron transport layer 13 is provided on the first conductive layer 12. The light absorption layer 14 is provided on the electron transport layer 13. The hole transport layer 15 is provided on the light absorption layer 14. The second conductive layer 16 is provided on the hole transport layer 15. The third conductive layer 17 is provided on the second conductive layer 16.

[0015] The substrate 11 is a base for laminating the first conductive layer 12, electron transport layer 13, light absorption layer 14, hole transport layer 15, second conductive layer 16, and third conductive layer 17. The substrate 11 can be selected from transparent glass substrates such as soda-lime glass or alkali-free glass, resin substrates, metal substrates, ceramic substrates, etc. The substrate 11 may be either a non-transparent substrate or a translucent substrate. The substrate 11 may also be a flexible substrate.

[0016] In this specification, "transmissive" means that 10% or more of light at any wavelength between 200 nm and 2000 nm is transmitted.

[0017] If the substrate 11 is translucent, light may be incident on the photoelectric conversion element 10 from the substrate 11 side (lower side in the figure) or from the third conductive layer 17 side (upper side in the figure). On the other hand, if the substrate 11 is not translucent, light is incident on the photoelectric conversion element 10 from the third conductive layer 17 side (upper side in the figure).

[0018] Details of the first conductive layer 12, electron transport layer 13, light absorption layer 14, hole transport layer 15, second conductive layer 16, and third conductive layer 17 will be described later.

[0019] Figure 2 is a cross-sectional view in the thickness direction showing another example of a photoelectric conversion element according to one embodiment. The photoelectric conversion element shown in Figure 2 may be a perovskite-type solar cell having a light-absorbing layer containing a compound having a perovskite structure. The photoelectric conversion element shown in Figure 2 is a so-called multi-junction type photoelectric conversion element. A multi-junction type photoelectric conversion element has a plurality of photoelectric conversion cells stacked on top of each other. That is, a multi-junction type photoelectric conversion element may have a plurality of light-absorbing layers.

[0020] In Figure 2, the photoelectric conversion element 10A has a stacked structure in which a top cell TC and a bottom cell BC are stacked on top of each other. In the configuration shown in Figure 2, light is incident on the photoelectric conversion element 10A from the top cell TC side (upper side in the figure). Of the incident light, the short wavelength light is photoelectrically converted in the top cell TC. Also, of the incident light, the long wavelength light that has passed through the top cell TC is photoelectrically converted in the bottom cell BC.

[0021] The top cell TC may have the same configuration as the perovskite-type photoelectric conversion element shown in Figure 1. Therefore, the top cell TC may have a substrate 11, a first conductive layer 12, an electron transport layer 13, a light absorption layer 14, a hole transport layer 15, a second conductive layer 16, and a third conductive layer 17. The first conductive layer 12 is provided on the substrate 11. The electron transport layer 13 is provided on the first conductive layer 12. The light absorption layer 14 is provided on the electron transport layer 13. The hole transport layer 15 is provided on the light absorption layer 14. The second conductive layer 16 is provided on the hole transport layer 15. The third conductive layer 17 is provided on the second conductive layer 16. Here, the substrate 11 is a translucent substrate.

[0022] The bottom cell BC may have a substrate 20, a first electrode layer 21, a photoelectric conversion layer (light absorption layer) 22, a buffer layer 23, and a second electrode layer 24. The first electrode layer 21 may be provided on the substrate 20. The photoelectric conversion layer 22 may be provided on the first electrode layer 21. The buffer layer 23 may be provided on the photoelectric conversion layer 22. The second electrode layer 24 may be provided on the buffer layer 23.

[0023] As the bottom cell BC, for example, known photoelectric elements (e.g., solar cells) such as compound photoelectric elements like CZTS, CIGS, CdTe, and GaAs, as well as silicon photoelectric elements and organic photoelectric elements can be used. Therefore, explanations regarding the configuration of the bottom cell BC are omitted. Note that the buffer layer 23 of the bottom cell BC may be omitted.

[0024] The photoelectric conversion element 10A shown in Figure 2 has a so-called four-terminal tandem structure, including four terminals: two positive electrodes and two negative electrodes. In this case, the photoelectric conversion element 10A may have an intermediate layer 19 between the top cell TC and the bottom cell BC. The intermediate layer 19 may be a transparent insulating layer.

[0025] Instead of the four-terminal tandem structure shown in Figure 2, the photoelectric conversion element may have a two-terminal tandem structure. In this case, the photoelectric conversion element does not need to have at least the second conductive layer 16, the third conductive layer 17, and the second electrode layer 24 shown in Figure 2.

[0026] Next, the first conductive layer 12, electron transport layer 13, light absorption layer 14, hole transport layer 15, second conductive layer 16, and third conductive layer 17 mentioned above will be described in detail.

[0027] The first conductive layer 12 may be a layer that acts as the cathode of the photoelectric conversion element. Examples of materials for the first conductive layer 12 include conductive transparent materials such as copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO), as well as metallic sodium, sodium-potassium alloy, metallic lithium, metallic magnesium, metallic aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, aluminum-aluminum oxide (Al / Al2O3) mixture, and aluminum-lithium fluoride (Al / LiF) mixture. The above materials may be used individually or as a mixture of two or more.

[0028] The first conductive layer 12 is preferably light-transmitting. However, when light is incident on the photoelectric conversion element from the third conductive layer 17 side, the first conductive layer 12 does not need to be light-transmitting.

[0029] The first conductive layer 12 can be formed by a film-forming method such as vapor deposition or sputtering. While not particularly limited, the thickness of the first conductive layer 12 is preferably 0.1 μm or more. This allows for sufficient conductivity to be maintained in the first conductive layer 12. Also, while not particularly limited, the thickness of the first conductive layer 12 is preferably 5.0 μm or less. This makes it easier to maintain a relatively high light transmittance in the first conductive layer 12.

[0030] The electron transport layer 13 is responsible for transporting electrons generated by photoexcitation of the light absorption layer 14 to the first conductive layer 12. Therefore, it is preferable that the electron transport layer 13 be formed from a material having properties that allow electrons generated in the light absorption layer 14 to easily move to the electron transport layer 13, and that electrons in the electron transport layer 13 to easily move to the first conductive layer 12.

[0031] Examples of materials for the electron transport layer 13 include inorganic materials such as titanium dioxide (TiO2), tungsten oxide (WO2, WO3, W2O3, etc.), zinc oxide (ZnO), niobium oxide (Nb2O5, etc.), tantalum oxide (Ta2O5, etc.), yttrium oxide (Y2O3, etc.), strontium titanate (SrTiO3, etc.), and tin oxide (SnO2), as well as fullerenes (C60, C70, etc.) and their derivatives (PC 60 BM, PC 70 Examples of organic materials include BM, ICBA, hydrogenated C60, and hydrogenated C60. These materials may be used individually or as a mixture of two or more.

[0032] The electron transport layer 13 may be a single-layer structure or a laminated structure containing multiple layers. In Figures 1 and 2, the electron transport layer 13 has a dense layer 13a having a dense structure and a porous layer 13b having a porous structure. The dense layer 13a is located between the first conductive layer 12 and the porous layer 13b, and the porous layer 13b is located between the dense layer 13a and the light-absorbing layer 14.

[0033] The dense layer 13a has a denser structure than the porous layer 13b. In other words, the voids in the dense layer 13a are fewer than those in the porous layer 13b. The dense layer 13a is a layer that is hardly permeated by the solution used to form the light absorption layer 14. The dense layer 13a has the function of preventing contact between the first conductive layer 12 and the second conductive layer 16, which causes a decrease in photovoltaic power, and also prevents contact between the first conductive layer 12 and the hole transport layer 15. Therefore, the decrease in photovoltaic power can be suppressed by the dense layer 13a.

[0034] The thickness of the dense layer 13a is preferably in the range of 5 nm to 200 nm, and more preferably in the range of 10 nm to 100 nm.

[0035] As an example, if the electron transport layer 13 is titanium oxide, the dense layer 13a can be formed by the following method. First, a coating solution containing a titanium chelate compound is prepared, and the coating solution is applied onto the first conductive layer 12 by a film formation method such as spin coating, screen printing, spray pyrolysis, or aerosol deposition. Then, the dense layer 13a containing titanium oxide is formed by firing. Alternatively, after firing, the dense layer 13a containing titanium oxide may be immersed in an aqueous solution of titanium tetrachloride. This can increase the density of the dense layer 13a. The titanium chelate compound used to form the dense layer 13a containing titanium oxide is preferably a compound having an acetoacetate ester chelate group or a compound having a β-diketone chelate group.

[0036] On the other hand, the porous layer 13b has larger voids compared to the dense layer 13a, and is a layer into which the solution used to form the light-absorbing layer 14 permeates. The material of the light-absorbing layer 14 can be filled and held in the voids of the porous layer 13b. Therefore, the porous layer 13b increases the contact area between the electron transport layer 13 and the light-absorbing layer 14, and plays a function in efficiently transferring electrons generated by photoexcitation in the light-absorbing layer 14 to the electron transport layer 13. As a result, the electrons generated by photoexcitation in the light-absorbing layer 14 can be efficiently charge-separated by the porous layer 13b, and the recombination of electrons and holes can be suppressed. As a result, the photoelectric conversion efficiency of the solar cell can be improved.

[0037] The thickness of the porous layer 13b is preferably in the range of 10 nm to 2000 nm, and more preferably in the range of 20 nm to 500 nm.

[0038] As an example, when the electron transport layer 13 is formed from titanium dioxide, the porous layer 13b can be formed by the following method. First, a coating solution containing titanium dioxide particles is prepared, and the coating solution is applied onto the dense layer 13a by a film formation method such as spin coating, screen printing, spray pyrolysis, or aerosol deposition. Subsequently, the porous layer 13b containing titanium dioxide is formed by firing. Although not particularly limited, when the porous layer 13b is formed from titanium dioxide, it is preferable to use anatase-type titanium dioxide particles.

[0039] The hole transport layer 15 is located between the light absorption layer 14 and the second conductive layer 16. The hole transport layer 15 is responsible for capturing holes generated in the light absorption layer 14 and moving them to the second conductive layer 16, which is the anode. The hole transport layer 15 may contain a matrix component consisting of, for example, 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (Spiro-OMeTAD) or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine](PTAA), or it may contain a thin film of an organic low molecular weight that preferentially captures holes, such as [2-(9Hcarbazol-9-yl)ethyl]phosphonic acid (2PACz). Optionally, a passivate layer (not shown) made of a metal oxide or organic thin film may be provided between the light absorption layer 14 and the hole transport layer 15 to suppress the recombination of holes and electrons.

[0040] The hole transport layer 15 may contain additives that increase carrier density. As an example, lithium (fluorosulfonyl)(trifluoromethyl)imide (LiTFSI) can be used as an additive.

[0041] The thickness of the hole transport layer 15 is preferably in the range of 1 nm to 500 nm, and more preferably in the range of 1 nm to 130 nm.

[0042] The hole transport layer 15 may be an amorphous layer. Furthermore, the hole transport layer 15 may contain an organic binder resin, a plasticizer, etc.

[0043] The hole transport layer 15 can be formed, for example, by the following method. First, a coating solution is prepared by dissolving the matrix component compound in an organic solvent, and this coating solution is applied onto the light absorption layer 14 (or the passivate layer). The hole transport layer 15 is then formed by removing the organic solvent. The organic solvent used in forming the hole transport layer 15 is preferably a solvent that does not disrupt the crystal structure of the organic-inorganic hybrid compound, as it is applied onto the light absorption layer 14. Examples of such solvents include chlorobenzene, toluene, and isopropanol. The method of applying the coating solution is not particularly limited, but examples include spin coating, screen printing, and immersion coating.

[0044] The second conductive layer 16 is a transparent conductive layer that is light-transmitting and acts as the anode of the photoelectric conversion element. The second conductive layer 16 is formed on the hole transport layer 15 and is in contact with the hole transport layer 15.

[0045] Any conductive transparent material can be used as the material for the second conductive layer 16. Preferably, the material for the second conductive layer 16 is a metal oxide containing, for example, indium, zinc, or tin. Examples of materials for the second conductive layer 16 include conductive transparent materials such as copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO), as well as conductive transparent polymers.

[0046] Although optional, a buffer layer (not shown) may be formed between the second conductive layer 16 and the hole transport layer 15. The buffer layer may be formed of, for example, molybdenum oxide.

[0047] The third conductive layer 17 is an auxiliary electrode layer formed by laminating it onto the second conductive layer 16. The third conductive layer 17 has the function of reducing the overall electrical resistance of the anode electrode. The third conductive layer 17 may be a transparent electrode or a collector electrode such as a metal grid. If the third conductive layer 17 is a transparent electrode, its material may be the same as the material of the second conductive layer 16 or a different material from the second conductive layer 16.

[0048] Examples of materials for the third conductive layer 17 include metallic materials such as gold, silver, copper, aluminum, and nickel, as well as conductive transparent materials such as copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO), and conductive transparent polymers. The above materials may be used individually or as a mixture of two or more.

[0049] The third conductive layer 17 can be manufactured, for example, by forming a film of anode material on the second conductive layer 16 using methods such as vapor deposition or printing. Alternatively, the third conductive layer 17 may be formed in a mesh or grid shape using a vapor deposition mask or the like.

[0050] The light-absorbing layer 14 contains a compound having a perovskite structure (perovskite-type compound) and is responsible for generating electrons and holes by absorbing incident light. In the light-absorbing layer 14, low-energy electrons in the material constituting the light-absorbing layer are photoexcited by the incident light, generating higher-energy electrons and holes. The electrons generated by photoexcitation move to the electron transport layer 13, and the holes generated by photoexcitation move to the hole transport layer 15.

[0051] Perovskite compounds are represented by the chemical formula AB-X3. Element A is located at each vertex of the unit cell. Element B is located near each body center of the unit cell. Element X is located near each face center of the unit cell.

[0052] Element A in the above composition formula is one or more elements selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Preferably, element A is cesium.

[0053] In this embodiment, element B in the above composition formula includes lead (Pb) or tin (Sn), or both of them. Element X in the above composition formula is iodine (I), or both iodine (I) and bromine (Br). Therefore, in this embodiment, the perovskite-type compound has the following composition formula: A(Pb 1-x Sn x )I 3-y Br y ).

[0054] x in the composition formula is a positive number greater than or equal to 0 and less than or equal to 1. y in the composition formula is a positive number greater than or equal to 0 and less than or equal to 3. More specific ranges of x and y will be described later. Since the perovskite-type compound having this composition formula does not contain organic molecules, it is likely to have high heat resistance.

[0055] The above perovskite-type compound can be formed into a film by applying and firing a perovskite precursor solution. Here, the perovskite precursor solution may be a mixture of an A-Pb-I3 solution, an A-Pb-Br3 solution, an A-Sn-I3 solution, and an A-Sn-Br3 solution in a desired amount. By changing the mixing ratio of these solutions, the values of x and y in the composition formula of the above perovskite-type compound can be appropriately set. The application method of the perovskite precursor solution is not particularly limited, and spin coating, screen printing, dip coating, etc. can be applied.

[0056] In this embodiment, from the perspective of the heat resistance of the perovskite-type compound, x and y in the composition formula belong to any of the following ranges (1) to (5). (1) 0.0 ≦ x < 0.0125 and 1.6 ≦ y ≦ 3.0 (2) 0.0125 ≦ x < 0.1 and 1.1 ≦ y ≦ 3.0 (3) 0.1 ≤ x < 0.3 and 0.8 ≤ y ≤ 3.0 (4) 0.3 ≤ x < 0.5, and 0.8 ≤ y ≤ 3.0 (5) 0.5 ≤ x < 0.7, and 0.8 ≤ y ≤ 2.8 (6) 0.7 ≤ x ≤ 0.8 and 0.8 ≤ y ≤ 1.8

[0057] From the viewpoint of the heat resistance of perovskite-type compounds, the more preferred ranges for x and y in the compositional formula are as follows: In the range where "0.0 ≤ x < 0.0125" is satisfied, it is preferable that "1.8 ≤ y ≤ 3.0" is satisfied, and it is more preferable that "2.0 ≤ y ≤ 3.0" is satisfied.

[0058] Within the range where "0.125≦x<0.1" is satisfied, it is preferable that "1.2≦y≦3.0" is satisfied, more preferable that "1.3≦y≦3.0" is satisfied, even more preferable that "1.4≦y≦3.0" is satisfied, and even more preferable that "1.5≦y≦3.0" is satisfied.

[0059] Within the range where "0.1 ≤ x < 0.3" is satisfied, it is preferable that "0.9 ≤ y ≤ 3.0" is satisfied, and it is even more preferable that "1.0 ≤ y ≤ 3.0" is satisfied.

[0060] Within the range where "0.3 ≤ x < 0.5" is satisfied, y is preferably 0.8 or greater, more preferably 0.9 or greater, and even more preferably 1.0 or greater. Also within the range where "0.3 ≤ x < 0.5" is satisfied, y is preferably 2.8 or less, more preferably 2.7 or less, even more preferably 2.6 or less, and even more preferably 2.5 or less.

[0061] Within the range where "0.5 ≤ x < 0.7" is satisfied, y is preferably 0.8 or greater, more preferably 0.9 or greater, and even more preferably 1.0 or greater. Furthermore, within the range where "0.5 ≤ x < 0.7" is satisfied, y is preferably 2.6 or less, more preferably 2.4 or less, even more preferably 2.2 or less, and even more preferably 1.8 or less. In addition, within the range where "0.5 ≤ x < 0.7" is satisfied, y may also be 1.5 or less.

[0062] Within the range where "0.7 ≤ x ≤ 0.8" is satisfied, y is preferably 0.8 or greater, more preferably 0.9 or greater, and even more preferably 1.0 or greater. Furthermore, within the range where "0.7 ≤ x ≤ 0.8" is satisfied, y is preferably 1.7 or less, more preferably 1.6 or less, and even more preferably 1.5 or less.

[0063] In a preferred embodiment, from the viewpoint of the heat resistance of the perovskite-type compound, x and y in the composition formula belong to any of the following ranges (1) to (5). (1) 0.0 ≤ x < 0.0125 and 2.0 ≤ y ≤ 3.0 (2) 0.0125 ≤ x < 0.1 and 1.5 ≤ y ≤ 3.0 (3) 0.1 ≤ x < 0.3 and 1.0 ≤ y ≤ 3.0 (4) 0.3 ≤ x < 0.5, and 1.0 ≤ y ≤ 2.5 (5) 0.5 ≤ x ≤ 0.7, and 1.0 ≤ y ≤ 1.5

[0064] Within the above x and y ranges, the perovskite-type compounds are considered to have high heat resistance. Specifically, when X-ray diffraction experiments were performed on the perovskite-type compounds before heating and after heating at 150°C, the peaks indicating perovskite-type compounds with diffraction angles (2θ) of 13-16° in the X-ray diffraction patterns of the perovskite-type compounds within the above x and y ranges hardly changed before and after heating. This suggests that the above perovskite-type compounds can withstand high temperatures of 150°C.

[0065] Preferably, the position of the X-ray diffraction peak observed at a diffraction angle 2θ of 13-16° in the perovskite compound after heating in a nitrogen atmosphere at 150°C for 500 hours is within 0.05° of the position of the X-ray diffraction peak of the perovskite compound before heating. In this case, the crystal structure of the perovskite compound is maintained for a long period of time under high temperature conditions of 150°C.

[0066] From the viewpoint of the efficiency of electron-hole pair production by sunlight, it is desirable that the band gap (Eg) between the valence band and the conduction band in perovskite-type compounds be smaller than the desired value. From this viewpoint, the band gap is preferably 1.9 eV or less, and more preferably 1.8 eV or less.

[0067] Similarly, from the viewpoint of efficiency in photoelectric conversion, the band gap between the valence band and the conduction band in the perovskite compound is preferably 1.5 eV or more, more preferably 1.6 eV or more, and even more preferably 1.7 eV or more. Perovskite compounds having the above band gap are suitably used as the light absorption layer of a photoelectric conversion element.

[0068] In particular, in the case of the multi-junction type photoelectric conversion element described above, the band gap of the light absorption layer of the top cell is preferably 1.6 eV to 1.9 eV, more preferably 1.7 eV to 1.8 eV. It is known that in this case the photoelectric conversion efficiency of the entire multi-junction type photoelectric conversion element becomes extremely high (see Non-Patent Document 3). Therefore, the band gap of the perovskite type compound according to this embodiment is preferably 1.6 eV to 1.9 eV, more preferably 1.7 eV to 1.8 eV.

[0069] Figure 3 shows Cs(Pb 1-x Sn x )I 3-y Br y This is a diagram showing the band gap of a perovskite-type compound having the compositional formula represented by . In Figure 3, the horizontal axis represents the x value in the compositional formula, and the vertical axis represents the y value in the compositional formula.

[0070] Each line drawn in the diagram represents a point where the energy gap (Eg) of the perovskite compound corresponds to 1.4eV, 1.5eV, 1.6eV, 1.7eV, 1.8eV, 1.9eV, 2.0eV, 2.1eV, or 2.2eV, respectively. The region between adjacent lines corresponds to a region with an energy gap between the two energy gap values ​​indicated by each line. Therefore, the region between the line labeled "Eg=1.7eV" and the line labeled "Eg=1.8eV" means that the energy gap is in the range of 1.7eV to 1.8eV.

[0071] The energy gap shown in Figure 3 can be calculated using the extinction coefficient α measured by ultraviolet-visible spectroscopy. The extinction coefficient α can be measured and calculated by ultraviolet-visible spectroscopy, for example, by a method compliant with JIS K0115:2020. The extinction coefficient α actually measured by ultraviolet-visible spectroscopy may vary depending on the frequency ν of light.

[0072] To calculate the energy gap, a Tauc plot is created from the measured extinction coefficient α. The Tauc plot has (hνα) on the vertical axis. 1 / n The graph shows the extinction coefficient α with hν on the horizontal axis (see also Figure 4). Figure 4 shows Tauc plots of the extinction coefficient α measured by ultraviolet-visible spectroscopy for several perovskite-type compounds.

[0073] Here, the band gap Eg of the semiconductor is given by the following relationship from the measured absorption coefficient α: "(hνα) 1 / n It is calculated based on the formula =k(hν-Eg), where "h" is Planck's constant and "ν" is the frequency of the irradiated light. 1-x Sn x )I 3-y Br y The transition in this case is considered a directly allowed transition, so "n=1 / 2". "k" is the proportionality constant.

[0074] In Figure 4, "(hνα) 1 / 2 The value of " " gradually increases or remains almost constant with increasing incident light energy hν, forming an upward curve that rises sharply near the band gap. The value of energy hν at the intersection of the tangent line passing through the inflection point of this sharp upward curve and the baseline of the Tauc plot is the band gap Eg. Here, the baseline can be determined by known methods. For example, the baseline may be defined by an approximate straight line obtained by the least squares method from multiple measurement points sufficiently lower in energy than the sharp upward curve near the band gap.

[0075] In this way, the band gap of a perovskite compound can be determined. In this specification, the band gap may be calculated by this method.

[0076] Referring to Figure 3, Cs(Pb 1-x Sn x )I 3-y Br y In this region, the area where the energy gap is 1.9 eV or less roughly corresponds to the area that satisfies "y ≤ 5.0x + 1.0". Therefore, in addition to the heat resistance conditions mentioned above, from the viewpoint of photoelectric conversion efficiency, Cs(Pb 1-x Sn x )I 3-y Br y Therefore, it is more preferable that the condition "y ≤ 5.0x + 1.0" is satisfied.

[0077] Furthermore, referring to Figure 3, we can see that if "2.5x + 0.25 ≤ y", then the energy gap is 1.6 eV or greater. Therefore, in addition to the heat resistance conditions mentioned above, from the viewpoint of photoelectric conversion efficiency, Cs(Pb 1-x Sn x )I 3-y Br y Therefore, it is more preferable that the condition "2.5x + 0.25 ≤ y" is satisfied.

[0078] [Example of experiment] Next, we will describe the experimental results regarding the heat resistance of the perovskite-type compound of the above embodiment. First, in the experimental example, the perovskite-type compound was manufactured by the following procedure.

[0079] First, solutions of CsPbI3, CsPbBr3, CsSnI3, and CsSnBr3 were prepared at a concentration of 0.4 M (Molar). The solvent used was dimethyl sulfoxide (DMSO).

[0080] Next, depending on the elemental composition ratio of the perovskite compound to be produced, some or all of the CsPbI3 solution, CsPbBr3 solution, CsSnI3 solution, and CsSnBr3 solution were mixed in the desired proportions as needed. This resulted in Cs(Pb) having the desired x,y values. 1-x Sn x )I 3-y Br y The solution was prepared.

[0081] Next, on a pre-cleaned glass substrate, in a nitrogen atmosphere, Cs(Pb 1-x Sn x )I 3-y Br y The solution was applied by spin coating. Spin coating was performed under the following conditions: 0 rpm for the first 10 seconds, 500 rpm for the next 10 seconds, and 2000 rpm for the next 80 seconds. Additionally, 0.15 ml of toluene was used as a poor solvent 80 seconds after the start of spin coating.

[0082] Next, a thin film of a perovskite-type compound was formed by sintering the solution applied to a glass substrate. Sintering was carried out at a temperature of 300°C for 2 minutes. As shown in Table 1 below, numerous thin films of perovskite-type compounds were produced by changing the combination of x and y in the compositional formula.

[0083] Next, experiments were conducted on the heat resistance of the fabricated perovskite-type compound thin films. First, X-ray diffraction experiments were performed on the perovskite-type compound thin films (before heating to 150°C) to measure the position (2θ) of the X-ray diffraction peak of the perovskite-type compound. Here, the position of the X-ray diffraction peak is determined by the position of the maximum intensity.

[0084] Next, a thin film of the perovskite compound was placed on a heater along with a glass substrate and heated at 150°C for 500 hours under a nitrogen atmosphere. Then, X-ray diffraction experiments were performed on the heated thin film of the perovskite compound, and the position of the X-ray diffraction peak of the perovskite compound was measured.

[0085] Figure 5 is a graph showing the results of X-ray diffraction experiments on several perovskite-type compounds. In Figure 5, the results of X-ray diffraction experiments on perovskite-type compounds before heating are shown by a dashed line. In Figure 5, the results of X-ray diffraction experiments on perovskite-type compounds after heating are shown by a solid line. From the graph in Figure 5, it can be seen that for some compounds, the X-ray diffraction peaks originating from the perovskite structure, where the diffraction angle 2θ is 13-16°, are not observed in the state before heating. This is thought to be because the relevant composition (corresponding to specific x,y values) is very unstable and cannot maintain the perovskite structure at room temperature. Furthermore, it can be seen that in some perovskite-type compounds, the position of the X-ray diffraction peaks originating from the perovskite structure, where the diffraction angle 2θ is 13-16°, changes between before and after heating. This is thought to be because the perovskite compound of the relevant composition decomposed or underwent phase separation due to heating. In other words, if a compound has an X-ray diffraction peak originating from a perovskite structure with a diffraction angle 2θ of 13-16° before heating, and the position of that peak hardly changes before and after heating, it can be said to be a perovskite-type compound with heat resistance up to 150°C.

[0086] Table 1 below is a plot showing experimental results of heat resistance for several perovskite-type compounds. In Table 1 below, the evaluation of heat resistance is clearly shown for each composition (values ​​of x, y) of the perovskite-type compound. Here, a "good" evaluation of heat resistance is defined as the presence of a perovskite structure in the X-ray diffraction peak before heating, and the shift in peak position (Δ2θ) between before and after heating being 0.05° or less. A "poor" evaluation of heat resistance is defined as the absence of a perovskite structure in the X-ray diffraction peak before heating, or the shift in peak position (Δ2θ) between before and after heating being greater than 0.05°.

[0087] (Table 1) TIFF0007865483000001.tif211139

[0088] Figure 6 is a plot showing experimental results of heat resistance for several perovskite-type compounds. Figure 6 is a diagrammatic representation of the experimental results shown in Table 1. In Figure 6, the horizontal axis represents the x value in the compositional formula, and the vertical axis represents the y value in the compositional formula. In Figure 6, a "good" evaluation of heat resistance is indicated by "○", and a "poor" evaluation of heat resistance is indicated by "×".

[0089] Referring to Figure 6, the region with high heat resistance generally extends from the region where x and y are moderate to the region where x is small and y is large. Specifically, in the interval where x is small, it is preferable that y is greater than or equal to a desired value and 3 or less. In the interval where x is moderate, it is preferable that the value of y is also moderate. As x becomes larger than moderate, the range of values ​​that y can take becomes narrower.

[0090] More specifically, Cs(Pb 1-x Sn x )I 3-y Br yIn this case, if x and y in the composition formula fall within any of the following ranges (1) to (5), it can be inferred from Figure 6 that a perovskite-type compound with high heat resistance will be obtained. (1) 0.0 ≤ x < 0.0125 and 1.6 ≤ y ≤ 3.0 (2) 0.0125 ≤ x < 0.1 and 1.1 ≤ y ≤ 3.0 (3) 0.1 ≤ x < 0.3 and 0.8 ≤ y ≤ 3.0 (4) 0.3 ≤ x < 0.5, and 0.8 ≤ y ≤ 3.0 (5) 0.5 ≤ x < 0.7, and 0.8 ≤ y ≤ 2.8 (6) 0.7 ≤ x ≤ 0.8 and 0.8 ≤ y ≤ 1.8

[0091] Preferably, when x and y fall within any of the following ranges (1) to (5), it can be seen from Figure 6 that a perovskite-type compound with higher heat resistance can be obtained more reliably. (1) 0.0 ≤ x < 0.0125 and 2.0 ≤ y ≤ 3.0 (2) 0.0125 ≤ x < 0.1 and 1.5 ≤ y ≤ 3.0 (3) 0.1 ≤ x < 0.3 and 1.0 ≤ y ≤ 3.0 (4) 0.3 ≤ x < 0.5, and 1.0 ≤ y ≤ 2.5 (5) 0.5 ≤ x ≤ 0.7, and 1.0 ≤ y ≤ 1.5

[0092] The range represented by x and y above can result in perovskite-type compounds that are heat-resistant at high temperatures of 150°C. Such high-temperature resistant perovskite-type compounds can be suitably used in environments where they may be exposed to high temperatures, such as in outer space, like artificial satellites.

[0093] In the above embodiment, a perovskite-type solar cell configuration was described as an example of a photoelectric conversion element. However, the photoelectric conversion element of the present invention may also be applied to, for example, photodiodes or light sensors.

[0094] In the above embodiments, the configuration of a single-junction cell, which is a single solar cell, and the configuration of a multi-junction solar cell, in which two layers of solar cells are stacked, were described. However, the configuration of the photoelectric conversion element of the present invention can also be applied to a multi-junction solar cell in which three or more layers of solar cells are stacked. In this case, the configuration of the photoelectric conversion element of the present invention is not limited to the top cell but can be applied to any cell.

[0095] 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. [Explanation of symbols]

[0096] 10,10A photoelectric conversion element 14 Light-absorbing layer

Claims

1. A(Pb) １－ｘ Sn ｘ )I ３－ｙ Br ｙ It contains a perovskite-type compound having the compositional formula represented by, Element A is one or more elements selected from the group consisting of Li, Na, K, Rb, and Cs. The condition "y ≤ 5.0x + 1.0" is satisfied, and x and y belong to one of the following ranges (1) to (5): (1) 0.0 ≤ x < 0.0125 and 2.0 ≤ y ≤ 3.0 (2) 0.0125 ≤ x < 0.1 and 1.5 ≤ y ≤ 3.0 (3) 0.1 ≤ x < 0.3 and 1.0 ≤ y ≤ 3.0 (4) 0.3 ≤ x < 0.5 and 1.0 ≤ y ≤ 2.5 (5) 0.5 ≤ x < 0.7, and 1.0 ≤ y ≤ 1.5, Solar cell.

2. The solar cell according to claim 1, wherein the band gap between the valence band and the conduction band of the perovskite compound is 1.9 eV or less.

3. The solar cell according to claim 1, wherein the band gap between the valence band and the conduction band of the perovskite compound is 1.5 eV or more.

4. The solar cell according to claim 1, wherein element A is Cs.

5. The solar cell according to any one of claims 1 to 4, having a light-absorbing layer containing the perovskite compound.

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