Photoelectric conversion element

Abstract

A solar cell (1) according to the present invention includes a hole transport layer (13), a light absorption layer (14), and an electron transport layer (15) between an upper electrode (16) and a transparent conductive layer (12) laminated on a transparent substrate (11). The light absorption layer (14) includes: a first light absorption layer (141) containing Ag, Bi, and a halogen element X; and a second light absorption layer (142) containing BiZ3 (Z represents a halogen element). The second light absorption layer (142) is laminated on the surface of the first light absorption layer (141) on the transparent conductive layer (12) side and / or the surface of the first light absorption layer (141) on the upper electrode (16) side. When the molar ratio of Ag, Bi, and the halogen element X included in the first light absorption layer (141) is denoted by x:y:z, x:y:z = 1:1 / 3–3:2–10.

Description

Photoelectric conversion element

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

[0002] Patent Document 1 discloses a solar cell having a substrate, a conductive metal oxide cathode layer, an electron transport layer, a BiI3 active light absorption layer, a hole conduction layer, and an anode layer, wherein the hole transport material is MoO3, PTB7-Th, spiro-OMeTAD, Poly-TPD, or PBDT-T.

[0003] Specification of Chinese Patent No. 108767112

[0004] However, the solar cell disclosed in Patent Document 1 has low conversion efficiency.

[0005] Therefore, the object of the present invention is to provide a photoelectric conversion element that can achieve high conversion efficiency.

[0006] The photoelectric conversion element according to the present invention includes a hole transport layer, a light absorption layer, and an electron transport layer between a transparent conductive layer laminated on a transparent substrate and an upper electrode. The light absorption layer includes a first light absorption layer containing Ag, Bi, and halogen element X, and a second light absorption layer containing BiZ3 (where Z represents a halogen element). The second light absorption layer is laminated on at least one of the surfaces of the first light absorption layer on the transparent conductive layer side and the surface on the upper electrode side. When the molar ratio of Ag, Bi, and halogen element X contained in the first light absorption layer is x:y:z, then x:y:z = 1:1 / 3 to 3:2 to 10.

[0007] The photoelectric conversion element according to the present invention can achieve high conversion efficiency.

[0008] Figure 1 is a diagram illustrating the photoelectric conversion element according to Embodiment 1. Figure 2A is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2B is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2C is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2D is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2E is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2F is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 2G is a diagram illustrating the manufacturing method of the photoelectric conversion element according to Embodiment 1. Figure 3 is a diagram illustrating the photoelectric conversion element according to Embodiment 2. Figure 4 is a diagram illustrating a modified photoelectric conversion element. Figure 5A is a diagram showing the measurement results of the current-voltage characteristics of the photoelectric conversion element of Embodiment 1 four days after manufacturing. Figure 5B is a diagram showing the measurement results of the current-voltage characteristics of the photoelectric conversion element of Embodiment 1 thirteen days after manufacturing. Figure 6A is a diagram showing the measurement results of the current-voltage characteristics of the photoelectric conversion element of Comparative Example 1 four days after manufacturing. Figure 6B shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Comparative Example 1 13 days after fabrication. Figure 7A shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Example 2 4 days after fabrication. Figure 7B shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Example 2 13 days after fabrication. Figure 8A shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Comparative Example 2 4 days after fabrication. Figure 8B shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Comparative Example 2 13 days after fabrication. Figure 9 shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Example 3 47 days after fabrication. Figure 10 shows the measurement results of the current-voltage characteristics of the photoelectric conversion element of Comparative Example 3 47 days after fabrication.

[0009] Embodiments for carrying out the present invention will be described in detail below. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by those skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the present invention.

[0010] The photoelectric conversion element according to the present invention includes a hole transport layer, a light absorption layer, and an electron transport layer between a transparent conductive layer laminated on a transparent substrate and an upper electrode. The light absorption layer includes a first light absorption layer containing Ag, Bi, and halogen element X, and a second light absorption layer containing BiZ3 (where Z represents a halogen element). The second light absorption layer is laminated on at least one of the surfaces of the first light absorption layer on the transparent conductive layer side and the upper electrode side. When the molar ratio of Ag, Bi, and halogen element X contained in the first light absorption layer is x:y:z, then x:y:z = 1:1 / 3 to 3:2 to 10. In this specification, the "transparent conductive layer side" is also referred to as the "lower layer side," and the "upper electrode side" is also referred to as the "surface layer side." Such a photoelectric conversion element can achieve high conversion efficiency. This is due to the provision of a second light absorption layer containing BiZ3 on the lower layer side and / or the surface side of the first light absorption layer. In other words, it is thought that the BiZ3 contained in the second light absorption layer not only absorbs incident light and generates carriers, but also plays a role in preventing the recombination of carriers generated in the first light absorption layer.

[0011] The embodiments of the photoelectric conversion element according to the present invention will be described in detail below.

[0012] <Photoelectric Conversion Element According to Embodiment 1> Figure 1 is a diagram illustrating the photoelectric conversion element according to Embodiment 1, and shows a cross-sectional view of the photoelectric conversion element according to Embodiment 1. The photoelectric conversion element 1 has a transparent conductive layer 12, a hole transport layer 13, a light absorption layer 14, an electron transport layer 15, and an upper electrode 16 stacked in this order on a transparent substrate 11. Furthermore, it usually has a lower electrode 17 on the transparent conductive layer 12. The photoelectric conversion element 1 is an inverse structure type photoelectric conversion element that generates a voltage between the lower electrode 17 and the upper electrode 16 and outputs a current from the lower electrode 17 in response to light incident on it through the transparent substrate 11 and the transparent conductive layer 12.

[0013] The transparent substrate 11 is capable of supporting the components included in the photoelectric conversion element 1 and is formed of a transparent material (for example, insulating glass) that transmits incident light incident on the photoelectric conversion element 1, with light absorbed by the light absorption layer 14 incident on one side. The transparent material is a material that transmits light of wavelengths absorbed by the light absorption layer 14, preferably a material with a transmittance of 80% or more of light in the wavelength range absorbed by the light absorption layer 14, and more preferably a material with a transmittance of 95% or more of light in the wavelength range absorbed by the light absorption layer 14. The transparent substrate 11 may be formed of a conductive material, or of a flexible synthetic resin such as polyimide, polyethylene naphthalate (PEN), or polyethylene terephthalate (PET). The transparent substrate 11 has a thickness of, for example, 0.1 mm or more and 5.0 mm or less. The transparent substrate 11 may have a flat plate shape, a film-like flat plate shape, or a cylindrical flat plate shape.

[0014] The transparent conductive layer 12 is formed from a material that is transparent like the transparent substrate 11 and has low resistance, capable of efficiently transporting holes. It is formed on the transparent substrate 11 so as to cover it, and is positioned so that one side of the transparent conductive layer 12 faces the other side of the transparent substrate 11. The transparent conductive layer 12 is, for example, a thin film formed from tin-doped indium oxide (ITO), which has a smooth surface, is very transparent, and has high conductivity. When the transparent substrate 11 is formed from a material with low heat resistance, such as polyimide, the transparent conductive layer 12 is formed from a material that can be formed by low-temperature heat treatment, is transparent, and has high conductivity. Examples of materials that can be formed by low-temperature heat treatment, are transparent, and have high conductivity include aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), and niobium-doped titanium oxide (TNO). Alternatively, fluorine-doped tin oxide (FTO), which shows little change in resistivity due to high-temperature heat treatment, may be used. The transparent conductive layer 12 preferably has a thickness of 0.01 μm or more and 10.0 μm or less, and more preferably has a thickness of 0.05 μm or more and 1.0 μm or less.

[0015] The hole transport layer 13 is a p-type semiconductor layer that blocks electrons generated in the light absorption layer 14 and efficiently transports holes generated in the light absorption layer 14 to the transparent conductive layer 12. The hole transport layer 13 is formed on the transparent conductive layer 12 so as to cover it, and is positioned so that one side faces the other side of the transparent conductive layer 12. The hole transport layer 13 is made of a transparent hole transport material with high hole transport properties, such as nickel oxide (NiO2). x It is formed from ). In addition, oxides such as cuprous oxide (Cu2O), copper oxide (CuO), molybdenum oxide (MoO3), and CuSCN may be used as hole transport materials. Furthermore, as hole transport materials, organic materials such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) composites (PEDOT:PSS), which are poorly soluble in the solvent used when forming the light absorption layer 14, may be used.

[0016] Nickel oxide (NiO x ) in NiOx (0 < x ≤ 2) is a p-type semiconductor with stable chemical properties, and Ni vacancies function as acceptors without the addition of impurities, making it suitable for use as a material for the hole transport layer 13. Nickel oxide with Zn added (NiO:Zn) can be modified by adding impurities to NiO x The resistivity becomes lower than (0 < x ≤ 2), and the hole transport characteristics improve. The Ni:Zn content ratio Ni:Zn is preferably 99 at% to 80 at%:1 at% to 20 at%. If the Zn content is higher than 20 at%, the conversion efficiency of the photoelectric conversion element 1 may decrease. If the Zn addition ratio is lower than 1 at%, the hole transport characteristics may not improve even with the addition of Zn. The hole transport layer 13 preferably has a film thickness of 10 nm to 300 nm. If the film thickness of the hole transport layer 13 is less than 10 nm, the light absorption layer 14 may not be sufficiently covered by the hole transport layer 13. If the film thickness of the hole transport layer 13 is thicker than 300 nm, the resistance between the transparent conductive layer 12 and the light absorption layer 14 increases, which may decrease the conversion efficiency of the photoelectric conversion element 1.

[0017] The light-absorbing layer 14 includes a first light-absorbing layer 141 and a second light-absorbing layer 142. The second light-absorbing layer 142 is laminated on the upper electrode 16 side (the surface side of the first light-absorbing layer 141) of the first light-absorbing layer 141. That is, the first light-absorbing layer 141 is formed on the hole transport layer 13 so as to cover it, and is positioned so that one side faces the other side of the hole transport layer 13. The second light-absorbing layer 142 is formed on the first light-absorbing layer 141 so as to cover it, and is positioned so that one side faces the other side of the first light-absorbing layer 141. The first light-absorbing layer 141 and the second light-absorbing layer 142 absorb light incident through the transparent conductive layer 12 and the hole transport layer 13, and electrons are excited by the absorbed light, generating electrons and holes inside. Holes generated inside the first light absorption layer 141 and the second light absorption layer 142 are transported to the lower electrode 17 via the hole transport layer 13 and the transparent conductive layer 12. Electrons generated inside the first light absorption layer 141 and the second light absorption layer 142 are transported to the upper electrode 16 via the electron transport layer 15. As holes generated inside the first light absorption layer 141 and the second light absorption layer 142 are transported to the lower electrode 17, and electrons generated inside the first light absorption layer 141 and the second light absorption layer 142 are transported to the upper electrode 16, the photoelectric conversion element 1 obtains an electromotive force.

[0018] The first light-absorbing layer 141 contains metallic elements Ag (silver) and Bi (bismuth) and a halogen element X. Examples of halogen element X include F (fluorine), Cl (chlorine), Br (bromine), and I (iodine), with I being preferred. Halogen element X may be used alone or in combination of two or more. For example, using I and Br is also preferable. Furthermore, when the molar ratio of Ag, Bi, and halogen element X contained in the first light-absorbing layer 141 is x:y:z, then x:y:z = 1:1 / 3 to 3:2 to 10. In other words, for Ag, Bi, and halogen element X contained in the first light-absorbing layer 141, the molar ratio of Bi to Ag (Bi / Ag) is 1 / 3 or more and 3 or less, and the molar ratio of halogen element X to Ag (halogen element X / Ag) is 2 or more and 10 or less. When two or more halogen elements X are used, the above molar ratio is a value obtained from the total number of moles of the two or more halogen elements X. Specifically, the first light absorption layer 141 may be composed of one type of compound containing Ag, Bi, and halogen element X. Alternatively, the first light absorption layer 141 may be composed of two or more types of compounds containing Ag, Bi, and elements selected from halogen element X, as long as they contain Ag, Bi, and halogen element X. Examples of compounds containing elements selected from Ag, Bi, and halogen element X include Ag2BiI5, AgBi2I7, and AgBi 2.25 I 7.75 These are some examples.

[0019] The second light-absorbing layer 142 contains BiZ3 (where Z represents a halogen element). Examples of halogen elements include F, Cl, Br, and I, with Br and I being preferred. In other words, the second light-absorbing layer 142 preferably contains BiI3 or BiBr3. BiX3 may be used alone or in combination of two or more types. Providing such a second light-absorbing layer 142 on the surface side of the first light-absorbing layer 141 can increase the conversion efficiency of the photoelectric conversion element 1. This is because the BiZ3 contained in the second light-absorbing layer 142 not only absorbs incident light and generates carriers, but also contributes to carrier generation in the first light-absorbing layer 141, and further plays a role in preventing the recombination of carriers generated in the first light-absorbing layer 141. In addition, the second light-absorbing layer 142 on the surface side also exhibits a passivation effect, which has the advantage of suppressing the degradation of the first light-absorbing layer 141. Note that X and Z may be the same halogen element or different halogen elements.

[0020] The first light-absorbing layer 141 preferably has a thickness of 10 nm to 10,000 nm, and more preferably has a thickness of 20 nm to 900 nm. The second light-absorbing layer 142 preferably has a thickness of 1 nm to 500 nm.

[0021] The electron transport layer 15 is an n-type semiconductor layer that blocks holes generated in the light absorption layer 14 and efficiently transports electrons generated in the light absorption layer 14 to the upper electrode 16. The electron transport layer 15 is formed on the second light absorption layer 142 so as to cover the second light absorption layer 142, and is positioned so that one side faces the other side of the second light absorption layer 142. The electron transport layer 15 is preferably formed from an electron transport material with high electron transport properties. Examples of electron transport materials include metal oxides such as titanium oxide (TiO2, etc.), tin oxide (SnO2, etc.), zinc oxide (ZnO), and aluminum oxide (Al2O3), and fullerene (C 60 ) and phenyl-C 61Examples include C-based semiconductors such as methyl butyrate (PCBM), and 2,2'-[[6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2',3'-d']-s-indaseno[1,2-b:5,6-b']dithiophene-2,8-diyl]bis[methylidine(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis[propanedinitrile] (ITIC). The electron transport material may be used alone or in combination of two or more. The electron transport layer 15 preferably has a thickness of 1 nm to 700 nm, and more preferably has a thickness of 2 nm to 60 nm.

[0022] The upper electrode 16 and lower electrode 17 may be constructed, for example, by laminating a Ti layer containing Ti (titanium) and an Au layer containing Au (gold) in that order from the electron transport layer 15 side and the transparent conductive layer 12 side, respectively. Alternatively, they may be constructed by laminating a Bi layer containing Bi (bismuth), a Ti layer containing Ti or a Cr layer containing Cr (chromium), and an Au layer containing Au in that order. Furthermore, the upper electrode 16 and lower electrode 17 may be formed from metals such as Ag, Al (aluminum), and Zn (zinc), and carbon-based electrodes such as graphite. The upper electrode 16 and lower electrode 17 may be formed as a single metal layer of any of Ti, Ag, Al, Au, and Zn, but oxidation by oxygen in the atmosphere can be prevented by further depositing a film of Au and Pt (platinum), which are difficult to oxidize. Furthermore, the upper electrode 16 and lower electrode 17 may be formed from a highly conductive transparent conductive film such as ITO.

[0023] Furthermore, the upper electrode 16 and the lower electrode 17 may each include a contact layer (not shown) on the electron transport layer 15 side and the transparent conductive layer 12 side, respectively. Bathocuproine (BCP) is preferably used as the material for forming the contact layer. The contact layer preferably has a thickness of 0.2 nm to 5 nm. The upper electrode 16 and the lower electrode 17 preferably have an overall thickness of 2 nm to 200 nm.

[0024] The photoelectric conversion element according to Embodiment 1 can be manufactured, for example, as described below. FIGS. 2A to 2G are diagrams for explaining the method for manufacturing the photoelectric conversion element according to Embodiment 1. In the transparent conductive layer film formation step shown in FIG. 2A, the transparent conductive layer 12 is formed, for example, on a transparent substrate 11 having a planar shape. The transparent conductive layer 12 is formed by a film formation method such as a vacuum deposition method, a sputtering method, a CVD method or a plating method, for example.

[0025] In the hole transport layer film formation step shown in FIG. 2B, the hole transport layer 13 is formed on the surface of the transparent conductive layer 12. The hole transport layer 13 is formed by a film formation method such as a vacuum deposition method, a sputtering method, a CVD method or a plating method, for example. The film formation can be performed by arranging a metal mask having an opening corresponding to the shape of the hole transport layer 13. Alternatively, the film formation may be performed by a photoresist process.

[0026] In the first light absorption layer film formation step shown in FIG. 2C, the first light absorption layer 141 is formed. The first light absorption layer 141 is formed, for example, by a spin coating method so as to cover the transparent conductive layer 12 and the hole transport layer 13 exposed on the surface. In the first light absorption layer film formation step, a precursor-containing solution of the first light absorption layer 141 is applied onto the hole transport layer 13 by spin coating, and the applied substrate is heated, dried and fired. In this way, the solvent is volatilized to form the first light absorption layer 141. As shown in FIG. 2D, in the second light absorption layer film formation step, a BiZ₃ layer that is the second light absorption layer 142 is formed on the first light absorption layer 141. The BiZ₃ layer is formed on the first light absorption layer 141, for example, by a vacuum deposition method or a liquid phase coating (spin coating method). The film formation can be performed by arranging a metal mask having an opening corresponding to the shape of the BiZ₃ layer.

[0027] In the electron transport layer film formation step shown in FIG. 2E, the electron transport layer 15 is formed. The electron transport layer 15 is formed, for example, by a spin coating method so as to cover the first light absorption layer 141 and the second light absorption layer exposed on the surface. In the electron transport layer film formation step, an electron transport layer solution in which an electron transport material is dissolved in an organic solvent is applied onto the first light absorption layer 141 and the second light absorption layer 142 by spin coating. Next, the applied electron transport layer solution is dried and the solvent is volatilized, whereby the electron transport layer 15 is formed.

[0028] In the forming layer removal step shown in FIG. 2F, a part of the formed first light absorption layer 141 and electron transport layer 15 is removed. Portions other than the region corresponding to the patterned hole transport layer 13 are removed with a solvent. By removing portions other than the region where the hole transport layer 13 is formed, the transparent conductive layer 12 is exposed.

[0029] In the electrode film formation step shown in FIG. 2G, an upper electrode 16 and a lower electrode 17 are formed on the surface of the transparent conductive layer 12 and the surface of the electron transport layer 15. The upper electrode 16 and the lower electrode 17 are formed, for example, by vacuum vapor deposition. The film formation can be performed by arranging a metal mask having openings corresponding to the shapes of the upper electrode 16 and the lower electrode 17. Through the above steps, the photoelectric conversion element 1 can be manufactured.

[0030] <Photoelectric Conversion Element According to Embodiment 2> FIG. 3 is a diagram for explaining the photoelectric conversion element according to Embodiment 2, and shows a cross-sectional view of the photoelectric conversion element according to Embodiment 2. In the photoelectric conversion element 2, a transparent conductive layer 22, an electron transport layer 23, a light absorption layer 24, a hole transport layer 25, and an upper electrode 26 are stacked in this order on a transparent substrate 21. Here, the light absorption layer 24 includes a first light absorption layer 241 and a second light absorption layer 242. The second light absorption layer 242 is stacked on the upper electrode 26 side (surface layer side) of the first light absorption layer 241. Furthermore, a lower electrode 27 is usually provided on the transparent conductive layer 22. The photoelectric conversion element 2 is a forward-structure photoelectric conversion element. The photoelectric conversion element according to Embodiment 2 (photoelectric conversion element 2) differs from the photoelectric conversion element according to Embodiment 1 (photoelectric conversion element 1) in the arrangement of the electron transport layer and the hole transport layer, as well as the preferred materials and preferred thicknesses constituting these layers. Otherwise, the details of the transparent substrate 21, transparent conductive layer 22, light absorption layer 24, upper electrode 26, and lower electrode 27 in the photoelectric conversion element 2 are the same as those of the transparent substrate 11, transparent conductive layer 12, light absorption layer 14, upper electrode 16, and lower electrode 17 in the photoelectric conversion element 1. Differences between the photoelectric conversion element 2 and the photoelectric conversion element 1 will be described below. Descriptions of features that the photoelectric conversion element 2 shares with the photoelectric conversion element 1 will be omitted.

[0031] The electron transport layer 23 is an n-type semiconductor layer that blocks holes generated in the light absorption layer 24 and extracts electrons generated in the light absorption layer 24, transporting them to the transparent conductive layer 22 with high efficiency. The electron transport layer 23 is formed on the transparent conductive layer 22 so as to cover it, and is positioned so that one side of the electron transport layer 23 faces the other side of the transparent conductive layer 22. In the photoelectric conversion element 2, the first light absorption layer 241 is formed on the electron transport layer 23 so as to cover it, and is positioned so that one side of the electron transport layer 23 faces the other side of the electron transport layer 23.

[0032] The electron transport layer 23 is preferably a transparent and dense electron transport layer, and is formed from, for example, titanium oxide (TiO2, etc.), tungsten oxide (WO2, WO3, W2O3, etc.), zinc oxide (ZnO), strontium titanate (SrTiO3, etc.), aluminum oxide (Al2O3), tin oxide (SnO2), etc.

[0033] Furthermore, it is preferable that the electron transport layer 23 is a light-transmitting porous electron transport layer. The porous electron transport layer has a porous structure. The porous structure is not particularly limited, but it is preferable that granular bodies, linear bodies, etc., are aggregated to have a porous property as a whole. Here, examples of linear bodies include needle-shaped, tubular, columnar, etc. Furthermore, it is preferable that the pore size of the porous structure is on the nanoscale. The pores of the porous electron transport layer may contain materials that constitute the light-absorbing layer 24. The porous electron transport layer is formed from, for example, titanium oxide (TiO2, etc.), 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.), tin oxide (SnO2), etc.

[0034] Furthermore, the electron transport layer 23 may include the dense electron transport layer and the porous electron transport layer described above. Specifically, the electron transport layer 23 may have a two-layer structure in which the dense electron transport layer and the porous electron transport layer described above are laminated in that order on the transparent conductive layer 22.

[0035] The thickness of the electron transport layer 23 is not particularly limited, but it is preferable that it has a thickness of 1 nm to 500 nm.

[0036] The hole transport layer 25 is a p-type semiconductor layer that blocks electrons generated in the light absorption layer 24 and efficiently transports holes generated in the light absorption layer 24 to the upper electrode 26. The hole transport layer 25 is deposited on the second light absorption layer 242 so as to cover it, and is positioned so that one side of the hole transport layer 25 faces the other side of the second light absorption layer 242. In the photoelectric conversion element 2, the upper electrode 26 is deposited on the hole transport layer 25, and is positioned so that one side of the upper electrode 26 faces the other side of the hole transport layer 25.

[0037] The hole transport layer 25 is formed from a hole transport material. Examples of hole transport materials include iodides such as selenium and copper iodide (CuI), cobalt complexes such as layered cobalt oxide, CuSCN, molybdenum oxide (MoO3, etc.), nickel oxide (NiO, etc.), 4CuBr·3S (C4H9), and organic hole transport materials. Examples of organic hole transport materials include polythiophene derivatives such as poly-3-hexylthiophene (P3HT) and polyethylenedioxythiophene (PEDOT), fluorene derivatives such as 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeO-TAD), carbazole derivatives such as polyvinylcarbazole, triphenylamine derivatives such as poly[bis(4-phenyl)(2,4,6-triphenylmethyl)amine](PTAA), diphenylamine derivatives, polysilane derivatives, and polyaniline derivatives. The hole transport layer 25 may optionally contain an organic binder and a plasticizer. The content of the hole transport material in the hole transport layer 25 is preferably 30% by mass or more and 100% by mass or less. The thickness of the hole transport layer 25 is not particularly limited, but it is preferably, for example, 0.01 μm or more and 10 μm or less.

[0038] In the photoelectric conversion element 2, the first light absorption layer 241 and the second light absorption layer 242 absorb light incident through the transparent conductive layer 22 and the electron transport layer 23. The absorbed light excites electrons, generating electrons and holes inside. Electrons generated inside the first light absorption layer 241 and the second light absorption layer 242 are transported to the lower electrode 27 via the electron transport layer 23. Holes generated inside the first light absorption layer 141 and the second light absorption layer 142 are transported to the upper electrode 26 via the hole transport layer 25. As electrons generated inside the first light absorption layer 241 and the second light absorption layer 242 are transported to the lower electrode 27, and holes generated inside the first light absorption layer 241 and the second light absorption layer 242 are transported to the upper electrode 26, the photoelectric conversion element 2 obtains an electromotive force.

[0039] In the photoelectric conversion element 2, the conversion efficiency is increased because a second light absorption layer 242 is provided on the surface side of the first light absorption layer 241. This is thought to be because, in the photoelectric conversion element 2, BiZ3 contained in the second light absorption layer 242 not only absorbs incident light and generates carriers, but also contributes to carrier generation in the first light absorption layer 241, and further plays a role in preventing the recombination of carriers generated in the first light absorption layer 241. In addition, the second light absorption layer 242 on the surface side also exhibits a passivation effect, which has the advantage of suppressing the degradation of the first light absorption layer 241.

[0040] The photoelectric conversion element according to Embodiment 2 can be manufactured in the same manner as the photoelectric conversion element according to Embodiment 1. However, the manufacturing process is carried out in the following order: transparent conductive layer deposition, electron transport layer deposition, first light absorption layer deposition, second light absorption layer deposition, hole transport layer deposition, formation layer removal, and electrode deposition.

[0041] <Modification> In the photoelectric conversion elements of Embodiments 1 and 2, the second light-absorbing layer is laminated on the upper electrode side (surface side) of the first light-absorbing layer. Alternatively, the second light-absorbing layer may be laminated on the transparent conductive layer side (lower layer side) of the first light-absorbing layer. Furthermore, the second light-absorbing layer may be laminated on both the upper electrode side (surface side) and the transparent conductive layer side (lower layer side) of the first light-absorbing layer. Even in such photoelectric conversion elements, the conversion efficiency can be increased. This is thought to be because, even when the second light-absorbing layer is laminated on the lower layer side, the BiZ3 contained in the second light-absorbing layer not only absorbs incident light and generates carriers, but also plays a role in preventing the recombination of carriers generated in the first light-absorbing layer. In addition, the second light-absorbing layer laminated on the lower layer side can also suppress the degradation of the first light-absorbing layer.

[0042] Figure 4 is a diagram illustrating a modified photoelectric element and shows a cross-sectional view of the modified photoelectric element. In the modified photoelectric element (photoelectric element 1'), a coating film 18 is provided on the upper electrode 16 compared to the photoelectric element (photoelectric element 1) according to Embodiment 1. The coating film is preferably made of an insulator. Examples of the insulator include organic materials such as epoxy resin and parylene (registered trademark, paraxylylene polymer), and inorganic materials such as SiO2. In addition, in the photoelectric element (photoelectric element 2) according to Embodiment 2, a coating film may also be provided on the upper electrode. Providing a coating film in this way has the advantage of improving the durability of the photoelectric element.

[0043] <Solar Cells> The solar cell includes the photoelectric conversion element described above as a solar cell element. The solar cell has high conversion efficiency and can be used stably for a long period of time. Furthermore, the solar cell is suitably used in portable devices.Specific examples of portable devices include wristwatches, pocket watches, gyro sensors, barometric pressure sensors, hearing aids, handheld GPS devices; digital cameras, video cameras, portable music players, IC recorders, portable video players, pocket computers, calculators, portable game consoles, laptop computers, PDAs, smartphones, portable printers, portable scanners, portable modems, electronic dictionaries and other information devices; and mobile phones, satellite phones, pagers, portable radios, portable televisions, one-segment TVs, IC cards with built-in processors, RFID tags and other communication devices.The solar cell and portable devices containing it can be manufactured by known methods using the photoelectric conversion element described above as a solar cell element.

[0044] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0045] [Examples] [Example 1] A photoelectric conversion element 1 shown in Figure 1 was fabricated by the process shown in Figures 2A to 2G. First, an ITO glass substrate having a planar shape of 25 mm × 25 mm and a transparent conductive layer 12 deposited on a transparent substrate 11 was prepared (Figure 2A, transparent conductive layer deposition process). The prepared ITO glass substrate was then UV ozone cleaned. Here, the thickness of the glass substrate corresponding to the transparent substrate 11 was 1 mm, and the thickness of the ITO film corresponding to the transparent conductive layer 12 was 0.2 μm.

[0046] Next, a NiO:Zn layer corresponding to the hole transport layer 13 is formed on the surface of the ITO film deposited on the ITO glass substrate by heating with an EB-gun via a vacuum deposition method using EX-200 manufactured by ULVAC, Inc. (FIG. 2B, hole transport layer deposition step). The material used for forming the hole transport layer 13 was prepared by adjusting NiO powder with ZnO powder such that the ratio of Ni:Zn is 90:10, mixing the mixture in a mortar, press-molding, and firing the mixture to obtain a tablet. The ITO glass substrate on which the transparent conductive layer 12 has been formed is placed on a metal mask having a hole of 25 mm×15 mm, the NiO:Zn of the tablet is filled into a water-cooled hearth, and 4×10 -5 The inside of the vacuum chamber was evacuated to Torr or lower. Next, after degassing the NiO:Zn sample and heating the NiO:Zn sample with an EB-gun, the shutter was opened, and evaporated particles evaporated from the NiO:Zn sample were deposited on the surface of the transparent conductive layer 12. The film thickness of the formed NiO:Zn layer was 30 nm.

[0047] Next, an AgBi₂I₇ film corresponding to the first light absorbing layer 141 was formed on the surface of the hole transport layer 13 by a spin coating method (FIG. 2C, first light absorbing layer deposition step). The film was formed so as to cover the transparent conductive layer 12 and the hole transport layer 13 exposed on the surface. The precursor-containing solution was prepared by placing AgI and BiI₃ in a container, adding DMSO to the container holding AgI and BiI₃, and dissolving them. AgI and BiI₃ placed in the container were adjusted such that the molar ratio of Ag:Bi:I in the precursor-containing solution was 1:2:7. The rotation speed in spin coating was 4000 rpm, and the coating time of the precursor-containing solution was 30 seconds. The ITO glass substrate coated with the precursor-containing solution was provisionally dried at a temperature of 70° C. for 4 minutes, and then fired at a temperature of 90° C. for 1 hour to form the AgBi₂I₇ film corresponding to the first light absorbing layer 141. The film thickness of the formed AgBi₂I₇ film was 400 nm.

[0048] Next, a BiI3 film corresponding to the second light absorption layer 142 was deposited on the surface of the first light absorption layer 141 by vacuum deposition using an EX-200 manufactured by ULVAC, Inc., and heated with an EB-gun (Figure 2D, second light absorption layer deposition process). The material used to deposit the second light absorption layer 142 is BiI3 powder. First, the ITO glass substrate on which the first light absorption layer 141 was deposited was placed on a metal mask with 25 mm x 15 mm holes, and BiI3 powder was filled into a water-cooled hearth, and 4 x 10 -5 The inside of the vacuum chamber was evacuated to below Torr. Next, gas was removed from the BiI3 powder, and the BiI3 powder was heated with an EB gun. Then, the shutter was opened, and the evaporated particles from the BiI3 powder were deposited onto the surface of the first light absorption layer 141. The thickness of the deposited BiI3 layer was 1 nm.

[0049] Next, ITIC and C corresponding to the electron transport layer 15 60 Layers including (ITIC+C 60 The second light absorption layer 142 was deposited on the surface of the second light absorption layer 142 by spin coating (Figure 2E, electron transport layer deposition process). The film was deposited so as to cover the first light absorption layer 141 and the second light absorption layer 142 that were exposed on the surface. ITIC and C 60 A precursor-containing solution was used. The spin-coating speed was 4000 rpm, and the coating time for the precursor-containing solution was 30 seconds. The ITO glass substrate coated with the precursor-containing solution was dried, and the ITIC+C corresponding to the electron transport layer 15 was applied. 60 A layer was deposited. The deposited ITIC+C 60 The thickness of the layer was 20 nm.

[0050] Next, the region where the hole transport layer 13 was formed was restricted with a metal mask, and the portions of the first light absorption layer 141 and the electron transport layer 15 exposed from the mask were removed by DMF (Figure 2F, formed layer removal process).

[0051] Next, a contact layer / Bi layer / Cr layer / Au layer corresponding to the upper electrode 16 and lower electrode 17 was formed (Figure 2G, electrode deposition process). The BCP layer corresponding to the contact layer was deposited on the surface of the transparent conductive layer 12 and electron transport layer 15 by vacuum deposition using an EX-200 manufactured by ULVAC, Inc., and heated with an EB-gun. The material used for depositing the contact layer was BCP powder. The ITO glass substrate on which the electron transport layer 15 was deposited was placed on a metal mask with holes so that the desired electrodes could be formed, and BCP powder was filled into a water-cooled hearth, 4 × 10 -5 The inside of the vacuum chamber was evacuated to below Torr. Next, gas was released from the BCP powder, and after heating the BCP powder with an EB gun, the shutter was opened, and the evaporated particles from the BCP powder were deposited onto the surfaces of the transparent conductive layer 12 and the electron transport layer 15. The thickness of the deposited contact layer was 0.2 nm. Next, the Bi layer / Cr layer / Au layer was deposited on the surface of the contact layer by a vacuum deposition method using an EX-200 manufactured by ULVAC, Inc., and heated with an EB gun. Here, the ITO glass substrate with the deposited contact layer was placed on the same metal mask used during the deposition of the contact layer. As an evaporation source, Bi with a diameter of 1 mm to 2 mm was filled into a water-cooled hearth, and 4 × 10 -5 After exhausting to below Torr, the material was degassed, heated with an EB gun, and then the shutter was opened to perform deposition so that the Bi layer thickness was 10 nm. Next, once the water-cooled hearth containing Bi had cooled sufficiently, a rotating mechanism was used to switch to a water-cooled hearth filled with Cr having a diameter of 1 mm to 2 mm, and 4 × 10 -5 After exhausting to below Torr, the material was degassed, heated with an EB-gun, and then the shutter was opened to perform deposition so that the Cr layer thickness was 2 nm. Next, once the water-cooled hearth containing Cr had cooled sufficiently, a rotating mechanism was used to switch to a water-cooled hearth filled with Au having a diameter of 1 mm to 2 mm, and 4 × 10 -5 We confirmed that the exhaust gas was below Torr. Next, we vented the gas from the material, heated it with an EB gun, opened the shutter, and performed deposition so that the Au layer thickness was 60 nm.

[0052] [Comparative Example 1] In Comparative Example 1, a photoelectric conversion element was fabricated in the same manner as in Example 1, except that only a first light absorption layer was formed as the light absorption layer, and a second light absorption layer was not formed.

[0053] [Example 2] In the first light absorption layer deposition process shown in Figure 2C, instead of the AgBi2I7 film corresponding to the first light absorption layer 141, AgBi2I 6.94 Br 0.06 A photoelectric conversion element 1 was fabricated in the same manner as in Example 1, except for the formation of a film. Specifically, the first light absorption layer deposition process shown in Figure 2C was carried out as follows: AgBi2I corresponding to the first light absorption layer 141 6.94 Br 0.06 The film was deposited on the surface of the hole transport layer 13 by spin coating. The film was deposited so as to cover the transparent conductive layer 12 and the hole transport layer 13 that were exposed on the surface. The precursor-containing solution was prepared by placing AgI, AgBr, and BiI3 in a container, and then adding DMSO to the container containing AgI, AgBr, and BiI3 and dissolving it. The AgI, AgBr, and BiI3 placed in the container were prepared so that the molar ratio of Ag:Bi:I:Br in the precursor-containing solution was 1:2:6.94:0.06. The spin coating speed was 4000 rpm, and the coating time for the precursor-containing solution was 30 seconds. The ITO glass substrate coated with the precursor-containing solution was pre-dried at 70°C for 4 minutes, and then fired at 90°C for 1 hour to produce AgBi2I corresponding to the first light absorption layer 141. 6.94 Br 0.06 A film was deposited. The deposited AgBi2I 6.94 Br 0.06 The film thickness was 400 nm.

[0054] [Comparative Example 2] In Comparative Example 2, the same procedure as in Example 2 was used, except that only the first light-absorbing layer was formed as the light-absorbing layer, and the second light-absorbing layer was not formed.

[0055] [Example 3] In the first light absorption layer deposition process shown in Figure 2C, instead of the AgBi2I7 film corresponding to the first light absorption layer 141, AgBi 2.25 I 7.75A photoelectric conversion element 1 was fabricated in the same manner as in Example 1, except that a film was formed and, in the second light absorption layer deposition process shown in Figure 2D, a BiBr3 film was formed instead of the BiI3 layer corresponding to the second light absorption layer 142. Specifically, the first light absorption layer deposition process shown in Figure 2C was carried out as follows: AgBi corresponding to the first light absorption layer 141 2.25 I 7.75 The film was deposited on the surface of the hole transport layer 13 by spin coating. The film was deposited so as to cover the transparent conductive layer 12 and the hole transport layer 13 that were exposed on the surface. The precursor-containing solution was prepared by placing AgI and BiI3 in a container, and then adding DMSO to the container containing the AgI and BiI3 and dissolving it. The AgI and BiI3 placed in the container were prepared so that the molar ratio of Ag:Bi:I in the precursor-containing solution was 1:2.25:7.75. The spin coating speed was 4000 rpm, and the coating time for the precursor-containing solution was 30 seconds. The ITO glass substrate coated with the precursor-containing solution was pre-dried at 70°C for 4 minutes, and then fired at 90°C for 1 hour to obtain the AgBi corresponding to the first light absorption layer 141. 2.25 I 7.75 A film was deposited. 2.25 I 7.75 The film thickness was 400 nm. Next, the second light absorption layer deposition process shown in Figure 2D was carried out as follows: A BiBr3 film corresponding to the second light absorption layer was deposited, and an AgBi film corresponding to the first light absorption layer 141 was deposited. 2.25 I 7.75 The film was deposited on the surface by spin coating. The precursor-containing solution was prepared by placing BiBr3 in a container and dissolving chlorobenzene in the container containing the BiBr3. The BiBr3 placed in the container was prepared so that its concentration in the precursor-containing solution was 0.2 mg / ml. The spinning speed during spin coating was 4000 rpm, and the coating time for the precursor-containing solution was 30 seconds. The material used for depositing the second light absorption layer 142 was BiBr3 powder, and the thickness of the deposited BiBr3 layer was 1 nm.

[0056] [Comparative Example 3] In Comparative Example 3, a solar cell element was fabricated in the same manner as in Example 3, except that only the first light-absorbing layer was formed as the light-absorbing layer, and the second light-absorbing layer was not formed.

[0057] <Evaluation Method and Results> The current-voltage characteristics under light irradiation were measured using the following method. From the time the photoelectric conversion element was fabricated until the measurement of the current-voltage characteristics, the photoelectric conversion element was stored at room temperature with a humidity of 50%. A BLD-100 manufactured by Spectrometer Co., Ltd. was used as the light source, and the illuminance was adjusted so that the incident light entering the photoelectric conversion element from the light source was 200 lx. The light emitted from the light source was adjusted to emit into a 2.5 mm x 2.5 mm area using a light-shielding mask, and the light source and photoelectric conversion element were positioned so that the light entered the photoelectric conversion element from the transparent substrate side of the photoelectric conversion element. The current-voltage characteristics were measured using a PECK2400-N manufactured by Pexel Technologies, Inc. Specifically, the voltage applied to the photoelectric conversion element was swept sequentially from the negative side to the positive side and measured (Forward measurement). Furthermore, the voltage applied to the photoelectric conversion element was swept sequentially from the positive side to the negative side and measured (Reverse measurement).

[0058] Figures 5A and 5B show the current-voltage characteristics measurement results for the photoelectric conversion element of Example 1, 4 days and 13 days after fabrication. Figures 6A and 6B show the current-voltage characteristics measurement results for the photoelectric conversion element of Comparative Example 1, 4 days and 13 days after fabrication. Figures 7A and 7B show the current-voltage characteristics measurement results for the photoelectric conversion element of Example 2, 4 days and 13 days after fabrication. Figures 8A and 8B show the current-voltage characteristics measurement results for the photoelectric conversion element of Comparative Example 2, 4 days and 13 days after fabrication. Figure 9 shows the current-voltage characteristics measurement results for the photoelectric conversion element of Example 3, 47 days after fabrication. Figure 10 shows the current-voltage characteristics measurement results for the photoelectric conversion element of Comparative Example 3, 47 days after fabrication. Note that Figures 5A to 8B, 9, and 10 are graphs that average the results of forward and reverse measurements. Furthermore, Figures 5A to 8B, 9, and 10 also show the conversion efficiency obtained from the measurement results of the current-voltage characteristics.

[0059] In Example 1, which used a laminate of the first light-absorbing layer, the AgBi2I7 film, and the second light-absorbing layer, the BiI3 film, a higher conversion efficiency was obtained compared to Comparative Example 1, which used only the AgBi2I7 film as the light-absorbing layer. In Example 2, which used the first light-absorbing layer in which part of I was replaced with Br, an improvement in conversion efficiency was also observed by using a laminate with the second light-absorbing layer, the BiI3 film. Furthermore, from the comparison between Figure 5A and Figure 5B and between Figure 7A and Figure 7B, it can be seen that the photoelectric conversion elements in Examples 1 and 2 can be used stably over a long period of time. In Example 3, which used the second light-absorbing layer in which I was replaced with Br, an improvement in conversion efficiency was also observed, similar to Examples 1 and 2.

[0060] Based on the above, the present invention relates to the following: [1] A photoelectric conversion element comprising a transparent conductive layer laminated on a transparent substrate and an upper electrode, wherein a hole transport layer, a light absorption layer, and an electron transport layer are included between the transparent conductive layer and the upper electrode, the light absorption layer comprising a first light absorption layer containing Ag, Bi, and halogen element X, and a second light absorption layer containing BiZ3 (where Z represents a halogen element), the second light absorption layer being laminated on at least one of the surfaces of the first light absorption layer on the transparent conductive layer side and the upper electrode side, and when the molar ratio of Ag, Bi, and halogen element X contained in the first light absorption layer is x:y:z, x:y:z = 1:1 / 3 to 3:2 to 10. [2] The photoelectric conversion element according to [1], wherein the second light absorption layer is laminated on the upper electrode side surface of the first light absorption layer.

[0061] 1, 1', 2: Photoelectric conversion element 11, 21: Transparent substrate 12, 22: Transparent conductive layer 13, 25: Hole transport layer 14, 24: Light absorption layer 141, 241: First light absorption layer 142, 242: Second light absorption layer 15, 23: Electron transport layer 16, 26: Upper electrode 17, 27: Lower electrode

Claims

1. A photoelectric conversion element comprising a transparent conductive layer laminated on a transparent substrate and an upper electrode, with a hole transport layer, a light absorption layer, and an electron transport layer between them, wherein the light absorption layer comprises a first light absorption layer containing Ag, Bi, and halogen element X, and a second light absorption layer containing BiZ3 (where Z represents a halogen element), the second light absorption layer is laminated on at least one of the surfaces of the first light absorption layer on the transparent conductive layer side and the upper electrode side, and when the molar ratio of Ag, Bi, and halogen element X contained in the first light absorption layer is x:y:z, x:y:z = 1:1 / 3 to 3:2 to 10.

2. The photoelectric conversion element according to claim 1, wherein the second light-absorbing layer is laminated on the upper electrode side surface of the first light-absorbing layer.

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