Photoelectric conversion element and power generation device

Abstract

To provide a photoelectric conversion element having high durability.SOLUTION: A photoelectric conversion element includes at least a pair of electrodes including an upper electrode and a lower electrode, an active layer that is disposed between the pair of electrode and contains an organic-inorganic hybrid semiconductor compound, and a buffer layer located between the active layer and the upper electrode or the lower electrode. At least one of the pair of electrodes includes at least a metal layer containing a metal belonging to Group 15 in the periodic table, and a first metal oxide layer disposed between the metal layer and the buffer layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion element and a power generation device.

Background Art

[0002] In a photoelectric conversion element, an active layer, a buffer layer, etc. are disposed between a pair of electrodes. In this active layer, the use of an organic-inorganic hybrid semiconductor material has attracted attention for high efficiency, and for example, the use of a perovskite-based compound has been studied. As the electrode, gold is often used, but since gold is expensive, the use of a metal other than gold, such as silver, has been studied in consideration of practicality.

[0003] When a halide-based organic-inorganic perovskite semiconductor compound is used in the active layer, it has been reported that a halide or a halogen element, such as iodide, diffuses through the electron transport layer or the hole transport layer and reaches the electrode. When silver is used as the electrode, silver reacts with iodide or the like that has diffused, and the electrode deteriorates, which may reduce the durability of the photoelectric conversion element. In addition, metal ions of the electrode may also diffuse through the electron transport layer or the hole transport layer over time and reach the active layer, causing a short circuit or a leak. In particular, silver ions are likely to move in the film.

[0004] In Patent Document 1, a technique is disclosed in which a metal oxide such as IZO is interposed between the active layer and the silver electrode to suppress the diffusion of halides and the like and improve the output characteristics and durability. In addition, Patent Document 2 discloses that an oxide such as ITO is also effective as a diffusion prevention layer for the electrode.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, especially in terms of power generation characteristics in low-light environments, which are important for energy harvesting applications, even a minute leak has a significant adverse effect on the power generation characteristics. For this reason, since the movement and diffusion of the metal electrode material pose a major problem in the durability performance of the photoelectric conversion element, there has been room for improvement in this regard.

[0007] In Patent Document 1 and Patent Document 2, a thin-film metal oxide is used as a diffusion prevention layer in order to suppress an increase in sheet resistance and reduce costs. However, in a low-light environment, since the amount of power generation is small, the limitation on the sheet resistance is relaxed. Instead, in order to improve durability, it is required to more reliably prevent the diffusion of metal ions in the electrode.

[0008] An object of the present invention is to provide a photoelectric conversion element having excellent durability. Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that by using a metal belonging to Group 15 of the periodic table as the metal layer constituting the electrode, it is possible to realize a photoelectric conversion element in which short circuits and leaks are suppressed during operation in a low-light environment, and have thus completed the present invention.

[0010] The present invention has the following aspects. [1] A photoelectric conversion element, The photoelectric conversion element includes at least a pair of electrodes having an upper electrode and a lower electrode, an active layer disposed between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound, and a buffer layer positioned between the active layer and the upper electrode or the lower electrode. A photoelectric conversion element, wherein at least one of the pair of electrodes has at least a metal layer containing a metal belonging to Group 15 of the periodic table and a first metal oxide layer disposed between the metal layer and the buffer layer. [2] The photoelectric conversion element according to [1], wherein the first metal oxide layer contains at least one selected from the group consisting of indium oxide, zinc oxide, tin oxide, indium tin oxide, fluorinated tin oxide, and indium zinc oxide. [3] The photoelectric conversion element according to [1] or [2], wherein the electrode having the metal layer and the first metal oxide layer further has a second metal oxide layer between the buffer layer and the first metal oxide layer. [4] The photoelectric conversion element according to [3], wherein the second metal oxide layer contains at least one selected from the group consisting of molybdenum oxide, vanadium oxide, and tungsten oxide. [5] The photoelectric conversion element according to any one of [1] to [4], wherein the buffer layer includes a hole transport layer. [6] The photoelectric conversion element according to any one of [1] to [5], wherein the organic-inorganic hybrid semiconductor compound includes a compound having a perovskite structure. [7] The photoelectric conversion element according to any one of [1] to [6], which is for an illumination environment. [8] A power generation device having the photoelectric conversion element according to any one of [1] to [7].

Advantages of the Invention

[0011] According to the present invention, a photoelectric conversion element excellent in durability is provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, these descriptions are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these contents unless it exceeds the gist thereof. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, and "A~B" means A or more and B or less.

[0014] [Photoelectric conversion element] A photoelectric conversion element according to an embodiment of the present invention (hereinafter, also simply referred to as "photoelectric conversion element") includes a pair of electrodes having a partial electrode and a lower electrode, an active layer disposed between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound, and a buffer layer located between the active layer and the upper electrode or the lower electrode. And at least one of the pair of electrodes has at least a metal layer containing a metal belonging to Group 15 of the periodic table and a first metal oxide layer disposed between the metal layer and the buffer layer.

[0015] In a conventional photoelectric conversion element, ions of the metal constituting the electrode may move to the buffer layer adjacent to the electrode, causing a short circuit or leakage. In particular, when silver is contained in the electrode, silver ions (silver + ) are likely to move in the film, so that a short circuit or leakage is likely to occur.

[0016] As a means for solving such problems, the present inventors have found that by adopting that at least one of the pair of electrodes has at least a metal layer containing a metal belonging to Group 15 of the periodic table and a first metal oxide layer disposed between the metal layer and the buffer layer, it is possible to suppress short circuits and leakage between the electrodes and improve durability.

[0017] Furthermore, by providing a second metal oxide layer between the buffer layer and the first metal oxide layer, good initial characteristics can be obtained. Specifically, when the second metal oxide layer covers the buffer layer, the buffer layer is protected from process damage during the formation of the first metal oxide layer, resulting in a high energy conversion efficiency (PCE). Also, usually, for the second metal oxide layer, which tends to have a high resistance and is difficult to thicken, a metal ion component M n+ (n is usually a natural number of 1, 2, or 3) that can cause short circuits or leaks by moving through the film while ensuring high conductivity is less likely to occur in the first metal oxide layer with a composition having a thickness of a specific value or more, thereby further improving the effect of suppressing short circuits and leaks, particularly the durability in a low-illumination environment. n+ (n is usually a natural number of 1, 2, or 3) By setting the thickness of the first metal oxide layer with a composition that is less likely to cause short circuits and leaks to a specific value or more, the effect of suppressing short circuits and leaks, particularly the durability in a low-illumination environment, can be further improved.

[0018] Hereinafter, each component of the photoelectric conversion element will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing an embodiment of the photoelectric conversion element. The photoelectric conversion element shown in FIG. 1 is a photoelectric conversion element used in a general thin-film solar cell, but the photoelectric conversion element according to the present invention is not limited to the one shown in FIG. 1.

[0019] In the photoelectric conversion element 100 shown in FIG. 1, a lower electrode 101, an active layer 103, and an upper electrode 108 are arranged in this order. Also, the photoelectric conversion element 100 has a buffer layer 102 existing between the lower electrode 101 and the active layer 103, and a buffer layer 104 existing between the upper electrode 108 and the active layer 103. At least one of these buffer layers 102 and buffer layer 104 is a hole transport layer.

[0020] The upper electrode 108 has a first metal oxide layer 106 and a metal layer 107. There may be a second metal oxide layer 105 between the buffer layer 104 and the first metal oxide layer 106. Further, as shown in FIG. 1, the photoelectric conversion element 100 may have a substrate 109 and may also have other layers such as an insulator layer and a work function tuning layer. Further, as shown in the examples described later, there may be an interface modification layer for repairing interface defects and energy level alignment between the active layer 103 and the buffer layer 104.

[0021] (Electrode) The electrode has a function of collecting holes and electrons generated by light absorption in the active layer 103. The photoelectric conversion element has a pair of electrodes, and at least one of the pair of electrodes has at least a metal layer containing a metal belonging to Group 15 of the periodic table as the metal constituting the electrode and a first metal oxide layer disposed between the metal layer and the buffer layer. The electrode may consist only of these layers or may have layers other than these layers. Hereinafter, an electrode including a metal layer and a first metal oxide layer is also referred to as a "specific electrode".

[0022] For the photoelectric conversion element 100, it is sufficient that at least one of the pair of electrodes is a specific electrode, and both electrodes may be specific electrodes. Specifically, the specific electrode may be disposed on the buffer layer side as a hole transport layer or on the buffer layer side as an electron transport layer when viewed from the active layer. In particular, when a non-transparent electrode that reflects light is used for the counter electrode located on the hole transport layer side, metal ions that can move in the film tend to be easily generated, so it is preferably disposed on the hole transport layer side.

[0023] It is preferable to have a second metal oxide layer between the buffer layer and the first metal oxide layer. By having the second metal oxide layer, the buffer layer is protected from process damage when forming the first metal oxide layer, and good initial characteristics can be obtained. Hereinafter, an electrode including a metal layer, a first metal oxide layer, and a second metal oxide layer may also be referred to as a "specific electrode".

[0024] In this specification, for convenience of explanation, one of a pair of electrodes is referred to as the upper electrode, and the other is also referred to as the lower electrode. When the photoelectric conversion element has a substrate or is provided on a substrate, the electrode closer to the substrate can be referred to as the lower electrode, and the electrode farther from the substrate can be referred to as the upper electrode, respectively. Also, the transparent electrode can be referred to as the lower electrode, and the electrode having lower transparency than the lower electrode can be referred to as the upper electrode, respectively. FIG. 1 shows a photoelectric conversion element 100 in which the upper electrode 108 is a specific electrode and the lower electrode is not a specific electrode, and the explanation will proceed along this configuration.

[0025] As a pair of electrodes, an anode suitable for hole collection and a cathode suitable for electron collection can be used. In this case, the photoelectric conversion element 100 may have a normal configuration in which the lower electrode 101 is an anode and the upper electrode 108 is a cathode, or may have an inverted configuration in which the lower electrode 101 is a cathode and the upper electrode 108 is an anode.

[0026] One of the pair of electrodes only needs to be translucent, and both may be translucent. Having translucency means that sunlight transmits 40% or more. Also, it is preferable that the sunlight transmittance of the transparent electrode is 70% or more so that more light can pass through the transparent electrode and reach the active layer 103. The light transmittance can be measured with a spectrophotometer (for example, U-4100 manufactured by Hitachi High-Tech Corporation).

[0027] Hereinafter, the configuration of the specific electrode will be specifically described. However, when the specific electrode is not adopted as one of the pair of electrodes, the mode of that electrode and its manufacturing method are not particularly limited, and well-known techniques can be used. For example, the members and their manufacturing methods described in known documents such as International Publication No. 2013 / 171517, International Publication No. 2013 / 180230, or Japanese Patent Application Laid-Open No. 2012-191194 can be used, and also the metal layers described below can be used.

[0028] The thickness of the specific electrode is not particularly limited, but metal ions M that can easily move in the film and can induce short circuits or leaks n+From the perspective of suppressing the movement of (n is usually a natural number of 1, 2, or 3), it is usually 80 nm or more, preferably 150 nm or more, more preferably 200 nm or more, still more preferably 250 nm or more. Also, it is usually 2000 nm or less, preferably 1500 nm or less, more preferably 1000 nm or less, still more preferably 600 nm or less, particularly preferably 500 nm or less, and most preferably 400 nm or less.

[0029] When an electrode that is not a specific electrode is adopted, its thickness is not particularly limited. However, from the perspective of ensuring the conductivity required for charge transport, it is usually 10 nm or more, preferably 30 nm or more, more preferably 50 nm or more, still more preferably 80 nm or more. Also, from the perspective of reducing the film formation time and the amount of material used, it is usually 1000 nm or less, preferably 800 nm or less, more preferably 600 nm or less, still more preferably 400 nm or less.

[0030] (Specific electrode) The specific electrode has at least a metal layer 107 and a first metal oxide layer 106 disposed between the metal layer 107 and the buffer layer. The specific electrode preferably further has a second metal oxide layer 105 disposed between the buffer layer and the first metal oxide layer 106. At this time, the material constituting the first metal oxide layer 106 is different from the material constituting the second metal oxide layer 105. By disposing these two metal oxide layers between the metal layer 107 and the buffer layer 104, it is possible to suppress the ions of the metal constituting the metal layer 107 from moving to the buffer layer 104 adjacent to the electrode over time and causing a short circuit or leakage while maintaining good initial characteristics. In addition, in this specification, the term "metal oxide layer" is a term that targets any metal oxide layer when used without distinguishing between the first metal oxide layer and the second metal oxide layer.

[0031] (Metal layer) The metal layer 107 contains a metal belonging to Group 15 of the periodic table. The metal layer may be composed of a single metal belonging to Group 15 of the periodic table, or may be composed of an alloy consisting of two or more metals including a metal belonging to Group 15 of the periodic table. When the metal layer 107 is composed of a single metal, the type of the metal is a metal belonging to Group 15 of the periodic table. For example, bismuth or antimony can be mentioned. Considering cost and practicality, it is preferable to have bismuth, and particularly, it is preferable to be bismuth in order to ensure conductivity even with a relatively thin film.

[0032] When the metal layer 107 is composed of an alloy, the alloy is not particularly limited except that it contains a metal belonging to Group 15 of the periodic table. For example, it can be an alloy containing two or more metals selected from the group consisting of metals such as gold, silver, copper, calcium, titanium, cobalt, nickel, and palladium. For the same reason as in the case of being composed of the above single metal, it is preferably an alloy containing two or more metals selected from metals other than precious metals such as gold and palladium in consideration of cost and practicality, and particularly preferably a metal alloy containing silver, copper, etc. that can ensure conductivity even with a relatively thin film.

[0033] The thickness of the metal layer 107 is not particularly limited, but from the viewpoints of ensuring conductivity and sufficient light reflection ability, it is usually 20 nm or more, preferably 30 nm or more, more preferably 40 nm or more, still more preferably 50 nm or more, and usually 500 nm or less, preferably 400 nm or less, more preferably 300 nm or less, still more preferably 200 nm or less.

[0034] Although the details are not clear, it is considered that when the metal layer 107 contains a metal belonging to Group 15 of the periodic table, a chemically extremely stable surface layer is formed. Therefore, the reaction on the electrode surface with respect to oxygen, moisture, etc. is suppressed. As a result, it is considered that the high conductivity of the metal layer 107 as an electrode is ensured in the metal bulk film except for the outermost surface.

[0035] (First metal oxide layer) The type of the material of the first metal oxide layer 106 is not particularly limited as long as it is different from the material of the second metal oxide layer 105. For example, indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), fluorinated tin oxide (FTO), indium zinc oxide (IZO), antimony-doped indium oxide (ATO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), etc. can be mentioned. From the viewpoints of ensuring transmittance, cost, low resistivity, etc., it is preferable to contain at least one selected from the group consisting of indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), fluorinated tin oxide (FTO), and indium zinc oxide (IZO). In particular, it is preferable to contain indium tin oxide (ITO) and indium zinc oxide (IZO). These metal oxides may be used alone, or two or more thereof may be used in combination in any type and ratio. Further, in order to prevent process damage to the underlying active layer and buffer layer, it is preferable that the film can be formed at a low temperature. From this viewpoint, indium zinc oxide (IZO) is particularly preferable.

[0036] When the first metal oxide layer 106 contains at least one selected from the group consisting of indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), fluorinated tin oxide (FTO), and indium zinc oxide (IZO), the total content of these metal oxides in the first metal oxide layer 106 is not particularly limited. However, from the viewpoints of ensuring transmittance, low resistivity, etc., it is usually 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, still more preferably 99% by mass or more. Also, the upper limit is not particularly limited and may be 100% by mass (a mode composed of only at least one selected from the group consisting of indium zinc oxide, indium tin oxide (ITO), antimony-doped indium oxide (ATO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO)), or may be 99.99% by mass or less, 99.9% by mass or less, 99% by mass or less, or 98% by mass or less. The conditions of the above content range can also be preferably applied as the conditions of the range of indium zinc oxide in the first metal oxide layer 106.

[0037] The thickness of the first metal oxide layer 106 is not particularly limited. However, from the perspective of suppressing short circuits and leakage, it is usually 60 nm or more, preferably 100 nm or more, more preferably 120 nm or more, further preferably 140 nm or more, particularly preferably 160 nm or more, and most preferably 200 nm or more. Also, from the perspective of saving film formation time and material costs, it is usually 1000 nm or less, preferably 800 nm or less, more preferably 600 nm or less, and further preferably 500 nm or less. The first metal oxide layer 106 preferably exists as a layer so that the buffer layer 104 and the metal layer 107 do not come into contact.

[0038] The volume resistivity of the first metal oxide layer 106 is not particularly limited. However, from the perspective of the function as an electrode and suppressing the electric field generated in the film, a smaller volume resistivity is preferred. Usually, it is 1×10 -2 Ω·cm or less, and more preferably 1×10 -3 Ω·cm or less. Particularly preferably, it is 8×10 -4 Ω·cm or less, and most preferably 5×10 -4 Ω·cm or less. When the volume resistivity is small, the electric field strength becomes small, so that the diffusion of metal ions generated from the electrode and halogen ions generated from the active layer can be suppressed more efficiently. The volume resistivity is usually 1×10 -5 Ω·cm or more.

[0039] The film formation method of the first metal oxide layer 106 is not particularly limited. However, it can be formed by dry film formation methods such as vacuum evaporation, sputtering, CVD, and ALD, or wet film formation methods such as spin coating, sol-gel, and spraying. In the embodiment, dry film formation by a dry method with less process damage to the perovskite compound and the buffer layer is preferred, and particularly, sputtering is preferred.

[0040] When indium zinc oxide is used as the material of the first metal oxide layer 106, the flow rate of oxygen in the production of indium zinc oxide is not particularly limited and can be adjusted as appropriate. In this case, the degree of oxygen deficiency in the first metal oxide layer 106 can be set as appropriate.

[0041] The dielectric constant of the first metal oxide layer 106 is not particularly limited and can be set as appropriate. The surface roughness (Ra) of the surface of the first metal oxide layer 106 in contact with the metal layer 107 is not particularly limited and can be set as appropriate.

[0042] (Second metal oxide layer) The type of material of the second metal oxide layer 105 is not particularly limited as long as it is different from the material of the first metal oxide layer 106. For example, molybdenum oxide, vanadium oxide, tungsten oxide, niobium oxide, or tantalum oxide, etc. can be mentioned. However, from the perspective of energy level adjustment ability, it preferably contains at least one selected from the group consisting of molybdenum oxide, vanadium oxide, and tungsten oxide, and particularly preferably contains molybdenum oxide. These metal oxides may be used alone, or two or more kinds may be used in combination in any kind and ratio. When the second metal oxide layer 105 contains at least one selected from the group consisting of molybdenum oxide, vanadium oxide, and tungsten oxide, the total content of these metal oxides in the second metal oxide layer 105 is not particularly limited. However, from the perspective of adjusting the energy level, it is usually 90% by mass or more, preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 98% by mass or more. Also, the upper limit is not particularly limited, and it may be 100% by mass (the mode composed of only at least one selected from the group consisting of molybdenum oxide, vanadium oxide, and tungsten oxide), or may be 99.99% by mass or less, 99.9% by mass or less, 99% by mass or less, or 98% by mass or less. The conditions of the above content range can also be preferably applied as the conditions of the molybdenum oxide range in the second metal oxide layer 105.

[0043] The thickness of the second metal oxide layer 105 is not particularly limited. From the viewpoint of ensuring the energy level adjustment ability and maintaining low resistance, it is usually 1 nm or more, preferably 2 nm or more, more preferably 4 nm or more, and even more preferably 6 nm or more. Also, the upper limit value is usually 100 nm or less, preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The second metal oxide layer 105 preferably exists as a layer so that the buffer layer 104 and the first metal oxide layer 106 do not come into contact.

[0044] The film formation method of the second metal oxide layer 105 is not particularly limited. If a sublimable compound is used, it can be formed by a dry film formation method such as vacuum evaporation or sputtering. Also, for a compound soluble in a solvent, it can be formed by a wet film formation method such as spin coating, inkjet method, die coating method, reverse roll coating method, gravure coating method, kiss coating method, roll brush coating method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, etc. In particular, in the case of a dry film formation method such as vacuum evaporation or sputtering, compared with the coating method, the second metal oxide layer 105 is conformally formed and easily covers the surface of the underlying layer. Therefore, it is expected and preferable that even if the film thickness is reduced, the contact between the underlying layer and the first metal oxide layer can be prevented. Among them, a manufacturing method with less process damage to the underlying active layer and buffer layer, such as vacuum evaporation, is preferable. The second metal oxide layer 105 can also be expected to play a role of protecting the active layer and buffer layer from process damage of the first metal oxide layer 106.

[0045] (Method for forming a specific electrode) The method for forming the specific electrode is not particularly limited, and any method can be used. As specific examples, the methods for forming the metal layer 107 include a coating method, a plating method, a vacuum evaporation method, and a sputtering film formation method. The methods for forming the first metal oxide layer 106 and the second metal oxide layer 105 include a sputtering method, an ion plating method, a vacuum evaporation method, a sol-gel method, a coating method, and the like.

[0046] (Active layer) In the embodiment of FIG. 1, the active layer 103 is a layer where photoelectric conversion occurs. When the photoelectric conversion element 100 receives light, the light is absorbed by the active layer 103 to generate carriers, and the generated carriers are taken out from the lower electrode 101 and the upper electrode 108. The active layer 103 is located between the pair of electrodes and contains an organic-inorganic hybrid semiconductor compound. The organic-inorganic hybrid semiconductor compound refers to a material in which an organic component and an inorganic component are combined at the molecular level or the nanolevel and exhibits semiconductor characteristics.

[0047] In this embodiment, the organic-inorganic hybrid semiconductor compound is preferably a compound having a perovskite structure (hereinafter sometimes referred to as a perovskite semiconductor compound). There is no particular limitation on the perovskite semiconductor compound, but it can be selected from those listed in, for example, Galasso et al. Structure and Properties of Inorganic Solids, Chapter 7 - Perovskite type and related structures. For example, the perovskite semiconductor compound includes those of the AMX3 type represented by the general formula AMX3 or those of the A2MX4 type represented by the general formula A2MX4. Here, M refers to a divalent cation, A refers to a monovalent cation, and X refers to a monovalent anion.

[0048] There is no particular limitation on the monovalent cation A, but those described in the above-mentioned book by Galasso can be used. More specific examples include cations containing Group 1 and Groups 13 to 16 elements of the periodic table. Among these, cesium ion, rubidium ion, potassium ion, ammonium ion which may have a substituent or phosphonium ion which may have a substituent are preferable. Examples of the ammonium ion which may have a substituent include primary ammonium ion or secondary ammonium ion. There is no particular limitation on the substituent either. Specific examples of the ammonium ion which may have a substituent include alkylammonium ion or arylammonium ion. In particular, in order to avoid steric hindrance, a monoalkylammonium ion having a three-dimensional crystal structure is preferable, and from the viewpoint of improving stability, it is preferable to use an alkylammonium ion substituted with one or more fluorine groups. Also, a combination of two or more kinds of cations can be used as the cation A.

[0049] Specific examples of the monovalent cation A include methylammonium ion, monofluoromethylammonium ion, difluoromethylammonium ion, trifluoromethylammonium ion, ethylammonium ion, isopropylammonium ion, n-propylammonium ion, isobutylammonium ion, n-butylammonium ion, t-butylammonium ion, dimethylammonium ion, diethylammonium ion, phenylammonium ion, benzylammonium ion, phenethylammonium ion, guanidinium ion, formamidinium ion, acetamidinium ion or imidazolium ion, etc.

[0050] There is no particular limitation on the divalent cation M either, but it is preferably a divalent metal cation or a metalloid cation. Specific examples include cations of Group 14 elements of the periodic table. More specific examples include lead cation (Pb 2+ ), tin cation (Sn 2+ ), germanium cation (Ge 2+) can be mentioned. Also, a combination of two or more types of cations can be used as the cation M. From the viewpoint of obtaining a stable photoelectric conversion element, it is particularly preferable to use a lead cation or a combination of two or more types of cations including a lead cation. On the other hand, when the photoelectric conversion element of the present embodiment is used in a low-illumination environment such as an indoor light source, it is preferable to contain a tin element from the viewpoint of safety. Also, from the viewpoint of making the perovskite semiconductor compound with a shallow HOMO, it is preferable to contain a tin element. Note that a shallow HOMO means that the ionization potential is relatively close to 0.

[0051] Examples of the monovalent anion X include halide ions, acetate ions, nitrate ions, sulfate ions, borate ions, acetylacetonate ions, carbonate ions, citrate ions, sulfur ions, tellurium ions, thiocyanate ions, titanate ions, zirconate ions, 2,4-pentanedionato ions, or silicon fluoride ions, etc. In order to adjust the bandgap, X may be one type of anion or a combination of two or more types of anions. In one embodiment, examples of X include halide ions or a combination of halide ions and other anions. Examples of the halide ion X include chloride ions, bromide ions, or iodide ions, etc. From the viewpoint of not overly widening the bandgap of the semiconductor, it is preferable to mainly use iodide ions or bromide ions, but iodide ions and bromide ions may be combined in an appropriate ratio. When a halide (or halogen element) is contained in the active layer in this way, the halide, for example, iodide, may pass through the buffer layer 104 and diffuse to reach the metal layer 107 in the upper electrode 108. Conventionally, an electrode that has reacted with iodide has accelerated the progress of electrode deterioration and sometimes reduced the durability of the photoelectric conversion element. However, by providing the first metal oxide layer 106 and the second metal oxide layer 105, the durability of the photoelectric conversion element does not decrease. This is because the deterioration of the electrode due to iodide does not affect the extraction of electric charge, but rather affects the increase in sheet resistance of metal layer 107. By laminating a conductive metal oxide layer that does not easily react with iodide on metal layer 107, the increase in sheet resistance of metal layer 107 is suppressed and durability is improved.

[0052] Specific examples of perovskite semiconductor compounds include CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, and CH3NH3PbI (3-x) Cl x , CH3NH3PbI (3-x) Br x , CH3NH3PbBr (3-x) Cl x , CH3NH3Pb (1-y) Sn y I3, CH3NH3Pb (1-y) SnyBr3, CH3NH3Pb (1-y) Sn y Cl3, CH3NH3Pb (1-y) Sn y I (3-x) Cl x , CH3NH3Pb (1-y) Sn y I (3-x) Br x , and CH3NH3Pb (1-y) Sn y Br (3-x) Cl x In addition, the above compounds may include those in which CFH2NH3, CF2HNH3, CF3NH3, NH2CH=NH2, or Cs is used instead of CH3NH3, or a mixture of these. Note that x is an arbitrary value between 0 and 3, and y is an arbitrary value between 0 and 1.

[0053] The active layer 103 may contain two or more kinds of perovskite semiconductor compounds. For example, two or more kinds of perovskite semiconductor compounds in which at least one of A, M, and X is different may be included in the active layer 103. The active layer 103 may also have a stacked structure formed of a plurality of layers containing different materials or having different components.

[0054] The amount of the perovskite semiconductor compound contained in the active layer 103 is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more so as to obtain good semiconductor characteristics. There is no particular limitation on the upper limit. In addition, the active layer 103 may contain an additive in addition to the perovskite semiconductor compound. Examples of the additive include inorganic compounds such as halides, oxides, or sulfides, and inorganic salts such as sulfates, nitrates, or ammonium salts, or organic compounds.

[0055] The ionization potential range of the active layer is preferably -6.5 eV or more and -5.0 eV or less, more preferably -6.3 eV or more and -5.3 eV or less, and particularly preferably -6.1 eV or more and -5.5 eV or less. In addition, the band gap of the active layer is preferably 1.2 eV or more and 2.6 eV or less, more preferably 1.4 eV or more and 2.4 eV or less, and particularly preferably 1.6 eV or more and 2.2 eV or less. By setting the ionization potential and the band gap of the active layer within the above ranges, the power generation efficiency can be improved with respect to fluorescent lamps and LED lamps, which are visible light sources widely used indoors and indoors. In particular, when the band gap of the active layer is within the above range, the energy generated by receiving indoor light sources becomes sufficient to separate excitons generated in the semiconductor into positive and negative charges, and does not become excessive, enabling good power generation efficiency.

[0056] The ionization potential can be calculated by irradiating the sample with light and measuring the minimum energy (eV) required for the irradiation energy to eject photoelectrons. Any measuring instrument can be used, for example, AC-2, AC-3, etc. of Riken Keiki Co., Ltd. can be used. In addition, the band gap can be calculated from the absorption edge wavelength and absorbance of the semiconductor compound. Specifically, a semiconductor compound thin film is formed on a suitable sample such as a transparent glass substrate, its transmission spectrum is measured, the horizontal axis wavelength is converted to eV, the vertical axis transmittance is converted to √(ahν), the rising edge of this absorption is fitted as a straight line, and the eV value intersecting the baseline can be calculated as the band gap. The transmission spectrum can be measured using a spectrophotometer such as U-4100 manufactured by Hitachi High-Tech, for example.

[0057] As a method for setting the ionization potential of the active layer within the above-mentioned desired range, for example, appropriately changing the cation component in the perovskite semiconductor compound can be mentioned. In addition, as a method for setting the band gap of the active layer within the above-mentioned desired range, for example, appropriately changing the composition ratio of the halogen element in the perovskite semiconductor compound can be mentioned.

[0058] There is no particular limitation on the thickness of the active layer 103. In terms of being able to absorb more light, the thickness of the active layer 103 is 10 nm or more in one embodiment, 50 nm or more in another embodiment, 100 nm or more in still another embodiment, and particularly 120 nm or more in yet another embodiment. On the other hand, in terms of reducing the series resistance or increasing the charge extraction efficiency, the thickness of the active layer 103 is 1500 nm or less in one embodiment, 1200 nm or less in another embodiment, and 800 nm or less in still another embodiment.

[0059] The method for forming the active layer 103 is not particularly limited, and any method can be used. Specific examples include the coating method and the vapor deposition method (or co-evaporation method). The coating method can be used because the active layer 103 can be easily formed. For example, a method of forming the active layer 103 by applying a coating solution containing a perovskite semiconductor compound or its precursor and heating and drying as necessary can be mentioned. In addition, after applying such a coating solution, a solvent with low solubility of the perovskite semiconductor compound can be further applied to precipitate the perovskite semiconductor compound.

[0060] The precursor of a perovskite semiconductor compound refers to a material that can be converted into a perovskite semiconductor compound after the coating solution is applied. As a specific example, a perovskite semiconductor compound precursor that can be converted into a perovskite semiconductor compound by heating can be used. For example, by heating the film obtained by applying the coating solution, the perovskite compound precursor can be converted into a perovskite compound, and a semiconductor layer containing the perovskite compound can be formed. Specific examples of the perovskite compound precursor include compounds that can be converted into the perovskite compound represented by the following (1) by heating. For example, a compound represented by the following formula (2) and a compound represented by the following formula (3) can be mentioned.

[0061] As an example, a method of preparing a coating solution containing a compound represented by the following formula (2), a compound represented by the following formula (3), and a solvent, and applying this coating solution can be mentioned. Such a coating solution can be prepared by heating and stirring the compound in a solution. According to this method, an active layer 103 containing the compound represented by the following formula (1) can be prepared. AMX3 ··· (1) AX ··· (2) MX2 ··· (3) The definitions of A, M, and X are as described above. Specific examples of AX include alkylammonium halide salts, and specific examples of MX2 include metal halides. AX and MX2 are precursors of the perovskite semiconductor compound AMX3.

[0062] As another example, there is a method in which a coating solution containing the compound represented by the above formula (2) and a solvent, and a coating solution containing the compound represented by the above formula (3) and a solvent are each prepared and applied. For example, first, a layer of the compound represented by the formula (3) is formed by applying a coating solution containing the compound represented by the formula (3) and a solvent. Then, an active layer 103 containing the compound represented by the following formula (1) can be produced by applying a coating solution containing the compound represented by the formula (2) and a solvent thereon. After each coating solution is applied, heating can be performed to dry the layer or control the crystallization of the perovskite semiconductor compound by, for example, dropping a poor solvent. The heating can be carried out, for example, at 40°C or higher and 350°C or lower.

[0063] As the solvent, those having a solubility parameter (SP value) of 9 or more, preferably 10 or more, described in "Polymer Handbook, 4th Ed." edited by Brandrup, J. et al. are preferred. For example, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, pyridine, γ-butyrolactone, etc. can be mentioned. As the solvent, a mixed solvent of two or more solvents may be used. Even when a mixed solvent is used, it is preferable that the solubility parameter of at least one solvent in the mixed solvent is 10 or more.

[0064] Any method can be used as the method for applying the coating solution. For example, spin coating method, inkjet method, doctor blade method, drop casting method, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation / coating method or curtain coating method, etc. can be mentioned.

[0065] An interfacial modification layer may be formed on the active layer 103. At the surface and grain boundaries of the active layer 103, a central metal ion (M) with insufficient coordination 2+) It is known that crystal defects such as cation vacancies and halide vacancies exist. The modifying material is not particularly limited, but a Lewis base having a free lone pair of electrons or an organic salt compound composed of a cation capable of substituting a cation vacancy and an anion capable of substituting an anion vacancy is effective in passivating these defects. For example, the Lewis base is a heterocyclic compound such as pyridine or quinoline, and the organic salt compound is an ammonium halide salt such as phenethylamine hydroiodide (PEAI) or butylamine hydroiodide (BAI). While the interface modification layer serves to reduce crystal defects, it can also be a resistance component, so it is preferably formed into a thin film. Any method can be used as the film formation method, but from the point of effectively penetrating not only the surface but also crystal defects, it is preferable to form it by a solution method such as spin coating, inkjet, drop casting, or spray coating. The spin coating method is particularly preferable because a thin film can be formed uniformly.

[0066] (Buffer layer) The photoelectric conversion element has a buffer layer located between a pair of electrodes. The photoelectric conversion element preferably has a hole transport layer as a buffer layer so as to sandwich the active layer. It is more preferable to further have an electron transport layer on the side opposite to the hole transport layer with respect to the active layer. In FIG. 1, at least one of the buffer layer 102 and the buffer layer 104 becomes a hole transport layer, but as described above, the specific electrode is preferably on the hole transport layer side.

[0067] In one example, the buffer layer different from the hole transport layer may be a layer as an electron transport layer. In another example, the buffer layer provided between the anode and the active layer may be called a hole transport layer, and the buffer layer provided between the cathode and the active layer may be called an electron transport layer.

[0068] (Hole transport layer) The buffer layer as the hole transport layer is not particularly limited as long as it has hole transport ability, but preferably contains an organic semiconductor compound having hole transport ability, and may contain other substances as long as the effects of the present invention can be obtained. In the case of an n-i-p stacked type photoelectric conversion element, it becomes easy to control the amount of charge transported by the hole transport layer. Hereinafter, in this section, the buffer layer is also referred to as the hole transport layer.

[0069] (organic semiconductor compound) The semiconductor compound refers to a compound that can be used as a semiconductor material exhibiting semiconductor characteristics. The "semiconductor" is defined by the magnitude of the carrier mobility in the solid state. As is well known, the carrier mobility is an index indicating how fast (or how much) a charge (electron or hole) can be moved. Specifically, the "semiconductor" in this specification preferably has a carrier mobility at room temperature of 1.0×10 -6 cm 2 / V·s or more, more preferably 1.0×10 -5 cm 2 / V·s or more, still more preferably 5.0×10 -5 cm 2 / V·s or more, and particularly preferably 1.0×10 -4 cm 2 / V·s or more. The carrier mobility can be measured, for example, by measuring the IV characteristics of a field effect transistor or by the time-of-flight method.

[0070] As the semiconductor compound, it is preferable to use an organic semiconductor compound, but the type thereof is not particularly limited, and for example, conventionally known ones can be used. As the organic semiconductor compound, low molecular weight compounds and high molecular weight compounds are known. Examples of the low molecular weight organic semiconductor compound include polycyclic aromatic compounds, and specific examples include acene compounds such as tetracene or pentacene, oligothiophene compounds, phthalocyanine compounds, perylene compounds, rubrene compounds, and arylamine compounds such as triarylamine compounds. Further, examples of the high molecular weight organic semiconductor compound include conjugated polymers such as polythiophene-based polymers, polyacetylene-based polymers, polyaniline-based polymers, polyphenylene-based polymers, polyphenylene vinylene-based polymers, polyfluorene-based polymers, or polypyrrole-based polymers, and arylamine polymers such as triarylamine polymers.

[0071] The organic semiconductor compound is preferably an arylamine-based compound, more preferably a triarylamine-based compound. The arylamine-based compound is a compound having an arylamine structure (bond between an aryl group and a nitrogen atom), and includes arylamine-based polymers. The arylamine-based polymer is a polymer in which the repeating unit contains an arylamine structure, and is also referred to as a polyarylamine-based compound. Further, the triarylamine-based compound is a compound having a triarylamine structure (bond of three aryl groups to the same nitrogen atom), and includes triarylamine-based polymers. The triarylamine polymer is a polymer in which the repeating unit contains a triarylamine structure, and is also referred to as a polytriarylamine-based compound. Such arylamine-based compounds or triarylamine-based compounds are preferable in that they can be stably oxidized by a dopant and exhibit good semiconductor characteristics, and among them, triarylamine-based compounds are more preferable. Further, from the viewpoint of using in combination with a metal layer containing a Group 15 metal, particularly bismuth, a triarylamine-based compound having a triarylamine structure and at least one fluorenyl structure in the repeating unit is preferable, and a triarylamine-based compound having a triarylamine structure and at least two fluorenyl structures in the repeating unit is more preferable.

[0072] Here, the aryl group (or aromatic group) refers to an aromatic hydrocarbon group or an aromatic heterocyclic group, and includes monocyclic ones, condensed ring ones, and those in which a monocyclic or condensed ring is linked. The aromatic group is not particularly limited, but preferably has 30 or less carbon atoms, and more preferably 12 or less carbon atoms. Specific examples of the aromatic hydrocarbon group include a phenyl group, a naphthyl group, or a biphenyl group. Specific examples of the aromatic heterocyclic group include a thienyl group, a furyl group, a pyrrolyl group, a pyridyl group, an imidazolyl group, and the like.

[0073] The aryl group may further have a substituent. The substituent that the aryl group may have is not particularly limited, but examples include a halogen atom, a hydroxyl group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, a thio group, a seleno group, an aromatic hydrocarbon group, an aromatic heterocyclic group, and the like. Preferably, the substituent of the aryl group is an amino group or an alkyl group having 1 to 6 carbon atoms. Here, the amino group is preferably a dialkylamino group having 2 to 12 carbon atoms, an alkylarylamino group having 7 to 20 carbon atoms, or a diarylamino group having 12 to 30 carbon atoms.

[0074] (Dopant) The buffer layer as the hole transport layer contains a dopant for the above organic semiconductor compound (preferably an arylamine polymer), but its form is not particularly limited. The dopant is a substance for optimizing the conductivity and hole transport ability of the hole transport layer with respect to the active layer. Examples of substances that can be used as dopants include boron compounds such as tetrakis(pentafluorophenyl)borate, molybdenum compounds such as tris[1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene]molybdenum, and organic compounds having a tetracyanoquinodimethane skeleton such as 2,3,4,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane. The dopant preferably undergoes a charge transfer reaction with at least one organic semiconductor compound before or after the formation of the hole transport layer. As the dopant, a hypervalent iodine compound is preferred in terms of excellent solubility and the generation of an electron-accepting active site that functions as an oxidizing agent upon heating or the like.

[0075] This hypervalent iodine compound is known to act as a dopant for organic semiconductor compounds and exhibit electron-accepting properties (i.e., function as an oxidizing agent). Also, an electron-accepting dopant can improve the conductivity or hole transport ability of a semiconductor compound by removing electrons from the semiconductor compound. Thus, the hypervalent iodine compound can improve the charge transport characteristics of the semiconductor compound.

[0076] A hypervalent iodine compound is a compound containing hypervalent iodine and is defined as a compound containing iodine with an oxidation number of +3 or higher. For example, the dopant can be an iodine(III) compound or an iodine(V) compound. The iodine(V) compound containing pentavalent iodine can be, for example, a periodinane compound such as Dess-Martin periodinane. Examples of the iodine(III) compound containing trivalent iodine include compounds having a structure in which iodobenzene such as (diacetoxyiodo)benzene is oxidized, or diaryliodonium salts. The dopant is preferably an organic compound containing trivalent iodine, and more preferably a diaryliodonium salt, in terms of exhibiting good electron-accepting properties and the reverse reaction being less likely to occur when the molecule is destroyed during the oxidation process.

[0077] A diaryliodonium salt is [Ar-I + -Ar]X- It is a salt having a structure. Here, each of the two Ar represents an aryl group. The aryl group (aromatic group) is not particularly limited and may be, for example, those already mentioned with respect to the organic semiconductor compound. X - represents an arbitrary anion. X - Examples of X include, for example, halide ions, trifluoroacetate ions, tetrafluoroborate ions, or tetrakis(pentafluorophenyl)borate ions, etc. In terms of high solubility and the smooth progress of the production reaction of the coating solution, it is preferable that X− is an anion having a fluorine atom.

[0078] Preferred examples of the dopant include those represented by the following formula (I). In formula (I), X - represents an arbitrary anion, and specific examples are as described above. [R 11 -I + -R 12 X - (I)

[0079] In formula (I), R 11 and R 12 are each independently a monovalent organic group. Examples of the monovalent organic group include an aliphatic group or an aromatic group. Examples of the aliphatic group include an aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aliphatic heterocyclic group having 4 to 20 carbon atoms. For example, examples of the aliphatic group include an alkyl group containing a cycloalkyl group, an alkenyl group, or an alkynyl group, etc., and specific examples include a methyl group, an ethyl group, a butyl group, a cyclohexyl group, a tetrahydrofuryl group, etc.

[0080] Examples of the aromatic group include an aromatic hydrocarbon group having 6 to 20 carbon atoms or an aromatic heterocyclic group having 2 to 20 carbon atoms. For example, examples of the aromatic group include a phenyl group, a naphthyl group, a biphenyl group, a thienyl group, a pyridyl group, etc.

[0081] Incidentally, the above aliphatic group and aromatic group may have substituents. The substituents that may be present are not particularly limited, and examples include halogen atoms, hydroxyl groups, cyano groups, amino groups, carboxyl groups, ester groups, alkylcarbonyl groups, acetyl groups, sulfonyl groups, silyl groups, boryl groups, nitrile groups, alkyl groups, alkenyl groups, alkynyl groups, alkoxy groups, thio groups, seleno groups, aromatic hydrocarbon groups, aromatic heterocyclic groups, and the like.

[0082] R 11 and R 12 are each independently preferably an aromatic hydrocarbon group having 6 to 20 carbon atoms, more preferably a phenyl group. Here, the aromatic hydrocarbon group preferably has no substituent or has an alkyl group having 1 to 6 carbon atoms as a substituent. R 11 and R 12 are particularly preferably a phenyl group having an alkyl group at the para position.

[0083] The content of the dopant in the hole transport layer is not particularly limited. However, from the viewpoint of chemically assisting the charge transport in the hole transport layer and imparting a hole mobility of a certain level or higher while ensuring the charge transport path (pass) in the organic semiconductor compound responsible for charge transport, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, further preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more. Also, it is usually 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 12% by mass or less, and particularly preferably 10% by mass or less. In addition, in the hole transport layer, the content ratio of the dopant to the organic semiconductor compound having the above-described hole transport ability is not particularly limited. However, from the viewpoint of chemically assisting the charge transport in the hole transport layer, imparting a hole mobility of a certain level or higher, and ensuring the charge transport path in the organic semiconductor compound responsible for charge transport, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, further preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more. Also, it is usually 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 12% by mass or less, particularly preferably 10% by mass or less. When the photoelectric conversion element has a plurality of buffer layers, it is sufficient if any one layer corresponding to the hole transport layer among them satisfies the above content range.

[0084] The buffer layer as the hole transport layer may contain substances other than the above-described organic semiconductor compound and dopant. For example, it may contain a photoelectric conversion (active layer) material, an adhesive functional material, a filler, or a strength assisting material, etc.

[0085] (Electron transport layer) The photoelectric conversion element may have a buffer layer as an electron transport layer in addition to the buffer layer as the hole transport layer described above. Hereinafter, in this section, the buffer layer is also referred to as an electron transport layer. Its form is not particularly limited, and any material that can improve the extraction efficiency of electrons from the active layer to the cathode may be used, and known materials can be used. Specifically, inorganic compounds, organic compounds, or the organic-inorganic hybrid semiconductor compounds according to the present invention described in known documents such as WO 2013 / 171517, WO 2013 / 180230, or JP 2012-191194 A can be mentioned. For example, as inorganic compounds, salts of alkali metals such as lithium, sodium, potassium, or cesium, and metal oxides such as zinc oxide, titanium oxide, aluminum oxide, and indium oxide can be mentioned. As organic compounds, bathocuproine (BCP), bathophenanthrene (Bphen), tris(8-hydroxyquinolinato)aluminum (Alq3), boron compounds, oxadiazole compounds, benzimidazole compounds, naphthalenetetracarboxylic dianhydride (NTCDA), perylenetetracarboxylic dianhydride (PTCDA), fullerene compounds, phosphine oxide compounds, phosphine sulfide compounds, and other phosphine compounds having a double bond with a Group 16 element of the periodic table can be mentioned.

[0086] The thickness of the buffer layer as the hole transport layer and the thickness of the buffer layer as the electron transport layer are not particularly limited and can be appropriately set according to the application. However, in one embodiment, independently, it can be 10 nm or more, in another embodiment 15 nm or more, and in still another embodiment 20 nm or more. On the other hand, in one embodiment, it can be 1 μm or less, in another embodiment 500 nm or less, in still another embodiment 300 nm or less, and particularly in another embodiment 200 nm or less. When the film thickness of the buffer layer is within the above range, the migration efficiency of carriers such as holes and electrons is likely to be improved, and the photoelectric conversion efficiency can be improved.

[0087] The unevenness of the buffer layer on the side in contact with the specific electrode is preferably smooth from the viewpoint of preventing contact between the active layer and the electrode. The surface roughness (Ra) of the buffer layer on the side in contact with the specific electrode is usually 50 nm or less, more preferably 20 nm or less, particularly preferably 10 nm or less, and most preferably 5 nm or less. In order to form such a buffer layer with a smooth surface having a small surface roughness (Ra), a buffer layer having a film thickness capable of covering the surface unevenness of the perovskite semiconductor compound may be formed by a coating method. In the present invention, by forming a relatively thick metal oxide layer having a thickness of 60 nm or more as the first metal oxide layer, an effect of reducing the influence of the unevenness of this buffer layer can also be obtained.

[0088] Also, neither the buffer layer as the hole transport layer nor the buffer layer as the electron transport layer is limited in the layer formation method, and the formation method can be selected according to the characteristics of the material. For example, a buffer layer can be formed by preparing a coating solution containing the above-mentioned organic semiconductor compound, dopant, and solvent, and using a wet film formation method such as a spin coating method or an inkjet method. Further, the buffer layer can also be formed by a dry film formation method such as a vacuum evaporation method.

[0089] (Substrate) The photoelectric conversion element 100 usually has a substrate 109 that serves as a support. However, the photoelectric conversion element according to the present invention may not have the substrate 109. The material of the substrate 109 is not particularly limited as long as the effects of the present invention are not significantly impaired. For example, materials described in known documents such as International Publication No. 2013 / 171517, International Publication No. 2013 / 180230, or Japanese Patent Application Laid-Open No. 2012-191194 can be used.

[0090] (Method for manufacturing a photoelectric conversion element) According to the above method, the photoelectric conversion element 100 can be manufactured by forming each layer constituting the photoelectric conversion element 100. There is no particular limitation on the formation method of each layer constituting the photoelectric conversion element 100, and it can be formed by a sheet-to-sheet (Man'yō) method or a roll-to-roll method.

[0091] The roll-to-roll method is a method in which a flexible substrate wound in a roll form is fed out and processed while being intermittently or continuously conveyed until it is wound up by a take-up roll. According to the roll-to-roll method, since it is possible to batch-process a long substrate on the order of km, the roll-to-roll method is more suitable for mass production than the sheet-to-sheet method. On the other hand, when attempting to form each layer by the roll-to-roll method, due to its structure, the film may be scratched or partially peeled off when the film-forming surface comes into contact with the roll.

[0092] The size of the roll that can be used in the roll-to-roll method is not particularly limited as long as it can be handled by the manufacturing apparatus of the roll-to-roll method. However, the upper limit of the outer diameter is preferably 5 m or less, more preferably 3 m or less, and even more preferably 1 m or less. On the other hand, the lower limit is preferably 10 cm or more, more preferably 20 cm or more, and even more preferably 30 cm or more. The upper limit of the outer diameter of the roll core is preferably 4 m or less, more preferably 3 m or less, and even more preferably 0.5 m or less. On the other hand, the lower limit is preferably 1 cm or more, more preferably 3 cm or more, even more preferably 5 cm or more, particularly preferably 10 cm or more, and most preferably 20 cm or more. The smallness of these diameters is preferable in terms of high handleability of the roll, and the largeness is preferable in terms of the lower possibility that the layers formed in each process are broken by bending stress. The lower limit of the width of the roll is preferably 5 cm or more, more preferably 10 cm or more, and even more preferably 20 cm or more. On the other hand, the upper limit is preferably 5 m or less, more preferably 3 m or less, and even more preferably 2 m or less. The narrowness of the width is preferable in terms of high handleability of the roll, and the broadness is preferable because the degree of freedom in the size of the photoelectric conversion element 100 increases.

[0093] After depositing the upper electrode 108, the photoelectric conversion element 100 can be heated in a temperature range of 50°C or higher, 80°C or higher, and on the other hand, 300°C or lower, 280°C or lower, or 250°C or lower (this process may be referred to as an annealing process). By performing the annealing process at a temperature of 50°C or higher, an effect can be obtained in which the adhesion between the layers of the photoelectric conversion element 100, for example, the adhesion between the buffer layer 102 and the lower electrode 101, and the adhesion between the buffer layer 102 and the active layer 103, etc., is improved. By improving the adhesion between the layers, the thermal stability, durability, etc. of the photoelectric conversion element can be improved. Setting the temperature of the annealing process to 300°C or lower reduces the possibility that the organic compounds contained in the photoelectric conversion element 100 will thermally decompose. In the annealing process, stepwise heating using different temperatures within the above temperature range may be performed.

[0094] As the heating time, in order to improve the adhesion while suppressing thermal decomposition, in one embodiment, it is 1 minute or longer, and in another embodiment, it is 3 minutes or longer. On the other hand, in one embodiment, it is 180 minutes or shorter, and in another embodiment, it is 60 minutes or shorter. The annealing process can be terminated when the open-circuit voltage, short-circuit current, and fill factor, which are parameters of the solar cell performance, reach constant values. Further, the annealing process can be carried out under normal pressure and in an inert gas atmosphere in order to prevent thermal oxidation of the constituent materials. As the heating method, the photoelectric conversion element may be placed on a heat source such as a hot plate, or the photoelectric conversion element may be placed in a heating atmosphere such as an oven. Further, the heating may be performed in a batch manner or in a continuous manner.

[0095] The method for manufacturing a photoelectric conversion element includes at least a step of forming a first metal oxide layer above the buffer layer and a step of forming a metal layer on the first metal oxide layer. However, the method for manufacturing a photoelectric conversion element may have steps other than the above steps. In a preferred example, the method for manufacturing a photoelectric conversion element may include a step of forming a second metal oxide layer between the buffer layer and the first metal oxide layer.

[0096] The method for forming each layer in each of the above steps is not particularly limited. For example, coating methods such as spin coating method, inkjet method, doctor blade method, drop casting method, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, or curtain coating method can be used.

[0097] (Photovoltaic conversion characteristics) The photovoltaic conversion characteristics of the photovoltaic conversion element 100 can be obtained as follows. The photovoltaic conversion element 100 is irradiated with light of an appropriate spectrum at a certain irradiation intensity, and the current-voltage characteristics are measured. From the obtained current-voltage curve, photovoltaic conversion characteristics such as photovoltaic conversion efficiency (PCE), short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), series resistance, and shunt resistance can be obtained. As an example, by irradiating the photovoltaic conversion element 100 with white LED light having a color temperature of 5000K at an appropriate irradiation intensity (illuminance), the current-voltage characteristics at each illuminance can be measured.

[0098] The photovoltaic conversion element 100 is preferably a photovoltaic conversion element for use in a low illuminance environment. The photovoltaic conversion element 100 is preferably used in an environment of 10 to 5000 lux, and more preferably used in an environment of 10 to 1000 lux. The said photovoltaic conversion element is easy to suppress leakage and excellent in power generation efficiency in a low illuminance environment. Especially when using a light source such as white LED light, the photovoltaic conversion efficiency can be 20% or more. Also, the photovoltaic conversion efficiency at 200 lux can be 25% or more. There is no particular limitation on the upper limit of this efficiency, and the higher the better.

[0099] The photovoltaic conversion efficiency (PCE) is the value (%) obtained by dividing the output (maximum output) at the optimum operating point of the current-voltage curve of the photovoltaic conversion element measured by a predetermined irradiation light by the total energy amount of this irradiation light (for example, if it is sunlight with an intensity of AM1.5G, it is 100mW / cm 2 )

[0100] (Power generation device) In one embodiment, the photoelectric conversion element 100 is suitably used as a power generation device. In particular, when used as a solar cell for low-illumination environments such as indoors, the amount of light irradiated on the photoelectric conversion element is small, so the generated charges are also limited. At this time, if there is an electrode-to-electrode leak, its influence becomes relatively large, the leak defect sensitivity is high, and it becomes a factor in reducing the photoelectric conversion efficiency. Therefore, it is particularly preferably used for the purpose of avoiding this.

[0101] FIG. 2 is a cross-sectional view schematically showing an example of a solar cell. The thin-film solar cell 14 shown in FIG. 2 includes a weather-resistant protection film 1, an ultraviolet cut film 2, a gas barrier film 3, a getter material film 4, a sealing material 5, a solar cell element 6, a sealing material 7, a getter material film 8, a gas barrier film 9, and a backsheet 10 in this order. The thin-film solar cell 14 according to the present embodiment has the photoelectric conversion element according to the present invention as the solar cell element 6. Then, light is irradiated from the side where the protection film 1 is formed (lower side in FIG. 2), and the solar cell element 6 generates electricity. In another example, the thin-film solar cell 14 does not necessarily have all of these constituent members, and necessary constituent members can be arbitrarily selected. The low-illumination environment means 10 to 5000 lux, and is typically around 200 lux.

[0102] There are no particular restrictions on these constituent members constituting the photoelectric conversion element and its manufacturing method, and well-known techniques can be used. For example, the techniques described in known documents such as WO 2013 / 171517, WO 2013 / 180230, or JP-A-2012-191194 can be used.

[0103] The solar cell according to this embodiment, particularly the thin-film solar cell 14 described above, is not limited to a particular use and can be used for any application. For example, the solar cell according to one embodiment can be used as a solar cell for building materials, a solar cell for automobiles, a solar cell for interiors, a solar cell for railways, a solar cell for ships, a solar cell for airplanes, a solar cell for spacecraft, a solar cell for home appliances, a solar cell for mobile phones, or a solar cell for toys. As described above, since the solar cell according to this embodiment including the photoelectric conversion element according to the present invention has excellent conversion efficiency in a low-illuminance environment, it can be suitably applied particularly to energy harvesting applications.

[0104] The solar cell according to this embodiment, particularly the thin-film solar cell 14 described above, may be used as it is, or may be used as a component of a solar cell module. For example, as shown in FIG. 3, a solar cell module 13 including the solar cell according to this embodiment, particularly the solar cell 14 described above, provided on a substrate 12 is fabricated, and this solar cell module 13 can be installed and used at the place of use.

Examples

[0105] Hereinafter, the present embodiment will be described in more detail with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0106] [Preparation of Coating Liquid for Electron Transport Layer] An aqueous dispersion of tin(IV) oxide (7.5 mass%) was obtained as a coating liquid for an electron transport layer by adding ultrapure water to a 15 mass% aqueous dispersion of tin(IV) oxide (manufactured by Alfa Aesar).

[0107] [Preparation of Coating Liquid for Active Layer] Lead(II) iodide was weighed into a vial and introduced into a glove box. N,N-Dimethylformamide was added as a solvent so that the concentration of lead(II) iodide became 1.3 mol / L, and then the mixture was heated and stirred at 100°C for 1 hour to prepare a coating liquid 1 for an active layer. Next, formamidine hydrobromide (FABr), methylamine hydrobromide (MABr), and methylamine hydrochloride (MACl) were weighed into another vial in a mass ratio of 7.27:1:1.5 and introduced into a glove box. Isopropyl alcohol was added thereto as a solvent to prepare a coating solution 2 for the active layer with a total concentration of FABr, MABr, and MACl of 0.54 mol / L.

[0108] [Preparation of Coating Solution for Interface Modification Layer] 2-Phenylethylamine Hydroiodide (manufactured by TCI) was weighed into a vial and introduced into a glove box. Isopropyl alcohol was added as a solvent to prepare a coating solution for the interface modification layer so that the concentration of 2-Phenylethylamine Hydroiodide was 1 mg / mL.

[0109] [Synthesis of Polymer Compound A for Hole Transport Layer] Using the following Compound 1 (349.4 mg, 1 mmol) and the following Compound 2 (783.7 mg, 0.98 mmol), and referring to the method described in JP-A-2019-175970 as the reaction conditions, 570 mg of the following Polymer Compound A was obtained. The weight-average molecular weight of the obtained Polymer Compound A was 37,500, and the PDI (weight-average molecular weight / number-average molecular weight) was 1.4.

[0110] [Chemical Formula]

[0111] [Preparation of Coating Solution for Hole Transport Layer] A host solution was obtained by preparing an o-dichlorobenzene solution of a polymer compound A at 40 mg / mL. Separately, a dopant solution was obtained by preparing an o-dichlorobenzene solution of 32 mg / mL of 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (manufactured by TCI, an electron-accepting dopant). The dopant solution was added to the host solution so that the electron-accepting dopant was 8 wt% on an external basis with respect to the polymer compound A. The resulting mixture was heated and stirred at 150 °C for 1 hour to prepare a coating solution for the hole transport layer.

[0112] [Example 1] A glass substrate (manufactured by Geomatec) equipped with a patterned indium tin oxide (ITO) transparent conductive film (lower electrode) was subjected to ultrasonic cleaning using ultrapure water, drying by nitrogen blowing, and UV-ozone treatment.

[0113] Next, the coating solution for the electron transport layer prepared as described above was spin-coated on the above substrate at a speed of 2000 rpm at room temperature to form an electron transport layer with a thickness of 35 nm. Thereafter, the substrate was heated on a hot plate at 150 °C for 10 minutes.

[0114] Next, the substrate was introduced into a glove box and heated to 100 °C. 150 μL of the coating solution 1 for the active layer was dropped onto the electron transport layer and spin-coated at a speed of 2000 rpm. Next, the substrate was heated and annealed on a hot plate at 100 °C for 10 minutes to form a lead iodide layer. Next, after the substrate returned to room temperature, 120 μL of the coating solution 2 for the active layer was spin-coated on the lead iodide layer at a speed of 2000 rpm and heated at 150 °C for 20 minutes to form an active layer (thickness 650 nm) of an organic-inorganic hybrid semiconductor compound. Further, 150 μL of the coating solution for the interface modification layer was spin-coated on the active layer at a speed of 2000 rpm and heated at 100 °C for 10 minutes to form an interface modification layer.

[0115] Next, after the substrate returned to room temperature, a hole transport layer coating solution (150 μL) was spin-coated on the active layer at a speed of 1000 rpm, and then heated on a hot plate at 90 °C for 5 minutes to form a hole transport layer (thickness 100 nm).

[0116] Next, on the hole transport layer, MoO3 was formed to a thickness of 10 nm by resistance heating type vacuum evaporation to form a second metal oxide layer. Then, by vacuum sputtering, IZO was formed to a thickness of 200 nm under the conditions of an argon (Ar) flow rate of 20 sccm, an oxygen (O2) flow rate of 0.05 sccm, and a pressure of 0.6 Pa to form a first metal oxide layer. Then, bismuth was deposited to a thickness of 50 nm by resistance heating vacuum evaporation to form the upper electrode. In the above manner, a photoelectric conversion element was fabricated.

[0117] [Comparative Example 1] Silver was deposited to a thickness of 50 nm by resistance heating vacuum evaporation to form the upper electrode. Otherwise, a photoelectric conversion element was fabricated in the same manner as in Example 1.

[0118] [Comparative Example 2] Copper was deposited to a thickness of 50 nm by resistance heating vacuum evaporation to form the upper electrode. Otherwise, a photoelectric conversion element was fabricated in the same manner as in Example 1.

[0119] [Evaluation of Energy Conversion Efficiency (PCE)] For the photoelectric conversion elements fabricated in the above Examples and Comparative Examples, white LED light set to an illuminance of 15,000 lx on the element surface was continuously irradiated in an open circuit, and the energy conversion efficiency (PCE) of the photoelectric conversion element at 200 lx was measured over time to evaluate the initial PCE and the maintenance rate (durability) of PCE over time. PCE was calculated from the current-voltage characteristics when the voltage was swept in the direction from V OC to J SC The evaluation results of the average value of the initial PCE and the average value of the PCE after a 544-hour test are shown in Table 1.

[0120]

Table 1

[0121] From the results shown in Table 1, it can be seen that in Example 1, the durability after the light irradiation test was improved. This verified that the durability of the photoelectric conversion element was improved.

Industrial Applicability

[0122] According to the present invention, a photoelectric conversion element excellent in durability is provided.

Explanation of Signs

[0123] 1 Weather resistance protection film 2 UV cut film 3, 9 Gas barrier film 4, 8 Getter material film 5, 7 Sealing material 6 Solar cell element 10 Backsheet 12 Substrate 13 Solar cell module 14 Thin film solar cell 100 Photoelectric conversion element 101 Lower electrode 102 Buffer layer 103 Active layer 104 Buffer layer 105 Second metal oxide layer 106 First metal oxide layer 107 Metal layer 108 Upper electrode 109 Substrate

Claims

1. A photoelectric conversion element, wherein the photoelectric conversion element includes at least: a pair of electrodes having an upper electrode and a lower electrode; an active layer disposed between the pair of electrodes and containing an organic-inorganic hybrid semiconductor compound; and a buffer layer positioned between the active layer and the upper electrode or the lower electrode. The photoelectric conversion element, wherein at least one of the pair of electrodes includes at least a metal layer containing a metal belonging to Group 15 of the periodic table and a first metal oxide layer disposed between the metal layer and the buffer layer.

2. The photoelectric conversion element according to Claim 1, wherein the first metal oxide layer contains at least one selected from the group consisting of indium oxide, zinc oxide, tin oxide, indium tin oxide, fluorinated tin oxide, and indium zinc oxide.

3. The photoelectric conversion element according to Claim 1, wherein the electrode having the metal layer and the first metal oxide layer further includes a second metal oxide layer between the buffer layer and the first metal oxide layer.

4. The photoelectric conversion element according to Claim 3, wherein the second metal oxide layer contains at least one selected from the group consisting of molybdenum oxide, vanadium oxide, and tungsten oxide.

5. The photoelectric conversion element according to Claim 1, wherein the buffer layer includes a hole transport layer.

6. The photoelectric conversion element according to Claim 1, wherein the organic-inorganic hybrid semiconductor compound includes a compound having a perovskite structure.

7. The photoelectric conversion element according to Claim 1, which is for use in a low-illuminance environment.

8. A power generation device having the photoelectric conversion element according to any one of Claims 1 to 7.

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