Hole transport layer, solar cell element, and solar cell module

Abstract

This hole transport layer has a hydrophobic group per molecule.

Description

Hole transport layer, solar cell element and solar cell module CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Application No. 2024-62742 (filed April 9, 2024), the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to a hole transport layer, a solar cell element, and a solar cell module.

[0003] Conventionally, devices have been proposed in which a negative electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and a positive electrode are stacked in this order (for example, Patent Documents 1 and 2).

[0004] JP 2009-252407 A International Publication No. 2022 / 244336

[0005] A hole transport layer, a solar cell element, and a solar cell module are disclosed.

[0006] In one embodiment, the hole transport layer comprises hydrophobic groups on the molecules.

[0007] In one embodiment, the solar cell element includes a positive electrode, a negative electrode, a photoelectric conversion layer, and a hole transport layer. The photoelectric conversion layer is located between the positive electrode and the negative electrode and generates electricity based on light. The hole transport layer is located between the positive electrode and the photoelectric conversion layer.

[0008] In one embodiment, the solar cell module includes a plurality of solar cell elements.

[0009] FIG. 1 is a perspective view schematically showing a portion of a solar cell element according to a first embodiment. FIG. 2 is a top view schematically showing a portion of a solar cell element according to the first embodiment. FIG. 3 is an end view of the solar cell element according to the first embodiment, taken along the line III-III in FIG. 2. FIG. 4 is a graph showing an example of the relationship between the contact angle of the hole transport moiety and the conductivity maintenance rate of the hole transport moiety. FIG. 5 is a cross-sectional view schematically showing an example of a portion of a solar cell element according to a second embodiment. FIG. 6 is a cross-sectional view schematically showing an example of a solar cell module according to a third embodiment.

[0010] Devices including a hole transport layer are known. A specific example of such a device is a solar cell element. When moisture penetrates the hole transport layer in such a device, the moisture may react with the hole transport layer. This reaction may increase the sheet resistance of the hole transport layer. In this case, the reliability of the hole transport layer is low.

[0011] Therefore, the inventors of the present disclosure have created a technique that can improve the reliability of the hole transport layer. First to third embodiments will be described below with reference to the drawings.

[0012] In the drawings, the same or similar components and parts having the same or similar functions are denoted by the same reference numerals, and redundant explanations will be omitted in the following description. The drawings are schematic illustrations. The drawings may include a right-handed XYZ coordinate system.

[0013] <1. First embodiment> <1-1. Solar cell element> A solar cell element 10, which is an example of a device including a hole transport part 1031 (described below) according to a first embodiment, will be described with reference to Figs. 1 to 3. Fig. 1 shows a part of the solar cell element 10 according to the first embodiment. Fig. 2 is a top view of a part of the solar cell element 10 according to the first embodiment. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Figs. 1 to 3 do not show the entire solar cell element 10, but show a part obtained by cutting out a part of the solar cell element 10.

[0014] As shown in Fig. 1, the solar cell element 10 has a light-receiving surface F1 that mainly receives light and a back surface F2 located on the opposite side of the light-receiving surface F1. In the first embodiment, the light-receiving surface F1 faces the +Z direction, and the back surface F2 faces the -Z direction. For example, the +Z direction may be set to face the sun at its zenith moment. Fig. 2 shows a portion of the solar cell element 10 as viewed from the light-receiving surface F1 side.

[0015] As shown in Fig. 3, the solar cell element 10 may include a first electrode unit 101, a diffusion reduction unit 102, a solar cell unit 103, a second electrode unit 104, and a substrate unit 105. Also, as shown in Fig. 3, the solar cell unit 103 may include a hole transport unit 1031, a photoelectric conversion unit 1032, and an electron transport unit 1033. In the first embodiment, the second electrode unit 104, the electron transport unit 1033, the photoelectric conversion unit 1032, the hole transport unit 1031, the diffusion reduction unit 102, and the first electrode unit 101 are stacked on the substrate unit 105 in this order.

[0016] Although not shown, an anti-reflection film may be positioned on the surface of the solar cell module 1 (described later). For example, an insulating film made of silicon nitride or the like is used as the anti-reflection film. Furthermore, although not shown, a passivation film may be positioned between the first electrode unit 101, the diffusion reduction unit 102, or the solar cell unit 103 and the anti-reflection film. For example, a thin film made of an oxide such as aluminum oxide or a nitride is used as the passivation film.

[0017] By connecting a plurality of solar cell elements 10 together, the plurality of solar cell elements 10 can form a solar cell module 1. For example, by connecting a plurality of solar cell elements 10, a solar cell module 1 having a size of about 1 m square can be produced. Furthermore, by connecting a plurality of solar cell modules 1 together, the plurality of solar cell modules 1 can form a solar cell string. By connecting a plurality of solar cell strings together, the plurality of solar cell strings can form a solar cell array.

[0018] Next, a description will be given of the parts included in the solar cell element 10. For ease of explanation, each part will be described below in order starting from the substrate part 105.

[0019] <1-1-1. Substrate portion 105> The substrate portion 105 is a base that forms the portion included in the solar cell element 10 (such as the solar cell portion 103). The material of the substrate portion 105 may be, for example, glass, plastic such as acrylic or polycarbonate, or metal such as stainless steel. The shape of the substrate portion 105 may be, for example, a flat plate, a sheet, or a film. The thickness of the substrate portion 105 may be, for example, about 0.01 millimeters (mm) to 5 mm. The substrate portion 105 may also be simply referred to as a support substrate.

[0020] <1-1-2. Second electrode unit 104> The second electrode unit 104 is located on the substrate unit 105. The second electrode unit 104 may also be simply referred to as a second electrode. Alternatively, the second electrode unit 104 may also be referred to as a second electrode layer. The second electrode unit 104 can collect carriers generated by photoelectric conversion in response to light irradiation of the solar cell unit 103 (described later). The second electrode unit 104 can, for example, function as an electrode (also referred to as a negative electrode) that collects electrons as carriers. As a material for the second electrode unit 104, for example, a metal with excellent conductivity such as silver (Ag), gold (Au), copper (Cu), titanium (Ti), indium (In), or tin (Sn) may be used.

[0021] The second electrode unit 104 may be made of, for example, a transparent conductive oxide (TCO) that is transparent to light in a specific wavelength range. The second electrode unit 104 may have a thickness of, for example, about 10 nanometers (nm) to 1000 nm. The second electrode unit 104 may be formed on the substrate unit 105 by a vacuum process such as sputtering.

[0022] Examples of TCO include indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), titanium-doped indium oxide (ITiO), and indium zinc oxide (ITiO). Indium Gallium Zinc Oxide (IZO), Indium Gallium Zinc Oxide (IGZO), Tantalum-doped Tin Oxide (Ta-doped Tin Oxide: SnO ２ :Ta), niobium-doped tin oxide (Nb-doped tin oxide:SnO ２ : Nb), tungsten-doped tin oxide (W-doped tin oxide: SnO ２ : W), molybdenum-doped tin oxide (Mo-doped tin oxide: SnO ２ : Mo), fluorine-doped tin oxide (F-doped tin oxide: SnO ２ :F), hydrogen-doped indium oxide (Hydrogen-doped Indium Oxide:IOH), etc., are not particularly limited. The transparent conductive oxide film may be a laminated film having a plurality of films, and in addition to the above oxides, a film of tin oxide or the like may be contained in the laminated film. The dopant for the tin oxide or the like film may be one or more selected from the group consisting of In, silicon (Si), germanium (Ge), Ti, Cu, antimony (Sb), Nb, F, Ta, W, Mo, bromine (Br), iodine (I), chlorine (Cl), etc., are not particularly limited.

[0023] <1-1-3. Solar Cell Unit 103> The solar cell unit 103 is located between the first electrode unit 101 and the second electrode unit 104. Specifically, the solar cell unit 103 is located on the second electrode unit 104. The -Z direction surface of the solar cell unit 103 may be in contact with the +Z direction surface of the second electrode unit 104. The solar cell unit 103 may also be called a power generation layer. The solar cell unit 103 converts light incident from the outside (e.g., sunlight) into electricity. For example, the solar cell unit 103 may generate carriers by photoelectric conversion in response to irradiation with light. The carriers include at least one of electrons and holes. The solar cell unit 103 has a light-receiving surface F1.

[0024] 3 , the solar cell section 103 may include a hole transport section 1031, a photoelectric conversion section 1032, and an electron transport section 1033. The hole transport section 1031 may also be called a hole transport layer. The photoelectric conversion section 1032 may also be called a photoelectric conversion layer. The electron transport section 1033 may also be called an electron transport layer.

[0025] The photoelectric conversion section 1032 is located between the first electrode section 101 and the second electrode section 104, the hole transport section 1031 is located between the first electrode section 101 and the photoelectric conversion section 1032, and the electron transport section 1033 is located between the photoelectric conversion section 1032 and the second electrode section 104. In the first embodiment, the electron transport section 1033, the photoelectric conversion section 1032, and the hole transport section 1031 are stacked in this order on the second electrode section 104. As shown in FIG. 3 , the +Z direction surface of the second electrode section 104 may be in contact with the −Z direction surface of the electron transport section 1033, the +Z direction surface of the electron transport section 1033 may be in contact with the −Z direction surface of the photoelectric conversion section 1032, and the +Z direction surface of the photoelectric conversion section 1032 may be in contact with the −Z direction surface of the hole transport section 1031. A p-type semiconductor is used for the hole transport section 1031, an intrinsic semiconductor (i.e., an i-type semiconductor) is used for the photoelectric conversion section 1032, and an n-type semiconductor is used for the electron transport section 1033. In this case, the hole transport section 1031, the photoelectric conversion section 1032, and the electron transport section 1033 form a PIN junction region. The PIN junction region can generate electricity through photoelectric conversion in response to light irradiation. Note that the photoelectric conversion section 1032 may be a p-type semiconductor or an n-type semiconductor.

[0026] In the first embodiment, the solar cell unit 103 will be described as a perovskite solar cell. However, this is merely an example, and other types of solar cells may be applied. For example, the solar cell may be an inorganic solar cell or an organic solar cell. The inorganic solar cell may be a silicon solar cell or a compound solar cell. The organic solar cell may be a dye-sensitized solar cell or an organic thin-film solar cell. Furthermore, for example, the solar cell may be a crystalline solar cell or a thin-film solar cell. The crystalline solar cell may be a silicon solar cell or a compound semiconductor solar cell such as a CIGS (Cu, In, Ga, Se) solar cell. The thin-film solar cell may be a perovskite solar cell, a dye-sensitized solar cell, an organic thin-film solar cell, or the like.

[0027] Next, a description will be given of each part included in the solar cell section 103. For ease of explanation, each part will be described below in order starting from the electron transport section 1033.

[0028] The electron transporting section 1033 is located on the second electrode section 104. For example, a semiconductor made of an inorganic material (also referred to as an inorganic semiconductor) having a higher electrical resistance than the second electrode section 104 may be used for the electron transporting section 1033.

[0029] In the first embodiment, an n-type semiconductor is used as the inorganic semiconductor material. The electron transport unit 1033 functions as a so-called hole blocking layer or electron transport layer (ETL). The electron transport layer, for example, collects and outputs electrons.

[0030] As the n-type semiconductor, in addition to inorganic semiconductors, semiconductors made of organic materials may be used. For example, the n-type semiconductor may be [6,6]-phenyl-C-61-methyl butyrate (PCBM), C60, or an oxide semiconductor layer. For example, the oxide semiconductor layer may be titanium(IV) oxide (TiO ２ ), zinc oxide (ZnO), indium(III) oxide (In ２ O ３ ), tin(IV) oxide (SnO ２ ), or magnesium oxide (MgO) may be applied.

[0031] The photoelectric conversion section 1032 is located on the electron transport section 1033. This photoelectric conversion section 1032 can absorb light that has passed through the diffusion reduction section 102 and the hole transport section 1031, which will be described later. In the first embodiment, for example, an i-type semiconductor is applied to the photoelectric conversion section 1032. For example, a semiconductor having a perovskite structure (also referred to as a perovskite semiconductor) may be applied to the i-type semiconductor. The perovskite semiconductor may include, for example, a halide-based organic-inorganic perovskite semiconductor. The halide-based organic-inorganic perovskite semiconductor may be, for example, an ABX ３ A is a semiconductor having a perovskite structure with the following composition: ３ NH ３ ), formamidinium (CH(NH ２ ) ２), cesium (Cs), rubidium (Rb), or potassium (K) ions are applied to B, for example, one or more ions of lead (Pb) or tin (Sn). X, for example, one or more ions of iodine (I), bromine (Br), or chlorine (Cl) are applied to X. Specifically, ABX ３ The semiconductor having a perovskite structure with the composition is, for example, CH ３ NH ３ PbI ３ or (CH(NH ２ ) ２ ,Cs)Pb(I,Br) ３ The photoelectric conversion unit 1032 may be configured of an organic perovskite such as SiO 2 or SiO 3 . The organic perovskite may be formed, for example, by applying a first source liquid onto the electron transport unit 1033 and drying the applied liquid. Here, the organic perovskite is a thin film having crystallinity. The first source liquid may be generated, for example, by dissolving the source materials, alkylamine halide and lead halide, in a solvent. The thickness of the photoelectric conversion unit 1032 may be, for example, approximately 100 nm to 2000 nm.

[0032] The hole transport section 1031 is located on the photoelectric conversion section 1032. The surface of the hole transport section 1031 opposite to the photoelectric conversion section 1032 may be the light-receiving surface F1. A p-type semiconductor is applied to the hole transport section 1031. The hole transport section 1031 functions as a so-called electron blocking layer or hole transport layer (HTL). The hole transport layer, for example, collects and outputs holes.

[0033] The hole transport section 1031 may have a hydrophobic group in its molecule. In this case, the hole transport section 1031 has hydrophobicity. This can improve the reliability of the hole transport section 1031 against humidity. This will be described in detail later in the first embodiment.

[0034] <1-1-4. Diffusion reduction unit 102> The diffusion reduction unit 102 is located on the solar cell unit 103. In other words, the diffusion reduction unit 102 is located on the light-receiving surface F1 of the solar cell unit 103. In further other words, the diffusion reduction unit 102 is located between the first electrode unit 101 and the solar cell unit 103.

[0035] A conductive inorganic material may be used as the material of the diffusion reduction portion 102. For example, a conductive oxide or a conductive nitride may be used. The diffusion reduction portion 102 may be formed on the hole transport portion 1031 by, for example, a vacuum process. The vacuum process may be sputtering, chemical vapor deposition (CVD), vacuum evaporation, atomic layer deposition (ALD), or the like. The thickness of the diffusion reduction portion 102 may be, for example, approximately 1 nm to 100 nm.

[0036] The diffusion reduction section 102 functions as a diffusion barrier film. That is, the diffusion reduction section 102 reduces at least one of the amount of metal migration from the first electrode section 101 to the hole transport section 1031 and the amount of metal migration from the hole transport section 1031 to the first electrode section 101. This reduces the possibility of deterioration of the hole transport section 1031 or the photoelectric conversion section 1032. Therefore, it is possible to reduce the possibility of deterioration in the conversion efficiency of the solar cell element 10.

[0037] <1-1-5. First electrode unit 101> The first electrode unit 101 is located on the diffusion reduction unit 102. The first electrode unit 101 can collect carriers generated by photoelectric conversion in response to light irradiation of the photoelectric conversion unit 1032. The first electrode unit 101 can, for example, function as an electrode (also referred to as a positive electrode) that collects holes as carriers. The first electrode unit 101 may also, for example, function as a collecting electrode.

[0038] The first electrode portion 101 may be made of a metal with excellent conductivity, such as Ag, Au, Cu, Ti, In, or Sn. The first electrode portion 101 may be formed on the diffusion reduction portion 102 by a vacuum process, such as sputtering. The average thickness of the first electrode portion 101 is not particularly limited, but may be in the range of 1 μm or more and 50 μm or less, for example.

[0039] The first electrode unit 101 may be formed, for example, by applying a metal paste as a coating liquid by screen printing or the like, followed by drying and solidifying the metal paste. The metal paste may be prepared, for example, by adding conductive particles with high light reflectance to a binder such as a translucent resin. Here, an epoxy resin or the like may be used as the translucent resin. The particles contained in the metal paste may be metal particles such as Cu, Al, Ni, and alloys of Zn and Ag. In this case, the first electrode unit 101 may contain a large number of conductive particles, and the conductivity of the first electrode unit 101 may be ensured by the large number of particles. The first electrode unit 101 may be, for example, layered.

[0040] The shape of the first electrode portion 101 is not limited to the shape shown in Figures 1 to 3 of the first embodiment. The shapes of the first electrode portion 101 and the diffusion reduction portion 102 may be changed as appropriate to improve carrier collection efficiency. The shapes of the first electrode portion 101 and the diffusion reduction portion 102 may be a so-called comb electrode structure, or may be a structure combining a so-called bus bar electrode and a so-called finger electrode.

[0041] Furthermore, the solar cell element 10 does not need to include the diffusion reduction portion 102. In this structure, the surface of the first electrode portion 101 in the −Z direction can come into contact with the surface of the hole transport portion 1031 in the +Z direction.

[0042] For example, a lead wire is electrically connected to each of the first electrode unit 101 and the second electrode unit 104. Specifically, for example, a first lead wire is electrically connected to the first electrode unit 101, and a second lead wire is connected to the second electrode unit 104. Each lead wire can be joined to each of the first electrode unit 101 and the second electrode unit 104 by, for example, soldering. Here, for example, the output obtained by photoelectric conversion in the solar cell element 10 can be extracted by the first lead wire and the second lead wire.

[0043] <1-2. Composition of the Hole Transport Section> Next, the composition of the hole transport section 1031 will be described in detail. The molecule of the hole transport section 1031 may contain a hydrophobic group. A substituent with a large π(X / PhH) value can be applied to the hydrophobic group. Table 1 shows the π values ​​of the substituents.

[0044]

[0045] Examples of the hydrophobic group include a halogeno group, a methyl (Me) group, an ethyl (Et) group, an isopropyl (i-Pr) group, and a trifluoromethyl (CF ３ ) group, phenyl (Ph) group, NMe ２ At least one of a fluorine (F) atom, a chlorine (Cl) atom, a bromine (Br) atom, and an iodine (I) atom can be applied as the halogeno group. Specifically, the hydrophobic group may be a halogeno group, and as a more specific example, it may be a fluorine atom. The hole transport unit 1031 has a hydrophobic group in its molecule, and therefore is hydrophobic.

[0046] The hole transport section 1031 may include a base material and a dopant. The base material may be formed of an organic semiconductor. The dopant is a p-type dopant and may be formed of, for example, an organic substance. When the hole transport section 1031 includes a base material and a dopant, only the base material molecules may include a hydrophobic group, only the dopant molecules may include a hydrophobic group, or both the base material and the dopant molecules may include a hydrophobic group. In other words, it is sufficient that at least one of the base material and the dopant molecules includes a hydrophobic group.

[0047] <1-2-1. Base Material> The base material may include a benzene ring, and as a more specific example, may include a triphenylamine skeleton. The triphenylamine skeleton has a structure in which three benzene rings are bonded to a nitrogen atom. As a specific example, the base material may include PTAA (Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), MeOTTVT (4-((E)-4-(bis(4-((E)-4-(bis(4-methoxyphenyl)amino)styryl)phenyl)amino)styryl)-N,N-bis(4-methoxyphenyl)aniline), or a derivative of PTAA or MeOTTVT. The base material may further include a spiro skeleton. Specifically, the base material may include Spiro-OMeTAD (2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene), Spiro-TTB (2,2',7,7'-Tetrakis(di-p-tolylamino)-9,9'-spirobi[fluorene]), or a derivative of Spiro-OMeTAD or Spiro-TTB.

[0048] When the base material contains a hydrophobic group, one or more hydrophobic groups may be bonded to at least one of the benzene rings in the base material molecule. For example, when the hydrophobic group is bonded to the benzene ring in PTAA, the base material molecule may have the repeating structure shown in the following formula EF1:

[0049]

[0050] In Formula EF1, a fluorine atom as a hydrophobic group is bonded to a benzene ring. The material represented by Formula EF1 may also be called Fluoro-PTAA (Poly(bis(4-phenyl)(4-fluoro-2-methylphenyl)amine).

[0051] As shown in formula EF1, a fluorine atom as a hydrophobic group is bonded to at least one benzene ring in a molecule of the base material. In formula EF1, one hydrophobic group is bonded to only one of the three benzene rings. Although different from formula EF1, hydrophobic groups may be bonded to three or more of the multiple benzene rings. Also, in the example of formula EF1, only one hydrophobic group is bonded to each benzene ring. However, multiple hydrophobic groups may be bonded to one benzene ring.

[0052] The hydrophobic group (e.g., a fluorine atom) may be located at a more outer portion of the molecule (e.g., a molecular unit structure). For example, in Formula EF1, the para and meta positions of each of the three benzene rings correspond to the outer portions of the molecule. The para and meta positions here refer to positions relative to the nitrogen atom. If the nitrogen atom is at position 1, the para position corresponds to position 4, and the meta position corresponds to position 3. In Formula EF1, the hydrophobic group is bonded to the para position of the benzene ring, and is therefore located at the outer portion of the molecule. In this way, if the hydrophobic group is located at a more outer portion of the molecule, the hydrophobic group can act quickly on water molecules entering from the outside, thereby more effectively improving the hydrophobicity of the base material. As shown in Formula EF1, the hydrophobic group does not need to be bonded to the ortho position of the benzene ring. The ortho position corresponds to position 2.

[0053] The base material molecule is not limited to formula EF1. For example, the base material may be a derivative of Spiro-OMeTAD. That is, a hydrophobic group may be bonded to the benzene ring in Spiro-OMeTAD. As a specific example, the base material may have a molecular structure shown in either formula EF2 or EF3 below.

[0054]

[0055]

[0056] In each of Formula EF2 and Formula EF3, a hydrophobic group (here, a fluorine atom) is bonded to the benzene ring instead of the methoxy (OMe) group of Spiro-OMeTAD. In Formula EF2, a hydrophobic group is bonded to each of four of the eight outer benzene rings. Here, the outer benzene rings correspond to benzene rings that do not belong to the spirobifluorene skeleton. On the other hand, the inner benzene rings correspond to benzene rings that belong to the spirobifluorene skeleton. In Formula EF3, a hydrophobic group is bonded to all eight outer benzene rings. In each of Formula EF2 and Formula EF3, the hydrophobic group is bonded to the outer benzene ring of the molecule, which can more effectively improve the hydrophobicity of the base material. As shown in Formula EF2 and Formula EF3, a hydrophobic group does not have to be bonded to the inner benzene ring of the molecule.

[0057] In each of Formula EF2 and Formula EF3, the para and meta positions of the eight outer benzene rings correspond to the outer portions of the molecules. In each of Formula EF2 and Formula EF3, the hydrophobic groups are bonded to the para positions of the outer benzene rings, which can further effectively improve the hydrophobicity of the base material.

[0058] <1-2-2. Dopant> For example, a material that reacts with moisture in the air to be doped, or a material that does not require moisture to be doped, is used as the dopant. The former material may include, for example, LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide). For example, a material that functions as a Lewis acid with respect to the base material is used as the latter material. In other words, a material that functions as a Lewis base with respect to the dopant is used as the base material. For example, a dopant that functions as a Lewis acid may include BCF (Tris(pentafluorophenyl)borane). For example, when BCF is used as the dopant, the dopant contains a hydrophobic group. BCF is represented by the following formula EF4.

[0059]

[0060] As shown in formula EF4, in a BCF molecule, three benzene rings are bonded to a boron atom. In each benzene ring, fluorine atoms, which function as hydrophobic groups, are bonded to all five carbon atoms other than the carbon atom to which the boron atom is bonded. Therefore, the dopant is also hydrophobic. On the other hand, when Li-TFSI is used, the dopant also contains fluorine, but in this case, the Li ions are easily ionized, making the dopant hydrophilic rather than hydrophobic.

[0061] The base material and the dopant may be materials that function as a soft Lewis base and a soft Lewis acid, respectively. The soft Lewis base and the soft Lewis acid may be defined, for example, by the HSAB principle (hard and soft acids and bases principle). The HSAB principle is mentioned, for example, in Aramaki, "Further Considerations on Corrosion and Inhibition Phenomena of Anions Based on the Hard and Soft Acids and Bases Principle," Materials and the Environment, Japan Society of Corrosion Engineering, 2014, Vol. 63, pp. 417-426. All of the specific examples of the base material materials described above in this embodiment correspond to soft Lewis bases, and all of the specific examples of the dopant materials correspond to soft Lewis acids.

[0062] <1-2-3. Film Formation Method> The hole transport section 1031 is formed, for example, as follows. First, a second raw material liquid obtained by dissolving a base material and a dopant in a solvent is applied onto the photoelectric conversion section 1032 by a coating method such as spin coating. The solvent is not particularly limited as long as it can dissolve the base material and the dopant, and may include, for example, an organic solvent such as toluene or chlorobenzene. The purity of the base material and the purity of the dopant may each be, for example, 85% or more, 90% or more, 95% or more, or 98% or more. A purity of 95% or more allows the formation of a better quality hole transport section 1031.

[0063] The second raw material is then dried. For example, the second raw material may be naturally dried, or the substrate including the photoelectric conversion section 1032 after the second raw material liquid is applied may be heated with a heater such as a hot plate to dry the second raw material liquid. This allows the hole transport section 1031 to be formed on the photoelectric conversion section 1032.

[0064] A Lewis acid dopant can form a required amount of holes inside the hole transport region 1031 without reacting with moisture. In other words, with a Lewis acid dopant, doping proceeds without the need for a reaction with moisture. This makes it possible to form the hole transport region 1031 more easily. In other words, even if the hole transport region 1301 is highly hydrophobic, the required number of holes can be easily formed in the hole transport region 1031 by using a Lewis acid dopant that does not require moisture for doping.

[0065] <1-3. Effect of Hydrophobicity> When the solar cell element 10 is placed outdoors, there is a risk that a large amount of moisture will penetrate into the solar cell element 10 if it rains or snows, or if the outdoor humidity is simply high. If the hole transport section 1031 is not hydrophobic, the reaction between the dopant in the hole transport section 1031 and moisture may proceed excessively. This may result in the detachment of the dopant. If the dopant is detached, the sheet resistance of the hole transport section 1031 increases, degrading the performance of the solar cell element 10.

[0066] In contrast, in the present embodiment, the hole transport section 1031 has hydrophobic properties because it contains a hydrophobic group in its molecule. Therefore, even if moisture enters the interior of the solar cell element 10, the moisture is blocked by the hydrophobic hole transport section 1031. Therefore, the dopant in the hole transport section 1031 is less likely to react with moisture, and the dopant is less likely to be released. This reduces the possibility of performance degradation of the solar cell element 10 even when the solar cell element 10 is exposed to a high-humidity environment, such as outdoors. In other words, the reliability of the hole transport section 1031 and the solar cell element 10 can be improved. This also reduces the need for a separate protective layer to prevent moisture penetration. Omitting such a protective layer can also reduce the manufacturing cost of the solar cell element 10.

[0067] FIG. 4 is a graph showing the relationship between the contact angle of the hole transport section 1031 and the conductivity maintenance rate. The relationship in FIG. 4 is a relationship obtained through an experiment. Here, the inventors formed the hole transport section 1031 on a predetermined substrate. Then, pure water was dropped on the surface of the hole transport section 1031, and the contact angle was measured. The contact angle of the hole transport section 1031 was measured using a predetermined contact angle meter. The contact angle meter used here was a contact angle meter with model number CA-V manufactured by Kyowa Interface Science Co., Ltd. The conductivity maintenance rate is the ratio of the conductivity of the hole transport section 1031 after a humidification test to the conductivity of the hole transport section 1031 before the humidification test, which will be described below. In the humidification test, the hole transport section 1031 was subjected to a temperature of 40° C. and a moisture content of 35 g / m for 120 hours. ３ The hole transport section 1031 was exposed to a nitrogen atmosphere of 1000 kJ / cm2. Since the conductivity can be expressed by the sheet resistance, the conductivity maintenance rate may be the ratio of the sheet resistance of the hole transport section 1031 before and after the humidification test.

[0068] 4, the conductivity maintenance rate increases as the contact angle of the hole transport section 1031 increases, that is, as the hydrophobicity of the hole transport section 1031 increases. This is thought to be because, as described above, the higher the hydrophobicity of the hole transport section 1031, the more the reaction between the hole transport section 1031 and moisture can be reduced, thereby reducing the possibility of the dopant being released.

[0069] Furthermore, as shown in FIG. 4 , the rate of increase in the conductivity maintenance ratio with increasing contact angle increases as the contact angle increases. In other words, the conductivity maintenance ratio improves more rapidly as the contact angle increases. This indicates that the conductivity maintenance ratio can be improved more effectively by setting a high contact angle. Specifically, the contact angle of the hole transport section 1031 may be 68 degrees or greater. That is, the composition of the hole transport section 1031 may be designed so that the contact angle of the hole transport section 1031 is 68 degrees or greater. As can be seen from FIG. 4 , this makes it possible to increase the conductivity maintenance ratio to 1 or greater. In other words, it is possible to prevent a decrease in the conductivity of the hole transport section 1031 due to humidification. The reason why the conductivity maintenance ratio is greater than 1 can be considered, for example, as follows. That is, if the hole transport section 1031 is highly hydrophobic, the hole transport section 1031 does not react much with moisture. However, since there was a large amount of moisture in the surrounding area in this humidification test, a slight reaction with moisture occurred. This may have caused a reaction similar to a doping reaction, resulting in a slight improvement in the conductivity maintenance ratio.

[0070] As described above, according to this embodiment, since the hole transport section 1031 is hydrophobic, even in a high humidity environment, it is possible to reduce the possibility that the conductivity of the hole transport section 1031 will decrease. In other words, it is possible to improve the reliability of the hole transport section 1031, and therefore the reliability of the solar cell element 10.

[0071] <1-3-1. Base Material and Dopant> As described above, the base material may contain a hydrophobic group. Furthermore, the proportion (e.g., volume proportion) of the base material in the hole transport section 1031 may be greater than the proportion of the dopant in the hole transport section 1031. In this case, the base material that accounts for a greater proportion contains a hydrophobic group, and therefore the hydrophobicity of the hole transport section 1031 can be effectively improved.

[0072] Furthermore, the higher the number or density of hydrophobic groups in the host material molecule, the greater the hydrophobicity of the host material. For example, in formula EF2, the host material molecule contains four hydrophobic groups, and in formula EF3, the host material molecule contains eight hydrophobic groups. Since the number and density of hydrophobic groups in the molecule represented by formula EF3 are higher than those of the molecule represented by formula EF2, the host material represented by formula EF3 has higher hydrophobicity than the host material represented by formula EF2. In other words, the host material represented by formula EF3 has the highest hydrophobicity. Specifically, the contact angle of the hole transport portion 1031 including the host material of formula EF2 and the dopant of formula EF4 was 82.3 degrees, and the contact angle of the hole transport portion 1031 including the host material of formula EF3 and the dopant of formula EF4 was 85.3 degrees. The contact angle of the hole transporting portion 1031 containing Spiro-OMeTAD and the dopant of formula EF4 was 71.7 degrees. The content (for example, volume ratio) of the dopant in the hole transporting portion 1031 was 20%.

[0073] Furthermore, the dopant molecules may be low-molecular-weight molecules having a molecular weight smaller than that of the base material molecules. If the dopant is low-molecular-weight, it is easier to arrange hydrophobic groups in the molecule at high density. For example, in a dopant of formula EF4, fluorine atoms are present at a higher density. This allows the hydrophobicity of the hole transport unit 1031 to be improved more efficiently.

[0074] When both the base material and the dopant contain a hydrophobic group, the hydrophobicity of the hole transport section 1031 can be further improved.

[0075] <1-3-2. Outer Portion> As shown in Formulae EF1 to EF4, the hydrophobic group may be located in the outer portion of the molecule. In this case, as described above, the hydrophobicity of the hole transport portion 1031 can be more effectively improved. Furthermore, as shown in Formulae EF2 and EF3, when the molecule has an inner first benzene ring and an outer second benzene ring, the hydrophobic group may be bonded to the outer second benzene ring. This also allows the hydrophobicity of the hole transport portion 1031 to be more effectively improved, as described above.

[0076] 2. Second Embodiment In the second embodiment, another aspect of the solar cell element to which the hole transport section 1031 is applied will be described. Differences from the first embodiment will be mainly described below. The solar cell element 50 according to the second embodiment is a multi-junction solar cell, a tandem solar cell, a stacked solar cell, a stacked solar cell, or the like. More specifically, the solar cell element of the multi-junction solar cell according to the fourth embodiment is a solar cell element in which thin-film solar cells are joined together. The combination of thin-film solar cells may be a combination of perovskite solar cells, or a combination of a perovskite solar cell and another thin-film solar cell such as a silicon-based thin-film solar cell. For example, a dye-sensitized solar cell or an organic thin-film solar cell may be applied as one of the thin-film solar cells.

[0077] 5 is a cross-sectional view perpendicular to the longitudinal direction of the first electrode unit 101 when the light-receiving surface F1 of the solar cell element 50 according to the second embodiment is viewed from above. The solar cell element 50 according to the second embodiment further includes a second solar cell unit 108 in addition to the first solar cell unit 107. In the second embodiment, the second electrode unit 104, the second solar cell unit 108, the first solar cell unit 107, the diffusion reduction unit 102, and the first electrode unit 101 are stacked on the substrate unit 105 in this order. The diffusion reduction unit 102 does not necessarily have to be provided.

[0078] The first solar cell unit 107 converts externally incident light (e.g., sunlight) into electricity. For example, the solar cell unit 103 may generate carriers through photoelectric conversion in response to light irradiation. The carriers include at least one of electrons and holes. The first solar cell unit 107 may be a perovskite solar cell, or other types of solar cells may be applied. For example, the solar cell type may be an inorganic solar cell or an organic solar cell. The inorganic solar cell may be a silicon solar cell or a compound solar cell. The organic solar cell may be a dye-sensitized solar cell or an organic thin-film solar cell. The first solar cell unit 107 may include a hole transport unit 1031, a photoelectric conversion unit 1032, and an electron transport unit 1033, as in the first embodiment.

[0079] Here, the material constituting the first solar cell unit 107 is translucent to light having an absorption wavelength of the second solar cell unit 108. By employing this structure, light having an absorption wavelength of the second solar cell unit 108 can be incident on the second solar cell unit 108.

[0080] The second solar cell unit 108 converts light (e.g., sunlight) incident from the outside into electric power. The second solar cell unit 108 has an absorption wavelength different from the absorption wavelength of the first solar cell unit 107. The absorption wavelength of the second solar cell unit 108 may be longer than the absorption wavelength of the first solar cell unit 107. The absorption wavelength may include not only one wavelength but also a certain wavelength band. For example, the absorption wavelength may be a wavelength band such as the visible light region, or may be a wavelength band from a first wavelength to a second wavelength.

[0081] The second solar cell unit 108 may be a perovskite solar cell, or other types of solar cells may be applied. For example, the solar cell type may be an inorganic solar cell or an organic solar cell. The inorganic solar cell may be a silicon solar cell or a compound solar cell. The organic solar cell may be a dye-sensitized solar cell or an organic thin-film solar cell. The second solar cell unit 108 may include a hole transport unit 1031, a photoelectric conversion unit 1032, and an electron transport unit 1033, as in the first embodiment.

[0082] By adopting this configuration, the plurality of solar cell units 103, such as the first solar cell unit 107 and the second solar cell unit 108, are stacked together, so that the plurality of solar cell units 103 are connected in series. This allows the output power of the solar cell element 50 to be increased, thereby improving the conversion efficiency of the solar cell element 50.

[0083] 5 , the solar cell element 50 according to the second embodiment may further include a buffer portion (not shown) between the first solar cell portion 107 and the second solar cell portion 108. The buffer portion is used to connect the first solar cell portion 107 and the second solar cell portion 108. The buffer portion is translucent to the absorption wavelength of the second solar cell portion 108.

[0084] 5 illustrates a two-layer multi-junction solar cell element, but the solar cell element 50 is not limited to this. For example, the solar cell element 50 may be a two-layer or more multi-junction solar cell element. Furthermore, although the above description shows that light is incident from the side opposite to the substrate portion 105, light may be incident from the substrate portion 105. In this case, the substrate portion 105 is translucent. Light passes through the substrate portion 105, and a portion of the light is absorbed by the second solar cell portion 108. Then, the light that has passed through the second solar cell portion 108 is absorbed by the first solar cell portion 107.

[0085] Furthermore, at least one of the first solar cell unit 107 and the second solar cell unit 108 may function as a support plate (i.e., the substrate unit 105). In this case, the substrate unit 105 is unnecessary. For example, if the second solar cell unit 108 is a crystalline silicon solar cell, the second solar cell unit 108 can function as a support plate for the first solar cell unit 107. The first solar cell unit 107 may be, for example, a perovskite solar cell.

[0086] 3. Third Embodiment In a solar cell module 1, as shown in FIG. 6 , a plurality of solar cell elements 10 are formed on a single substrate 105. In other words, the plurality of solar cell elements 10 share the substrate 105. In this case, the substrate 105 can support the plurality of solar cell elements 10 and protect the plurality of solar cell elements 10. For example, a flat plate having a rectangular surface is used as the substrate 105. For example, glass or a resin such as acrylic or polycarbonate is used as the material of the substrate 105. For example, a material with high light transmittance such as white plate glass, tempered glass, or heat reflective glass can be used as the glass.

[0087] The plurality of solar cell elements 10 are arranged in a plane along the +X direction as a first direction. Here, "arranged in a plane" means that each solar cell element 10 is positioned along a virtual or actual plane and the plurality of solar cell elements 10 are arranged in a line. In the third embodiment, the plurality of solar cell elements 10 are arranged on the substrate portion 105 along the surface of the substrate portion 105.

[0088] More specifically, for example, the plurality of solar cell elements 10 may include five solar cell elements 10 arranged along the first direction (+X direction) on the substrate portion 105. The five solar cell elements 10 include, for example, a first solar cell element 111, a second solar cell element 112, a third solar cell element 113, a fourth solar cell element 114, and a fifth solar cell element 115 arranged in order in the +X direction. In other words, the plurality of solar cell elements 10 includes an n-th solar cell element 11n (n is a natural number from 1 to 5).

[0089] In the third embodiment, each solar cell element 10 has a rectangular shape with its longitudinal direction in the +Y direction. Each solar cell element 10 has a first electrode portion 101, a diffusion reduction portion 102, a solar cell portion 103, and a second electrode portion 104.

[0090] In the third embodiment, five second electrode units 104 are arranged in a planar arrangement in the +X direction on the substrate unit 105. Here, the second electrode unit 104 of the mth solar cell element 11m (m is a natural number from 1 to 4) and the second electrode unit 104 of the (m+1)th solar cell element 11(m+1) are arranged with a gap (also referred to as a first gap) G1 sandwiched between them. For example, the second electrode unit 104 of the first solar cell element 111 and the second electrode unit 104 of the second solar cell element 112 are arranged with a gap (also referred to as a first gap) G1 sandwiched between them. Each first gap G1 has a longitudinal direction along the +Y direction. Furthermore, a first groove P1 is present, with the substrate unit 105 serving as the bottom surface and the two opposing end faces of the two second electrode units 104 sandwiching the first gap G1 as side surfaces.

[0091] In the third embodiment, five first electrode units 101 are arranged in order in a planar manner in the +X direction. Here, the first electrode unit 101 of the mth solar cell element 11m and the first electrode unit 101 of the (m+1)th solar cell element 11(m+1) are arranged with a gap (also referred to as a second gap) G2 sandwiched between them. For example, the first electrode unit 101 of the first solar cell element 111 and the first electrode unit 101 of the second solar cell element 112 are arranged with a gap (second gap) G2 sandwiched between them. Each second gap G2 has a longitudinal direction along the +Y direction, for example. A third groove P3 is also formed with the second electrode unit 104 as its bottom surface. In each solar cell element 10, the second electrode unit 104 protrudes in the +X direction more than the first electrode unit 101. From another perspective, the first gap G1 is located at a position offset in the first direction (+X direction) from the second gap G2.

[0092] The connection portion 12 electrically connects two adjacent solar cell elements 10 among the plurality of solar cell elements 10 in series. In the third embodiment, the mth connection portion 12m electrically connects the mth solar cell element 11m and the (m+1)th solar cell element 11(m+1). For example, the first connection portion 121 electrically connects the first solar cell element 111 and the second solar cell element 112. More specifically, the mth connection portion 12m electrically connects the second electrode portion 104 of the mth solar cell element 11m and the first electrode portion 101 of the (m+1)th solar cell element 11(m+1). For example, the first connection portion 121 electrically connects the second electrode portion 104 of the first solar cell element 111 and the first electrode portion 101 of the second solar cell element 112. This allows the plurality of solar cell elements 10 to be electrically connected in series.

[0093] Furthermore, the connection portions 12 are located between the solar cell portions 103 in the +X direction. From another perspective, there is a second groove P2 having the solar cell portions 103 as both side surfaces and the -Z direction surface of the second electrode portion 104 as its bottom surface. The second groove P2 has a longitudinal direction along the +Y direction. Then, for example, the connection portions 12 are provided in the second groove P2. In this case, the connection portions 12 may be formed by filling the second groove P2 with the first electrode portion 101.

[0094] In the first solar cell element 111, the first electrode unit 101 has a first protrusion 101e that protrudes in the −X direction further than the diffusion reduction unit 102, the solar cell unit 103, and the second electrode unit 104. In the fifth solar cell element 115, the second electrode unit 104 has a second protrusion 104e that protrudes in the +X direction further than the first electrode unit 101, the diffusion reduction unit 102, and the solar cell unit 103. A first conductor W1 for positive output is electrically connected to the first protrusion 101e. A second conductor W2 for negative output is electrically connected to the second protrusion 104e.

[0095] <3. Other Devices> In the above examples, the solar cell element 10 and the solar cell element 10 are described as examples of devices including the hole transport section 1031, but the device is not necessarily limited to this. The device according to this embodiment may be various devices including a semiconductor section that functions as a photoelectric conversion section that converts light to electricity and a hole transport section 1031 located on the semiconductor section. For example, an organic LED (Light Emitting Diode) or an organic EL (Electro Luminescence) display may be applied as the device. Such a device includes a photoelectric conversion section that converts electricity to light and emits light, and a hole transport section 1031 located on the photoelectric conversion section. Alternatively, the device according to this embodiment may be an organic transistor. The organic transistor also includes a semiconductor section and a hole transport section 1031 located on the semiconductor section.

[0096] As described above, the hole transport section 1031, which is a hole transport layer, and the solar cell element and solar cell module including the hole transport section 1031 have been described in detail. However, the above description is merely an example in all respects, and this disclosure is not limited thereto. Furthermore, the various examples described above can be applied in combination as long as they are not mutually contradictory. It is understood that countless examples not illustrated can be envisioned without departing from the scope of this disclosure.

[0097] This disclosure includes the following:

[0098] In one embodiment, (1) the hole transport layer can have hydrophobic groups on its molecules.

[0099] (2) The hole transport layer of (1) above can include a base material and a dopant, and at least one of the base material and the dopant can include the hydrophobic group in the molecule.

[0100] (3) In the hole transport layer of (2) above, the base material may contain the hydrophobic group in its molecule.

[0101] (4) In the hole transport layer of (2) or (3) above, the dopant may contain the hydrophobic group in its molecule.

[0102] (5) In the hole transport layer according to any one of (2) to (4), the dopant may be a Lewis acid for the base material.

[0103] (6) Any one of the hole transport layers (1) to (5) above may have a first benzene ring and a plurality of second benzene rings located outside the first benzene ring in the molecule, and the hydrophobic group may be bonded to the second benzene ring.

[0104] (7) The hole transport layer according to any one of (1) to (6) above may have a contact angle of 68 degrees or more.

[0105] (8) The hole transport layer according to any one of (1) to (7) above may have one or more triphenylamine skeletons in the molecule, and the hydrophobic group may be bonded to the para position of a benzene ring belonging to the triphenylamine skeleton.

[0106] (9) The solar cell element may include a positive electrode, a negative electrode, a photoelectric conversion layer located between the positive electrode and the negative electrode and generating electricity based on light, and a hole transport layer described in any one of (1) to (8) above located between the positive electrode and the photoelectric conversion layer.

[0107] (10) A solar cell module may include a plurality of solar cell elements according to (9) above.

[0108] REFERENCE SIGNS LIST 1 Solar cell module 10 Solar cell element 101 Positive electrode (first electrode portion) 104 Negative electrode (second electrode portion) 1032 Photoelectric conversion layer (photoelectric conversion portion) 1031 Hole transport layer (hole transport portion)

Claims

1. A hole transport layer, with hydrophobic groups on the molecules.

2. A hole transport layer according to claim 1, comprising a host material and a dopant, wherein at least one of the host material and the dopant contains the hydrophobic group in the molecule.

3. A hole transport layer according to claim 2, wherein the base material contains the hydrophobic group in its molecule.

4. A hole transport layer according to claim 2 or 3, wherein the dopant contains the hydrophobic group in its molecule.

5. A hole transport layer according to any one of claims 2 to 4, wherein the dopant is a Lewis acid for the host material.

6. A hole transport layer according to any one of claims 1 to 5, comprising a molecule comprising a first benzene ring and a plurality of second benzene rings positioned outside the first benzene ring, and the hydrophobic group is bonded to the second benzene ring.

7. A hole transport layer according to any one of claims 1 to 6, wherein the contact angle is 68 degrees or more.

8. A hole transport layer according to any one of claims 1 to 7, comprising one or more triphenylamine skeletons in the molecule, and the hydrophobic group is bonded to the para position of a benzene ring belonging to the triphenylamine skeleton.

9. A solar cell element comprising: a positive electrode; a negative electrode; a photoelectric conversion layer located between the positive electrode and the negative electrode and generating electricity based on light; and a hole transport layer according to any one of claims 1 to 8 located between the positive electrode and the photoelectric conversion layer.

10. A solar cell module comprising a plurality of solar cell elements according to claim 9.

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