Hole transport material and solar cell using hole transport material

Abstract

To provide a hole transport material capable of stably and continuously exhibiting superior hole transport properties.SOLUTION: The present invention provides a hole transport layer material having a structure represented by the following formula (1), wherein Lc and Ld are independently -CH2- or -C2H4-, and D represents a structure such as the group (II) shown below, and a solar cell.SELECTED DRAWING: Figure 26

Description

[Technical Field]

[0001] The present invention relates to a hole transport material and a solar cell using the hole transport material. [Background technology]

[0002] Solar cells generally use elements such as silicon, compound semiconductors, and organic semiconductors, but hybrid solar cells (perovskite solar cells) are attracting attention because of their high light-harvesting ability and the ability to be thin-filmed and low-cost.

[0003] Non-Patent Document 1 discloses a perovskite solar cell comprising a glass substrate with a transparent conductive film, a blocking layer made of a dense titanium dioxide (TiO2) film, a power generation layer formed by layering lead bromide (PbBr2), lead iodide (PbI2), methylamine hydrobromide (CH5N·HBr: hereinafter sometimes abbreviated as "MABr"), and formamidine hydroiodide (CH4N2·HI: hereinafter sometimes abbreviated as "FAI"), which are perovskite compounds that are excited by light to generate electrons, on porous titanium dioxide (TiO2), a hole transport layer, and electrodes.

[0004] This power generation layer is a mixed halide (FAPbI3) 0.85 (MAPbBr3) 0.15 It is formed as a perovskite layer.

[0005] Conventionally, the hole transport material commonly used in the hole transport layer is 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (commonly referred to as "spiro-OMeTAD"; hereinafter, this name will be used), which is represented by the following general formula (A) and is described in Non-Patent Document 2. Crystals of perovskite compounds absorb light, generating electrons and holes. Holes are transported to the counter electrode by the hole transport material, and electrons move to the photoelectrode, and this cycle is repeated to generate electricity.

[0006] [ka]

[0007] Spiro-OMeTAD is commercially available and easily available. However, as reported in Non-Patent Document 1, spiro-OMeTAD requires many synthesis and purification steps, making it inherently difficult to reduce the cost. Furthermore, although spiro-OMeTAD can exhibit high initial performance when incorporated into solar cells as a hole-transport material, there are problems with the sustainability of this performance. Therefore, research is underway to develop hole-transport materials that can be provided at low cost and that exhibit efficient and stable hole-transport effects.

[0008] Therefore, Non-Patent Document 1 reports a compound called LD29 as a novel hole-transporting material, which has a carbazole ring in the acceptor (hereinafter referred to as "A") moiety and a triphenyldimethoxyamino group in the donor (hereinafter referred to as "D") moiety linked in a donor-acceptor-donor (hereinafter referred to as "DAD type") structure, and is represented by the following general formula (B). In a solar cell using LD29 as the hole-transporting material, the conversion efficiency was 14.29% without dopant. However, by adding lithium bis(trifluoromethanesulfonyl)imide (hereinafter sometimes referred to as "LiTFSI"), 4-tert-butylpyridine (TBP), and a cobalt complex (FK209) as dopants, the conversion efficiency improved to 18.0%, achieving a conversion efficiency comparable to that of spiro-OMeTAD.

[0009] [ka]

[0010] In LD29, a carbazole ring is introduced into the A moiety. However, the lone electron pair on the heteroatom (nitrogen atom) at the 9th position of the carbazole ring is thought to act as a barrier to electron withdrawal. This reduces the hole transport ability within the LD29 molecule, making it difficult to achieve sufficient solar cell efficiency in solar cells using LD29 as a hole transport material. Furthermore, these solar cells have durability issues, such as a decrease in solar cell efficiency over time. Furthermore, the lone electron pair is known to be an obstacle during synthesis and purification.

[0011] Furthermore, Non-Patent Document 3 reports a compound called YN1 represented by the following general formula (C), and Non-Patent Document 4 reports a compound called PTZ2 represented by the following general formula (D). Both compounds have a DAD-type structure, but suffer from the same problems as the above-mentioned LD29.

[0012] [ka]

[0013] [ka]

[0014] Thus, much research has been conducted on small-molecular-weight organic materials, such as hole transport materials, having a DAD structure. However, no clear rules have been reported regarding the relationship between the combination of the D and A moieties and solar cell performance. The present inventors also reported in Patent Document 1 a small-molecular-weight organic material called DHCF-3, represented by the following general formula (E). DHCF-3 stably exhibits excellent hole transport properties and functions well as a hole transport material. It was also confirmed that when incorporated into solar cells, it exhibited excellent solar cell performance. Here, DHCF-3 has a fluorene ring in the A moiety, a 4-(bis(4-methoxyphenyl)amino)phenyl group in the D moiety, and a structure in which the same substituent as in the D moiety is introduced via a C-C double bond to the carbon at the 9-position of the fluorene ring in the A moiety. Constructing the A moiety as a fluorene ring in this way allows for a simple structure. Furthermore, since the fluorene ring does not contain a heteroatom, it has the advantage of avoiding the aforementioned interference with the electron-withdrawing ability of the A moiety due to the unpaired electron pair of the heteroatom, as well as obstacles during synthesis and purification.

[0015] [ka]

[0016] However, in the hole-transport material described in Patent Document 1, the substituents on the A moiety are bulky, resulting in a sterically close arrangement between the D moiety and the A moiety, with the D moiety on the closer side assuming a more twisted configuration relative to the fluorene ring of the A moiety. This weakens the π-conjugation and is thought to inhibit the hole-transport effect. Furthermore, during the synthesis process, a reaction technique known as Suzuki-Miyaura coupling is used to introduce the D moiety into the 2- and 7-positions of the fluorene ring. However, the reagents used in this reaction are expensive, making the synthesis of DCFH-3 costly. Furthermore, avoiding this reaction requires multiple steps, further increasing costs. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Patent Publication No. 2023-46046 [Non-patent literature]

[0018] [Non-Patent Document 1] XuepengLiu et al., “A star-shaped carbazole-based hole-transporting material with triphenylamine side arms for perovskite solarcells,” J.Mater.Chem.C., 2018, 6, 12912-12918 (DOI:10.1039 / c8tc04191a) [Non-patent document 2] Michael Saliba et al., “How to Make over 20% Efficient Perovskite SolarCells in Regular (nip) and Inverted (pin) Architectures”, Chem. Mater. 2018,30, 13, 4193-4201(DOI:10.1021 / acs.chemmater.8b00136) [Non-patent document 3] Peng Xu et al., “DAD-Typed Hole Transport Materials for Efficient Perovskite SolarCells: Tuning Photovoltaic Properties via the Acceptor Group”, ACS Appl. Mater. Interfaces 2018, 10, 23 (DOI:10.1021 / acsami.8b04003) [Non-patent document 4] Roberto Grisorio et al., “Molecular Tailoring of Phenothiazine-BasedHole-Transporting Materials for High-Performing Perovskite Solar Cells,” ACS Energy Lett. 2017, 2, 5, 1029-1034 (DOI:10.21 / acsenergylett.7b00054) Summary of the Invention [Problem to be solved by the invention]

[0019] In view of the above-mentioned problems of the conventional technology, there remains a need for a hole transport material that stably and continuously exhibits excellent hole transport properties. There is also a need for a hole transport material that can be provided at low cost. There is also a need for a solar cell with high cell performance that can be provided at low cost. [Means for solving the problem]

[0020] The hole transport material according to the present invention has the following characteristic features: A hole transport material having a structure represented by the following general formula (1): [ka] {In general formula (1), The two D regions are regions having the same structure, The D portion is represented by the structure of the following group (I) or group (II): [ka] [In group (I), X is an integer of 0 or 1, R 1a and R 1b independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8), R 2a1 , R 2a2 , R 2b1 and R 2b2 are independently selected from -H or -F; R 3a1 , R 3a2 , R 3b1 and R 3b2 are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8), [ka] [In group (II), R D1 and R D2 are independently represented by the structure of the following group (I'): [ka] (Group (I´) inside X' is an integer of 0 or 1, R 1a´ and R 1b´ independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1(wherein m is an integer selected from 1 to 8), R 2a1´ , R 2a2´ , R 2b1´ and R 2b2´ are independently selected from -H or -F; R 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8) L c and L d are independently -CH2- or -C2H4-, R c1 , R c2 , R c3 , R c4 and R c5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2), R d1 , R d2 , R d3 , R d4 and R d5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1(where m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).

[0021] The above-described structure provides a hole transport material with excellent hole transport properties, capable of stably and efficiently capturing and transporting holes. Specifically, the hole transport material of this structure has a DAD structure, in which the A moiety is a fluorene ring, and two substituted or unsubstituted benzene rings are introduced to the 9-position of the fluorene ring via a short hydrocarbon-chain linker. This structure allows the two benzene rings to be arranged perpendicular to the fluorene ring. Furthermore, the linker maintains an appropriate distance between the fluorene ring and the benzene ring, thereby suppressing steric hindrance between the benzene ring and the D moieties introduced at the 2- and 7-positions of the fluorene ring. This results in smooth π-conjugation between the A moiety composed of a fluorene ring and the D moiety introduced into the A moiety, enhancing the intramolecular push-pull effect and improving intramolecular and intermolecular charge transfer properties. Furthermore, smooth electron transfer within the molecule results in clearer HOMO-LUMO charge separation. That is, in the hole transport material of this configuration, electrons are concentrated in the D portion at the HOMO and HOMO-1 levels, and electrons are concentrated in the A portion at the LUMO level. Thus, the hole transport material of this configuration can exhibit excellent hole transport properties due to improved intramolecular and intermolecular charge transfer properties. Therefore, this configuration solves conventional technical problems, such as a decrease in hole transport performance due to a decrease in π-conjugation caused by steric interference between the substituent in the A portion and the D portion, and provides a hole transport material that can stably and sustainably exhibit excellent hole transport properties.

[0022] Furthermore, by using a fluorene ring containing no heteroatom as the A portion, the problem of the inhibition of electron-withdrawing ability due to the lone pair of the heteroatom, which occurs in LD29 and the like as described in the [Prior Art] section, is resolved, and the compound can function as a hole-transporting material more efficiently.

[0023] Furthermore, the hole transport material of this configuration has a deep HOMO energy level, which allows appropriate adjustment of the arrangement with the HOMO level of the perovskite, thereby improving the hole transport properties and facilitating the improvement of solar cell efficiency.

[0024] The hole transport material of this configuration exhibits almost no light absorption in the visible light range and only weak light absorption in the 400 to 450 nm range. Therefore, solar cells using this hole transport material can minimize light absorption loss due to the hole transport material, and are expected to have high photoelectric conversion efficiency.

[0025] The hole transport material of this configuration also has excellent solubility in solvents, which allows it to be applied using wet processes such as spin coating, facilitating the formation of a hole transport layer for a solar cell.

[0026] Furthermore, the hole transport material of the present invention can be synthesized in a short time with few synthetic steps using inexpensive raw materials, and a high-purity product can be obtained through a simple purification process. Therefore, expensive reagents and complicated processes are not required, and the costs required for synthesis and purification can be reduced, making it possible to provide an inexpensive, high-performance hole transport material.

[0027] Furthermore, the hole transport material of this configuration allows smooth intramolecular and intermolecular hole movement, which is expected to suppress molecular oxidation and improve durability. Furthermore, because the hole transport material of this configuration has improved hydrophobicity, a hole transport layer formed using the hole transport material of this configuration can also function as a protective film for the perovskite layer, which decomposes in water, resulting in the advantage of improved durability of the solar cell.

[0028] As described above, the hole transport material of the present invention has excellent properties and can be suitably used as a hole transport material for solar cells. When the hole transport material of the present invention is used in the hole transport layer of a perovskite solar cell or the like, excellent cell performance was demonstrated in initial experiments. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic cross-sectional view of a perovskite solar cell. [Figure 2] FIG. 1 is a perspective view from above of a perovskite solar cell. [Figure 3] FIG. 1 is an explanatory diagram of power generation in a perovskite solar cell. [Figure 4] FIG. 1 is an explanatory diagram showing a procedure for fabricating a perovskite solar cell. [Figure 5] FIG. 1 shows the synthesis schemes of the hole transport materials (DHCF-32, DHCF-31, and DHCF-39) prepared in Examples 1 to 3. [Figure 6] FIG. 2 shows the results of 1H NMR analysis confirming the synthesis of the hole transport material (DHCF-32) prepared in Example 1. [Figure 7] FIG. 1 shows the results of mass spectrometry confirming the synthesis of the hole transport material (DHCF-32) prepared in Example 1. [Figure 8] FIG. 1 shows the results of HPLC analysis confirming the synthesis of the hole transport material (DHCF-32) prepared in Example 1. [Figure 9] FIG. 2 shows the results of ultraviolet-visible-near-infrared spectroscopic analysis confirming the synthesis of the hole transport material (DHCF-32) prepared in Example 1. [Figure 10] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-31) prepared in Example 2. [Figure 11] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-39) prepared in Example 3. [Figure 12] FIG. 1 shows the synthesis schemes of the hole transport materials (DHCF-33, DHCF-34, DHCF-35, and DHCF-36) prepared in Examples 4 to 7. [Figure 13] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-33) prepared in Example 4. [Figure 14] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-34) prepared in Example 5. [Figure 15] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-35) prepared in Example 6. [Figure 16] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-36) prepared in Example 7. [Figure 17] FIG. 1 shows the synthesis schemes of the hole transport materials (DHCF-43, DHCF-44, DHCF-45, and DHCF-46) prepared in Examples 8 to 11. [Figure 18] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-43) prepared in Example 8. [Figure 19] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-44) prepared in Example 9. [Figure 20] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-45) prepared in Example 10. [Figure 21]FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-46) prepared in Example 11. [Figure 22] FIG. 1 shows the synthesis schemes of the hole transport materials (DHCF-47, DHCF-48, and DHCF-49) prepared in Examples 12 to 14. [Figure 23] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-47) prepared in Example 12. [Figure 24] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-48) prepared in Example 13. [Figure 25] FIG. 1 shows the results of H NMR analysis (a), mass spectrometry (b), HPLC analysis (c), and UV-Vis-NIR spectroscopy (d) confirming the synthesis of the hole transport material (DHCF-49) prepared in Example 14. [Figure 26] 1 is a graph showing the results of cell performance evaluation-1 (DHCF-32, DHCF-39) of solar cells investigated in Example 16, showing the IV characteristics of each solar cell investigated. DETAILED DESCRIPTION OF THE INVENTION

[0030] An embodiment of a perovskite solar cell 10 (an example of a solar cell 10; hereinafter referred to as "solar cell 10") using a hole transport material according to the present invention will be described below with reference to the drawings. In this embodiment, as an example of solar cell 10, a solar cell 10 configured with a perovskite layer 44 made of an organic and inorganic hybrid compound will be described. However, the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0031] (Basic configuration of solar cell 10 according to this embodiment) As shown in FIGS. 1 and 2 , a solar cell 10 according to this embodiment includes a substrate 2 having a transparent substrate 21 and a transparent conductive film 22; a blocking layer 3 provided on the substrate 2, which transfers electrons to the transparent conductive film 22 and separates the hole transport layer 5 from the transparent conductive film 22 to prevent recombination of electrons and holes (reverse electron transfer); a power generation layer 4 provided on the blocking layer 3 and formed by stacking a perovskite layer 44, which generates electrons upon excitation by light, on a porous semiconductor 41; and a hole transport layer 5 provided on the power generation layer 4 and through which holes generated in the perovskite layer 44 pass. The solar cell 10 also includes an electrode 6 provided on the surface of the blocking layer 3, which includes a photoelectrode 61 that emits electrons through the transparent conductive film 22, and a counter electrode 62 that receives electrons and is provided on the surface of the hole transport layer 5. The arrangement of the electrode 6 is not particularly limited as long as electrons can be transferred; for example, the photoelectrode 61 may be formed by connecting a conductor to the transparent conductive film 22. In order to improve the durability of the solar cell 10, the counter electrode 62 may be protected by a transparent substrate 21 or the like.

[0032] The transparent substrate 21 is made of a light-transmitting material. For example, a transparent glass substrate, a frosted semi-transparent glass substrate, a transparent resin substrate, etc. The transparent conductive film 22 can be made of, for example, fluorine-doped tin oxide (FTO), tin oxide (TO), tin-doped indium oxide (ITO), zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), etc.

[0033] Metal oxides such as titanium dioxide (TiO), zinc oxide (ZnO), niobium oxide (NbO), tin dioxide (SnO), and aluminum oxide (AlO) are suitable for the blocking layer 3 and the porous semiconductor 41. A sintered body of titanium dioxide (TiO) is particularly preferable, as it provides a large surface area for laminating the perovskite layer 44. The blocking layer 3 extends partially into the transparent conductive film 22, thereby defining the transparent conductive film 22. The blocking layer 3 also includes a dense insulating layer 31 that allows electrons to pass through in the lamination direction but restricts their lateral movement. In other words, electrons entering from the blocking layer 3 smoothly move in the lamination direction of the transparent conductive film 22 and are supplied to the photoelectrode 61. At the same time, the insulating layer 31 prevents electrons from moving to the counter electrode 62, preventing short-circuiting.

[0034] The perovskite layer 44 is produced by reacting a compound composed of lead and a halogen element X (PbX2, X = halogen element) with methylammonium iodide (CH3NH3I, hereinafter sometimes abbreviated as "MAI"). Specifically, a solution 42 containing lead and a halogen element X is infiltrated into the pores of a porous semiconductor 41, dried, and then immersed in a mixed solution 43 of MAI, whereby crystals of the perovskite compound (CH3NH3PbI3 when X = I) that forms the perovskite layer 44 are rapidly produced. The halogen element X can be iodine, bromine, or chlorine, but iodine is preferred due to its high morphological stability. Alternatively, a mixed cation-mixed halide (FAPbI3) using MABr and 0.2 M lead bromide (PbBr2), or FAI and lead iodide (PbI2) can be used. 1-x (MAPbBr3) x ) can also be used. For example, (FAPbI3) 0.85 (MAPbBr3) 0.15 etc. can be suitably used.

[0035] A hole transport material, which will be described later, is used for the hole transport layer 5. For the electrode 6, for example, a simple metal or alloy of a metal such as gold, platinum, silver, or copper, or an oxide conductor such as fluorine-doped tin oxide (FTO) or tin-doped indium oxide (ITO) can be used.

[0036] Here, the principle of how solar cell 10 generates electricity will be explained with reference to Figure 3. When light such as sunlight or room light is incident on transparent substrate 21, this incident light passes through substrate 2 and blocking layer 3 without being absorbed much, and most of it reaches power generation layer 4. When the incident light that has reached power generation layer 4 is irradiated onto perovskite layer 44, this perovskite layer 44 absorbs the light energy and becomes excited. When this excitation raises the energy level of perovskite layer 44 to a predetermined level higher than the conduction band potential of the metal oxide that is porous semiconductor 41, electrons are injected from perovskite layer 44 into porous semiconductor 41. The injected electrons pass through blocking layer 3 and are collected by photoelectrode 61.

[0037] Meanwhile, holes generated in the perovskite layer 44 reach the counter electrode 62 via the hole transport layer 5, where they recombine with electrons that have passed through the external load 7. In other words, a potential gradient is generated between the photoelectrode 61 and the counter electrode 62, and power can be supplied by connecting the external load 7 between the two electrodes.

[0038] (Procedure for producing solar cell 10 according to this embodiment) The procedure for fabricating the solar cell 10 according to this embodiment will be described with reference to FIG. 4. However, the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the invention. Furthermore, the solar cell 10 can be fabricated with reference to known techniques such as those described in Michael Saliba et al., "Correction to 'How to Makeover 20% Efficient Perovskite Solar Cells in Regular (nip) and Inverted (pin) Architectures," Chem. Mater., 2018, 30, 4193-4218.

[0039] First, a transparent conductive film 22 is formed on a transparent substrate 21 to prepare the substrate 2. The transparent conductive film 22 is laminated on the transparent substrate 21 by, for example, chemical vapor deposition (CVD) or sputtering. Next, laser scribing is performed to partially remove the transparent conductive film 22, forming recesses 221 for the insulating layer 31, followed by cleaning. Next, a blocking layer 3 is formed over the entire surface of the substrate 2 by, for example, atomic layer deposition (ALD) or spray pyrolysis (SPD). The blocking layer 3 is preferably formed as a dense TiO layer. Next, a porous semiconductor 41, which is a nanoparticle sintered layer, is formed near the center of the masked substrate 2 and blocking layer 3. It is preferably formed as a porous layer of TiO (p-TiO). This porous semiconductor 41 is formed by diluting a nanoparticle paste with a solvent, applying and drying it by, for example, spin coating at a rotation speed of 4000 rpm to 6000 rpm, and then removing the mask and heating it at 450°C to 550°C to form a sintered layer.

[0040] For example, a PbI2 solution 42 in N,N-dimethylformamide is prepared and dropped onto the porous semiconductor 41. After that, the solution is permeated into the pores (p-TiO2) and excess solution is removed by spin coating at a rotation speed of, for example, 5000 rpm to 8000 rpm. The solution is then dried at 60°C to 120°C (preferably 70°C to 90°C) to form a PbI2 layer.

[0041] The porous semiconductor 41, which contains the substrate 2, blocking layer 3, and lead iodide impregnated therein, is immersed in an isopropyl alcohol solution 43 of MAI (CH3NH3I) (2-20 mg / ml) at 0°C to 80°C (preferably at room temperature) (MAI immersion method). The PbI2 reacts with MAI to form a perovskite compound [(CH3NH3)PbI3(MAPbI3)] as a perovskite layer 44 inside and on top of the pores of the porous semiconductor 41. The porous semiconductor 41 is then rinsed with pure isopropyl alcohol and dried at 60°C to 120°C (preferably 70°C to 100°C). The mixed cation-mixed halide ((FAPbI3) 1-x (MAPbBr3) x)-based perovskite compounds can also be prepared in a similar manner.

[0042] The hole transport material according to this embodiment is prepared as a 60 to 90 mg / ml chlorobenzene solution, for example. The solution is dropped onto the perovskite layer 44, excess solution is removed by spin coating, and the solution is dried to form the hole transport layer 5. The hole transport material may contain an additive such as 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (hereinafter, sometimes referred to as "TPFB"). When TPFB is added, the TPFB content of the hole transport material is preferably 0.01 to 100% by weight, and more preferably 0.1 to 50% by weight. For example, the hole transport material according to this embodiment is weighed out to a concentration of 30 mM, and TPFB equivalent to 10% by weight is added. The hole transport layer 5 can be formed using this solution dissolved in chlorobenzene.

[0043] The steps from forming the PbI2 layer to forming the hole transport layer 5 are preferably carried out in a dry nitrogen atmosphere such as in a glove box. Finally, a thin film of gold or the like is deposited on the surfaces of the blocking layer 3 and the hole transport layer 5 by vacuum deposition or the like to form an electrode 6.

[0044] In the above-described fabrication procedure, the crystal growth of the perovskite compound forming the perovskite layer 44 is controlled in two steps, but this process may be performed in one step. For example, a perovskite ((CH3NH3)PbI3) solution is infiltrated into the pores of the porous semiconductor 41 by spin coating. Toluene is added dropwise during spinning to precipitate microcrystals and give the surface a mirror finish (poor solvent precipitation method). Subsequently, the hole transport layer 5 may be formed using the hole transport material according to this embodiment.

[0045] (Hole transport material according to this embodiment) The hole transport material according to this embodiment has a DAD structure, and a suitable example thereof is a compound represented by the following general formula (1):

[0046] [ka]

[0047] An electron-accepting group (electron-withdrawing group) is introduced into the A moiety, which is configured as a fluorene ring, and two units of a substituted or unsubstituted benzene ring are introduced at the 9-position of the fluorene ring via a short hydrocarbon chain linker. The fluorene ring is composed of carbon atoms and hydrogen atoms and does not contain heteroatoms such as nitrogen atoms. Furthermore, the fluorene ring is linked to the D moieties at the 2- and 7-positions, respectively. The D moieties linked to the 2- and 7-positions of the fluorene ring are preferably configured as the same group.

[0048] The D portion is configured as an electron-donating group, and is preferably represented by a structure selected from the following group (I) or group (II): The wavy line in the group indicates the bonding position with the A portion.

[0049] [ka]

[0050] In group (I), X is an integer of either 0 or 1. Therefore, group (I) includes an embodiment in which a structure constituted by a substituted diphenylamino group is introduced into the A moiety via a benzene ring, and an embodiment in which a structure constituted by a substituted diphenylamino group is introduced directly into the A moiety.

[0051] The substituents of the substituted diphenylamino group are R 1a , R 1b , R 2a1 , R 2a2 , R 2b1 , R 2b2 、 R 3a1 , R 3a2 , R 3b1 , and ,R 3b2 It is defined as follows:

[0052] In group (I), R 1a and R 1b independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8). R in group (I) 1a and R 1b may be the same or different.

[0053] R 1a and R 1b -C is one of the options m H 2m+1is an alkyl group having a chain length of 1 to 8 carbon atoms. The alkyl group may be linear or branched, and is not particularly limited as long as it has 1 to 8 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n-pentyl group, isopentyl group, neopentyl group, t-pentyl group, s-pentyl group, 2-methylbutyl group, 1-ethylpropyl group, 2-ethylpropyl group, n-hexyl group, isohexyl group, neohexyl group, t-hexyl group, 2,2-dimethylbutyl group, 2-methylpentyl group, 3-methylpentyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-propylpropyl group, n-heptyl group, isoheptyl group, s-heptyl group, t-heptyl group, 2,2-dimethylpentyl group, 3,3-dimethylpentyl group, 1-methylhexyl group, 2 Examples of the alkyl group include 1-methylhexyl group, 3-methylhexyl group, 4-methylhexyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-ethylpentyl group, 1-propylbutyl group, 2-propylbutyl group, n-octyl group, isooctyl group, t-octyl group, neooctyl group, 2,2-dimethylhexyl group, 3,3-dimethylhexyl group, 4,4-dimethylhexyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 5-methylheptyl group, 1-ethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 4-ethylhexyl group, 1-propylpentyl group, 2-propylpentyl group, and 3-propylpentyl group.

[0054] R 1a and R 1b -OC is one of the options m H 2m+1 is an alkoxy group having a chain length of 1 to 8 carbon atoms. An alkoxy group is a group in which an alkyl group is bonded to an oxygen atom. The definition of an alkyl group is as above.

[0055] In group (I), R 1a and R 1b is preferably a methoxy group or a methyl group, and is preferably constituted as the same group.

[0056] In group (I), R 2a1 , R 2a2 , R 2b1 , and R 2b2 are independently -H or -F. When -F is introduced, the number is 1 to 4. The position of F introduction is not particularly limited. Therefore, R 2a1 and R 2b1 , or R 2a2 and R 2b2 In addition, all of the -F may be -F or -H. 2a1 and R 2a2 , R 2b1 and R 2b2 , R 2a1 and R 2b2 , or R 2a2 and R 2b1 Alternatively, only one of them may be -H and the other three may be -F, or conversely, only one of them may be -F and the other three may be -H.

[0057] In group (I), R 2a1 , R 2a2 , R 2b1 and R 2b2 is preferably —H and is preferably configured as the same group.

[0058] In group (I), R 3a1 , R 3a2 , R 3b1 and R 3b2 are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (where m is an integer selected from 1 to 8). 3a1 , R 3a2 , R 3b1 and R 3b2may be the same or different, or some may be the same or different. Substituents other than -H may be introduced symmetrically or asymmetrically. -C m H 2m+1 and -OC m H 2m+1 The details of the definition are as above.

[0059] In group (I), R 3a1 , R 3a2 , R 3b1 and R 3b2 is preferably —H and is preferably configured as the same group.

[0060] [ka]

[0061] In group (II), R D1 and R D2 is preferably independently selected from the following groups (I'): D1 and R D2 may be the same or different, and are preferably configured as the same group.

[0062] [ka]

[0063] Thus, group (II) is R D1 and R D2 The group (I') is introduced into the 3-position and the 6-position of the carbazole ring, respectively, and two units of the group (I') are introduced into the A portion via the carbazole ring.

[0064] In the group (I'), X' is an integer of either 0 or 1. Therefore, the group (I') includes an embodiment in which a structure constituted by a substituted diphenylamino group is introduced into a carbazole ring via a phenyl group, and an embodiment in which a structure constituted by a substituted diphenylamino group is introduced directly into a carbazole ring.

[0065] The substituents of the substituted diphenylamino group are R 1a´ , R 1b´ , R 2a1´ , R 2a2´ , R 2b1´ , R 2b2´ , R 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ It is defined as follows:

[0066] In the group (I´), R 1a´ and R 1b´ independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8). 1a´ and R 1b´ may be the same or different.

[0067] R 1a´ and R 1b´ is one of the options -C m H 2m+1 is an alkyl group having a chain length of 1 to 8 carbon atoms, and R 1´ -OC is one of the options m H 2m+1 is an alkoxy group with a chain length of 1 to 8 carbon atoms. m H 2m+1 and -OC m H 2m+1 The details of the definition are as above.

[0068] In the group (I´), R 1a´ and R 1b´ is preferably a methoxy group or a methyl group, and is preferably constituted as the same group.

[0069] In the group (I´), R 2a1´ , R 2a2´ , R 2b1´ , and R2b2´ are independently -H or -F, and when -F is introduced, the number is 1 to 4. The position where F is introduced is not particularly limited. Therefore, R 2a1´ and R 2b1´ , or R 2a2´ and R 2b2´ In addition, all of the -F may be -F or -H. 2a1´ and R 2a2´ , R 2b1´ and R 2b2´ , R 2a1´ and R 2b2´ , or R 2a2´ and R 2b1´ Alternatively, only one of them may be -H and the other three may be -F, or conversely, only one of them may be -F and the other three may be -H.

[0070] In the group (I´), R 2a1´ , R 2a2´ , R 2b1´ and R 2b2´ is preferably —H and is preferably configured as the same group.

[0071] In the group (I´), R 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (where m is an integer selected from 1 to 8). 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ may be the same or different, or some may be the same or different. Substituents other than -H may be introduced symmetrically or asymmetrically. -C m H 2m+1 and -OC m H 2m+1The details of the definition are as above.

[0072] In the group (I´), R 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ is preferably —H and is preferably configured as the same group.

[0073] The D moiety is preferably a bis(4-alkoxyphenyl)amino group. The alkoxy group contained in this group is preferably selected from a methoxy group, an ethoxy group, a propoxy group, a butoxy group, etc., and is particularly preferably a bis(4-methoxyphenyl)amino group. Also preferably, it is a 4-(bis(4-alkoxyphenyl)amino)phenyl group. The alkoxy group contained in this group is preferably selected from a methoxy group, an ethoxy group, a propoxy group, a butoxy group, etc., and is particularly preferably a 4-(bis(4-methoxyphenyl)amino)phenyl group. Furthermore, it is preferably a bis(4-alkylphenyl)amino group. The alkyl group contained in this group is preferably selected from a methyl group, an ethyl group, a propyl group, a butyl group, etc., and is particularly preferably a bis(4-methylphenyl)amino group. Preferably, the structure may also be one in which a bis(4-alkoxyphenyl)amino group, a 4-(bis(4-alkoxyphenyl)amino)phenyl group, a bis(4-alkylphenyl)amino group, or the like is introduced at the 3- and 6-positions of the carbazole ring, and the amino group portion of the carbazole ring is introduced into the A moiety.

[0074] As shown in the above general formula (1), two units of substituted or unsubstituted benzene rings are introduced into the fluorene ring of the A portion via a linker of a short hydrocarbon chain.

[0075] In general formula (1), L c and L d is a linker connecting the fluorene ring of the A portion to the substituted or unsubstituted benzene ring, and is independently -CH2- or -C2H4-. Thus, the fluorene ring and the substituted or unsubstituted benzene ring are bonded via a linker composed of a hydrocarbon chain.c and L d may be the same or different.

[0076] The substituents of the substituted phenyl group are as follows: c1 , R c2 , R c3 , R c4 , R c5 , R d1 , R d2 , R d3 , R d4 and R d5 It is defined as follows:

[0077] In general formula (1), R c1 , R c2 , R c3 , R c4 and R c5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).

[0078] R c1 , R c2 , R c3 , R c4 and R c5 One of the options is -CN, which is a cyano group.

[0079] R c1 , R c2 , R c3 , R c4 and R c5 -COO-C m H 2m+1 is a carboxyl group (-COOH), and the hydrogen of the carboxyl group is -C m H 2m+1 -C in the group is a group substituted with m H2m+1 is an alkyl group having a chain length of 1 to 4 carbon atoms. The alkyl group may be straight-chain or branched, and is not particularly limited as long as the number of carbon atoms is within the range of 1 to 4. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, and a t-butyl group.

[0080] R c1 , R c2 , R c3 , R c4 and R c5 -OC is one of the options m H 2m+1 is an alkoxy group having a chain length of 1 to 4 carbon atoms. An alkoxy group is a group in which an alkyl group is bonded to an oxygen atom. The definition of an alkyl group is as above.

[0081] R c1 , R c2 , R c3 , R c4 and R c5 -C is one of the options m+n H 2m F 2n+1is -F or a fluoroalkyl group with a chain length of 1 to 6 carbon atoms. A fluoroalkyl group with a chain length of 1 to 6 carbon atoms is an alkyl group with 1 to 6 carbon atoms in which one or several -H are substituted with -F. Therefore, it may be a group in which some -H are substituted with -F, or a perfluoroalkyl group in which all -H are substituted with -F. The alkyl group substituted with -F is not particularly limited, regardless of whether it is linear or branched, as long as it has 1 to 6 carbon atoms. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a t-pentyl group, an s-pentyl group, a 2-methylbutyl group, a 1-ethylpropyl group, a 2-ethylpropyl group, an n-hexyl group, an isohexyl group, a neohexyl group, a t-hexyl group, a 2,2-dimethylbutyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, and a 1-propylpropyl group.

[0082] In general formula (1), R d1 , R d2 , R d3 , R d4 and R d5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).

[0083] R d1 , R d2 , R d3 , R d4 and R d5 The alternatives are -CN, -COO-C m H 2m+1 , -OC m H 2m+1 , and -Cm+n H 2m F 2n+1 For details on the definition of R c1 , R c2 , R c3 , R c4 , and R c5 It is as defined in

[0084] where R c1 , R c2 , R c3 , R c4 , and R c5 Choices and R d1 , R d2 , R d3 , R d4 , and R d5 Although the options for R are the same, these substituents are independently selected and may be the same or different. c1 , R c2 , R c3 , R c4 , R c5 , R d1 , R d2 , R d3 , R d4 , and R d5 Some or all of these may be the same, or all may be different.

[0085] Preferably, R c1 , R c2 , R c3 , R c4 , R c5 , R d1 , R d2 , R d3 , R d4 , and R d5 One or more of the following are -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1(wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).

[0086] In general formula (1), R c1 , R c2 , R c3 , R c4 and R c5 is preferably -H, -CN, -F, or -CF3, and preferably one or several are substituted with -CN, -F, or -CF3. For example, R c1 is -CN or -CF3, and the remaining R c2 , R c3 , R c4 and R c5 is -H, R c2 and R c4 is -CF3 and the remaining R c1 , R c3 and R c5 is -H, R c1 , R c2 , R c3 , R c4 and R c5 In addition, in the general formula (1), R d1 , R d2 , R d3 , R d4 and R d5 is preferably -H, -CN, -F, or -CF3, and preferably one or several are substituted with -CN, -F, or -CF3. For example, R d1 is -CN or -CF3, and the remaining R d2 , R d3 , R d4 and R d5 is -H, R d2 and R d4 is -CF3, and the remaining R d1 , R d3 and R d5 is -H, R d1 , R d2 , R d3 , R d4 and R d5 More preferably, R c1 and Rd1 However, the above -CN, -COO-C m H 2m+1 , -OC m H 2m+1 , and -C m+n H 2m F 2n+1 and particularly preferably selected from -CN and -CF3. c1 may be -CN, and R d1 may be -CF3, and vice versa.

[0087] Preferred examples of the A moiety include a structure in which two units of p-trifluoromethylbenzyl groups are introduced at the 9-position of the fluorene ring, a structure in which two units of 3,5-bis(trifluoromethyl)benzyl groups are introduced, a structure in which two units of p-cyanobenzyl groups are introduced, and a structure in which two units of 2,3,4,5,6-pentafluorobenzyl groups are introduced.

[0088] [Suitable Examples of Hole Transport Materials According to the Present Embodiment] Suitable examples of compounds of the hole transport material according to this embodiment are summarized in the table below.

[0089] [Table 1-1] [Table 1-2]

[0090] The structure of a compound of general formula (2), which is one suitable example of a hole transport material according to this embodiment, will be described in detail. The compound of general formula (2) has a DAD structure. The A moiety is a fluorene ring, and two units of p-trifluoromethylbenzyl groups are introduced at the 9-position of the fluorene ring. Furthermore, di(4-methoxyphenyl)amino groups are introduced at the 2- and 7-positions of the fluorene ring as the D moiety.

[0091] [Method for synthesizing hole transport material according to this embodiment] The hole transport material according to this embodiment can be easily synthesized by referring to the synthesis methods described in Examples 1 to 14 below. Examples 1 to 14 show examples of synthesis methods for suitable examples of the hole transport material according to this embodiment. However, the synthesis is not limited to these methods, and other suitable methods can also be used.

[0092] A preferred example of the hole transport material according to this embodiment has a DAD structure, in which the A moiety is a fluorene ring, two substituted or unsubstituted benzene rings are introduced to the 9-position of the fluorene ring via a hydrocarbon chain linker, and D moieties are introduced to the 2- and 7-positions of the fluorene ring. The synthesis begins with synthesizing a compound in which two substituted or unsubstituted benzene rings are introduced to the 9-position of the fluorene ring constituting the A moiety via a linker. This compound can be synthesized by reacting a fluorene ring with a compound in which the end of the linker connected to the desired substituted or unsubstituted benzene ring is substituted with a halogen in the presence of potassium or sodium tert-butoxide. At this time, a halogen atom is introduced into the fluorene ring at the D moiety's insertion position; for example, a bromine atom can be introduced by bromination using NBS or the like. Subsequently, the D moiety is introduced by cross-coupling or other methods known in the art, thereby synthesizing the hole transport material according to this embodiment. For example, in the above-mentioned preferred examples such as DHCF-32, DHCF-39, and DHCF-35, the D moiety can be introduced at the 2- and 7-positions of the fluorene ring of the A moiety by Buchwald-Hartwig coupling. In addition, in the case of DHCF-33, the D moiety can be introduced at the 2- and 7-positions of the fluorene ring of the A moiety by Suzuki-Miyaura coupling. [Example]

[0093] The present invention will be described in detail with reference to the following examples.

[0094] Example 1: Preparation of hole transport material (DHCF-32) The hole transport material prepared in this example is designated "DHCF-32," and is represented by the general formula (2) above. DHCF-32 is a compound in which the A moiety is a fluorene ring, two p-trifluoromethylbenzyl groups are introduced at the 9-position of the fluorene ring, and di(4-methoxyphenyl)amino groups are introduced as the D moiety at the 2- and 7-positions of the fluorene ring. The preparation of DHCF-32 is described below with reference to Figure 5, which summarizes the synthetic scheme.

[0095] (Synthetic Procedure) [Step 1] Synthesis of Compound 3 (2,7-dibromo-9,9-bis(4-(trifluoromethyl)benzyl)-9H-fluorene) To a 25 mL round-bottom flask were added 2,7-dibromo-9H-fluorene 1 (0.50 g, 1.5432 mmol, 1.0 molar equivalent (eq.)), 1-(bromomethyl)-4-(trifluoromethyl)benzene 2 (0.92 g, 3.858 mmol, 2.5 molar equivalents), and 12 mL of tetrahydrofuran (THF) (20 mL). Potassium tert-butoxide (tBuOK) (0.52 g, 4.6296 mmol, 3.0 molar equivalents) was then added to the reaction mixture. The reaction mixture was then heated to reflux under argon for 1-2 h. After completion of the reaction, the reaction mixture was cooled to room temperature, extracted with dichloromethane (DCM), washed with water, and saturated brine. The organic layer was separated and concentrated. The crude residue was purified by filter column chromatography (silica gel 100-200 mesh) using petroleum ether:DCM=97:3 as eluent to give the desired compound 3 as a light brown solid (0.84 g, 85% yield).

[0096] [Step 2] Synthesis of DHCF-32 In a 25 mL round-bottom flask, compound 3 (2,7-dibromo-9,9-bis(4-(trifluoromethyl)benzyl)-9H-fluorene) (0.35 g, 0.5466 mmol), bis(4-methoxyphenyl)amine 4 (0.28 g, 1.2026 mmol), and sodium tert-butoxide (NaOtBu) (0.16 g, 1.6399 mmol) were dissolved in 16 mL of dry toluene. The reaction mixture was degassed under an argon atmosphere for 30 min, and then bis(dibenzylideneacetone)palladium (Pd(dba)) (0.019 g, 0.0328 mmol) and tri-tert-butylphosphonium tetrafluoroborate ((tBu)PH BF) (0.014 g, 0.0492 mmol) were added to the reaction mixture. The reaction mixture was refluxed at 130 °C for 24 h under an argon atmosphere. After completion of the reaction, the reaction mixture was cooled to room temperature. The reaction mixture was extracted with DCM, washed with water and saturated brine, and the organic layer was separated and concentrated. The crude residue was purified by column chromatography (silica gel 100-200 mesh) using petroleum ether:DCM = 3:2 as the eluent to obtain DHCF-32 as a pale purple solid (0.32 g, 62.47%).

[0097] (Purification and confirmation) For the obtained DHCF-32, 1 The synthesis and purification of DHCF-32 were confirmed by H NMR analysis, mass spectrometry (hereinafter sometimes referred to as "Mass"), high-performance liquid chromatography analysis (hereinafter sometimes referred to as "HPLC"), and ultraviolet-visible-near-infrared spectroscopy (hereinafter sometimes referred to as "UV-Vis") analysis. 1 The results of the 1 H NMR analysis are shown in Figure 7, the results of the mass analysis in Figure 7, the results of the high performance liquid chromatography analysis in Figure 8, and the results of the ultraviolet-visible-near infrared spectroscopic analysis in Figure 9.

[0098] (Examples 2 and 3) Preparation of hole transport materials DHCF-31 and DHCF-39 The hole transport materials prepared in this example are designated "DHCF-31" (Example 2) and "DHCF-39" (Example 3), respectively, and are designated "DHCF-39" (Example 3), respectively, and are designated "DHCF-31" and "DHCF-39" (Example 3), respectively. DHCF-31 and DHCF-39 can be prepared according to the same procedures as in Example 1. The synthesis scheme is summarized in Figure 5. DHCF-31 was synthesized in the same manner as in Example 1, except that in step 1, 1-(bromomethyl)-4-(trifluoromethyl)benzene 2 was replaced with 4-(bromomethyl)benzonitrile 5. DHCF-39 was synthesized in the same manner as in Example 1, except that in step 2, bis(4-methoxyphenyl)amine 4 was replaced with bis(4-methylphenyl)amine 7.

[0099] Figure 10 shows the results for DHCF-31. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy analysis are shown in Figure 11. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy analysis are shown.

[0100] (Examples 4 to 7) Preparation of hole transport materials DHCF-33 to DHCF-36 The hole transport materials prepared in this example are designated "DHCF-33" (Example 4) represented by the above general formula (5), "DHCF-34" (Example 5) represented by the above general formula (6), "DHCF-35" (Example 6) represented by the above general formula (7), and "DHCF-36" (Example 7) represented by the above general formula (8). DHCF-33 to DHCF-36 can be prepared according to Example 1 above. The synthesis scheme is summarized in Figure 12. DHCF-33 and DHCF-34 were synthesized in the same manner as in Examples 2 and 1, except that bis(4-methoxyphenyl)amine 4 was replaced with 4-methoxy-N-(4-methoxyphenyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline 8 in Step 2 above. DHCF-35 and DHCF-36 were prepared by replacing bis(4-methoxyphenyl)amine 4 with N-(4-methoxyphenyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline 8 in Step 2 above.3 ,N 3 ,N 6 ,N 6 The synthesis was carried out in the same manner as in Examples 2 and 1, except that 9H-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine was used instead.

[0101] Figure 13 shows the results for DHCF-33. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy are shown in Figure 14. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy are shown in Figure 15. 1 The results of H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy analysis are shown in Figure 16. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy analysis are shown.

[0102] (Example 8) Preparation of hole transport material DHCF-43 The hole transport material prepared in this example is designated "DHCF-43" and is represented by the general formula (9). The preparation of DHCF-43 will be explained based on Figure 17, which summarizes the synthesis scheme.

[0103] (Synthetic Procedure) [Step 1] Synthesis of Compound 10 To a 25 mL round-bottom flask were added 2,7-dibromo-9H-fluorene 1 (0.40 g, 1.2345 mmol, 1.0 molar equivalent (eq.)), 1-(bromomethyl)-4-(trifluoromethyl)benzene 2 (0.32 g, 1.358 mmol, 1.1 molar equivalent), 4-(bromomethyl)benzonitrile 5 (0.27 g, 1.358 mmol, 1.1 molar equivalent), and 12 mL of THF (20 mL). Potassium tert-butoxide (tBuOK) (0.42 g, 3.7037 mmol, 3.0 molar equivalent) was then added to the reaction mixture. The reaction mixture was then heated to reflux under argon for 2-3 h. After completion of the reaction, the reaction mixture was cooled to room temperature, extracted with DCM, washed with water, and brine solution. The organic layer was separated and concentrated. The crude residue was purified by filter column chromatography (silica gel 100-200 mesh) using petroleum ether:DCM=2:3 as eluent to give the desired compound 10 as a light green solid (0.45 g, 61% yield).

[0104] [Step 2] Synthesis of DHCF-43 Using compound 10 synthesized in step 1, synthesis was carried out in the same manner as in [Step 2] of Example 1 to obtain DHCF-43.

[0105] (Purification and confirmation) Regarding the obtained DHCF-43 1 The results of 1 H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy analysis are shown in Figure 18.

[0106] (Examples 9 to 11) Preparation of hole transport materials DHCF-44 to DHCF-46 The hole transport materials prepared in this example are designated "DHCF-44" (Example 9) represented by the above general formula (10), "DHCF-45" (Example 10) represented by the above general formula (11), and "DHCF-46" (Example 11) represented by the above general formula (12). The synthesis scheme is summarized in Figure 17. DHCF-44 to DHCF-46 were synthesized in the same manner as in Examples 1, 4, and 3, respectively, except that in step 1 above, 1-(bromomethyl)-4-(trifluoromethyl)benzene 2 or 4-(bromomethyl)benzonitrile 5 was replaced with 1-bromo-3,5-bis(trifluoromethyl)benzene 11.

[0107] Figure 19 shows the results for DHCF-44. 1 The results of H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy are shown in Figure 20. 1 The results of H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy are shown in Figure 21. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy analysis are shown.

[0108] (Examples 12 to 14) Preparation of hole transport materials DHCF-47 to DHCF-49 The hole transport materials prepared in this example are designated "DHCF-47" (Example 12) represented by the above general formula (13), "DHCF-48" (Example 13) represented by the above general formula (14), and "DHCF-49" (Example 14) represented by the above general formula (15). The synthesis scheme is summarized in Figure 22. DHCF-47 to DHCF-49 were synthesized in the same manner as in Examples 1, 4, and 3, respectively, except that in Step 1 above, 1-(bromomethyl)-4-(trifluoromethyl)benzene 2 or 4-(bromomethyl)benzonitrile 5 was replaced with bromopentafluorobenzene 13.

[0109] Figure 23 shows the results for DHCF-47. 1The results of H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy are shown in Figure 24. 1 The results of H NMR analysis, mass spectrometry, high performance liquid chromatography analysis, and ultraviolet-visible-near infrared spectroscopy are shown in Figure 25. 1 The results of H NMR analysis, mass spectrometry, high-performance liquid chromatography analysis, and ultraviolet-visible-near-infrared spectroscopy analysis are shown.

[0110] (Comparative Example 1) Preparation of DHCF-3 The hole transport material prepared in Comparative Example 1 is designated "DHCF-3" and represented by the general formula (E) above. It is a compound described in Patent Document 1 (JP 2023-46046 A), which was explained in the Background Art section above. Specifically, DHCF-3 is a compound in which a 4-(bis(4-methoxyphenyl)amino)phenyl group is introduced as the D moiety at each of the 2- and 7-positions on the fluorene ring constituting the A moiety, and a 4-(bis(4-methoxyphenyl)amino)phenyl group, the same group as the D moiety, is introduced via a carbon-carbon double bond at the 9-position on the fluorene ring constituting the A moiety. Synthesis and purification can be performed based on the description in Patent Document 1, but will be briefly described below.

[0111] (synthesis) 2,7-Di(4-(bis(4-methoxyphenyl)amino)phenyl)-9H-fluorene (1) (0.01 g, 0.13 mmol), 4-(bis(4-methoxyphenyl)amino)benzaldehyde (2) (0.056 g, 0.17 mmol), TBAB (0.015 g, 0.45 mmol), and dry toluene (8 mL) were added to a 25 mL round-bottom flask. 40% sodium hydroxide (NaOH) (6 mL) was then added. The reaction mixture was heated to reflux under an argon atmosphere for 8 hours. After cooling, the reaction mixture was poured into water and extracted with DCM. The mixture was then washed with brine and concentrated in vacuo to give the crude product.

[0112] (purification) The obtained crude product was purified by column chromatography (silica gel: 100-200 mesh) using petroleum ether:DCM=5:95 as an eluent two to three times to obtain a yellow solid DHCF-3 (yield: 0.10 g, 71.02%).

[0113] Example 15: Fabrication of solar cell 10 Hereinafter, an example of fabricating a solar cell 10 will be described as Example 16. The solar cell 10 can be fabricated with reference to known techniques such as those described in Chem. Mater., 2018, 30, 4193-4218, among others.

[0114] As an example, a fluorine-doped tin oxide (FTO) glass (23 mm × 14 mm × 1.6 mm) was used as the transparent substrate 21. This FTO glass was laser scribed to form recesses 221 by removing the FTO, and then thoroughly cleaned. Next, a TiO2 dense film was formed as the blocking layer 3 using the spray pyrolysis method (SPD method). Furthermore, a solution of commercially available TiO2 nanoparticle paste diluted with ethanol was dropped onto the substrate, which was then applied by spin coating and dried at 100°C. After drying, the substrate was baked at 450°C to form a TiO2 nanoparticle layer that would become the porous semiconductor 41. After baking, the substrate was cooled to room temperature.

[0115] Next, a perovskite precursor solution for forming the perovskite layer 44 was prepared. First, FAI (CH(NH2)2I) was weighed out, and a 1.7 M PbI2 / dimethylformamide (DMF) + dimethyl sulfoxide (DMSO) solution that had been prepared in advance was poured into the weighed FAI to prepare a FAPbI3 solution. Next, MAI (CH3NH3I) was weighed out, and a 1.7 M PbBr2 / dimethylformamide (DMF) + dimethyl sulfoxide (DMSO) solution that had been prepared in advance was poured into the weighed MAI to prepare a MAPbBr3 solution.

[0116] Finally, the FAPbI3 solution, the MAPbBr3 solution, and a previously prepared 1.7 M CsI / dimethyl sulfoxide (DMSO) solution were mixed to prepare a precursor solution for spin coating.

[0117] The perovskite layer 44 was formed by dropping the precursor solution onto the TiO2 porous film and applying it by spin coating. After application was completed, the film was heated at 100°C for 60 minutes and then cooled to room temperature.

[0118] Next, a hole transport layer 5 was prepared. The hole transport material used was a hole transport material selected from those synthesized in Examples 1 to 14 above, or DHCF-3 synthesized in Comparative Example 1 above. Each hole transport material solution was weighed out to a final concentration of 30 mM, and TPFB equivalent to 10% by weight of the solution was added to the hole transport material. A mixture of the hole transport material and TPFB was dissolved in chlorobenzene to prepare a hole transport material solution. The hole transport layer 5 was formed by dropping the hole transport material solution onto the perovskite film and spin coating it.

[0119] After the hole transport layer 5 was formed, a gold film of about 100 nm was formed by vacuum deposition, which was then removed and used as the electrode 6, which was then laminated.

[0120] (Example 16) Cell performance evaluation of solar cell 10-1 In this example, the cell performance of solar cell 10 was evaluated. Here, solar cells 10 using DHCF-32 prepared in Example 1 above, DHCF-39 prepared in Example 3 above, and DHCF-3 prepared in Comparative Example 1 above as hole transport materials were investigated.

[0121] The hole transport materials investigated in this example, DHCF-32 (general formula (2)) in Example 1, DHCF-39 (general formula (4)) in Example 3, and DHCF-3 (general formula (E)) in Comparative Example 1, all have a DAD structure. The A moiety in each case is composed of a fluorene ring, but they differ in the substituent introduced into the A moiety. Specifically, in DHCF-32, two p-trifluoromethylbenzyl groups are introduced at the 9-position on the fluorene ring constituting the A moiety, whereas in DHCF-3 in Comparative Example 1, a 4-(bis(4-methoxyphenyl)amino)phenyl group identical to that in the D moiety is introduced at the 9-position on the fluorene ring constituting the A moiety via a carbon-carbon double bond.

[0122] Table 2 below and Figure 26 show the results of the cell performance evaluation of solar cell 10. Table 2 summarizes the parameters of solar cell 10: short-circuit current density (hereinafter sometimes referred to as "Jsc"), open-circuit voltage (hereinafter sometimes referred to as "Voc"), fill factor (hereinafter sometimes referred to as "FF"), and conversion efficiency. FF is the maximum output P at the point where the product of current and voltage is maximum. max is calculated by dividing by (Voc × Jsc), and the conversion efficiency (PCE (%)) is calculated by (Voc × Jsc × FF ÷ incident light intensity).

[0123] [Table 2]

[0124] The results in Table 2 show that the conversion efficiency of DHCF-32 in Example 1 was 20.5%, and that of DHCF-39 in Example 3 was 20.0%, both of which were above 20% and exhibited excellent solar cell characteristics equivalent to those of DHCF-3 in Comparative Example 1. The characteristic structures of DHCF-32 and DHCF-39 improve the electron-withdrawing properties of the A moiety and eliminate steric interference between the D moiety and the substituent introduced into the A moiety. This increases the intramolecular push-pull effect, improving the charge transfer properties both intramolecularly and intermolecularly, presumably resulting in the excellent solar cell characteristics.

[0125] Furthermore, DHCF-32 of Example 1 and DHCF-39 of Example 3 exhibit smooth intramolecular and intermolecular hole migration, which is expected to suppress molecular oxidation and enhance durability. Furthermore, DHCF-32 and DHCF-39 have two p-trifluoromethylbenzyl groups at the 9-position of the fluorene ring constituting the A moiety. This high fluorine content enhances hydrophobicity. Therefore, they have good solubility in solvents, and after dissolving DHCF-32 and DHCF-39 in an appropriate solvent, the hole transport layer 5 can be formed by a wet process such as spin coating, which simplifies the fabrication of the solar cell 10. Furthermore, the hole transport layer 5 formed using DHCF-32 and DHCF-39 as hole transport materials can also function as a protective film for the perovskite layer 44, which decomposes in water, thereby improving the durability of the solar cell 10.

[0126] In the above embodiment, the following configurations are envisioned.

[0127] (1) A hole transport material having a structure represented by the following general formula (1): [ka] {In general formula (1), The two D regions are regions having the same structure, The D portion is represented by the structure of the following group (I) or group (II): [ka] [In group (I), X is an integer of 0 or 1, R 1a and R 1b independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8), R 2a1 , R 2a2 , R 2b1 and R 2b2 are independently selected from -H or -F; R 3a1 , R 3a2 , R 3b1 and R 3b2 are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8), [ka] [In group (II), R D1 and R D2 are independently represented by the structure of the following group (I'): [ka] (Group (I´) inside X' is an integer of 0 or 1, R 1a´ and R 1b´ independently, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1 (wherein m is an integer selected from 1 to 8), R 2a1´ , R 2a2´ , R 2b1´ and R 2b2´ are independently selected from -H or -F; R 3a1´ , R 3a2´ , R 3b1´ and R 3b2´ are independently -H, -C m H 2m+1 (wherein m is an integer selected from 1 to 8), or -OC m H 2m+1(wherein m is an integer selected from 1 to 8) L c and L d are independently -CH2- or -C2H4-, R c1 , R c2 , R c3 , R c4 and R c5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2), R d1 , R d2 , R d3 , R d4 and R d5 are independently -H, -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).}

[0128] According to the above embodiment, a hole transport material having excellent hole transport properties, capable of stably and efficiently capturing and transporting holes, can be provided. Specifically, the hole transport material according to this embodiment has a DAD structure, in which the A moiety is a fluorene ring, and two substituted or unsubstituted benzene rings are introduced to the 9-position of the fluorene ring via a hydrocarbon chain linker. This configuration allows the two benzene rings to be arranged perpendicular to the fluorene ring. Furthermore, the linker maintains an appropriate distance between the fluorene ring and the benzene ring, thereby suppressing steric hindrance between the benzene ring and the D moieties introduced at the 2- and 7-positions of the fluorene ring. This allows smooth π-conjugation between the A moiety composed of a fluorene ring and the D moiety introduced into the A moiety, thereby enhancing the intramolecular push-pull effect and improving intramolecular and intermolecular charge transfer properties. Furthermore, smooth electron transfer within the molecule results in clearer HOMO-LUMO charge separation. That is, in the hole transport material according to this embodiment, electrons are concentrated in the D moiety at the HOMO and HOMO-1 levels, and electrons are concentrated in the A moiety at the LUMO level. Thus, the hole transport material according to this embodiment exhibits excellent hole transport properties due to improved intramolecular and intermolecular charge transfer properties. Therefore, this embodiment solves conventional technical problems, such as a decrease in hole transport performance due to a decrease in π-conjugation caused by steric interference between the substituent in the A moiety and the D moiety, and provides a hole transport material that can stably and sustainably exhibit excellent hole transport properties.

[0129] Furthermore, by using a fluorene ring containing no heteroatom as the A portion, the problem of the inhibition of electron-withdrawing ability due to the lone pair of the heteroatom, which occurs in LD29 and the like as described in the [Prior Art] section, is resolved, and the compound can function as a hole-transporting material more efficiently.

[0130] Furthermore, since the hole transport material according to this embodiment has a deep HOMO energy level, the arrangement with the HOMO level of the perovskite can be appropriately adjusted, which has the advantage of improving the hole transport properties and facilitating the improvement of solar cell efficiency.

[0131] The hole transport material according to this embodiment exhibits almost no light absorption in the visible light region and only weak light absorption in the 400 to 450 nm region. Therefore, a solar cell 10 using the hole transport material according to this embodiment can minimize light absorption loss due to the hole transport material, and is expected to have high photoelectric conversion efficiency.

[0132] The hole transport material according to this embodiment also has excellent solubility in solvents, which allows for the use of wet processes such as spin coating, facilitating the formation of the hole transport layer 5 of the solar cell 10.

[0133] Furthermore, the hole transport material according to this embodiment can be synthesized using inexpensive raw materials with a few synthesis steps in a short time, and a high-purity product can be provided through a simple purification step. Therefore, expensive reagents and complicated steps are not required, and the costs required for synthesis and purification can be reduced, making it possible to provide an inexpensive, high-performance hole transport material.

[0134] Furthermore, the hole transport material according to this embodiment allows smooth intramolecular and intermolecular hole movement, which is expected to suppress molecular oxidation and improve durability. Furthermore, because the hole transport material according to this embodiment has improved hydrophobicity, the hole transport layer 5 formed using the hole transport material according to this embodiment can also function as a protective film for the perovskite layer 44, which decomposes in the presence of water, resulting in improved durability of the solar cell 10.

[0135] As described above, the hole transport material according to this embodiment has excellent properties and can be suitably used as a hole transport material for the solar cell 10. When the hole transport material according to this embodiment is used in the hole transport layer 5 of the perovskite solar cell 10 or the like, excellent cell performance was demonstrated in initial experiments.

[0136] (2) In the hole transport material of (1), R c1 , R c2 , R c3 , R c4 , R c5 , R d1 , R d2 , R d3 , R d4 , and R d5 One or more of the following are -CN, -COO-C m H 2m+1 (wherein m is an integer selected from 0 to 4), -OC m H 2m+1 (wherein m is an integer selected from 1 to 4), and -C m+n H 2m F 2n+1 (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2).

[0137] In the hole transport material according to this embodiment, the introduction of the above-described substituents into the two benzene ring units introduced into the A moiety further improves the electron-withdrawing properties of the A moiety, further smoothens the π-conjugation between DAD groups within the molecule, and allows for appropriate control of the intramolecular push-pull effect, further improving the intramolecular and intermolecular charge transfer properties. This makes it possible to provide a hole transport material with excellent hole transport properties, particularly capable of stably and efficiently capturing and transporting holes. Furthermore, the improved intramolecular and intermolecular hole mobility is expected to further suppress molecular oxidation and further improve durability.

[0138] (3) In the hole transport material of (1), it is preferable that the D portion is a di(4-methoxyphenyl)amino group.

[0139] In the hole transport material according to this embodiment, the introduction of a di(4-methoxyphenyl)amino group as the D moiety further improves the electron donating property of the D moiety, further smoothens the intramolecular π-conjugation between DAD, allows for appropriate control of the intramolecular push-pull effect, and further improves the intramolecular and intermolecular charge transfer properties. Furthermore, when the di(4-methoxyphenyl)amino group as the D moiety is introduced into the fluorene ring of the A moiety, there is no need to use expensive reagents, such as boronic acid or boronic acid esters, which are required for Suzuki coupling and the like, thereby further reducing the cost required for synthesizing the hole transport material according to this embodiment.

[0140] (4) In the hole transport material of (2), R c1 and R d1 is preferably a trifluoromethyl group.

[0141] In the hole transport material according to this embodiment, the introduction of a trifluoromethyl group at the p-position of two benzene rings introduced into the A moiety further improves the electron-withdrawing properties of the A moiety, further smooths the π-conjugation between DADs within the molecule, allows for appropriate control of the intramolecular push-pull effect, and further improves the intramolecular and intermolecular charge transfer properties. This makes it possible to provide a hole transport material with excellent hole transport properties, particularly capable of stably and efficiently capturing and transporting holes. Furthermore, the improved intramolecular and intermolecular hole mobility further suppresses molecular oxidation, which is expected to further improve durability. Furthermore, the trifluoromethyl group contains many fluorine atoms, thereby improving the hydrophobicity of the hole transport material according to this embodiment. The improved solubility of the hole transport material according to this embodiment in solvents further facilitates the formation of the hole transport layer 5 of the solar cell 10 using this hole transport material. Furthermore, the hole transport layer 5 also functions as a protective film for the perovskite layer 44, which decomposes in water, further improving the durability of the solar cell 10.

[0142] (5) The hole transport material of (1) is preferably a hole transport material represented by the following general formula (2) or (4). [ka] [ka]

[0143] In the hole transport material according to this embodiment, the introduction of trifluoromethyl groups at the p-positions of the benzene rings of the two units introduced into the A moiety further improves the electron-withdrawing properties of the A moiety, and the introduction of a di(4-methoxyphenyl)amino group or a di(4-methylphenyl)amino group into the D moiety further improves the electron-donating properties of the D moiety. This further smoothens the π-conjugation between DAD within the molecule, allowing for appropriate control of the intramolecular push-pull effect and further improving the intramolecular and intermolecular charge transfer properties. Therefore, a hole transport material can be provided that has excellent hole transport properties, particularly the ability to stably and efficiently capture and transport holes.

[0144] (6) A solar cell 10 using the hole transport material of (1), comprising: a substrate 2 having a transparent conductive film 22; a blocking layer 3 that transfers electrons to the transparent conductive film 22 and prevents reverse electron transfer; a power generation layer 4 formed by stacking a perovskite layer 44 that is excited by light to generate the electrons on a porous semiconductor 41; and a hole transport layer 5 through which holes generated from the perovskite layer 44 pass and which contains the hole transport material; and an electrode 6 comprising a photoelectrode 61 that emits the electrons via the transparent conductive film 22 and a counter electrode 62 provided on the surface of the hole transport layer 5.

[0145] The solar cell 10 according to this embodiment includes a hole transport layer 5 formed using the hole transport material according to this embodiment, which has the above-described excellent properties. Specifically, the hole transport material according to this embodiment has excellent hole transport properties, capable of stably and efficiently capturing and transporting holes. In particular, the hole transport material according to this embodiment has a large intramolecular push-pull effect, exhibits excellent intramolecular and intermolecular charge transfer properties, and can therefore exhibit excellent hole transport properties. Furthermore, as described above, the hole transport material according to this embodiment has excellent light absorption properties and also excellent durability. Therefore, by using a hole transport material with excellent properties as the hole transport layer 5, the solar cell 10 according to this embodiment can improve the photoelectric conversion efficiency, thereby improving cell performance and further improving the durability of the solar cell 10.

[0146] Furthermore, as described above, the hole transport material according to this embodiment can be synthesized inexpensively and simply without requiring expensive reagents or complicated processes. By using the cost-effective hole transport material according to this embodiment, it is possible to reduce the price of the solar cell 10 according to this embodiment itself.

[0147] [Other embodiments] In the above embodiment, a perovskite solar cell 10 is shown as an example of a solar cell 10 using the hole transport material according to this embodiment, but this hole transport material may also be used in devices using OPV (organic thin film solar cell), organic EL, organic semiconductors, etc. [Industrial Applicability]

[0148] The present invention can be used as a hole transport material for use in perovskite solar cells 10 and the like, which include perovskite compounds formed from organic and inorganic hybrid compounds. [Explanation of symbols]

[0149] 2 boards 3 Blocking Layer 4 Power generation layer 5. Hole transport layer 6 electrodes 10. Solar Cells 11 Laminate 21 Transparent substrate 22 Transparent conductive film 41 Porous Semiconductors 44 Perovskite Layer 61 Photoelectrode 62 Counter electrode

Claims

1. (1) A hole transport material having a structure represented by the following general formula (1): 【Chemistry 1】 {In general formula (1), The two D portions are regions having the same structure, The D portion is represented by the structure of the following group (I) or group (II): 【Chemistry 2】 [In group (I), X is an integer of 0 or 1; R １a and R １ｂ are independently -C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 8), or —O—C ｍ H ２ｍ＋１ where m is an integer selected from 1 to 8; R ２ａ１ , R ２ａ２ , R ２ｂ１ and R ２ｂ２ is independently selected from —H or —F; R ３ａ１ , R ３ａ２ , R ３ｂ１ and R ３ｂ２ are independently —H, —C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 8), or —O—C ｍ H ２ｍ＋１ wherein m is an integer selected from 1 to 8; 【Transformation 3】 [In group (II), R Ｄ１ and R Ｄ２ are independently represented by the structure of the following group (I'): 【Chemistry 4】 (in group (I') X' is an integer of 0 or 1, R １a´ and R １ｂ´ are independently -C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 8), or —O—C ｍ H ２ｍ＋１ where m is an integer selected from 1 to 8; R ２ａ１´ , R ２ａ２´ , R ２ｂ１´ and R ２ｂ２´ is independently selected from —H or —F; R ３ａ１´ , R ３ａ２´ , R ３ｂ１´ and R ３ｂ２´ are independently —H, —C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 8), or —O—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 8) L ｃ and L ｄ are independently —CH ２ -or-C ２ H ４ - and R ｃ１ , R ｃ２ , R ｃ３ , R ｃ４ and R ｃ５ are independently —H, —CN, —COO—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 0 to 4), —O—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 4), and -C ｍ＋ｎ H ２ｍ F ２ｎ＋１ wherein m is an integer selected from 0 to 4 and n is an integer selected from 0 to 2; R ｄ１ , R ｄ２ , R ｄ３ , R ｄ４ and R ｄ５ are independently —H, —CN, —COO—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 0 to 4), —O—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 4), and -C ｍ＋ｎ H ２ｍ F ２ｎ＋１ (wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2)}

2. R ｃ１ , R ｃ２ , R ｃ３ , R ｃ４ , R ｃ５ , R ｄ１ , R ｄ２ , R ｄ３ , R ｄ４ , and R ｄ５ One or more of the groups are -CN, -COO-C ｍ H ２ｍ＋１ (wherein m is an integer selected from 0 to 4), —O—C ｍ H ２ｍ＋１ (wherein m is an integer selected from 1 to 4), and -C ｍ＋ｎ H ２ｍ F ２ｎ＋１ 2. The hole transport material of claim 1, wherein m is an integer selected from 0 to 4, and n is an integer selected from 0 to 2.

3. 2. The hole transport material of claim 1, wherein the D moiety is a di(4-methoxyphenyl)amino group.

4. R ｃ１ and R ｄ１ The hole transport material according to claim 2, wherein is a trifluoromethyl group.

5. 2. The hole transport material according to claim 1, represented by the following general formula (2) or (4): 【Transformation 5】 【Transformation 6】

6. A solar cell using the hole transport material according to any one of claims 1 to 5, a substrate having a transparent conductive film; a blocking layer that transfers electrons to the transparent conductive film and prevents reverse electron transfer; a power generation layer formed by laminating a perovskite layer that is excited by light to generate the electrons on a porous semiconductor; a hole transport layer through which holes generated from the perovskite layer pass and which contains the hole transport material; and a laminate in this order. a photoelectrode that emits the electrons through the transparent conductive film, and an electrode that is composed of a counter electrode provided on a surface of the hole transport layer.

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