Organic solar cell and photoelectric conversion element

Abstract

An organic solar cell (100) comprises: a substrate (1); a first electrode (2) that is an electron injection electrode laminated on the substrate (1); an electron transport layer (3) that is laminated on the first electrode (2); a photoelectric conversion layer (4) that is laminated on the electron transport layer (3); a hole transport layer (5) that is laminated on the photoelectric conversion layer (4); and a second electrode (6) that is a hole injection electrode laminated on the hole transport layer (5). The hole transport layer (5) contains, as a dopant, at least one compound represented by chemical formula (1) or general formula (2). (In formula (2), Z1 and Z2 may be the same or different, and each is an oxygen atom, a sulfur atom, or a selenium atom. Each R may be the same or different and is a substituted or unsubstituted phenyl group or biphenyl group.)

Description

Organic solar cell and photoelectric conversion element

[0001] The present invention relates to an organic solar cell and a photoelectric conversion element.

[0002] An organic solar cell contains a p-type semiconductor and an n-type semiconductor, and often has a hole transport layer (hole transport layer) provided between a photoelectric conversion layer that absorbs light and generates positive and negative charges and an anode. The hole transport layer plays a role in improving the photoelectric conversion efficiency of the solar cell by enabling the positive charges (holes) and negative charges (electrons) generated by photoexcitation to move efficiently without recombination.

[0003] Among organic solar cells, in particular, a solar cell having a photoelectric conversion layer containing a perovskite compound (hereinafter also referred to as a perovskite solar cell) has been reported to exhibit a higher photoelectric conversion efficiency than an amorphous silicon solar cell in a weak indoor light environment, and reports on further improvement of the photoelectric conversion efficiency have also been successively made. The basic structure of a perovskite solar cell generally is a laminate in which a transparent electrode (cathode), an electron transport layer, a photoelectric conversion layer (perovskite layer), a hole transport layer, and a metal electrode (anode) are laminated in this order. This structure may also include a mesoporous titania layer between the electron transport layer and the perovskite layer, and the photoelectric conversion layer is composed of the perovskite layer and the mesoporous titania layer. Among these layers, the hole transport layer is generally composed of a material containing an organic semiconductor.

[0004] Examples of the organic semiconductor contained in the materials of the hole transport layer reported so far include 2,2′,7,7′-tetrakis-(N,N-di-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), which was developed as a material for the hole transport layer of a dye-sensitized solar cell and described in Non-Patent Document 1, and is also often used in the aforementioned perovskite solar cells.

[0005] When Spiro? OMeTAD is used as the material for the hole transport layer, it cannot be said that sufficiently good photoelectric conversion performance is achieved. Therefore, when using this material, it is generally necessary to add a large amount of dopant such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI salt) to improve photoelectric conversion performance, but the problem is that the solar cell has poor durability at high temperatures and high humidity due to the doping of a large amount of LiTFSI salt. Non-patent document 2 proposes a method using a substance called tetracyanoquinodimethane (TCNQ) as a p-type dopant that does not absorb moisture.

[0006] Nature volume (1998) 395, P583-585Nanoscale (2019) 11, 19586

[0007] Generally, organic solar cells and photoelectric conversion elements are sealed with encapsulating materials such as resins to avoid contact with water and oxygen in the air, and heating is often performed during this sealing process. However, TCNQ, as mentioned above, has a low molecular weight and sublimes at around 100°C. Therefore, when TCNQ is used as a p-type dopant in organic solar cells and photoelectric conversion elements, the heat resistance of the element decreases, the element degrades due to heating during sealing, and the photoelectric conversion efficiency decreases. On the other hand, if the heating temperature is lowered to prevent element degradation, the sealing may not be sufficient, or the usable encapsulating materials (resins, etc.) may be limited, resulting in a reduced sealing effect.

[0008] In view of the above problems, the present invention aims to provide an organic solar cell and a photoelectric conversion element that have high heat resistance and excellent photoelectric conversion performance even in weak light such as indoor light.

[0009] To achieve the above objective, the first configuration of the present invention is an organic solar cell comprising a substrate, a first electrode which is an electron injection electrode laminated on the substrate, an electron transport layer laminated on the first electrode, a photoelectric conversion layer laminated on the electron transport layer, a hole transport layer laminated on the photoelectric conversion layer, and a second electrode which is a hole injection electrode laminated on the hole transport layer, wherein the hole transport layer contains at least one of the compounds represented by the following chemical formula (1) or general formula (2) as a dopant. In formula (2), Z1 and Z2 may be the same or different, and are an oxygen atom, a sulfur atom, or a selenium atom. R may be the same or different, and is a substituted or unsubstituted phenyl group or a biphenyl group.

[0010] According to the first configuration of the present invention, by using a compound represented by formula (1) or general formula (2) as a dopant in the hole transport layer of an organic solar cell, high-temperature durability and charge (hole) mobility can be improved, thereby improving the energy conversion efficiency of the organic solar cell.

[0011] A partial cross-sectional view of an organic solar cell 100 according to one embodiment of the present invention, showing an example in which the first electrode 2 is an electron injection electrode and the second electrode 6 is a hole injection electrode.

[0012] [1. Structure of Organic Solar Cell] First, a solar cell using the hole transport material of the present invention will be described. Figure 1 is a partial cross-sectional view of an organic solar cell 100 according to one embodiment of the present invention. The organic solar cell 100 (hereinafter simply referred to as solar cell 100) comprises a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. The first electrode 2 is provided on the substrate 1. The photoelectric conversion layer 4 is laminated on the first electrode 2 via the electron transport layer 3. The second electrode 6 is laminated on the photoelectric conversion layer 4 via the hole transport layer 5. Note that the photoelectric conversion layer 4 may be directly laminated on the first electrode 2 without an electron transport layer. In this case, the electron transport layer 3 shown in Figure 1 is omitted. When the solar cell 100 is used, for example, light (for example, sunlight or indoor light) is irradiated onto the substrate 1 side of the solar cell 100. Note that when the solar cell 100 is used, light may be irradiated onto the second electrode 6 side of the solar cell 100.

[0013] <Substrate> The substrate 1 is not particularly limited as long as it can be used for the solar cell 100. The substrate 1 may be transparent or opaque. However, if the surface of the solar cell 100 that faces the substrate 1 is the light-receiving surface, it is preferable that the substrate 1 be transparent. Examples of transparent substrates include transparent rigid substrates such as glass like quartz glass or synthetic quartz plates, and transparent flexible substrates such as transparent resin films or optical resin plates. Transparent flexible substrates have advantages such as ease of processing, reduced manufacturing costs, lighter weight, resistance to breakage, and applicability to curved surfaces.

[0014] <First Electrode> The first electrode 2 is, for example, an electron injection electrode. The first electrode 2 is not limited to a conductive material. Examples of materials with a high work function that can be used as the first electrode 2 include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), and zinc oxide (ZnO).

[0015] Furthermore, the material of the first electrode 2 is appropriately selected considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 side or the surface on the second electrode 6 side. When the light-receiving surface is the surface on the substrate 1 side, the first electrode 2 is preferably a transparent electrode. Examples of materials used when the first electrode 2 is a transparent electrode include indium zinc oxide (IZO), ITO, FTO, ZnO-Al, and Zn-Sn-O.

[0016] The total light transmittance of the first electrode 2 is preferably 85% or more, more preferably 90% or more, and particularly preferably 92% or more. When the total light transmittance of the first electrode 2 is 85% or more, when the light-receiving surface of the solar cell 100 is the surface facing the substrate 1, light can be sufficiently transmitted through the first electrode 2 on the substrate 1, and the photoelectric conversion layer 4 can efficiently absorb the light.

[0017] The sheet resistance of the first electrode 2 is preferably 20 [Ω / sq] or less, and more preferably 15 [Ω / sq] or less. When the sheet resistance of the first electrode 2 is 20 [Ω / sq] or less, the charge generated in the photoelectric conversion layer 4 is sufficiently transmitted to the external circuit. The sheet resistance can be measured, for example, using a resistivity meter (Loresta AXMCP-T370, manufactured by Nitto Seiko Analytech Co., Ltd., 4-probe type) in accordance with JIS (Japanese Industrial Standards) R1637 (Test method for resistivity of fine ceramic thin films - Measurement method by 4-probe method).

[0018] The film thickness of the first electrode 2 is preferably 0.1 nm or more and 500 nm or less, and more preferably 1 nm or more and 300 nm or less. When the film thickness of the first electrode 2 is 0.1 nm or more, the sheet resistance of the first electrode 2 does not become too large, and the charge (holes) generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit. On the other hand, when the film thickness of the first electrode 2 is 500 nm or less, the total light transmittance of the first electrode 2 is high.

[0019] The first electrode 2 may be a single layer. Alternatively, the first electrode 2 may be composed of multiple layers having different work functions. When the first electrode 2 consists of multiple layers, the film thickness of the first electrode 2 as described above refers to the total film thickness of the multiple layers.

[0020] The first electrode 2 may be formed in a sheet shape over the entire surface of the substrate 1, or it may be formed in a pattern shape on the substrate 1. The shape of the first electrode 2 may be flat or uneven. Examples of uneven shapes include a textured structure, a pyramidal structure, a wave-shaped structure, a comb-shaped structure, and a nanopillow structure. When the first electrode 2 is uneven, the incident light is scattered by the unevenness of the first electrode 2, so that more light is taken up by the photoelectric conversion layer 4, and the energy conversion efficiency of the solar cell 100 is improved.

[0021] <Electron Transport Layer> The electron transport layer 3 is laminated between the first electrode 2 and the photoelectric conversion layer 4. The electron transport layer 3 is provided to facilitate the injection (movement) of electrons from the photoelectric conversion layer 4 to the first electrode 2 (electron injection electrode). By laminating the electron transport layer 3, the electron injection efficiency from the photoelectric conversion layer 4 to the first electrode 2 is increased, and the energy conversion efficiency of the solar cell 100 is improved.

[0022] The material contained in the electron transport layer 3 (electron transport layer material) is not particularly limited as long as it is a material that can stably inject electrons from the photoelectric conversion layer 4 to the second electrode 6. Examples of electron transport layer materials include conductive organic compounds, charge transfer complexes, alkali metals, alkaline earth metals, and organic compounds and metal oxides doped with alkali metals or alkaline earth metals.

[0023] Examples of alkali metals that can be used as electron transport layer materials include lithium, sodium, potassium, rubidium, and cesium. Examples of alkaline earth metals that can be used as electron transport layer materials include beryllium, magnesium, calcium, strontium, and barium. Examples of alkali metal or alkaline earth metal-doped organic compounds that can be used as electron transport layer materials include bathocuproine (BCP) and batphenanthroline (Bphen) doped with alkali metals or alkaline earth metals. Preferred alkali metals and alkaline earth metals used for doping are lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, or barium, with lithium, cesium, barium, or strontium being more preferred. Examples of metal oxides that can be used as electron transport materials include titanium oxide, zinc oxide, and tin oxide.

[0024] When the electron transport layer material is a conductive organic compound, a charge transfer complex, or a metal oxide, the film thickness of the electron transport layer 3 is preferably 10 nm or more and 200 nm or less. When the electron transport layer material is an alkali metal, an alkaline earth metal, or an organic compound doped with an alkali metal or alkaline earth metal, the film thickness of the electron transport layer 3 is preferably 0.1 nm or more and 50 nm or less.

[0025] <Photoelectric Conversion Layer> The photoelectric conversion layer 4 may be a bulk heterojunction type photoelectric conversion layer containing a donor (electron donor) and an acceptor (electron acceptor), or it may be a photoelectric conversion layer having a perovskite layer, which is a so-called perovskite.

[0026] In the case of a bulk heterojunction type photoelectric conversion layer, the donor is not particularly limited as long as it functions as a donor, but it is preferably an electron-donating conductive polymer (electron-donating organic material). An electron-donating organic material refers to the organic compound with the lower electron affinity when two organic compounds are brought into contact. In other words, any organic compound that is electron-donating can be used as a donor. The donor is preferably a compound that can be formed into a thin film using a solution in which the donor is dissolved in an organic solvent (for example, a coating method such as the casting method and the spin coating method). The photoelectric conversion layer 4 may contain only the donor and acceptor, or it may contain other compounds.

[0027] Examples of electron-donating conductive polymers that can be used as donors include polyphenylene, polyphenylene vinylene, polysilane, polythiophene, polybenzodithiophene, polycarbazole, polyvinylcarbazole, porphyrin, polyacetylene, polypyrrole, polyaniline, polyfluorene, polyvinylpyrene, polyvinylanthracene, and derivatives thereof. The donor may be a copolymer obtained by copolymerizing at least two of these electron-donating conductive polymers. Other examples of electron-donating conductive polymers include phthalocyanine-containing polymers, carbazole-containing polymers, and organometallic polymers.

[0028] As an electron-donating conductive polymer that can be used as a donor, a polymer having at least one of a thiophene structure, a benzothiophene structure, and a benzodithiophene structure (polythiophene polymer) is preferred. The polythiophene polymer is preferably capable of absorbing visible light. Furthermore, the polythiophene polymer is preferably of the donor-acceptor (DA) type.

[0029] The acceptor is not particularly limited as long as it functions as an acceptor, but it is preferably a conductive polymer (electron-accepting organic material) that has electron-accepting properties. Electron-accepting organic materials are mainly represented by electron-transporting organic compounds and refer to organic compounds that have a property of readily accepting electrons. More specifically, it refers to the organic compound with the greater electron affinity when two organic compounds are used in contact. In other words, any organic compound that has electron-accepting properties can be used as an acceptor.

[0030] Examples of electron-accepting organic materials include fullerenes and their derivatives (such as PCBMs), carbon nanotubes and their derivatives, perylenes and their derivatives (such as PTCDAs and PTCDIs), naphthalene derivatives (such as NTCDAs and NTCDIs), oligomers and polymers having pyridines and their derivatives as a backbone, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and their derivatives, tris(8-hydroxyquinolinate)aluminum complexes, bis(4-methyl-8-quinolinate)aluminum complexes, distylyl arylene derivatives, and silole compounds. Fullerene derivatives (such as PCBMs) are particularly preferred, but the material is not limited thereto.

[0031] In the photoelectric conversion layer 4, the ratio of the acceptor mass (MA) to the donor mass (MD) (MA / MD) is preferably 0.1 or more and 2.0 or less, and more preferably 1.0 or more and 2.0 or less. When the ratio (MA / MD) is within this range, the balance between the acceptor and donor of the solar cell 100 is good, and the energy conversion efficiency of the solar cell 100 is improved.

[0032] The photoelectric conversion layer having a perovskite layer uses a compound represented by the general formula (ABX3). This compound may be a perovskite crystal or a perovskite complex. A can be an organic amino compound such as methylamine, ethylamine, n-butylamine, di-n-butylamine, trimethylamine, triethylamine, methyl-n-hexylamine, methyldiethylamine, tri-n-hexylamine, imidazole, pyrrole, aziridine, formamidine, guanidine, pyridine, 4-t-butylpyridine, phenethylamine, 5-aminovaleric acid, or a monovalent cation formed from cesium, potassium, rubidium, etc., and may be used alone or as a mixture of two or more. B can be a divalent cation such as lead or tin, and may be used alone or in a mixture. In addition, a small amount of a trivalent cation such as indium or antimony may be mixed in. X can be a halogen atom or anion source such as chlorine, bromine, or iodine, and may be used alone or in a mixture of two or more.

[0033] The film thickness of the photoelectric conversion layer 4 is not particularly limited, as long as the desired energy conversion efficiency can be obtained, whether it is a bulk heterojunction photoelectric conversion layer or a perovskite-type photoelectric conversion layer. The film thickness of the photoelectric conversion layer 4 is preferably 0.2 nm or more and 3000 nm or less, and more preferably 10 nm or more and 600 nm or less. When the film thickness of the photoelectric conversion layer 4 is 3000 nm or less, the sheet resistance of the photoelectric conversion layer 4 is more likely to be the desired value. On the other hand, when the film thickness of the photoelectric conversion layer 4 is 0.2 nm or more, a short circuit between the first electrode 2 and the second electrode 6 is less likely to occur.

[0034] <Hole Transport Layer> The hole transport layer 5 is laminated between the photoelectric conversion layer 4 and the second electrode 6. The hole transport layer 5 is provided to facilitate the injection (movement) of holes from the photoelectric conversion layer 4 to the second electrode 6 (hole injection electrode). By laminating the hole transport layer 5, the hole injection efficiency from the photoelectric conversion layer 4 to the second electrode 6 is increased, and the energy conversion efficiency of the solar cell 100 is improved. The hole transport layer 3 includes a hole transport material and a dopant.

[0035] (Dopant) The organic solar cell of the present invention contains, as a dopant, 2,2'-(1,3,4,5,7,8-hexafluoro-2,6-naphthalenediylidene) bis-propanedinitrile represented by the following chemical formula (1) (hereinafter referred to as F6-TCNNQ), or a compound represented by the following general formula (2).

[0036]

[0037]

[0038] In formula (2), Z1 and Z2 may be the same or different and are an oxygen atom, a sulfur atom, or a selenium atom. R may be the same or different and is a substituted or unsubstituted phenyl group or biphenyl group.

[0039] R in formula (2) preferably has at least one electron-withdrawing group.

[0040] By using at least one of F6-TCNNQ represented by chemical formula (1) or a compound represented by general formula (2) as the dopant constituting the hole transport layer 5, the mobility of charges (holes) can be improved, and the energy conversion efficiency of the solar cell 100 is improved. F6-TCNNQ or a compound represented by general formula (2) may be used alone or in combination of two or more.

[0041] Note that F6-TCNNQ is a compound known as a p-type dopant for doping the hole transport layer of an organic light-emitting device. However, the fact that high energy conversion efficiency can be obtained by using it as a p-type dopant for doping the hole transport layer of an organic solar cell and a photoelectric conversion device is a finding obtained by the present inventors for the first time.

[0042] As the compound represented by the general formula (2), 2-[4,8-bis[3,5-bis(trifluoromethyl)phenyl]-2-(dicyanomethylidene)-[1,3]oxazolo[5,4-f][1,3]benzoxazol-6-ylidene]propanedinitrile represented by the following chemical formula (3) and 2-[2-(dicyanomethylidene)-4,8-bis[4-(trifluoromethyl)phenyl]-[1,3]oxazolo[5,4-f][1,3]benzoxazol-6-ylidene]propanedinitrile represented by the chemical formula (4) can be mentioned.

[0043]

[0044]

[0045] (Hole transport material) In the organic solar cell of the present invention, a conventionally known hole transport material can be used as the hole transport material. Specific examples of the hole transport material include TTF-1, P3HT, Spiro-OMeTAD, X19, X51, Spiro(TFSI)2, S197, PFO, TFB, PFB, PTAA, PEDOT:PSS, OMeTPA-FA, OMeTPA-TPA, etc. represented by the following chemical formulas.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060] The hole transport layer 3 may contain only the hole transport material and dopant described above, or it may further contain additives. Conventional known additives such as interface treatment agents can be used as additives.

[0061] <Second Electrode> The second electrode 6 is, for example, a hole injection electrode. The second electrode 6 is provided opposite the first electrode 2. The second electrode 6 is not particularly limited as long as it is conductive. The material of the second electrode 6 is appropriately selected, for example, taking into consideration the work function of the hole transport layer 5. If the material of the hole transport layer 5 is a material with a high work function, it is preferable that the material of the second electrode 6 is a material with a low work function.

[0062] Examples of materials that can be used as the material for the second electrode 6 include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), and zinc oxide (ZnO).

[0063] Furthermore, the material of the second electrode 6 is appropriately selected, for example, by considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 side or the surface on the second electrode 6 side. If the light-receiving surface is the surface on the substrate 1 side, the first electrode 2 is preferably a transparent electrode, but the second electrode 6 does not have to be a transparent electrode.

[0064] The film thickness of the second electrode 6 is preferably 0.1 nm or more and 500 nm or less, and more preferably 1 nm or more and 300 nm or less. When the film thickness of the second electrode 6 is 0.1 nm or more, the sheet resistance of the second electrode 6 does not become too large, and the charge generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit.

[0065] The second electrode 6 may be a single layer. Alternatively, the second electrode 6 may be composed of multiple layers having different work functions. When the second electrode 6 consists of multiple layers, the film thickness of the second electrode 6 as described above refers to the total film thickness of the multiple layers.

[0066] The second electrode 6 may be formed in a sheet shape over the entire surface of the hole transport layer 5, or it may be formed in a pattern shape on the hole transport layer 5.

[0067] <Other Components> In addition to the substrate 1, first electrode 2, electron transport layer 3, photoelectric conversion layer 4, hole transport layer 5, and second electrode 6 described above, the solar cell 100 may further include other components as needed. Examples of other components include a protective sheet layer, filler layer, barrier layer, protective hard coat layer, strength support layer, anti-fouling layer, high light reflectivity layer, light containment layer, ultraviolet blocking layer, infrared blocking layer, and sealing layer. Furthermore, adhesive layers may be laminated between each layer of the solar cell 100 as needed.

[0068] Furthermore, the solar cell 100 is not limited to the structure shown in Figure 1. For example, the first electrode 2 may be a hole injection electrode and the second electrode 6 may be an electron injection electrode. In that case, the stacking order of the hole transport layer 5 and the electron transport layer 3 will be the reverse of that in Figure 1. Specifically, as shown in Figure 2, the hole transport layer 5 is stacked between the first electrode 2 and the photoelectric conversion layer 4, and the electron transport layer 3 is stacked between the photoelectric conversion layer 4 and the second electrode 6.

[0069] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the embodiments described above, an example was given in which F6-TCNNQ or a compound represented by general formula (2) was used as a dopant in the hole transport layer 5 of the solar cell 100, but it is not limited to the solar cell 100, and can also be used, for example, in the hole transport layer of a photoelectric conversion element.

[0070] As an example of a photoelectric conversion element, for instance, a semiconductor electrode (first electrode) is fabricated by laminating a hole-blocking layer and a porous electron transport layer on a glass substrate, and further supporting a photosensitizing material. A hole transport layer is formed on this semiconductor electrode (first electrode) by spin coating using a solution of hole transport material dissolved in an organic solvent, and a second electrode is formed by laminating silver on the formed hole transport layer using a vacuum deposition method. The effects of the present invention will be further explained in detail below with reference to examples.

[0071] [Manufacturing of Perovskite Organic Solar Cells] (Substrate Preparation) A 1.6 mm thick conductive glass substrate (FTN1.6, manufactured by Nippon Sheet Glass Co., Ltd., hereinafter referred to as FTO substrate) with a fluorine-doped tin oxide layer (first electrode) formed on it was used as the substrate. The FTO substrate was cut into 20 mm x 20 mm squares.

[0072] The FTO substrate was protected with masking tape except for the edges (5 mm), and the FTO portion was etched and removed using a cotton swab soaked in 6N hydrochloric acid and zinc powder. After removal, it was washed with deionized water, and the masking tape was removed. Then, the FTO substrate was ultrasonically cleaned for 15 minutes each in the following order: 10% neutral detergent solution (Clean Ace S, manufactured by AS ONE), deionized water, isopropyl alcohol, and acetone. After cleaning, the surface of the FTO substrate was treated with UV-ozone for 30 minutes.

[0073] (Formation of electron transport layer) Next, 200 μL of a 4% aqueous solution of tin(IV) nanoparticles (manufactured by Thermo Fisher, a mixture of SnO2 aqueous dispersion (15% concentration) and deionized water in a 4:11 ratio) was dropped onto the FTO substrate, and spin coating was performed with acceleration for 3 seconds, rotation for 20 seconds (4000 rpm), and deceleration for 3 seconds until stopping. After that, the substrate was annealed (heat treated) on a hot plate at 150°C for 30 minutes to form an electron transport layer with a thickness of 20 nm on the FTO substrate.

[0074] The FTO substrate, on which this electron transport layer was formed, was subjected to UV-ozone treatment again for 15 minutes, and then placed in a glove box under conditions of 23°C ± 1°C and a dew point of -20 ± 5°C.

[0075] (Formation of perovskite power generation layer) Separately, under a glove box, 0.692 g (1.5 mmol) of lead iodide (L0279, manufactured by Tokyo Chemical Industry Co., Ltd.), 0.059 g (0.225 mmol) of cesium iodide (C2205, manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.219 g (1.275 mmol) of formamidine hydroiodide (F0974, manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed with 1.25 mL of a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 4:6), and the mixture was stirred at 70°C for 1 hour to dissolve.

[0076] After the dissolved coating solution was cooled to room temperature, 150 μL of the coating solution was dropped onto the electron transport layer and the coated substrate. After 30 seconds, spin coating was performed with acceleration for 0.8 seconds, rotation for 50 seconds (3000 rpm), further acceleration for 0.8 seconds, rotation for 30 seconds (6000 rpm), and deceleration for 1 second until stopping. Four seconds after reaching 6000 rpm, 200 μL of ethyl acetate was dropped onto the surface. After stopping the rotation, the surface was annealed (heat treated) on a hot plate at 135°C for 15 minutes to form a perovskite power generation layer (photoelectric conversion layer) on the electron transport layer.

[0077] (Formation of Hole Transport Layer) Next, Spiro-OMeTAD was weighed out as the hole transport material to a final concentration of 30 mmol. In addition, F6-TCNNQ (compound 1) was weighed out as the p-dopant to a concentration of 20 mol% relative to the hole transport material, and the mixture of the hole transport material and the p-dopant was dissolved in chlorobenzene to prepare a hole transport layer forming composition. Using the prepared hole transport layer forming composition solution, a film was deposited on the substrate by spin coating at a rotation speed of 4000 rpm for 30 seconds to form a 100 nm hole transport layer on the perovskite power generation layer. The prepared device was left in an environment of 5% humidity for 12 hours. After that, a gold electrode (second electrode) was formed on the hole transport layer by vacuum deposition to deposit 80 nm of gold, thereby producing the perovskite type organic solar cell S-1 of the present invention 1.

[0078] Perovskite-type organic solar cell S-2 of the present invention was manufactured in the same manner as in the present invention 1, except that 2-[4,8-bis[3,5-bis(trifluoromethyl)phenyl]-2-(dicyanomethylidene)-[1,3]oxazolo[5,4-f][1,3]benzoxazole-6-ylidene]propanedinitrile (compound 2-1) was added as the p-dopant instead of compound 1.

[0079] Perovskite-type organic solar cell S-3 of the present invention was manufactured in the same manner as in the present invention 1, except that 2-[2-(dicyanomethylidene)-4,8-bis[4-(trifluoromethyl)phenyl]-[1,3]oxazolo[5,4-f][1,3]benzoxazole-6-ylidene]propanedinitrile (compound 2-2) was added as the p-dopant instead of compound 1.

[0080] A perovskite-type organic solar cell S-4 of Comparative Example 1 was manufactured in the same manner as in Invention 1, except that F4-TCNQ was added as a p-dopant in an amount of 2 mol% relative to the hole transport material, instead of compound 1.

[0081] A perovskite-type organic solar cell S-5 of Comparative Example 2 was manufactured in the same manner as in Invention 1, except that 9.1 mg of LiTFSI and 26.5 mg of t-BP (4-t-butylpyridine) were added to 75 mg of hole transport material as p-dopants instead of compound 1.

[0082] A perovskite-type organic solar cell S-6 of Comparative Example 3 was manufactured by the same method as in Invention 1, except that a p-dopant was not added.

[0083] [Evaluation of Photoelectric Conversion Characteristics of Perovskite-Type Organic Solar Cells] The photoelectric conversion efficiency of organic solar cells of the present invention 1 to 3 and Comparative Examples 1 to 3, manufactured in Example 1, was evaluated. A solar simulator (HAL-320, manufactured by Asahi Spectrometer Co., Ltd.) was used as the measurement device, and the light intensity of the measurement light source was adjusted to 100 mW / cm2 using a reference solar cell. In the actual measurement, the measurement area was 0.1 cm². 2The J-V curve characteristics were measured using a source meter (voltage / current generator with measurement function, model 6242, manufactured by ADC) while irradiating a masked solar cell element with light. The measurement was performed once each (total of two measurements) under Forward (forward scan, scanning in the direction of voltage increase) and Reverse (reverse scan, scanning in the direction of voltage decrease) conditions, and the conversion efficiency was determined.

[0084] From the measurement results, the short-circuit current (Jsc [mA / cm²]) for both Forward and Reverse was determined. 2 ]), open-circuit voltage (Voc [V]), curve factor (FF [mW / cm 2 The following was derived: PCE = (Jsc × Voc × FF / 100) × 100 The PCE of organic solar cells S-1 to S-3 of Invention 1 to 3, and organic solar cells S-4 and S-5 of Comparative Examples 1 and 2 are shown in Table 1 together with Jsc, Voc, FF, thermal stability, moisture resistance, and hole transport layer forming composition.

[0085]

[0086] As shown in Table 1, the organic solar cells S-1 to S-3 of the present invention, using compound 1, compound 2-1, or compound 2-2 as the p-dopant, all had a PCE of 4.5% or more, and had a higher photoelectric conversion efficiency than the organic solar cell of Comparative Example 3, which did not contain a p-dopant. They also exhibited excellent thermal stability at 150°C and superior moisture resistance.

[0087] On the other hand, in Comparative Examples 1 and 2, which used F4-TCNQ or LiTFSI salt as the p-dopant, the PCE was equal to or better than that of the organic solar cells S-1 to S-3 of the present invention 1 to 3. However, the organic solar cell of Comparative Example 1 had poor thermal stability at 150°C. In addition, the organic solar cell of Comparative Example 2 had poor moisture resistance.

[0088] Based on these results, it was confirmed that using compound 1, compound 2-1, or compound 2-2 as a p-dopant effectively improves the photoelectric conversion efficiency of solar cells, and also provides excellent thermal stability and moisture resistance.

[0089] The present invention is applicable to organic solar cells and photoelectric conversion elements. By utilizing the present invention, it is possible to provide organic solar cells and photoelectric conversion elements that have excellent resistance to high temperatures and high humidity, and that have excellent photoelectric conversion performance even under weak light conditions such as indoor light.

Claims

1. An organic solar cell comprising: a substrate; a first electrode which is an electron injection electrode laminated on the substrate; an electron transport layer laminated on the first electrode; a photoelectric conversion layer laminated on the electron transport layer; a hole transport layer laminated on the photoelectric conversion layer; and a second electrode which is a hole injection electrode laminated on the hole transport layer, wherein the hole transport layer contains at least one of the compounds represented by the following chemical formula (1) or general formula (2) as a dopant. (In formula (2), Z1 and Z2 may be the same or different, and are an oxygen atom, a sulfur atom, or a selenium atom. R may be the same or different, and is a substituted or unsubstituted phenyl group or biphenyl group.) 2. An organic solar cell comprising: a substrate; a first electrode which is a hole injection electrode laminated on the substrate; a hole transport layer laminated on the first electrode; a photoelectric conversion layer laminated on the electron transport layer; an electron transport layer laminated on the photoelectric conversion layer; and a second electrode which is an electron injection electrode laminated on the hole transport layer, wherein the hole transport layer contains at least one of a compound represented by the following chemical formula (1) or general formula (2) as a dopant. (In formula (2), Z1 and Z2 may be the same or different, and are an oxygen atom, a sulfur atom, or a selenium atom. R may be the same or different, and is a substituted or unsubstituted phenyl group or biphenyl group.) 3. The organic solar cell according to claim 1 or 2, characterized in that R in the general formula (2) has at least one electron-withdrawing group.

4. The organic solar cell according to claim 3, wherein the compound represented by the general formula (2) is a compound represented by the following chemical formula (3) or (4).

5. A photoelectric conversion element comprising: a substrate; a first electrode having a hole blocking layer and a porous electron transport layer laminated on the substrate and further supporting a photosensitizing material; a hole transport layer laminated on the first electrode; and a second electrode laminated on the hole transport layer, wherein the hole transport layer contains at least one of the compounds represented by the following chemical formula (1) or general formula (2) as a dopant. (In formula (2), Z1 and Z2 may be the same or different, and are an oxygen atom, a sulfur atom, or a selenium atom. R may be the same or different, and is a substituted or unsubstituted phenyl group or biphenyl group.) 6. The photoelectric conversion element according to claim 5, characterized in that R in the general formula (2) has at least one electron-withdrawing group.

7. The photoelectric conversion element according to claim 6, characterized in that the compound represented by the general formula (2) is a compound represented by the following chemical formula (3) or (4).

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