Solar cell, nanomaterial, dispersion liquid, and method for manufacturing solar cell

Abstract

The purpose of the present invention is to provide: a solar cell (101) which enables the implementation of a wet process; and a method for producing the same. A solar cell (101) according to the present invention comprises an electron transport layer (43), an active layer (44), and a hole transport layer (45), and is characterized in that the active layer (44) includes a perovskite semiconductor, the electron transport layer (43) includes at least one compound from among ZnO, MgZnO, and SnO, and the hole transport layer (45) includes at least one compound from among NiO and MoO.

Description

Solar cell, nanomaterial, dispersion, and method for manufacturing solar cell

[0001] The present invention relates to perovskite solar cells.

[0002] Patent Document 1 below discloses a perovskite solar cell. According to this patent document, the perovskite solar cell is formed by stacking a first electrode, an electron transport layer, a photoelectric conversion layer, and a second electrode in this order, and the electron transport layer contains SnO.

[0003] JP 2023-130980 A

[0004] However, the invention described in Patent Document 1 does not describe anything about a preferred combination of materials for the electron transport layer and the hole transport layer in relation to the absorption edge.

[0005] The present invention has been made in view of the above points, and has an object to provide a solar cell that allows selection of a preferred combination of materials for the electron transport layer and the hole transport layer.

[0006] The present invention provides a solar cell comprising an electron transport layer, an active layer, and a hole transport layer, wherein the active layer contains a perovskite semiconductor, the electron transport layer contains at least one of ZnO, MgZnO, and SnO, and the hole transport layer contains at least one of NiO and MoO.

[0007] The present invention is characterized in that the material used in the electron transport layer constituting the solar cell described above has a slope of a Tauch plot of the absorption edge that is greater than that of the bulk material. The present invention is characterized in that the dispersion of the material described above has a polydispersity index of less than 0.1 when measured by DLS.

[0008] According to the solar cell of the present invention, the absorption edge can be sharply extended by the combination of materials constituting the electron transport layer and the hole transport layer.

[0009] 1 is a partial cross-sectional view of a solar cell according to the present embodiment; FIG. 2 is a diagram showing a perovskite structure; FIG. 3 is a schematic diagram of quantum dots according to the present embodiment; FIG. 4 is an energy level diagram when quantum dots with a core-shell structure are used; FIG. 5 is a partial cross-sectional view of a solar cell according to an embodiment different from that of FIG. 1; FIG. 6 is a partial cross-sectional view of a solar cell according to an embodiment different from that of FIG. 1; FIG. 7 is a synthesis flow of ZnO; FIG. 8 is a synthesis flow of MgZnO; FIG. 9 is a synthesis flow of SnOx; FIG. 10 is a synthesis flow of NiOx; FIG. 11 is a synthesis flow of MoOx; FIG. 12 is a graph showing UV spectra and band gap energy; FIG. 13 is a synthesis flow of NiO; FIG. 14 is an XRD of NiO; FIG. 15 is a UV spectrum of NiO; FIG. 16 is a graph (Tauk plot) showing band gap energy of NiO; FIG. 17 is a XANES spectrum in Ni valence evaluation; and FIG. 18 is a graph showing the relationship between particle size and scattering intensity distribution in Examples 1 to 3.

[0010] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist thereof.

[0011] FIG. 1 is a partial cross-sectional view showing an example of a solar cell according to this embodiment. The solar cell 101 shown in FIG. 1 includes a first electrode 41, which is a cathode, and a second electrode 42, which is an anode. Between the first electrode 41 and the second electrode 42, an electron transport layer 43, an active layer 44, and a hole transport layer 45 are provided. Note that the stacked structure may be reversed. For example, the first electrode 41 is formed on a glass substrate 46. A plastic substrate or film may be used instead of the glass substrate 46. The substrate and film are preferably transparent substrates.

[0012] The second electrode 42 is conductive. Note that, of the first electrode 41 and the second electrode 42, as long as the electrode on the light incident side is translucent, the other electrode does not need to be translucent. For example, the second electrode 42 is formed of a transparent and conductive material.

[0013] The first electrode 41 and the second electrode 2 have the function of collecting holes and electrons generated by light absorption in the active layer 44. This allows electricity to be generated.

[0014] In this embodiment, the electron transport layer 43 preferably contains at least one of ZnO, MgZnO, and SnO, and the hole transport layer 45 preferably contains at least one of NiO and MoO.

[0015] In addition, in this embodiment, the oxygen deficiency of the metal oxide constituting the electron transport layer 43 and the hole transport layer 45 is preferably smaller than that of the bulk material. In other words, a stoichiometric composition is preferable. According to the synthesis flow of the metal oxide of this embodiment, oxygen deficiency can be suppressed. The "bulk material" refers to a mass containing the metal oxide, regardless of size or shape. In this embodiment, the active layer 44 is a photoelectric conversion layer that absorbs light incident on the solar cell 101 and generates electrons and holes.

[0016] In solar cell 101, the semiconductor material of active layer 44, which receives sunlight and generates electrons and holes, may be any of i-type, n-type, and p-type. Electron transport layer 43 is an n-type semiconductor, and hole transport layer 45 is a p-type semiconductor. A solar cell 101 in which a transparent electrode is formed on the electron transport layer 43 side to allow sunlight to enter is called an n-i-p type solar cell, and one in which a transparent electrode is formed on the hole transport layer 45 side is called a p-i-n type solar cell.

[0017] Conventionally, silicon-based (single crystal, polycrystalline, amorphous) or silicon compound semiconductors have been used as semiconductors for the active layer 44, but in this embodiment, a perovskite semiconductor is used for the active layer 44.

[0018] The structure of a perovskite semiconductor is shown in Figure 2. For example, M in Figure 2 is Pb, O is Br or I, and R is NH ３ CH ３ is.

[0019] Perovskite solar cells are sensitive to the entire visible light range and have excellent power generation efficiency. In addition, compared to conventional silicon solar cells, they have the advantage of having a smaller dependency of power generation efficiency on the intensity of incident light (illuminance). This means that they can be used both outdoors and indoors.

[0020] By using a perovskite semiconductor for the active layer 44, it becomes possible to apply low-temperature processes such as coating, which were difficult to achieve with conventional silicon semiconductors. This makes it possible to increase the area of ​​the solar cell 101 and achieve high-speed mass production, while reducing material and manufacturing costs.

[0021] Therefore, in this embodiment, in order to achieve a large area by applying a low-temperature process, the active layer 44, the electron transport layer 43, and the hole transport layer 45 are formed by a wet process, which makes it possible to reduce manufacturing costs and further improve characteristics such as an increase in power generation efficiency.

[0022] Furthermore, by using a wet process, patterning by inkjet or the like can be easily performed. That is, although it is necessary to pattern the electron transport layer 43, active layer 44, and hole transport layer 45 to ensure an electrode extraction area, the wet process allows for easy patterning, thereby reducing manufacturing costs. The perovskite semiconductor is preferably a perovskite quantum dot. A large number of quantum dots are dispersed and arranged within the active layer 44.

[0023] The quantum dots are preferably spherical. Here, "spherical" is not limited to a perfect sphere, but refers to a sphericity of 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more. The sphericity can be measured, for example, by processing images using an electron microscope and calculating the sphericity from the area and perimeter of the observed quantum dots by 4π × (area) ÷ (perimeter). ２ Alternatively, if the aspect ratio of the observed quantum dots, expressed as the major axis / minor axis, is 1.5 or less, preferably 1.2 or less, and more preferably 1.3 or less, then the quantum dot is defined as "spherical."

[0024] For example, in this embodiment, the active layer 44 can be formed using a resin composition in which a plurality of spherical quantum dots are dispersed in a resin. Here, the resin in which the quantum dots are dispersed is not particularly limited, and examples thereof include polypropylene, polyethylene, polystyrene, AS resin, ABS resin, methacrylic resin, polyvinyl chloride, polyacetal, polyamide, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polysulfone, polyethersulfone, polyphenylene sulfide, polyamideimide, polymethylpentene, liquid crystal polymer, epoxy resin, phenolic resin, urea resin, melamine resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, polyimide, polyurethane, silicone resin, cyclic polyolefin polymer (COP), cyclic polyolefin copolymer (COC), ethylene vinyl alcohol, polymethylpentene, polyvinylidene fluoride, and the like.

[0025] Alternatively, in this embodiment, a plurality of spherical quantum dots dissolved in a solvent can be applied using an inkjet method. In this case, the quantum dot layer after drying is composed of almost spherical quantum dots, but some solvent components may remain in the quantum dot layer.

[0026] The quantum dots have an emission wavelength at least in the visible light region. In this embodiment, perovskite quantum dots are used, and quantum dots other than perovskite quantum dots may also be included. For example, PbS, PbSe, CdHgTe, Ag ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ , InAs. ２S does not fall under the RoHS Directive. In addition, a paper on PbS was published in 2003 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim. ADVANCED MATERIALS 2003, 15.NO.21 November 4. In addition, Ag ２ The quantum dots in this embodiment are nanoparticles having a particle size of, for example, several nanometers to several tens of nanometers.

[0027] As shown in Fig. 3A, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dots 20. This makes it possible to suppress aggregation of the quantum dots 20, and to achieve the desired optical properties. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples: (1) Aliphatic primary amines Oleylamine: C １８ H ３５ NH ２ , stearyl(octadecyl)amine: C １８ H ３７ NH ２ , dodecyl(lauryl)amine: C １２ H ２５ NH ２ , decylamine: C １０ H ２１ NH ２ , octylamine: C ８ H １７ NH ２ (2) Fatty acid Oleic acid: C １７ H ３３ COOH, stearic acid: C １７ H ３５ COOH, palmitic acid: C １５ H ３１ COOH, myristic acid: C １３ H ２７ COOH, lauric acid: C １１ H ２３ COOH, decanoic acid: C ９ H １９ COOH, octanoic acid: C ７ H １５COOH (3) Thiol-based Octadecanethiol: C １８ H ３７ SH, hexanedecanethiol: C １６ H ３３ SH, tetradecanethiol: C １４ H ２９ SH, dodecanethiol: C １２ H ２５ SH, decanethiol: C １０ H ２１ SH, octanethiol: C ８ H １７ SH (4) Phosphine system Trioctylphosphine: (C ８ H １７ ) ３ P, triphenylphosphine: (C ６ H ５ ) ３ P, tributylphosphine: (C ４ H ９ ) ３ P (5) Phosphine oxide series Trioctylphosphine oxide: (C ８ H １７ ) ３ P═O, triphenylphosphine oxide: (C ６ H ５ ) ３ P═O, tributylphosphine oxide: (C ４ H ９ ) ３ P=O

[0028] In this embodiment, it is preferable to use a short ligand as the organic ligand 21. Although not limited thereto, the organic ligand 21 can be 3-mercaptopropionic acid (MPA).

[0029] The ligands of the quantum dots 20 contained in the quantum dot layer are preferably shorter than the ligands when the quantum dots 20 are formed by liquid phase synthesis.

[0030] In this way, by using short ligands for the quantum dots 20 contained in the quantum dot layer, the roughness of the quantum dot layer can be reduced and the electron and hole extraction efficiency can be improved. On the other hand, by using long ligands when forming the quantum dots 20 by liquid phase synthesis, the dispersion and film formation properties can be improved.

[0031] Alternatively, quantum dots 20 with long ligands may be synthesized by a liquid phase synthesis method, and then the composition containing the quantum dots 20 may be replaced with a short ligand (e.g., 3-mercaptopropionic acid) before or after application.

[0032] 3B, the quantum dot 20 may have a core-shell structure having a core 20a and a shell 20b covering the surface of the core 20a. As shown in FIG. 3B, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dot 20. The organic ligands 21 are as described above. The core 20a of the quantum dot 20 shown in FIG. 3B is the nanoparticle shown in FIG. 3A. Therefore, the core 20a is formed, for example, from the material of the quantum dot 20 listed above.

[0033] The shell 20b may be in a state of being solid-solutioned on the surface of the core 20a. In Fig. 3B, the boundary between the core 20a and the shell 20b is shown by a dotted line, but this means that the boundary between the core 20a and the shell 20b may or may not be confirmed by analysis. Although not shown, it is preferable to have a buffer layer between the core 20a and the shell 20b. The buffer layer is a region in which at least some or all of the elements constituting the core 20a and at least some or all of the elements constituting the shell 20b are mixed.

[0034] In this embodiment, the structure is one in which spherical quantum dots are applied, and quantum dots (particularly spherical quantum dots) formed by, for example, a liquid phase synthesis method are used, so that the sensitivity is excellent in all directions, and the variation in sensitivity can be reduced compared to, for example, microfabricated quantum dots.

[0035] In this embodiment, the quantum dots are PbS, PbSe, CdHgTe, Ag２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ These have an emission wavelength of 800 nm to 1600 nm and can be suitably applied to solar cells.

[0036] When the quantum dots used in this embodiment have a core-shell structure, the energy level diagram will be any one of those shown in Figures 4A to 4D. Of these, the shell of the core-shell structure is important in terms of improving the quantum confinement effect. In particular, in the type I structure shown in Figure 4A, the LUMO of the shell is higher in energy than the LUMO of the core, and the HOMO of the shell is lower in energy than the HOMO of the core. In this embodiment, a type II structure is preferred to facilitate extraction of carriers (electrons and holes). Since hole mobility is usually lower than electron mobility, it is preferable to select type II(1) or (3). It should be noted that quantum dots with a core structure having a ligand, rather than a core-shell structure, can also be used. In type II(1), the LUMO of the shell is lower in energy than the LUMO of the core, and the HOMO of the shell is higher in energy than the HOMO of the core. In type II(3), the LUMO of the shell is higher in energy than the LUMO of the core, and the HOMO of the shell is higher in energy than the HOMO of the core. In this embodiment, the film thickness of the active layer is preferably 5 nm or more and 50 nm or less.

[0037] (Electron Transport Layer 43) The electron transport layer 43 is made of an inorganic or organic material having a function of transporting electrons. In this embodiment, the electron transport layer 43 contains at least one of ZnO, MgZnO, and SnO. Two or more of these may be selected. The electron transport layer 43 is particularly made of ZnO. ＸIt is preferable that the metal oxide is formed of nanoparticles of the metal oxide. The metal oxide may be doped with Li, Mg, Al, Mn, etc. X is not limited to, but is about 0.8 to 1.2, and it is preferable that there is no oxygen deficiency.

[0038] Like the active layer 44, the electron transport layer 43 is preferably formed by printing a solvent containing nanoparticles using a printing method such as an inkjet method.

[0039] (Hole (Positive Hole) Transport Layer 45) The hole transport layer 45 is made of an inorganic or organic material having a function of transporting holes. In this embodiment, the hole transport layer 45 preferably contains at least one of NiO and MoO. The hole transport layer 45 may also contain, for example, NiO with Al. ２ O ３ The metal oxide may be doped with Li, Mg, Al, etc. It is preferable that the metal oxide constituting the hole transport layer 45 does not have oxygen deficiency.

[0040] The solar cell 102 shown in Fig. 5 has an inverted stack structure of the solar cell 101 shown in Fig. 1. That is, the solar cell 102 shown in Fig. 5 has a second electrode 42 serving as an anode, a hole transport layer 45, an active layer 44, an electron transport layer 43, and a first electrode 41 serving as a cathode stacked in this order from bottom to top on the surface of a glass substrate 46.

[0041] For example, the active layer 44, the electron transport layer 43, and the hole transport layer 45 are formed by a wet process, but depending on the stacking order, the active layer 44 having a perovskite semiconductor may be susceptible to the wet process, which may affect the characteristics.

[0042] Therefore, it is possible to appropriately select a layering order that will prevent the active layer 44 from being affected by the wet process.

[0043] The solar cell 103 shown in Figure 6 is a tandem solar cell, and has a structure in which, for example, the perovskite solar cell 105 of the present embodiment shown in Figures 1 and 5 and a thin-film solar cell 104 having crystalline silicon are stacked via an intermediate layer 106. This allows the leaf to absorb light over a wide wavelength range. The structure of the tandem solar cell 103 in Figure 6 is one example, and the stacking order of the perovskite solar cell 105 and the thin-film solar cell 104 may be different, and it is also possible to place the perovskite solar cell 105 above and below the thin-film solar cell 104.

[0044] In the method for manufacturing a solar cell according to the present embodiment, the electron transport layer 43, the active layer 44, and the hole transport layer 45 are formed by a wet process. In the present embodiment, it is preferable to form the active layer by applying a resin composition containing quantum dots.

[0045] To improve the dispersibility of quantum dots, it is preferable to use long-chain ligands. Therefore, quantum dots having long-chain ligands are preferable for application, but for device fabrication, short-chain ligands are preferable to increase the efficiency of carrier (electron, hole) extraction. Although not limited thereto, the number of carbon atoms in the short-chain ligand is 2 to 5 (preferably 2 to 3). For example, 3-mercaptopropionic acid can be used as the short-chain ligand.

[0046] In this embodiment, quantum dots can be synthesized by liquid-phase synthesis, and then the quantum dot ligands can be replaced with short ligands. For example, a quantum dot-containing composition (including quantum dots and a solvent) can be applied using a spin coater. Long-chain ligands have better dispersibility and can form films with good roughness. However, long-chain ligands are disadvantageous for carrier extraction. Therefore, for example, after application, short-chain ligands can be dripped onto the coating film. This naturally replaces the long-chain ligands with short-chain ligands, and the coating is then washed away. Alternatively, quantum dots can be synthesized by liquid-phase synthesis, and then the long-chain ligands can be replaced with short-chain ligands before application, and then a quantum dot-containing composition (which may be a resin composition) can be applied. In this embodiment, the electron transport layer 43 is formed from ZnO, MgZnO, or SnO. The synthesis flow for these metal oxides is described below.

[0047] Figure 7 shows the synthesis flow of ZnO. As shown in Figure 7, Zn(OAc) ２ ・2H ２ O (6.22 g, 28.3 mmmol) and 0.5 wt % hydrous methanol (198.8 g, 251 ml) were mixed, and the temperature was raised to 60°C.

[0048] Next, 13 ml of KOH / 0.5 wt % hydrous methanol was added to the flask over a period of 10 minutes, and the temperature was maintained at 60° C. for 2 hours.

[0049] After cooling, the mixture was transferred to two centrifuge tubes and centrifuged at 7000 pm for 5 minutes. The supernatant was then removed from each tube, and the mixture was sonicated and centrifuged again at 7000 pm for 5 minutes. The process of removing the supernatant, sonicating, and centrifugation was repeated once more.

[0050] Then, the supernatant was removed and ultrasonication was performed, and between the removal of the supernatant and the ultrasonication, ethanol (5 ml) and aminoethanol (0.5 ml) were added to each centrifuge tube, and the tubes were then stored overnight in a dark place.

[0051] Next, the mixture was transferred to two other centrifuge tubes, and about 35 to 40 ml of ethyl acetate was added to each tube, followed by centrifugation at 5500 rpm for 5 minutes. The supernatant was then discarded from each tube, and the mixture was transferred to a G-BOX and dispersed using a vortex mixer.

[0052] Next, the solution was passed through a 0.45 μm filter and transferred to a 50 ml tube, from which 0.7 ml was taken, and the remainder was stored in a G-BOX. The concentration was measured using the taken 0.7 ml, and the concentration and dilution ratio were calculated. Based on this calculation, the dilution ratio was adjusted using dehydrated ethanol in the G-BOX to the calculated value. The completed G-BOX was then stored. A 1.6 ml aliquot was taken from this completed G-BOX, and DLS, UV value, PL value, and concentration were analyzed.

[0053] 8 shows the synthesis flow of MgZnO. As shown in FIG. 8, first, anhydrous ethanol (30 mL) was prepared, and Zn(OAc) ２ ・2H ２ O (560 mg, 2.55 mmol) and Mg (OAc) ２ ・4H ２ O (96.5 mg, 0.45 mmol) was added and stirred at room temperature for 30 minutes. Subsequently, KOH (309 mg, 5.5 mmol) / absolute ethanol (20 mL) was added. Then, stirring was continued at room temperature for 1 hour. Subsequently, hexane (80 mL) was added. This resulted in the mixture becoming cloudy white. Ethanolamine (1 mL) was added to this mixture until it dissolved, and further hexane was added to precipitate the solid, which was then dispersed in ethanol. This resulted in the production of MgZnO with a particle size of approximately 4.2 nm. The band gap energy E of MgZnO was ｇ was 3.79 eV.

[0054] Figure 9 shows the synthesis flow of SnOx. As shown in Figure 9, ethylene glycol (100 mL) was prepared, and SnCl ４ ・5H ２ O (11.57 g, 0.33 mol), acetic acid (10 mL), and 30% aqueous tetramethylammonium hydroxide solution (25 mL) were mixed and stirred at 50°C for 30 minutes, then the temperature was raised to 160°C and stirring was continued for 4 hours.

[0055] Subsequently, the mixture was washed with ethanol-ethyl acetate, and 2 ml of ethanolamine was added thereto, followed by dispersion in ethanol.

[0056] In this embodiment, the hole transport layer 45 is formed of NiO or MoO. The synthesis flow of these metal oxides will be described below.

[0057] Fig. 10 shows the synthesis flow of NiOx. As shown in Fig. 10, DMSO (100 mL) was prepared and Ni(NO ３ ) ２ ・6H ２ O (10 mmol) and KOH (673 mg, 12 mmol) in absolute ethanol (100 mL) were mixed and stirred at room temperature for 30 minutes. Subsequently, after washing with ethanol, DMSO (150 mL) was mixed and stirred at a temperature of 160°C for 4 hours. Next, it was washed with ethanol-ethyl acetate, and ethanolamine (0.2 mL) was added and dispersed in ethanol. A dark gray precipitate was obtained.

[0058] 11 shows the synthesis flow of MoOx. 1-octadecene and octanoic acid (total volume 60 mL, volume ratio of 1-octadecene:octanoic acid = 1:9) and MoOx were placed in a sealed tube. ２ (acac) ２ (244.62 mg, 0.75 mmol) and acetic acid (10 mL) were mixed and stirred at 50°C for 30 minutes. The temperature was then raised to 180°C and stirred for 40 minutes, and n-octane (250 mL) was added to obtain a dark blue precipitate. The precipitate was dispersed in ethanol.

[0059] According to the synthesis flow of this embodiment, a metal oxide free from oxidation defects can be obtained. Furthermore, by using the electron transport layer and hole transport layer of this embodiment, it is possible to effectively and sharply extend the absorption edge in the visible light region.

[0060] FIG. 12A is a graph showing the UV spectrum, and FIG. 12B is a graph (Tauk plot) showing the band gap energy. In the experiment, the amount of Mg doping in MgZnO was changed. Note that the MgZnO used in the experiment was immediately after synthesis and dispersed in DEGME. As shown in FIG. 12, as the amount of Mg doping increased, the band gap energy E ｇ was found to increase.

[0061]

[0062] FIG. 13 shows a synthesis flow of NiO. Note that this is a synthesis flow different from that of FIG. 10. That is, as shown in FIG. 13, ３ ) ２ ・6H ２ O, dimethyl sulfoxide, and KOH / absolute ethanol solution were mixed and stirred at room temperature for 30 minutes. This resulted in a green precipitate. This was mixed with DMSO, kept at 160°C for 3 hours, and washed with ethanol / ethyl acetate. Ethanolamine was then added and dispersed in ethanol.

[0063] Figure 14 shows the XRD of NiO. The NiO used in the experiment was obtained using the synthesis flow shown in Figure 13. As shown in Figure 14, NiO was observed. However, Ni was not observed, indicating that the NiO was properly synthesized. Figure 15 shows the UV spectrum of NiO, and Figure 16 is a graph (Tauk plot) showing the band gap energy.

[0064] As shown in FIG. 16, the slope of the Tauch plot of the absorption edge was found to be greater than that of the bulk material. This indicated that the absorption edge could be sharply extended. Furthermore, as shown in FIG. 16, the nanoparticles exhibited a steeper rise in the Tauch plot than the bulk material, with a smaller tail. Because all of the electron transport materials in this example were semiconductors, the slope of the Tauch plot for all electron transport materials was greater than that of the bulk material. Furthermore, as shown in FIG. 16, the regions A and B enclosed by the tangent line indicating the slope, the plot curve, and the horizontal axis were found to be smaller in region A for the nanoparticles than in region B for the bulk material. Since the oxygen vacancies become smaller as this region becomes smaller, it was proven that nanoparticles have smaller oxygen vacancies than bulk materials.

[0065] <Regarding Ni valence of NiO> Standard samples with known valence (NiO: divalent, LiNiO ２ A calibration curve of the rise position of the XANES spectrum and the Ni valence was created using the BL08W beamline and the transmission method for the measurement.

[0066] Next, the Ni valence was evaluated from the XANES spectrum of NiO prepared by the synthesis method of this example. The experimental results are shown in FIG.

[0067] As shown in Figure 17, it was found that the XANES spectrum shifted due to the change in valence. ２ Since the XANES spectrum of the example exists between the trivalent and trivalent states, the Ni valence of the NiO of the example is between 2 and 3, leaning toward divalent NiO. Therefore, it was found that the Ni valence of the example is greater than 2 and less than 2.5, preferably 2.1 or more and 2.4 or less. In the example of Fig. 17, the Ni valence is predicted to be about 2.2. This proves that the NiO of the example is a hole carrier.

[0068] Furthermore, the polydispersity index of the metal oxide dispersion used in the electron transport layer of this example was less than 0.1 when measured by DLS. Dynamic light scattering (DLS) is applied to nanoparticles suspended and dispersed in a liquid. DLS measurement is a method for calculating particle diameter by measuring the diffusion rate of nanoparticles moving by Brownian motion.

[0069] The polydispersity index (PDI) is used to represent the width of the particle size distribution. In the experiments, ZnO particles were prepared as the metal oxide used in the electron transport layer. Figure 18 is a graph showing the relationship between particle size and scattering intensity distribution in each example. As shown in Table 2, the polydispersity index was less than 0.1 in Examples 1 to 3. This indicates that all particles measured in each example had approximately the same particle size.

[0070]

[0071] Metal oxides such as ZnO and NiO exist as a film in solar cells. In this embodiment, the polydispersity index is set to less than 0.1 as described above to improve dispersibility, but the performance of the film can be defined as the surface roughness after film formation.

[0072] That is, the surface roughness Ra (arithmetic mean roughness) of the film is preferably less than 1.0 nm. The surface roughness (Ra) can be analyzed by AFM measurement or the like.

[0073] According to the present invention, the active layer, electron transport layer, and hole transport layer of a perovskite solar cell are formed by a wet process, which reduces costs and increases the solar cell area. This improves power generation efficiency both indoors and outdoors, making the solar cell suitable for a variety of applications.

[0074] This application is based on Japanese Patent Application No. 2023-211607, filed December 15, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A solar cell comprising an electron transport layer, an active layer, and a hole transport layer, wherein the active layer contains a perovskite semiconductor, the electron transport layer contains at least one of ZnO, MgZnO, or SnO, and the hole transport layer contains at least one of NiO or MoO.

2. The solar cell according to claim 1, wherein the perovskite semiconductor is a perovskite quantum dot.

3. The solar cell according to claim 2, wherein the perovskite quantum dots include an organic ligand on the surface thereof, the organic ligand including 3-mercaptopropionic acid.

4. The display device according to claim 2, wherein the perovskite quantum dots contain a ligand on the surface, and the number of carbon atoms in the ligand is 2 or more and 5 or less.

5. The solar cell according to claim 1, wherein the oxygen deficiency of the metal oxide constituting the electron transport layer and the hole transport layer is smaller than that of the bulk material.

6. A nanoparticle material used in the electron transport layer constituting the solar cell according to claim 1, characterized in that the slope of the Tauch plot of the absorption edge is greater than that of the bulk material.

7. A dispersion of the material of claim 4, characterized in that the polydispersity index, as measured by DLS, is less than 0.

1.

8. A method for producing the solar cell according to claim 1, characterized in that the electron transport layer, the active layer and the hole transport layer are formed by a wet process.

9. The method for producing a solar cell according to claim 8, wherein the perovskite semiconductor is a perovskite quantum dot, and when the perovskite quantum dots are synthesized by a liquid phase synthesis method, the perovskite quantum dots having long ligands are synthesized, and then the ligands are replaced with short ligands before or after applying a composition containing the perovskite quantum dots.

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