Perovskite solar cells

Abstract

To provide a perovskite solar cell having high photoelectric conversion efficiency without using an expensive metal electrode.SOLUTION: A perovskite solar cell 100 includes a light-transmitting conductive layer 111, a dense electron transportation material layer 112, a porous electron transportation material layer 113, a porous non-conductive oxide layer 114, a porous nickel oxide layer 115, and a porous carbon electrode layer 116 including nickel oxide nanoparticles 117. The porous electron transportation material layer 113, the porous non-conductive oxide layer 114, the porous nickel oxide layer 115, and the porous carbon electrode layer 116 include a perovskite crystal 103 filling the internal space.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to perovskite solar cells. Background Art

[0002] Solar cells that convert sunlight into electricity have attracted attention as power sources that do not emit greenhouse gases. In particular, perovskite solar cells using organic-inorganic perovskite crystals have a larger light energy absorption coefficient than silicon-based solar cells, and are expected to enable realization of thin solar cells with high conversion efficiency.

[0003] A thin-film perovskite solar cell having a thin film of perovskite crystal sandwiched between a cathode and an anode requires expensive materials such as silver and gold for the anode. However, solar cells using such metal anodes react with ionic perovskite materials, as well as oxygen and moisture in the atmosphere, leading to degradation and rapid deterioration. Therefore, they have low durability and cannot be used stably for a long period of time. Accordingly, carbon electrode perovskite solar cells using carbon for the anode have been studied (see, for example, Non-Patent Document 1). Prior Art Documents Non-Patent Documents

[0004] Non-Patent Document 1 Anyi Mei et al., Science, Volume 345, Issue 6194, pp.295-298 (2014) Non-Patent Document 2 Fatemeh Behrouznejad et al., ACS Appl. Mater. Interfaces, Volume 9, pp.25204-25215 (2017) Non-Patent Document 3 Da Li et al., ACS Sustainable Chem. Eng, Volume 7, pp.2619-1625 (2019) Summary of the Invention Problems to be Solved by the Invention

[0005] However, while carbon electrodes are effective in improving durability, they have tens of times more resistance than metal electrodes, resulting in lower charge extraction and transport capabilities and lower photoelectric conversion efficiency compared to perovskite solar cells using metal electrodes.

[0006] Therefore, attempts have been made to improve photoelectric conversion efficiency by forming a nickel oxide layer between the spacer layer and the carbon electrode, or by impregnating the carbon electrode with a metal oxide, but sufficient effects have not been obtained (see, for example, Non-Patent Documents 2 and 3).

[0007] The objective of this disclosure is to realize a perovskite solar cell with high photoelectric conversion efficiency without using expensive metal electrodes. [Means for solving the problem]

[0008] One embodiment of the perovskite solar cell of the present disclosure comprises a translucent conductive layer and a dense electron transport material layer, a porous electron transport material layer, a porous insulated oxide layer, a porous nickel oxide layer, and a porous carbon electrode layer containing nickel oxide nanoparticles, which are sequentially formed on the translucent conductive layer, wherein the porous electron transport material layer, the porous insulated oxide layer, the porous nickel oxide layer, and the porous carbon electrode layer contain perovskite crystals that fill the internal voids.

[0009] The perovskite solar cell of this disclosure comprises a porous nickel oxide layer and a porous carbon electrode layer containing nickel oxide nanoparticles, which can reduce current loss and improve the open-circuit voltage, thereby significantly improving photoelectric conversion efficiency.

[0010] In one embodiment of the perovskite solar cell of this disclosure, the proportion of nickel oxide nanoparticles contained in the porous carbon electrode layer is 5% by mass or more and 25% by mass or less, and the thickness of the porous nickel oxide layer can be 0.5 μm or more and 2.0 μm or less.

[0011] One embodiment of the method for manufacturing a perovskite solar cell according to the present disclosure comprises the steps of forming a dense electron transport material layer and a porous electron transport material layer on a translucent conductive layer, then sequentially applying a material for forming a porous insulator oxide layer, a material for forming a porous nickel oxide layer, and a material for forming a porous carbon electrode layer containing nickel oxide nanoparticles onto the porous electron transport material layer and firing to form a porous insulator oxide layer, a porous nickel oxide layer, and a porous carbon electrode layer containing nickel oxide nanoparticles, and impregnating the porous carbon electrode layer with a perovskite precursor solution from the porous carbon electrode layer side to fill the voids of the porous electron transport material layer, the porous insulator oxide layer, the porous nickel oxide layer, and the porous carbon electrode layer with perovskite crystals. [Effects of the Invention]

[0012] The perovskite solar cell of this disclosure can improve photoelectric conversion efficiency without using expensive metal electrodes. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view showing a perovskite solar cell according to one embodiment. [Figure 2] This is an electron microscope image of a porous carbon electrode layer containing nickel oxide nanoparticles. [Figure 3] This graph shows the results of current density-voltage measurements. [Figure 4] This graph shows the relationship between the thickness of the porous nickel oxide layer and the normalized PCE. [Figure 5] This graph shows the relationship between the concentration of nickel oxide nanoparticles and the normalized PCE. [Figure 6] This graph shows the results of the heat and humidity endurance test. [Modes for carrying out the invention]

[0014] A perovskite solar cell 100 according to one embodiment, as shown in FIG. 1, comprises a light-transmissive dense electron transport material layer 112, a porous electron transport material layer 113, a porous non-conductive oxide layer 114, a porous nickel oxide layer 115, and a porous carbon electrode layer 116 containing nickel oxide nanoparticles 117, which are sequentially formed on a light-transmissive substrate 105 having a light-transmissive conductive layer 111. A porous layer 101 including the porous electron transport material layer 113, the porous non-conductive oxide layer 114, the porous nickel oxide layer 115, and the porous carbon electrode layer 116 contains perovskite crystals 103.

[0015] The light-transmissive conductive layer 111 is a layer made of a light-transmissive conductive compound formed on the surface of the light-transmissive substrate 105 made of glass or the like. As the light-transmissive conductive compound, fluorine-doped tin oxide (FTO), indium tin oxide (ITO), gallium-doped zinc oxide, aluminum-doped zinc oxide, niobium-doped titanium oxide, and the like can be used.

[0016] The dense electron transport material layer 112 is a layer formed on the light-transmissive conductive layer 111, which is made of a light-transmissive electron transport material and has a smooth structure. By providing the dense electron transport material layer 112, generated holes can be prevented from flowing into the light-transmissive conductive layer 111, and only electrons can be allowed to flow, so leakage current can be suppressed. From the viewpoint of leakage current suppression, the thickness of the dense electron transport material layer 112 is preferably 1 nm or more, more preferably 20 nm or more, and preferably 100 nm or less, more preferably 50 nm or less. The dense electron transport material layer 112 can be formed of a material excellent in photoelectron conductivity such as titanium oxide, tungsten oxide, zinc oxide, niobium oxide, tantalum oxide, and strontium titanate. These may be used alone or in combination, and may also be in a donor-doped state. When titanium oxide is used, an anatase crystal form is preferred.

[0017] The dense electron transport material layer 112 can be formed, for example, by applying a mixed solution of titanium (di-i-propoxide) bis(acetylacetonate) and ethanol to the patterned conductive surface of an FTO glass substrate by spray pyrolysis. The dense electron transport material layer 112 is not limited to such a method, and can also be formed from a transparent and conductive oxide material such as indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO).

[0018] The porous electron transport material layer 113 is a layer formed in contact with the dense electron transport material layer 112 and having a porous structure made of a light-transmitting electron transport material. Among these, a structure in which electron transport materials in the form of granules, linear bodies, acicular bodies, tubular bodies, columnar bodies, or the like are aggregated to form a structure having nanoscale voids as a whole is preferable. By providing the porous electron transport material layer 113, the electron collection ability and photoelectric conversion efficiency can be improved. From the viewpoint of electron collection ability, the thickness of the porous electron transport material layer 113 is preferably 50 nm or more, more preferably 200 nm or more, and preferably 2 μm or less, more preferably 1.5 μm or less.

[0019] Similar to the dense electron transport material layer 112, the porous electron transport material layer 113 can be formed of titanium oxide, tungsten oxide, zinc oxide, niobium oxide, tantalum oxide, yttrium oxide, strontium titanate, or the like. These may be used alone or in combination, and may also be in a state doped with a donor. When titanium oxide is used, an anatase crystal form is preferable.

[0020] The porous electron transport material layer 113 can be formed, for example, by applying a paste for a porous electron transport material layer onto the surface of the dense electron transport material layer 112 by screen printing or the like, and firing the paste at 500°C. The paste for a porous electron transport material layer can be, for example, a mixture in which fine particles of an electron transport material such as titanium oxide are dispersed in terpineol.

[0021] The porous insulated oxide layer 114 is a layer having a porous structure made of an insulating material formed between the porous electron transport material layer 113 and the porous nickel oxide layer 115. The porous insulated oxide layer 114 has the function of suppressing the recombination of generated electrons and holes by physically separating the porous electron transport material layer 113 from the porous nickel oxide layer 115 or the porous carbon electrode layer 116. For this reason, its thickness is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 5 μm or less, and more preferably 3 μm or less. Also, similar to the porous electron transport material layer 113, a structure having nanometer-scale voids is preferred. The porous insulated oxide layer 114 can be formed from various insulating oxides, but from the viewpoint of the stability of the porous insulated oxide layer 114 against moisture and heat, zirconium oxide (ZrO2), aluminum oxide (Al2O3), and silicon oxide (SiO2) are preferred.

[0022] The porous nickel oxide layer 115 is a layer having a porous structure made of nickel oxide formed in contact with the porous insulated oxide layer 114. The porous nickel oxide layer 115 functions as a hole transport electrode together with the porous carbon electrode layer 116 containing nickel oxide nanoparticles 117.

[0023] The porous carbon electrode layer 116 is formed in contact with the porous nickel oxide layer 115, has a porous structure made of carbon, and contains nickel oxide nanoparticles 117 in its voids. From the viewpoint of efficient charge transport and stability, the thickness of the porous carbon electrode layer 116 is preferably 5 μm or more, more preferably 10 μm or more, preferably 50 μm or less, and more preferably 30 μm or less. The porous carbon electrode layer 116 is not particularly limited, but it is preferable to include flake-shaped (thin flake-shaped) graphite particles. By including flake-shaped graphite particles, it is easy to obtain a porous carbon electrode layer 116 in which nickel oxide nanoparticles 117 and perovskite crystals 103 are sufficiently dispersed and packed.

[0024] The nickel oxide nanoparticles 117 contained in the porous carbon electrode layer 116 are not particularly limited, but from the viewpoint of a size that does not obstruct the conductive path of the carbon electrode, the particle size is preferably 5 nm or larger, more preferably 10 nm or larger, preferably 100 nm or smaller, and more preferably 50 nm or smaller.

[0025] The nickel oxides forming the porous nickel oxide layer 115 and the nickel oxides contained in the porous carbon electrode layer 116 include not only nickel monoxide (NiO) but also nickel dioxide (NiO2) and nickel trioxide (Ni2O3), etc., which have the general formula NiO x These can be various compounds formed by the bonding of nickel and oxygen, as represented by [formula]. These compounds can be single compositions or mixtures of multiple compositions.

[0026] A porous carbon electrode layer 116 containing a porous non-conductive oxide layer 114, a porous nickel oxide layer 115, and nickel oxide nanoparticles 117 can be formed by sequentially applying pastes for each layer formation to the surface of a porous electron transport material layer 113 by screen printing or the like, and then firing at 400°C. The paste for forming the porous non-conductive oxide layer can be a paste in which a non-conductive oxide such as zirconium oxide and an organic binder thickener are dispersed in terpineol. The paste for forming the porous nickel oxide layer can be a paste in which nickel oxide and an organic binder thickener are dispersed in terpineol. The paste for forming the porous carbon electrode layer can be a paste in which nickel oxide, graphite, carbon black, zirconium oxide, and an organic binder thickener are dispersed in terpineol. Nickel oxide can be formed, for example, by adding an aqueous solution of sodium hydroxide (NaOH) to nickel nitrate hydrate (Ni(NO3)2·6H2O), heating it at 80°C for 18 hours to form beta-nickel hydroxide (β-Ni(OH)2), and then heating the resulting mixture at 270°C for 2 hours.

[0027] The perovskite solar cell 100 of this embodiment has a porous nickel oxide layer 115 between a porous insulator oxide layer 114 and a porous carbon electrode layer 116. By forming the porous nickel oxide layer 115, the hole extraction efficiency is increased and current loss can be reduced. As a result, the short-circuit current density can be improved, and the photoelectric conversion efficiency is improved. Furthermore, since the porous carbon electrode layer 116 contains nickel oxide nanoparticles 117, compared to the case where nickel oxide nanoparticles are not included, the nickel oxide shifts the work function of the density of states at the top of the valence band to the negative side, bringing it closer to the density of states of the perovskite crystal, thus improving the open-circuit voltage. Therefore, the photoelectric conversion efficiency can be further improved.

[0028] From the viewpoint of improving the short-circuit current density, the thickness of the porous nickel oxide layer 115 is preferably 0.5 μm or more, more preferably 0.7 μm or more, preferably 2.0 μm or less, and more preferably 1.8 μm or less. Furthermore, from the viewpoint of improving the open-circuit voltage, the ratio (concentration) of nickel oxide nanoparticles to the entire porous carbon electrode layer 116 is preferably 5% by mass or more, more preferably 7% by mass or more, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0029] The perovskite solar cell 100 of this embodiment contains perovskite crystals in its porous layer 101, porous carbon electrode layer 116, porous nickel oxide layer 115, porous insulated oxide layer 114, and porous electron transport material layer 113. The perovskite crystal can be an organometallic halogen perovskite crystal represented by the general formula ABX3. Here, the A site is a monovalent cation to maintain charge neutrality, the B site is a divalent cation such as lead, tin, copper, nickel, cobalt, iron, manganese, palladium, cadmium, germanium, cesium, or europium, and the X site is a halogen. For example, methylammonium (CH3NH3) is preferred for the A site, and for example, lead (Pb) is preferred for the B site. Iodine, chlorine, and bromine can be used as the halogen, with iodine being preferred.

[0030] The perovskite crystal 103 can be formed by sequentially forming each layer by coating and firing, then dropping a solution of the perovskite crystal precursor onto the porous carbon electrode layer 116 and allowing it to permeate each layer, followed by heating and drying at 50°C. In this way, a porous layer 101 filled with perovskite crystal 103 in its voids can be easily formed. The solution of the perovskite crystal precursor can be formed, for example, by heating and stirring a solution containing lead iodide (PbI2), methylammonium iodide (MAI), 5-aminovaleric acid hydroiodide (5-AVAI), and gamma butyrolactone. [Examples]

[0031] The perovskite solar cells of this disclosure will be described in more detail with reference to examples. The following examples are illustrative and are not intended to limit the invention.

[0032] <Perovskite solar cell formation> After cleaning the surface of an FTO glass electrode with a patterned conductive surface, a mixed solution of titanium(di-i-propoxide)bis(acetylacetonate) and ethanol was applied by spray pyrolysis to form a dense electron transport material layer made of titanium oxide. A titanium oxide paste was applied to the surface of the dense electron transport material layer by screen printing and fired at 500°C to form a porous electron transport material layer. Zirconium oxide paste, nickel oxide paste, and a carbon paste containing nickel oxide, graphite, carbon black, zirconium oxide, and an organic binder thickener were sequentially applied to the surface of the porous electron transport material layer and fired at 400°C to form a porous non-conductive oxide layer, a porous nickel oxide layer, and a porous carbon electrode layer.

[0033] A perovskite solar cell was formed by dropping a perovskite precursor solution onto a porous carbon electrode layer, impregnating the porous layer with the perovskite precursor solution, and then heating and drying it at 50°C. The perovskite precursor solution was a mixed solution of lead iodide, methylammonium iodide, 5-aminovaleric acid hydroiodide, and gamma butyrolactone. Nickel oxide particles were formed by adding an aqueous sodium hydroxide (NaOH) solution to nickel nitrate hydrate (Ni(NO3)2·6H2O), heating it at 80°C for 18 hours to form beta-nickel hydroxide (β-Ni(OH)2), and then heating it at 270°C for 2 hours. For investigation, a perovskite solar cell without a porous nickel oxide layer and a perovskite solar cell without nickel oxide nanoparticles in the porous carbon electrode layer were formed.

[0034] The obtained porous carbon electrode layer was observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). As shown in Figure 2, nickel oxide nanoparticles filled the voids in the porous carbon electrode layer containing graphite and carbon black.

[0035] <Measurement of photoelectric conversion efficiency> For the created solar cell, the measurement area was 0.09 cm². 2 As a result, current density-voltage measurement is performed, and the short-circuit current density (J) is determined based on the measurement results. sc ), open-circuit voltage (V oc The photoelectric conversion efficiency (PCE) was calculated from the following: ), and the fill factor (FF).

[0036] <Effects of each layer> In the case of a solar cell (Sample 1) having a porous nickel oxide layer with a thickness of 1.0 μm and a porous carbon electrode layer containing 10 mass% nickel oxide nanoparticles, as shown in Figure 3, the decrease in current density did not occur up to higher voltages compared to the other samples. The PCE of Sample 1 was 15.3%. On the other hand, the PCE of a solar cell without a porous nickel oxide layer (Sample 2) and a solar cell with a porous nickel oxide layer but without nickel oxide nanoparticles in the porous carbon electrode layer (Sample 3) were both 14.6%. The PCE of a solar cell without a porous nickel oxide layer and without nickel oxide nanoparticles in the porous carbon electrode layer (Sample 4) was 13.0%.

[0037] [Table 1]

[0038] <Optimization of porous nickel oxide layers> For porous nickel oxide layers with thicknesses of 0.4 μm, 0.7 μm, 0.9 μm, 1.8 μm, and 2.7 μm, the normalized PCE (Placement Control Value) normalized by the PCE for a thickness of 0 μm was 1.08, 1.08, 1.12, 1.11, and 1.00, respectively. Figure 4 shows the relationship between the thickness of the porous nickel oxide layer and the normalized PCE.

[0039] <Optimization of nickel oxide nanoparticle concentration> When the concentrations of nickel nanoparticles contained in the porous carbon electrode layer were 5% by mass, 10% by mass, 25% by mass, and 50% by mass, the normalized PCE, standardized using the PCE for a 0% concentration, was 1.04, 1.12, 0.96, and 0.65, respectively. Figure 5 shows the relationship between the concentration of nickel oxide nanoparticles and the normalized PCE.

[0040] <Measurement of thermal and humidity resistance> Solar cells having a 1.0 μm thick porous nickel oxide layer and a porous carbon electrode layer containing 10 mass% nickel oxide nanoparticles were sealed and left at a temperature of 85°C and a humidity of 85%, and the photoelectric conversion efficiency (PCE) was measured up to 1000 hours. Figure 6 shows the change in normalized PCE, which is normalized to the value at the start of storage (0 hours). The normalized PCE after 1000 hours was 1.0, and no decrease in PCE from the start of storage was observed. On the other hand, when the porous carbon electrode layer did not contain nickel oxide nanoparticles, the normalized PCE after 1000 hours was 0.9, indicating a decrease in PCE. [Industrial applicability]

[0041] The perovskite solar cell of this disclosure can improve photoelectric conversion efficiency without using expensive metal electrodes and is useful in the field of solar cells. [Explanation of symbols]

[0042] 100 Perovskite Solar Cells 101 Porous layer 103 Perovskite crystal 105 Transparent substrate 111 Transparent conductive layer 112 Dense electron transport material layer 113 Porous electron transport material layer 114 Porous non-conductive oxide layer 115 Porous nickel oxide layer 116 Porous carbon electrode layer 117 Nickel oxide nanoparticles

Claims

1. A light-transmitting conductive layer, The transparent conductive layer comprises, sequentially formed on the aforementioned light-transmitting conductive layer, a dense electron transport material layer, a porous electron transport material layer, a porous non-conductive oxide layer, a porous nickel oxide layer, and a porous carbon electrode layer containing nickel oxide nanoparticles. The porous electron transport material layer, the porous insulator oxide layer, the porous nickel oxide layer, and the porous carbon electrode layer each contain perovskite crystals filling the internal voids. The nickel oxide nanoparticles are contained within the voids of the porous carbon electrode layer in a perovskite solar cell.

2. The proportion of nickel oxide nanoparticles contained in the porous carbon electrode layer is 5% by mass or more and 25% by mass or less. The perovskite solar cell according to claim 1, wherein the thickness of the porous nickel oxide layer is 0.5 μm or more and 2.0 μm or less.

3. The process involves forming a dense electron transport material layer and a porous electron transport material layer on a translucent conductive layer, then sequentially applying a material for forming a porous non-conductive oxide layer, a material for forming a porous nickel oxide layer, and a material for forming a porous carbon electrode layer containing nickel oxide nanoparticles onto the porous electron transport material layer and firing them to form a porous non-conductive oxide layer, a porous nickel oxide layer, and a porous carbon electrode layer containing nickel oxide nanoparticles. The process includes impregnating the porous carbon electrode layer with a perovskite precursor solution from the porous carbon electrode layer side, thereby filling the voids in the porous electron transport material layer, the porous insulator oxide layer, the porous nickel oxide layer, and the porous carbon electrode layer with perovskite crystals. A method for manufacturing a perovskite solar cell, wherein the nickel oxide nanoparticles are contained within the voids of the porous carbon electrode layer.

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