photoelectric conversion element

Abstract

To provide inverse structure type photoelectric conversion elements with high conversion efficiency.SOLUTION: A photoelectric conversion element 1 according to the invention has a substrate 10, a lower conductive layer 11 deposited on the substrate 10, a hole transport layer 12 deposited on the lower conductive layer 11, a light absorption layer 13 deposited on the hole transport layer 12 and having the composition formula AgaBibIc, an electron transport layer 14 deposited on the light absorption layer 13, and an upper electrode 16 deposited on the electron transport layer 14, and in the compositional formula, c=a+3b and 2≤b / a≤4 are satisfied to convert light incident through the lower conductive layer into photoelectricity.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion element. [Background technology]

[0002] Solar cells using lead halide perovskite crystals in the light absorption layer are known (see, for example, Non-Patent Document 1). The solar cell described in Non-Patent Document 1 is a dye-sensitized solar cell that uses a dye as a sensitizing material, but instead of the dye, uses a compound having a perovskite crystal structure (hereinafter referred to as a "perovskite compound") as the sensitizing material. Solar cells that use perovskite compounds are called perovskite solar cells, named after Lev Perovski, who discovered the perovskite crystal structure. The conversion efficiency of the perovskite solar cell described in Non-Patent Document 1 is 3.8%, but as research into perovskite solar cells has progressed, the conversion efficiency of perovskite solar cells has rapidly improved, and development is underway to commercialize perovskite solar cells.

[0003] However, since perovskite compounds contain lead, a harmful element, there is a demand for the development of a sensitizing material that can replace the lead-containing perovskite compounds, and various studies have been conducted. a B b X c In the general formula, A: Ag, Cu; B: Bi, Sb; X: I, Br, and c=a+3b, Ag3BiI6, Ag2BiI5, AgBiI4, AgBi2I7, etc. are described as photovoltaic halogen compounds. Also, in Non-Patent Document 2, based on the name of Walter Rudorff, who discovered the oxide NaVO2, a B b X c It is described that the Ag-Bi-halogen compound Ag a Bi b I cis called a Rudolfphyte material, a solar cell using the Rudolfphyte material is called a Rudolfphyte solar cell, and a light absorbing layer using the Rudolfphyte material is called a Rudolfphyte light absorbing layer.

[0004] Furthermore, Non-Patent Document 2 describes a Rudolf Physics solar cell in which FTO / c-TiO2 / m-TiO2 / Ag3BiI6 / PTAA / Au are sequentially stacked from the light incident side. FTO stands for fluorine-doped tin oxide, PTAA stands for poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], c stands for compact, and m stands for mesoporous. In the Rudolf Physics solar cell described in Non-Patent Document 2, FTO is the base electrode, c-TiO2 and m-TiO2 are electron transport layers that are n-type semiconductors, and Ag3BiI6 is the light absorption layer that is an i-type semiconductor. PTAA is the hole transport layer that is a p-type semiconductor, and Au is the top electrode. The conversion efficiency of the Rudolf Physics solar cell described in Non-Patent Document 2 is 4.3%.

[0005] A Rudolfphyte solar cell in which a base electrode / electron transport layer / light absorption layer / hole transport layer / upper electrode are stacked in this order from the substrate side, which is the light incident side, like the Rudolfphyte solar cell described in Non-Patent Document 2, is called a forward-structured Rudolfphyte solar cell. On the other hand, in contrast to the forward-structured Rudolfphyte solar cell described in Non-Patent Document 2, a Rudolfphyte solar cell in which a base electrode / hole transport layer / light absorption layer / electron transport layer / upper electrode are stacked in this order from the light incident side is called an inverted-structured Rudolfphyte solar cell. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] “Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells” Akihiro Kojima et al., Journal of the American Chemical Society 131(17):6050-1, May 2009 [Non-patent document 2] “Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites” Dr. Ivan Turkevych et al.,ChemSusChem Volume10, 3754-3759, October 9, 2017 Summary of the Invention [Problem to be solved by the invention]

[0007] For applications such as power supply devices for IoT, it is desirable to form Rudolf Phyto solar cells on flexible substrates and use Rudolf Phyto solar cells to realize flexible solar cells that are flexible enough to bend.

[0008] In the forward-structured Rudolf Phyto solar cell described in Non-Patent Document 2, TiO2, which is heat-treated at high temperatures, is located near the substrate, making it difficult to use a flexible substrate made of a synthetic resin such as polyimide resin, which deteriorates at high temperatures, as the substrate. Since it is difficult to use a flexible substrate as the substrate for a forward-structured Rudolf Phyto solar cell, it is not easy to form a flexible solar cell. Furthermore, TiO2, which is the material of the electron transport layer that contacts the light-absorbing layer at the interface where light is incident, functions as a photocatalyst and absorbs irradiated ultraviolet light, oxidizing the interface of the light-absorbing layer. Therefore, there is a risk of deterioration of the light-absorbing layer in a forward-structured Rudolf Phyto solar cell.

[0009] On the one hand, in the inverted-structured Rudolf fight solar cell, since the TiO2 heat-treated at high temperature is arranged separately from the substrate, it can be formed without exposing the substrate to high temperature, so a flexible substrate can be adopted as the substrate. Also, in the inverted-structured Rudolf fight solar cell, TiO2, which is the material of the electron transport layer, contacts on the side opposite to the incident side of the light absorption layer, so there is no risk that the interface of the light absorption layer is oxidized by TiO2 functioning as a photocatalyst. However, the conversion efficiency of the inverted-structured Rudolf fight solar cell is lower compared to that of the normal-structured Rudolf fight solar cell, and an inverted-structured Rudolf fight solar cell with high conversion efficiency is desired.

[0010] The present invention solves such problems and provides an inverted-structured photoelectric conversion element with high conversion efficiency.

Means for Solving the Problems

[0011] The photoelectric conversion element according to the present invention includes a substrate, a lower conductive layer formed on the substrate, a hole transport layer formed on the lower conductive layer, and a light absorption layer formed on the hole transport layer and having a composition formula Ag a Bi b I c and an electron transport layer formed on the light absorption layer and an upper electrode formed on the electron transport layer. In the composition formula, c = a + 3b and 2 ≤ b / a ≤ 4 are satisfied, and the light incident through the lower conductive layer is photoelectrically converted.

[0012] Also, in the photoelectric conversion element according to the present invention, the hole transport layer is a nickel oxide (NiO x ) layer, and it is preferable that x is 0 < x ≤ 1.

[0013] Also, in the photoelectric conversion element according to the present invention, the electron transport layer preferably contains fullerene and phenyl-C 61 -methyl butyrate.

[0014] In addition, the photoelectric conversion element according to the present invention preferably further comprises an interdiffusion suppression layer formed between the hole transport layer and the light absorption layer to suppress interdiffusion of elements contained in the hole transport layer and the light absorption layer.

[0015] In the photoelectric conversion element according to the present invention, the interdiffusion suppression layer is preferably an SiO2 layer.

[0016] In the photoelectric conversion element according to the present invention, the composition ratio preferably satisfies 2≦b / a≦2.5.

[0017] In the photoelectric conversion element according to the present invention, the substrate is preferably flexible. [Effects of the Invention]

[0018] The photoelectric conversion element according to the present invention can increase the conversion efficiency in an inverted structure. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 3 is a schematic diagram of an energy band of a photoelectric conversion element according to a first comparative example. [Figure 2] FIG. 10 is a schematic diagram of an energy band of a photoelectric conversion element according to a second comparative example. [Figure 3] FIG. 2 is a schematic diagram of an energy band of an inverted-structure photoelectric conversion element according to an embodiment. [Figure 4] FIG. 4 is a plan view of the photoelectric conversion element shown in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line AA′ shown in FIG. [Figure 6] 4A to 4F are diagrams showing a method for manufacturing the photoelectric conversion element shown in FIG. 3, in which (a) shows a lower conductive layer forming step, (b) shows a hole transport layer forming step, (c) shows a light absorbing layer forming step, (d) shows an electron transport layer forming step, (e) shows a light absorbing layer removing step, and (f) shows an electrode forming step. [Figure 7] FIG. 10 is a plan view of a photoelectric conversion element according to a second embodiment. [Figure 8]FIG. 8 is a cross-sectional view taken along the line BB′ in FIG. [Figure 9] 8A and 8B are diagrams showing a method for manufacturing the photoelectric conversion element shown in Fig. 7, in which (a) shows a lower conductive layer forming step, (b) shows a hole transport layer forming step, (c) shows an interdiffusion suppression layer forming step, (d) shows a light absorbing layer forming step, (e) shows an electron transport layer forming step, (f) shows a light absorbing layer removing step, and (g) shows an electrode forming step. [Figure 10] FIG. 10 is a plan view of a photoelectric conversion element according to a modified example. [Figure 11] FIG. 11 is a cross-sectional view taken along CC' shown in FIG. [Figure 12] FIG. 3 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Example 1 under light irradiation. [Figure 13] FIG. 10 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Example 2 under light irradiation. [Figure 14] FIG. 10 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Example 3 under light irradiation. [Figure 15] FIG. 10 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Example 4 under light irradiation. [Figure 16] FIG. 10 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Example 5 under light irradiation. [Figure 17] FIG. 10 is a diagram showing the current-voltage characteristics of the photoelectric conversion element according to Comparative Example 1 under light irradiation. [Figure 18] FIG. 10 is a diagram showing the current-voltage characteristics of a photoelectric conversion element according to Comparative Example 2 under light irradiation. [Figure 19] 1 is a diagram showing open circuit voltage VOC in the current-voltage characteristics of Examples 1 to 4 and Modifications 1 and 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferred embodiments of the photoelectric conversion element according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0021] The term "photoelectric conversion element" refers to an element that converts light energy into electrical energy, and includes solar cell elements, photovoltaic cell elements, and photovoltaic elements that convert light energy, including indoor light and sunlight, into electrical energy. The photoelectric conversion element according to the embodiment may be used as a solar cell module, also known as a solar panel, and as a power supply for portable devices, etc.

[0022] (Outline of photoelectric conversion element according to embodiment) The inventors of the present invention have discovered that the compound of the formula Ag a Bi b I c It has been found that in an inverted structure photoelectric conversion element using a Rudolf Physics light absorbing layer (hereinafter simply referred to as light absorbing layer) represented by the formula: the conversion efficiency can be improved by specifying the composition ratio of Ag, Bi, and I within a predetermined range. Figures 1 to 3 are diagrams for explaining the mechanism by which the conversion efficiency is improved in an inverted structure photoelectric conversion element.

[0023] FIG. 1 is a schematic diagram of the energy band of a photoelectric conversion element according to a first comparative example, which is a normal-structure photoelectric conversion element having high conversion efficiency. FIG. 2 is a schematic diagram of the energy band of a photoelectric conversion element according to a second comparative example, which is an inverted-structure photoelectric conversion element having the same light absorption layer as the normal-structure photoelectric conversion element shown in FIG. 1. FIG. 3 is a schematic diagram of the energy band of an inverted-structure photoelectric conversion element according to an embodiment. In FIGS. 1 to 3, E f denotes the Fermi level, and E C denotes the energy level at the bottom of the conduction band, and E V indicates the energy level at the top of the valence band. Furthermore, black circles indicate electrons, white circles indicate holes, thick arrow A indicates the direction of light incident on the photoelectric conversion element, and thin arrows indicate the diffusion direction of electrons and holes, i.e., carriers.

[0024] The photoelectric conversion element 100 according to the first comparative example is a normal-structure photoelectric conversion element having a lower conductive layer 101, an electron transport layer 102, a light absorbing layer 103, a hole transport layer 104, and an electrode 105, and light is incident through the lower conductive layer 101 and the electron transport layer 102. In the photoelectric conversion element 100, the light absorbing layer 103 has a composition formula Ag aBi b I c In the photoelectric conversion element 100, the difference between the work function of the electron transport layer 102 and the work function of the light absorption layer 103 is larger than the difference between the work function of the light absorption layer 103 and the work function of the hole transport layer 104.

[0025] In the photoelectric conversion element 100, since the difference between the work function of the electron transport layer 102 and the work function of the light absorption layer 103 is large, a large internal electric field is generated between the electron transport layer 102 and the light absorption layer 103 in accordance with the difference in work function between the electron transport layer 102 and the light absorption layer 103. On the other hand, since the difference between the work function of the light absorption layer 103 and the work function of the hole transport layer 104 is small, the internal electric field generated between the light absorption layer 103 and the hole transport layer 104 is small.

[0026] In the photoelectric conversion element 100, light is incident through the lower conductive layer 101 and the electron transport layer 102, and therefore, in the electron transport layer 102, more light is absorbed in the region X near the interface in contact with the electron transport layer 102, and therefore more carriers are generated in the region X. In the photoelectric conversion element 100, many carriers are generated in the region X where the internal electric field between the electron transport layer 102 and the region X is large, so that the generated electrons and holes are efficiently separated and recombination is suppressed, and the generated carriers are efficiently transported to the lower conductive layer 101 and the electrode 105.

[0027] The photoelectric conversion element 200 according to the second comparative example is an inverted structure photoelectric conversion element having a lower conductive layer 201, a hole transport layer 202, a light absorbing layer 203, an electron transport layer 204, and an electrode 205, and light is incident through the lower conductive layer 201 and the hole transport layer 202. In the photoelectric conversion element 200, the light absorbing layer 203 has the same composition formula as the light absorbing layer 103, Ag a Bi b I c In the photoelectric conversion element 200, the difference between the work function of the hole transport layer 202 and the work function of the light absorption layer 203 is smaller than the difference between the work function of the light absorption layer 203 and the work function of the electron transport layer 204.

[0028] In the photoelectric conversion element 200, the difference between the work function of the hole transport layer 202 and the work function of the light absorption layer 203 is small, so the internal electric field generated between the hole transport layer 202 and the light absorption layer 203 is small.

[0029] In the photoelectric conversion element 200, light is incident through the lower conductive layer 201 and the hole transport layer 202, and therefore, in the light absorption layer 203, more light is absorbed in region Y near the interface where the light absorption layer 203 contacts the hole transport layer 202, and therefore more carriers are generated in region Y. In the photoelectric conversion element 200, many carriers are generated in region Y where the internal electric field between the light absorption layer 203 and the hole transport layer 202 is small, making it difficult for electrons and holes to be separated, and making it easier for recombination to occur. In the photoelectric conversion element 200, it is difficult for electrons and holes to be separated, and making it easier for recombination to occur, so the amount of carriers transported to the lower conductive layer 201 and the electrode 205 decreases, and the conversion efficiency decreases.

[0030] The photoelectric conversion element 1 according to the embodiment is an inverted structure photoelectric conversion element having a lower conductive layer 11, a hole transport layer 12, a light absorbing layer 13, an electron transport layer 14, and an upper electrode 16, and light is incident through the lower conductive layer 11 and the hole transport layer 12. In the photoelectric conversion element 1, the light absorbing layer 13 has a composition formula Ag a Bi b I c wherein the composition ratio (b / a) satisfies 2≦b / a≦4. In the photoelectric conversion element 1, the difference between the work function of the hole transport layer 12 and the work function of the light absorption layer 13 is larger than the difference between the work function of the light absorption layer 13 and the work function of the electron transport layer 14.

[0031] In the photoelectric conversion element 1, since there is a large difference between the work function of the hole transport layer 12 and the work function of the light absorption layer 13, a large internal electric field is generated between the hole transport layer 12 and the light absorption layer 13 in accordance with the difference in work function between the hole transport layer 12 and the light absorption layer 13.

[0032] In the photoelectric conversion element 1, light is incident through the lower conductive layer 11 and the hole transport layer 12, and therefore, in the light absorbing layer 13, more light is absorbed in a region Z near the interface where the light absorbing layer 13 comes into contact with the hole transport layer 12, and therefore more carriers are generated in the region Z. In the photoelectric conversion element 1, many carriers are generated in the region Z where the internal electric field between the light absorbing layer 13 and the hole transport layer 12 is large, and therefore, the generated electrons and holes are efficiently separated, thereby suppressing recombination, and the generated carriers are efficiently transported to the lower conductive layer 11 and the upper electrode 16.

[0033] The photoelectric conversion element 1 of the embodiment has a band structure different from that of the photoelectric conversion elements 100 and 200 by satisfying the composition ratio (b / a) of the light absorption layer of 2≦b / a≦4, thereby realizing an inverted structure photoelectric conversion element with high conversion efficiency.

[0034] (Photoelectric conversion element according to the first embodiment) FIG. 4 is a plan view of the photoelectric conversion element 1 shown in FIG. 3, and FIG. 5 is a cross-sectional view taken along line AA′ shown in FIG.

[0035] The photoelectric conversion element 1 further includes a substrate 10 and a lower electrode 15, and a lower conductive layer 11, a hole transport layer 12, a light absorption layer 13, and an electron transport layer 14 are sequentially stacked on the substrate 10. The photoelectric conversion element 1 is an inverted structure photoelectric conversion element that generates a voltage between the lower electrode 15 and an upper electrode 16 in response to light incident through the substrate 10 and the lower conductive layer 11, and outputs a current from the lower electrode 15.

[0036] The substrate 10 is formed of a transparent material, such as an insulating glass substrate, that can support the components included in the photoelectric conversion element 1 and transmits incident light entering the photoelectric conversion element 1. The transparent material is a material that transmits light of a wavelength absorbed by the light absorption layer 13, and is preferably a material that has a transmittance of 80% or more for light in the wavelength range absorbed by the light absorption layer 13, and more preferably a material that has a transmittance of 95% or more for light in the wavelength range absorbed by the light absorption layer 13. The substrate 10 may be formed of a conductive material or a flexible synthetic resin such as a polyimide resin. The substrate 10 has a thickness of, for example, 0.1 mm or more and 5.0 mm or less. The substrate 10 may have, for example, a flat plate shape, a film-like flat plate shape, or a cylindrical flat plate shape.

[0037] The lower conductive layer 11 is formed on the substrate 10 so as to cover it. The lower conductive layer 11 is transparent like the substrate 10 and is made of a low-resistance material capable of highly efficient hole transport. The lower conductive layer 11 is, for example, a thin film formed of fluorine-doped tin oxide (FTO), which has a low change in resistivity due to high-temperature heat treatment and is transparent and highly conductive. When the substrate 10 is formed of a material with low heat resistance, such as polyimide resin, the lower conductive layer 11 is formed of a transparent and highly conductive material that can be formed by low-temperature heat treatment. Examples of transparent and highly conductive materials that can be formed by low-temperature heat treatment include tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), and niobium-doped titanium oxide (NTO). The lower conductive layer 11 preferably has a thickness of 0.01 μm to 10.0 μm, more preferably 0.05 μm to 1.0 μm.

[0038] The hole transport layer 12 is a p-type semiconductor layer that blocks electrons generated in the light absorption layer 13 and transports holes generated in the light absorption layer 13 to the lower conductive layer 11 with high efficiency, and is formed on the lower conductive layer 11 so as to cover the lower conductive layer 11. The hole transport layer 12 is made of a transparent material with high hole transport properties, such as nickel oxide (NiO xIt is formed by or formed by other oxides such as cuprous oxide (Cu2O) and molybdenum trioxide (MoO3). Further, it is preferably formed of an organic material such as PEDOT:PSS that is hardly soluble in the solvent used when forming the light absorption layer 13. The hole transport layer 12 is, for example, nickel oxide (NiO x ) is formed by cuprous oxide (Cu2O) and molybdenum trioxide (MoO3).

[0039] In nickel oxide (NiO x ), NiO x (0 < x ≦ 1) has stable chemical properties and is a p-type semiconductor in which Ni vacancies function as acceptors without adding impurities, so it can be used as a material for the hole transport layer 12. Nickel oxide doped with Zn (NiO:Zn) has a lower resistivity than NiO x (0 < x ≦ 1) and the hole transport characteristics are improved. The content ratio of Ni to Zn, Ni:Zn, is preferably 99 mol% to 80 mol%: 1 mol% to 20 mol%. When the content ratio of Zn is higher than 20 mol%, it has been confirmed that the conversion efficiency of the photoelectric conversion device 1 decreases, so the addition ratio of Zn is preferably less than 20 mol%. When the addition ratio of Zn is lower than 1 mol%, the hole transport characteristics do not improve even when Zn is added, so the addition ratio of Zn is preferably 1 mol% or more. The hole transport layer 12 preferably has a film thickness of 10 nm or more and 300 nm or less. When the film thickness of the hole transport layer 12 is thinner than 10 nm, there is a possibility that the light absorption layer 13 is not sufficiently covered by the hole transport layer 12. When the film thickness of the hole transport layer 12 is thicker than 300 nm, the resistance value between the lower conductive layer 11 and the light absorption layer 13 increases, and the conversion efficiency of the photoelectric conversion device 1 decreases.

[0040] The light absorption layer 13 is formed of a rudolfite material represented by the composition formula Ag a Bi b I c and is formed on the lower conductive layer 11. In the composition formula, Ag a Bi b I cIn the formula, a, b, and c represent composition ratios, satisfying the relationship c=a+3b, preferably 2≦b / a≦4, and more preferably 2≦b / a≦2.5. The light-absorbing layer 13 preferably has a thickness of 10 nm or more and 10,000 nm or less, and more preferably 20 nm or more and 900 nm or less. The light-absorbing layer 13 absorbs incident light through the lower conductive layer 11 and the hole-transport layer 12, and electrons are excited by the absorbed light, generating electrons and holes therein. The holes generated in the light-absorbing layer 13 are transported to the lower electrode 15 via the hole-transport layer 12 and the lower conductive layer 11, and the electrons generated in the light-absorbing layer 13 are transported to the upper electrode 16 via the electron-transport layer 14. The holes generated in the light-absorbing layer 13 are transported to the lower electrode 15, and the electrons generated in the light-absorbing layer 13 are transported to the upper electrode 16, thereby generating an electromotive force in the photoelectric conversion element 1.

[0041] The electron transport layer 14 is an n-type semiconductor that blocks holes generated in the light absorption layer 13 and transports electrons generated in the light absorption layer 13 to the upper electrode 16 with high efficiency, and is formed on the light absorption layer 13 so as to cover the light absorption layer 13. The electron transport layer 14 is preferably formed of a material with high electron transport properties. The electron transport layer 14 is preferably formed of a metal oxide such as titanium oxide (TiO2, etc.), tin oxide (SnO2, etc.), zinc oxide (ZnO), and aluminum oxide (Al2O3), as well as fullerene (C 60 ) and phenyl-C 61 The electron transport layer 14 is formed of a C-based semiconductor such as polybutyric acid methyl ester (PCBM), etc. The electron transport layer 14 preferably has a thickness of 5 nm or more and 200 nm or less, and more preferably has a thickness of 20 nm or more and 60 nm or less.

[0042] The lower electrode 15 and the upper electrode 16 are, for example, Ti / Au layers formed by depositing a gold (Au) layer on a titanium (Ti) layer. They are formed of a material that provides ohmic contact at the interface between the underlying lower conductive layer 11 and electron transport layer 14. The lower electrode 15 is deposited on the lower conductive layer 11, and the upper electrode 16 is deposited on the electron transport layer 14. The lower electrode 15 and the upper electrode 16 may be formed of any material that provides ohmic contact with the lower conductive layer 11 and the electron transport layer 14. They may be formed of metals with relatively low work functions, such as Ag, Al, and Zn, or carbon-based electrodes, such as graphite. The lower electrode 15 and the upper electrode 16 may be formed as single metal layers of Ti, Ag, Al, and Zn. However, by further depositing a layer of resistant metals, such as Au and Pt, oxidation by atmospheric oxygen can be prevented. The lower electrode 15 and the upper electrode 16 may also be formed of a highly conductive transparent conductive film, such as ITO. The lower electrode 15 and the upper electrode 16 preferably have a thickness of 2 nm or more and 200 nm or less. If the thickness of the lower electrode 15 and the upper electrode 16 is thinner than 2 nm, the resistance value in the extension direction of the lower electrode 15 and the upper electrode 16 increases, the efficiency of collecting electrons and holes decreases, and the conversion efficiency of the photoelectric conversion element 1 decreases. If the thickness of the lower electrode 15 and the upper electrode 16 is thicker than 200 nm, the resistance value in the film thickness direction of the lower electrode 15 and the upper electrode 16 increases, the conversion efficiency of the photoelectric conversion element 1 decreases, and the amount of material used to form the lower electrode 15 and the upper electrode 16 increases, resulting in higher manufacturing costs.

[0043] Fig. 6 shows a method for manufacturing the photoelectric conversion element 1, in which Fig. 6(a) shows the lower conductive layer forming step, Fig. 6(b) shows the hole transport layer forming step, Fig. 6(c) shows the light absorbing layer forming step, Fig. 6(d) shows the electron transport layer forming step, Fig. 6(e) shows the light absorbing layer removing step, and Fig. 6(f) shows the electrode forming step.

[0044] First, in the lower conductive layer forming step, an FTO layer is formed as the lower conductive layer 11 on a substrate 10 having a rectangular planar shape. The lower conductive layer 11 is formed by a film forming method such as a vacuum deposition method, a sputtering method, a CVD method, or a plating method. After the lower conductive layer forming step is completed, the substrate 10 on which the lower conductive layer 11 has been formed is preferably cleaned in a cleaning step such as UV ozone cleaning.

[0045] Next, in the hole transport layer formation step, a Zn-doped NiO (NiO:Zn) layer is formed as the hole transport layer 12 on the surface of the lower conductive layer 11 formed on the substrate 10. The NiO:Zn layer is formed by, for example, vacuum deposition. A sample used as an evaporation source when forming the hole transport layer 12 by vacuum deposition may be a tablet-shaped sample obtained by mixing NiO powder and ZnO powder in a mortar to a Ni:Zn ratio of 99-80:1-20, pressing the mixture into a mold, and then firing the mixture. An evaporation apparatus used when forming the hole transport layer 12 by vacuum deposition is, for example, an EX-200 manufactured by Al-Pac Corporation.

[0046] In the hole transport layer forming step, first, the lower conductive layer 11 formed on the substrate 10 in the lower conductive layer forming step is placed on a metal mask having rectangular holes formed therein corresponding to the shape of the lower conductive layer 11, so that part of the surface of the lower conductive layer 11 is exposed through the rectangular holes. Next, tablet-shaped samples of NiO:Zn are loaded into a water-cooled hearth, and 4 × 10 -5 The inside of the vacuum chamber is evacuated to a pressure of Torr or less. Next, the NiO:Zn sample is degassed and heated with an EB gun. After that, a shutter is opened and particles evaporated from the NiO:Zn sample are deposited on the surface of the lower conductive layer 11, forming the hole transport layer 12. In the hole transport layer deposition process, the gas pressure and substrate temperature are not controlled during deposition. Instead, the thickness of the hole transport layer 12 is measured with a thickness sensor such as a quartz film thickness meter. The deposition process ends when the hole transport layer 12 reaches the desired thickness.

[0047] Next, in the light absorption layer formation process,a Bi b I c The light absorbing layer 13 is formed so that the composition ratio (b / a) satisfies 2≦b / a≦4. The light absorbing layer 13 is formed on the hole transport layer 12 by, for example, spin coating. In the light absorbing layer forming step, first, a Rudolf-phyte material precursor-containing solution containing a Rudolf-phyte material precursor and an organic solvent is applied by spin coating to the hole transport layer 12 formed in the hole transport layer forming step, and then temporarily dried. Next, the substrate 10 on which the Rudolf-phyte material precursor-containing solution has been applied is baked at a temperature between 70°C and 130°C for a predetermined time, thereby forming the light absorbing layer 13. If the baking temperature is lower than 70°C, the light absorbing layer 13 is not formed. On the other hand, if the baking temperature is higher than 130°C, I is desorbed from the light absorbing layer 13, and many defects are formed inside the light absorbing layer 13.

[0048] Examples of the precursors of the rudolphite material include AgI and BiI3. When the precursors of the rudolphite material are AgI and BiI3, the rudolphite material precursor-containing solution is a solution in which AgI and BiI3 are dissolved in an organic solvent. Examples of organic solvents in which the rudolphite material precursors are dissolved include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), γ-butyrolactone (GBL), 1-N-methyl-2-pyrrolidone (NMP), and n-butylamine. The rudolphite material precursor-containing solution may be prepared by pouring the organic solvent into a container containing AgI and BiI3. Alternatively, the rudolphite material precursor-containing solution may be prepared by pouring the organic solvent into a container containing BiI3 and then adding AgI. The proportion of the rudolfphyte material contained in the light absorbing layer 13, i.e., mol %, is the same as the proportion of Ag ions, Bi ions, and I ions contained in the rudolfphyte material precursor-containing solution. When preparing the rudolfphyte material precursor-containing solution, the amounts of AgI and BiI3 added are appropriately set so that the rudolfphyte material contains Ag, Bi, and I in the desired proportions. By preparing the rudolfphyte material precursor-containing solution so that BiI3 is 2 mol or more and 4 mol or less per 1 mol of AgI, the rudolfphyte material having the composition formula Aga Bi b I c The light absorbing layer 13 is formed such that the composition ratio (b / a) satisfies 2≦b / a≦4.

[0049] Next, in the electron transport layer formation step, a TiO layer is formed as the electron transport layer 14 on the surface of the light absorption layer 13 formed on the substrate 10. The TiO layer is formed, for example, by vacuum deposition, similar to the hole transport layer 12. The sample used as the evaporation source when forming the electron transport layer 14 by vacuum deposition may be a tablet-shaped sample obtained by pressing and sintering TiO powder. The deposition apparatus used when forming the electron transport layer 14 by vacuum deposition is, for example, an EX-200 manufactured by Alpac Co., Ltd., similar to the hole transport layer formation step.

[0050] In the electron transport layer formation process, first, the light absorbing layer 13 formed on the substrate 10 in the light absorbing layer formation process is placed on a metal mask having rectangular holes formed therein corresponding to the shape of the light absorbing layer 13, so that part of the surface of the light absorbing layer 13 is exposed through the rectangular holes. Next, a tablet-shaped sample of TiO2 is loaded into a water-cooled hearth, and 4 × 10 -5 The inside of the vacuum chamber is evacuated to a pressure of Torr or less. Next, the TiO2 sample is degassed and heated with an EB gun. After that, the shutter is opened and particles evaporated from the TiO2 sample are deposited on the surface of the light absorption layer 13, forming the electron transport layer 14. In the electron transport layer formation process, the gas pressure and substrate temperature are not controlled during deposition. Instead, the thickness of the electron transport layer 14 is measured with a thickness sensor such as a quartz film thickness gauge. The deposition process ends when the electron transport layer 14 reaches the desired thickness.

[0051] Next, in the light absorbing layer removal step, the region where the electron transport layer 14 is formed is limited by a metal mask, and the hole transport layer 12, the light absorbing layer 13, and the portions of the electron transport layer 14 exposed from the mask are removed with dimethylformamide (DMF). By removing the portions other than the region where the electron transport layer 14 is formed, the lower conductive layer 11 is exposed, and the lower electrode 15, through which holes that have migrated to the lower conductive layer 11 flow, can be connected to the lower conductive layer 11. Note that in the light absorbing layer removal step, the portion of the light absorbing layer 13 exposed from the mask does not need to be removed entirely, as long as the lower electrode 15 can be connected to the lower conductive layer 11.

[0052] In the electrode deposition process, a Ti / Au layer is deposited as a lower electrode 15 on the surface of the lower conductive layer 11 deposited on the substrate 10, and as an upper electrode 16 on the surface of the electron transport layer 14. The Ti / Au layer is deposited by, for example, vacuum deposition, similar to the hole transport layer 12 and the electron transport layer 14. In the electrode deposition process, the lower electrode 15 and the upper electrode 16 are deposited, thereby manufacturing the photoelectric conversion element 1. The sample used as the evaporation source when depositing the lower electrode 15 and the upper electrode 16 by vacuum deposition may be a tablet-shaped sample of Ti and Au having a diameter of 1 mm to 2 mm. The deposition apparatus used when depositing the lower electrode 15 and the upper electrode 16 by vacuum deposition is, for example, an EX-200 manufactured by Alpac Co., Ltd., similar to the hole transport layer deposition process and the electron transport layer deposition process.

[0053] In the electrode film formation step, first, the light absorbing layer 13, a portion of which has been removed in the light absorbing layer removal step, is placed on a metal mask. The mask used in the electrode film formation step has a pair of rectangular holes formed therein corresponding to the shape of the lower electrode 15 to be formed on the lower conductive layer 11. The mask used in the electrode film formation step also has six rectangular holes formed therein corresponding to the shape of the upper electrode 16 to be formed on the electron transport layer 14.

[0054] Next, a tablet-shaped sample of Ti was placed in the water-cooled hearth. -5The inside of the vacuum chamber is evacuated to a pressure of Torr or less. Next, the Ti sample is degassed and heated with an EB gun, after which the shutter is opened and the evaporated particles from the Ti sample are deposited on the surfaces of the lower conductive layer 11 and the electron transport layer 14. Next, the water-cooled hearth on which the Ti is placed is cooled sufficiently. Next, the cooling hearth is switched using a rotation mechanism, and a cooling hearth on which a tablet-shaped Au sample is placed is placed in the vacuum chamber in place of the water-cooled hearth on which the Ti is placed. Next, the water-cooled hearth placed in the vacuum chamber is switched by switching the cooling hearth using a rotation mechanism, without opening the vacuum chamber. Next, 4 × 10 -5 The vacuum chamber is evacuated to below Torr, and the Au sample is degassed and heated with an EB gun. The shutter is then opened, and particles evaporated from the Au sample are deposited on the Ti film surfaces of the lower conductive layer 11 and the electron transport layer 14. In the electrode deposition process, the gas pressure and substrate temperature are not controlled during deposition. Instead, the thicknesses of the lower electrode 15 and upper electrode 16 are measured using a thickness sensor such as a quartz-crystal film thickness meter. The deposition process ends when the desired thicknesses of the lower electrode 15 and upper electrode 16 are reached. After the deposition process is complete, the photoelectric conversion element 1 may be subjected to further processing, such as deposition of a protective film, cutting to deform the electrode into a desired shape, and connecting wiring to the lower electrode 15 and upper electrode 16, to enable it to function as a photoelectric conversion element.

[0055] The photoelectric conversion element 1 has the composition formula Ag a Bi b I c Since the composition ratio (b / a) of the light absorbing layer 13 formed from the Rudolf Physics material represented by the formula (1) is in the range of 2≦b / a≦4, a large internal electric field is generated in the region where a large number of electrons and holes are generated. In the photoelectric conversion element 1, a large internal electric field is generated in the region where a large number of electrons and holes are generated, so that the recombination of electrons and holes can be suppressed and high conversion efficiency can be achieved.

[0056] Furthermore, since the photoelectric conversion element 1 has an inverted structure, the electron transport layer 14, which is made of TiO2 and is heat-treated at high temperatures, is disposed at a distance from the substrate 10, and therefore the element can be formed without exposing the substrate 10 to high temperatures, allowing a flexible substrate to be used as the substrate 10. By using a flexible substrate as the substrate 10, the photoelectric conversion element 1 can be formed as a flexible photoelectric conversion element.

[0057] The photoelectric conversion element 1 is made of NiO x Since the layer is deposited as the hole transport layer 12, the hole transport layer 12 can have high stability in chemical properties. x Since the layer is deposited as the hole transport layer 12, the hole transport layer 12 can have high hole transport properties.

[0058] (Photoelectric Conversion Element According to Second Embodiment) FIG. 7 is a plan view of the photoelectric conversion element according to the second embodiment, and FIG. 8 is a cross-sectional view taken along line BB' in FIG.

[0059] Photoelectric conversion element 2 differs from photoelectric conversion element 1 in that it has an interdiffusion suppression layer 17. The configurations and functions of the components of photoelectric conversion element 2 other than interdiffusion suppression layer 17 are the same as the configurations and functions of the components of photoelectric conversion element 1 that are assigned the same reference numerals, and therefore detailed explanations thereof will be omitted here.

[0060] The interdiffusion-preventing layer 17 is formed between the hole transport layer 12 and the light absorption layer 13 to suppress interdiffusion of elements contained in the hole transport layer 12 and the light absorption layer 13. The material forming the interdiffusion-preventing layer 17 is preferably a material with high barrier properties against element diffusion, and metal oxides such as SiO2 and Al2O3 are preferred. SiO2 is preferred because it can be easily formed at low cost. The interdiffusion-preventing layer 17 preferably has a thickness of 0.1 to 2 nm. If the thickness of the interdiffusion-preventing layer 17 is thinner than 0.1 nm, the interdiffusion of elements contained in the hole transport layer 12 and the light absorption layer 13 is not suppressed. If the thickness of the interdiffusion-preventing layer 17 is thicker than 2 nm and the interdiffusion-preventing layer 17 is formed of an insulating material such as a SiO2 layer, the resistance between the hole transport layer 12 and the light absorption layer 13 increases, resulting in a decrease in the conversion efficiency of the photoelectric conversion element 2.

[0061] 9(a) shows a manufacturing method of the photoelectric conversion element 2, in which FIG. 9(a) shows a lower conductive layer forming step, FIG. 9(b) shows a hole transport layer forming step, FIG. 9(c) shows an interdiffusion suppression layer forming step, and FIG. 9(d) shows a light absorbing layer forming step. FIG. 9(e) shows an electron transport layer forming step, FIG. 9(f) shows a light absorbing layer removing step, and FIG. 9(g) shows an electrode forming step. The steps other than the interdiffusion suppression layer forming step are the same as those described with reference to FIG. 6, and therefore detailed description thereof will be omitted here.

[0062] In the interdiffusion-preventing layer forming step, an SiO2 layer is formed as an interdiffusion-preventing layer 17 on the surface of the hole transport layer 12 formed on the substrate 10 immediately after the hole transport layer forming step without opening the vacuum chamber. The interdiffusion-preventing layer 17 is formed, for example, by vacuum deposition, similar to the hole transport layer 12. The sample used as the evaporation source when forming the interdiffusion-preventing layer 17 by vacuum deposition may be particulate SiO2 having a particle size of approximately 1 mm to 3 mm. The deposition apparatus used when forming the interdiffusion-preventing layer 17 by vacuum deposition is, for example, an EX-200 manufactured by Al-Pac Co., Ltd., similar to the hole transport layer forming step.

[0063] In the interdiffusion suppression layer film formation process, first, the water-cooled hearth on which the NiO:Zn tablet used in the hole transport layer film formation process is placed is sufficiently cooled. Next, the cooling hearth is switched using a rotation mechanism, and the cooling hearth on which the SiO2 sample is placed is placed in the vacuum chamber instead of the water-cooled hearth on which the NiO:Zn tablet is placed. Next, 4 × 10 -5 The inside of the vacuum chamber is evacuated to below Torr, and the SiO2 sample is degassed and heated by an EB gun. Next, the shutter is opened, and particles evaporated from the SiO2 sample are deposited on the surface of the SiO2 film that forms the hole transport layer 12. In the interdiffusion barrier layer deposition process, the gas pressure and substrate temperature are not controlled during deposition. Instead, the thickness of the interdiffusion barrier layer 17 is measured using a thickness sensor such as a quartz thickness gauge. The deposition process ends when the interdiffusion barrier layer 17 reaches the desired thickness.

[0064] The photoelectric conversion element 2 has the interdiffusion suppression layer 17, which allows the elements contained in the hole transport layer 12 and the light absorption layer 13 to suppress interdiffusion between the hole transport layer 12 and the light absorption layer 13, thereby suppressing the occurrence of defects at the interface between the hole transport layer 12 and the light absorption layer 13. By suppressing the occurrence of defects at the interface between the hole transport layer 12 and the light absorption layer 13, the photoelectric conversion element 2 reduces the recombination of electrons and holes through defects that occur at the interface, allowing electrons and holes generated by the incidence of light to move more efficiently to the conductive layer or electrode and be extracted.

[0065] (Photoelectric Conversion Element According to Modification) In the photoelectric conversion elements 1 and 2, the lower conductive layer 11 is an FTO layer and the electron transport layer 14 is a TiO2 layer, but in the photoelectric conversion element according to this embodiment, the lower conductive layer 11 and the electron transport layer 14 may have layer structures other than an FTO layer and a TiO2 layer, respectively. For example, in the photoelectric conversion element according to the embodiment, the lower conductive layer may be an ITO layer and the electron transport layer may be a C 60 and PCBM.

[0066] Furthermore, the photoelectric conversion element of the embodiment may have a lower collecting electrode instead of the lower conductive layer 11 when the hole transporting property of the hole transport layer 12 is sufficiently high.

[0067] FIG. 10 is a plan view of a photoelectric conversion element according to a modified example, and FIG. 11 is a cross-sectional view taken along CC' shown in FIG.

[0068] Photoelectric conversion element 3 differs from photoelectric conversion element 1 in that it has a plurality of lower collector electrodes 18 instead of lower conductive layer 11. The configurations and functions of the components of photoelectric conversion element 3 other than the plurality of lower collector electrodes 18 are the same as the configurations and functions of the components of photoelectric conversion element 1 with the same reference numerals, and therefore detailed description thereof will be omitted here.

[0069] Each of the plurality of lower collector electrodes 18 has a rectangular planar shape extending in the short-side extension direction of the electron transport layer 14, and is arranged so that its ends are connected to each of the pair of lower electrodes 15. By having the plurality of lower collector electrodes 18 in place of the lower conductive layer 11, the photoelectric conversion element 3 is able to extract holes that are generated by light absorption in the light absorption layer 13 and move to the hole transport layer 12 partially by the plurality of lower collector electrodes 18, rather than extracting them over the entire surface of the hole transport layer 12. [Example]

[0070] Photoelectric conversion elements according to Examples and Comparative Examples were fabricated, and the power generation characteristics obtained by performing current-voltage measurements on the fabricated photoelectric conversion elements will be described below.

[0071] (Method for measuring current-voltage characteristics under light irradiation) The current-voltage characteristics under light irradiation were measured using the following method. A BLD-100 light source manufactured by Bunkoukeiki Co., Ltd. was used, and the illuminance was adjusted so that the incident light from the light source onto the photoelectric conversion element was 200 lx. The light emitted from the light source was adjusted to be emitted onto an area of ​​2.5 mm x 2.5 mm using a light-shielding mask, and the light source and photoelectric conversion element were positioned so that the light was incident on the photoelectric conversion element from the substrate side. The current-voltage characteristics were measured using a PECK2400-N manufactured by Peccell Technologies Co., Ltd., by sequentially sweeping the voltage applied to the photoelectric conversion element from the positive side to the negative side.

[0072] Example 1 Example 1 was produced by the manufacturing method shown in Fig. 6. First, an FTO glass substrate having a planar shape of 25 mm x 25 mm and having a lower conductive layer 11 formed on a substrate 10 was prepared, and the prepared FTO glass substrate was subjected to UV ozone cleaning. Here, the thickness of the glass substrate corresponding to the substrate 10 was 1 mm, and the thickness of the FTO film corresponding to the lower conductive layer 11 was 1 µm.

[0073] Next, a NiO:Zn layer corresponding to the hole transport layer 12 was formed on the surface of the FTO film formed on the FTO glass substrate by vacuum deposition using an EX-200 manufactured by Alpac Corporation, by heating with an EB-gun. The materials used to form the hole transport layer 12 were prepared by mixing NiO powder and ZnO powder in a mortar so that the Ni:Zn ratio was 90:10, press-molding, and then firing the mixture into tablets. The FTO glass substrate on which the lower conductive layer 11 was formed was placed on a metal mask with a 25 mm × 15 mm hole, and the NiO:Zn tablets were filled into a water-cooled hearth, and 4 × 10 -5 The inside of the vacuum chamber was evacuated to a pressure of Torr or less. Next, the NiO:Zn sample was degassed and heated with an EB gun. After that, the shutter was opened and the evaporated particles from the NiO:Zn sample were deposited on the surface of the lower conductive layer 11.

[0074] Next, an AgBi2I7 film corresponding to the light-absorbing layer 13 was formed on the surface of the hole-transport layer 12 by spin coating. The Rudolf Phyt material precursor-containing solution was prepared by placing AgI and BiI3 in a container and dissolving them in DMSO. The AgI and BiI3 placed in the container were adjusted so that the Ag:Bi:I ratio in the Rudolf Phyt material precursor-containing solution was 1:2:7. The spin-coating speed was 4000 rpm, and the Rudolf Phyt material precursor-containing solution was applied for 30 seconds. The FTO glass substrate coated with the Rudolf Phyt material precursor-containing solution was pre-dried at 90°C for 5 minutes and then baked at 120°C for 1 hour to form an AgBi2I7 film corresponding to the Rudolf Phyt material-containing light-absorbing layer 13. The thickness of the AgBi2I7 film was 60 nm.

[0075] Next, a TiO2 layer corresponding to the electron transport layer 14 was formed on the surface of the Ag1Bi2I7 film by heating with an EB gun using a vacuum deposition method using an EX-200 manufactured by Alpac Corporation. The material used to form the electron transport layer 14 was made by pressing TiO2 powder and then firing it into a tablet shape. After placing the FTO glass substrate on which the Ag1Bi2I7 film had been formed, the TiO2 tablets were filled into a water-cooled hearth and 4 × 10 -5 The inside of the vacuum chamber was evacuated to a pressure of Torr or less. Next, the TiO2 sample was degassed and heated with an EB gun, and then the shutter was opened. The evaporated particles from the TiO2 sample were deposited on the surface of the lower conductive layer 11 so that the TiO2 layer had a thickness of 30 nm.

[0076] Next, the region where the electron transport layer 14 is formed is limited by a metal mask, and the portions of the hole transport layer 12, the light absorption layer 13, and the electron transport layer 14 exposed from the mask are removed with DMF.

[0077] The Ti / Au layers corresponding to the lower electrode 15 and the upper electrode 16 were formed on the surfaces of the FTO film and the TiO2 layer by heating with an EB-gun using a vacuum deposition method using an EX-200 manufactured by Alpac Corporation. The FTO glass substrate was placed on a metal mask having two holes of 3.25 mm x 20 mm for electrodes collecting holes and ten holes of 3.2 mm x 3.2 mm for electrodes collecting electrons, and the area to be deposited was limited so that the area of ​​the Ti / Au layer would be the desired area. Ti particles with a diameter of 1 mm to 2 mm were filled into a water-cooled hearth as an evaporation source, and 4 x 10 -5 After evacuating to below Torr, the material was degassed and heated with an EB gun, then the shutter was opened and deposition was performed to a thickness of 2 nm. Next, after the water-cooled hearth containing Ti was cooled sufficiently, it was switched by the rotation mechanism to a water-cooled hearth filled with Au having a diameter of 1 mm to 2 mm, and 4 × 10 -5 It was confirmed that the chamber was evacuated to a pressure of Torr or less. Next, the material was degassed, heated with an EB gun, and the shutter was opened to perform deposition to a thickness of 70 nm.

[0078] (Examples 2 to 4 and Comparative Examples 1 and 2) In Examples 2 to 4 and Comparative Examples 1 and 2, Ag corresponding to the light absorbing layer 13 a Bi b I c The composition ratios of Ag, Bi, and I contained in the layers differ from those of Example 1. Example 2 was prepared so that Ag:Bi:I was 2:5:17, Example 3 was prepared so that Ag:Bi:I was 1:3:10, and Example 4 was prepared so that Ag:Bi:I was 1:4:13. Comparative Example 1 was prepared so that Ag:Bi:I was 1:1:4, and Comparative Example 2 was prepared so that Ag:Bi:I was 1:6:19. Examples 2 to 4 and Comparative Examples 1 and 2 have the same configuration as Example 1 except for the composition ratios of Ag, Bi, and I, so detailed explanations will be omitted here.

[0079] Example 5 Example 5 differs from Example 1 in the layer structure of the layers corresponding to the lower conductive layer 11 and the electron transport layer 14. In Example 5, an ITO glass substrate on which an ITO layer having a thickness of 1 μm is formed is used instead of the FTO glass substrate, so that the ITO layer is formed on the lower conductive layer 11 instead of the FTO layer. 60 and PCBM-containing layer is deposited as the electron transport layer 14 in place of the TiO layer. 60 The layer containing PCBM was formed by spin coating. An electron transport layer precursor solution containing an electron transport layer precursor and an organic solvent was applied by spin coating and dried. The electron transport layer precursor solution was a solution of PCBM dissolved in chlorobenzene and C 60 The electron transport layer precursor solution was mixed in dichlorobenzene at a volume ratio of 1:1. The rotation speed in spin coating was 1500 rpm, and the electron transport layer precursor solution was applied for 30 seconds.

[0080] Table 1 shows the Ag corresponding to the light absorbing layer 13 in Examples 1 to 5 and Comparative Examples 1 and 2. a Bi b I c The composition ratio of the layers and the layer structures of the hole transport layer 12 and the electron transport layer 14 are shown.

[0081] [Table 1]

[0082] FIG. 12 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Example 1 under light irradiation, FIG. 13 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Example 2 under light irradiation, and FIG. 14 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Example 3 under light irradiation. FIG. 15 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Example 4 under light irradiation, and FIG. 16 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Example 5 under light irradiation. FIG. 17 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Comparative Example 1 under light irradiation, and FIG. 18 is a graph showing the current-voltage characteristics of the photoelectric conversion element according to Comparative Example 2 under light irradiation. In FIGS. 12 to 18, the horizontal axis represents the voltage generated between lower electrode 15 and upper electrode 16 when irradiated with light, and the vertical axis represents the current flowing from lower electrode 15 when irradiated with light.

[0083] Ag a Bi b I c The conversion efficiency of Example 1, in which the composition ratio a:b:c of the film is 1:2:7 and the composition ratio (b / a) is 2, is 6.66%. a Bi b I c The conversion efficiency of Example 2, in which the composition ratio a:b:c of the film is 2:5:17 and the composition ratio (b / a) is 2.5, is 5.86%. a Bi b I c The conversion efficiency of Example 3, in which the composition ratio a:b:c of the film is 1:3:10 and the composition ratio (b / a) is 3, is 1.43%. a Bi b I c The conversion efficiency of Example 4, in which the composition ratio a:b:c of the film is 1:4:13 and the composition ratio (b / a) is 4, is 1.56%. a Bi b I c The composition ratio of the film is 1:2:7, the composition ratio (b / a) is 2, and C 60 The conversion efficiency of Example 5, in which a layer containing ZnO and PCBM is deposited as the electron transport layer 14, is 4.90%.

[0084] 3, in a region of the light absorbing layer 13 in which the composition ratio (b / a) satisfies 2≦b / a≦4, which is in contact with the hole transport layer 12 and to which light is incident through the hole transport layer 12, electrons and holes are excited by light absorption and generated in large numbers. In addition, a large internal electric field is applied to the region where electrons and holes are generated in large numbers, so that the generated electrons and holes are separated, making it difficult for recombination between electrons and holes to occur. As a result, more electrons and holes are transported to the lower electrode 15 and the upper electrode 16, and the conversion efficiency is improved.

[0085] Unlike Examples 1 to 4, Example 5 has an ITO layer corresponding to the lower conductive layer 11 and a C 60 and PCBM, but the composition ratio of the light absorbing layer 13 satisfies 2≦b / a≦4, similarly to Examples 1 to 4, so that the conversion efficiency is high. 60 A layer containing PEG and PCBM can be prepared at a lower temperature and can be prepared, for example, by a coating method.

[0086] On the other hand, Ag a Bi b I c The conversion efficiency of Comparative Example 1, in which the composition ratio a:b:c of the film is 1:1:4 and the composition ratio (b / a) of Ag and Bi is 1, is 0.05%. a Bi b I c In Comparative Example 2, in which the composition ratio a:b:c of the film is 1:6:19 and the composition ratio of Ag and Bi (b / a) is 6, the conversion efficiency is 0.65%.

[0087] Comparative Example 1, in which the composition ratio (b / a) of Ag and Bi is 1, has a significantly lower conversion efficiency than Examples 1 to 5, which have a light absorbing layer 13 with a composition ratio (b / a) that satisfies 2≦b / a≦4. In Comparative Example 1, the difference in work function between the hole transport layer 12 and the light absorbing layer 13 is small, so the generated internal electric field is small, and electrons and holes generated in large amounts in the region of the light absorbing layer 13 that is in contact with the hole transport layer 12 are difficult to separate. In Comparative Example 1, recombination between electrons and holes occurs more easily, and fewer electrons and holes are transported to the lower electrode 15 and the upper electrode 16, resulting in a lower conversion efficiency.

[0088] Furthermore, Comparative Example 2, in which the Ag / Bi composition ratio (b / a) is 6, has a higher conversion efficiency than Comparative Example 1 but a lower conversion efficiency than Examples 1 to 5. In Comparative Example 2, as in Examples 1 to 5, a large internal electric field is generated in the region of the light-absorbing layer 13 in contact with the hole-transport layer 12, where a large number of electrons and holes are generated, and the generated electrons and holes are separated and recombination is unlikely to occur. However, when the composition ratio (b / a) is greater than 4, the energy offset between the top of the valence band of the NiO:Zn layer corresponding to the hole-transport layer 12 and the top of the valence band of the light-absorbing layer 13 is large, and therefore the generated internal electric field is smaller than in Examples 1 to 5. In Comparative Example 2, the internal electric field generated in the region of the light-absorbing layer 13 in contact with the hole-transport layer 12 is reduced, resulting in a lower open-circuit voltage and increased recombination between electrons and holes. This reduces the number of electrons and holes transported to the lower electrode 15 and the upper electrode 16, resulting in a lower conversion efficiency. A high open-circuit voltage is desirable for practical use of photoelectric conversion elements. Specifically, the open circuit voltage is preferably equal to or greater than 0.4 V. The open circuit voltage of Comparative Example 2 is 0.36 V, which is less than 0.4 V, and is therefore not preferred.

[0089] FIG. 19 shows the open-circuit voltage V in the current-voltage characteristics of Examples 1 to 4 and Modifications 1 and 2. OC FIG.

[0090] In Comparative Example 1, the difference between the work function of the hole transport layer 12 and the work function of the light absorbing layer 13 is small, so the internal electric field generated in the region of the light absorbing layer 13 that contacts the hole transport layer 12 is small, and in the region where a large number of electrons and holes are generated, the electrons and holes are difficult to separate. Since the internal electric field generated in the region of the light absorbing layer 13 that contacts the hole transport layer 12 is small, recombination of electrons and holes occurs easily, and the open circuit voltage V OC On the other hand, in Comparative Example 2, the energy offset between the top of the valence band of the NiO:Zn layer corresponding to the hole transport layer 12 and the top of the valence band of the light absorption layer 13 becomes large, and the open-circuit voltage V OC becomes lower, and the open circuit voltage V OC In Examples 1 to 4, the open circuit voltage V OCIn Examples 1 and 2 in which the composition ratio (b / a) of Ag and Bi is 2≦b / a≦2.5, the open-circuit voltage V OC is at a maximum, and it is more preferable that the photoelectric conversion element has a light absorbing layer in which the composition ratio (b / a) of Ag and Bi is 2≦b / a≦2.5. [Explanation of symbols]

[0091] 1-3 Photoelectric conversion element 10 Substrate 11, 101 Lower conductive layer 12, 104, 202 Hole transport layer 13, 103, 203 Light absorbing layer 14, 102, 204 Electron transport layer 15 Lower electrode 16 Upper electrode 17 Interdiffusion suppression layer 18 Lower collector electrode 105, 205 electrode

Claims

1. A substrate; a lower conductive layer deposited on the substrate; a hole transport layer deposited on the lower conductive layer; A film having the composition formula Ag a Bi b I c a light absorbing layer represented by an electron transport layer formed on the light absorbing layer; an upper electrode formed on the electron transport layer; In the composition formula, the composition ratios a, b, and c satisfy c=a+3b and 2≦b / a≦4, converting incident light through the lower conductive layer into an electric signal; the hole transport layer is a nickel oxide (NiO x ) layer, where x is 0<x≦1; a difference between the work function of the hole transport layer and the work function of the light absorbing layer is greater than a difference between the work function of the light absorbing layer and the work function of the electron transport layer; A photoelectric conversion element characterized by:

2. 2. The photoelectric conversion element according to claim 1, further comprising an interdiffusion suppression layer formed between the hole transport layer and the light absorption layer, the interdiffusion suppression layer suppressing interdiffusion of elements contained in the hole transport layer and the light absorption layer.

3. The interdiffusion suppression layer is made of SiO 2 The photoelectric conversion element according to claim 2 , which is a layer.

4. 4. The photoelectric conversion element according to claim 1, wherein the composition ratio satisfies 2≦b / a≦2.

5.

5. 5. The photoelectric conversion element according to claim 1, wherein the substrate is flexible.

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