Solar cell and solar cell manufacturing method

Abstract

The present invention aims to provide a solar cell in which a decrease in photoelectric conversion efficiency due to continuous exposure to light (photodegradation) is reduced, and a method of producing the solar cell. The present invention relates to a solar cell, including: an electrode; a counter electrode; and a photoelectric conversion layer between the electrode and the counter electrode, the photoelectric conversion layer containing an organic-inorganic perovskite compound represented by the formula R-M-X.sub.3 where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom, the solar cell satisfying the formula (1):
N(T,I)/N(0,I)<5  (1)
where N(0, I) is a carrier density of the organic-inorganic perovskite compound immediately after start of exposure of the solar cell to light at an intensity of I mW/cm.sup.2, and N(T, I) is the carrier density of the organic-inorganic perovskite compound after continuous exposure of the solar cell to light at an intensity of I mW/cm.sup.2 for T hour/hours.

Claims

1. A solar cell, comprising: an electrode; a counter electrode; a photoelectric conversion layer between the electrode and the counter electrode; an electron transport layer between the electrode and the photoelectric conversion layer; and a hole transport layer between the photoelectric conversion layer and the counter electrode, the photoelectric conversion layer containing a layer comprising an organic-inorganic perovskite compound represented by the formula R-M-X.sub.3 where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom, and at least one element selected from the group consisting of an element of group 11 of the periodic table, calcium, strontium, manganese, antimony, titanium, neodymium, iridium, and lanthanum, the organic-inorganic perovskite compound being a crystalline semiconductor having a degree of crystallinity of 70% or higher, wherein the photoelectric conversion layer is formed by a printing method using a solution containing a metal halide compound and a solution containing an amine compound, wherein the at least one element is incorporated into one or both of the solution containing a metal halide compound and the solution containing an amine compound, and wherein a content ratio (mol) of the at least one element selected from the group consisting of an element of group 11 of the periodic table, calcium, strontium, manganese, antimony, titanium, neodymium, iridium, and lanthanum relative to 100 mol of the metal atom M in the organic-inorganic perovskite compound is 1 to 5.

2. A method of producing the solar cell according to claim 1, the method comprising the steps of: forming the photoelectric conversion layer containing the organic-inorganic perovskite compound by a printing method using a solution containing a metal halide compound and a solution containing an amine compound; and heating the photoelectric conversion layer under conditions of a heating temperature of 100° C. or higher but lower than 200° C. and a heating time of three minutes or longer but within two hours, the method including incorporating, into one or both of the solution containing a metal halide compound and the solution containing an amine compound, at least one element selected from the group consisting of an element of group 2 of the periodic table, an element of group 11 of the periodic table, manganese, antimony, titanium, neodymium, iridium, and lanthanum.

3. The solar cell according to claim 1, wherein, in the organic-inorganic perovskite compound represented by the formula R-M-X.sub.3, X is iodine or bromine.

4. The solar cell according to claim 1, wherein, in the organic-inorganic perovskite compound represented by the formula R-M-X.sub.3, R is formamidinium or an ion thereof.

5. The solar cell according to claim 1, wherein, in the organic-inorganic perovskite compound represented by the formula R-M-X.sub.3, M is lead or tin.

6. The solar cell according to claim 5, wherein, in the organic-inorganic perovskite compound represented by the formula R-M-X.sub.3, X is iodine or bromine.

7. The solar cell according to claim 6, wherein, in the organic-inorganic perovskite compound represented by the formula R-M-X.sub.3, R is formamidinium or an ion thereof.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view of an exemplary crystalline structure of an organic-inorganic perovskite compound.

DESCRIPTION OF EMBODIMENTS

(2) Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not intended to be limited by these Examples.

EXAMPLE 1

(3) (1) Preparation of Titanium-Containing Coating Liquid

(4) Ten millimoles of titanium powder was precisely weighed and put in a beaker. To the beaker were further added 40 g of aqueous hydrogen peroxide and 10 g of aqueous ammonia. The mixture was cooled with water for two hours before adding 30 mmol of L-lactic acid. The mixture was then heated on a hot plate set at 80° C. for one day. To the mixture was then added 10 mL of distilled water, thus a titanium-containing coating liquid was prepared.

(5) (2) Preparation of Solar Cell

(6) A FTO film having a thickness of 1,000 nm as an electrode (cathode) was formed on a glass substrate, ultrasonically washed with pure water, acetone, and methanol each for 10 minutes in the stated order, and then dried.

(7) The titanium-containing coating liquid was applied at 1,500 rpm by the spin coating method and then fired in air at 550° C. for 10 minutes to form a thin film-shaped electron transport layer. Onto the thin film-shaped electron transport layer was applied titanium oxide paste containing polyisobutyl methacrylate as an organic binder and titanium oxide (mixture of powders with an average particle sizes of 10 nm and 30 nm) by the spin coating method. The paste was then fired at 500° C. for 10 minutes to form a porous electron transport layer having a thickness of 300 nm.

(8) Subsequently, lead iodide as a metal halide compound was dissolved into N,N-dimethylformamide (DMF) to prepare a 1 M solution. In order to add copper, copper chloride as an additive was dissolved into the lead iodide solution in DMF to achieve a concentration of 0.01 M. The obtained solution was applied onto the porous electron transport layer by the spin coating method to form a film.

(9) Separately, methylammonium iodide as an amine compound was dissolved into 2-propanol to prepare a 1 M solution. The sample with the above lead iodide film was immersed into this solution to form a layer containing CH.sub.3NH.sub.3PbI.sub.3, which is an organic-inorganic perovskite compound. After immersion, the obtained sample was subjected to heat treatment at 80° C. for 30 minutes.

(10) Further, 1 wt % solution of poly(4-butylphenyl-diphenyl-amine) (available from 1-Material) in chlorobenzene was applied onto the organic-inorganic perovskite compound part by the spin coating method to a thickness of 50 nm, thus forming a hole transport layer.

(11) A gold film having a thickness of 100 nm was formed as a counter electrode (anode) on the obtained hole transport layer by vacuum deposition, whereby a solar cell was prepared.

(12) (3) Measurement of Degree of Crystallinity and Crystallite Size of Organic-Inorganic Perovskite Compound

(13) The degree of crystallinity was determined by: separating a crystalline substance-derived scattering peak and an amorphous portion-derived halo by fitting in the region where 2θ is 13° to 15° in a spectrum detected by X-ray scattering intensity distribution measurement; determining their respective intensity integrals; and calculating the ratio of the crystalline portion to the whole. The crystallite size was calculated from the obtained spectrum by the Halder-Wagner method using data analysis software PDXL available from Rigaku Corporation.

(14) (4) Measurement of Carrier Density of Organic-Inorganic Perovskite Compound

(15) A C-V measurement was performed on the solar cell with an impedance analyzer (available from Solartron, S11287) while exposing the solar cell to artificial sunlight from HAL-320 (available from Asahi Spectra Co., Ltd.) at 100 mW/cm.sup.2. The measurement was performed at a frequency of 1,000 Hz and at a scan rate of 100 mV/s from +2 V to −2 V. The carrier density N(0, I) of the organic-inorganic perovskite compound immediately after the start of exposure to light and the carrier density N(T, I) of the organic-inorganic perovskite compound after one-hour exposure to light were determined by conversion to the Mott-Schottky plot based on the C-V graph obtained by the C-V measurement, and N(T, I)/N(0, I) was calculated.

EXAMPLES 2 TO 14

(16) A solar cell was obtained in the same manner as in Example 1 except that instead of 0.01 M of copper chloride of Example 1, the compound and the amount shown in Table 1 were employed in the preparation of the solution for organic-inorganic perovskite compound formation, and that the material of the hole transport layer was changed to that shown in Table 1. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

EXAMPLES 15 AND 16

(17) On the porous electron transport layer of Example 1, CH.sub.3NH.sub.3I and PbI.sub.2 were dissolved at a mole ratio of 1:1 into N,N-dimethylformamide (DMF) as a solvent to achieve a Pb concentration of 1 M, thereby preparing a solution for organic-inorganic perovskite compound formation. In order to add strontium or titanium, strontium chloride or titanium iodide as an additive was dissolved into the thus prepared solution to a concentration of 0.01 M. The resulting solution was applied onto the above porous electron transport layer by the spin coating method to form a film. Further, 1 wt % solution of poly(4-butylphenyl-diphenyl-amine) (available from 1-Material) in chlorobenzene was applied onto the organic-inorganic perovskite compound part by the spin coating method to a thickness of 50 nm to form a hole transport layer, whereby a photoelectric conversion layer was formed. A gold film having a thickness of 100 nm was formed as a counter electrode (anode) on the photoelectric conversion layer by vacuum deposition, thus a solar cell was prepared.

EXAMPLE 17

(18) On the porous electron transport layer of Example 1, CH.sub.3NH.sub.3I and PbCl.sub.2 were dissolved at a mole ratio of 3:1 into N,N-dimethylformamide (DMF) as a solvent to achieve a Pb concentration of 1 M, thereby preparing a solution for organic-inorganic perovskite compound formation. In order to add strontium, strontium chloride as an additive was dissolved into the thus prepared solution to a concentration of 0.01 M. The resulting solution was applied onto the above porous electron transport layer by the spin coating method to form a film. Further, 1 wt % solution of poly(4-butylphenyl-diphenyl-amine) (available from 1-Material) in chlorobenzene was applied onto the organic-inorganic perovskite compound part by the spin coating method to a thickness of 50 nm to form a hole transport layer, whereby a photoelectric conversion layer was formed. A gold film having a thickness of 100 nm was formed as a counter electrode (anode) on the photoelectric conversion layer by vacuum deposition, thus a solar cell was prepared.

COMPARATIVE EXAMPLE 1

(19) A solar cell was obtained in the same manner as in Example 1 except that no additive was used in the preparation of the solution for organic-inorganic perovskite compound formation. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

COMPARATIVE EXAMPLE 2

(20) A solar cell was obtained in the same manner as in Example 3 except that no additive was used in the preparation of the solution for organic-inorganic perovskite compound formation. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

COMPARATIVE EXAMPLES 3 TO 7

(21) A solar cell was obtained in the same manner as in Example 1 except that the type and concentration of the additives used in the preparation of the solution for organic-inorganic perovskite compound formation were changed as shown in Table 1. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

COMPARATIVE EXAMPLE 8

(22) A solar cell was obtained in the same manner as in Example 15 except that no additive was used in the preparation of the solution for organic-inorganic perovskite compound formation. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

COMPARATIVE EXAMPLE 9

(23) A solar cell was obtained in the same manner as in Example 17 except that no additive was used in the preparation of the solution for organic-inorganic perovskite compound formation. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

COMPARATIVE EXAMPLE 10

(24) A solar cell was obtained in the same manner as in Example 1 except that after the formation of the layer containing the organic-inorganic perovskite compound CH.sub.3NH.sub.3PbI.sub.3, the obtained sample was heat-treated at 200° C. for 30 minutes. The properties of the organic-inorganic perovskite compound including the degree of crystallinity and carrier density were measured in the same manner as in Example 1.

(25) <Evaluation>

(26) The solar cells obtained in Examples 1 to 17 and Comparative Examples 1 to 9 were subjected to the following evaluations. Table 1 shows the results.

(27) (1) Photodegradation Test

(28) A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell. The solar cell was exposed to light at an intensity of 100 mW/cm.sup.2 using a solar simulator (available from Yamashita Denso Corp.). The photoelectric conversion efficiency immediately after the start of exposure to light and the photoelectric conversion efficiency after one-hour exposure to light were measured. The value of photoelectric conversion efficiency after one-hour light exposure/photoelectric conversion efficiency immediately after the start of light exposure was calculated. A value of 0.9 or greater was rated “∘∘∘ (Excellent)”, a value of 0.8 or greater but smaller than 0.9 was rated “∘∘ (Very Good)”, a value of 0.6 or greater but smaller than 0.8 was rated “∘ (Good)”, and a value of smaller than 0.6 was rated “× (Poor)”.

(29) (2) Initial Conversion Efficiency

(30) A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell. The photoelectric conversion efficiency was measured by exposing the solar cell to light at an intensity of 100 mW/cm.sup.2 using a solar simulator (available from Yamashita Denso Corp.). In Examples 1-14 and Comparative Examples 2-7, a photoconversion efficiency of 1 or greater was rated “∘ (Good)” and a photoconversion efficiency of smaller than 1 was rated “× (Poor)” with the conversion efficiency of Comparative Example 1 normalized to 1. In Examples 15-16, a photoconversion efficiency of 1 or greater was rated “∘ (Good)” and a photoconversion efficiency of smaller than 1 was rated “× (Poor)” with the conversion efficiency of Comparative Example 8 normalized to 1. In Example 17, a photoconversion efficiency of 1 or greater was rated “∘ (Good)” and a photoconversion efficiency of smaller than 1 was rated “× (Poor)” with the conversion efficiency of Comparative Example 9 normalized to 1.

(31) TABLE-US-00001 TABLE 1 Photoelectric conversion layer Electron Degree of Crystallite transport Organic-inorganic Additive crystallinity size layer perovskite compound Additive concentration (%) (nm) N(T, I)/N(0, I) Example 1 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Cu CuCl 1 mol % 95 25 1.4 Example 2 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Cu CuCl 5 mol % 98 26 1.3 Example 3 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Cu CuCl 1 mol % 97 25 1.3 Example 4 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Ag AgCl 1 mol % 95 25 1.3 Example 5 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sr SrCl.sub.2•6H.sub.2O 1 mol % 99 30 1.2 Example 6 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sr SrI.sub.2 1 mol % 97 28 1.3 Example 7 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sr SrI.sub.2 5 mol % 95 24 1.4 Example 8 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Ca CaCl.sub.2 1 mol % 94 25 1.4 Example 9 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Nd NdCl.sub.3 1 mol % 90 20 2.3 Example 10 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Ir IrCl.sub.3 1 mol % 89 18 2.5 Example 11 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Ti TiI.sub.4 1 mol % 86 10 3.2 Example 12 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Mn MnCl.sub.2 1 mol % 88 15 3.3 Example 13 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sb SbCl.sub.3 1 mol % 85 11 4.5 Example 14 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—La LaCl.sub.3•7H.sub.2O 1 mol % 90 20 3.2 Example 15 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sr SrCl.sub.2•6H.sub.2O 1 mol % 93 24 1.8 Example 16 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Ti TiI.sub.4 1 mol % 86 12 4.3 Example 17 TiO.sub.2 CH.sub.3NH.sub.3Pb(I,Cl).sub.3—Sr SrCl.sub.2•6H.sub.2O 1 mol % 95 25 1.5 Comparative Example 1 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3 — — — — 5.3 Comparative Example 2 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3 — — — — 5.4 Comparative Example 3 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Bi BiCl.sub.3 1 mol % — — 6.2 Comparative Example 4 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Zn ZnCl.sub.2 1 mol % — — 5.7 Comparative Example 5 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Sc ScCl.sub.3 1 mol % — — 5.6 Comparative Example 6 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Rh RhCl.sub.3 1 mol % — — 5.3 Comparative Example 7 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Cs CsCl 1 mol % — — 5.2 Comparative Example 8 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3 — — — — 6.2 Comparative Example 9 TiO.sub.2 CH.sub.3NH.sub.3Pb(I,Cl).sub.3 — — — — 5.8 Comparative Example 10 TiO.sub.2 CH.sub.3NH.sub.3PbI.sub.3—Cu CuCl 1 mol %  0  0 5.2 Evaluation Initial Hole transport Photodegradation conversion layer test efficiency Example 1 Poly-TPD ◯◯◯ ◯ Example 2 Poly-TPD ◯◯◯ ◯ Example 3 Spiro-OMeTAD ◯◯◯ ◯ Example 4 Poly-TPD ◯◯◯ ◯ Example 5 Poly-TPD ◯◯◯ ◯ Example 6 Poly-TPD ◯◯ ◯ Example 7 Poly-TPD ◯◯ ◯ Example 8 Poly-TPD ◯◯◯ ◯ Example 9 Poly-TPD ◯◯ X Example 10 Poly-TPD ◯◯ X Example 11 Poly-TPD ◯ ◯ Example 12 Poly-TPD ◯ ◯ Example 13 Poly-TPD ◯ ◯ Example 14 Poly-TPD ◯◯ ◯ Example 15 Poly-TPD ◯◯◯ ◯ Example 16 Poly-TPD ◯ ◯ Example 17 Poly-TPD ◯◯◯ ◯ Comparative Example 1 Poly-TPD X — Comparative Example 2 Spiro-OMeTAD X — Comparative Example 3 Poly-TPD X X Comparative Example 4 Poly-TPD X X Comparative Example 5 Poly-TPD X X Comparative Example 6 Poly-TPD X ◯ Comparative Example 7 Poly-TPD X ◯ Comparative Example 8 Poly-TPD X — Comparative Example 9 Poly-TPD X — Comparative Example 10 Poly-TPD X X

EXAMPLE 18

(32) (1) Preparation of Solar Cell

(33) A FTO film having a thickness of 1,000 nm as an electrode (cathode) was formed on a glass substrate, ultrasonically washed with pure water, acetone, and methanol each for 10 minutes in the stated order, and then dried.

(34) A titanium-containing coating liquid was applied at 1500 rpm by the spin coating method and then fired at 550° C. in air for 10 minutes to form a thin film-shaped electron transport layer. Onto the thin film-shaped electron transport layer was applied titanium oxide paste containing polyisobutyl methacrylate as an organic binder and titanium oxide (mixture of powders with an average particle sizes of 10 nm and 30 nm) by the spin coating method. The paste was then fired at 500° C. for 10 minutes to form a porous electron transport layer having a thickness of 300 nm.

(35) Subsequently, lead iodide as a metal halide compound was dissolved into N,N-dimethylformamide (DMF) to prepare a 1 M solution. The solution was applied onto the titanium oxide layer by the spin coating method to form a film. Separately, a methylammonium iodide as an amine compound was dissolved into 2-propanol to prepare a 1 M solution. The sample with the above lead iodide film was immersed into this solution to form a layer containing CH.sub.3NH.sub.3PbI.sub.3, which is an organic-inorganic perovskite compound. Further, the obtained layer was subjected to immersion treatment (washing treatment) in 2-propanol (solvent that dissolves methylammonium iodide) for 20 seconds. After the immersion treatment, the obtained sample was heat-treated at 150° C. for 30 minutes.

(36) A solution containing 68 mM of Spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM of tert-butylpyridine, and 9 mM of lithium bis(trifluoromethylsulfonyl)imide salt was applied onto the organic-inorganic perovskite compound part by the spin coating method to a thickness of 50 nm, thus forming a hole transport layer.

(37) A gold film having a thickness of 100 nm was formed as a counter electrode (anode) on the obtained hole transport layer by vacuum deposition, whereby a solar cell was prepared.

(38) (2) Measurement of Carrier Density of Organic-Inorganic Perovskite Compound

(39) A C-V measurement was performed on the solar cell with an impedance analyzer (available from Solartron, S11287) while exposing the solar cell to artificial sunlight from HAL-320 (available from Asahi Spectra Co., Ltd.) at 100 mW/cm.sup.2. The measurement was performed at a frequency of 1,000 Hz and at a scan rate of 100 mV/s from +2 V to −2 V. The carrier density N(0, I) of the organic-inorganic perovskite compound immediately after the start of light exposure and the carrier density N(T, I) of the organic-inorganic perovskite compound after one-hour light exposure were determined by conversion to the Mott-Schottky plot based on the C-V graph obtained by the C-V measurement, and N(T, I)/N(0, I) was calculated.

EXAMPLES 19 TO 21

(40) A solar cell was obtained in the same manner as in Example 18 except that the heating temperature or heating time was changed in the heat treatment after the immersion treatment (washing treatment), or the heat treatment was not performed.

EXAMPLE 22

(41) A solar cell was obtained in the same manner as in Example 18 except that formamidinium iodide was used instead of methylammonium iodide, and that the heating temperature or the heating time was changed in the heat treatment after the immersion treatment (washing treatment).

EXAMPLES 23 TO 25

(42) A solar cell was obtained in the same manner as in Example 18 except that the time of the immersion treatment (washing treatment) in 2-propanol was changed so that the amount (residual amount) of the amine compound remaining in the layer containing an organic-inorganic perovskite compound was changed to the value shown in Table 2, and that the type of the metal halide compound and the amine compound was changed as shown in Table 2.

EXAMPLE 26

(43) A solar cell was obtained in the same manner as in Example 18 except that ethanol was used instead of 2-propanol as the solvent for the immersion treatment (washing treatment).

COMPARATIVE EXAMPLE 11

(44) A solar cell was obtained in the same manner as in Example 18 except that the immersion treatment (washing treatment) in 2-propanol (solvent that dissolves methylammonium iodide) was not performed after the formation of the layer containing CH.sub.3NH.sub.3PbI.sub.3.

COMPARATIVE EXAMPLE 12

(45) A solar cell was obtained in the same manner as in Comparative Example 11 except that the heat treatment after the immersion treatment (washing treatment) was not performed.

(46) <Evaluation>

(47) The solar cells obtained in Examples 18 to 26 and Comparative Examples 11 and 12 were evaluated for the following parameters. Table 2 shows the results.

(48) (1) Initial Conversion Efficiency Evaluation

(49) A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell. The solar cell was exposed to light at an intensity of 100 mW/cm.sup.2 using a solar simulator (available from Yamashita Denso Corp.), and the photoelectric conversion efficiency immediately after the start of exposure to light was measured.

(50) ∘ (Good): Photoelectric conversion efficiency of 10% or higher

(51) Δ (Fair): Photoelectric conversion efficiency of lower than 10% but 7% or higher

(52) × (Poor): Photoelectric conversion efficiency of lower than 7%

(53) (2) Photodegradation Test

(54) A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell. The solar cell was exposed to light at an intensity of 100 mW/cm.sup.2 using a solar simulator (available from Yamashita Denso Corp.). The open-circuit voltage and the short-circuit current immediately after the start of light exposure, and those after twenty-minute light exposure were measured. The value of open-circuit voltage after twenty-minute exposure to light/open-circuit voltage immediately after the start of exposure to light (relative open-circuit voltage), and the value of short-circuit current after twenty-minute light exposure/short-circuit current immediately after the start of light exposure (relative short-circuit current) were calculated.

(55) (3) Measurement of Residual Amine Compound Content

(56) After the completion of the photodegradation test, the solar cell was washed with 2-propanol (solvent that only elutes methylammonium iodide and formamidinium iodide). The wash solution was subjected to elemental analysis by gas chromatography-mass spectrometry (GCMS) (JMS-Q1050GC, available from JEOL Ltd.). Thereafter, the organic-inorganic hybrid compound was eluted with DMF, and the resulting wash solution was subjected to elemental analysis by the RBS method to determine the residual amine compound content (mol) relative to 1 mol of the organic-inorganic perovskite compound.

(57) TABLE-US-00002 TABLE 2 Photoelectric conversion layer Residual amine Organic-inorganic Heat treatment compound Metal halide perovskite Solvent for Temperature(° C.)/ content N(T, I)/ compound Amine compound compound immersion time (min) (mol) N(0, I) Example 18 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol 150/30 0.04 3.4 iodide Example 19 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol 100/30 0.03 4.3 iodide Example 20 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol  100/100 0.04 3.3 iodide Example 21 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol No heat treatment 0.03 4.5 iodide Example 22 Lead iodide Formamidinium HC(NH.sub.2).sub.2PbI.sub.3 2-Propanol 125/30 0.03 2.5 iodide Example 23 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol 150/30 0.1 3.4 iodide Example 24 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol 150/30 0.28 3.4 iodide Example 25 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 2-Propanol 150/30 0.5 4.1 iodide Example 26 Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 Ethanol 150/30 0.05 3.4 iodide Comparative Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 — 150/30 0.8 5.2 Example 11 iodide Comparative Lead iodide Methylammonium CH.sub.3NH.sub.3PbI.sub.3 — No heat treatment 0.8 6.5 Example 12 iodide Evaluation Initial Photodegradation test Photodegradation test conversion (relative open-circuit (relative short-circuit efficiency voltage) current) Example 18 ◯ 0.95 0.9 Example 19 ◯ 0.96 0.85 Example 20 ◯ 0.95 0.87 Example 21 Δ 0.92 0.6 Example 22 ◯ 0.97 0.95 Example 23 ◯ 0.94 0.9 Example 24 ◯ 0.88 0.89 Example 25 ◯ 0.82 0.86 Example 26 Δ 0.95 0.89 Comparative ◯ 0.5 0.84 Example 11 Comparative ◯ 0.5 0.55 Example 12

INDUSTRIAL APPLICABILITY

(58) The present invention provides a solar cell in which a decrease in photoelectric conversion efficiency due to continuous exposure to light (photodegradation) is reduced, and a method of producing the solar cell.