SOLAR CELL

Abstract

An object of the present invention is to provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), and has high-temperature durability. The present invention provides a solar cell including: a laminate having an electrode, a counter electrode, and a photoelectric conversion layer disposed between the electrode and the counter electrode; and an encapsulation resin layer covering the counter electrode to encapsulate the laminate, the photoelectric conversion layer including an organic-inorganic perovskite compound represented by the formula: R-M-X.sub.3, R representing an organic molecule, M representing a metal atom, X representing a halogen atom or a chalcogen atom, the encapsulation resin layer including a resin having a solubility parameter, i.e., a SP value, of 10 or less.

Claims

1. A solar cell comprising: a laminate having an electrode, a counter electrode, and a photoelectric conversion layer disposed between the electrode and the counter electrode; and an encapsulation resin layer covering the counter electrode to encapsulate the laminate, the photoelectric conversion layer including an organic-inorganic perovskite compound represented by the formula: R-M-X.sub.3, R representing an organic molecule, M representing a metal atom, X representing a halogen atom or a chalcogen atom, the encapsulation resin layer including a resin having a solubility parameter, i.e., a SP value, of 10 or less.

2. The solar cell according to claim 1, wherein the solar cell further includes an inorganic layer between the laminate and the encapsulation resin layer or on the encapsulation resin layer, and the inorganic layer contains a metal oxide, a metal nitride, or a metal oxynitride.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0084] FIG. 1 is a schematic view illustrating an exemplary crystal structure of the organic-inorganic perovskite compound.

[0085] FIG. 2 is a cross-sectional view schematically illustrating an exemplary solar cell of the present invention.

DESCRIPTION OF EMBODIMENTS

[0086] 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

Preparation of a Laminate

[0087] A FTO film having a thickness of 1,000 nm was formed as an electrode on a glass substrate, ultrasonically washed with pure water, acetone, and methanol each for ten minutes in the stated order, and then dried.

[0088] An ethanol solution of titanium isopropoxide adjusted to 2% was applied onto the surface of the FTO film by the spin coating method and then fired at 400° C. for 10 minutes to form a thin film-shaped electron transport layer having a thickness of 20 nm. A titanium oxide paste containing polyisobutyl methacrylate as an organic binder and titanium oxide (mixture of powders having average particle sizes of 10 nm and 30 nm) was further applied onto the thin film-shaped electron transport layer by the spin coating method and then fired at 500° C. for 10 minutes to form a porous electron transport layer having a thickness of 500 nm.

[0089] Subsequently, CH.sub.3NH.sub.3I and PbI.sub.2 were dissolved at a molar ratio of 1:1 in N,N-dimethylformamide (DMF) as a solvent to prepare a solution for organic-inorganic perovskite compound formation having a total concentration of CH.sub.3NH.sub.3I and PbI.sub.2 of 20% by weight. This solution was applied onto the electron transport layer by the spin coating method to form a photoelectric conversion layer.

[0090] Further, 68 mM spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM tert-butylpyridine and 9 mM lithium bis(trifluoromethylsufonyl)imide salt were dissolved in 25 μL of chlorobenzene to prepare a solution. This solution was applied to a thickness of 300 nm onto the photoelectric conversion layer by the spin coating method to form a hole transport layer.

[0091] A gold film having a thickness of 100 nm was formed as a counter electrode on the hole transport layer by vacuum deposition to obtain a laminate.

(Sealing of a Laminate)

[0092] The obtained laminate was further laminated with aluminum foil on which a polyisobutylene resin (OPPANOL 100 available from BASF SE, SP value of 7.2) was stacked to a thickness of 10 μm at 100° C. A solar cell was thus prepared.

Examples 2 to 5

[0093] A solar cell was obtained in the same manner as in Example 1, except that in preparation of the laminate, the components contained in the solution for organic-inorganic perovskite compound formation was changed to form a photoelectric conversion layer (organic-inorganic perovskite compound) shown in Table 1.

[0094] In Example 2, CH.sub.3NH.sub.3Br, CH.sub.3NH.sub.3I, PbBr.sub.2, and PbI.sub.2 were dissolved at a molar ratio of 1:2:1:2 in N,N-dimethylformamide (DMF) as a solvent. In Example 3, CH.sub.3NH.sub.3I and PbCl.sub.2 were dissolved at a molar ratio of 3:1 in N,N-dimethylformamide (DMF) as a solvent. In Example 4, CH.sub.3NH.sub.3Br and PbBr.sub.2 were dissolved at a molar ratio of 1:1 in N,N-dimethylformamide (DMF) as a solvent. In Example 5, CH.sub.3(NH.sub.3).sub.2I and PbI.sub.2 were dissolved at a molar ratio of 1:1 in N,N-dimethylformamide (DMF) as a solvent.

Examples 6 to 10

[0095] A solar cell was obtained in the same manner as in Example 1, except that an encapsulation resin (SP value) as specified in Table 1 was used.

[0096] In Example 6, a silicone resin was used as an encapsulation resin. The silicon resin was cured by heating at 120° C. after lamination. In Example 7, a polyethylene resin (available from Wako Pure Chemical Industries, Ltd., SP value of 8.6) was used. In Example 8, a polybutadiene resin (available from Wako Pure Chemical Industries, Ltd., SP value of 8.4) was used. In Example 9, a mixture of 4 mol % of a peroxide (PERCUMYL D, available from NOF Corporation) as a curing agent and ethyl methacrylate (available from Kyoeisha Chemical Co., Ltd., LIGHT ESTER E, SP value of 9.4) was used. The mixture was cured by heating at 120° C. for one hour after lamination. In Example 10, polymethyl methacrylate (PMMA) (available from Wako Pure Chemical Industries, Ltd., SP value of 9.6) was used.

[0097] The silicone resin was prepared by polymerization as described below.

[0098] A 1000-mL separable flask equipped with a thermometer, a dripping device, and a stirrer was charged with 164.1 g of dimethyldimethoxysilane, 6.6 g of methyl vinyl dimethoxysilane, and 4.7 g of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, and they were stirred at 50° C. To the mixture was slowly dripped a solution prepared by dissolving 2.2 g of potassium hydroxide in 35.1 g of water. After the dripping, the mixture was stirred at 50° C. for six hours to be reacted. A reaction solution was thus obtained. Next, volatile components were removed by depressurization, and 2.4 g of acetic acid was added to the reaction solution. The resulting reaction solution was heated under reduced pressure. Then, potassium acetate was filtered off, thereby preparing a polymer A.

[0099] Separately, a 1000-mL separable flask equipped with a thermometer, a dripping device, and a stirrer was charged with 80.6 g of dimethyldimethoxysilane and 45 g of 1,1,3,3-tetramethyldisiloxane, and they were stirred at 50° C. To the mixture was dripped slowly a solution prepared by blending 100 g of acetic acid with 27 g of water. After the dripping, the mixture was stirred at 50° C. for six hours to be reacted. A reaction solution was thus prepared. Next, volatile components were removed by depressurization, thereby preparing a polymer. The obtained polymer was blended with 150 g of hexane and 150 g of ethyl acetate, and washed with 300 g of ion exchange water ten times. Volatile components therein were removed by depressurization, thereby preparing a polymer B.

[0100] An amount of 90 parts by weight of the polymer A, 12 parts by weight of the polymer B, and 0.2% by weight of a hydrosilylation catalyst (platinum-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex) were mixed to prepare the silicone resin.

Examples 11 to 13

[0101] A solar cell was prepared in the same manner as in Example 1, except that lamination with aluminum foil on which an encapsulation resin was stacked was performed after formation of an inorganic layer as shown in Table 1.

(Method for Forming an Inorganic Layer)

[0102] The obtained laminate was set in a substrate holder of a sputtering device. In addition, a Zn—Sn alloy (Zn:Sn=95:5 (% by weight)) target was mounted on cathode A of the sputtering device, and a Si target was mounted on cathode B of the sputtering device. A film-forming chamber of the sputtering device was evacuated using a vacuum pump to reduce the pressure to 5.0×10.sup.−4 Pa. Then, sputtering was performed under the sputtering condition A to form a thin film of ZnSnO(Si) as an inorganic layer on the laminate (perovskite solar cell).

<Sputtering Condition A>

[0103] Argon gas flow rate: 50 sccm, oxygen gas flow rate: 50 sccm Power output: cathode A=500 W, cathode B=1500 W

[0104] In a case where a SiO.sub.2 inorganic layer was formed, a Si target was used as a metal target. In a case where a SnO.sub.2 inorganic layer was formed, a Sn target was used as a metal target.

Example 14

[0105] A solar cell was prepared in the same manner as in Example 1, except that an encapsulation resin (SP value) as specified in Table 1 was used for encapsulation of the laminate.

[0106] In Example 14, a solution of a polymer of isobornyl methacrylate (LIGHT ESTER IB-X, available from Kyoeisha Chemical Co., Ltd.) in cyclohexane was applied using a doctor blade to the laminate (perovskite solar cell) to stack an encapsulation resin to a thickness of 10 μm, and the solvent was dried at 100° C. for 10 minutes. Then, a thin film of ZnSnO(Si) was formed as an inorganic layer in the same manner as in Example 11.

Example 15

[0107] A solar cell was prepared in the same manner as in Example 1, except that a solar cell structure as shown in Table 1 was employed in encapsulation of the laminate.

[0108] In Example 15, a solution of polyisobutylene in cyclohexane was applied to the laminate (perovskite solar cell) using a doctor blade to stack an encapsulation resin to a thickness of 10 μm, and the solvent was dried at 100° C. for 10 minutes.

Examples 16 and 17

[0109] A solar cell was prepared in the same manner as in Example 15, except that an encapsulation resin (SP value) as specified in Table 1 was used for encapsulation of the laminate.

[0110] In Example 16, a solution of a norbornene resin (TOPAS6013, available from Polyplastics Co., Ltd.) in cyclohexane was applied to the laminate (perovskite solar cell) using a doctor blade to stack an encapsulation resin to a thickness of 10 μm, and the solvent was dried at 100° C. for 10 minutes. In Example 17, a solution of a polymer of isobornyl methacrylate (LIGHT ESTER IB-X, available from Kyoeisha Chemical Co., Ltd.) in cyclohexane was applied to the laminate (perovskite solar cell) using a doctor blade to stack an encapsulation resin to a thickness of 10 μm, and the solvent was dried at 100° C. for 10 minutes.

Comparative Examples 1 to 3

[0111] A solar cell was prepared in the same manner as in Example 1, except that, as the encapsulation resin for encapsulation of the laminate, polyvinyl alcohol (PVA) (available from Wako Pure Chemical Industries, Ltd., 160-11485, SP value of 14.1), bisphenol A epoxy polymer (available from Mitsubishi Chemical Corporation, EPIKOTE 828, SP value of 10.8), or phenolic resin (available from Dainippon Ink and Chemicals, TD-2090, SP value of 13.5) was used. The bisphenol A epoxy polymer and the phenolic resin were blended with 2-ethyl-4-methylimidazole and hexamethylenetetramine, respectively, each in an amount of 4% by weight as a curing agent, and cured at 120° C. for one hour after lamination.

Comparative Example 4

[0112] A solar cell was obtained in the same manner as in Example 1, except that encapsulation of the laminate was not performed.

EVALUATION

[0113] The solar cells obtained in Examples and Comparative Examples were evaluated as described below.

(1) Degradation During Encapsulation (Initial Degradation)

[0114] A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell immediately after encapsulation. The photoelectric conversion efficiency was measured using a solar simulator (available from Yamashita Denso Corp.) having an intensity of 100 mW/cm.sup.2 to determine the value of photoelectric conversion efficiency immediately after encapsulation/initial conversion efficiency.

∘ (Good): The value of photoelectric conversion efficiency immediately after encapsulation/initial conversion efficiency was 0.5 or more.
x (Poor): The value of photoelectric conversion efficiency immediately after encapsulation/initial conversion efficiency was less than 0.5.

(2) High-Temperature Durability

[0115] The solar cell was left for 24 hours under the condition of 100° C. or for 72 hours under the condition of 120° C. to conduct a durability test at high temperatures. A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell after the durability test. The photoelectric conversion efficiency was measured using a solar simulator (available from Yamashita Denso Corp.) having an intensity of 100 mW/cm.sup.2, and the value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was determined.

∘ (Good): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was 0.5 or more.
Δ (Average): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was 0.2 or more and less than 0.5.
x (Poor): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was less than 0.2.

(3) High-Humidity Durability

[0116] The solar cell was left for 24 hours under conditions of 30° C. and 80% to conduct a durability test at a high humidity. A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell after the durability test. The photoelectric conversion efficiency was measured using a solar simulator (available from Yamashita Denso Corp.) having an intensity of 100 mW/cm.sup.2 to determine the value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation.

∘∘∘ (Outstanding): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was 0.95 or more.
∘∘ (Excellent): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was 0.9 or more and less than 0.95.
∘ (Good): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was 0.5 or more and less than 0.9.
x (Poor): The value of photoelectric conversion efficiency after the durability test/photoelectric conversion efficiency immediately after encapsulation was less than 0.5.

TABLE-US-00001 TABLE 1 Photoelectric SP value of Inorganic layer conversion encapsulation Thickness layer Encapsulation resin resin Material (nm) Example 1 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 7.2 Not used — Example 2 CH.sub.3NH.sub.3PbI.sub.2Br Polyisobutylene 7.2 Not used — Example 3 CH.sub.3NH.sub.3PbI.sub.2Cl Polyisobutylene 7.2 Not used — Example 4 CH.sub.3NH.sub.3PbBr.sub.3 Polyisobutylene 7.2 Not used — Example 5 CH.sub.3(NH.sub.3).sub.2PbI.sub.3 Polyisobutylene 7.2 Not used — Example 6 CH.sub.3NH.sub.3PbI.sub.3 Silicone 7.4 Not used — Example 7 CH.sub.3NH.sub.3PbI.sub.3 Polyethylene 8.6 Not used — Example 8 CH.sub.3NH.sub.3PbI.sub.3 Polybutadiene 8.4 Not used — Example 9 CH.sub.3NH.sub.3PbI.sub.3 Ethylmethacrylate 9.4 Not used — Example 10 CH.sub.3NH.sub.3PbI.sub.3 PMMA 9.6 Not used — Example 11 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 7.5 ZnSnO(Si) 100 Example 12 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 7.5 SiO.sub.2 100 Example 13 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 7.5 SnO.sub.2 100 Example 14 CH.sub.3NH.sub.3PbI.sub.3 Isobornyl 9.2 ZnSnO(Si) — methacrylate Example 15 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 7.2 Not used — Example 16 CH.sub.3NH.sub.3PbI.sub.3 Norbornene 8.9 Not used — Example 17 CH.sub.3NH.sub.3PbI.sub.3 Isobornyl 9.2 Not used — methacrylate Comparative CH.sub.3NH.sub.3PbI.sub.3 PVA 14.1 Not used — Example 1 Comparative CH.sub.3NH.sub.3PbI.sub.3 Epoxy 10.8 Not used — Example 2 Comparative CH.sub.3NH.sub.3PbI.sub.3 Phenolic resin 13.5 Not used — Example 3 Comparative CH.sub.3NH.sub.3PbI.sub.3 Not used Not used Not used — Example 4 Evaluation High- High- High- Initial temperature temperature humidity Solar cell structure degradation durability.sup.1) durability.sup.2) test Example 1 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 2 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 3 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 4 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 5 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 6 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 7 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 8 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/aluminum foil Example 9 Counter electrode/encapsulation ∘ ∘ Δ ∘∘ resin/aluminum foil Example 10 Counter electrode/encapsulation ∘ Δ Δ ∘∘ resin/aluminum foil Example 11 Counter electrode/inorganic ∘ ∘ ∘ ∘∘∘ layer/encapsulation resin/ aluminum foil Example 12 Counter electrode/inorganic ∘ ∘ ∘ ∘∘∘ layer/encapsulation resin/ aluminum foil Example 13 Counter electrode/inorganic ∘ ∘ ∘ ∘∘∘ layer/encapsulation resin/ aluminum foil Example 14 Counter electrode/encapsulation ∘ ∘ ∘ ∘∘ resin/inorganic layer Example 15 Counter electrode/encapsulation resin ∘ ∘ ∘ ∘ Example 16 Counter electrode/encapsulation resin ∘ ∘ ∘ ∘ Example 17 Counter electrode/encapsulation resin ∘ ∘ ∘ ∘ Comparative Counter electrode/encapsulation x — — — Example 1 resin/aluminum foil Comparative Counter electrode/encapsulation x — — — Example 2 resin/aluminum foil Comparative Counter electrode/encapsulation x — — — Example 3 resin/aluminum foil Comparative Counter electrode — — — x Example 4 .sup.1)100° C. 24 h .sup.2)120° C. 72 h

INDUSTRIAL APPLICABILITY

[0117] The present invention can provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), and has high-temperature durability.

REFERENCE SIGNS LIST

[0118] 1: solar cell [0119] 2: electrode [0120] 3: counter electrode (patterned electrode) [0121] 4: photoelectric conversion layer [0122] 5: encapsulation resin layer [0123] 6: substrate