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), has high-humidity durability, and is excellent in temperature cycle resistance. 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 material 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 material including a resin having at least one skeleton selected from the group consisting of polyisobutylene, polyisoprene, and polybutadiene.

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 material 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 material including a resin having at least one skeleton selected from the group consisting of polyisobutylene, polyisoprene, and polybutadiene.

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

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

Description

BRIEF DESCRIPTION OF DRAWINGS

[0077] FIG. 1 is a schematic view illustrating an exemplary crystal structure of the organic-inorganic perovskite compound.

[0078] FIG. 2 is a cross-sectional view schematically illustrating an exemplary solar cell of the present invention.

DESCRIPTION OF EMBODIMENTS

[0079] 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 Laminate)

[0080] 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.

[0081] 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.

[0082] 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 laminated onto the electron transport layer by the spin coating method to form a photoelectric conversion layer.

[0083] 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 laminated to a thickness of 300 nm onto the photoelectric conversion layer by the spin coating method to form a hole transport layer.

[0084] 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.

(Encapsulation of Laminate)

[0085] To the obtained laminate, a solution of a resin having a polyisobutylene skeleton (OPPANOL B 50, available from BASF SE) in cyclohexane is applied by spin coating, and dried at 100° C. for 10 minutes to form an encapsulation material having a thickness of 10 μm. A solar cell was thus prepared.

Examples 2 to 5

[0086] 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.

[0087] 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.

Example 6

[0088] A solar cell was obtained in the same manner as in Example 1, except that in encapsulation of the laminate, the encapsulation material thickness was changed as shown in Table 1.

Examples 7 to 10

[0089] A solar cell was obtained in the same manner as in Example 1, except that in encapsulation of the laminate, the encapsulation material was changed to that shown in Table 1.

[0090] In Example 7, a resin having a polyisobutylene skeleton (OPPANOL B 100, available from BASF SE) was used.

[0091] In Example 8, to the laminate, a mixture containing 4 mol % of a peroxide (PERCUMYL D, available from NOF Corporation) as a curing agent and a liquid monomer (acrylate having a butadiene skeleton, NISSO PB GI-3000, available from Nippon Soda Co., Ltd.) which is to be an encapsulation material was applied and then heated at 120° C. for one hour for polymerization of the liquid monomer.

[0092] In Example 9, a resin having a polyisoprene skeleton (available from Wako Pure Chemical Industries, Ltd.) was used.

[0093] In Example 10, a resin having a polybutadiene skeleton (available from Ube Industries, Ltd.) was used.

Examples 11 to 13

[0094] A solar cell was obtained in the same manner as in Example 1, except that the encapsulation material was laminated after formation of the inorganic layer shown in Table 1 on the laminate.

(Method for Forming Inorganic Layer)

[0095] The obtained laminate was set in a substrate holder of a sputtering device. In addition, a ZnSn 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 exhausted 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) having a thickness of 100 nm as an inorganic layer on the laminate.

<Sputtering Condition A>

[0096] Argon gas flow rate: 50 sccm, oxygen gas flow rate: 50 sccm

[0097] Power output: cathode A=500 W, cathode B=1500 W

[0098] In Example 11, a Si target was used as a metal target. In Example 12, a Sn target was used as a metal target.

Examples 14 and 15

[0099] A solar cell was obtained in the same manner as in Example 1, except that in encapsulation of the laminate, the encapsulation material was changed to that shown in Table 1.

[0100] In Example 14, the encapsulation material used was a mixture of a resin having a polyisobutylene skeleton (OPPANOL B 100, available from BASF SE) and a norbornene resin (TOPAS6015, available from Polyplastics Co., Ltd.) mixed at a weight ratio of 5:5.

[0101] In Example 15, the encapsulation material used was a mixture of a resin having a polyisobutylene skeleton (OPPANOL B 100, available from BASF SE) and a norbornene resin (TOPAS6015, available from Polyplastics Co., Ltd.) mixed at a weight ratio of 2:8.

Comparative Examples 1 to 4

[0102] A solar cell was obtained in the same manner as in Example 1, except that in encapsulation of the laminate, the encapsulation material was changed to that shown in Table 1.

[0103] In Comparative Example 1, polyvinyl alcohol (PVA) (available from Wako Pure Chemical Industries, Ltd.) was used as the encapsulation material. In Comparative Example 2, the laminate was laminated with aluminum foil on which a mixture containing 4 mol % of an imidazole compound 2MZA (available from Shikoku Chemicals Corporation) as a curing agent and a bisphenol A epoxy resin (available from Mitsubishi Chemical Corporation) was stacked at 100° C., followed by curing with heat at 120° C. for one hour. In Comparative Example 3, a silicone resin not having a polyisobutylene skeleton or the like was used, and the laminate was laminated with aluminum foil on which the silicone resin was stacked, followed by curing with heat at 120° C. for one hour. In Comparative Example 4, a norbornene resin (TOPAS6015, available from Polyplastics Co., Ltd.) was used.

[0104] The silicone resin was prepared by polymerization as described below.

[0105] 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 methylvinyldimethoxysilane, and 4.7 g of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, and they were stirred at 50° C. To the mixture was dripped slowly 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 prepared. 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.

[0106] 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.

[0107] 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 a silicone resin.

Comparative Example 5

[0108] A solar cell was obtained in the same manner as in Example 1, except that encapsulation of the laminate was not performed.

<Evaluation>

[0109] The solar cells obtained in Examples and Comparative Examples were evaluated as described below.

(1) Degradation During Encapsulation (Initial Degradation)

[0110] A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the laminate before 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, and the obtained value was taken as the initial conversion efficiency.

[0111] 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-Humidity Durability

[0112] The solar cell was left for 24 hours under conditions of 70% and 30° C. to conduct a high-humidity durability test. A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell after the high-humidity 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 high-humidity durability test/photoelectric conversion efficiency immediately after encapsulation was determined.

∘∘ (Excellent): The value of photoelectric conversion efficiency after the high-humidity durability test/photoelectric conversion efficiency immediately after encapsulation was 0.9 or more.
∘ (Good): The value of photoelectric conversion efficiency after the high-humidity 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 high-humidity durability test/photoelectric conversion efficiency immediately after encapsulation was less than 0.5.

(3) Temperature Cycle Resistance

[0113] In a temperature cycle test, the solar cell obtained in each of Examples 1 to 12 and Comparative Examples 3, 4, and 6 was subjected to 300 cycles of temperature cycling from −55° C. to 125° C. A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell after the temperature cycle 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 temperature cycle test/photoelectric conversion efficiency immediately after encapsulation.

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

TABLE-US-00001 TABLE 1 Thick- Evaluation ness High- Tem- of encap- Inorganic layer humid- perature Photoelectric sulation Thick- Initial ity cycle conversion Encapsulation material ness degra- dura- resis- layer material (μm) Material (nm) Solar cell structure dation bility tance Example 1 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 2 CH.sub.3NH.sub.3PbI.sub.2Br Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 3 CH.sub.3NH.sub.3PbI.sub.2Cl Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 4 CH.sub.3NH.sub.3PbBr.sub.3 Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 5 CH.sub.3(NH.sub.3).sub.2PbI.sub.3 Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 6 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 5 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 7 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 8 CH.sub.3NH.sub.3PbI.sub.3 Polybutadiene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ acrylate polymer Example 9 CH.sub.3NH.sub.3PbI.sub.3 Polyisoprene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 10 CH.sub.3NH.sub.3PbI.sub.3 Polybutadiene 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ Example 11 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 10 ZnSnO(Si) 100 Counter electrode/inorganic layer/ ∘ ∘∘ ∘ encapsulation material Example 12 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 10 SiO.sub.2 100 Counter electrode/inorganic layer/ ∘ ∘∘ ∘ encapsulation material Example 13 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene 10 SnO.sub.2 100 Counter electrode/inorganic layer/ ∘ ∘∘ ∘ encapsulation material Example 14 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene/ 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ norbomene resin Example 15 CH.sub.3NH.sub.3PbI.sub.3 Polyisobutylene/ 10 Not used — Counter electrode/encapsulation material ∘ ∘ ∘ norbomene resin Comparative CH.sub.3NH.sub.3PbI.sub.3 PVA 10 Not used — Counter electrode/encapsulation material x x — Example 1 Comparative CH.sub.3NH.sub.3PbI.sub.3 Epoxy resin 10 Not used — Counter electrode/encapsulation material x ∘ — Example 2 Comparative CH.sub.3NH.sub.3PbI.sub.3 Silicone resin 10 Not used — Counter electrode/encapsulation material ∘ x ∘ Example 3 Comparative CH.sub.3NH.sub.3PbI.sub.3 Norbomene resin 10 Not used — Counter electrode/encapsulation material ∘ ∘ x Example 4 Comparative CH.sub.3NH.sub.3PbI.sub.3 Not used — Not used — Counter electrode — — x Example 5

INDUSTRIAL APPLICABILITY

[0114] The present invention can provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), has high-humidity durability, and is excellent in temperature cycle resistance.

REFERENCE SIGNS LIST

[0115] 1. solar cell [0116] 2. electrode [0117] 3. counter electrode (patterned electrode) [0118] 4. photoelectric conversion layer [0119] 5. encapsulation material [0120] 6. substrate