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-temperature 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 (meth)acrylic resin having a C atom/O atom ratio of 4 or more in the molecule.

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 (meth)acrylic resin having a C atom/O atom ratio of 4 or more in the molecule.

2. 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.

3. 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.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0095] FIG. 1 is a schematic view illustrating an exemplary crystal structure of the organic-inorganic perovskite compound.

[0096] FIG. 2 is a cross-sectional view schematically illustrating an exemplary solar cell of the present invention.

DESCRIPTION OF EMBODIMENTS

[0097] 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)

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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)

[0103] A mixture containing a 2-methacryloyloxyethyl isocyanate (MOI, available from Showa Denko K.K.) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of isobornyl acrylate (iB, available from Kyoeisha Chemical Co., Ltd.), ethylhexyl acrylate (EH, available from Mitsubishi Chemical Corp.), and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added; available from Kyoeisha Chemical Co., Ltd.), and a reaction catalyst peroxide (Percumyl D, available from NOF Corp.) was laminated to a thickness of 10 μm on the obtained laminate using a doctor blade, followed by a cross-linking reaction of the copolymer at 150° C. for 10 minutes to prepare an encapsulation material.

[0104] The added monomer ratio of iB, EH and MOI was 4.5:4.5:1 (molar ratio). As a result of measurement by CHN/O elemental analysis, the C atom/O atom ratio in the molecule of the obtained copolymer was 6.

(Formation of Inorganic Layer)

[0105] The obtained laminate was set in a substrate holder of a sputtering device. Further, 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 evacuated using a vacuum pump to reduce the pressure to 5.0×10.sup.−4 Pa. Then, sputtering was performed under the condition shown as Sputtering condition A to form a 100 nm ZnSnO(Si) thin film as an inorganic film (encapsulation layer) on the laminate. A thin-film solar cell was thus obtained.

<Sputtering Conditions A>

[0106] Argon gas flow rate: 50 sccm, oxygen gas flow rate: 50 sccm

[0107] Power output: Cathode A=500 W, Cathode B=1500 W

Examples 2 to 5

[0108] 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.

[0109] 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

[0110] 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 9

[0111] 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.

[0112] In Example 7, a copolymer of isobornyl acrylate (iB) and ethylhexyl acrylate (EH) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 6. The added monomer ratio of iB and EH was 5:5 (molar ratio). In Example 8, a 2-methacryloyloxyethyl isocyanate (MOI) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of isobornyl acrylate (iB) and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 6.5. The added monomer ratio of iB and MOI was 9:1 (molar ratio).

[0113] In Example 9, a 2-methacryloyloxyethyl isocyanate (MOI) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of ethylhexyl acrylate (EH) and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 5.5. The added monomer ratio of EH and MOI was 9:1 (molar ratio).

Examples 10 to 12

[0114] 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 on the laminate, instead of forming the inorganic layer on the encapsulation material; and the inorganic layer was changed as specified in Table 1.

[0115] In Example 11, a Si target was used as a metal target. In Example 12, a Sn target was used as a metal target.

Example 13

[0116] A solar cell was obtained in the same manner as in Example 1, except that the inorganic layer was not formed on the encapsulation material.

Examples 14 to 16

[0117] 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.

[0118] In Example 14, a 2-methacryloyloxyethyl isocyanate (MOI) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of cyclohexyl acrylate (CH, available from Tokyo Chemical Industry Co., Ltd.) and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 4.5. The added monomer ratio of CH and MOI was 9:1 (molar ratio).

[0119] In Example 15, a 2-methacryloyloxyethyl isocyanate (MOI) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of t-butyl methacrylate (tB, available from Tokyo Chemical Industry Co., Ltd.) and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 4. The added monomer ratio of tB and MOI was 9:1 (molar ratio).

[0120] In Example 16, methyl acrylate (Me, available from Mitsubishi Chemical Corp.) was used instead of ethylhexyl acrylate (EH, available from Mitsubishi Chemical Corp.). The C atom/O atom ratio in the molecule of the obtained copolymer was 4.5.

Comparative Examples 1 to 5

[0121] 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.

[0122] In Comparative Example 1, a solution of polyvinyl alcohol (PVA) (available from Wako Pure Chemical Industries, Ltd.) was applied onto the laminate using a doctor blade and dried to prepare an encapsulation material.

[0123] In Comparative Example 2, a mixture containing 4 mol % of an imidazole compound 2MZA (available from Shikoku Chemicals Corp.) as a curing agent and a bisphenol A epoxy resin (available from Mitsubishi Chemical Corp.) was applied onto the laminate and cured by heating at 120° C. for one hour to prepare an encapsulation material.

[0124] In Comparative Example 3, a solution of a polyisobutylene resin (OPPANOL B 50, available from BASF SE) was applied onto the laminate using a doctor blade and dried to prepare an encapsulation material.

[0125] In Comparative Example 4, a solution of a norbornene resin (available from Polyplastics Co., Ltd.) was applied onto the laminate using a doctor blade and dried to prepare an encapsulation material. In Comparative Example 5, a solution of a polymethyl methacrylate resin (available from Wako Pure Chemical Industries, Ltd.) was applied onto the laminate using a doctor blade and dried to prepare an encapsulation material.

[0126] In Comparative Example 5, a 2-methacryloyloxyethyl isocyanate (MOI) adduct (having a methacryloyloxy group as the reactive functional group) of a copolymer of t-butyl acrylate (tB, available from Osaka Organic Chemical Industry Ltd.) and acryloyloxyethyl-succinic acid ((meth)acrylate having a carboxyl group as the group to which a reactive functional group can be added) was used. The C atom/O atom ratio in the molecule of the obtained copolymer was 3.5. The added monomer ratio of tB and MOI was 9:1 (molar ratio).

Comparative Example 6

[0127] A solar cell was obtained in the same manner as in Example 1, except that encapsulation of the laminate was not performed.

<Evaluation>

[0128] The solar cells obtained in Examples and Comparative Examples were evaluated as described below.

(1) Degradation During Encapsulation (Initial Degradation)

[0129] 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.

[0130] 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

[0131] 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) High-Temperature Durability

[0132] The solar cell was heated for 30 minutes on a hot plate set to 150° C. to conduct a high-temperature durability test. A power source (236 model, available from Keithley Instruments, Inc.) was connected between the electrodes in the solar cell after the high-temperature 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 high-temperature durability test/photoelectric conversion efficiency immediately after encapsulation.

∘∘ (Excellent): The value of photoelectric conversion efficiency after the high-temperature durability test/photoelectric conversion efficiency immediately after encapsulation was 0.9 or more.
∘ (Good): The value of photoelectric conversion efficiency after the high-temperature durability test/photoelectric conversion efficiency immediately after encapsulation was 0.7 or more and less than 0.9.
Δ (Average): The value of photoelectric conversion efficiency after the high-temperature durability test/photoelectric conversion efficiency immediately after encapsulation was 0.5 or more and less than 0.7.
x (Poor): The value of photoelectric conversion efficiency after the high-temperature durability test/photoelectric conversion efficiency immediately after encapsulation was less than 0.5.

(4) Temperature Cycle Resistance

[0133] In a temperature cycle test, the solar cell 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.

(5) Sputtering Resistance

[0134] In the production process of the solar cell, the surface of the encapsulation material was visually observed when the inorganic layer was formed on the encapsulation material by the sputtering method.

∘ (Good): Not changed.
Δ (Average): Slight whitening was found on the encapsulation material.
x: Whitening was found on the encapsulation material.

TABLE-US-00001 TABLE 1 C atom/O atom Thickness of Photoelectric ratio of encapsulation Inorganic layer conversion (meth) acrylic material Thickness layer Encapsulation material resin (μm) Material (nm) Example 1 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 2 CH.sub.3NH.sub.3PbI.sub.2Br iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 3 CH.sub.3NH.sub.3PbI.sub.2Cl iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 4 CH.sub.3NH.sub.3PbBr.sub.3 iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 5 CH.sub.3(NH.sub.3).sub.2PbI.sub.3 iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 6 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6  5 ZnSnO(Si) 100 Example 7 CH.sub.3NH.sub.3PbI.sub.3 iB/EH 6 10 ZnSnO(Si) 100 Example 8 CH.sub.3NH.sub.3PbI.sub.3 iB-MOI adduct 6.5 10 ZnSnO(Si) 100 Example 9 CH.sub.3NH.sub.3PbI.sub.3 EH-MOI adduct 5.5 10 ZnSnO(Si) 100 Example 10 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6 10 ZnSnO(Si) 100 Example 11 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6 10 SiO.sub.2 100 Example 12 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6 10 SnO.sub.2 100 Example 13 CH.sub.3NH.sub.3PbI.sub.3 iB/EH-MOI adduct 6 10 — — Example 14 CH.sub.3NH.sub.3PbI.sub.3 CH-MOI adduct 4.5 10 ZnSnO(Si) 100 Example 15 CH.sub.3NH.sub.3PbI.sub.3 tBu-MOI adduct 4 10 ZnSnO(Si) 100 Example 16 CH.sub.3NH.sub.3PbI.sub.3 iB/Me-MOI adduct 4.5 10 ZnSnO(Si) 100 Comparative CH.sub.3NH.sub.3PbI.sub.3 PVA — 10 ZnSnO(Si) 100 Example 1 Comparative CH.sub.3NH.sub.3PbI.sub.3 Epoxy resin — 10 ZnSnO(Si) 100 Example 2 Comparative CH.sub.3NH.sub.3PbI.sub.3 Norbomene resin — 10 ZnSnO(Si) 100 Example 3 Comparative CH.sub.3NH.sub.3PbI.sub.3 Polymethylmethacrylate 2.5 10 SiO.sub.2 100 Example 4 Comparative CH.sub.3NH.sub.3PbI.sub.3 Polybutyl acrylate 3.5 10 SiO.sub.2 100 Example 5 Comparative CH.sub.3NH.sub.3PbI.sub.3 Not used — Not used — — Example 6 Evaluation High- Temperature Initial Humidity temperature cycle Sputtering Solar cell structure degradation resistance durability resistance resistance Example 1 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 2 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 3 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 4 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 5 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 6 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 7 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ Δ material/inorganic layer Example 8 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ ∘ material/inorganic layer Example 9 Counter electrode/encapsulation ∘ ∘∘ ∘∘ ∘ Δ material/inorganic layer Example 10 Counter electrode/inorganic ∘ ∘∘ ∘∘ ∘ ∘ layer/encapsulation material Example 11 Counter electrode/inorganic ∘ ∘∘ ∘∘ ∘ ∘ layer/encapsulation material Example 12 Counter electrode/inorganic ∘ ∘∘ ∘∘ ∘ ∘ laver/encapsulation material Example 13 Counter electrode/encapsulation ∘ ∘ ∘∘ ∘ — material Example 14 Counter electrode/encapsulation ∘ ∘∘ ∘ ∘ ∘ material/inorganic layer Example 15 Counter electrode/encapsulation ∘ ∘∘ Δ ∘ Δ material/inorganic layer Example 16 Counter electrode/inorganic ∘ ∘∘ ∘ ∘ ∘ layer/encapsulation material Comparative Counter electrode/encapsulation x — — — — Example 1 material/inorganic layer Comparative Counter electrode/encapsulation x — — — — Example 2 material/inorganic layer Comparative Counter electrode/encapsulation ∘ ∘∘ ∘∘ x ∘ Example 3 material/inorganic layer Comparative Counter electrode/encapsulation ∘ ∘∘ x — x Example 4 material/inorganic layer Comparative Counter electrode/encapsulation ∘ ∘∘ x — x Example 5 material/inorganic layer Comparative Counter electrode — x — x — Example 6

INDUSTRIAL APPLICABILITY

[0135] The present invention can provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), has high-temperature durability, and is excellent in temperature cycle resistance.

REFERENCE SIGNS LIST

[0136] 1: solar cell [0137] 2: electrode [0138] 3: counter electrode (patterned electrode) [0139] 4: photoelectric conversion layer [0140] 5: encapsulation material [0141] 6: substrate