SOLAR CELL

Abstract

The present invention aims to provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), and has excellent durability. The present invention relates to 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 inorganic 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 inorganic layer containing a metal oxide, a metal nitride, or a metal oxynitride.

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 inorganic 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 inorganic layer containing a metal oxide, a metal nitride, or a metal oxynitride.

2. The solar cell according to claim 1, wherein the inorganic layer contains an oxide, a nitride, or an oxynitride of Si, Al, Zn, or Sn.

3. The solar cell according to claim 1, wherein the inorganic layer contains an oxide, a nitride, or an oxynitride of Zn or Sn.

4. The solar cell according to claim 1, wherein the inorganic layer contains an oxide, a nitride, or an oxynitride of metal elements including both Zn and Sn.

5. The solar cell according to claim 1, wherein the inorganic layer contains a metal oxide represented by the formula Zn.sub.aSn.sub.bO.sub.c where a, b, and c each represent a positive integer.

6. The solar cell according to claim 1, wherein the inorganic layer has a thickness of 30 to 3,000 nm.

7. The solar cell according to claim 1, wherein the solar cell further includes a planarizing resin layer disposed between the counter electrode and the inorganic layer.

8. The solar cell according to claim 1, wherein the solar cell further includes an encapsulation resin layer on the inorganic layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0085] FIG. 1 is a schematic view illustrating an exemplary crystal structure of the organic-inorganic perovskite compound.

[0086] FIG. 2 is a cross-sectional view schematically illustrating an exemplary solar cell of the present invention.

DESCRIPTION OF EMBODIMENTS

[0087] 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)

[0088] 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.

[0089] 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.

[0090] 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. 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.

[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.

(Encapsulation of Laminate)

[0092] The obtained laminate was set in a substrate holder of a sputtering device. Further, Si targets were mounted on cathode A and 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 shown below to form a 20 nm SiO.sub.2 thin film as an inorganic layer on the laminate.

<Sputtering Conditions A>

[0093] Argon gas flow rate: 50 sccm, oxygen gas flow rate: 50 sccm

[0094] Power output: cathode A=500 W, cathode B=1,500 W

[0095] Next, 100 parts by weight of a dicyclopentadiene-type epoxy resin (HP-7200HH, available from Dainippon Ink and Chemicals) and 3 parts by weight of an imidazole curing agent (2E4MZ, available from Shikoku Chemical Corporation) were dissolved in 300 parts by weight of toluene. The obtained solution was applied to aluminum foil, and the organic solvent was dried to prepare aluminum foil with an encapsulation resin having a thickness of 10 μm. The inorganic layer was laminated with the obtained aluminum foil with an encapsulation resin at 80° C., followed by curing at 60° C. for one hour. A solar cell was thus prepared.

Examples 2 to 11

[0096] Each solar cell was obtained in the same manner as in Example 1, except that in encapsulation of the laminate, an inorganic layer (material, thickness) specified in Table 1 was formed by changing the metal target used in the sputtering method and the thickness of the inorganic layer.

[0097] In the case where a SnO.sub.2 inorganic layer was formed, a Sn target was used as the metal target. In the case where a ZnSnO inorganic layer was formed, a ZnSn alloy (Zn:Sn=95:5 (% by weight)) target was used. In the case where a ZnSnO(Si) inorganic layer was formed, a ZnSn alloy (Zn:Sn=95:5 (% by weight)) target was used as the metal target for cathode A and a Si target was used as the metal target for cathode B. In the case where a ZnSnO(Al) inorganic layer was formed, a ZnSn alloy (Zn:Sn=95:5 (% by weight)) target was used for cathode A and an Al target was used for cathode B.

Examples 12 to 15

[0098] A solar cell was obtained in the same manner as in Example 2, 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.

[0099] In Example 12, 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 13,

[0100] 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 14, 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 15, 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 16 to 19

[0101] Each solar cell was obtained in the same manner as in Example 2, except that in encapsulation of the laminate, an inorganic layer (material, thickness) specified in Table 1 was formed by changing the metal target used and the sputtering condition employed in the sputtering method.

[0102] In the case where an aluminum nitride (AlN) inorganic layer was formed, an Al target was used as the metal target and the sputtering condition B was employed. In the case where a Si(O,N) inorganic layer was formed, a Si target was used as the metal target and the sputtering condition C was employed. In the case where a ZrO.sub.2 inorganic layer was formed, a Zr target was used as the metal target and the sputtering condition A was employed. In the case where a MgO inorganic layer was formed, a Mg target was used as the metal target and the sputtering condition A was employed.

(Sputtering condition B)

[0103] Argon gas flow rate: 50 sccm, nitrogen gas flow rate: 50 sccm

[0104] Power output: cathode A=500 W, cathode B=1,500 W

(Sputtering condition C)

[0105] Argon gas flow rate: 50 sccm, nitrogen gas flow rate: 10 sccm, oxygen gas flow rate: 40 sccm

[0106] Power output: cathode A=500 W, cathode B=1,500 W

Examples 20 and 21

[0107] Solar cells were obtained in the same manner as in Examples 2 and 7, respectively, except that lamination with aluminum foil was not performed in encapsulation of the laminate.

Examples 22 and 23

[0108] Solar cells were obtained in the same manner as in Examples 2 and 7, respectively, except the following. In encapsulation of the laminate, to a PET film subjected to mold release treatment in advance was applied an encapsulation resin to form a film with a thickness of 10 μm, and the inorganic thin layer was laminated with the obtained PET film at 80° C. Then, the PET film alone was removed from the laminate to provide a solar cell.

Examples 24 and 25

[0109] The solar cells were obtained through encapsulation of the laminate in the same manner as in Examples 2 and 7, respectively. Then, a SiO.sub.2 film in Example 24 and a ZnSnO film in Example 25 each with a thickness of 100 nm were formed under the same sputtering conditions as in Examples 2 and 7, respectively. Solar cells of Examples 24 and 25 were thus prepared.

Examples 26 and 27

[0110] Solar cells were obtained in the same manner as in Examples 2 and 7, respectively, except that in encapsulation of the laminate, a planarizing layer was introduced between the counter electrode and the inorganic layer. The planarizing layer was formed using a cyclohexane solution of a norbornene resin (TOPAS6013, available from Polyplastics Co., Ltd.) by a spin coating method.

Examples 28 and 29

[0111] Each solar cell was obtained in the same manner as in Example 2, except that the inorganic layer was formed on the encapsulation material by EB vapor deposition or ion plating, not by sputtering, and that the inorganic layer was changed as specified in Table 2.

Examples 30 and 31

[0112] Each solar cell was obtained in the same manner as in Example 26, except that the inorganic layer was formed on the encapsulation material by EB vapor deposition or ion plating, not by sputtering, and that the inorganic layer was changed as specified in Table 2.

Comparative Examples 1 to 3

[0113] Each solar cell was obtained in the same manner as in Example 1, except the following: in preparation of the laminate, a solution (2% by weight chlorobenzene solution) of P3HT (polythiophene) (available from Aldrich) and PCBM (fullerene) (available from Aldrich) mixed at a ratio of 1:1 was applied as the organic semiconductor to a thin-film electron transport layer to a thickness of 200 nm by a spin coating method, instead of stacking a porous electron transport layer and an organic-inorganic perovskite compound on a thin-film electron transport layer; as a hole transport layer, a 3-fold diluted solution of PEDOT:PSS (available from Aldrich) in methanol, instead of Spiro-OMeTAD, was applied to a thickness of 50 nm by spin coating; and in encapsulation of the laminate, an inorganic layer (material, thickness) as specified in Table 2 was formed by changing the metal target used and the sputtering condition employed in the sputtering method.

Comparative Examples 4 and 5

[0114] Solar cells were obtained in the same manner as in Example 1 and Comparative Example 1, respectively, except that, in encapsulation of the laminate, encapsulation using an inorganic layer was not performed but the laminate was directly encapsulated with the encapsulation resin.

<Evaluation>

[0115] The solar cells obtained in Examples and Comparative Examples were evaluated as described below. Tables 1 and 2 show the results.

(1) Photoelectric conversion efficiency before encapsulation (initial conversion efficiency)

[0116] 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.

◯ (Good): Initial conversion efficiency was 4% or higher.
x (Poor): Initial conversion efficiency was less than 4%.

(2) Degradation During Encapsulation (Initial Degradation)

[0117] 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.

(3) Durability

[0118] The solar cell was left for 24 hours under conditions of 90% RH and 60° C. to conduct a durability test. 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.

◯◯◯ (Outstanding): The value of photoelectric conversion efficiency after durability test/photoelectric conversion efficiency immediately after encapsulation was 0.95 or more.
◯◯ (Excellent): The value of photoelectric conversion efficiency after 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 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 durability test/photoelectric conversion efficiency immediately after encapsulation was 0.6 or more and less than 0.7.
x (Poor): The value of photoelectric conversion efficiency after durability test/photoelectric conversion efficiency immediately after encapsulation was less than 0.6.

(4) Comprehensive Evaluation

[0119] ◯ (Good): None of the (1) to (3) was rated x (Poor).
x (Poor): One or more of the (1) to (3) was rated x (Poor).

TABLE-US-00001 TABLE 1 Photoelectric Evaluation conversion Inorganic layer Initial conversion Initial Comprehensive layer Material Thickness Solar cell structure efficiency degradation Durability evaluation Example 1 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2  20 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 2 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 3 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 200 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 4 CH.sub.3NH.sub.3PbI.sub.3 SnO.sub.2  50 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 5 CH.sub.3NH.sub.3PbI.sub.3 SnO.sub.2 200 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 6 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO  50 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 7 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 100 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 8 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 300 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 9 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 500 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 10 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO(Si) 300 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 11 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO(Al) 300 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 12 CH.sub.3NH.sub.3PbI.sub.2Br SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 13 CH.sub.3NH.sub.3PbI.sub.2Cl SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 14 CH.sub.3NH.sub.3PbBr.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 15 CH.sub.3(NH.sub.3).sub.2PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 16 CH.sub.3NH.sub.3PbI.sub.3 AlN 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 17 CH.sub.3NH.sub.3PbI.sub.3 Si(O, N) 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 18 CH.sub.3NH.sub.3PbI.sub.3 ZrO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 19 CH.sub.3NH.sub.3PbI.sub.3 MgO 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum 1) 90% RH, 60° C./24 h

TABLE-US-00002 TABLE 2 Photoelectric Evaluation conversion Inorganic layer Initial conversion Initial Comprehensive layer Material Thickness Solar cell structure efficiency degradation Durability evaluation Example 20 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ Δ ∘ inorganic layer Example 21 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 100 nm Counter electrode/ ∘ ∘ Δ ∘ inorganic layer Example 22 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin Example 23 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin Example 24 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ SiO.sub.2 Example 25 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 100 nm Counter electrode/ ∘ ∘ ∘∘ ∘ inorganic layer/ encapsulation resin/ZnSnO Example 26 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘∘ ∘ encapsulation resin/ inorganic layer/ encapsulation resin/ aluminum Example 27 CH.sub.3NH.sub.3PbI.sub.3 ZnSnO 100 nm Counter electrode/ ∘ ∘ ∘∘∘ ∘ encapsulation resin/ inorganic layer/ encapsulation resin/ aluminum Example 28 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 29 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘ ∘ inorganic layer/ encapsulation resin/ aluminum Example 30 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘∘ ∘ encapsulation resin/inorganic layer/ encapsulation resin/ aluminum Example 31 CH.sub.3NH.sub.3PbI.sub.3 SiO.sub.2 100 nm Counter electrode/ ∘ ∘ ∘∘ ∘ encapsulation resin/ inorganic layer/ encapsulation resin/ aluminum Comparative Organic SiO.sub.2 100 nm Counter electrode/ x x ∘ x Example 1 semiconductor inorganic layer/ encapsulation resin/ aluminum Comparative Organic ZnSnO 300 nm Counter electrode/ x x ∘ x Example 2 semiconductor inorganic layer/ encapsulation resin/ aluminum Comparative Organic AlN 100 nm Counter electrode/ x x ∘ x Example 3 semiconductor inorganic layer/ encapsulation resin/ aluminum Comparative CH.sub.3NH.sub.3PbI.sub.3 — — Counter electrode/ ∘ x x x Example 4 encapsulation resin/aluminum Comparative Organic — — Counter electrode/ x ∘ x x Example 5 semiconductor encapsulation resin/aluminum 1) 90% RH, 60° C./24 h

INDUSTRIAL APPLICABILITY

[0120] The present invention can provide a solar cell that is excellent in photoelectric conversion efficiency, suffers little degradation during encapsulation (initial degradation), and has excellent durability.

REFERENCE SIGNS LIST

[0121] 1: solar cell [0122] 2: electrode [0123] 3: counter electrode (patterned electrode) [0124] 4: photoelectric conversion layer [0125] 5: inorganic layer [0126] 6: substrate