SOLAR CELL

Abstract

The present invention aims to provide a solar cell having high photoelectric conversion efficiency that is less likely to decrease even under prolonged application of a voltage. Provided is a solar cell including a cathode, a photoelectric conversion layer, a diffusion prevention layer, and an anode in the stated order, the cathode being a transparent electrode, the anode containing at least one selected from the group consisting of aluminum, copper, antimony, and molybdenum, the photoelectric conversion layer containing an organic-inorganic perovskite compound represented by the formula AMX wherein A represents an organic base compound and/or an alkali metal, M represents a lead or tin atom, and X represents a halogen atom, the diffusion prevention layer being a diffusion prevention layer that contains molybdenum, tungsten, tantalum, niobium, zirconium, hafnium, or an alloy of two or more thereof and has a thickness of 5 to 30 nm, a diffusion prevention layer that contains an oxide containing titanium, gallium, zinc, tin, indium, antimony, molybdenum, tungsten, vanadium, chromium, nickel, or lead, a diffusion prevention layer that contains a nitride containing titanium, vanadium, chromium, niobium, tantalum, molybdenum, zirconium, or hafnium and has a thickness of 5 to 50 nm, or a diffusion prevention layer that contains graphite and has a thickness of 2 nm to 50 nm.

Claims

1. A solar cell comprising: a cathode; a photoelectric conversion layer; a diffusion prevention layer; and an anode in the stated order, the cathode being a transparent electrode, the anode containing at least one selected from the group consisting of aluminum, copper, antimony, and molybdenum, the photoelectric conversion layer containing an organic-inorganic perovskite compound represented by the formula AMX wherein A represents an organic base compound and/or an alkali metal, M represents a lead or tin atom, and X represents a halogen atom, the diffusion prevention layer being: a diffusion prevention layer that contains molybdenum, tungsten, tantalum, niobium, zirconium, hafnium, or an alloy containing one or more thereof and has a thickness of 5 to 30 nm; a diffusion prevention layer that contains an oxide containing titanium, gallium, zinc, tin, indium, antimony, molybdenum, tungsten, vanadium, chromium, nickel, or lead; a diffusion prevention layer that contains a nitride containing titanium, vanadium, chromium, niobium, tantalum, molybdenum, zirconium, or hafnium and has a thickness of 5 to 50 nm; or a diffusion prevention layer that contains graphite and has a thickness of 2 nm to 50 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0071] FIG. 1 is a schematic view illustrating an exemplary crystal structure of an organic-inorganic perovskite compound.

DESCRIPTION OF EMBODIMENTS

[0072] The present invention is more specifically described with reference to, but not limited to, the following examples.

Example 1

[0073] A 300-nm-thick ITO film was formed as a cathode on a glass substrate, and ultrasonically washed with pure water, acetone, and methanol in the stated order, each for 10 minutes, and then dried.

[0074] On the surface of the ITO film was formed, by sputtering, a thin-film titanium oxide electron transport layer having a thickness of 20 nm. Furthermore, a titanium oxide paste containing titanium oxide (mixture of particles with an average particle size of 10 nm and particles with an average particle size of 30 nm) was applied to the thin-film electron transport layer by a spin coating method, whereby a porous electron transport layer having a thickness of 100 nm was formed.

[0075] Subsequently, 550 mg of lead iodide as a metal halide was dissolved in a solvent mixture of 1 mL of N,N-dimethylformamide (DMF) and 80 μL of dimethyl sulfoxide, whereby a solution was prepared. This solution was formed into a film on the porous electron transport layer by a spin coating method, whereby a first film was formed. Furthermore, methylammonium iodide as an amine compound was dissolved in 2-propanol to prepare a 6% by weight solution. This solution was formed into a film on the first film by a spin coating method, followed by heating treatment at 150° C. for five minutes. Thus, a 400-nm-thick photoelectric conversion layer containing a perovskite compound CH.sub.3NH.sub.3PbI.sub.3 was formed.

[0076] Next, a 2% by weight solution of Spiro-OMETAD (produced by Merck) in chlorobenzene was applied to the photoelectric conversion layer by spin coating, whereby a hole transport layer having a thickness of 100 nm was formed.

[0077] Then, on the hole transport layer was formed a 10-nm-thick diffusion prevention layer made of molybdenum by an electron beam vapor deposition method.

[0078] On the obtained diffusion prevention layer was formed, by sputtering, a 100-nm-thick aluminum film as an anode. Thus, a solar cell was obtained in which the cathode, the electron transport layer, the photoelectric conversion layer, the hole transport layer, the diffusion prevention layer, and the anode were stacked in the stated order (cathode/electron transport layer/photoelectric conversion layer/hole transport layer/diffusion prevention layer/anode).

[0079] The obtained solar cell was cut with a focused ion beam (FIB), and the cut plane was observed using a transmission electron microscope (JEM-2010-FEF produced by JEOL Ltd.). In transmission electron microscopic pictures taken at arbitrary ten sites, the upper and lower layers having the diffusion prevention layer therebetween were not in contact at any part, which confirmed that the diffusion prevention layer was a dense film.

Examples 2 to 48 and Comparative Examples 6 to 22

[0080] A solar cell in which a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, a diffusion prevention layer, and an anode were stacked in the stated order (cathode/electron transport layer/photoelectric conversion layer/hole transport layer/diffusion prevention layer/anode) was obtained as in Example 1, except that the anode and the type and thickness of the diffusion prevention layer were changed as shown in Tables 1 to 3.

Comparative Examples 1 to 5

[0081] A solar cell in which a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode were stacked in the stated order (cathode/electron transport layer/photoelectric conversion layer/hole transport layer/anode) was obtained as in Example 1, except that no diffusion prevention layer was formed and an anode shown in Table 3 was formed on the hole transport layer by an electron beam vapor deposition method.

Comparative Example 23

[0082] A 300-nm-thick ITO film was formed as a cathode on a glass substrate, and ultrasonically washed with pure water, acetone, and methanol in the stated order, each for 10 minutes, and then dried. Subsequently, on the surface of the ITO film was formed, by sputtering, a thin-film titanium oxide electron transport layer having a thickness of 20 nm. Then, a 1:1 solution of PTB7 (produced by Aldrich) and PCBM (produced by Aldrich) in chlorobenzene was formed into a film on the electron transport layer by a spin coating method, whereby a 100-nm-thick photoelectric conversion layer containing an organic semiconductor was formed. Thereafter, a PEDOT:PSS (produced by Aldrich) film was formed on the photoelectric conversion layer by a spin coating method, whereby a 50-nm-thick hole transport layer was formed. Thereafter, a diffusion prevention layer and an electrode shown in Table 3 were formed by the same procedure as in Example 1. Thus, a solar cell was obtained in which the cathode, the electron transport layer, the photoelectric conversion layer, the hole transport layer, the diffusion prevention layer, and the anode were stacked (cathode/electron transport layer/photoelectric conversion layer/hole transport layer/diffusion prevention layer/anode).

Comparative Examples 24 and 25

[0083] A solar cell in which a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode were stacked in the stated order (cathode/electron transport layer/photoelectric conversion layer/hole transport layer/anode) was obtained as in Comparative Example 23, except that no diffusion prevention layer was formed and an anode shown in Table 3 was formed by an electron beam evaporation method.

Evaluation

[0084] The solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

(1) Evaluation of Photoelectric Conversion Efficiency

[0085] A power source (model 236 produced by Keithley Instruments Inc.) was connected between the electrodes of the solar cell immediately after the production of the solar cell. The photoelectric conversion efficiency was measured using a solar simulator (produced by Yamashita Denso Corp.) at an intensity of 100 mW/cm.sup.2. The obtained photoelectric conversion efficiency was taken as the initial conversion efficiency. The obtained photoelectric conversion efficiency values were standardized with the photoelectric conversion efficiency of the solar cell obtained in Comparative Example 11 set as a benchmark.

[0086] 6: Standardized initial conversion efficiency value was 1.8 or more.

[0087] 5: Standardized initial conversion efficiency value was 1.5 or more and less than 1.8.

[0088] 4: Standardized initial conversion efficiency value was 1.3 or more and less than 1.5.

[0089] 3: Standardized initial conversion efficiency value was 1.2 or more and less than 1.3

[0090] 2: Standardized initial conversion efficiency value was 1.0 or more and less than 1.2.

[0091] 1: Standardized initial conversion efficiency value was less than 1.0.

(2) Evaluation of Durability (Light Resistance) Under Prolonged Application of Voltage

[0092] A power source (model 236 produced by Keithley Instruments Inc.) was connected between the electrodes of the solar cell. The photoelectric conversion efficiency was measured after application of a voltage at 25° C. for 24 hours using a solar simulator (produced by Yamashita Denso Corp.) at an intensity of 100 mW/cm.sup.2.

[0093] 5: The photoelectric conversion efficiency after a lapse of 24 hours was 95% or higher relative to the initial conversion efficiency.

[0094] 4: The photoelectric conversion efficiency after a lapse of 24 hours was 90% or higher and lower than 95% relative to the initial conversion efficiency.

[0095] 3: The photoelectric conversion efficiency after a lapse of 24 hours was 80% or higher and lower than 90% relative to the initial conversion efficiency.

[0096] 2: The photoelectric conversion efficiency after a lapse of 24 hours was 60% or higher and lower than 80% relative to the initial conversion efficiency.

[0097] 1: The photoelectric conversion efficiency after a lapse of 24 hours was lower than 60% relative to the initial conversion efficiency.

TABLE-US-00001 TABLE 1 Thickness of Photoelectric Diffusion diffusion Photoelectric Light conversion prevention prevention conversion resistance Cathode layer layer layer (nm) Anode efficiency test Example 1 ITO Perovskite Mo 10 Al 4 5 Example 2 ITO Perovskite Mo 5 Al 4 4 Example 3 ITO Perovskite Mo 20 Al 4 5 Example 4 ITO Perovskite Mo 30 Al 3 5 Example 5 ITO Perovskite Mo 20 Cu 4 4 Example 6 ITO Perovskite Mo 20 Sb 3 5 Example 7 ITO Perovskite W 10 Al 4 5 Example 8 ITO Perovskite Ta 10 Al 4 5 Example 9 ITO Perovskite Nb 10 Al 3 5 Example 10 ITO Perovskite Zr 10 Al 3 5 Example 11 ITO Perovskite Hf 10 Al 3 5 Example 12 ITO Perovskite Nb doped 50 Cu 4 5 TiO.sub.2 Example 13 ITO Perovskite ITO 50 Cu 5 4 Example 14 ITO Perovskite ITO 50 Al 3 4 Example 15 ITO Perovskite ITO 50 Sb 4 5 Example 16 ITO Perovskite GZO 50 Cu 4 5 Example 17 ITO Perovskite NiO 50 Cu 4 4 Example 18 ITO Perovskite MoOx 20 Cu 6 4 Example 19 ITO Perovskite WOx 20 Cu 5 4 Example 20 ITO Perovskite VOx 20 Cu 6 4 Example 21 ITO Perovskite CrOx 20 Cu 5 4 Example 22 ITO Perovskite MoOx 5 Mo 6 5 Example 23 ITO Perovskite MoOx 3 Mo 5 5 Example 24 ITO Perovskite MoOx 10 Mo 6 5

TABLE-US-00002 TABLE 2 Thickness of Photoelectric Diffusion diffusion Photoelectric Light conversion prevention prevention conversion resistance Cathode layer layer layer (nm) Anode efficiency test Example 25 ITO Perovskite MoOx 30 Mo 6 5 Example 26 ITO Perovskite MoOx 100 Mo 5 5 Example 27 ITO Perovskite MoOx 200 Mo 4 5 Example 28 ITO Perovskite ATO 50 Al 5 5 Example 29 ITO Perovskite PbO 50 Al 4 5 Example 30 ITO Perovskite TiN 50 Al 3 5 Example 31 ITO Perovskite TiN 20 Al 3 5 Example 32 ITO Perovskite TiN 5 Al 3 4 Example 33 ITO Perovskite VN 20 Al 3 5 Example 34 ITO Perovskite CrNx 20 Al 3 5 Example 35 ITO Perovskite CrNx 20 Cu 3 4 Example 36 ITO Perovskite CrNx 20 Sb 3 5 Example 37 ITO Perovskite NbN 20 Al 3 5 Example 38 ITO Perovskite TaN 20 Al 4 5 Example 39 ITO Perovskite MoN 20 Al 5 5 Example 40 ITO Perovskite ZrN 20 Al 4 5 Example 41 ITO Perovskite HfN 20 Al 4 5 Example 42 ITO Perovskite Graphite 5 Al 4 4 Example 43 ITO Perovskite Graphite 20 Al 5 4 Example 44 ITO Perovskite Graphite 50 Al 4 5 Example 45 ITO Perovskite Graphite 20 Cu 5 4 Example 46 ITO Perovskite Graphite 20 Mo 5 5 Example 47 ITO Perovskite Graphite 5 Mo 5 5 Example 48 ITO Perovskite Graphite 50 Mo 4 5

TABLE-US-00003 TABLE 3 Thickness of Photoelectric Diffusion diffusion Photoelectric Light conversion prevention prevention conversion resistance Cathode layer layer layer (nm) Anode efficiency test Comparative ITO Perovskite — — ITO 2 5 Example 1 Comparative ITO Perovskite — — Au 6 2 Example 2 Comparative ITO Perovskite — — Ag 6 1 Example 3 Comparative ITO Perovskite — — Cr 2 2 Example 4 Comparative ITO Perovskite — — Al 1 1 Example 5 Comparative ITO Perovskite ITO 50 Ti 2 5 Example 6 Comparative ITO Perovskite ITO 50 Ag 4 2 Example 7 Comparative ITO Perovskite ITO 50 Cr 2 5 Example 8 Comparative ITO Perovskite Mo 3 Al 3 3 Example 9 Comparative ITO Perovskite TiN 70 Al 2 5 Example 10 Comparative ITO Perovskite TiN 3 Al 2 3 Example 11 Comparative ITO Perovskite Mo 40 Al 2 5 Example 12 Comparative ITO Perovskite AlN 20 Al 1 5 Example 13 Comparative ITO Perovskite Al.sub.2O.sub.3 20 Al 1 5 Example 14 Comparative ITO Perovskite MgO 10 Al 1 5 Example 15 Comparative ITO Perovskite Zn 10 Al 1 1 Example 16 Comparative ITO Perovskite Ti 10 Al 2 2 Example 17 Comparative ITO Perovskite Graphite 1 Al 3 2 Example 18 Comparative ITO Perovskite Graphite 100 Mo 2 5 Example 19 Comparative ITO Perovskite Carbon 20 Al 3 2 Example 20 nanotube Comparative ITO Perovskite C60 20 Al 2 2 Example 21 Comparative ITO Perovskite Graphene 20 Al 3 2 Example 22 Comparative ITO Organic Mo 10 Al 2 3 Example 23 semiconductor Comparative ITO Organic — — ITO 2 4 Example 24 semiconductor Comparative ITO Organic — — Au 2 4 Example 25 semiconductor

INDUSTRIAL APPLICABILITY

[0098] The present invention can provide a solar cell having high photoelectric conversion efficiency that is less likely to decrease even under prolonged application of a voltage.