PHOTOELECTRIC CONVERSION ELEMENT, METHOD FOR PRODUCING PHOTOELECTRIC CONVERSION ELEMENT, AND SOLAR CELL

Abstract

The present invention aims to provide a photoelectric conversion element having high photoelectric conversion efficiency, a method for producing the photoelectric conversion element, and a solar cell including the photoelectric conversion element. Provided is a photoelectric conversion element containing a 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 is a halogen atom, the photoelectric conversion element having an intensity ratio of a nitrate ion to a halogen ion (NO.sub.3/X) of 0.0010 or more and less than 0.2000 as determined by TOF-SIMS measurement.

Claims

1. A photoelectric conversion element comprising a 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 is a halogen atom, the photoelectric conversion element having an intensity ratio of a nitrate ion to a halogen ion (NO.sub.3/X) of 0.0010 or more and less than 0.2000 as determined by TOF-SIMS measurement.

2. The photoelectric conversion element according to claim 1, which has an intensity ratio of a potassium ion to a lead or tin ion (K/M) of 0.4 or more and less than 2.0 as determined by the TOF-SIMS measurement.

3. The photoelectric conversion element according to claim 1, wherein the K/M is 0.8 or more and the NO.sub.3/X is 0.0030 or more as determined by the TOF-SIMS measurement.

4. A method for producing the photoelectric conversion element according claim 1, comprising: a first film forming step of forming a first film from a mixed solution (first solution) that contains a metal nitrate represented by MNO.sub.3 wherein M is a lead or tin atom and a metal halide represented by MX wherein M is a lead or tin atom and X is a halogen atom; a second film forming step of forming a second film on the first film from a solution (second solution) of AX wherein A represents an organic base compound or an alkali metal and X is a halogen atom; and a step of performing heating treatment after the second film forming step.

5. The method for producing the photoelectric conversion element according to claim 4, wherein the first solution contains a potassium halide represented by KX wherein X is a halogen atom.

6. A solar cell comprising a cathode, the photoelectric conversion element according claim 1, and an anode in the stated order.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0078] FIG. 1 is a schematic view illustrating an exemplary crystal structure of a perovskite compound.

DESCRIPTION OF EMBODIMENTS

[0079] The present invention is more specifically described with reference to, but not limited to, the following examples.

Example 1

[0080] A 1000-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.

[0081] On the surface of the ITO film was formed, by sputtering, a thin-film 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.

[0082] Subsequently, 550 mg of lead iodide as a metal halide, lead nitrate as a metal nitrate in an amount of 0.2% by weight relative to the lead iodide, and potassium iodide as a potassium halide in an amount of 0.1% by weight relative to the lead iodide were dissolved in a solvent mixture of 1 mL of N,N-dimethylformamide (DMF) and 80 μL of dimethyl sulfoxide, whereby a first solution was prepared. A film was formed from this solution 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 (second solution). A film was formed from the second solution 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 element containing a perovskite compound CH.sub.3NH.sub.3PbI.sub.3, nitrate ions, and potassium was formed.

[0083] Subsequently, a 9% by weight solution of Spiro-OMETAD (produced by Merck) in chlorobenzene was applied to the photoelectric conversion element by spin coating, whereby a hole transport layer having a thickness of 200 nm was formed.

[0084] Then, on the hole transport layer was formed a 100-nm-thick gold film as an anode by vapor deposition. Thus, a solar cell was obtained in which the cathode, the electron transport layer, the photoelectric conversion element, the hole transport layer, and the anode were stacked (cathode/electron transport layer/photoelectric conversion element/hole transport layer/anode).

[0085] (Tof-Sims Measurement)

[0086] A measurement sample consisting only of a photoelectric conversion element was prepared by the above method. The prepared sample was subjected to TOF-SIMS measurement using “TOF-SIMS5”, produced by ION-TOF GmbH, with a Bi.sub.3.sup.++ ion gun as a primary ion source for measurement. From the obtained measurement results, the intensity ratio of a nitrate ion to an iodine ion (NO.sub.3/I) was calculated based on the NO.sub.3 peak and the iodine peak. Furthermore, the intensity ratio of a potassium ion to a lead ion (K/Pb) was calculated from the potassium ion peak and the lead ion peak. Table 1 shows the results. The specific TOF-SIMS conditions were as follows.

Primary ion: Bi.sub.3.sup.++
Ionic voltage: 25 kV
Ion current: 0.1 to 0.2 pA (pulsed current)
Mass range: 1 to 500 mass
Analyzed area: 500 μm×500 μm (imaging)
Charging prevention: neutralization by electron irradiation
Random scan mode

Examples 2 to 15 and Comparative Examples 3 and 4

[0087] A solar cell was obtained as in Example 1 except that the amounts of lead nitrate and potassium iodide in the first solution were changed as shown in Table 1.

Comparative Examples 1 and 2

[0088] A solar cell was obtained as in Example 1 except that no lead nitrate was used in the first solution and the amount of potassium iodide was changed as shown in Table 1.

<Evaluation>

[0089] The solar cells obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

(Evaluation of Photoelectric Conversion Efficiency)

[0090] 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 obtained 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 photoelectric conversion efficiency values of the examples and comparative examples were standardized with the photoelectric conversion efficiency of the solar cell obtained in Comparative Example 1 set as a benchmark.

TABLE-US-00001 TABLE 1 Photoelectric conversion element Evaluation Amount of Photoelectric PbNO.sub.3 Amount of KI conversion (% by weight) (% by weight) NO.sub.3/I K/Pb efficiency Example 1 0.2 0.1 0.001 0.2 1.04 Example 2 0.4 0.1 0.005 0.2 1.08 Example 3 0.5 0.1 0.01 0.2 1.10 Example 4 0.6 0.1 0.05 0.2 1.06 Example 5 0.2 1.5 0.001 0.8 1.06 Example 6 0.2 1.8 0.001 0.9 1.07 Example 7 0.4 1.8 0.005 0.9 1.10 Example 8 0.6 1.8 0.05 0.9 1.12 Example 9 0.8 1.8 0.10 0.9 1.09 Example 10 0.2 3.0 0.001 1.4 1.08 Example 11 0.2 4.0 0.001 1.8 1.08 Example 12 0.2 5.0 0.001 2.2 1.03 Example 13 0.2 5.5 0.001 2.4 1.02 Example 14 1.3 1.8 0.15 0.9 1.06 Example 15 1.6 1.8 0.18 0.9 1.02 Comparative Example 1 0 0.1 0.0004 0.2 1.00 Comparative Example 2 0 1.5 0.0004 0.8 1.01 Comparative Example 3 2.0 0.1 0.22 0.2 0.98 Comparative Example 4 2.5 0.1 0.25 0.2 0.90

INDUSTRIAL APPLICABILITY

[0091] The present invention can provide a photoelectric conversion element having high photoelectric conversion efficiency, a method for producing the photoelectric conversion element, and a solar cell including the photoelectric conversion element.