Optimization of PbI2/MAPbI3 Perovskite Composites by Scanning Electrochemical Microscopy

• Published in: Journal of physical chemistry. C Vol. 120; no. 35; pp. 19890 - 19895
• Main Authors: Hsu, Hsien-Yi, Ji, Li, Du, Minshu, Zhao, Ji, Yu, Edward T, Bard, Allen J
• Format: Journal Article
• Language: English; Japanese
• Published: American Chemical Society 08.09.2016
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.6b07850

A variety of PbI2/MAPbI3 perovskites were prepared and investigated by a rapid screening technique utilizing a modified scanning electrochemical microscope (SECM) in order to determine how excess PbI2 affects its photoelectrochemical (PEC) properties. An optimum ratio of 2.5% PbI2/MAPbI3 was found to enhance photocurrent over pristine MAPbI3 on a spot array electrode under irradiation. With bulk films of various PbI2/MAPbI3 composites prepared by a spin-coating technique of mixed precursors and a one-step annealing process, the 2.5% PbI2/MAPbI3 produced an increased photocurrent density compared to pristine MAPbI3 for 2 mM benzoquinone (BQ) reduction at −0.4 V vs Fc/Fc+. As a result of the relatively high quantum yield of MAPbI3, a time-resolved photoluminescence quenching experiment could be applied to determine electron–hole diffusion coefficients and diffusion lengths of PbI2/MAPbI3 composites, respectively. The diffusion coefficients combined with the exciton lifetime of the pristine 2.5% PbI2/MAPbI3 (τPL = 103.3 ns) give the electron and hole exciton diffusion lengths, ∼300 nm. Thus, the 2.5% PbI2/MAPbI3 led to an approximately 3.0-fold increase in the diffusion length compared to a previous report of ∼100 nm for the pristine MAPbI3 perovskite. We then demonstrated that the efficiency of liquid-junction solar cells for 2.5% excess PbI2 of p-MAPbI3 was improved from 6.0% to 7.3%.