title: Adverse Effects of Excess Residual PbI2on Photovoltaic Performance, Charge Separation, and Trap-State Properties in Mesoporous Structured Perovskite Solar Cells.
abstract: Organic-inorganic halide perovskite solar cells have rapidly come to prominence in the photovoltaic field. In this context, CH3NH3PbI3, as the most widely adopted active layer, has been attracting great attention. Generally, in a CH3NH3PbI3layer, unreacted PbI2inevitably coexists with the perovskite crystals, especially following a two-step fabrication process. There appears to be a consensus that an appropriate amount of unreacted PbI2is beneficial to the overall photovoltaic performance of a device, the only disadvantageous aspect of excess residual PbI2being viewed as its insulating nature. However, the further development of such perovskite-based devices requires a deeper understanding of the role of residual PbI2. In this work, PbI2-enriched and PbI2-controlled perovskite films, as two extreme cases, have been prepared by modulating the crystallinity of a pre-deposited PbI2film. The effects of excess residual PbI2have been elucidated on the basis of spectroscopic and optoelectronic studies. The initial charge separation, the trap-state density, and the trap-state distribution have all been found to be adversely affected in PbI2-enriched devices, to the detriment of photovoltaic performance. This leads to a biphasic recombination process and accelerates the charge carrier recombination dynamics.
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Hao-Yi
authors.initials: HY
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Ming-Yang
authors.initials: MY
authors.lastname: Hao
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Han
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Man
authors.initials: M
authors.lastname: Yu
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Pu
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Zhi-Xin
authors.initials: ZX
authors.lastname: Guo
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Ai
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing, 100872, P.R. China.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
keywords: dynamics; excess PbI2; fluorescence; organic-inorganic hybrid composites; perovskites