title: Credible evidence for the passivation effect of remnant PbI₂ in CH₃NHCH₃PbICH₃ films in improving the performance of perovskite solar cells.
abstract: The role of remnant PbI2 in CH3NH3PbI3 films is still controversial, some investigations have revealed that the remnant PbI2 plays a passivation role, reduces the charge recombination in perovskite solar cells (PSCs), and improves the performance of PSCs, but the opposing views state that remnant PbI2 has no passivation effect and it would deteriorate the stability of the devices. In our investigation, the CH3NH3PbI3 films have been prepared by a two-step spin-coating method and the content of the remnant PbI2 in CH3NH3PbI3 films has been tuned by varying the preparation temperature. It has been found that increasing the heating temperature could increase the coverage of spin-coated PbI2 films, which has led to high coverage CH3NH3PbI3 films and more remnant PbI2 in CH3NH3PbI3 films, and as a result, the performance of PSCs was enhanced obviously and the maximum power conversion efficiency of 14.32 ± 0.28% was achieved by the PSCs prepared at 130/120 °C (PbI2 films were heated at 130 °C and CH3NH3PbI3 films were heated at 120 °C). Furthermore, the dark current, electrochemical impedance spectroscopy and time-resolved fluorescence emission decay measurements revealed that the charge recombination in PSCs has been gradually suppressed and the fluorescence emission lifetime has gradually increased with the content of remnant PbI2 increasing. Thus, the passivation effects of the unreacted and decomposed PbI2 in improving the performance of PSCs have been confirmed unquestionably.
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Shimao
authors.initials: S
authors.lastname: Wang
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Dong
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China and School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, P. R. China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Fang
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn.
authors.forename: Qingli
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn.
authors.forename: Shu
authors.initials: S
authors.lastname: Zhou
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Zanhong
authors.initials: Z
authors.lastname: Deng
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Ruhua
authors.initials: R
authors.lastname: Tao
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn and Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Jingzhen
authors.initials: J
authors.lastname: Shao
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn.
authors.forename: Rui
authors.initials: R
authors.lastname: Xia
authors.affiliation: Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, P. R. China. wwdong@aiofm.ac.cn xdfang@aiofm.ac.cn.
authors.forename: Chao
authors.initials: C
authors.lastname: Song
authors.affiliation: Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Linhua
authors.initials: L
authors.lastname: Hu
authors.affiliation: Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences, Hefei 230031, P. R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu