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Chloride Incorporation Process in CH₃NH₃PbI₃–xClx Perovskites via Nanoscale Bandgap Maps

2015
Authors

Jungseok Chae, Qingfeng Dong, Jinsong Huang, and Andrea Centrone

Abstract

CH3NH3PbI3-xClx perovskites enable fabrication of highly efficient solar cells. In this work, the photothermal-induced resonance, is leveraged to measure the bandgap of CH3NH3PbI3-xClx films obtained by a multicycle coating process that produces high efficiency solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing the films consist of Cl-rich and Cl-poor phases that upon further annealing evolve into a homogeneous Cl-poorer phase, suggesting that methylammonium-chloride is progressively expelled from the film. Despite the small chloride content, CH3NH3PbI3-xClx films show better thermal stability up to 140°C with respect to CH3NH3PbI3 films fabricated with the same methodology.

PTIR image ratios close to the absorption band gap in MAPbl₃-ₓClₓ mirroring the Cl- distribution. The above images show PTIR absorption ratio maps recorded by illuminating the sample at 702 nm (a), at 678 nm (b) and at 645 nm (c).