Perovskite solar cells increasingly feature mixed-halide mixed-cation compounds (FA1- x - y MAx Csy PbI3- z Brz ) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti-solvent processing window for the fabrication of high-quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI3 , FAPbI3 , and FAPbBr3 ), to several minutes for mixed systems. In situ X-ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol-gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti-solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti-solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol-gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high-efficiency perovskite solar cells produced with ease and with high reproducibility.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): OSR-CARF URF/1/3079-33-01
Acknowledgements: K.W. and M.-C.T. contributed equally to this work. The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award no. OSR-CARF URF/1/3079-33-01. CHESS is supported by the NSF award DMR-1332208. Temperature-dependent XRD measurements were performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the NSF award no. ECCS-1542015.