Multi-cation Synergy Suppresses Phase Segregation in Mixed-Halide Perovskites

Hoang X. Dang, Kai Wang, Masoud Ghasemi, Ming-Chun Tang, Michele de Bastiani, Erkan Aydin, Emilie Dauzon, Dounya Barrit, Jun Peng, Detlef M. Smilgies, Stefaan De Wolf, Aram Amassian

Research output: Contribution to journalArticlepeer-review

165 Scopus citations


Mixed lead halide perovskite solar cells have been demonstrated to benefit tremendously from the addition of Cs+ and Rb+, but its root cause is yet to be understood. This hinders further improvement, and processing approaches remain largely empirical. We address the challenge by tracking the solidification of precursors in situ and linking the evolutions of different crystalline phases to the presence of Cs+ and Rb+. In their absence, the perovskite film is inherently unstable, segregating into MA-I- and FA-Br-rich phases. Adding either Cs+ or Rb+ is shown to alter the solidification process of the perovskite films. The optimal addition of both Cs+ and Rb+ drastically suppress phase segregation and promotes the spontaneous formation of the desired α phase. We propose that the synergistic effect is due to the collective benefits of Cs+ and Rb+ on the formation kinetics of the α phase and on the halide distribution throughout the film.
Original languageEnglish (US)
Pages (from-to)1746-1764
Number of pages19
Issue number7
StatePublished - Jun 6 2019

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): OSR-CARF URF/1/3079-33-01
Acknowledgements: 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 and NIH/NIGMS via NSF award DMR-1332208. H.X.D thanks Dr. Ching-Chang Chung for helping with the temperature-dependent XRD measurements. This work was 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. H.X.D. A.A. and S.D.W. designed all the experiments. H.X.D. fabricated and performed the characterization of thin films and solar cells. H.X.D. M.-C.T. E.D. D.B. D.-M.S. and A.A. contributed to the GIWAXS experiments and data analysis. A.A. guided GIWAXS and XRD measurements and analysis and assisted with phase identification. K.W. synthesized Cl-TiO2 and measured the stabilized PCE. K.W. and E.A. assisted with the device optimization. J.P. helped in defining the additive contents. M.G. contributed to the ToF-SIMS measurements. H.X.D. drafted the manuscript. M.D.B. A.A. and S.D.W. assisted in revising the manuscript. A.A. and S.D.W. supervised the project. The authors declare no competing interests.


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