Atomistic and Electronic Origin of Phase Instability of Metal Halide Perovskites
Junke Jiang a, Feng Liu b, Ionut Tranca c, Qing Shen b, Shuxia Tao a
a Eindhoven University of Technology, Department of Applied Physics, 5600MB, Eindhoven, Netherlands
b Faculty of Informatics and Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan
c Eindhoven University of Technology (TU/e), PO Box 513, Eindhoven, 5600, Netherlands
Proceedings of Online International Conference on Hybrid and Organic Photovoltaics (OnlineHOPV20)
Online, Spain, 2020 May 26th - 29th
Organizers: Tracey Clarke, James Durrant, Annamaria Petrozza and Trystan Watson
Poster, Junke Jiang, 082
Publication date: 22nd May 2020

The excellent optoelectronic properties of metal halide perovskites (MHPs) have attracted extensive scientific interests and boosted their application in optoelectronic devices. Despite their attractive optoelectronic properties, their poor stability under ambient conditions remains the major challenge, hindering their large-scale practical applications. In particular, some MHPs undergo spontaneous phase transitions from three-dimensional perovskites (3DP) to two-dimensional non-perovskites (2DNP). Compositional engineering via mixing cations or anions has been widely reported to be effective in suppressing such unwanted phase transition. However, the atomistic and electronic origins of the stabilization effect remain unexplored. Here, by combining Density Functional Theory (DFT) calculations and Crystal Orbital Hamilton Population (COHP) analysis, we provide insights for the undesired phase transition of pristine perovskites (FAPbI3, CsPbI3, and CsSnI3) and reveal the mechanisms of the improved phase stability of the mixed compounds (CsxFA1-xPbI3, CsSnyPb1-yI3, and CsSn(BrzI1-z)3). We identify that the phase transition is determined by the relative strength of the M-X bonds as well as that of the hydrogen bonds (for hybrid compositions) in 3D and 2D phases. The phase transition can be suppressed by mixing ions, giving rise to either increased bond strength for the 3DP or decreased bond strength in their 2DNP counterparts. Our results present a comprehensive understanding of the mechanisms for the phase instability of metal halide perovskites and provide design rules for engineering phase-stable perovskite compositions.

S. Tao and J. Jiang acknowledge funding by the Computational Sciences for Energy Research (CSER) tenure track program of Shell and NWO (Project number15CST04-2). Q. Shen and F. Liu acknowledge funding by the Japan Science and Technology Agency (JST) Mirai program (JPMJMI17EA), the MEXT KAKENHI Grant (Grant 26286013, 17H02736), and JSPS International Research Fellow (Faculty of Informatics and Engineering, UEC). Dr. Peter Klaver is acknowledged for his technical support in the computational study in this work.

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