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Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites



Eve M. Mozur, Michael A. Hope, Julia C. Trowbridge, David M. Halat, Luke L. Daemen, Annalise E. Maughan, Timothy R Prisk, Clare P. Grey, James R. Neilson


While hybrid perovskites show great promise for photovoltaic applications, several of the most technologically relevant hybrid perovskites degrade rapidly when exposed to water, oxygen, or infrared and ultraviolet radiation. Empirical studies have shown that chemical substitution of hybrid perovskites prevents their decomposition while preserving their advantageous optoelectronic properties, but the underlying influence of chemical substitution remains ambiguous. The hybrid perovskite formamidinium lead bromide (CH(NH2)2PbBr3) exhibits complex phase behavior manifesting in a series of crystallographically-unresolvable phase transitions. Here, we characterize the molecular and lattice dynamics of CH(NH2)2PbBr3) as a function of temperature, and their evolution upon chemical substitution of CH(NH2)2+ for cesium (Cs+) with crystallography, neutron scattering, 1H and 14N nuclear magnetic resonance spectroscopy, and 79Br nuclear quadrupolar spectroscopy. Cs+ substitution suppresses the four low-temperature phase transitions of CH(NH2)2PbBr3, which propagate through concerted changes in the dynamic degrees of freedom of the organic sub-lattice and local or long-range distortions of the octahedral framework. We propose that cesium suppresses the phase transitions through the relief of geometric frustration associated with the electrostatic quadrupolar interactions between CH(NH2)2+ molecules, which may in turn explain the greater phase stability on substitution.
Chemistry of Materials


, E. , , M. , , J. , , D. , , L. , , A. , , T. , , C. and , J. (2020), Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites, Chemistry of Materials, [online], (Accessed August 2, 2021)
Created July 27, 2020, Updated September 3, 2020