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Entropy-Driven Structural Transition and Kinetic Trapping in Formamidinium Lead Iodide Perovskite



Tianran Chen, Benjamin J. Foley, Changwon Park, Craig Brown, Leland Harriger, Jooseop Lee, Jacob Ruff, Mina Yoon, Joshua J. Choi, Seugn-Hun Lee


A challenge for hybrid perovskite solar cells is device instability, which calls for understanding of the perovskite structural stability and phase transitions. Here, using neutron diffraction and ab-initio calculations on HC(NH2)2PbI3, we show that the entropy contribution to the Gibbs free energy due to isotropic rotations of the HC(NH2)2+ cation play a crucial role in the cubit-to-hexagonal structural phase transition. Futhermore, we observe that the cubic-to-hexagonal phase transition exhibits a large thermal hysteresis. Our ab-initio calculations confirm the existence of a potential barrier between the cubic and the hexagonal structure, which provides an explanation for the observed thermal hysteresis. By exploiting the potential barrier, we demonstrate kinetic trapping of the cubic phase, that is desirable for solar cells, even at 8.2 K by thermal quenching.
Science Advances


Structure, crystallography, Phase transition, solar cell, entropy


Chen, T. , Foley, B. , Park, C. , Brown, C. , Harriger, L. , Lee, J. , Ruff, J. , Yoon, M. , Choi, J. and Lee, S. (2016), Entropy-Driven Structural Transition and Kinetic Trapping in Formamidinium Lead Iodide Perovskite, Science Advances, [online], (Accessed February 27, 2024)
Created October 20, 2016, Updated October 12, 2021