Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across its Tetragonal-Cubic Structural Phase Transition
Hoque, Md Nadim Ferdous
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Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, whether the structural phase transition could result in dramatic changes in these properties, are not well studied. Herein, we report a striking contrast at ~45 oC in the ionic/electrical properties of MAPbI3 due to a change of the ion activation energy from 0.7 eV to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the “continuous” nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature when tetragonal-cubic structural phase transition occurs.