Electron-lattice interaction governs the fundamental working principles of multiple energy materials, and modifications of the lattice characteristics may give rise to their different material properties, such as superconductivity, thermoelectricity, photovoltaics and supercapacitors. Being an outstanding photovoltaic material, methylammonium lead iodide (CH3NH3PbI3, or MAPbI3) is composed of two parts—inorganic framework PbI3- that extends three-dimensionally, and intercalated cation MA+ that is electrostatically pinned in the voids formed by PbI6 octahedra in proximity. Distinctively, MA+ also undergoes rotational motions that results in spatial reorientation of the cationic charge. Therefore, it is intriguing to reveal the perturbation of photocarrier dynamics that exclusively occurs in the inorganic sublattice, by tuning the rotational frequency of organic MA+. Herein, hydrogen atoms in methyl group and/or ammonium group were substituted by deuterium atoms to modulate the rotational frequency of MA+ while keeping its chemical nature and electronic structure intact. Strikingly, time-resolved photoluminescence studies configured a significant difference in carrier lifetimes among CH3NH3PbI3, CH3ND3PbI3, CD3NH3PbI3 and CD3ND3PbI3 single crystals. To account for such phenomenon, a polaron model of photocarriers was established. DFT calculations reveal the density of states of CH3NH3PbI3 near band edges and polaron trapping energies are highly dependent on MA+ orientation. The discovery of electron-rotor interaction in hybrid lead iodide perovskites should provide a theoretical foundation in the quest for better photovoltaic properties.

Optoelectronic structures of hybrid lead iodide perovskites probed by electron-rotor interaction

253rd National Meeting (2017)

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