Ultralow thermal conductivity in pristine hybrid perovskite, methylammonium lead trihalide (MAPbI3), has been extensively revealed theoretically. However, phonon transport in defective MAPbI3, which is more relevant to experimental sample conditions, has remained elusive. Here we study the effect of defect type and concentration on the thermal conductivity, ionic diffusivity and intrinsic phonon properties in MAPbI3 using molecular dynamics simulations and the spectral energy density method. At the same defective concentration iodine-MA Schottky defects reduce the thermal conductivity more strongly than the iodine vacancy defects. When increasing the vacancy defect concentration, the thermal conductivity decreases, while the diffusivity of iodine increases. The thermal conductivity of MAPbI3 with 2%-iodine vacancy defects decreases by 15% than that of the pristine counterpart at 350 K. A strong phonon’s anharmonicity is observed in vacancy-defect MAPbI3 and attributed to not only the defect, but also the iodine diffusion. Meanwhile, the phonon density of states of MAPbI3 with 2%-iodine vacancy is slightly suppressed compared to that of the pristine counterpart in the low-frequency acoustic phonon modes (&lt;1 THz) which contributes significantly to heat transfer. The reduction in thermal conductivity is mainly attributed to reduced phonon lifetime due to the phonon’s anharmonicity. This work not only provides fundamental understanding of the phonon transport in defective MAPbI3, but also gives guidelines to study phonon transport in diffusion-mediated thermoelectric materials.

Diffusion-Mediated Anharmonic Phonon Transport and Thermal Conductivity Reduction in Defective Hybrid Perovskites

Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2021/volume/84874

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