Effect of vacancy concentration on the lattice thermal conductivity of CH₃NH₃PbI₃: a molecular dynamics study

Hybrid halide perovskites are drawing great interest for photovoltaic and thermoelectric applications, but the relationship of thermal conductivities with vacancy defects remains unresolved. Here, we present a systematic investigation of the thermal conductivity of perfect and defective CH₃NH₃PbI₃, performed using classical molecular dynamics with an ab initio-derived force field. We calculate the lattice thermal conductivity of perfect CH₃NH₃PbI₃ as the temperature increases from 300 K to 420 K, confirming a good agreement with the previous theoretical and experimental data. Our calculations reveal that the thermal conductivities of defective systems at 330 K, containing vacancy defects such as V_MA, V_Pb and V_I, decrease overall with some slight rises, as the vacancy concentration increases from 0 to 1%. We show that such vacancies act as phonon scattering centers, thereby reducing the thermal conductivity. Moreover, we determine the elastic moduli and sound velocities of the defective systems, revealing that their slower sound speed is responsible for the lower thermal conductivity. These results could be useful for developing hybrid halide perovskite-based solar cells and thermoelectric devices with high performance.