Diffuson‐Dominated and Ultra Defect‐Tolerant Two‐Channel Thermal Transport in Hybrid Halide Perovskites

Abstract Organic‐inorganic hybrid halide perovskites show a unique two‐channel thermal transport through propagons and diffusons, largely affecting other energy carriers for opto‐ and thermoelectric applications. Taking CH 3 NH 3 PbI 3 as a prototype, the impact of iodine vacancy point defects on the two‐channel thermal transport is investigated using theoretical calculations and experimental validations. This work finds that iodine vacancies suppress the thermal transport in the propagon channel significantly, but less in the diffuson channel. This results in a weaker reduction of the total thermal conductivity (TC) than that predicted by the classical Klemens model. The TC reduction in the diffuson channel is mainly attributed to the declined vibrational density of states. Moreover, low‐frequency diffusons transformed from propagons compensate the reduction of TC in the diffuson channel, resulting in a dominant contribution from the diffuson channel to the total TC, which is 55% to 85% for 0% to 6% vacancy concentration. CH 3 NH 3 PbI 3 also shows ultra‐defect‐tolerant diffusonic thermal transport, ≈1–2 orders of magnitude lower than diamond in the defect sensitivity factor. This work shows both scientific insights into the new two‐channel thermal transport mechanism in complex material systems with disorder, and technological significance on halide perovskites for solar cell, light‐emitting diode, thermoelectric, and memristor applications.