Electric Field‐Induced Thermal Conductivity Switching in Low‐Temperature Hybrid Perovskites via Crystal Symmetry Reduction

Abstract Using reversible external fields to modulate and study properties of materials has yielded new scientific insights and improves device performances. In this work, the effect of an external electric field on the thermal transport of methylammonium lead triiodide (MAPbI 3 ) under different temperatures is investigated, discovering different electric field‐triggered thermal conductivity behavior and their associated governing mechanisms. At a temperature of 350 K, the thermal conductivity of cubic‐MAPbI 3 is independent of the electric field. However, for an orthorhombic‐MAPbI 3 at 100 K, its thermal conductivity decreases by 44.5% under an electric field of 0.35 V Å −1 . In the latter case, the electric field imparts sufficient energy to overcome the MA rotation energy barrier and reorientate the MA cations, resulting in a lower symmetry crystal and weaker interatomic bonding strength. Using the phonon Wigner transport equation, it is revealed that the electric field lowers the population‐channel thermal conductivity but leaves the coherence‐channel unaffected. In the cubic‐MAPbI 3 at 350 K, although the electric field aligns the orientation of the MA cations and reduces their dynamic disorder, its thermal conductivity remains unaffected. Comparing the thermal conductivity changes with those from other typical perovskites, the orthorhombic‐MAPbI 3 at 100 K exhibits the largest reported thermal conductivity decrease under an electric field.