Abstract
Understanding lattice dynamics and thermal transport mechanisms in cubic hybrid organic-inorganic perovskites remain challenging due to strong anharmonicity and phase transitions. Here, we investigate the thermal transport behavior in benchmark cubic hybrid perovskite FAPbI(3) by coupling first principles-based anharmonic lattice dynamics with a linearized Wigner transport equation. Using the Temperature-Dependent Effective Potential (TDEP) method, we stabilize the negative soft modes, primarily dominated by organic FA(+) cations. Our calculations predict an ultra-low thermal conductivity of ~ 0.63 Wm-1K-1 at 300 K, following a temperature dependence of T (-0.740). Contrary to common assumptions, we find that the [PbI(3)](1-) units, rather than FA(+) cations, dominate thermal resistance. Furthermore, we demonstrate that anharmonic force constants are highly temperature-sensitive, relying on 0-K force constants significantly underestimates thermal conductivity. Our study not only elucidates the microscopic mechanisms governing thermal transport in FAPbI(3) but also provides a robust framework for modeling heat conduction in hybrid organic-inorganic compounds.