Molecular Rotor-Rotor Heat Diffusion at the Origin of the Enhanced Thermal Conductivity of Hybrid Perovskites at High Temperatures

We demonstrate a new regime of heat conduction in hybrid metal halide perovskites where the thermal conductivity increases with temperature due to the rotational and librational motion of the organic cations. Our molecular dynamics simulations on MAPbI3 show that as the temperature is increased across the orthorhombic-tetragonal-cubic phase transitions, the contributions to the total thermal conductivity from the organic cations monotonically increases to similar to 60%, whereas the contributions from the inorganic framework decrease with a similar temperature dependence that is often associated with anharmonic phonon scattering processes of crystalline solids. The increase in the organic constituent contributions to the total thermal conductivity as the temperature is increased leads to a temperature-independent thermal conductivity at high temperatures. By comparing MAPbI3 results with the corresponding inorganic CsPbI3 lead halide (by using a new specifically designed MYP parametrization), we unambiguously ascribe a unique temperature trend of the hybrid perovskites to the collective rotational motion of the organic molecules leading to additional channels of heat flow at higher temperatures in these materials. Our findings are relevant for the thermal stability of hybrid perovskites to optimize heat dissipation and working conditions in optoelectronic, thermoelectric, and phononic devices based on hybrid perovskites.

Automated summary

We demonstrate a new regime of heat conduction in hybrid metal halide perovskites, where the thermal conductivity increases with temperature due to the rotational and librational motion of the organic cations. This finding is relevant for optimizing the thermal stability and working conditions of hybrid perovskites in optoelectronic, thermoelectric, and phononic devices.