Anomalous Pressure-Resilient Thermal Conductivity in Hybrid Perovskites with Strong Lattice Anharmonicity and Small Bulk Modulus

The pressure-enhanced electronic properties of metal halide perovskites are advantageous for photovoltaic and thermoelectric applications. However, another critical performance factor, the thermal conductivity behavior under pressure, has received much less attention. Using the state-of-the-art phonon Wigner transport equation, we studied the prototypical methylammonium lead triiodide in its cubic phase (c-MAPbI3) to discover a new anomalous pressure effect, where the dominant coherence-channel thermal conductivity is invariant with changing pressure. The straightening of the octahedra and the shortening of the lattice constant with increasing pressure help create this anomalous behavior that suppresses the overall thermal conductivity changes. By comparing with the bulk modulus and Grüneisen parameter of several materials, we unveil another unusual phenomenon in c-MAPbI3. The thermal conductivity of this soft and strongly anharmonic material under pressure behaves like those of stiff and weakly anharmonic materials. Together with the reported enhanced optoelectronic properties, our findings support MAPbI3 as a pressure-modulated energy conversion material with decoupled thermal and electrical properties.