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

Thepressure-enhanced electronic properties of metal halide perovskitesare advantageous for photovoltaic and thermoelectric applications.However, another critical performance factor, the thermal conductivitybehavior under pressure, has received much less attention. Using thestate-of-the-art phonon Wigner transport equation, we studied theprototypical methylammonium lead triiodide in its cubic phase (c-MAPbI(3)) to discover a new anomalous pressure effect, where the dominantcoherence-channel thermal conductivity is invariant with changingpressure. The straightening of the octahedra and the shortening ofthe lattice constant with increasing pressure help create this anomalousbehavior that suppresses the overall thermal conductivity changes.By comparing with the bulk modulus and Gru''neisen parameterof several materials, we unveil another unusual phenomenon in c-MAPbI(3). The thermal conductivity of this soft and strongly anharmonicmaterial under pressure behaves like those of stiff and weakly anharmonicmaterials. Together with the reported enhanced optoelectronic properties,our findings support MAPbI(3) as a pressure-modulated energyconversion material with decoupled thermal and electrical properties.