Temperature-Dependent Thermal Conductivity Study of MAPbI₃: Using Mild Aging To Reach a Thermal Percolation Threshold for Greatly Improved Heat Transport

We report the thermal conductivity in the range from 7 to 300 K for methylammonium lead triiodide (MAPbI₃) perovskite in different stages of environmental degradation. The results showed that thermal conductivity of the degraded perovskite pellet quickly approached that of lead iodide rather than pure MAPbI₃, even while X-ray diffraction data of the degraded perovskite showed mostly peaks of the perovskite phase, alongside minor peaks from impurity phases belonging to the precursors and to an intermediate phase. For reference, a sample of pure lead iodide was also prepared and analyzed in the same way, and to our knowledge, thermal conductivity for lead iodide in the 7–300 K temperature range has not yet been published. The combination of thermal conductivity and materials characterization provides more detailed knowledge of the composition and structural changes of aged MAPbI₃ perovskite. Moreover, we demonstrate that a thermal percolation threshold can be achieved through mild aging while preserving most of the MAPbI₃ crystal structure.