Ultralow Thermal Conductivity and Ultrahigh Thermal Expansion of Single-Crystal Organic–Inorganic Hybrid Perovskite CH3NH3PbX3 (X = Cl, Br, I)

Improving device lifetime and stability remains the stumbling block of the commercialization of hybrid perovskite-based devices (HPDs). Although extensive efforts have been paid, thermal property, one of the most crucial parameters in conventional solid-state electronic devices, has rarely been studied for HPDs. Here, we investigate the temperature-dependent ultralow thermal conductivity and ultrahigh thermal expansion of single-crystalline MAPbX3 (MA = CH3NH3), which are found distinct from traditional thin-film solar cells materials. Particularly, for MAPbI3, thermal conductivity is observed being only 0.3 W·m–1·K–1 and linear thermal expansion coefficient along [100] direction is as high as 57.8 × 10–6 K–1 (tetragonal) and much higher at the structural phase transition point. We attribute the ultralow thermal conductivity and ultrahigh thermal expansion to the weak chemical bonds associated with the soft perovskite materials. These unique properties can be very challenging for the multilayer device design, but their ultralow thermal conductivity may unveil a new thermoelectric material concept.