Simultaneous Mapping of Thermal Conductivity, Thermal Diffusivity, and Volumetric Heat Capacity of Halide Perovskite Thin Films: A Novel Nanoscopic Thermal Measurement Technique

Local thermal conductivity, thermal diffusivity, and volumetric heat capacity of all-inorganic halide perovskite thin films are mapped simultaneously and with highest spatial resolution for the first time. These various thermal properties are detected by a scanning near-field thermal microscope operated at two different frequencies simultaneously. We apply this technique to analyze the thermal properties of halide perovskites on the nanoscale. In addition to an ultralow thermal conductivity of 0.43 +/- 0.03 and 0.33 +/- 0.02 W/(m.K), a low thermal diffusivity of 0.3 +/- 0.1 mm(2)/s and a small heat capacity of 0.29 +/- 0.9 and 0.18 +/- 0.6 J/(g.K) are obtained for CsPbBr3 and CsPb2Br5 films, respectively. The findings of our thermal microscopy are of great general importance for the thermal design of thin-film devices based on halide perovskites, while the measurement technique itself is generally applicable for other thin-film optoelectronic materials.