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Understanding thermal transport at the micro- to nanoscale is cruciallyimportant for a wide range of technologies ranging from device thermalmanagement and protection systems to thermal-energy regulation and harvesting.In the past decades, non-contact optical methods such as time-domain andfrequency-domain thermoreflectance (TDTR and FDTR) have emerged as extremelypowerful and versatile thermal metrological techniques for the measurement ofmaterial thermal conductivities. Here, we report the measurement of thermalconductivity of thin films of CH3NH3PbI3 (MAPbI3), a prototypical metal-halideperovskite, by developing a time-resolved optical technique calledvibrational-pump visible-probe (VPVP) spectroscopy. The VPVP technique relieson the direct thermal excitation of MAPbI3 by femtosecond (fs) mid-infrared(MIR) optical pump pulses that are wavelength-tuned to a vibrational mode ofthe material, after which the time dependent optical transmittance across thevisible range is probed in the ns to the us time window using a broadbandpulsed laser. Using the VPVP method, we determine the thermal conductivities ofMAPbI3 thin films deposited on different substrates. The transducer-free VPVPmethod reported here is expected to permit spectrally resolving andspatiotemporally imaging the dynamic lattice temperature variations in organic,polymeric, and hybrid organic-inorganic semiconductors.

Time-resolved vibrational-pump visible-probe spectroscopy for thermal conductivity measurement of metal-halide perovskites