Transducer-free probing of thermal transport in semiconducting molecular and polymer thin films

Abstract Thermal management is critical for improving the stability and performance of organic electronics, including organic light-emitting diodes, photovoltaics, and flexible electronics. The inherently low thermal conductivity of organic semiconductors leads to inefficient heat dissipation, decreasing device performance and lifetime. Standard thermal transport measurement techniques such as time-domain thermoreflectance require metallic transducer layers that are destructive and encounter poor sensitivity at cryogenic temperatures. Herein, a transducer-free approach is demonstrated using vibrational pump-visible probe spectroscopy to measure the thermal transport properties of thin films of both small molecule-based and conjugated polymer-based semiconductors, from 295 K to 8 K. Copper phthalocyanine (CuPc) and indacenodithiophene-co-benzothiadiazole (IDTBT) films are impulsively heated with mid-infrared pulses while temperature-dependent optical transmittances are probed to track thermal decay kinetics. CuPc exhibits a thermal diffusivity several times higher than that of IDTBT, attributed to the structural disorder and thermally insulating alkyl chains in IDTBT compared to the higher crystalline order in CuPc. Thermal transport in IDTBT stays relatively temperature-independent, suggesting disorder-induced scattering dominates. In contrast, CuPc shows stronger temperature dependence, consistent with thermal transport dominated by phonon-phonon and grain boundary scattering. This versatile transducer-free approach enables low-temperature study to connect structural characteristics of thermal transport mechanisms across diverse organic semiconductor families.