Multiple Phase Transition Induced Enhancement of Low-Temperature Thermoelectric Power in Ductile AgCuS-Based Thin Films

The increasing demand for energy autonomy in microscale and wearable electronics has intensified research interest in thermoelectric thin-film-based power generators. However, the development of such devices is challenging due to the intrinsic brittleness of inorganic materials and the poor performance of thin films. Recently, Ag₂S-based compounds have emerged as ductile thermoelectric semiconductors. Nonetheless, the thermoelectric performance of their thin films remains constrained, especially at low temperatures. Herein, we present a solution-processed fabrication of a high-performance AgCuS/Cu₂S composite thin film operable below 100 °C. These composite thin films underwent multiple phase transitions below 100 °C, notably increasing the thermoelectric power factors. Furthermore, the films exhibited significant intrinsic stretchability up to a strain of 16.1% owing to their intrinsic ductility. Wrinkled thin-film-based devices demonstrated enhanced power generation owing to multiple phase transitions and retained properties under 30% stretching, highlighting the potential of these films as viable energy harvesters for emerging electronic systems.