Flexible freestanding Ag2Se thermoelectric films with high performance for sap flow monitoring

Flexible inorganic thermoelectrics are promising for the Internet of Things and wearable electronics. While solution processing offers a facile route to such materials, simultaneously achieving mechanical flexibility and substantial power output remains challenging. Here, we report a microstructure-engineering strategy to fabricate freestanding Ag 1.8 Se/carbon nanotube (CNT) composite films with ultralow CNT content (0.9 wt %). An interwoven CNT network establishes dense, conductive interfaces with Ag 1.8 Se nanowires, enabling efficient carrier transport and exceptional flexibility. The ∼10-μm films achieve a power factor of 20.9 μW cm −1 K −2 at 380 K and retain >95% of their performance after 20,000 bending cycles at a 2-mm radius. An assembled flexible device delivers an output power of 15.4 μW and a normalized power density of 4.63 μW cm −1 K −2 under a 50 K temperature gradient. Integrated with biodegradable supports, the devices demonstrate recyclability and enable sap flow monitoring. This facile and sustainable approach is generalizable to other systems such as Bi 2 Te 3 and Cu 2 Se.