Indium-Doping Advances High-Performance Flexible Ag₂Se Thin Films

Enhancing the thermoelectric performance of Ag₂Se thin films via physical vapor deposition remains challenging. In this study, a precursor doping strategy is introduced to fabricate In-doped Ag₂Se thin films. In substitutional doping at the Ag cation sites increases the charge density distribution of Ag₂Se, improving electrical conductivity, while maintaining a high Seebeck coefficient and relatively low thermal conductivity. This approach yields a competitive room-temperature power factor of ≈26.3 µW cm^-1 K^-2 and a ZT value approaching 1. The films, supported by a polyimide substrate and optimized for thickness, exhibit uniform composition and excellent flexibility, retaining over 90% of their initial electrical conductivity after 500 bending cycles with a 5 mm bending radius. Additionally, a five-leg flexible thermoelectric device constructed from these films achieves a power density of up to 630.6 µW cm^-2 under a temperature difference of 18 K, corresponding to a normalized power density of nearly 2 µW cm^-2 K^-2, highlighting its potential for practical applications.