Screen-printed Bi2Se3-modified Ag2Se-based free-standing nanocomposite films for high-performance flexible thermoelectrics

The growing demand for self-powered wearable electronics has spurred significant interest in flexible thermoelectric films for direct conversion from body heat into electricity. However, most thermoelectric films rely on flexible substrates and involve complex fabrication processes, proposing an urgent demand for cost-effective, high-performance, free-standing alternatives. Herein, we report a free-standing Ag2Se-based nanocomposite film modified with Bi2Se3, fabricated via scalable screen-printing followed by co-sintering. By tuning the Bi2Se3 content in the ink, nanocomposite structures primarily composed of Bi-doped Ag2Se or AgBiSe2/Ag2Se were constructed. Theoretical calculations and experimental analyses reveal that Bi doping promotes band convergence and electrical conductivity, while the in-situ formed AgBiSe2 and the heterointerface-induced energy-filtering effect boost the Seebeck coefficient. The film attains a maximum room-temperature power factor of ~ 2000 µW m− 1 K− 2, with an ultralow in-plane thermal conductivity below 0.8 W m− 1 K− 1, attributed to the synergistic effects of residual carbon, multi-dimensional defects, and nano-interfaces. The film achieves a maximum ZT value of 0.8 at room temperature. The excellent crystallinity and carbon acting as a nano-binder endow the outstanding flexibility. A six-leg flexible thermoelectric device delivers a power density of 3.20 mW cm− 2 under a temperature gradient of 37 K, indicating great potential for wearable applications.