Ultra-high-performance Ag2Se-based flexible thermoelectric generator

While flexible thermoelectric materials hold promise for wearable electronics, the low performance of films and the inefficiency of devices fundamentally restrict their practical applications. Herein, we have presented a microstructure engineering strategy to fabricate high-performance Ag2Se films. Via regulation of the grain-growth process, Ag2Se grains with large sizes are obtained, in which the carrier mobility is significantly enhanced to up to ∼1300 cm2 V−1 s−1 at room temperature due to the reduced electron scattering, and low-angle grain boundaries are developed, with the room-temperature lattice thermal conductivity decreasing to 0.26 W m−1 K−1 because of the increased mid-frequency phonon scattering, thus partially decoupling the electrical and thermal properties. Benefiting from this, a high ZT of 1.15 is achieved at 300 K. Using these films, a flexible and wearable thermoelectric generator incorporating 100 pairs of thermoelectric legs was successfully developed. In the generator, a sputtering Ag buffer layer was introduced to reduce the contact resistance and interfacial reaction. As a result, this thermoelectric generator exhibits an ultra-high normalized power density of ∼9.09 μW m−1 K−2, which is also the current record-breaking value among thermoelectric film devices. The superior performance allows the thermoelectric generator to power various portable electronics, including LED lights, wristwatches, and, particularly, smartphones. This work establishes a generalizable framework for developing high-performance and manufacturable thermoelectric materials and devices, narrowing the gap between laboratory breakthroughs and industrial adoption in wearable energy harvesting.