Coherent Ag-rich nanoprecipitates/β-Ag₂Se flexible film with unprecedented thermoelectric performance by liquid-like...

β-Ag₂Se holds a great promise for wearable thermoelectric generators due to its good mechanical properties and biocompatibility. However, optimizing its power factor through alterations in the Ag/Se stoichiometric ratio or incorporating secondary phases has reached the limitation. This work adopts a liquid-like sintering strategy, namely employing the migration and precipitation of silver ions from metallic silver to the silver selenide during the spark plasma sintering process to construct significantly sized and coherent Ag-rich nanoprecipitates within flexible Ag/β-Ag₂Se composite films, thereby achieving an unprecedented power factor exceeding 4000 μWm^-1K^-2 at 303 K. The Ag-rich nanoprecipitates play a crucial role in elevating the carrier concentration, enhancing the density-of-states effective mass, and mitigating carrier scattering caused by phase interfaces and acoustic phonons. The generator containing 5 pieces of optimal films shows an normalized output power density of 10.89 μWcm^-1K^-2 under a temperature difference of 26.0 K. This study strongly suggests that the creation of Ag-rich nanoprecipitates is an effective avenue for improving the electrical performance of β-Ag₂Se-based thermoelectric materials.