Ultrahigh Seebeck Coefficient and Power Factor in Low‐Temperature Fused Ag ₂ Se Films via Superionic‐Driven Plastic Deformation

Thermoelectric technologies enable the direct solid-state conversion of heat into electricity, but performance improvement is challenging due to the strong interdependences among parameters. Here, the grain boundary-based energy filtering effect is explored to selectively scatter the low-energy carriers and thus enhance the Seebeck coefficient without degrading other properties. A superionic-induced fluid-like plastic deformation mechanism is utilized to fabricate dense and flexible Ag₂Se films at a very low temperature (≈150 °C), which not only effectively sinters nanoparticles, but is also sufficiently low to maintain a high density of effective grain boundaries by suppressing excess fusing. The success of this low-temperature fusion process is attributed to the existence of excess Ag atoms, which serve as fusing agents to enhance the plastic deformation and thus facilitate the formation of closely contacted grains. As a result, the grain boundaries between those close-contacted grains boost the energy filtering effect while maintain the high electric conductivity, and therefore the obtained Ag₂Se films achieve an outstanding Seebeck coefficient of -215 µV K^-1 and a high power factor of 2500 µW m^-1 K^-2 at room temperature, representing a significant advancement in room temperature thermoelectric materials.