Sn‐Doping‐Induced Biphasic Structure Advances Ductile Ag₂S‐Based Thermoelectrics

Due to its inherent ductility, Ag₂S shows promise as a flexible thermoelectric material for harnessing waste heat from diverse sources. However, its thermoelectric performance remains subpar, and existing enhancement strategies often compromise its ductility. In this study, a novel Sn-doping-induced biphasic structuring approach is introduced to synergistically control electron and phonon transport. Specifically, Sn-doping is incorporated into Ag₂S_0.7Se_0.3 to form a biphasic composition comprising (Ag, Sn)₂S_0.7Se_0.3 as the primary phase and Ag₂S_0.7Se_0.3 as the secondary phase. This biphasic configuration achieves a competitive figure-of-merit ZT of 0.42 at 343 K while retaining exceptional ductility, exceeding 90%. The dominant (Ag, Sn)₂S_0.7Se_0.3 phase bolsters the initially low carrier concentration, with interfacial boundaries between the phases effectively mitigating carrier scattering and promoting carrier mobility. Consequently, the optimized power factor reaches 5 µW cm^-1 K^-2 at 343 K. Additionally, the formation of the biphasic structure induces diverse micro/nano defects, suppressing lattice thermal conductivity to a commendable 0.18 W m^-1 K^-1, thereby achieving optimized thermoelectric performance. As a result, a four-leg in-plane flexible thermoelectric device is fabricated, exhibiting a maximum power density of ≈49 µW cm^-2 under the temperature difference of 30 K, much higher than that of organic-based flexible thermoelectric devices.