Sn-Doping-Induced Biphasic Structure Advances Ductile AgS-Based Thermoelectrics.

Due to its inherent ductility, AgS 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 AgSSe to form a biphasic composition comprising (Ag, Sn)SSe as the primary phase and AgSSe 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)SSe 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 K 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 K, 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 under the temperature difference of 30 K, much higher than that of organic-based flexible thermoelectric devices.