Optimized Thermoelectric Performance and Plasticity of Ductile Semiconductor Ag₂S_0.5Se_0.5 Via Dual-Phase Engineering

Inorganic semiconductor Ag₂S with excellent plasticity is highly desired in flexible and wearable thermoelectrics. However, the compromise between plasticity and thermoelectric performance limits the advances in Ag₂S-based thermoelectric materials and their devices. Here, a 0.5 mol.% Ag₂Te-alloyed Ag₂S_0.5Se_0.5 bulk material is designed, which has a competitively high near-room-temperature figure of merit of ≈0.43 at 323 K and an ultra-high bending strain of ≈32.5% without cracks. Introducing Ag₂Te can optimize the carrier concentration and mobility of the Ag₂S_0.5Se_0.5 matrix due to its metal-like conducting features, leading to a maximum power factor of ≈6 µW cm⁻¹ K⁻². Simultaneously, Ag₂Te induces Ag-poor amorphous phase boundaries, serving as buffer layers to enhance the overall plasticity. Moreover, such amorphous phase boundaries combined with multiscale phonon scattering sources can significantly suppress the lattice thermal conductivity to ≈0.28 W m⁻¹ K⁻¹ at 323 K, leading to a high figure of merit. This study demonstrates an innovative route to simultaneously boost the thermoelectric performance and plasticity of ductile semiconductors.