Dopant-dependent pore formation in plastic Ag2Se contributing to ultrahigh thermoelectric performance

Abstract

Porous bulk materials demonstrate a diverse range of functional applications, including catalysis, energy storage, and thermal management. However, the available synthesis methods are not applicable or complex for a variety of materials. In this work, we discovered that minor doping induced a compromise between plasticity and porosity in Ag₂Se bulk materials, enabling the general synthesis of high-performance porous thermoelectric materials. Li/Na/Br doping reduces plasticity, increasing initial pores and suppressing plastic flow to yield grain-refined porous structures. Conversely, Cu/In/Te doping sustains/enhances plasticity, resulting in dense microstructures comparable to undoped Ag₂Se. Moreover, Li doping reduces carrier concentration (n_H) through cation vacancy regulation, demonstrated by density functional theory (DFT) calculations. Benefiting from the reduced electrical thermal conductivity from lowered n_H and diminished lattice thermal conductivity via hierarchical phonon scattering, ultralow thermal conductivity of 0.63 W·m^-1·K^-1 is realized at 300 K for Ag_1.95Li_0.05Se. Combined with maintained high power factors, the Ag_1.95Li_0.05Se achieves an exceptionally high average ZT of 0.93 between 300 and 383 K. Our findings have fundamentally changed the synthesis process for thermoelectric materials, providing a new perspective on the role of doping-induced microstructural modulation and advancing the design of high-performance porous materials.