Self-Doping Enables Flexible Ag2Se Bulks for Room-Temperature Thermoelectric Generators and Coolers

Abstract

Achieving both deformability and high efficiency in thermoelectric materials (TEs) remains challenging, as most high-performance TEs are inherently brittle and rely on toxic tellurium. We demonstrate that off-stoichiometry in silver chalcogenides intrinsically tailors both transport and mechanical properties, enabling enhanced and bendable TEs without extrinsic doping. Adjusting the Ag-Se stoichiometry to yield Ag₂Se_1.04 (SeAg₂Se) and Ag_2.02Se (AgAg₂Se) reveals a strong correlation among defect chemistry, structural stability, and mechanical adaptability. Notably, SeAg₂Se sustains a compressive strain of up to 15% before fracture, underscoring its exceptional bendability. This ductile behavior originates from nanoscale Se inclusions that serve as internal stress relievers and phonon scatterers, leading to an ultralow lattice thermal conductivity of 0.3 W m^-1 K^-1 (480 K) and an enhanced zT of 0.7, indicative a soft yet efficient thermoelectrics. The SeAg₂Se single-leg outperforms its AgAg₂Se counterpart, underscoring its potential as a tellurium-free thermoelectric generator (TEG). In addition, SeAg₂Se demonstrates excellent cooling capability, achieving a maximum temperature difference of 49.1 K, comparable to that of commercial Bi₂Te₃. Intrinsic stoichiometric control provides a sustainable design strategy, where self-doping bridges mechanical toughness and thermoelectric efficiency, paving the way for durable, tellurium-free energy devices.