Largely Enhanced Thermoelectric Performance of Flexible Ag₂Se Film by Cationic Doping and Dual-Phase Engineering

Recent studies have shown that silver selenide is a promising thermoelectric material at room temperature. Herein, flexible films with a nominal composition of (Ag_1-Cu)₂Se are prepared by a simple and efficient one-pot method combined with vacuum-assisted filtration and hot pressing. The thermoelectric properties of the films are regulated by both cationic doping and a dual-phase strategy via a wet chemical method. As the x increases, not only Cu is doped into the Ag₂Se, but different new phases (CuAgSe and/or CuSe₂) also appear. The (Ag_1-Cu)₂Se film with x = 0.02 composed of Cu-doped Ag₂Se and CuAgSe shows a high PF of ∼2540 μW m^-1 K^-2 (ZT ∼ 0.90) and outstanding flexibility at room temperature. The high thermoelectric properties of the film are due to the effect of Cu doping and the CuAgSe phase, including the increase in electrical conductivity caused by doping, the enhanced phonon scattering at the Ag₂Se/CuAgSe interface, and the interaction between the energy filtering effect and the doping effect. In addition to the high output performance (PD_max = 28.08 W m^-2, ΔT = 32.2 K), the flexible device assembled with the (Ag_0.98Cu_0.02)₂Se film also has potential applications as a temperature sensor.