Fig. 1. Introduction of Ag₂Se thin films with both high thermoelectric performance and flexibility by Te-doping-induced band and orientation engineering.

Unit cells of Ag₂Se before and after Te-doping viewed along the (a) c- and (b) a-axis. Illustrations of fabricating Ag₂Se thin films (c) without and (d) with Te-doping by a vacuum thermal co-evaporation method. The transmission electron microscopy (TEM) image in c indicates the polycrystalline feature of pristine Ag₂Se thin film, and the TEM image in (d) indicates the highly (00l)-orientated feature of Te-doped Ag₂Se thin film. e Comparison of power factor S²σ and dimensionless figure-of-merit ZT values between this work and reported works including printed Ag-Se-based thin film²⁷, Ag₂Se film on nylon membrane²¹, poly(3,4-ethylenedioxythiophene) (PEDOT)/Ag₂Se/CuAgSe composite film¹⁷, printed β-Ag₂Se³³, Ag/Ag₂Se composite film²³, Ag₂Se film on porous nylon membrane²², Ag_1.8Se film⁹, Ag_2.06Se film³⁴, Ag₂Se/Ag/CuAgSe composite film¹⁴, Ag/ Ag₂Se composite film³⁵, Ag-rich Ag₂Se film³⁰, Ag₂Se/Se/polypyrrole (PPy) composite film¹³, Ag₂Se film prepared by pulsed hybrid reactive magnetron sputtering (PHRMS)²⁸, and microstructurally tailored β-Ag₂Se thin film¹⁹ (from left to right). f Measured increased normalized resistance ΔR/R₀ of Te-doped Ag₂Se thin films with and without coating as a function of bending radius. The coating is composed of 90% poly(vinyl laurate) and 10% N-methylpyrrolidone. The insets show the illustration of the spin coating process (left) and the photo of testing the flexibility of the as-fabricated thin film (right).