Largely enhanced performance of Cu2Se film by doping sulfur for flexible thermoelectric generators

Herein, a facile method to prepare flexible S-doped Cu2Se thermoelectric films on porous nylon membranes is developed. First, S-doped Cu2Se powders with nominal compositions of Cu2Se1-xSx (x = 0, 0.02, 0.04, or 0.06) are synthesized by a hydrothermal method. Then, the as-prepared powders are deposited onto nylon substrates by vacuum-assisted filtration and hot-pressing. By adjusting the amount of S doping, the carrier concentration and mobility of the films are tuned, and the thermoelectric properties of the films are effectively optimized. As a result, the Cu2Se0.96S0.04 film displays a highest power factor of ∼662.2 μW m−1 K−2 at 300 K, representing one of the highest values reported for Cu2Se-based flexible films. The film also exhibits excellent flexibility (after 1500 bending cycles around a 4 mm radius rod, 90.8% of the initial electrical conductivity is retained). Additionally, a six-leg flexible thermoelectric generator is assembled with the Cu2Se0.96S0.04 film and outputs a peak power of 1.89 μW at a temperature difference of 23.1 K. This work presents a new method for preparing cost-effective and high-performance Cu2Se flexible thermoelectric films.