Largely Enhanced Thermoelectric Power Factor of Flexible Cu_2-xS Film by Doping Mn

Copper-sulfide-based materials have attracted noteworthy attention as thermoelectric materials due to rich elemental reserves, non-toxicity, low thermal conductivity, and adjustable electrical properties. However, research on the flexible thermoelectrics of copper sulfide has not yet been reported. In this work, we developed a facile method to prepare flexible Mn-doped Cu_2-xS films on nylon membranes. First, nano to submicron powders with nominal compositions of Cu_2-xMn_yS (y = 0, 0.01, 0.03, 0.05, 0.07) were synthesized by a hydrothermal method. Then, the powders were vacuum-filtrated on nylon membranes and finally hot-pressed. Phase composition and microstructure analysis revealed that the films contained both Cu₂S and Cu_1.96S, and the size of the grains was ~20-300 nm. By Mn doping, there was an increase in carrier concentration and mobility, and ultimately, the electrical properties of Cu_2-xS were improved. Eventually, the Cu_2-xMn_0.05S film showed a maximum power factor of 113.3 μW m^-1 K^-2 and good flexibility at room temperature. Moreover, an assembled four-leg flexible thermoelectric generator produced a maximum power of 249.48 nW (corresponding power density ~1.23 W m^-2) at a temperature difference of 30.1 K, and had good potential for powering low-power-consumption wearable electronics.