Greatly Enhanced Thermoelectric Performance of Flexible Cu 2-x S Composite Film on Nylon by Se Doping.

In this work, flexible Cu 2-x S films on nylon membranes are prepared by combining a simple hydrothermal synthesis and vacuum filtration followed by hot pressing. The films consist of Cu 2 S and Cu 1.96 S two phases with grain sizes from nano to submicron. Doping Se on the S site not only increases the Cu 1.96 S content in the Cu 2-x S to increase carrier concentration but also modifies electronic structure, thereby greatly improves the electrical properties of the Cu 2-x S. Specifically, an optimal composite film with a nominal composition of Cu 2-x S 0.98 Se 0.02 exhibits a high power factor of ~150.1 μW m -1 K -2 at 300 K, which increases by ~138% compared to that of the pristine Cu 2-x S film. Meanwhile, the composite film shows outstanding flexibility (~97.2% of the original electrical conductivity is maintained after 1500 bending cycles with a bending radius of 4 mm). A four-leg flexible thermoelectric (TE) generator assembled with the optimal film generates a maximum power of 329.6 nW (corresponding power density of 1.70 W m -2 ) at a temperature difference of 31.1 K. This work provides a simple route to the preparation of high TE performance Cu 2-x S-based films.