# Greatly Enhanced Thermoelectric Performance of Flexible Cu2−xS Composite Film on Nylon by Se Doping

## TL;DR

This paper shows how adding selenium improves the thermoelectric performance of flexible Cu2−xS films on nylon, making them more efficient and durable.

## Contribution

The novel contribution is the use of Se doping to enhance the thermoelectric properties and flexibility of Cu2−xS composite films.

## Key findings

- Se doping increases the power factor of Cu2−xS films by ~138% at room temperature.
- The composite film retains ~97.2% of its conductivity after 1500 bending cycles.
- A four-leg TE generator made from the film produces a maximum power of 329.6 nW at a 31.1 K temperature difference.

## Abstract

In this work, flexible Cu2−xS films on nylon membranes are prepared by combining a simple hydrothermal synthesis and vacuum filtration followed by hot pressing. The films consist of Cu2S and Cu1.96S two phases with grain sizes from nano to submicron. Doping Se on the S site not only increases the Cu1.96S content in the Cu2−xS to increase carrier concentration but also modifies electronic structure, thereby greatly improves the electrical properties of the Cu2−xS. Specifically, an optimal composite film with a nominal composition of Cu2−xS0.98Se0.02 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 Cu2−xS 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 Cu2−xS-based films.