High thermoelectric performance of Cu2Se-based thin films with adjustable element ratios by pulsed laser deposition

Copper selenide (Cu2Se) is a P-type thermoelectric (TE) semiconductor that is environmentally friendly and has rich crust content and high cost performance–price ratio. Present studies on Cu2Se focus on the high TE performance of the bulks because of the intrinsic low thermal conductivity resulting from the ‘liquid-like’ behavior of Cu ions. Compared with three-dimensional bulks, two-dimensional thin films are more compatible with modern semiconductor technology and have unique advantages in the construction and application of TE micro- and nano-devices. In this study, b-axis–oriented Cu2Se epitaxial thin films were successfully prepared using pulsed laser deposition (PLD) technology. The element ratios (Cu:Se) were adjusted in a small range (2.0:0.899–0.942). Correspondingly, the Cu vacancy concentration was optimized by changing the deposition temperature of the substrate. The in-plane directional power factor of the thin film is as high as ∼20.02 μW/cm K−2 at 580 K and ∼8.44 μW/cm K−2 at room temperature, which are higher than that of Cu2Se bulks. As per theoretical calculation, the estimated zT value of the Cu2Se film with a thickness of 295.0 nm reaches ∼0.58 at 580 K. The relatively high TE performance and good repeatability demonstrate that Cu2Se films have great application potential in solid-state refrigeration and power generation. The PLD preparation and performance control methods involved in this research will promote the development of high-performance Cu2Se films and devices.