Thermoelectric Power Factor of BiCuSeO Thin Film Fabricated by Two-Step Reactive Magnetron Co-sputtering Technique

Abstract Bismuth copper oxyselenide (BiCuSeO) is a highly promising p-type thermoelectric (TE) material due to its intrinsically layered structural property. However, conventional thin-film fabrication methods, such as pulsed laser deposition and multi-step selenization, often struggle with industrial scalability, stoichiometric control, and phase purity. In this study, we report the successful fabrication of high-quality BiCuSeO thin films using a scalable, two-step reactive magnetron co-sputtering technique utilizing Bi2Se3 and Cu targets in an Ar/O2 atmosphere. Thin films subjected to vacuum annealing at 350 °C exhibited a highly crystalline tetragonal P4/nmm phase, as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. X-ray photoelectron and Raman spectroscopies validated the expected chemical states and vibrational modes, while surface analysis revealed a dense, uniform, and crack-free morphology optimal for charge transport. TE evaluations up to 250 °C demonstrated a clear transition from n-type conduction in pristine Bi2Se3 to robust p-type transport in the quaternary films. By effectively decoupling the inverse relationship between electrical conductivity and the Seebeck coefficient, the BiCuSeO phase achieved a superior peak power factor of 1.71 mW m–1 K–2 at 250 °C. The power factor is approximately 1.5 folds higher than that of pristine Bi2Se3 and 3 folds higher than that of the intermediate BiSe–Cu films. Our findings establish reactive magnetron co-sputtering as a highly effective, industry-compatible platform for developing next-generation oxychalcogenide thin-film TE devices.