Electrodeposition Process for Optimizing Cu₂Se Films with Controlled Surface Morphology and Structural Properties

Thick copper selenide (Cu₂Se) films were synthesized potentiostatically in acidic aqueous solutions, demonstrating a controlled and scalable pathway for fabricating high-performance microdevices. The study systematically examined the influence of solution composition and pH on film morphology, revealing that pH is critical in achieving compact, nonporous, and smooth-surfaced films. For the first time, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed the deposition of up to 12.5 μm-thick Cu₂Se films with an impressively low average surface roughness of 130 nm in a solution with a pH value less than 1.5, a significant improvement over previously reported values in the literature. With higher pH values exceeding 1.5, the experimental data indicated increased surface roughness and reduced current efficiency. Electrochemical deposition was explored within a potential window of +0.1 to -0.6 V vs Ag/AgCl (sat, KCl), where more positive potentials favored the formation of Cu₃Se₂ while Cu₂Se was stabilized at more negative potentials. For potentials below -0.37 V, the films were loosely attached to the substrate. X-ray diffraction (XRD) confirmed the polycrystalline nature of the films, with an average crystal size of 18.4 nm, and no detection of elemental Cu or Se at potentials below -1.3 V.