Impact of bath temperature on the optical, structural, and photoelectrochemical properties of thin films of copper (II) oxide synthesized via electrodeposition method

This study investigates how bath temperature influences the properties of CuO thin films grown on FTO substrates using the electrochemical deposition method. CuO films were fabricated at bath temperatures ranging from 40 degrees C to 80 degrees C under a constant voltage of 0.5 V, using a bath solution containing copper sulfate, tartaric acid, and sodium hydroxide to maintain pH. CuO films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, photocurrent measurements, Mott-Schottky (MS) measurements, and electrochemical impedance spectroscopy (EIS). XRD analysis definitively verifies the presence of a monoclinic structure in the CuO films, exhibiting a dominant orientation along the (200) plane. Raman analysis identified shifts in characteristic CuO vibrational modes at 270 cm-1, 317 cm-1, and 605 cm-1, reflecting changes in crystallographic structure. SEM revealed that particle size varied significantly with bath deposition temperature increased. UV-Vis spectra showed a systematic decrease in the optical bandgap from 1.67 eV to 1.39 eV with increasing temperature, attributed to improved crystallinity and reduced defect states. PL spectra of CuO thin films indicated two distinct photoluminescence maxima at about 465 nm and 517 nm with difference in the intensity for all samples due to changes in defect density and crystallinity. Photocurrent measurements and Mott-Schottky analyses demonstrated that the CuO films behave as p-type semiconductor, and with increasing the bath temperature the acceptor carrier increased. EIS analyses demonstrated improvements in electrochemical properties, with the flat band potential and charge transfer resistance showing significant temperature dependence. The results indicate that deposition temperature critically affects the structural, optical, and electrochemical performance of CuO thin films, providing insights for optimizing their application in optoelectronic devices and energy systems.