THE EFFECT OF PH AND ANNEALING TEMPERATURE ON CUPROUS OXIDE (CU₂O) THIN FILM DEPOSITED VIA SOL-GEL DIP-COATING METHOD

This study investigates the effect of pH variation on the structural and optical properties of cuprous oxide (Cu₂O) thin films deposited using the sol-gel dip-coating technique. Cuprous oxide is a low-cost, non-toxic, and earth-abundant semiconductor material with promising applications in optoelectronics and photovoltaics. In this work, a 1 M solution of copper(II) acetate was prepared and combined with isopropyl alcohol as solvent. The pH of the solution was adjusted using trioxonitrate(V) acid and sodium hydroxide to pH values of 3, 4, 5, 8, 9, and 11. The films were deposited on glass substrates via dip coating and annealed at 350°C, 400°C, and 450°C. Characterization was carried out using UV-Visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The optical results showed that both pH and annealing temperature strongly influenced the absorption characteristics and bandgap energies of the films. The optical bandgap ranged from 2.86 eV to 4.62 eV, increasing with annealing temperature and being highest at moderate alkaline pH. FTIR analysis confirmed the formation of Cu–O bonds, with reduced organic content at higher annealing temperatures. XRD analysis revealed polycrystalline Cu₂O with dominant (111) orientation. Crystallite size and peak sharpness improved with increasing pH (up to pH 8) and higher annealing temperatures. The study concludes that the combined influence of controlled pH and thermal treatment is critical for tuning the physical properties of Cu₂O thin films. Optimal film quality was achieved at pH values between 5 and 8, especially when annealed at 450°C. These findings demonstrate the importance of pH control in solutionbased synthesis and offer valuable guidance for future applications in thin-film devices.