Cuprous to cupric oxide phase transformation in thin films deposited by spray pyrolysis subjected to rapid thermal annealing: effect of film thickness on their properties

Cupric oxide (CuO) thin films were obtained from cuprous oxide (Cu2O) precursor films deposited by spray pyrolysis and subsequently transformed by rapid thermal annealing (RTA) under a controlled atmosphere. Cu2O films with different thicknesses were deposited at a low substrate temperature (280 °C) using diethanolamine as a reducing agent, and then subjected to RTA to induce the Cu2O-to-CuO phase transformation. X-ray diffraction and Raman spectroscopy confirmed that single-phase CuO films were obtained over a wide thickness range under optimized RTA conditions, independently of film thickness. Structural and morphological analyses showed that as thickness increased, crystallinity and density improved. Optical examination revealed a direct band gap of approximately 1.58 eV, a high absorption coefficient (105 cm− 1), and a progressive decrease in the Urbach energy, indicating diminished structural disorder. Electrical experiments confirmed p-type conductivity and a notable reduction in resistivity for thicker CuO films. The results show that the combined spray pyrolysis and RTA method enables rapid production of high-quality CuO thin films with strong potential for solar cell and optoelectronic devices applications. In addition, the functional response of the CuO films to acetone vapor exhibited a clear thickness dependence, with a maximum response at intermediate thicknesses.