Optimization of CuO–TiO2 Thin Films through Nitrogen Annealing for Optoelectronic Applications

Abstract

CuO–TiO2‚ heterostructured thin films are promising materials for photocatalytic, optoelectronic, photovoltaic and energy-conversion applications due to their complementary optical and electrical properties. In the present work, CuO–TiO thin films were fabricated on fluorine-doped tin oxide (FTO) glass substrates using the spin-coating tech- ‚nique at different deposition speeds of 7000, 8000 and 9000 rpm. The prepared films were subjected to nitrogen annealing at 450 °C for 1 h to investigate the influence of nitrogen treatment on their structural, optical and electrical characteristics. Raman and FTIR analyses confirmed the formation of CuO–TiO composite films and revealed mod- ‚ ifications in bonding, crystallinity and defect structure after nitrogen annealing. UV–Visible spectroscopy demonstrated enhanced optical absorption following nitrogen treatment. The optical band gap decreased from 3.00–2.88eV for the unannealed films to 2.43–2.48 eV after nitrogen annealing, indicating improved visible-light absorption.Photoluminescence measurements further indicated modification of defect-related states and reduced electron–hole recombination in the nitrogen-annealed films. Electrical measurements showed nearly linear and symmetric I–V characteristics, confirming ohmic conduction. A significant enhancement in electrical current was observed after nitrogen annealing, with the N–CuO–TiO film prepared at 9000 rpm exhibiting the highest current of approximately ‚0.092 A at 1.2 V. Finally , the results demonstrate that nitrogen annealing is an effective approach for tailoring the optical absorption, defect characteristics and charge-transport properties of CuO–TiO thin films. The optimized films, ‚particularly the 9000 rpm nitrogen-annealed sample, show considerable potential for photocatalytic, photodetector, solar-cell and optoelectronic applications.

Keywords: Thin films; nitrogen annealing; optoelectronic properties