Investigations on the role of alkali to obtain modulated defect concentrations for Cu2O thin films

An economic successive ionic layer adsorption and reaction (SILAR) method has been investigated for depositing thin Cu2O layers on steel. The mole ratios of the Cu+ ions to OH− ions in the alkali bath were varied and the changes in the properties were characterised by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and Ultraviolet–visible spectroscopy techniques. The increase in the binding energy values of the Cu 2p peaks in XPS established that an optimum copper vacancy concentration can be obtained for a Cu+/OH− mole ratio between 1:10 and 1:15; SEM studies confirmed a dense, uniform microstructure for Cu2O thin films coated with these compositions. The strongest absolute peak intensity counts in PL for the peak at 580 nm along with low energy peaks (1.2–1.4 eV) due to Cu vacancy was found to be most prominent for thin film made with Cu+/OH− mole ratio 1:15. The role of alkali concentration has been explained in relation to create a stable Cu2−δO structure with optimum copper vacancy. This is an easy way to modulate surface reactivity of the Cu2O thin layers and the concept can be utilised for large area device integrations for various electrical and mechanical applications.