Synthesis and properties of copper doped zinc oxide thin films by sol-gel, spin coating and dipping: A characterization review

Numerous studies on Cu-doped ZnO (CZO) thin film doped as a p-type material have been reported due to its applications in optoelectronic and gas sensing devices. The synthesis and fabrication of CZO thin films by various techniques have been reported, but the sol-gel technique for both spin and dip coating has attracted much attention due to its safety, low cost and simple deposition equipment on a large surface-area. Motivated by the fact that reviews on CZO thin films have not been reported yet, this review summarizes the main chemical processes used in the fabrication of CZO thin films with special focus on the sol-gel synthesis involving several chemical and physical parameters such as solvent, additive, solution stirring and aging time, substrate and coating method which includes both dip and spin coating. It also highlights the various parameters influencing the structural, morphological, electronic, optical, vibrational and magnetic properties of the CZO thin films. For this purpose, a summary of various parameters of CZO thin films, reported in the literature survey of the past ten years (2010-2020), is tabulated and discussed. The influence of Cu doping on the synthesis and properties of CZO thin films is also reviewed. The structural, electronic, optical, magnetic and vibrational properties, as well as the elemental composition and surface morphology of the CZO thin films are also discussed. At the end of this review, an outlook is presented to gain more insights into the combined effects of the method-preparation-dopant combination on the properties of CZO thin films for future potential applications. This review should be a useful benchmark for researchers to explore the various physicochemical properties of CZO, their dependence on the experimental conditions and applications.