Recent Advances in Solution-Processed Zinc Oxide Thin Films for Ultraviolet Photodetectors

Zinc oxide (ZnO) is versatile among semiconducting metal oxides with properties such as high photosensitivity, highly tunable specific surface area, nontoxicity, piezoelectricity, almost 85% optical transparency in the visible region, large exciton binding energy, and good biocompatibility. ZnO also shows excellent chemical and thermal stability. This n-type semiconducting material finds several applications in optoelectronic devices such as photodetectors (PDs) due to its wide and direct band gap. Beyond these, the nanostructured ZnO shows unique and tunable properties suitable for flexible and wearable devices. Recently, solution-based deposition techniques have achieved device-quality films at a low cost. This is mainly because the ease of intermixing and controlling the stoichiometry of the precursors is possible with a variety of solution-based synthesis methods, unlike physical deposition methods. This review summarizes the recent developments related to solution-derived ZnO-based thin films for ultraviolet (UV) detector applications. The different strategies used for the fabrication of UV detectors, major improvements achieved with solution-processed ZnO thin films of different morphologies, and their UV photoresponse behavior while in conjugation with other potential materials are discussed in this Review. However, a few shortcomings of the solution-based ZnO thin films, such as low quality and high defect density, remain challenges for the advancement of UV PD application. Thus, this Review concludes with a brief overview of such challenges and an outlook on the emerging research directions toward improving the capabilities of solution-processed ZnO-based UV detectors for various purposes.