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

Zinc oxide (ZnO) is versatile amongsemiconducting metal oxideswith properties such as high photosensitivity, highly tunable specificsurface area, nontoxicity, piezoelectricity, almost 85% optical transparencyin the visible region, large exciton binding energy, and good biocompatibility.ZnO also shows excellent chemical and thermal stability. This n-typesemiconducting material finds several applications in optoelectronicdevices such as photodetectors (PDs) due to its wide and direct bandgap. Beyond these, the nanostructured ZnO shows unique and tunableproperties suitable for flexible and wearable devices. Recently, solution-baseddeposition techniques have achieved device-quality films at a lowcost. This is mainly because the ease of intermixing and controllingthe stoichiometry of the precursors is possible with a variety ofsolution-based synthesis methods, unlike physical deposition methods.This review summarizes the recent developments related to solution-derivedZnO-based thin films for ultraviolet (UV) detector applications. Thedifferent strategies used for the fabrication of UV detectors, majorimprovements achieved with solution-processed ZnO thin films of differentmorphologies, and their UV photoresponse behavior while in conjugationwith other potential materials are discussed in this Review. However,a few shortcomings of the solution-based ZnO thin films, such as lowquality and high defect density, remain challenges for the advancementof UV PD application. Thus, this Review concludes with a brief overviewof such challenges and an outlook on the emerging research directionstoward improving the capabilities of solution-processed ZnO-basedUV detectors for various purposes.