Zinc Oxide Nanostructures in Photovoltaics: Recent Progress, Technical Challenges and Perspectives

Zinc oxide (ZnO), an n-type inorganic semiconductor, and its nanostructures are versatile and multipurpose materials that exhibit excellent electronic and optoelectronic properties, such as a wide bandgap, superior electron mobility, strong photocatalytic activity, and higher thermal, chemical, and mechanical stability. In nanostructured form, ZnO demonstrates distinct size-dependent characteristics, including enhanced surface area, high optical absorption, tunable electrical and optical properties, tunable surface morphology (nanorods, nanosheets, nanowires, etc.), and quantum confinement effects. Due to its inherent characteristics, ZnO is widely utilized in numerous fields, such as photocatalysis, light-emitting diodes (LEDs), sensing technologies, and most notably solar cell applications. The facile physical mixing and blending of ZnO with various organic semiconductors offer easy fabrication of hybrid organic-inorganic heterojunctions and emerging solar cell technologies. Due to higher charge transport, compatibility with variety of materials, simple low-cost synthesis, and environmental friendliness, ZnO nanostructures have been used to enhance the photovoltaic performance as an electron transport layer and photoactive absorber layer in different solar cell architectures such as perovskite solar cells, heterojunction solar cells, quantum dots sensitized, and dye-sensitized solar cells. We aim this review to cover the potential use of ZnO nanostructures in various types of solar cells, the progress, bottlenecks, and applications in emerging solar cell technologies.