Progress in perovskite solar cells based on ZnO nanostructures

The rapid development of organometal halide perovskite solar cells (PSCs) has led to reports of power conversion efficiencies of over 22%. TiO2 is the most commonly used material for the electron transport layer in PSCs. ZnO is an excellent inorganic semiconductor material owing to its large surface area, easy synthesis, direct electron pathways, large variety of synthesizable nanostructures, and low cost of fabrication. It can potentially replace TiO2 as the electron transport layer material in high efficiency perovskite solar cells based on flexible substrates. However, the number of reported high performance PSCs using ZnO nanostructures is still limited. This review focuses on the recent developments in the application of ZnO nanostructures in PSCs. The current state-of-the-art techniques and the open questions in the area of ZnO-based PSCs are also highlighted. Finally, we present a brief analysis on the opportunities and challenges for the use of ZnO in PSCs.