Zinc Oxide Nanoparticles as Electron Transporting Interlayer in Organic Solar Cells

Zinc oxide nanoparticles (ZnO NPs) are one of the well-known electron transporting layers (ETLs) in flexible electronics, especially for organic solar cells (OSCs). This is due to their high mobility and transparency, annealing-free and solution-processable features, large-area fabrication technique compatibility, etc. This review summarizes the synthetic methods of ZnO NPs, aiming to acquire homogeneous, size-controllable, and long-term stable ZnO NPs colloidal dispersion. Moreover, different strategies have been reviewed to modify ZnO NPs in surface traps, work function, dispersity, conductivity, and surface energy. The modifications were generally utilized to realize high-quality ETLs and ultimately improve the performance and stability of the OSC devices. Also, the large-area fabrication techniques on coating or printing ZnO NPs films are discussed. At last, we will conclude and discuss their advantages and shortages for application in OSCs and provide an outlook of ZnO NPs. We hope that this review will highlight the importance of ZnO NPs and inspire researchers to employ ZnO NPs in other electronic devices.