Simultaneous improvement in efficiency and photostability of organic solar cells by modifying the ZnO electron-transport layer with curcumin

As a representative electron transport layer (ETL), zinc oxide (ZnO) has been widely used in inverted organic solar cells (i-OSCs), while its surface defects and intrinsic "light-soaking" issues are yet to be addressed. Herein, we employ a natural antioxidant curcumin (E100) as a modifier for ZnO to simultaneously improve the photovoltaic performance and photostability of i-OSCs. It is found that modifying ZnO with E100 can align the energy levels and optimize its surface morphology, leading to improved charge transport and recombination properties of the OSCs. Meanwhile, using E100 as a modifier can passivate the surface defects of ZnO via the coordination of its strong polar carbonyl groups with Zn2+ ions of ZnO and quench the photo-generated free radicals to prevent the decomposition of the photoactive materials. As a result, the PM6:Y6-based i-OSCs using ZnO/E100 as the ETL exhibit enhanced efficiency and photostability compared to the control device using ZnO as the ETL. Curcumin is exploited as a modifier for ZnO electron-transport layers to simultaneously improve the efficiency and photostability of inverted organic solar cells.