Monodispersed ZnO nanoink and ultra-smooth large-area ZnO films for high performance and stable organic solar cells

Abstract

In the organic solar cells (OSCs), zinc oxide nanoparticles (ZnO NPs) have been widely used to fabricate electron transporting layer (ETL). However, spontaneous aggregation of NPs and film surface defects are two issues that limit the application of ZnO NPs in the printed photovoltaics. To simultaneously solve the two problems, the ZnO nanoinks were modified with a 2-(2-methoxyethoxy) acetic acid (MEA) solution, in which a monodispersed nanoink was obtained, and no aggregation occurred after 18 months of storage at room temperature. Meanwhile, the ZnO:MEA ETL had fewer surface hydroxyl groups defects because of Lewis acid-base interactions. The monodispersibility and passivated surface defects ensured an ultra-smooth ZnO film, leading to an improved device performance, longer lifetime, and higher thickness tolerance. As a result, an efficiency of 15.84% was achieved for the 1 cm2 PM6:Y6 ZnO:MEA ETL-based OSCs, and the T 80 lifetime was also increased to 6600 h. The thickness of ZnO:MEA ETL could be increased to 225 nm with less performance degradation. ZnO:MEA NPs were dispersed well in alcohols with high boiling points, which ensured a high-quality slot-die coated film. The ZnO:MEA ETL also has a unique advantage in flexible organic OSCs, with enhanced bending resistance during 10000 times bending. These properties demonstrated the great potential of ZnO:MEA nanoinks in the printed electronics.