Low‐Temperature Modification of ZnO Nanoparticles Film for Electron‐Transport Layers in Perovskite Solar Cells

An electron-transport layer (ETL) that selectively collects photogenerated electrons is an important constituent of halide perovskite solar cells (PSCs). Although TiO2 films are widely used as ETL of PSCs, the processing of TiO2 films with high electron mobility requires high-temperature annealing and TiO2 dissociates the perovskite layer through a photocatalytic reaction. Here, we report an effective surface-modification method of a room-temperature processed ZnO nanoparticles (NPs) layer as an alternative to the TiO2 ETL. A combination of simple UV exposure and nitric acid treatment effectively removes the hydroxyl group and passivates surface defects in ZnO NPs. The surface modification of ZnO NPs increases the power conversion efficiency (PCE) of PSCs to 14 % and decreases the aging of PSCs under light soaking. These results suggest that the surface-modified ZnO film can be a good ETL of PSCs and provide a path toward low-temperature processing of efficient and stable PSCs that are compatible with flexible electronics.