Cationic nitrogen-doped graphene coated silver as low-work function electrode for inverted perovskite solar cells

Abstract

Interfacial layers (ILs) located between the cathode and electron transport layer (ETL) in inverted perovskite solar cells are commonly required to achieve high-performance devices. Therefore, it is essential to develop excellent IL materials to improve efficiency and stability. This paper introduces the graphene-based IL material, namely cationic nitrogen-doped graphene (CNG), and evaluates its performance on a methylammonium lead iodide (MAPbI3)-type inverted perovskite solar cells. The device with a CNG IL achieved a power conversion efficiency of 13.5%, which is higher than a state-of-the-art reference using bathocuproine IL. Mechanistic studies demonstrated that the CNG IL can (1) efficiently collect electrons from the lowest unoccupied molecular orbital of ETL by lowering the work function of the silver cathode, (2) improve the conductivity of the silver electrode for better electron transfer, and (3) smooth out the interface contact between ETL and cathode to reduce defects in the device. As a result, the CNG IL enhanced the inverted perovskite solar cells performance by simultaneously increasing the open-circuit voltage, short-circuit current density, and fill factor. Moreover, the unencapsulated CNG IL-applied device demonstrated good long-term stability, with 96% efficiency retained over 1000 h in nitrogen atmosphere at room temperature.