Solid-State Ligand-Capped Metal Oxide Electron-Transporting Layer for Efficient and Stable Fullerene-Free Perovskite Solar Cells

Although perovskite solar cells (PSCs) can be prepared with excellent optoelectronic properties and solution processability, the common use of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) as the electron-transporting layer (ETL), with its high cost and low stability, has hindered their commercialization. Metal oxides are inexpensive and highly chemically stable, making them potential alternatives to PCBM as ETLs, but requisite polar host solvents and high-temperature treatment limit the possibility of their direct deposition on perovskite layers. Herein, Ta-doped SnO2 nanoparticles (NPs) are dispersed in a nonpolar solvent and they are also directly deposited to form a Ta-SnO2 layer on a perovskite film. Then, room-temperature solid-state ligand exchange is applied to remove insulating molecules from the Ta-SnO2 surface and thereby, enhance the band alignment between the Ta-SnO2 layer and the Ag electrode. The highest power conversion efficiency of a PSC fabricated with Ta-SnO2 as the ETL is 15.48%. In addition, the stability of the SnO2-based devices toward damp heat and light soaking is superior to that of corresponding PCBM-based PSCs. Therefore, this effective strategy for incorporating metal oxides as ETLs appears to be an inexpensive method for manufacturing highly efficient PSCs with long-term stability.