Incorporation of quaternary ammonium salts containing different counterions to improve the performance of inverted perovskite solar cells

In this research, three quaternary ammonium salts containing different counterions, including tetrabutylammonium bromide (TBABr), tetrabutylammonium tetrafluoroborate (TBABF₄), and tetrabutylammonium hexafluorophosphate (TBAPF₆), were incorporated into [6,6]-phenyl-C₆₁butyric acid methyl ester (PCBM) as electron transporting layer (ETL). These salts-doped PCBM films revealed higher electron mobility and Fermi levels compared with the un-doped one. Better charge transfer at the interface between perovskite and salts-doped PCBM was also obtained from PL quenching experiments. Inverted perovskite solar cells with the configuration of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM + salts/Ag were fabricated, and the J_SCand FF of devices were significantly enhanced using salts-doped PCBM as ETL. The best device based on TBABF₄-doped PCBM delivered a power conversion efficiency (PCE) up to 13.41%, which was superior to the one with undoped PCBM layer (PCE = 8.77%).