Post-treatment by an ionic tetrabutylammonium hexafluorophosphate for improved efficiency and stability of perovskite solar cells

Interface engineering is an effective way to improve efficiency and long-term stability of perovskite solar cells (PSCs). Herein, an ionic compound tetrabutylammonium hexafluorophosphate (TP6) is adopted to passivate surface defects of the perovskite film. It is found that TP6 effectively reduced the surface defects, especially at the grain boundaries where the defects are abundant. Meanwhile, the exposed long alkyl chains and fluorine atoms in the TP6 enhanced the moisture stability of the perovskite film due to its strong hydrophobicity. In addition, the driving force of charge carrier separation and transport is increased by enlarged built-in potential. Consequently, the power conversion efficiency (PCE) of PSCs is significantly improved from 20.59% to 22.41% by increased open-circuit voltage (Voc) and fill factor (FF). The unencapsulated device with TP6 treatment exhibits better stability than the control device, and the PCE retains ~ 80% of its initial PCE after 30 days under 15%–25% relative humidity in storage, while the PCE of the control device declines by more than 50%.