Passivation of Low-Dimensional Quasi-2D Ruddlesden–Popper Perovskite Solar Cells with Ionic Liquid

Quasi-2D Ruddlesden–Popper (RP) perovskites are more stable but yield a lower efficiency than 3D perovskites. This paper shows that an ionic liquid interlayer can improve the efficiency and stability of low-dimensional 2D PEA 2 MA 4 Pb 5 I 16 ( n = 5) perovskites. Adding ionic liquid BMIMBF 4 at the interface with PEDOT:PSS boosts the power conversion efficiency (PCE) from 9.73 to 10.94%. The ionic liquid passivates the perovskite interface, reducing recombination losses and enhancing the short-circuit current ( J sc ) from 13.42 to 15.92 mA/cm 2 . The devices with the ionic liquid are also more stable. Compared to standard devices, which retain just 75% of their initial PCE after 4000 h, the ionic-liquid-treated devices maintain 92% of their initial PCE when stored inside a glovebox in the dark. The films with the ionic liquid show only marginal degradation after 240 min of continuous exposure at 80 °C in air. This study presents a promising approach to achieve high efficiency and stability in low-dimensional perovskite solar cells.