Uncovering synergistic effect of chloride additives for efficient quasi-2D perovskite solar cells

Methylammonium chloride (MACl) and lead chloride (PbCl₂) are commonly used for improving perovskite film quality. However, the rapid release of volatile MACl would lead to low-quality perovskite films with pinholes and defects. Here, we report a strategy of employing MACl&PbCl₂ binary additives together to prepare high-quality quasi-two-dimensional (Q-2D) Ruddlesden–Popper (RP) perovskite films. We found that MAPbCl₃ intermediate phase is formed via a reaction between MACl and PbCl₂, which suppresses the fast volatilization of MACl, resulting in a compact and pinhole-free perovskite film with large grains. Moreover, the trap states are passivated via the incorporation of Cl^– into the Q-2D perovskite crystals along with the addition of PbCl₂, leading to a reduced charge recombination loss and an improved charge extraction. A remarkable power conversion efficiency (PCE) of 18.67% is achieved in such Q-2D RP PSCs, one of the highest PCE values among the low-dimensional RP PSCs with n ≤ 4. The environmental stability of the devices is also significantly enhanced. Our results provide an effective strategy by using chloride based additives for fabricating high-quality low-dimensional RP perovskite films for efficient solar cells.