A vertically oriented two-dimensional Ruddlesden–Popper phase perovskite passivation layer for efficient and stable inverted perovskite solar cells†
Two-dimensional Ruddlesden–Popper (RP) phase perovskites are gaining increasing attention for passivating the defects of the bulk absorber layer in perovskite solar cells (PSCs). However, owing to their anisotropic structural features, the RP perovskite orientation substantially influences the charge transport efficiency, and thereby the PSC performance. We demonstrate the use of a highly oriented butylammonium RP perovskite as a surface passivation layer with bottom-up growth on the bulk perovskite absorber layer via vacuum deposition. In this process, the crystal formation time directly affects the crystallographic orientation of the passivation layer. By leveraging the passivating properties and controlled crystallinity, the RP perovskite considerably reduces the trap density of bulk perovskite and enhances the charge transport, reaching 21.4% of power conversion efficiency for vacuum-processed PSCs and improving the operational stability. The proposed passivation strategy allows the growth of highly oriented RP phase perovskite passivation layers toward the development of efficient, stable, and scalable PSCs.