Uniform Phase Permutation of Efficient Ruddlesden-Popper Perovskite Solar Cells via Binary Spacers and Single Crystal Coordination

2D Ruddlesden-Popper perovskites (RPPs) have attracted extensive attention in recent years due to their excellent environmental stability. However, the power conversion efficiency (PCE) of RPP solar cells is much lower than that of 3D perovskite solar cells (PSCs), mainly attributed to their poor carrier transport performance and excessive heterogeneous phases. Herein, the binary spacers (n-butylammonium, BA and benzamidine, PFA) are introduced to regulate the crystallization kinetics and n-value phase distribution to form uniform phase permutation of RPP films. The study then incorporates n = 5 BA2MA4Pb5I16 memory single crystal to achieve ultrafast stepped-type carrier transport from the low n-value phases to the high n-value phases in the high-quality (BA0.75PFA0.25)2MA4Pb5I16 films. These binary spacers and single-crystal-assisted crystallization strategies produce high-quality films, leading to fast carrier extraction and significant nonradiative recombination suppression. The resulting PSC presents a champion PCE of 21.15% with an impressive open circuit voltage (VOC) of 1.26 V, which is the record high efficiency and VOC for low n-value RPP solar cells (n <= 5). By employing the FA derivative PFA cation and BA2MA4Pb5I16 single crystals, the 2D perovskite film exhibits a long carrier lifetime, a low exciton binding energy, and an orderly stepped-type arrangement between different n phases, greatly improving the carrier transport performance. Based on this strategy, an excellent VOC of 1.26 V and a recorded PCE of 21.15% in solar cells are achieved. image