Nucleation‐Layer Assisted Quasi‐2D Ruddlesden‐Popper Tin Perovskite Solar Cells With High Oxygen Stability

Abstract Tin (Sn)‐based perovskite solar cells (PSCs) are extremely vulnerable to oxygen. Nevertheless, mechanism understanding and fundamental strategies to achieve oxygen‐stable Sn‐based PSCs are lacking. Here a nucleation‐layer assisted (NLA) strategy by forming nucleation layer at the interface of hole transport layer and perovskite to attain highly oxygen‐stable quasi‐2D Ruddlesden‐Popper (RP) Sn‐based PSCs is reported. The formation process of nucleation layer consists of washing off the prepared perovskite film and annealing the residue on the substrate, which produces a new substrate for perovskite film fabrication. Such nucleation layer can transform the subsequently deposited perovskite film from a small‐n‐value dominated wide phase distribution with random crystal orientation into an intermediate‐n‐value dominated narrow phase distribution with vertical crystal orientation. This nucleation layer also improves the perovskite film morphology with highly coadjacent flake‐like grains, leading to reduced grain boundaries and pinholes. The resultant NLA perovskite film shows more efficient carrier transport capability, lower exciton‐binding energy, weakened electron‐phonon coupling, and significantly decreased oxygen diffusion rate upon oxygen exposure. Consequently, a quasi‐2D RP Sn‐based PSC with a champion efficiency of 11.18% is obtained. The unencapsulated device preserves 95% of its initial efficiency after a 2700‐h oxygen aging test, creating a record oxygen stability for Sn‐based PSCs.