Nucleation-Layer Assisted Quasi-2D Ruddlesden-Popper Tin Perovskite Solar Cells with High Oxygen Stability

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.