Enhancing air-stability and reproducibility of lead-free formamidinium-based tin perovskite solar cell by chlorine doping

Organometal halide perovskite solar cells (PeSCs) with efficiency over 25% and high stability have been reported, however, lead (Pb)-free PeSCs should be developed for the commercialization due to the toxicity of Pb. Among the candidates to replace Pb, tin (Sn) based PeSCs are leading for their low band gap and high efficiency compared to other metal candidates. In the research for Sn-based PeSCs, Sn oxidation is a critical issue to influence on both of the efficiency and stability. Here, we present a simple Cl‾-doping method to increase the resistance to oxidation in Sn-based PeSCs. Cl‾-doped perovskite film had large grains and highly-oriented crystals; these traits increased the electron and hole mobility and reduced the density of trap states in the perovskite film. Cl‾ became located at surface defects, and thereby prevented Sn oxidation. Cl‾ doping yielded PeSCs that had efficiency as high as 7.14%, with high reproducibility and stability under ambient conditions.