Stable and High‐Efficiency Perovskite Solar Cells Using Effective Additive Ytterbium Fluoride

Abstract With better light utilization, larger tolerance factor, and higher power conversion efficiency (PCE), the HC(NH₂)₂⁺(FA)‐based perovskite is proven superior to the popular CH₃NH₃⁺ (MA)‐ and Cs‐based halide perovskites in solar cell applications. Unfortunately, limited by intrinsic defects within the FA‐based perovskite films, the perovskite films can be easily transformed into a yellow δ‐phase at room temperature in the fabrication process, a troublesome challenge for its further development. Here, ytterbium fluoride (YbF₃) is introduced into the perovskite precursor for three objectives. First of all, the partial substitution of Yb³⁺ for Pb²⁺ in the perovskite lattice increases the tolerance factor of the perovskite lattice and facilitates the formation of the α phase. Second, YbF₃ and DMSO in the solvent form a Lewis acid complex YbF₃·DMSO, which can passivate the perovskite film, reduce defects, and improve device stability. Consequently, the YbF₃ modified Perovskite solar cell exhibits a champion conversion efficiency of 24.53% and still maintains 90% of its initial efficiency after 60 days of air exposure under 30% relative humidity.