Bifunctional Lewis Base‐Assisted Fabrication of High‐Quality CsPbIBr₂ Perovskite for Efficient and Stable Solar Cells

The inferior phase stability and unsatisfactory crystal quality of inorganic lead halide perovskites have severely impeded the development of inorganic perovskite solar cells. Herein, a bifunctional Lewis base additive, phenylthiourea (PTU), is incorporated into the CsPbIBr 2 precursor to simultaneously enhance the quality and ameliorate the stability of the CsPbIBr 2 perovskite film. The CS group of PTU strongly coordinates with PbBr 2 to form the intermediate phase in the perovskite precursor, which effectively tunes the crystallization process of CsPbIBr 2 and enables the formation of high‐quality CsPbIBr 2 perovskite film with high crystallinity, large crystal grains, and indistinct grain boundaries. Meanwhile, the introduction of PTU additive leads to the sulfur insertion into the interstices of CsPbIBr 2 perovskite lattice, which can stabilize the perovskite phase structure and passivate the undercoordinated Pb 2+ defects. With these benefits, the assembled carbon‐based perovskite solar cell based on PTU‐CsPbIBr 2 perovskite film delivers a high power conversion efficiency of 10.09%. In addition, the unencapsulated device maintains over 80% of its initial efficiency after 800 h of storage under ambient air. These results demonstrate an effective strategy to improve the performance and stability of inorganic perovskite solar cells.