Pseudohalide Anion Surface Engineering for Mixed Cation Perovskite Nanocrystals

Lead halide perovskite nanocrystals (NCs) have undergone great development in the optoelectrical field. The mixed cation perovskite Cs_1–xFA_xPbI₃ NCs exhibit great potential in photoelectric devices because of their improved structural stability and increased light absorption range. However, achieving homogeneous Cs_1–xFA_xPbI₃ NCs with fewer surface defects remains challenging. In this work, we employ a two-step exchange-passivation method for the preparation of Cs_1–xFA_xPbI₃ NCs and adopt a surface repair strategy based on pseudohalide ions to decrease the surface trap density. Owing to the similar radius of the pseudohalide ions to that of the iodine ions and their strong electronegativity from F atoms, the pseudohalide ions can fill the surface iodine vacancies of the NCs and form Hydron bonds with FA⁺, resulting in improved photoelectric properties and suppressed nonrecombination of carriers. This work highlights the importance of surface chemistry in perovskite NCs and may provide insights for synthesizing high-performance mixed A-site perovskite NCs for future applications.