Enhanced Photovoltaic Performance and Stability of CsPbI₃ Quantum Dots via Ligand Exchange and Compositional Defect Passivation

Inorganic CsPbI3 perovskite quantum dots (PQDs) possess excellent optical properties, holding broad application prospects in the field of photovoltaics. However, the issues of a complex surface chemical environment and high compositional defect density for CsPbI3 PQDs have severely influenced the performance of CsPbI3 PQD solar cells (PQDSCs). Herein, the sequential treatment strategy based on the ligand exchange of trimethyliodosilane (TMIS) and the compositional defect regulation of formamidinium iodide (FAI) is introduced. Short-chain ligands of TMIS are used to replace the original ligands of CsPbI3 PQDs and robustly anchor to the PQD surface, which guarantees the high stability and efficient charge carrier transport of CsPbI3 PQDs. Furthermore, FAI is introduced by the vacancies and dangling bonds as the driving force on the PQD surface to passivate the defects of Cs and I vacancies while reducing the exciton binding energy and band gap of the CsPbI3 PQDs. Consequently, the power conversion efficiency of PQDSCs is achieved to be 15.07%, which is greatly enhanced compared with that of the control device (12.09%), and only 26% of the initial efficiency is lost after aging under ambient conditions (20–30% RH) for 14 days.