Retarding anion exchanges in lead halide perovskite nanocrystals by ligand immobilization

CsPbX₃ (X = Cl^-, Br^-, I^-) perovskite nanocrystals (PNCs) undergo rapid anion exchange, allowing easy bandgap tuning across the entire visible range. However, despite being highly luminescent, the same facile anion exchange process poses significant challenges for their use in tandem optoelectronic devices and white light-emitting diodes (WLEDs). This anion exchange occurs primarily due to the dynamic nature of loosely bound oleylamine ligands on the surface of the PNCs. The mobility of these loosely bound ligands is a key factor in the rapid anion exchange, suggesting that immobilizing these ligands could effectively inhibit the process. To address this, we report a unique approach involving the immobilization of ligands through crosslinking. By crosslinking the ligands on the surface of the PNCs, we can significantly retard the anion exchange process. Our research demonstrates that the anion exchange process can be effectively slowed down by carefully controlling the extent of ligand immobilization. Furthermore, our findings provide the reaction kinetics of anion exchange retardation in CsPbX₃ NCs through ligand immobilization by plasma treatment.