Enhanced stability of lead-free double perovskite Cs2AgInxBi1-xCl6 crystals under a high humidity environment by surface capping treatment

Lead-free double perovskite (DP) crystals have received considerable attention for solving the toxicity and instability issues of traditional lead-based perovskites. However, recent studies have focused mainly on the improved optical performance of lead-free DP crystals, with less attention paid to their optical stability under high humidity environments. In this study, ligand-free lead-free DP Cs2AgIn0.93Bi0.07Cl6 nanocrystals (NCs) with excellent optical properties were prepared as research objects, and the larger surface area of the NCs caused them to be rapidly transformed into other phases after contact with water molecules, accompanied by a complete loss of optical properties, which significantly limited their application under high humidity environments. Therefore, surface capping treatment for Cs2AgIn0.93Bi0.07Cl6 NCs with an oleic acid (OA) ligand and polyvinylidene difluoride (PVDF) was proposed to achieve Cs2AgIn0.93Bi0.07Cl6 NCs-OA and Cs2AgIn0.93Bi0.07Cl6/PVDF composite films (CFs) with high water stability. In particular, the optically outstanding Cs2AgIn0.93Bi0.07Cl6/PVDF CFs exhibited stable fluorescence emission even after being stored in water solution for 10 days, and the assembled LED device operated well for a long time under 85% relative humidity (RH), which will bring a new dawn for the commercialization of next-generation lead-free DP optoelectronic devices.