Highly Emissive and Stable Cs2AgInCl6 Double Perovskite Nanocrystals by Bi3+ Doping and Potassium Bromide Surface Passivation

In this study, a facile approach is used to enhance the broad orange emission efficiency and stability as well as monodispersity of Cs2AgInCl6 nanocrystals (NCs) via doping Bi3+ and surface passivation with potassium bromide. While the pristine Cs2AgInCl6 NCs show an excitonic absorption peak at 280 nm, the doped NCs have an additional absorption peak at 365 nm, which is attributed to direct bismuth s–p transition. Compared to the low photoluminescence (PL) quantum yield (QY) of 0.04% for the pristine Cs2AgInCl6 NCs due to parity forbidden transition, the doped NCs show a PLQY of 5.82%, a significant improvement due to breaking of the parity forbidden transition. The PLQY can be further increased to 8.59% for Cs2AgIn0.9Bi0.1Cl6 when passivated with KBr. This work demonstrates that the combination of doping and surface passivation can substantially improve the PL of the Cs2AgInCl6 double perovskite. A model is proposed to explain the observed enhancement in PL and stability.