Lead‐Free Sodium–Indium Double Perovskite Nanocrystals through Doping Silver Cations for Bright Yellow Emission

Lead-free halide perovskite nanocrystals (NCs) have drawn wide attention for solving the problem of lead perovskites toxicity and instability. Herein, we synthesize the direct band gap double perovskites undoped and Ag-doped Cs₂ NaInCl₆ NCs by variable temperature hot injection. The Cs₂ NaInCl₆ NCs have little photoluminescence because of dark self-trapped excitons (STEs). The dark STEs can be converted into bright STEs by doping with Ag⁺ to produce a bright yellow emission, with the highest photoluminescence quantum efficiency of 31.1 %. The dark STEs has been directly detected experimentally by ultrafast transient absorption (TA) techniques. The dynamics mechanism is further studied. In addition, the Ag-doped NCs show better stability than the undoped ones. This result provides a new way to enhance the optical properties of lead-free perovskites NCs for high-performance light emitters.