Enhanced photoluminescence quantum yield in metal halide perovskites via trace Ag doping
Self-trapped excitons (STEs) in metal halide perovskites (MHPs) enable broadband emission with large Stokes shifts, but their photoluminescence quantum yields (PLQYs) are constrained by high exciton binding energy and halogen-vacancy-associated non-radiative recombination. Here, trace Ag doping into Cs2NaBiCl6 double perovskites enhances PLQY from 16% to 89%, a factor of 5.6, surpassing previous Cs2NaBiCl6-based emitters. Experimental and theoretical analyses reveal that Ag-initiated covalent interactions reduce exciton binding energy by 0.12 eV via local symmetry breaking, improving photoexcitation. These interactions also passivate Cl vacancy defects, suppressing non-radiative recombination. Consequently, Cs2NaBiCl6:0.7% Ag+ accumulates active STEs, achieving high PLQY. Near-infrared light-emitting diodes assembled with this material demonstrate utility in nondestructive spectral analysis and night vision illumination. This work presents an effective strategy for enhancing photoemission in MHPs with high PLQY for advanced optoelectronic applications.