Enhanced photoluminescence quantum yield in metal halide perovskites via trace Ag doping

• • Trace Ag doping (0.7% Ag+) into Cs2NaBiCl6 double perovskites boosts PLQY from 16% to 89%, a 5.6-fold enhancement, exceeding prior Cs2NaBiCl6-based emitters (max 51% PLQY). This enables high-efficiency NIR LEDs for night vision and non-destructive spectral analysis, where low PLQY previously limited signal-to-noise ratios and detection sensitivity. • • Ag doping reduces exciton binding energy by 0.12 eV through local symmetry breaking, facilitating exciton dissociation and enhancing photoexcitation. This reduction is critical for lowering the energy threshold for STE formation, directly improving device turn-on characteristics and reducing non-radiative losses under operational voltages. • • Covalent Ag–Cl interactions passivate Cl vacancy defects, suppressing non-radiative recombination pathways. This defect passivation is essential for maintaining high PLQY under prolonged illumination, addressing a key degradation mechanism that plagues lead-free perovskite emitters in commercial lighting and display applications. • • The optimized Cs2NaBiCl6:0.7% Ag+ composition achieves a PLQY of 89%, demonstrating a viable route for lead-free perovskite emitters with performance metrics competitive with lead-based counterparts. This addresses regulatory and toxicity concerns, enabling deployment in consumer electronics and medical diagnostics where lead-free certification is mandatory.