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

Self-trapped excitons are prevalent in metal halide perovskites (MHPs) characterized by soft lattices and strong exciton-phonon coupling, emitting photons with broadband emission and large Stokes shifts, rendering them particularly well-suited for applications in light-emitting diodes. But their photoluminescence quantum yields (PLQY) are limited by both high exciton binding energy and halogen-vacancy-associated non-radiative recombination. Here, we show that PLQY could be enhanced by a factor of 5.6 from 16% to 89% through doping trace Ag into Cs₂NaBiCl₆ double perovskites, superior to those of previous Cs₂NaBiCl₆-based emitters. Experimental and theoretical studies reveal that trace Ag-initiated covalent interactions could reduce the exciton binding energy by 0.12 eV due to local symmetry breaking, thus improving the photoexcitation process. Also, this covalent interaction could passivate Cl vacancy defects, suppressing non-radiative recombination. Therefore, Cs₂NaBiCl₆: 0.7% Ag⁺ could accumulate active self-trapped excitons to obtain high PLQY. Assembly of near-infrared light-emitting diodes using Cs₂NaBiCl₆: 0.7% Ag⁺ illustrates their valuable applications in nondestructive spectral analysis and night vision illumination. This work shows an effective strategy of improving photoemission of MHPs with high PLQY for advanced optoelectronic applications. (Figure presented.).