Narrowband Pure-Green AgInGaS ₂ Double-Shell Quantum Dots for High-Performance Light-Emitting Diodes

Colloidal AgInGaS2 quantum dots (QDs) with bandgap-tunable green emission have attracted surging interest for next-generation Cd- and Pb-free displays, yet their intrinsically broad emission and poor stability remain critical bottlenecks. Here, AgInGaS2/AgGaS2/ZnS double-shell QDs are synthesized by single-vessel successive epitaxial growth, that delivers narrow-band pure-green emission at 531 nm with full width at half-maximum of 32 nm. Systematic tuning of the inner AgGaS2 thickness to five monolayers suppresses donor–acceptor-pair recombination, raising the band-edge contribution from 8% to 96% and boosting the photoluminescence quantum yield (PL QY) to 54%. Subsequent epitaxial ZnS overcoating preserves the peak position and line width while increasing the PL QY to 70% and prolonging the average lifetime from 116 to 211 ns, concurrently stabilizing the emission so that 91% of the initial intensity is retained after 60 days in ambient air. Femtosecond transient-absorption spectroscopy shows a pronounced slowdown of ground-state bleach recovery, consistent with suppressed nonradiative recombination evidenced by the concurrent PL QY enhancement. Green QD light-emitting diodes fabricated with the double-shell QDs exhibit an external quantum efficiency of 1.05% and a maximum luminance of 1882 cd m–2, outperforming single-shell analogues by 84% and 81%, respectively. These results demonstrate a practical route to narrow-band green emitters that simultaneously achieve high color purity, enhanced stability and improved device performance without relying on toxic heavy metals.