Unlocking High-Efficiency Narrow-Band Blue Emission: GaS Interlayer Design in Eco-Friendly CuGaS ₂ Quantum Dots as a Superior Alternative

Nontoxic CuGaS 2 (CGS) quantum dots (QDs) are promising for next-generation displays due to their unique optical properties. However, their wide photoluminescence (PL) full width at half-maximum (FWHM), arising from intraband defect-state-mediated radiative recombination, hinders compliance with the narrow bandwidth requirements for ultrahigh-definition displays. Herein, we introduce a Ga 2 S 3 (GaS) interlayer strategy via a hot-injection method to mitigate lattice mismatch and interface strains between the CGS core and the ZnS shell. Precisely controlling the GaS shell thickness further promotes structural ordering and suppresses sulfur vacancies (V S ), thereby reducing nonradiative recombination and enhancing near-band-edge emission. Under optimized conditions, the as-prepared CGS/GaS/ZnS QDs exhibit narrow-band blue emission with a PL quantum yield (QY) of 44% and an FWHM of 24 nm, which is the narrowest value reported to date for Cu-based QDs. As integrated into solid-state light-emitting diode (LED) devices, the QDs yield narrow emission under various operating currents and demonstrate excellent operational stability. These findings highlight the critical role of multishell structures in controlling the defect states and lattice strain in CGS-based QDs, offering a design strategy for next-generation display materials demanding high color purity.