Strain-Activated Shell Phonon Coupling and Defect Passivation for Ultranarrow and Efficient Near-Infrared-Emitting CuInZnSe/ZnS Quantum Dots

Near-infrared-emitting copper-based I-III-VI quantum dots (QDs) hold significant promise for photonics and bioapplications, yet their broad photoluminescence (PL) emission severely limits color purity and device efficiency. Herein, we report a hierarchically staged synthesis that decouples and sequentially suppresses defect- and phonon-induced broadening. Starting with Zn-poor CuInSe 2 QDs via cation exchange, we introduce Zn 2+ alloying to passivate cation vacancies and homogenize composition, forming a defect-minimized core. Subsequent epitaxial overcoating with a thick ZnS shell strongly localizes excitons, evidenced by suppressed thermal quenching and dominant coupling to a higher-order longitudinal optical ( LO ) phonon mode of ZnS ( E LO ≈ 141 meV). This shifts recombination from defect-assisted to near-band-edge emission, yielding CuInZnSe/ZnS QDs with an ultranarrow linewidth of 111 meV, high PL quantum yield of 73%, and minimal Stokes shift of 42 meV at 977 nm. When integrated into luminescent solar concentrators, these QDs enable an optical efficiency of 8.81% and a power conversion efficiency of 2.79%, underscoring their practical utility. Beyond reporting materials, this work provides profound insights into the interplay of exciton confinement and defect engineering, establishing a general and instructive strategy for achieving high color purity in multinary QDs.