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

ABSTRACT 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.