Defect-Cascades-Induced Photodegradation in InP/ZnSe/ZnS Quantum Dots

By integrating light-induced in situ electron spin resonance (ESR) spectroscopy with density functional theory (DFT) calculations, it is revealed that surface sulfur vacancies (s-V_S) in InP/ZnSe/ZnS quantum dots (QDs) act as critical initiation centers for cascade defect formation, directly compromising photostability and optoelectronic performance of QDs. Blue-light irradiation initiates defect propagation from s-V_S, inducing sequential formation of Zn, S, and Se vacancies that extend toward the ZnSe/ZnS interface. This defect cascade disrupts the entire band alignment, shifting it from type-I to type-II and drastically reducing external quantum efficiency (EQE). By contrast, the targeted passivation of s-V_S sites effectively suppresses defect evolution, thereby enhancing photostability and preserving high EQE under prolonged illumination. These findings establish s-V_S as a principal accelerator of light-induced degradation, underscoring the necessity of surface defect control for developing highly stable and high-performance QDs.