Photostable Quantum Dots for Energy‐Efficient Color Conversion: Mapping Irradiance‐Driven Degradation Pathways and Facet‐Protected Structure

Abstract Quantum dots (QDs) are promising for next‐generation optoelectronics, but their limited photostability under continuous illumination hinders broader application. In this study, the irradiance‐dependent photoaging behavior of alloyed ZnCdSeS/ZnS QDs under blue‐light excitation is systematically investigated. By correlating photoluminescence (PL) kinetics with changes in optical absorption, surface chemistry, and crystal structure, two dominant degradation pathways are identified: ligand desorption and surface photooxidation. Under low irradiance, trap states are passivated reversibly. This maintains PL stability and retains the QD crystalline structure. In contrast, irradiance levels exceeding 150 W m − 2 accelerate ligand loss and induce irreversible oxidation of the ZnS shell, particularly at reactive facets such as (111), resulting in surface amorphization and colloidal instability. Kinetic reaction model is developed to quantify transitions between photo‐brightening and photo‐darkening regimes, and a regime‐based degradation map is proposed to guide QD device operation under realistic conditions. Based on these insights, a facet‐engineered QD design with selectively thickened ZnS growth along sensitive crystal planes is introduced. These facet‐protected QDs demonstrate significantly enhanced photostability, exhibiting less than 10% PL intensity loss under high irradiance conditions and maintaining over 99% of their initial intensity under lower irradiance, offering a promising pathway toward durable, energy‐efficient QD‐based light conversion technologies.