Significant progresses made in the performance of quantum dot (QD) light-emitting diodes have often been associated with basic changes in QD synthesis, particularly with respect to composition and structure. Here we show that the absolute photoluminescence (PL) quantum yield (QY) of QD can reach 88% with a full width of 21 nm at half-maximum (FWHM) when an optimal thickness is chosen for the outer shell of alloyed, graded core/shell QDs. Thicker shell QD-LEDs with a maximum current efficiency of 56.6 cd A−1, an external quantum efficiency of 14.8%, and a brightness of 62 000 cd m−2 are demonstrated. Green emitting QDs of CdSe@ZnS/ZnS with this optimal thickness is also most resistant to photo-stimulated degradation by UV exposure. Only a 7% loss in PL intensity results even after more than 400 hours of exposure to harsh conditions of 85 °C and 85% relative humidity.
