Bright alloy type-II quantum dots and their application to light-emitting diodes

Type-II quantum dots (QDs) are emerging as a promising candidate for full color light sources owing to their advantages in achieving full color light by tuning the heterostructures. Despite the recent developments in type-II QDs, the choices of proper materials are limited for the composition of a high-quality QD and it still remains a big challenge to enhance the photoluminescence (PL) quantum yields (QYs) of type-II QDs for light-emitting diode (LED) applications. Here, we develop Cd_xZn_1-xS/ZnSe/ZnS type-II QDs with a maximum quantum yield as high as 88.5%. Time-resolved PL results show that the ZnS shell suppresses non-radiative pathways by passivating the surface of Cd_xZn_1-xS/ZnSe, thus leading to a high QY. Moreover, our results demonstrate that the outer ZnS also benefits the charge injection and radiative recombinations of the Cd_xZn_1-xS/ZnSe. The LED based on green Cd_0.2Zn_0.8S/ZnSe/ZnS QDs achieves a current efficiency (CE) of 9.17cdA^-1, an external quantum efficiency (EQE) of 8.78% and a low turn-on voltage of ∼2.3V.