Effect and mechanism of encapsulation on aging characteristics of quantum-dot light-emitting diodes

The aging characteristics, e.g., the evolution of efficiency and luminance of quantum-dot light-emitting diodes (QLEDs) are greatly affected by the encapsulation. When encapsulated with ultraviolet curable resin, the efficiency is increased over time, a known phenomenon termed as positive aging which remains one of the unsolved mysteries. By developing a physical model and an analytical model, we identify that the efficiency improvement is mainly attributed to the suppression of hole leakage current that is resulted from the passivation of ZnMgO defects. When further encapsulated with desiccant, the positive aging effect vanishes. To fully take the advantage of positive aging, the desiccant is incorporated after the positive aging process is completed. With the new encapsulation method, the QLED exhibits a high external quantum efficiency of 20.19% and a half lifetime of 1,267 h at an initial luminance of 2,800 cd center dot m(-2), which are improved by 1.4 and 6.0 folds, respectively, making it one of the best performing devices. Our work provides an in-depth and systematic understanding of the mechanism of positive aging and offers a practical encapsulation way for realizing efficient and stable QLEDs.