To improve the performance of green light-emitting devices by enhancing hole injection efficiency

For the quantum dots (QDs) based light-emitting diodes (QLEDs), the performance is determined mostly by the carrier injection. Unfortunately, the large band offset between QDs and the hole transport materials makes hole injection efficiency lagging far behind electron injection efficiency. Therefore, it is critical for the QLEDs to improve hole injection efficiency. While, the materials with high valence band maximum (VBM), such as ZnSe, are apt to be oxidated. Therefore, if the QDs could combine the merits of high hole injection efficiency of materials with high VBM and the stability of the materials with large band gap, the QLEDs are expected to be with better performance and more efficient. In this article, the QDs with high VBM intermediate shell and thin ZnS outer shell were employed as the emitting layer to fabricate QLEDs. The highest luminance and maximum external quantum efficiency of 550,000 cd/m2 and 20.06% are achieved, respectively. The fun part is that the highest efficiency of QLEDs can be achieved at high luminance (50,000 cd/m2). More importantly, the device exhibits long half lifetime of over 214,000 h at 100 cd/m2. All these excellent characteristics (high efficiency, luminance and stability) are quite beneficial for the devices aiming at lighting devices.