Highly efficient quantum dot light-emitting diodes with the utilization of an organic emission layer

The relative balance of electron and hole injection is crucial for the achievement of highly efficient quantum dot (QD) light-emitting diodes (QLEDs). Here, an inverted red QLED with the utilization of an organic emitting layer (EML) was obtained, exhibiting peak current efficiency (CE) and external quantum efficiency (EQE) of 25.63 cd/A and 23.20%, respectively. In the proposed device, the organic EML, which is a blend of fac-tris(2-phenylpyridine)iridium (Ir(ppy)3) and 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), works as an exciton harvester to capture the leaked electrons from QD layer and the injected holes from hole transporting layer (HTL), then affording energy transfer from organic EML to the adjacent QD layer so that the emission of QD is enhanced significantly. At the same time, according to the results of hole-only and electron-only devices, the insertion of organic EML promotes the hole injection, and eliminates excess electrons from QD to HTL, thus leading to a better match of hole and electron injection in the device. On the basis of the above benefits, the optimal QLED with a 10 nm organic EML offered ∼ 2-fold improvements of CE and EQE, respectively, relative to the control device. Furthermore, a better operational lifetime of QLEDs based on the organic EML was achieved.