On the electroluminescence overshoot of quantum-dot light-emitting diodes

The charge-carrier dynamics is a fundamental question in quantum-dot light-emitting diodes (QLEDs), determining the electroluminescence (EL) properties of the devices. By means of a hole-confined QLED design, the distribution and storage/residing of the charge carriers in the devices are deciphered by the transient electroluminescence (TrEL) spectroscopic technology. It is demonstrated that the holes stored in the quantum dots (QDs) are responsible for the EL overshoot during the rising edge of the TrEL response. Moreover, the earlier electroluminescence turn-on behavior is observed due to the holes residing in the hole-confined structure. The hole storage effect should be attributed to the ultralow hole mobility of QD films and large barrier for hole escape from the cores of the QDs. Our findings provide a deep understanding of the charge transport and storage at the most critical interface between QDs and hole-transport layer, where the excitons are formed.