Transient Electroluminescence Delay and Capacitive Charging of the Hole Transport Layer in Quantum Dot Light-Emitting Diodes

The first critical steps of electroluminescence in quantum dot light-emitting diodes are the charge accumulation and transport processes upon the application of a driving voltage. Transient electroluminescence measurements with systematically varying offset voltages are carried out to separate out the capacitive charging effects from charge transport. Capacitive charging around the organic hole transport layer is shown to be the dominant contribution to the delay time between driving voltage application and the onset of electroluminescence. The minimum voltage required for light emission may be dictated by the capacitance of the hole transport layer when the electron injection barrier is small. Further implications of these findings are discussed.