Transient electroluminescence of single and multilayer organic light emitting devices

The transient current and electroluminescence response induced by a positive step voltage excitation in both single layer NPB and bi-layer NPB–Alq3 devices were analyzed in detail. The transport of hole and electron in single NPB layer and bi-layer NPB–Alq3 devices was investigated, respectively. The hole mobility was measured to be (1–3)×10−4 cm2 V−1 s−1 in NPB, while the electron mobility in the NPB–Alq3 device was measured to be (4–8)×10−6 cm2 V−1 s−1. The charge transport delay time in each layer of the bi-layer structure was resolved from the transient current characteristics for voltage pulse amplitude near the turn-on voltage of the device. Such unique measurements applied to the organic bi-layer structures revealed the dynamics of the charge carriers, particularly in terms of the field-dependent mobility.