Manipulation of transient electroluminescence spike induced by polar Alq3 electron transport layer

The electroluminescence (EL) performance of tris-(8-hydroxyquinolate) aluminum (Alq₃)-based organic light-emitting diodes (OLEDs) and the associated interfacial charge behaviors are comprehensively investigated using transient EL measurements. The transient EL decay reveals that no spike is observed at the end of the positive bias, but an overshoot appears at the onset of reverse bias. The spike at the failing edge is suppressed by the large spontaneous orientation polarization (SOP) of Alq₃, while the overshoot under reverse bias is attributed to the de-trapping and recombination of accumulated interfacial charges. The intensity of overshoot in transient EL decay strongly correlates with the quantity of interfacial charges, which can be manipulated through controlled deposition parameters, such as film thickness, substrate temperature, and deposition rate. To optimize device performance, a critical thickness and substrate temperature should be maintained during polar Alq₃ deposition. These findings highlight the critical role of SOP regulation in maximizing OLED performance.