Understanding of degradation process by voltage-sweep loop method in exciplex host-based phosphorescent organic light-emitting diodes

Abstract

We analyzed the degradation mechanism by deteriorating the exciplex host-based phosphorescent organic light-emitting diodes (PhOLEDs) while repeatedly applying voltages in the range of several nA to mA. To identify the most significant degradation factors represented by bleaching, quenching, and charge imbalance, the degradation process was described from various perspectives by the capacitance (C)-voltage (V) curves (CV), and magneto-electroluminescence (MEL). Comparing the MEL of the non-doped and the doped devices, the bleaching of the dopant was confirmed as degradation progressed. Since the highest occupied molecular orbital (HOMO) of the dopant aligns with that of the hole-transporting layer, the injected holes are easily trapped. As a result, the trap-induced Shockley-Read Hall recombination became dominant. Thus, it was identified that the bleaching of the dopant itself acts as the major degradation factor. © 2023, John Wiley and Sons Inc. All rights reserved.