Unveiling the Aging Process of Organic Light‐Emitting Devices with Langevin and Hole Trap‐Assisted Recombination Exciplex Cohosts

Abstract

AbstractExciplex‐forming cohosts have gained increasing interest due to their promising performances in organic light‐emitting diodes (OLEDs). Such electroluminescent stabilities of the exciplex cohosts depend on their charge‐carrier recombination. But intrinsic relationships between the recombination schemes and the electrical aging process of the exciplex cohosts are yet to be revealed. In this case, exciplex cohosts with two different recombination schemes, namely trap‐assisted recombination (TAR) and trimolecular Langevin recombination (LR), are compared. The LR‐dominated device achieves T90 lifetime (time to 90% of initial luminance) of ≈8600 h at luminance of 1000 cd m−2, which is >2.3‐time lifetime improvement compared with the hole TAR‐dominated ones. The corresponding degradation analyses confirms that hole carriers in hole TAR‐dominated cohosts are captured by phosphorescent guests, accelerating p‐type cohost deterioration through exciton‐polaron decomposition on susceptible aromatic amine groups, which reveals the electrical aging mechanism of exciplex cohost based devices. Moreover, exciton managements of the recombination region further suppress luminous decline and release undesirable exciton–exciton annihilations. The current findings offer an in situ technique to observe exciton and charge carrier aging processes with different recombination mechanisms and provide a general guidance for the development of highly efficient and long‐lifespan exciplex cohost based OLEDs.