Degradation of organic/organic interfaces in organic light-emitting devices due to polaron-exciton interactions.

We study the stability of common hole transport material/electron transport material (HTM/ETM) interfaces present in typical organic light-emitting devices (OLEDs) under various stress scenarios. We determined that these interfaces degrade rapidly, because of an interaction between HTM positive polarons and HTM singlet excitons. The phenomenon results in a deterioration in conduction across the interface, and contributes to the commonly observed increase in OLED driving voltage with electrical driving time. This interfacial degradation can be slowed if the exciton lifetime becomes shorter. The findings uncover a new degradation mechanism that is interfacial in nature, which affects organic/organic interfaces in OLEDs and contributes to their limited electroluminescence stability, and shed light on approaches for reducing it. Although this study has focused on OLEDs, we can expect the same degradation mechanism to affect organic/organic interfaces in other organic optoelectronic devices where both excitons and polarons are present in high concentrations, such as in organic solar cells or photodetectors.