Investigation of Microcavity Effect on Exciton-Polaron Quenching in Organic Light-Emitting Devices

Despite their widespread use in displays, organic light-emitting devices (OLEDs) can suffer from bimolecular exciton quenching that leads to efficiency roll-off and degradation. The roll-off often reflects exciton-polaron quenching (EPQ) and electron-hole charge imbalance. In prior work, optical microcavities have been applied to accelerate the radiative decay of the exciton and reduce the roll-off due to bimolecular quenching. Direct device-level probing of EPQ is often complicated by competing loss mechanisms and inconsistencies in estimating the polaron density. Here, we systematically probe the impact of an optical microcavity on EPQ in an OLED. By designing OLEDs based on an electron transport layer (ETL) that exhibits spontaneous orientation polarization (SOP), a localized, predictable, and voltage-tunable density of polarons can be generated in the OLED emissive layer. With the emissive layer optically pumped under applied bias, the interaction of optically generated excitons and accumulated polarons can be monitored via the EML photoluminescence intensity. Since accumulation occurs prior to turn-on voltage, other loss pathways can be excluded. We find that in full-λ Fabry-Pérot microcavity OLEDs, a ~10% reduction in quenching is observed when a metallic microcavity is applied. This work will be discussed in the context of how cavity design directly impacts exciton-polaron quenching as well as the impact of coupling strength on the observed behavior.