Analysis of Exciton-Polaron Quenching in Organic Light-Emitting Diodes Based on Exciton and Polaron Distributions

Spontaneous orientation polarization (SOP) in organic molecules is used in organic light-emitting diodes (OLEDs) and induces an internal electric field that facilitates charge injection and transport; however, excessive interfacial charge accumulation can lead to exciton quenching and efficiency loss. In particular, exciton-polaron quenching (EPQ) is significant in devices employing a polar electron-transport layer (ETL), where the SOP-induced field drives a carrier imbalance. Therefore, how the polaron distribution within the emitting layer (EML) changes with the SOP and how it interacts with excitons must be understood to improve device efficiency. In this study, we investigated these relationships by controlling the ETL polarity and the exciton formation position in OLEDs. Displacement current measurements, electroluminescence spectroscopy, and transient electroluminescence analysis revealed that polarons accumulated near the EML/ETL interface when a positively polarized ETL was used. Pronounced exciton quenching occurred only when the exciton recombination zone was located near a polaron-rich region near the EML/ETL interface. These findings demonstrate that the spatial decoupling of the exciton formation region from the polaron accumulation zone effectively suppresses EPQ, providing a universal design strategy for enhancing the efficiency and stability of OLEDs.