P‐212: Exciton Dynamics and Degradation Mechanism in TADF OLEDs Assessed by Modulated Electroluminescence Spectroscopy

An in‐depth understanding of physical processes in OLEDs is crucial for the design and optimization of high‐efficiency and long lifetime devices. Here we investigate the exciton dynamics of TADF OLEDs by combining advanced measurement techniques with an electrooptical simulation model covering the frequency‐dependent charge and exciton transport coupled with dipole emission. We complement traditional impedance analysis with a novel characterization of the frequency dependent electroluminescence response and demonstrate its sensitivity to extract excitonic key parameters like decay rates and intersystem‐crossing rates from a full OLED stack. Moreover we measure the lifetime of the TADF OLED upon constant current stressing and investigate the role of possible degradation mechanisms based on the full electrooptical simulation. We find that the efficiency roll‐off can be attributed to exciton quenching with trapped electrons, whereas the number of trapping sites increases with increasing stressing time, resulting in a strong reduction in the current efficiency above onset.