Theory of Purcell effect enhancement on the operational lifetime of phosphorescent organic light-emitting devices*

The short operational lifetime of blue phosphorescent organic light-emitting devices (PHOLEDs) remains a major challenge in organic electronics. The device degradation processes include triplet-polaron annihilation (TPA) and triplet-triplet annihilation (TTA) that elevate the excited state energy to significantly greater than the intramolecular bond strength thus resulting in molecular fragmentation and exciton quenching. Previous studies show that the Purcell effect enhanced by polaritons increases Ir-based blue PHOLED operational lifetime up to 5.6 X that of conventional devices, matching a power law of m = 1.7-2.4 between Purcell factor (PF) and device lifetime. Here, we propose a model to explain the mechanism of Purcell effect enhancements by linking the transient current-voltage and triplet exciton dynamics to the device degradation process. By combining the exciton profiles and the bimolecular rate coefficients, the model elucidates the power law dependence between PF and device lifetime. From both photonic and electronic perspectives, this model provides a convenient tool for designing stable PHOLEDs for practical applications.