Revealing Degradation Mechanism of Blue Fluorescent OLEDs Based on Triplet–Triplet Annihilation Upconversion Hosts by Numerically Modeling Exciton Dynamics

So far, the operational lifetime of blue organic light‐emitting diodes (OLEDs) has not yet met the requirements for commercialized display technologies. Furthermore, the intrinsic degradation process of OLEDs adopting triplet–triplet annihilation upconversion (TTA‐UC) materials still remains unclear. In this work, the degradation mechanism of blue fluorescent OLEDs based on TTA‐UC host is systematically investigated by numerically modeling the exciton dynamics in the emitting layer. It is presented that defect formation is the predominant degradation pathway through defect‐exciton quenching and charge transport impediment, as evidenced by transient electroluminescence characteristics and voltage rise. Quantitative analysis demonstrates that the formation rate of defect density during aging obeys a time‐dependent power law. This work reveals the critical impact of defects on device stability and provides a fundamental basis to further enhance the operational lifetime of blue OLEDs.