Quantitative Correlation of Triplet Exciton Management in Host with the Device Lifetime of Blue Phosphorescent Organic Light‐Emitting Diodes

Abstract The improvement of the device stability of blue phosphorescent organic light‐emitting diodes (PhOLEDs) has proven to be a challenging issue in terms of enhancing the efficiency of blue organic light‐emitting diodes in practical applications. This work comprehensively investigates the exciton dynamics of electroplex hosts and quantitatively correlates the steady‐state triplet excitons in the host with the device lifetime of state‐of‐the‐art blue PhOLEDs. The kinetic processes of electrically generated singlet excitons, triplet excitons, and polarons explored via transient electroluminescence and numerical modeling reveal that the triplet exciton density in the host is governed by reverse intersystem crossing and the triplet–triplet annihilation rates. A degradation modeling that takes into account the simultaneous material degradation due to the triplet excitons in the host and the dopant is newly established. The results indicate that the suppressed host degradation due to the reduction (1.5×) in host triplet excitons leads to enhanced operational stability. The characterization method and the numerical modeling in this work facilitate the determination of the exciton and polaron behavior of the host and allow for predicting the host‐dependent device lifetime of PhOLEDs for specific host materials.