Analysis of Efficiency Roll-Off and Degradation Mechanisms in Nondoped Blue OLEDs Based on Aggregation-Induced Delayed Fluorescence and Achievement of High-Efficiency/Low Roll-Off Blue OLEDs by Insertion Phosphorescence Doping Layer

A comprehensive understanding of the mechanisms of efficiency roll-off (ERO) and degradation is essential to facilitate the development of high-efficiency/low roll-off and stable organic light-emitting diodes (OLEDs) based on aggregation-induced delayed fluorescence (AIDF). In this study, a design strategy for blue OLEDs based on AIDF molecules is proposed to improve efficiency roll-off and operational lifetime. The exciton dynamics analysis reveals that the excess polarons are the origin of the efficiency roll-off, and the polarons also induce the formation of a quencher, which accelerates the degradation of the nondoped blue OLEDs. The incorporation of a 5 nm blue phosphorescence layer within the nondoped AIDF emission layer results in a notable enhancement in the maximum external quantum efficiency (EQE) of the resulting blue OLEDs, from 21 to 28.7% with low-efficiency roll-off, which is only 5% at a luminance of 1000 cd/m2 and the operational lifetime is also enhanced by over 30 times. The phosphorescence layer greatly improves the formation of polarons, thus improving the operation lifetime and efficiency roll-off without sacrificing efficiency. Our results demonstrate the important influence of polarons on device efficiency roll-off and degradation and provide guidance for the design of high-performance and low roll-off blue OLEDs.