Nonuniform Degradation in the Efficiency of Organic Light-Emitting Diodes

Despite the widespread adoption of organic light-emitting diodes (OLEDs) in displays, the intricate mechanisms governing their degradation and limited lifetimes remain elusive, impeding their progress for innovative applications. In this work, we present a distinctive degradation phenomenon in OLEDs termed "nonuniform external quantum efficiency (EQE) degradation". After operating at a specific current density (J0), OLEDs exhibit a decline in overall EQE across all current densities (J), with EQE at lower J degrading more rapidly than at J0, while EQE at higher J experiences only marginal degradation. This nonuniform EQE degradation, particularly pronounced at lower current densities, significantly impacts the high dynamic range (HDR) imaging, which is crucial for accurately rendering dark colors at very low luminance levels in OLED displays. Our investigation into the root cause of nonuniform EQE degradation, using blue phosphorescent OLEDs, reveals the pivotal role of charge trapping by degradation-induced defects, with the impact varying significantly with current density. This finding allows for the improvement of nonuniform EQE degradation by judiciously modifying charge transport and trapping properties, albeit with a slight compromise in the initial OLED performance. Our findings underscore the importance of comprehending and mitigating nonuniform EQE degradation to unlock the full potential of HDR imaging in OLED displays, offering insights for the design of optimal device architectures and materials combinations.