Efficient and Stable OLEDs with Inverted Device Structure Utilizing Solution‐Processed ZnO‐Based Electron Injection Layer

Abstract To realize low‐cost, efficient, and stable organic light‐emitting diodes (OLEDs) in future large area displays and lighting, the development of suitable solution‐processed functional materials is highly desirable. Herein, a series of efficient and stable OLEDs with an inverted device architecture is reported, employing both a vapor‐deposited phosphorescent aggregate emitter, i.e., Pd(II) 7‐(3‐(pyridine‐2‐yl‐κN)phenoxy‐κC)(benzo‐κC)([c]benzo[4,5]imidazo‐κN)[1,2‐a][1,5]naphthyridine, and a solution‐processed ZnO layer as potential electron injection layer and electron‐transporting layer. One of the optimized OLED devices exhibits its peak external quantum efficiency (EQE) of 23.9% and retains EQEs of 23.5% and 18.7% at 1000 and 10 000 cd m⁻², with a low efficiency roll‐off. Such an efficient device also demonstrates a measured lifetime (LT₉₅) of 98.6 h with an initial brightness of 10 435 cd m⁻² corresponding to an estimated LT₉₅ of 5313 h at 1000 cd m⁻². By depositing a 2 nm Al on the ZnO surface, an estimated LT₉₅ at 1000 cd m⁻² of such a device can be further extended to 73 244 h, making it the longest‐lived OLED reported in the literature domain. This study lays the strong foundation for the future deployment of efficient and stable inverted OLEDs with solution‐processed ZnO layers for a wide range of displays and lighting applications.