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

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-kappa N)phenoxy-kappa C)(benzo-kappa C)([c]benzo[4,5]imidazo-kappa N)[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.