Simplified Hybrid White Organic Light‐Emitting Diodes with a Mixed Fluorescent Blue Emitting Layer for Exciton Managing and Lifetime Improving

The authors demonstrate a simple but effective way to manage the exciton, reduce the efficiency roll‐off, enhance the color stability and improve the lifetime of hybrid white organic light‐emitting diodes simultaneously. Red and green phosphorescent emission layers (EMLs) are connected by a mixed fluorescent blue‐emitting layer (MBL), which is composed of two self‐host fluorescent materials of N,N ′‐di‐1‐naphthalenyl‐ N,N ′‐diphenyl‐[1,1′:4′,1″:4″,1″′‐quaterphenyl]‐4,4′″‐diamine and bis[2‐(2‐hydroxyphenyl)‐pyridine]beryllium. By adjusting the mixture ratio and the thickness of MBL, the intensity of blue and green emissions can be tuned independently. A maximum power efficiency of 41.1 lm W −1 and external quantum efficiency of 15.8% is obtained without any out‐coupling schemes or doping strategies. In addition, the device shows a stable electroluminescence spectrum with Commission International de L'Eclairage coordinates of (0.47, 0.43) in the practical range of 1000–5000 cd m −2 . Furthermore, the fuzzy interfaces between MBL and phosphorescent EMLs, and the wide distribution of charges and excitons, result in four times prolonged device lifetime.