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.