Red phosphorescent OLEDs based on solution-processed small molecular emissive layer

Most of the recent studies are mainly focused on the single-host OLEDs, where the host is only hole-or electron-transporting for inducing the imbalance injection of holes and electrons in the emissive layer, thus it has a detrimental effect on device efficiency. In this work, simple high efficient solution-processed organic light-emitting diodes are developed using red commercial phosphorescent material Ir (pq)₂ (acac). This paper presents our effort on exploring mixed-host devices based on a hole-transporting host 4, 4', 4''-tris (N-carbazolyl)-triphenylamine (TCTA) blended with a bipolar host material 4, 4'-bis-(carbazol-9-yl) biphenyl (CBP). The emitting layer is spin-coated with doping Ir (pq)₂ (acac) as the red emitter. The optimized PhOLEDs doped with 6 wt% of Ir (pq)₂ (acac) shows a maximum luminance efficiency of 16.6 cd/A, it is 1.5 times than that of the device with CBP as the single host.