Power Efficiency Improvement of White Phosphorescent Organic Light Emitting Diode with Thin Double Emitting Layers and Hole Trapping Mechanism
This study is carried out to discuss how to reduce the driving voltage of blue phosphorescent organic light emitting diodes (PHOLEDs) by using a thin double emission layer. A hole transport type host (TCTA) is inserted between the hole transport layer (TAPC) and the emitting layer (EML) constituting a buffer layer between them with the aim of improving charge carrier balance. Furthermore, in this study, we also utilize the interface between double light emitting layers of devices by codoping them with a red phosphorescent dopant [Os(bpftz)2(PPh2Me)2] An Os complex with a high lying highest occupied molecular orbital (HOMO) energy level (trapping holes) is codoped at the interface between emitting layers and an exciton formation zone is expanded to obtain a white PHOLED with high efficiency. From the results, the optimal structure of the white device exhibits a yield of 35 cd A 1, a power efficiency of 22 lm W 1, and CIE coordinates of (0.33,0.38) at a luminance of 1000 cd m 2. Furthermore, the power efficiency can be improved to 30 lm W 1 by attaching the outcoupling enhancement film.