White organic light-emitting diodes with single active layer using a solution process based on a co-host emitter system

A two-color white organic light-emitting diode (WOLED) with a co-host system in solution process method was demonstrated. The device configuration was ITO/PEDOT:PSS (40 nm)/emitting layer (50 nm)/TPBi (20 nm)/LiF (1 nm)/Al. The emitting layer consisted of TAT, (α- or β -) NPB, DPAVBi (blue dopant), and Rubrene (yellow dopant). The device using α -NPB or β -NPB showed a white color of CIE (0.29, 0.40) and (0.28, 0.39). The device using the α -NPB co-host showed a luminance efficiency of 3.39 cd/A, which is 21% higher than β -NPB (2.80 cd/A). Power efficiency was increased by 16% in α -NPB (2.34 lm/W) compared to β -NPB (2.02 lm/W). The Co-host emitter system of HTL and single blue emitter using a solution process for WOLED was shown before, but the HTL role was not understood clearly. From this study, the WOLED device efficiency can be attributed to the HTL's energy transfer property in the emitter mixing system.