White organic light-emitting diodes showing nearly 100% internal quantum efficiency

The authors have demonstrated white organic light-emitting diodes (WOLED) using all phosphorescent emitters for blue, green, and red, such as FCNIrpic, Ir(ppy)3 and Ir(pq)2(acac). Various electron-transporting materials such as Bebq2, BPhen, TAZ, BAlq, and TPBI were also investigated for improving quantum efficiency of phosphorescence of WOLED by fabricating and characterizing white devices using these materials as an electron-transporting layer (ETL). It was found that WOLED with an ETL of TPBI exhibits a peak external quantum efficiency (EQE) of 19.5% and a peak power efficiency of 39.2 lm/W at very low light intensity. The optimized device also shows an EQE of 16.4% at 1000 cd/m2. It was also found that the optimized white device with TPBI shows minimal change with Δ Commission Internationale de I’Eclairage coordinates of ±(0.02, 0.00) from 100 to 10,000 cd/m2. In order to understand the mechanism for achieving nearly 100% IQE with this device structure, various analyses were also executed, such as UV/visible absorbance measurements of FCNIrpic and photoluminance (PL) measurements of mCP, fabrications of hole- and electron-only devices, UV/visible absorbance measurements of Ir(ppy)3 and Ir(pq)2(acac) and PL of FCNIrpic, and surface roughness measurements of various ETL films.