Codoped Spacer Ratio Effect on Electroluminescence Characteristics of Hybrid White Organic Light-Emitting Diodes for Reduced Efficiency Roll-Off

We demonstrated hybrid white organic light-emitting diodes (HWOLEDs) using 1,4-bis{2-[7-N-diphenyamino-2-(9,9-diethyl-9H-fluoren-2-yl)]vinyl} benzene as the fluorescent blue emitter and iridium(III) bis(2-phenylquinoline) acetylacetonate as the phosphorescent red emitter. We also investigated the codoped spacer ratio (CSR) effects of 4,4',4''-tris(N-carbazolyl)-triphenylamine (TCTA) and 2,2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI) on the electroluminescence characteristics of HWOLEDs. The optimized HWOLED with a CSR of 1:3 (TCTA:TPBI) exhibited a lower efficiency roll-off of 32% than the control device (67%) with a CSR of 1:1 (TCTA:TPBI). The HWOLED also showed a current efficiency of 12.76 cd/A, an external quantum efficiency of 6.95%, and Commission Internationale de I'Eclairage coordinates of (0.38,0.39) at 1000 cd/m2.