Effect of Charge Carrier Transport Property and Energy Level of Host Material on Phosphorescent White Organic Light-Emitting Device

Phosphorescent white organic light-emitting devices (PhWOLEDs) with a double emitting layer (EML) structure were fabricated. The EMLs were doped with blue and yellow phosphors of iridium(III) bis[4,6-(difluorophenyl)-pyridinato-N,C2'] picolinate and [2-(4-tert-butylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate). Comparing the performance of PhWOLEDs with the host of yellow EML varying from p- to n-type materials, the results showed that the PhWOLED fabricated with 4,7-diphenyl-1,10-phenanthroline (BPhen) as the yellow host had the highest performance, exhibiting a peak current efficiency of 31.7 cd/A, a peak power efficiency of 17.1 lm/W, and the Commission Internationale del'Eclairage coordinates of (0.33, 0.41) at a bias of 9 V. The enhancement was attributed to the improved charge carrier balance, broadened recombination region, and adequate energy levels between the BPhen host and the dopants, which made distinct roles for the dopants to effectively harvest the charge carriers. (C) 2011 The Japan Society of Applied Physics