Highly efficient blue- and white-organic light-emitting diode based on dual recombination zones with a charge control
Seok Jae Lee1, Ja Ryong Koo, Hyun Su Shin
1Department of Information Display, Hongik University, Seoul 121-791, Korea.
Abstract:
Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.
