Tandem white organic light emitting diodes consisting of blue and red phosphorescent unit devices connected with a transparent Al:LiF/Mo0_3 connecting layer

摘要

Tandem white organic light emitting diodes (WOLEDs) are fabricated with blue and red unit devices connected by a transparent Al:LiF/molybdenum oxides (MoO_3) connecting layer. The blue and red unit devices have been fabricated with standard structure based on 8 % iridium (III)bis(4,6-(di-fluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) and 8 % bis(l-phenylisoquinolinato-N.C~2 )iridium(acetylacetonate) ((piq)_2Ir(acac)) doped in 4,4'-7WV'-dicarbazolebiphenyl (CBP), respectively. The doping concentration of LiF in the Al:LiF composite layer is 10 % and the Al:LiF layer thickness is varied from 3 nm up to 10 nm to optimize the performance of tandem WOLEDs while the MoO_3 thickness is fixed at 10 nm. We found that electron injection efficiency decreases for thicker Al:LiF layer, resulting lower electroluminescence (EL) efficiency. The maximum brightness and current luminous efficiency for the tandem WOLEDs are about 32,230 cd/m~2 and 18.5 cd/A, respectively, for the Al:LiF (10 %) thickness of 3 nm.