Color tuning of the OLEDs using the Ir complexes of white emission by adjusting the band gap of host materials

Abstract

We have reported white organic light-emitting diodes (WOLEDs) based on single white dopants, Ir(pq)2 (F2-ppy) and Ir(F 2-ppy)2(pq). It was found that the similar phosphorescent lifetime of two ligands led to emit luminescence in two ligands at the same time and the emission wavelength of single white dopants had a broad peak and emit white color without the intermolecular energy transfer. The configuration of fabricated WOLEDs was 4,4′, 4″-tris[2-naphthylphenyl-amino] triphenylamine (2-TNATA) (60 nm)/4, 4′-bis[N-(naphthyl)-/V-phenyl-amino] biphenyl (NPB) (20 nm)/10% Ir complex doped in 4, 4, N, N'-dicarbazolebiphenyl (CBP) (30 nm)/bathocuproine (BCP) (10 nm)/tris-(8-hydroxyquinoline) aluminum (Alq2) (20 nm)/lithium quinolate (Liq) (2 nm)/Al (100 nm), where Ir(pq)2(F2-ppy) and Ir(F2-ppy)2 (pq) were used as white dopant, respectively. However, emission color of fabricated devices was reddish because the energy was not transferred efficiently from the CBP to the F2-ppy ligand due to the small band gap of the CBP. Therefore, we used 1, 4-phenylenesis(triphenylsilane) (UGH2) of large band gap instead of CBP as host material. As a result, high efficient OLED of white emission was fabricated for device with Ir(F2-ppy)2(pq). Furthermore, The luminous efficiency of device with Ir(F2-ppy)2(pq) doped in UGH2 was about 11 cd/A at 0.06 cd/m2.