Sky-blue phosphorescent organic light-emitting diodes with dibenzo-24-crown-8 substituted iridium(III) complexes as the dopants

Abstract

We report several sky-blue phosphorescent organic light-emitting diodes (PhOLEDs) fabricated by spin-coating technique, using dibenzo-24-crown-8 unit-based iridium complexes (B1, B2 and B3) as the dopants and poly(N-vinylcarbazole) (PVK) as the polymer host. Among these, the single emissive layer PhOLEDs from B3 exhibited the best electroluminescent performances with a maximum luminous efficiency (LEmax) of 10.7 cd A−1 at a current density of 4.6 mA cm−2 and a maximum brightness (Lmax) of 4604 cd m−2. Compared to B1 and B3, the devices with B2 as dopant displayed much lower device's performances (LEmax = 4.2 cd A−1 and Lmax = 1433 cd m−2) as the presence of p-terphenyl unit in the auxiliary ligand of B2, the triplet energy level of which is slightly less than that of iridium (III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic). This present work demonstrates that the triplet energy level of the cyclometalated and/or auxiliary ligands of the iridium complexes should be considered to design novel electrophosphorescent materials for highly efficient PhOLEDs.