New homoleptic iridium complexes with C∧NN type ligand for high efficiency orange and single emissive-layer white OLEDs

Abstract

In this study, we developed two new strong orange-emission and thermally stable iridium complexes, IrCzPPya {tris[9-(6-phenylpyridazin-3-yl)-9H-carbazole]iridium(III)} and IrNPPya [tris(N,N,6-triphenylpyridazin-3-amine)iridium(III)] by introducing a hole transporting moiety to the C^∧NN type ligand, i.e. carbazole and diphenylamine. Based on experimental results plus quantum chemistry calculations, the link between molecular structures and material properties was demonstrated. Using IrNPPya as the dopant emitter, the organic light-emitting device (OLED) showed extremely high efficiency of 70.8 cd A⁻¹ (75.4 lm W⁻¹, 30.8%) with wavelength up to 560 nm. More importantly, the efficiency was still as high as 63.3 cd A⁻¹ (43.5 lm W⁻¹, 21.8%) at a brightness of 1000 cd m⁻², showing very low efficiency roll-off. By combining IrNPPya with the blue emitter FIrpic [bis(4,6-difluorophenyl-pyridinato-N,C2′)(picolinate)iridium(III)], a single emissive-layer white OLED (WOLED) with high efficiency and good Commission Internationale de l'Eclairage (CIE) coordinates was successfully constructed. The device achieved maximum efficiencies of 55.9 lm W⁻¹, 49.9 cd A⁻¹, and 23.9% with CIE coordinates of (0.33, 046), which are among the best with similar CIE coordinates. The strategies for obtaining high efficiency WOLED with simple three organic layers were highlighted.