Highly Efficient Light-Emitting Electrochemical Cells (LECs) from Host-Guest Cationic Iridium(III) Complexes

Five charged iridium(III) complexes with a different number and position of methyl group; [Ir(phen)(ppy)(2)]PF6 (1), [Ir(4-phen)(PPY)(2)PF6 (2), [Ir(2,9-phen)(PPY)(2)]PF6 (3), [Ir(4,7-phen)(ppy)(2)PF6 (4) and [Ir(4,5,6,7phen)(ppy)(2)]PF6(5) were synthesized and characterized by NMR, IR, UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. The host-guest light-emitting electrochemical cells (LECs) based on ITO/PEDOT:PSS/15:PVK (1:4)/Al were investigated, which resulted in a maximum current efficiency at 1.35 cdA(-1) and a brightness at 717 cdm(-2) from 5. The host-guest LECs can be improved by the insertion of the TPBi and LiF layers. We found that the highly efficient electroluminescence device gave the peak current efficiency to 4.49 cdA(-1), the maximum brightness at 1,200 cdm(-2) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.54) from 3.