Ytterbium β-diketonate complexes for near infra-red organic light-emitting devices

A series of NIR emitting novel ytterbium tris β-diketonate ternary complexes, [Yb(tta)3(L)]·H2O {tta = thenoyltrifluoroacetylacetone and L = dibenzyl sulphoxide (dbso), diphenyl sulphoxide (dpso) and benzoguinamine (bga)} was synthesised, and the photophysical and optoelectronic properties of their films were studied. Nuclear Magnetic Resonance (NMR) analysis indicates that the complexes are seven-coordinate which is a highly asymmetric structure enhancing the radiative transitions. It is an indicative of efficient energy transfer from coordinated ligands to Yb ion. The complexes were doped in Tris(4-carbazoyl-9-ylphenyl)amine (TcTa) organic matrix and the doped samples were used as the emitting layers to fabricate near-infrared organic light emitting diodes (NIR-OLEDs) with the structure: Indium tin oxide/{N,N′-bis(naphtalen-2-yl)-N,N′-bis(phenyl) benzidine} (25 nm)/[Yb-complexes] (10%): TcTa (40 nm)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline) (15 nm)/tris(8-hydroxy-quinolinato) aluminium (10 nm)/LiF (0.5 nm)/Al (120 nm). The complex, [Yb(tta)3(dpso)]·H2O shows the highest electroluminescence (EL) efficiency with maximum irradiance of 22.48 μW/cm2 and current density of 29.5 mA/cm2 at 15 V. It indicates an improved EL performance over the reported devices based on the Yb (III) complexes. In view of electrical characteristics, the current-voltage responses were interpreted by using Mott-Gurney model which allows us to determine the carrier mobility of the complexes.