Abstract
Several iridium(III) complexes have been synthesized and their luminescent properties have been studied. We demonstrate very high-efficiency red phosphorescence from a multi-layer organic light-emitting diode formed by vacumn deposition. Highly efficient red (hex>10 %) to pure red (hex>5 %) emission has been demonstrated by the Iridium(III) complexes. The Commission Internationale de I’Eclairage chromaticity coordinates (x,y) for the best red emission from the complexes are (0.66, 0.33).When they were doped into a wide-gap (4,4-N,N’-dicarbazole-biphenyl) host displays a peak external quantum efficiency of 15.4 % and current efficiency of 22.3 cd/A at a brightness of 3450 cd/m2 and a current density of 13.1 mA/cm2. A peak power efficiency of 8.4 lm/W was measured at 1475 cd/m2 and 5 mA/cm2. Novel Ir complexes comprising of Quinoxaline and Pyrazine ligands have been developed through simple synthesis procedure. Emission wavelength could be tuned by controlling the conjugation length of the ligands and different ancillary ligands because the emission originates from triplet metal-to-ligand-charge-transfer excited state. OLEDs based on these materials display orange to infrared electrophosphorescence with low turn-on voltages (~ 4 V), maximum luminance approaching 70000 cd /m2 and efficiency up to 22.3 cd /A. The iridium complexes have two cyclometalated (C^N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C^N2Ir(LX). The C^N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all â-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. Bis-cyclometallated iridium complexes containing benzoimidazole- and thiazole-based ligands can be fabricated into green, yellow, and red-emitting devices of high performance. The Ir complexes trap both electrons and holes, which facilitates the direct recombination of holes and electrons on the complex sites. These results suggest that Bis-cyclometallated iridium complexes are an effective material for producing efficient phosphorescent devices by vacumn deposition.