Efficient solution-processed yellow/orange phosphorescent OLEDs based on heteroleptic Ir(III) complexes with 2-(9,9-diethylfluorene-2-yl) pyridine main ligand and various ancillary ligands

Efficient solution-processible yellow/orange emissive phosphors are highly required in solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs). With respect to phenyl pyridine (ppy)-type Ir(III) complexes, 2-(9,9-diethylfluoren-2-yl) pyridine (Flpy)-type Ir(III) complexes have huge potential in yellow/orange s-PhOLEDs due to their extended conjugation and excellent solubility in common organic solvents. Herein, a new series of phosphorescent Ir(III) complexes, i. e. Ir(Flpy)(2)pic-NeO, Ir(Flpy-CF3)(2)pic-NeO, Ir(Flpy-CF3)(2)dbm and Ir(Flpy-CF3)(2)acac, based on Flpy main ligand and picolinic N-oxide (pic-NeO), acetylacetone (acac), and dibenzoyl methane (dbm) ancillary ligands are synthesized. The photophysical, electrochemical, and electroluminescent (EL) properties of these phosphorescent Ir(III) complexes are investigated in details. By introducing the CF3 group in Flpy ligand and varying the ancillary ligands, the emission spectra of these phosphorescent complexes are tuned in a large range with EL emission peaks from 544 nm to 588 nm. The s-PhOLEDs employing these phosphors show promising EL performance with maximum external quantum efficiency (EQE) from 15.4% to 23.7% and high power efficiency from 61.9 l m W-1 to 80.4 l m W-1. These highly efficient phosphorescent Ir (III) complexes may serve as ideal chromaticity components in solution-processed full-color displays and lighting devices.