Simple molecular structure design of iridium(III) complexes: Achieving highly efficient non-doped devices with low efficiency roll-off

2016 
Abstract To construct efficient emitters suitable for non-doped devices and deeply understand the relationship between structures and performances, we designed and synthesized two heteroleptic iridium(III) complexes based on 1,2-diphenyl-1 H -benzoimidazole (PBI) ligands whose substituents are varied simply from methyl (complex 2 ) to tert -butyl groups (complex 3 ). The parent complex 1 with non-substituent on PBI ligand has also been presented for a better comparison. Their photophysical, electrochemical and electroluminescent (EL) performances are investigated systematically. Despite their structural modification, all complexes exhibit almost identical emission and excited-state characters, which are rationalized by the quantum-chemical calculations. However, the obvious differences on device performances are found. Non-doped device employing 3 as emitting layer displays the highest EL performance with maximum current efficiency ( η c, max ) of 18.6 cd A −1 and power efficiency ( η p, max ) of 16.2 lm W −1 accompanied by low efficiency roll-off values, which is much higher than those of complexes 1 and 2 . The obtained results herein suggest that introduction of the simple substituent into PBI ligand is an effective and feasible approach to develop highly efficient non-doped phosphors.
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