Phosphorescent PtAu₂ Complexes with Differently Positioned Carbazole-Acetylide Ligands for Solution-Processed Organic Light-Emitting Diodes with External Quantum Efficiencies of over 20%

The utilization of phosphorescent metal cluster complexes as new types of emitting materials in organic light-emitting diodes (OLEDs) is becoming an alternative and viable approach for achieving high-efficiency electroluminescence. We report herein the design of cationic PtAu₂ cluster complexes with differently positioned 9-phenylcarbazole-acetylides to serve as phosphorescent emitters in OLEDs. The rigid structures of PtAu₂ complexes cause intense phosphorescence with quantum yields of over 85%, which originates from ³[π(phenylcarbazole-acetylide) → π∗(dpmp)] ligand-to-ligand and ³[π(phenylcarbazole-acetylide) → p/s(PtAu₂)] ligand-to-metal charge-transfer triplet excited states. When 8 wt % PtAu₂ is doped to blended host materials of TCTA and OXD-7 (2:1 weight ratio) as light-emitting layers, solution-processed OLEDs give a current efficiency of 78.2 cd A^-1 and an external quantum efficiency (EQE) of 21.5% at a practical luminance of 1029 cd m^-2 with a slow efficiency roll-off upon increasing luminance. This represents the best device performance and the highest efficiency recorded at practical luminance for solution-processed OLEDs.