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.