Sensitized ligand narrow-band phosphorescence for high-efficiency solution-processed OLEDs

Narrow-band emission is crucial for high color purity in panel display. Nevertheless, attaining narrow-band emission is highly challenging because either thermally activated delayed fluorescence or phosphorescence in organic and metal-organic compounds originates primarily from multiple charge transfer transitions featured with broad bandwidths. In this work, a general tactic for achieving highly efficient narrow-band emission is proposed by the sensitization of ligand-centered phosphorescence through substantial intermetallic interaction. Relative to weak phosphorescence in mononuclear Pt(II) precursors, highly efficient ligand-centered phosphorescence is dramatically activated in Pt(II)-Au(I) heteronuclear complexes with quantum yield as high as 81% in solutions and 97% in doping films. High-efficiency solution-processed organic light-emitting diodes (OLEDs) with narrow-band emission are successfully attained with external quantum efficiency (EQE) of 21.6% and a full width at half maxima (FWHM) of 36 nm for yellow electroluminescence and EQE of 20.8% and FWHM of 32 nm for green electroluminescence.