Single-dopant organic white electrophosphorescent diodes with very high efficiency and its reduced current density roll-off

Very high-efficiency organic white light electrophosphorescent diodes =WLEDs have been fabricated using an efficient N∧C∧N-coordinated platinum =II complex phosphor dopant. Their white light emanation is underlain by the simultaneous emission of monomer in blue and excimer in red. By optimizing the phosphor concentration and confining the electron-hole recombination zone to the emitter layer in the devices, the authors achieve their unusually high forward viewing external quantum efficiency =QE up to 15.5±0.2% and 13.0±0.2% photons/electron at low and high drive current densities, corresponding to 40 and 1300 cd/m2, respectively. The current density where QE drops by half of its peak value is greater than three times that of the highest efficiency single-dopant WLEDs reported hitherto. The performance parameters of the presented devices can be further improved by using efficient dopants with the emission spectrum shifted towards blue.