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 ${\mathrm{N}}^{\wedge }{\mathrm{C}}^{\wedge }\mathrm{N}$ -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 $15.5\pm 0.2\%$ and $13.0\pm 0.2\%$ photons/electron at low and high drive current densities, corresponding to 40 and $1300\mathrm{cd}∕{\mathrm{m}}^2$ , 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.