Efficient Hybrid White Organic Light-Emitting Devices with a Reduced Efficiency Roll-off Based on a Blue Fluorescent Emitter of Which Charge Carriers Are Ambipolar and Electric-Field Independent

Efficient hybrid white organic light-emitting devices (WOLEDs) were developed using an ambipolar blue fluorescent emitter 2-diphenyl-amino-7-(2,2 ''-diphenylvinyl)-9,9'-spirobifluorene (DPV) which has a relatively electric-field independent hole and electron mobilities. The effects of the triplet energies and charge transporting properties of the blue materials on the performance of the device are discussed. By using such a blue emitter in the device, a broader charge recombination zone is formed, and the energy loss is reduced. WOLEDs with a maximum current efficiency of 2.5.1 cd/A which shift to 19.5 cd/A at 10000 cd/m(2) have been achieved. The power efficiency and the Commission Internationale de l'Eclairage coordinates of the device are 14.1 lm/W and (0.41, 0.41) at 1000 cd/m(2). By attaching a microlens array (MLA) on the backside of the substrate, the outcoupling of electrokuninescence in the forward direction is enhanced, resulting in elevated power efficiency 18.6 lm/W at 1000 cd/m(2).