Emitting layer design of a white organic light-emitting device

A white organic light-emitting device (WOLED) based on a phosphorescent blue and green emitter combined with red fluorescent one doped in a single host is presented. In such a device, efficient phosphorescent sensitization (PS) was achieved from the green phosphorescent emitter to the red fluorescent one, which was directly observed from transient electroluminescence. An undoped region was inserted between the green and blue dopant region to stabilize the emission spectra. In this configuration, the main recombination zone was at the blue-emitting region, and the minor one was located at the green one near the undoped region. To avoid carrier trapping, the red fluorescent emitter with a reasonably high concentration (0.5%) was doped away from the minor recombination zone. That WOLED exhibited a longer operation lifetime than the phosphorescent blue/green device, because the PS provided a radiative efficient energy relaxation from the green phosphorescent emitter to the red fluorescent one. (C) 2011 Elsevier B. V. All rights reserved.