White organic light-emitting devices with ultra-high color stability over wide luminance range

A white organic light-emitting device (WOLED) with ultra-high color stability was achieved by introducing an appropriate emitting layer (EML) structure with a spacer, and engineering a blue EML (B-EML) with a selectively doped profile. The advantage of the selectively doped profile over the conventional, uniformly doped profile was to minimize direct exciton formation on dopants with lower exciton energies to suppress electroluminescence (EL) spectrum variations. The recombination zone was found to be located at the spacer/B-EML interface, with a width of 4.5 nm. With the selectively doped profile, the WOLED exhibited ultra-high color stability, with the CIE coordinates shifting from (0.399, 0.483) to (0.395, 0.479) as the luminance increased from 145 to 12,100 cd/m(2) and from (0.401, 0.481) to (0.400, 0.479) as the luminance increased from 1240 to 4850 cd/m(2), the practical luminance range for display and lighting applications. In addition to the small CIE coordinates variation of (-0.004, -0.004) over the broad luminance range of about two orders of magnitude, we also achieved a high device efficiency of 34.1 cd/A, which stayed larger than 30 cd/A below 2000 cd/m(2). (C) 2011 Elsevier B.V. All rights reserved.