| Popis: |
The intrinsic deterioration in device performance of polymeric single layer OLEDs that were doped with a fluorescent emitter was studied. The specific focus was on the role that thermal aging, at sub-glass transition temperatures of the polymeric layer, has on the phase separation of the active layer. This was accomplished by the rational design of an oxadiazole-containing methylacrylate monomer that was energetically similar to the technologically important electron- transporting small molecule 2-biphenyl-4-yl-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD). This monomer was copolymerized with a carbazole containing hole-transporting monomer 2-(9H-carbazol-9-yl)ethyl 2-methylacrylate (CE) and the resulting copolymer was utilized as the active layer with coumarin 6. With coumarin 6, the devices exhibited a stable mean luminance of ca. 400 cd/m 2 with thermal aging at temperatures ranging from 23 °C to 130 °C, while a comparable poly(9-vinyl-9H-carbazole)/tBu-PBD blend device exhibited a drop from an initial mean luminance of 2500 cd/m 2 to 1.6 cd/m 2 . The reduction in luminance and luminance efficiency for the blend system was attributed to phase separation in the blend. |
