Sensitized fluorescence in organic light emitting diodes

We have studied the effects of incorporating phosphorescent sensitizers into fluorescent organic-light emitting diode (OLED) devices. In the emissive layer of this system, the host material is co-doped at low concentrations with both a phosphorescent and a fluorescent dye. The purpose of the phosphorescent dopant is to capture both singlet and triplet excitons from the host material and to transfer them into the singlet state of the fluorescent dye. Ideally, recombination of excitons and the emission of light would occur solely on the fluorescent dye. This sensitized fluorescent system can potentially achieve 100% internal quantum efficiency as both triplet and singlet states are being harvested. We have observed an almost two-fold improvement in the quantum efficiency of a sensitized fluorescent system, utilizing rubrene as the fluorescent dye and Ir(ppy)(2)(acac) as the sensitizer, versus a standard rubrene-based host-guest system. By testing various dopant concentrations, the optimal emissive layer composition for this system was determine to be similar to 2 wt.% rubrene and similar to 7 wt.% Ir(ppy)(2)(acac) in a CBP host.