Electroluminescence from ionic polymers doped with cationic dyes

Electroluminescent (EL) devices were constructed from thin films of the ionic fluoropolymer Nafion doped with cationic dyes. A 40-50 nm hole injecting layer made from a blend of Nafion and the conducting polymer, poly(ortho-toluidine), was first spincoated onto a transparent, conducting anode. On this substrate, a Nafion solution, doped with the blue laser dye 5-Phenyl-2-(4-pyridyl)oxazole (PPyO), methyl tosylate salt or the yellow emitting LysoSensor dye, was spincoated to form a 40-50 nm emitter layer. Some devices were made with an additional electron transport layer (Nafion or poly(methylmethacrylate) doped with an oxadiazole dye) spincoated on top of the emitter layer. The final layer was a 400 nm aluminum cathode which was vacuum deposited. Other devices were constructed with a hybrid CdS/Nafion hole transport layer and the same PPyO/Nafion emitter layer. Two layer devices (hole transport layer and emitter layer) performed marginally by emitting 4-5 nW of optical power at biases of 10 VDC and current densities of 100 mA/cm{dollar}{bsol}sp2.{dollar} Three layer devices performed substantially better with optical power outputs of 68 nW at 24 VDC biases and current densities of only 4 mA/cm{dollar}{bsol}sp2.{dollar} EL emissions from PPyO containing devices were primarily blue whereas the LysoSensor device emitted mostly in the green region. All devices were easily constructed with commercially available dyes and polymers without the use of a clean room or specialized equipment. Device emission was tuned from blue to green by either substituting another dye or using the CdS hole transport layer. Reliable emitters that were stable in air produced usable light output perhaps suitable for electronic displays or device backlighting.