Solvent dependent behaviour of poly( 9-vinylcarbazole)-based polymer light emitting diodes

Polymeric light emitting diodes with active layer cast from different mixtures of solvents have been fabricated. Poly( 9-vinylcarbazole) has been used as a reliable emissive polymer. Mixtures of toluene and tetrahydrofuran solvents in several proportions are used to process it. A lower turn-on voltage has been found for devices in which the active layer has been spin-coated using more toluene than tetrahydrofuran. The relative intensities of the two principal peaks from the electroluminescence curves are directly correlated with the proportion of solvent used in the fabrication process. Thickness measurements reveal that the proportion of solvents in the mixture is directly correlated to the thickness of the emissive layer. In fact, choosing different concentrations of the polymer in toluene and tetrahydrofuran but assuring equal layer thickness, the same experimental results have been found no matter which solvent is used.