Polymer bilayer structure via inkjet printing

We report the formation of a polymer bilayer structure by inkjet printing poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT) from p-xylene solution onto a poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine (TFB) thin film. Despite the compatibility of both polymers with the same organic solvent, a TFB layer under the later-deposited F8BT was directly observed through fluorescence microscopy. Micro-Raman spectroscopy reveals that this bottom layer is ∼10nm thick for a film made by inkjet printing F8BT onto a TFB film of ∼20nm thickness. The bilayer structure leads to enhanced efficiency for light-emitting diodes in comparison with devices made from spin-coated TFB:F8BT blend films.