Flexible multilayer inverted polymer light-emitting diodes with a gravure contact printed $Cs2CO3$ electron injection layer

Here we demonstrate high efficiency, flexible inverted polymer light-emitting diodes in which the bottom-contact cesium carbonate electron injection layer is gravure contact printed. The poly(9,9-dioctylfluorene-alt-benzothiadiazole) emissive/electron transport layer, the poly(9,9-dioctylfluorene-alt-$N$-(4-butylphenyl)-diphenylamine) hole transport/electron blocking layer and the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) hole injection layer were sequentially spin-coated from solution using orthogonal solvent formulations with appropriate wetting properties. By switching from indium-tin-oxide (ITO) on glass to ITO on poly(ethylene terephthalate) and using gravure contact printing instead of spin-coating, $Cs2CO3$ smoothness and morphology was optimized, resulting in an approximately fivefold increase in current efficiency and power efficiency at $100cd/m2$⁠.