Inkjet printed polystyrene sulfuric acid-doped poly(3,4-ethylenedioxythiophene) (PEDOT) uniform thickness films in confined grooves through decreasing the surface tension of PEDOT inks

A uniform thickness of inkjet printed polystyrene sulfuric acid-doped poly(3,4-ethylenedioxythiophene) (PEDOT) films in confined grooves is very important for their application in inkjet printed polymer light-emitting displays (PLEDs). PEDOT films with a concave or convex cross section are often obtained during inkjet printing. We obtained uniform thickness printed PEDOT films through the low surface tension modification of PEDOT inks using isopropanol (IPA). The thickness fluctuation along the cross section of the PEDOT films was decreased from similar to 30 nm for the convex condition and similar to 20 nm for the concave condition to less than 10 nm through replacing the original PEDOT ink with 10% IPA modified PEDOT ink. The meniscus profile at gelation of the PEDOT inks was used to explain the morphology change of the PEDOT films. IPA modification of PEDOT inks induced lower surface tension and increased the Bond number, which decreased the curvature of the meniscus and improved film uniformity both under concave and convex conditions. IPA modification has no obvious effect on the PEDOT morphology, work function and performance of organic light-emitting diodes.