Due to their unique characteristics, direct-writing techniques have a large potential in the production of modern, large-area electronic devices. Inkjet printing offers several attractive features, including additive deposition, direct patterning with micrometre resolution, and easy pattern modifications. Yet, a high complexity of the printing process - extending from the jetting concerns to the issues connected with the morphology of dried deposit - has impaired the fabrication of electronic devices using inkjet printing.

We report on the inkjet printing of functional metal-oxide structures for applications in transparent electronics. The structures with the thickness in nanometre range are deposited from solution-based inks, which consist of metal oxide precursors dissolved in a suitable solvent. The printed structures commonly dry in a way that the ring-like deposit forms; the phenomenon known as “coffee stain” effect. [1] A standard approach to improve the uniformity of dried deposits is by combining a solvent and a co-solvent with different boiling points and surface tensions. Consequently, these solvents evaporate with different rates, which leads to variations in the solvent composition in the drying feature. Moreover, the composition variations can lead to the changes in the physical properties, and thus produce a rich variety of complex phenomena observed when the printed features are drying.

We highlight the influence of the ink’s solvent composition, wetting of the substrate, and drying temperature on the morphology of wet and dried structures. These parameters appear to be interrelated in the drying process; well-defined structures with the flat thickness profile can be printed only when all three parameters are optimized. We demonstrate such optimization for inkjet printing of transparent thin-film capacitors composed of tantalum oxide-based dielectric and indium-zinc oxide electrodes. The capacitors were uniform and showed good electrical and optical properties.