Inkjet printing of silver ink has been widely used to print conductive patterns in flexible electronic devices, and the printed patterns are commonly known to be colorless. We demonstrate that by printing a single type of ordinary silver nanoparticle ink on top of a substrate patterned with polymer nanostructures, the printed silver is molded by the nanostructures and gains robust structural colors. The colors are tunable by varying the geometries of nanostructures, and a broad range of visual colors can be achieved by mixing the red, green, and blue colors displayed from silver dots printed on different nanostructures. Such mechanism can enable full-color, scalable, high-throughput, versatile, and cost-effective printing of structural color images for regular publishing and displaying purposes. In experiments, we implemented a transparent polymer substrate patterned with diffractive nanostructure arrays to print full-color images. The printed images display color-shifting optically variable effects useful for security and authentication applications that demand customizable anticounterfeiting features.

Recently, our group demonstrated an inkjet-based technique to enable high-throughput, versatile and full-colour printing of structural colours on generic pixelated nanostructures, termed as molded ink on nanostructured surfaces. The printed colours are controlled by the area of printed silver on the pixelated red, green and blue polymer nanostructure arrays. This paper investigates the behaviour of jetted silver ink droplets on nanostructured surfaces and the microscale dot patterns implemented during printing process, for achieving accurate and consistent colours in the printed images. The surface wettability and the schemes of filling silver dots inside the subpixels are crucial to the quality of printed images. Several related concepts and definitions are introduced, such as filling ratio, full dots per subpixel (DPSP), number of printable colours, colour leaking and dot merging. In our experiments, we first chemically modified the surface to control the wettability and dot size. From each type of modified surface, various filling schemes were experimented and the printed results were evaluated with comprehensive considerations on the number of printable colours and the negative effects of colour leaking and dot merging. Rational selection of the best filling scheme resulted in a 2-line filling scheme using 20 μm dot spacing and line spacing capable of printing 9261 different colours with 121 pixel per inch display resolution, on low-wettability surface. This study is of vital importance for scaling up the printing technique in industrial applications and provides meaningful insights for inkjet-printing on nanostructures.