A copper ion ink capable of screen printing and intense pulsed-light (IPL) sintering on poly(ethylene terephthalate) (PET) substrates was developed. Using copper nitrate trihydrate as a copper precursor, we prepared this ink with 2butoxyethanol solvent and an ethyl cellulose additive to ensure excellent wettability with PET substrates and screen printability. After screen printing on PET substrates with this transparent ion ink, the printed ink patterns dry quickly at a low temperature of 100 °C, and an excellent electrical resistivity of 5 μΩ•cm was obtained by short IPL sintering of 20 ms. Because of the high boiling point of 2-butoxyethanol used as a solvent, this ink has a very low evaporation rate at room temperature, so it is suitable for screen printing without clogging of the screen mesh. With this ion ink, it was possible to screen-print copper patterns with a line width of 200 μm. We compared screen-printing properties using this copper ion ink with those of silver and copper nanoparticle inks. Nanoparticle inks showed significant spread in the printed patterns during the screen printing, whereas this copper ion ink showed the lowest spread to enable the formation of fine patterns. In addition, it was confirmed that this ion ink had the least damage to the PET substrate during the IPL sintering process compared to other nanoparticle inks. This ink also has a long storage stability over 4 weeks without precipitation or phase separation. The optimal ink composition and process conditions for securing such excellent copper pattern printing characteristics were suggested in this study.

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The role of a self-assembled monolayer obtained by vacuum deposition of 4-aminopyridine (4-AP), a small organic molecule having amine and pyridine groups, as a metal nucleation inducer and adhesion promoter was verified, and the applicability was evaluated. 4-AP deposited to an extremely thin thickness effectively changed the substrate surface properties, increasing the nucleation density of silver (Ag) more than 3 times and eventually forming a more transparent, low-resistance Ag thin film. The optical transmittance of the Ag thin film, which was less than 60% when 4-AP was not applied, could be increased to about 77% by simply applying 4-AP, and the electrical resistance could be lowered from 37 to 14 Ω/square at the same time. Transmittance could be further improved to higher than 90% by depositing an antireflection layer for use as a transparent Ag electrode. It was also verified that 4-AP not only serves as a nucleation inducer but also contributes to improving interfacial adhesion. The Ag transparent electrode using 4-AP provided the improved performance of the organic light-emitting device due to higher transmittance, lower resistance, and surface roughness. Small organic molecules including functional groups that can be vacuum deposited, such as 4-AP, are expected to be used as surface pretreatment materials for various depositions because they can be easily patterned and can efficiently modify the surface even with extremely thin thickness.