Application of nanocomposite metallic ink for fabrication of conductive coatings at low-temperature sintering 

Pajor-Świerzy A. 1, Szendera F. 2, Pawłowski R. 2, Szczepanowicz K.1
1 Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8, 30-239 Kraków, Poland
E-mail: ncpajor@cyf-kr.edu.pl
2 Abraxas Jeremiasz Olgierd, Piaskowa 27, 44-300 Wodzisław Śląski, Poland.

In future developments of the flexible printed electronics global market, the ability to produce highly conductive patterns by using low-cost technology, the thermal sensitivity of the flexible substrates is one of the most critical parameters for the fabrication of printed electronics and displays. Therefore, during the last years, growing interest has been observed in the field of sintering methods, which can be performed at a low temperature to avoid the destruction of the heat-sensitive substrates. 
Currently, most inks used for the fabrication of conductive flexible patterns are based on silver NPs. However, large-scale production of such conductive circuits requires low-cost inks. Since nickel is much cheaper than silver but possesses still satisfactory conductivity, can be considered as an alternative to silver NPs. However, Ni NPs are easily oxidized in the air, resulting in poor conductivity. As a suitable option to overcome the high cost of Ag and to prevent the spontaneous oxidation of nickel, Ni-Ag core-shell nanoparticles can be synthesized. 
In this study, spherical, air-stable Ni-Ag nanoparticles at the size of about 220 nm were synthesized by using the transmetallation process. The obtained Ni-Ag NPs were utilized as the main filler of ink for the preparation of conductive coatings. Besides, the effect of silver nanoparticles, as doping material on the conductive properties of Ni-Ag-based coatings was studied. Two types of prepared nanocomposite ink coatings showed promising properties for future application: (1) doped with 0.5% of Ag NPs sintered at 200°C as low cost for larger industrial application and, (2) containing 1% of Ag NPs sintered at 150°C for the fabrication of conductive printed patterns on flexible substrates. The conductivity of such nanocomposite films was similar and corresponds to 35% of that for a bulk nickel.

Acknowledgements
This research was funded by the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund, grant number Homing/2016-3/28. The work was also partially supported by the Development Research Project for Young Employees of ICSC PAS.