Zhou, Ye; (2023) Design and Synthesis of Inkjet Printable Silver based MOD Inks for Deposition of Functional Patterns. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The increasing concerns of the environmental problems relating to electronics wastes have encouraged the development of printed electronics, as a cost-effective, convenient and waste-free replacement to electrical circuits and devices fabricated by traditional manufacturing methods. Nanoparticle (NPs) inks have been widely used in industry for producing large volume flexible printed electronics in past two decades. Metal organic decomposition (MOD) inks are becoming popular in recent research and considered to have potential to substitute or supplement NPs inks. Due to the particle-free feature and the unique decomposition mechanics, MOD inks could avoid some common limitations of NPs inks, such as the blockage of nozzles, requirement of high sintering temperature and short shelf-life. One research study of MOD inks is to synthesis MOD precursors which could be formulated into inkjet-printable inks and sintered at low temperature to fabricate conductive patterns on thermally sensitive substrates like papers or polymer films. In this study, novel silver-based MOD precursors which could decompose at low temperature were synthesized and developed into inks which could be used to fabricate highly conductive silver films by inkjet printing and sintering at temperature of 100 °C. To electronic functionalization of an extremely thermally sensitive silk/epoxy composite substrate, a further optimized silver-based MOD ink was formulated. This ink could be inkjet printed and sintered at room temperature, without any damage to the substrate, to form functional metallic patterns with outstanding resolution and high electrical conductivity. The rapid expending potential application scenarios of printed electronics in the area of wearable devices, especially those using bio-tissue based or bio-synthetic substrates, urges the demand of inkjet printable metal-based inks, which could be deposited and sintered at low temperature and fabricate skin-contacted or biofluid-contacted conductive patterns with high resolution and accuracy. And to decrease the printing steps, hybrid inks which could be used to form patterns with complex micro/nano structures were developed for specific applications. In this study, for the first time, Density Functional Theory (DFT) was used to show the Gibbs free energies of individual Ag and Cu MOD precursors are strongly negative in all cases, ruling out the potential for ligand scrambling upon mixing the precursors when making hybrid inks. Through combining with the experimental data, a single hybrid Ag-Cu based MOD ink was developed. When sintering at low temperature of 135 °C, two self-regulated laminated structures: highly conductive copper on top of silver, when sintered under N2. Upon changing to air, the same ink yielded a highly functional CuO decorated silver layer with a silver-copper core shell structure beneath. This easily switchable system produced films which were shown to be versatile enough to be printed on a range of substrates from paper to plastic. This scalable process has resulted in the realization of a low-cost biosensor, demonstrating a simple route to a glucose sensor with an inbuild silver electrode, removing the need for multi-step fabrication methods.

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