Improving the Density and Electrical Properties of Self-Reducing Reactive Silver Inks by Suppressing Complexing Agent Evaporation

Abstract

Self-reducing reactive silver inks are promising for printed electronics due to their low processing temperatures, high performance, and prolonged shelf life. Previous research showed that dense, high-quality silver can be printed without needing any postprint sintering steps by preferentially growing silver at the ink–substrate interface while also minimizing silver growth at the ink–vapor interface. This work builds on this concept and highlights importances of suppressing complexing agent evaporation rate to improve ink performance. By suppressing complexing agent evaporation increases silver formation at the ink–substrate interface, electrical conductivity improvement by over 2.5× for some ink formulations. Two independent studies demonstrate the benefits of this approach: one compares inks synthesized with varying vapor pressure complexing agents and the other prints inks in a complexing agent-rich environment to slow evaporation rates. Both approaches consistently yielded denser silver with lower resistances. For instance, using a propylamine complexing agent instead of ammonia at 40 °C resulted in a 96% decrease in resistance. Additionally, the ink printed at 100 °C with propylamine achieved state-of-the-art conductivity equivalent to 80% of bulk silver’s conductivity. The results confirm that slower complexing agent evaporation rates lead to denser silver with significantly lower resistances. This work introduces a unique strategy for enhancing ink performance that differs from conventional methods such as elevated temperatures, ink chemistry alterations, or postprocessing. The significantly improved low-temperature performance may broaden the applications of reactive silver inks and inspire future strategies that leverage suppressed complexing agent evaporation.