
Steven’s latest silver reactive ink paper is an important one. Published in ACS Applied Electronic Materials, Improving the Density and Electrical Properties of Self-Reducing Reactive Silver Inks by Suppressing Complexing Agent Evaporation (doi: 10.1021/acsaelm.4c01305), provides clear evidence that suppressing complexing agent evaporation is critically important when trying to improve the performance of printed reactive silver diamine inks. Steven developed a novel set of experiments that suppressed complexing agent evaporation without changing the overall chemistry or thermal environment.
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 has shown that dense, high-quality silver can be printed without needing any post-print sintering techniques by preferentially growing silver at the ink/substrate interface while minimizing silver growth at the ink/vapor interface. This work builds on this concept and highlights the critical role of complexing agent (CA) evaporation rate in enhancing ink performance. Suppressing CA evaporation increases silver formation at the ink/substrate interface, resulting in electrical conductivity improvements above 2.5×. Two independent studies demonstrate the benefits of this approach: one compares inks synthesized with varying vapor pressure CAs, and the other prints inks in a CA-rich environment to slow evaporation rates. Both approaches consistently yield denser silver with lower resistances. For instance, using a propylamine CA instead of ammonia at 40 °C printing temperatures 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. The results confirm that slower CA evaporation rates lead to denser silver with significantly lower resistances. This work introduces a novel strategy for enhancing ink performance that differs from conventional methods such as elevated temperatures, ink chemistry alterations, or post-processing. The significantly improved low-temperature performance may broaden the applications of reactive silver inks and inspire future strategies that leverage suppressed CA evaporation.