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Interfacial reduction phenomena in self-reducing reactive silver ink systems
DiGregorio, Steven J.
DiGregorio, Steven J.
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2023
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2024-05-29
Abstract
Conductive inks are becoming increasingly important as printed electronics gain popularity. However, forming highly conductive patterns at low-processing temperatures still presents a major challenge for conductive inks. Self-reducing reactive silver inks have emerged as a promising solution due to their low processing temperatures, high performance, and extended ink shelf life. These inks contain chemical precursors that react on the substrate after printing to form silver through complexing agent loss and thermal reduction mechanisms. This work investigates how the silver reduction at different ink interfaces, i.e., liquid/vapor and solid/liquid, impacts the resulting electrical properties and morphologies of self-reducing reactive silver inks.
The hypothesis posits that faster reaction rates at the solid/liquid interface lead to denser silver with better electrical properties. To test this, a heat treatment scheme study compared top-down and bottom-up heating sources to differentially heat the ink’s interfaces. Printing directly onto 90 °C heated substrates led to the highest reaction rates at the solid/liquid interface, yielding the best low-temperature performance. Expanding on this concept, a study showed that slowing the complexing agent evaporation rate by utilizing low vapor pressure complexing agents decreased the liquid/vapor interface reaction rates, leading to denser silver films.
The impact of these insights was demonstrated with a study on metallizing thermally-sensitive silicon heterojunction (SHJ) solar cells with reactive silver inks. Printing directly onto heated cells and utilizing low vapor pressure complexing agents achieved silver fingers with resistances only 1.9× higher than bulk silver at 60 °C printing temperatures. This outstanding performance allowed for cell metallization with 90% less silver consumption compared to industrially used particle-based silver pastes. These studies shed light on previously unexplored aspects of reactive inks, highlighting the importance of considering the silver reduction interface and maximizing silver formation at the solid/liquid interface. Implementing these approaches can significantly improve ink performance and enable new thermally sensitive applications for printed electronics.
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