Abstract
Electrically conductive films are key components in most printed and flexible electronics applications. For the solution processing of conductive films, inks containing silver nanoparticles (AgNPs) remain important because of their relatively easy processing and generally low resistivity after a sintering procedure. Because the commonly used, moderate sintering temperatures of 150–300 °C are still too high for most low-cost flexible substrates, expanding the knowledge of surface-ink interactions that affect the sintering temperature is desirable. It is known that chloride ions can assist the sintering of AgNP films by displacing capping agents on the surfaces of AgNPs. However, very little is known about other possible Cl-AgNP interactions that affect the resistivity and no interaction having the opposite effect (sintering inhibition) has been identified before. Here we identify such a Cl-AgNP interaction giving sintering inhibition and find that the mechanism involves the formation of AgCl nanocrystals within the AgNP film. The AgCl formation was observed after inkjet-printing of AgNP inks with polyvinylpyrrolidone (PVP) as the capping agent onto papers with quick-absorbing coatings containing 0.3 wt % KCl. Our findings show that chloride can have opposite roles during sintering, either assisting or inhibiting the sintering depending on the prevalence of AgCl formation. The prevalence of AgCl formation depends on the absorption properties and the capping agent.
Highlights
The solution processing of functional materials and their deposition by various coating and printing methods have established a foundation for flexible and printed electronics
By examining the AgNP film nanostructure in detail, we find that the resistivity increase is due to the formation of AgCl nanocrystals on the surfaces of AgNPs
AgNP Films Were Inkjet-Printed onto Active Papers and Reference Papers
Summary
The solution processing of functional materials and their deposition by various coating and printing methods have established a foundation for flexible and printed electronics. The NaCl concentration was sufficiently low as to not affect the stability of the ink in the dispersion but, upon drying, the increase in the concentration induced room-temperature sintering These researchers demonstrated that the sintering was induced by the desorption of the capping polymer by chloride ions replacing the polymer anchoring groups at the AgNP surface. Paper with active coatings containing a low concentration of KCl induced room-temperature sintering of inkjet-printed AgNP films [13]. There has been at least one conflicting report that chloride and other halides induced a reverse effect on paper coatings, significantly increasing the AgNP film resistivity [14] Such increased resistivity is not consistent with the known mechanism of capping agent desorption, calling for further investigations. This new insight is useful for the proper design and implementation of sintering methods for printed electronics
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