Abstract
We have used the capillary suspension phenomenon to design conductive pastes for printed electronic applications, such as front side metallization of solar cells, without non-volatile, organic additives that often deteriorate electrical properties. Adding a small amount of a second, immiscible fluid to a suspension creates a network of liquid bridges between the particles. This capillary force-controlled microstructure allows for tuning the flow behavior in a wide range. Yield stress and low-shear viscosity can be adjusted such that long-term stability is provided by inhibiting sedimentation, and, even more importantly, narrow line widths and high aspect ratios are accessible. These ternary mixtures, called capillary suspensions, exhibit a strong degree of shear thinning that allows for conventional coating or printing equipment to be used. Finally, the secondary fluid, beneficial for stability and processing of the wet paste, completely evaporates during drying and sintering. Thus, we obtained high purity silver and nickel layers with a conductivity two times greater than could be obtained with state-of-the-art, commercial materials. This revolutionary concept can be easily applied to other systems using inorganic or even organic conductive particles and represents a fundamental paradigm change to the formulation of pastes for printed electronics.
Highlights
We have used the capillary suspension phenomenon to design conductive pastes for printed electronic applications, such as front side metallization of solar cells, without non-volatile, organic additives that often deteriorate electrical properties
This demand for printable electronics is rapidly increasing with the potential to grow to a $50 billion global market in the few years[1]
Printable electronic products range from microscale devices to large scale units made of either inorganic or organic material systems (e.g. OLEDs)
Summary
Solder glass (total solids loading 33.4 vol%), which is a crucial component during the firing step in the photovoltaic production for proper contact with the underlying substrate This additional solid phase does not interfere with the formation of the capillary network and led to an even higher yield stress when compared to the silver capillary suspension with 29 vol% silver and 5 vol% added water. With a high aspect ratio, are desired for small scale circuits and even more complex, e.g. triangular shapes advantageous for the front side metallization of solar cells, may be possible In addition to these benefits directly related to the unique flow behavior, the capillary suspension concept offers a significant advantage in printed electronic applications due to the lack of non-volatile organic additives. The proposed high conductivity formulation concept may even enable silver to be replaced, e.g. in large scale applications like solar cells, by more abundant conductive materials such as copper in the future
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