Polyethylene glycol-assisted stabilization of low-silver electrically conductive adhesives for solar cell interconnection

Electrically conductive adhesives (ECAs) represent a low-temperature alternative to solder in electronic and photovoltaic applications. Their electrical performance relies on a conductive filler content typically ranging from 20-30 vol% silver flakes, which ensures percolation and high conductivity but raises cost and sustainability concerns. Here, we demonstrate that an ECA comprising an epoxy resin, a non-miscible polar fluid and silver flakes used in commercial products meets the specifications for shingled solar cell interconnection in terms of volume and contact resistivity as well as mechanical strength at a silver content of only 4 vol%. Such a low-filled ECA, however, suffers from poor stability against de-mixing and its flow properties are not suitable for screen printing or dispensing. This can be remedied by adding a small amount of polyethylene glycol (PEG) 200. PEG 200 partially dissolves in the epoxy resin but also in the polar fluid, thereby reducing the three-phase contact angle of the polar fluid on the silver flake surface. This appears to enable the formation of a “capillary” state capillary suspension with 2-3 vol% added PEG, which provides a high yield stress guaranteeing high stability and good application behavior. The corresponding coarsening of the microstructure does not affect the electrical properties. The application of this concept enables the formulation of an ECA that meets industrial performance criteria even at very low particle content. The transfer to other filler systems, such as silver-coated copper or glass particles, is straightforward and offers a pathway toward robust, cost-effective, and sustainable ECAs for next-generation photovoltaic modules.