Anisotropic Conductive Adhesives for Interdigitated Back Contact (IBC) Silicon Solar Cells

The current manufacturing process for solar panels using interdigitated back contact (IBC) silicon solar cells involves a multi-step metallization and interconnection process in which a substantial amount of silver is used. This work focuses on a new process using conductive adhesives (CA) which would increase efficiency and lower cost through a one-step metallization and interconnection process that combines with encapsulation using little silver and only requiring metal patterning on the back sheet or back glass. It would also not require direct metallization of the silicon, which would result in fewer defects, while increasing voltage and therefore efficiency. Silver-coated Poly(Methyl Methacrylate) Microsphere (AgMS) and indium powder are the primary materials used as the conductive particles in an ethyl vinyl acetate (EVA)/toluene adhesive. The CA is prepared by mixing the components in toluene. The resulting mixture is used to produce 300μm thick CA sheets using a universal applicator, cut into pieces, and pressed between a piece of glass with coplanar Ag electrodes and a silicon wafer at varying temperatures and pressures. This yields ~3 Ωcm2 for both the AgMS and indium fillers. Significantly lower values are required for the target application, and possible new approaches in attaining lower resistivity are discussed