Cu backside busbar tape: Eliminating Ag and enabling full al coverage in crystalline silicon solar cells and modules

A Cu tape was developed and tested for use as a backside busbar for any silicon solar cell having a screen-printed and fired Al backside, particularly the Al BSF cell and the PERC cell. A key element of the tape is the adhesive which penetrates through the full Al thickness and bonds to the underlying Si surface under short-duration heat and pressure. Such tape eliminates the need for backside silver (reducing cost), and allows the Al layer to remain continuous (increasing efficiency). Measured 180° peel strength of standard interconnect ribbon soldered to Cu tape exceeded 100 g-force/mm. Cu/Al contact resistivity measured 2.6 mΩ-cm
²
. Five 60-cell modules were fabricated with commercially-produced 156 mm Al BSF cells having full Al backside and Cu tape busbars. Tape was applied using prototype semi-automated production equipment, designed for production-scale throughput. Cells were interconnected with standard production stringing equipment. Module power exceeded 260 W, as fabricated. Module power degradation was well within the limits allowed by IEC 61215, even after doubling the IEC test requirements to 2000 hours of damp heat and 400 thermal cycles. EL imaging showed no cell cracking in the modules as-fabricated or after IEC stress testing.