Comparative study of active solder and conventional solder on silicon photovoltaic cells

Solders´ formulations activated with Ti, Ce, Mg and Ga have been developed for optimum joining to silicon and SiO₂. These solders are being evaluated for the attachment of copper and/or aluminum buss strips to the back planes of silicon photovoltaic cells without a need for solder pads. Active solders are melted and disrupted to create a strong bond between the back contact, aluminized surface of polycrystalline Si photovoltaic cells and a copper buss strip. This paper demonstrates how an active solder joined through thermasonic bonding (process of ultrasonic energy and heat) compares with conventional soldering processes in terms of pull strength, contact resistance, and the current-voltage characteristics of silicon photovoltaic cells.