Efficiency Enhancement and Characterization of Copper Contacted PERC Solar Cells with Screen Printable Copper Pastes

Screen printable Cu paste offers an excellent low-cost alternative to widely used silver metallization in silicon solar cells which faces cost and sustainability challenges due to rising prices and increased consumption of Ag. This paper reports on the understanding and optimization of the screen-printed Cu contacts on the emitter of large-area p-PERC solar cells by tailoring the firing temperature, belt speed, paste chemistry, line width, and n+ emitter. In this study, we raised the Cu-contacted PERC cell efficiency from 17% to 20.5%. The firing temperature optimization using our starting Cu paste increased efficiency from ~17% to 18.8% at 616°C optimum firing due to the tradeoff between series resistance and junction shunting. Next, increasing the belt speed from 300 to 360 IPM during contact firing raised the cell performance to 19.7% by lowering series resistance as well as Cu-induced shunting and junction recombination. Increased aggressiveness of paste by modifying its chemistry reduced the line width from 105 um to 45~60 um, and lowered the optimum firing temperature to 575°C, further enhancing the cell efficiency to 19.9%. Finally, the implementation of the selective emitter resulted in the best p-PERC cell efficiency of 20.5% with Voc of 680mV and Jsc of 41.2mA/cm². Further understanding and optimization of screen-printed Cu contacts to PERC solar cells is in progress to bridge the gap between Ag and Cu-contacted solar cells.