Development of Innovative Application Films for Silicon Solar Cells Using a Copper–Phosphorus Alloy by an Atmospheric Sintering Process

In this paper we aim to develop copper (Cu)-based backside soldering tabs/pads for crystalline silicon (Si) solar cells using atmospheric sintering. In our previous study, we found that a Cu network can be formed in an application film (AF) by self-deoxidization when the AF consisting of copper-phosphorus (Cu-P) alloy paste is sintered in an atmospheric environment, and the Cu AF showed low electrical resistivity that satisfied the criteria for backside soldering tabs/pads. In this study, Si solar cells using Cu AF for front-side contacts were evaluated to confirm that Cu AF is applicable to Si solar cells in principle. The Cu-P alloy paste using Cu-7 mass%P particles was printed on an Si wafer and, finally, sintered at 640 °C in atmosphere. The resulting AF showed low electrical resistivity of 2.96 × 10 ^-5 Ωcm. The solar cell using the Cu AF and conductive glass layer had conversion efficiency (η) of 6.6%. We demonstrated the need for a barrier layer to prevent the formation of Cu 3Si compound on the Si wafer surface when applying it to Cu AF on the solar cells. Our results may improve the potential for the widespread use of an atmospheric sintered Cu AF as backside soldering tabs/pads for Si solar cells.