Interconnection of Silicon Heterojunction Solar Cells by Infrared Soldering - Solder Joint Analysis and Temperature Study

Interconnection of silicon heterojunction (SHJ) solar cells by soldering is challenging due to the temperature sensitivity of the passivation layers. Within our study, we evaluate solder joints on SHJ solar cells interconnected by infrared (IR) soldering. We screen printed various low-temperature metallization pastes on industrial precursors and interconnected them with Sn60Pb40 coated Cu ribbons on an industrial IR stringer. For our analysis, we used a temperature profile for soldering according to the industrial standard of PERC cells (~240 °C, < 3 s). Adhesion after soldering was characterized by 90° peel tests, yielding improved values of 0.9 N/mm. Microstructural investigations reveal a defined Ag3Sn layer, indicating a proper metallurgical bond. With electrical characterizations at cell and module level, we show IR soldering to be feasible for the interconnection of SHJ solar cells. We built 3-cell-modules and measure a power degradation below 1.5 % after 200 temperature cycles (&#8722;40 °C/+85 °C). A successful interconnection is also shown by a cell-to-module power ratio of 98.8 % for a 60-cellmodule achieving 324 W.