Multi-wire Interconnection of Busbar-free Solar Cells

The interconnection of busbar-free solar cells by multiple wires is a simple and evolutionary concept to lower the cost of PV modules by reducing silver consumption for the front side metallization and to increase the module efficiency by lower series resistance and improved light harvesting. A 0.33 % absolute higher performance of MBB against the established H-pattern solar cell has already been demonstrated by Braun [1]. This work focuses on the interconnection of Multi Busbar cells (MBB) by infrared soldering and the optimization of the front metallization design in order to achieve reliable solder joints. We find the following factors to be crucial for the MBB-interconnection process: a homogeneous radiation field, a process-adapted down-holder device, a homogeneous wire coating, a precise wire positioning and a method to absorb the wire expansion caused by the elevated solder temperatures. We measure peel forces up to 5.7 N/mm as the average peel force value of five pad rows from the center of two MBB cells containing 160 soldered pads. Furthermore a one-cell MBB-module shows a more homogeneous series resistance with an approximately 0.3 Ωcm2 lower series resistance compared to a one-cell 3-busbar module, which we determine by C-DCR (coupled determination of the dark saturation current and the series resistance). Finally two 20-cell MBB modules manufactured with an automated MBB-stringer pass the TC-200 test without significant changes in IV, EL and module optical appearance.