Flip-Flop Cell Interconnection Enabled by an Extremely High Bifacial Factor of Screen-Printed Ion Implanted n-PERT Si Solar Cells

32nd European Photovoltaic Solar Energy Conference and Exhibition; 407-412
We present bifacial fully ion implanted and screen-printed n-PERT cells, fabricated either by applying a single co-anneal process to cure the implant damage or by applying two separate anneals after boron/BF2 and phosphorous implant, respectively. In the first case of boron implant and co-anneal our best cells achieve an independently measured front (rear) side efficiency of 21.0 % (20.43 %) and for the boron implant and separate anneal the efficiency is 21.5 % (21.31 %). To the best of our knowledge these values are the highest efficiencies reported so far for fully ion implanted and screen-printed bifacial n-PERT cells. We furthermore show that light treatment of boron-implanted and co-annealed n-PERT cells increases the cell efficiency by 0.6 %abs. This diminish the efficiency gap to separately annealed cells. We measure a bifacial factor of 99.4 % that is the highest value reported so far for any high-efficiency Si cell. The high bifaciality enables an adapted module interconnection scheme called here Flip-Flop, which is based on a front-to-front and rear-to-rear interconnection of cells with alternating orientation (n+ or p+ side facing up). Based on the measured IV-characteristic of a cell with a bifacial factor of 97 % (“conservative scenario”) we demonstrate that the Flip-Flop interconnection scheme has the potential for a module efficiency improvement of 0.5 %abs on aperture area (as compared to the conventional “all cells emitter up” configuration) despite the 3 % current mismatch. We experimentally demonstrate a monofacial 16-cell Flip-Flop module that achieves an aperture area efficiency of 20.5 %.