PERC-Based Shingled Solar Cells and Modules at Fraunhofer ISE
Achieving high output power densities pout of silicon-based PV modules requires an increase of cell efficiency as well as a reduction of cell-to-module (CTM) losses. Solar cell shingling, an approach first introduced in the 1950s, targets the reduction of CTM losses mainly by: 1) eliminating the cell spacing through the overlapping of neighbouring cells; 2) decreasing the shading losses by covering the busbar with a neighbouring cell's active area; and 3) reducing the series resistance losses at the interconnection level. This paper reports on the latest advances in passivated emitter and rear cell (PERC)-based shingled solar cell activities at Fraunhofer ISE. The approach taken is to fabricate 6" host wafers from Czochralski-grown silicon and separate them after metallization and contact firing into bifacial p-type shingled passivated edge, emitter and rear (pSPEER) solar cells. The separation is performed by laser-assisted processes: 1) laser scribing and mechanical cleaving, or 2) thermal laser separation. Since the separation process leaves the edges without the intended passivation, high edge recombination rates are expected. For that reason, a photoluminescence-based method to characterize edge recombination has been developed and verified by Quokka3 simulations. In order to further increase the pSPEER output power density pout for a cell without the intended edge passivation, a post-metallization/separation edge passivation method, i.e. Passivated Edge Technology (PET), has been developed. The implementation of PET in pSPEERPET solar cells leads to an enhanced designated area pout = 23.5mW/cm2 (considering an additional rear-side irradiance G r = 100W/m2). In the transition to shingled-module assembly, the study follows up with the cure kinetics of electrically conductive adhesives (ECAs) and mechanical-model-based methods to gain a better understanding of the joint between pSPEER cells within strings. A CTM analysis using the SmartCalc.CTM software shows a comparison of a parallel-stringing topology with a matrix topology of the cell interconnection. The reduced form factor of shingled solar cells makes them very appealing and effective for use in integrated module products, which is demonstrated by a successful automotive application, additionally profiting from the high pout attained. Drawing from the authors' expertise in customized module and surface design, a vehicle integrated PV solution with a highly aesthetic appearance is presented.