A group of scientists from Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE), with support from Oxford PV Germany, have examined shingling as an interconnection method for perovskite-silicon tandem (PVST) cells.
Full-format perovskite-silicon tandem shingle modules produced at Fraunhofer ISE in collaboration with Oxford PV. Image from Solar Energy Materials and Solar Cells.
The scientists explained that the combination of PVST cells with shingling allows boosting the module efficiency even further due to the increase of the photoactive area through the absence of cell gaps. They went on to say that shingling suits the temperature limitations of the PVST cells since the main factor for the choice of the processing temperature is the curing conditions of the electrically conductive adhesive.
Shingled panels feature a busbar-free structure in which only a small proportion of cells are not exposed to sunlight. The cells are bonded with electrically conductive adhesive to form a shingled high-density string and the resulting strips are connected. The reduced number of busbars reduces shadowing losses.
According to the team, a significant advantage of combining PVST cells and shingling is the relaxed requirements on finger resistivity due to the relatively low cell current density. Shingling also does not utilize ribbons and requires only one cell side to be printed with electrically conductive adhesives (ECAs). They also said that shingling utilizes less material while lowering thermomechanical stress in the panels. It also increases a cell's active area, thus raising the device's fill factor and power conversion efficiency. Furthermore, shingled solar modules have an improved shading resilience compared to non-shingled products.
The researchers used M6 (166 mm x 166 mm) precursors with a two-terminal (2T) configuration provided by solar perovskite specialist Oxford PV. Metallization with low-temperature silver paste by means of screen printing deploying 60 fingers and continuous busbar took place at Fraunhofer ISE whereas cutting the cells into 1/5 shingles with 24.5% efficiency was realized at Oxford PV’s plant in Brandenburg, Germany. Shingles were shipped back to Fraunhofer ISE in Freiburg for interconnection and module integration.
Through their analysis, the academics found that the 1/6 cut PVST cells with 25 % initial shingle cell efficiency would be able to achieve a module efficiency of 23.4 %.
The scientists summarized that their recent work demonstrated the feasibility of the shingling approach as well as module integration with PVST cells by producing full-format modules, and that it produced real bifacial glass-glass solar panels based on industrial production equipment, which reached efficiencies of up to 22.8 %. They added that metallization of PVST precursors with low-temperature silver paste by means of screen-printing with subsequent cutting with laser scribe and mechanical cleave method was successful.