Publication:

The SPEER solar cell - simulation study of shingled bifacial PERC-technology-based stripe cells

Increasing the output power density of a photovoltaic module is a reliable way of lowering electricity production costs. Besides increasing the solar cells' conversion efficiency, a further option is lowering electrical and optical cell to module losses. The method of shingling singulated monofacial solar cell stripes is known since Dickson Jr.'s patent in 1956. First, it increases the packing density of active cell area in the module. Second, the active cell area is busbar-less reducing shading losses. Third, due to the reduced area of the solar cell stripes, the generated current per cell is less which results in a reduction of the overall series resistance of the cell interconnection within the module. We call our cell concept for this approach - which is based on the p-type silicon bifacial passivated emitter and rear cell (PERC) concept - ""shingled passivated edge, emitter, and rear"" - or ""SPEER"". These cells are then to be interconnected by shingling the p-busbar of the first cell onto the n-busbar of the second cell, constituting the first bifacial shingled module of its kind. Each adjacent shingle covers the busbar with active cell area and minimizes spacing losses in the module. This work covers the optimization of the SPEER concept on cell level with the simulation tool Quokka3. The optimized cell provides the basis for full usage of the cell-to-module gains compared to standard modules. Key issues for optimizing the SPEER cells, which will form the module, concern the characteristics and amount of recombination at their cut edges. This directly affects the question of ideal contour-to-area ratio and thus, the width of the SPEER cells. Using latest experience from bifacial PERC cells and literature values for edge recombination as simulation input, we are able to define a region of interest between 15 mm and 25 mm stripe width for building the first SPEER prototypes. We identify the need for edge treatment, be it an emitter window or edge passivation, as crucial for the success of stripe cells against more conventional cell layouts.