Analysis of edge losses on silicon heterojunction half solar cells

Halved and shingled solar cells are a powerful technology to reduce cell-to-module losses and ultimately increase the output power of a photovoltaic module. The combination of this approach with high-efficiency silicon solar cells architectures, like heterojunction or passivated contacts solar cells, is a promising option, but comes also with new challenges. In particular, the low level of carrier recombination in these cells makes them highly sensitive to any additional defects, as it is the case for the unpassivated edge created when splitting in half a solar cell. In order to optimize the cutting processes, an accurate method to characterize edge losses, adapted to high-efficiency solar cells, is required. In this work, two approaches are proposed and compared. In the first one, edge losses are modelled with a parallel diode, and the associated recombination current (J02edge) is fitted with current-voltage measurements, as usually done in previous studies. The conditions of application of this method are widely discussed and precisely redefined for an accurate extraction of parameters in the case of high-efficiency solar cells. The second method proposed consists in simply calculating relative losses out of the main current-voltage parameters. We demonstrate that simple estimation of open-circuit voltage (Voc) losses is perfectly adapted to our characterization needs, provided that adapted measurement methodology is applied. Results obtained with both methods are then compared on heterojunction cells and discussed. If these two characterization techniques both provide accurate results for the laser scribing processes tested, the method based on open-circuit voltage loss comparison shows slightly less dispersion. Moreover, this last method does not rely on curve fitting, making it faster and insensitive to modeling issues. The Voc approach appears thus more adapted for a fine optimization of different cutting processes and eventual characterization step implemented in an industrial environment. However, the alternative J02edge method based on curve fitting remains of high interest, for example to compare cell losses obtained with usual values reported in the literature, provided that extraction of this parameter is done with the conditions assessed in this work.