Understanding the Influence of Busbars in Large-Area IBC Solar Cells by Distributed SPICE Simulations

In this paper we model a large-area high-efficiency interdigitated back-contact (IBC) solar cell by means of a distributed electrical network. The simulation tool allows accounting for the distributed resistive effects in diffusions and metallization. The model also considers the electrical shading effect and resistive losses due to both BSF and emitter busbars. A calibrated model is used to investigate the case of a large-area (15.6x15.6 cm2) IBC cell, in which we investigate the influence of key busbar parameters: number of busbars; busbar width; soldering pitch (for module connection); metal sheet resistance. The predictive simulations allow finding out the optimum number of busbars, arising from a tradeoff between the electrical shading effect due to the BSF busbars and resistive losses due to the emitter busbars and the fingers. Moreover, we show how the distance between soldering points on the metal busbars, influences the choice of the busbar width. We found out that, if an adequate number (>7) of soldering points is adopted, the busbar width should be kept lower than 0.5mm. On the other hand, the adoption of a thick Cu-plating (15μm) leads to an increase of efficiency of 0.2«s with respect to the case of sputtered Al metal (3μm thick).