A numerical model of p–n junctions bordering on surfaces

Many solar cell structures contain regions where the emitter p–n junction borders on the surface. If the surface is not well passivated, a large amount of recombination occurs in such regions. This type of recombination is influenced by the electrostatics of both the p–n junction and the surface, and hence it is different from the commonly described recombination phenomena occurring in the p–n junction within the bulk. We developed a two-dimensional model for the recombination mechanisms occurring in emitter p–n junctions bordering on surfaces. The model is validated by reproducing the experimental I–V curves of specially designed silicon solar cells. It is shown under which circumstances a poor surface passivation, near where the p–n junction borders on the surface, reduces the fill factor and the open-circuit voltage. The model can be applied to many other types of solar cells.