Effects of pn-junctions bordering on surfaces investigated by means of 2D-modeling

Several new solar cell designs, among them the emitter wrap through (EWT) and the POWER solar cell, suffer from reduced fill factors. These cells have interdigitated p- and n-type regions. At the margin of these regions, the p-n junction borders on the surface causing additional recombination. We investigate by means of two-dimensional modeling the recombination mechanisms occurring in such device regions, and we give an experimental example. It is shown that a poor quality of the surface passivation near to where the pn-junction borders, is mainly responsible for the observed losses in fill factor and open-circuit voltages.