Two-Dimensional Modeling of the Metallization-Induced Recombination Losses of Screen-Printed Solar Cells

We present an approach of implementing the experimental microscopic observations at metal-Si emitter interface into a 2-D simulation model to investigate the metallization-induced recombination losses of crystalline Si solar cells with firing through metallization. This metal-Si interface is typically characterized by few Ag crystallites grown into Si, whereas the main part of the interface area is covered by a glass layer. By using this simulation model, we were able to disentangle the effect that each of these microscopic features has on solar cell performance. The model assumes the metal-Si interface to be either Ohmic or Schottky, with current extraction occurring only through the direct Ag crystallites-Si interface. The simulation results show negligible degradation in open-circuit voltage (V_OC) and pseudo-fill factor (pF F) if the metal-Si interface comprises the sole presence of Ag crystallites, as long as these crystallites grow only superficially and are not penetrating the p-n junction. A more detrimental effect is observed if the emitter area beneath the glass layer is affected by etching. For more aggressive metallization pastes or for overfiring scenarios where larger in-grown crystallites are observed that are protruding through the p-n junction, the model assuming a Schottky contact qualitatively explains the shunting behavior observed experimentally.