Rear Local Contact Formation for High-efficiency Crystalline Silicon Wafer Solar Cells

Abstract

For advanced silicon wafer solar cell architectures, local contacts are increasingly used at the rear to minimize surface recombination losses. In this thesis the local contact formation for p-type Al-LBSF (Aluminium Local Back Surface Field) solar cells and n-type PERT (Passivated Emitter Rear Total diffused) solar cells is investigated in detail. For p-type Al-LBSF cells, it is found that the rear local opening pattern and Al thickness have a significant impact on the formation of voids at the rear local contact, resulting in increased recombination and resistive losses. For n-type PERT cells, the emitter saturation current at the rear local contact is increased after laser ablation, and is injection-level dependent. Limitations of different methods to determine the series resistance of Al-LBSF solar cells are also discussed. A severe underestimation of the series resistance of these cells due to an injection-level dependent saturation current is observed for several of these methods.