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Development and modelling of crystalline silicon based metal wrap through (MWT) solar cells
25th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2010. Proceedings : 5th World Conference on Photovoltaic Energy Conversion, 6-10 , September 2010, Valencia, Spain
München: WIP-Renewable Energies, 2010
|European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <25, 2010, Valencia>|
World Conference on Photovoltaic Energy Conversion <5, 2010, Valencia>
| Conference Paper, Electronic Publication|
|Fraunhofer ISE ()|
A detailed analysis of the Al-BSF MWT solar cell specific loss mechanisms is presented. It is shown that final efficiency is hardly affected by the MWT vias. A tremendous impact on fill factor is associated to the rear side located unpassivated p-n junction. If the dimensions of this p-n junction are varied experimentally a strong increase in the series resistance is observed leading to a drop in fill factor which can not be explained fully by lateral ohmic resistance in the base. Therefore, 2D "Sentaurus Device" simulations have been carried out matching this behavior very well. The simulations also show a great impact on fill factor by base doping. According to the simulation, strategies in order to minimize fill factor losses are revealed. Rear contact separation should be done as close as possible to the aluminum located emitter. As major leverage for increasing the fill factor of a MWT solar cell the reduction of the rear p-n junction area by minimizing the Ag-Al gap andthe rear Ag busbar could be addressed. Furthermore, a decreasing influence arising from the rear p-n junction is observed when bulk material with lower lifetime is utilized. A transition point is observed where the MWT solar cell exceeds the conventional cell. This transition point is related to the lifetime of the bulk material utilized and shifts towards lower doping with decreasing bulk lifetime (vice versa).