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This work deals with the application of passivating contacts, specifically POLO contacts, which can increase the selectivity of the charge carriers at the metal contact and thus the efficiency due to their excellent passivating effect. These poly-Si based contacts, also called TOPCon, are just establishing themselves in industrial solar cell manufacturing. However, there are still some open questions regarding their operation and optimal fabrication. The first part of the paper is focused on the so-called POLO2-IBC cell, with which Felix Hasse’s team, with the collaboration of the author of this thesis, was able to achieve a record efficiency of 26.1 % for p-type material in 2018. With an area of 4 cm² and very complex patterning processes, this back-contacted record cell is not an industrially relevant cell, but it demonstrates the great potential of POLO contacts. A distinctive feature of this cell is the continuous layers of thin oxide and overlying poly-Si that form the so-called „poly-Si on oxide“ (POLO) junctions. The electron-collecting and hole-collecting contacts, fabricated by doping via ion implantation, are separated only by narrow intrinsic POLO regions. Extensive monitoring of the fabrication process and a simulation study show that the potential of this cell type with 26.1 % has not yet been fully exploited. Furthermore, the comparison with a high resistivity base material shows the significantly higher susceptibility of the passivation quality with decreasing doping concentration, so that despite higher intrinsic recombination, the used 1.3 Ohm cm material is identified as most suitable. Separating the p+ and n+ contact through the undoped region proves to be an elegant solution, which, however, only works under certain conditions. Diffusion of dopants from the n+ and p+ regions into the intrinsic region improves the otherwise poor passivation quality there. At the same time, however, this increases the unwanted recombination current between the contacts, so the choice of the appropriate width is ...