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Co-diffused back-contact back-junction silicon solar cells without gap regions
In this paper, first generation back-contact back-junction (BC-BJ) silicon solar cells with cell efficiencies well above eta = 20% were fabricated. The process sequence is industrially feasible, requires only one high-temperature step (co-diffusion), and relies only on industrially available pattering technologies. The silicon-doping is performed from pre-patterned solid diffusion sources, which allow for the precise adjustment of phosphorus-and boron-doping levels. Based on the investigated process technologies, BC-BJ solar cells with gap and without gap between adjacent n+-and p+-doped areas were processed. On the one hand, a strong reduction of the process effort is possible by omitting the gap regions. On the other hand, parasitic tunneling currents through the narrow space charge region may occur. Hence, deep doped areas were realized to avoid tunneling currents in gap-free BC-BJ cells. This paper finishes with a detailed characterization of the manufactured cells including important cell measurements like I-V, SunsVOC, quantum efficiency, and an analysis of the cell specific fill factor losses.