Effective In-Situ TOPCon Gettering of Epitaxially Grown Silicon Wafers during Bottom Solar Cell Fabrication

Epitaxially grown silicon wafers (EpiWafers) have a lower carbon footprint than conventional wafers produced by ingot crystallization but have also a lower initial material quality which can be significantly improved by gettering. We show that in situ gettering during the application of asymmetric n-type and p-type tunnel oxide passivating contacts (TOPCon) increases the material quality of n-type EpiWafers when fabricating bottom solar cells for a perovskite-silicon tandem device. In specific, the gettering effect of the TOPCon layers is compared to phosphorus gettering by systematically evaluating minority charge carrier lifetimes of n-type EpiWafers with base resistivities between 0.5 and 16 Ωcm. For the 1.3 Ωcm EpiWafers, the average lifetimes increase from above 100  µs in the initial state to above 1 ms after TOPCon gettering as well as after phosphorus gettering. To evaluate the impact of the EpiWafers’ quality on cell performance, implied solar cell parameters are calculated from injection-dependent lifetime images for TOPCon bottom solar cell precursors with and without previous phosphorus gettering. The very high electronic wafer quality obtained after TOPCon processing demonstrates that the EpiWafers are very well suited for TOPCon bottom solar cells without the need of an additional phosphorus gettering step.