Influence of Interfacial Oxides at TCO/Doped Si Thin Film Contacts on the Charge Carrier Transport of Passivating Contacts

Minimizing transport losses in novel solar cell concepts is often linked to improvements at the transparent conductive oxide (TCO)/doped silicon contact. A detailed understanding of the determining factors for an efficient transport at this heterojunction is essential, such as work function matching and efficient tunneling transport. In this article, we analyze the different TCO contact parameters experimentally and by numerical device simulations. We show that work function matching by using a proper interlayer [e.g., tungsten oxide (WOx)] can be an effective means to improve the fill factor of silicon heterojunction solar cells. However, we showcase that an improved work function matching achieved by changing the doping of a TCO interlayer can be superimposed by a less efficient tunneling transport, for e.g., due to an interfacial oxide. Furthermore, we show that for n-tunnel oxide passivating contacts, an unintentionally grown oxide at the TCO/poly-Si contact could be a possible explanation for recently observed transport losses.