Improving the Stability of Polycrystalline Silicon Passivated Contacts Using Titanium Dioxide

Polycrystalline silicon (poly-Si) passivated junctions/contacts have been shown as a key technology to achieve high efficiency silicon solar cells. However, there remain some issues with this technology related to its thermal stability during/after metallization. In this work, we introduce the use of metal oxide based materials as an interlayer between the poly-Si and the metal electrode. We initially focus on TiO
2
interlayers, which we find can improve the thermal stability of n-type poly-Si contacts. The passivation quality of poly-Si contacts is maintained and even slightly improved for very thin
$(\sim \mathbf{8}\ \mathbf{nm})$
TiO
2
interlayers, when subjected to a post-metallization anneal at 400 °C, This improvement in passivation stability comes at the expense of higher contact resistivity, however, the obtained contact resistivity values are still acceptable for full area contacts. The thermal stability of the passivation can be further improved up to 500 °C by thickening the TiO
2
interlayer
$(\sim \mathbf{28}\ \mathbf{nm})$
, resulting in increased contact resistivity. Nevertheless, we believe the high contact resistivities can be overcome by exploring different materials, for example in the families of the transparent conductive metal oxides and metal nitrides. The protective effects of this interlayer structure may allow the thinning of poly-Si layers, reducing their parasitic absorption, and permitting their usage on the sunward side of cells. This approach will also be impactful for silicon-based bottom cells in tandem solar cells as it can provide more flexibility in terms of top cell fabrication thermal budget.