Electrical properties manipulation of nanocrystalline silicon/silicon oxide passivating contacts via Si/O elemental concentration ratios for use in Si solar cells

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Abstract
In this study, the structural, compositional, and electrical properties of nanocrystalline silicon/silicon oxide (nc-Si/SiO x ) composite films fabricated by plasma-enhanced chemical vapor deposition were investigated for high-performance Si solar cells. The Si-rich layers in the composite layer precursor were deposited using various [CO 2 ]/([SiH 4 ] + [CO 2 ]) flow rate ratios and post-deposition annealing was performed to induce nc-Si formation. Auger electron spectroscopy confirmed that the Si/O ratio of the Si-rich layers can be tuned by the gas flow rate ratio. Cross-sectional transmission electron microscope images revealed nc-Si formation was promoted and its areal density increased by decreasing the gas flow rate ratio. The passivation performance exhibited a clear optimum at an oxygen concentration of ∼5 at.%, whereas both higher and lower O contents degraded the effective carrier lifetime. In contrast, the electrical resistance increased monotonically with O concentration, suggesting improved carrier transport in Si-rich films with higher nc-Si density. No trade-off was observed between conductivity and passivation, demonstrating that both can be independently optimized. These results show that controlling the gas flow rate ratio and annealing enables simultaneous improvement of passivation and carrier conduction in nc-Si/SiO x layers.

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