Blistering-free polycrystalline silicon carbide films for double-sided passivating contact solar cells

Polysilicon (poly-Si) passivating contacts have attracted considerable attentions in the academic community and photovoltaic industry due to their remarkable advantages of outstanding passivation quality and low contact resistivity. Plasma enhanced chemical vapor deposition (PECVD), as one of the widely adopted techniques to prepare doped poly-Si films, is usually limited by the occurrence of blistering, especially for boron-doped (B doped) poly-Si films. In this work, we present a study of PECVD preparation of B-doped polycrystalline silicon carbide (poly-SiCx) films with a blistering-free appearance by incorporating carbon (C) and optimizing the annealing process. It demonstrates that a thick poly-Si deposited on polished c-Si substrates with a low surface roughness tends to blister, which thus leads to a poor passivation performance. Moreover, the investigation of C content and annealing condition suggests that increasing C content or lowering incipient annealing temperature is beneficial to suppress the blistering. However, the C content needs to be well controlled to balance the passivation and contact properties, because the excessive CH4 flow during the film deposition would degrade the contact performance with a high contact resistivity (>100 m Omega cm(2)). Finally, the proof-of-concept devices featuring the double-sided passivating contacts (DPPCs) were fabricated with a front n-type poly-Si and rear p type poly-SiCx, and presented an open-circuit voltage of 695 mV and an efficiency of 19.82%. The results clarify the correlation of C contents, c-Si substrate roughness and annealing process with the blistering levels and the passivation/contact properties, providing a valuable guidance for fabricating high-efficiency DPPC solar cells.

Automated summary

This study demonstrates the preparation of blistering-free boron-doped poly-SiCx films by plasma enhanced chemical vapor deposition (PECVD) through the incorporation of carbon and optimization of the annealing process. It is found that thick poly-Si deposited on polished c-Si substrates tends to blister, while increasing the carbon content or lowering the annealing temperature can suppress the blistering. However, the carbon content needs to be controlled to balance the passivation and contact properties.