Carrier-selective, passivated contacts for high efficiency silicon solar cells based on transparent conducting oxides

We describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO₂ and indium tin oxide. High-temperature silicon dioxide is grown on both surfaces on an n-type Si wafer to a thickness <;50 Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high recombination parameter, J_0,contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter current density of the contact (J_0,contact) and the specific contact resistivity (ρ_contact) using a transmission line method (TLM) pattern. The best ITO/SiO₂ passivated contact in this study has J_0,contact = 93.5 fA/cm² and ρ_contact = 11.5 mOhm-cm². These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J_0,contact, ρ_contact) values. The ITO/SiO₂ contacts are found to have a higher J_0,contact, but a similar ρ_contact compared to the best reported passivated contacts.