Tunnel oxide passivated carrier-selective contacts based on ultra-thin SiO2 layers grown by photo-oxidation or wet-chemical oxidation in ozonized water

A successful application of carrier selective contacts was demonstrated by using the tunnel oxide passivated contact (TOPCon) approach yielding a 24.9% efficient solar cell. A key factor of this contact is the ultra-thin SiO_x tunnel layer which reduces interface recombination significantly but must not restrict carrier flow. Within this paper a comparison between the standard wet-chemical HNO₃ oxide, a dry-grown UV/O₃ oxide, and a wet-chemically grown oxide by using ozonized DI-H₂O is drawn. The oxides´ stoichiometry and structure are analyzed and will be set in relation with the effective surface passivation. It will be demonstrated that beneath certain UV/O₃ oxides also wet-chemically grown oxides offer a high thermal stability during the annealing and can improve the passivation of n-TOPCon, especially on textured surfaces.