TiO₂ Films from the Low‐Temperature Oxidation of Ti as Passivating‐Contact Layers for Si Heterojunction Solar Cells

Abstract

Crystalline silicon (c‐Si) heterojunction solar cells featuring dopant‐free and carrier‐selective contacts have drawn considerable attention due to their potential in achieving high efficiency with extremely simple fabrication procedures. Here, a low‐temperature thermal oxidation process is developed to fabricate a titanium dioxide (TiO 2 ) ultrathin layer directly from a titanium (Ti) film that was predeposited onto Si substrates, leading to a surface recombination velocity as low as 15 cm s −1 . Detailed interfacial and structural characterizations show that the excellent contact passivation property was mainly attributed to the amorphous nature of TiO 2 and the presence of a Ti‐contained SiO x interlayer. By applying this ultrathin TiO 2 layer as a passivating‐contact layer, test heterojunction solar cells employing a core structure of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/n‐Si/TiO 2 obtained an efficiency as high as 14.6% (only 13.0% for the reference device), demonstrating the potential for applications of this thermal oxidation‐derived TiO 2 layer in dopant‐free heterojunction solar cells.