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

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 (TiO2) ultrathin layer directly from a titanium (Ti) film that was predeposited onto Si substrates, leading to a surface recombination velocity as low as 15cms(-1). Detailed interfacial and structural characterizations show that the excellent contact passivation property was mainly attributed to the amorphous nature of TiO2 and the presence of a Ti-contained SiOx interlayer. By applying this ultrathin TiO2 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/TiO2 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 TiO2 layer in dopant-free heterojunction solar cells.