Understanding the role of mobility of ITO films for silicon heterojunction solar cell applications

Transparent conducting oxides (TCO) are crucial in amorphous/crystalline silicon heterojunction solar cells performance as they have to be highly conductive to ensure the transport of photogenerated charges while remaining highly transparent to the sun spectrum. The key parameter to improve the transparency/conductivity compromise of TCO is mobility, since it allows increasing conductivity without losing transparency in the infrared region. A deep understanding of the factors influencing the mobility is then fundamental, and this is the objective of this paper. For this study, thin films of tin-doped indium oxide (ITO) were prepared by magnetron sputtering with different oxygen content. They were deeply characterized by standard and Low Temperature Hall Effect measurement, scanning and transmission electron microscopy and X-ray diffraction. The impact of oxygen on the microstructure was studied and the electrical properties were deeply investigated. In particular, the different mechanisms impacting the mobility were quantified as a function of oxygen content during ITO deposition.