Optimizing Conductivity And Mobility Of ITO-97/3 Coatings For Photovoltaic Applications

To achieve high solar cell efficiency the Transparent Conductive Oxide (TCO) layer in heterojunction a-Si/c-Si solar cells needs to provide on the one hand high mobility in order to achieve low resistivity and on the other hand low free carrier density to reduce absorption in the near infrared part of the solar spectrum. Because of these requirements, often an ITO grade with a SnO₂ concentration of 3wt% (ITO-97/3) is chosen as a TCO in such photovoltaic applications. It has been demonstrated several years ago that the addition of hydrogen to the sputter gas is a determining factor in enhancing the ITO-97/3 coating performance. Within this study, the amount of hydrogen gas added during the magnetron sputter process was optimized in order to improve resistivity (< 450 µohm.cm) by increasing Hall mobility (> 50 cm²/(V.s)) combined with low free carrier density (3.5E+20 cm^-3). In addition, this study brings insight in the role that hydrogen plays in determining the transport properties of the ITO 97/3 coatings.