Minimising bulk lifetime degradation during the processing of interdigitated back contact silicon solar cells

In this work, we develop a fabrication process for an interdigitated back contact solar cell using BBr3 diffusion to form the p(+) region and POCl3 diffusion to form the n(+) regions. We use the industry standard technology computer-aided design modelling package, Synopsys Sentaurus, to optimize the geometry of the device using doping profiles derived from electrochemical capacitance voltage measurements. Cells are fabricated using n-type float-zone silicon substrates with an emitter fraction of 60%, with localized back surface field and contact holes. Key factors affecting cell performance are identified including the impact of e-beam evaporation, dry etch damage, and bulk defects in the float zone silicon substrate. It is shown that a preoxidation treatment of the wafer can lead to a 2 ms improvement in bulk minority carrier lifetime at the cell level, resulting in a 4% absolute efficiency boost.