Thermally Diffused Point Contacting by Localized Dielectric Breakdown Solar Cells with Boron Etch Back

The Point contacting by Localized Dielectric Breakdown method utilises dielectric breakdown above a locally doped region to form ohmic contacts for a solar cell rear surface. A complete cell with thermally diffused local doping regions has been fabricated, giving 17.9% efficiency and 0.74 fill factor. Characterization indicates that the major fill factor loss is due to an unexpected high contact resistance at the rear surface. Measurements on the contact resistivity indicate that the low surface doping concentration $(7 \times 10 ^{18} cm ^{-3})$ for the local boron diffused region is the main cause for this high contact resistance. This paper demonstrates the fabrication of PLDB cells with an improved boron doping profile with increased surface doping concentrations. The surface doping concentration is then modified using HNA etch-back in order to investigate the impact of surface doping concentration on the contact properties and cell efficiency.