High Efficiency Fully Implanted and Co-annealed Bifacial N-type Solar Cells

The aim of the study was to develop a very simple process for the fabrication of large area n-type PERT cells by means of ion implantation. We showed an improvement of the implanted boron activation rate with the annealing temperature by comparing boron SIMS and ECV concentration profiles. A direct positive impact on the boron emitter saturation current density (J0e) was measured. We also investigated the effect of varying the oxidation conditions during the annealing on the implanted boron emitter and the phosphorus BSF quality. Low emitter saturation current density (J0e) of 131 fA/cm2 was measured on textured surfaces, close to the value obtained with diffused B-emitters.A process flow was developed leading to an average efficiency of 19% on 239 cm2 bifacial solar cells, using only eight processing steps with two implantations and one activation annealing.