Effects of metal impurities at the edges of cast Si ingot on crystal quality and solar cell performance

•The region of low lifetime (i.e., red zone) in Si wafers can be narrowed down by using the annealing treatment.•A novel slicing direction allowed the fabrication of Si wafers with complete red zone or not in the same side Si block.•The η of the solar cells based on Si wafers without red-zone was 1.7 % higher than that of Si wafers with all red-zone.•The mean η of cells based on wafers from the novel slicing method was 0.11 % higher than that from the traditional slicing method.