Process optimization for the front side of P-type silicon solar cells

In this work, we optimize the front side of p-type Czochralski-grown silicon (Cz-Si) solar cells by investigating industrial-type phosphorus diffusion processes, and by adapting the front-side metallization. The utilization of a metallization grid with less coverage, combined with double printing, results in an increase in conversion efficiency of 0.5 %abs for p-type Cz-Si H-pattern cells with aluminium back surface field. By incorporating in-situ oxidation into the diffusion process, we realize a surface doping concentration of ≈ 2·1020 cm-3 for our improved emitter. With this diffusion process, a low emitter dark saturation current density of 85 fA/cm2 is achieved while maintaining low specific contact resistance ≤ 4 mΩcm2. The application of this emitter results in a gain in of 0.4 %abs for p-type Cz-Si high-performance metal wrap trough (HIP-MWT) solar cells in comparison to a diffusion process without in-situ oxidation. For the best performing HIP-MWT cell, reaches 20.5 %. Furthermore, we test the stability and reproducibility of our improved diffusion process in ten runs with 200 wafers each. The mean sheet resistance is found to be (85 ± 2) Ω/sq, revealing high homogeneity over full-load runs.