Process influences on LeTID in Ga-doped silicon

Light- and elevated temperature-induced degradation (LeTID), which can lead to significant module power loss in the field, has been extensively studied for boron (B)-doped silicon solar cells in the past. Current mass-production has shifted to gallium (Ga)-doped silicon substrates. Therefore, process influences on LeTID must be re-investigated for the changed acceptor species, as the LeTID-degradation extent and kinetics can be drastically different. We study the influence of the dielectric layer and the firing profile on the LeTID extent in Ga-doped lifetime samples. Furthermore, the effect of the bulk doping concentration is investigated. We find that a dielectric layer with high hydrogen content, a-SiNx:H (PECVD), leads to largest LeTID degradation. However, AlOx (PECVD) interlayers serve as very effective diffusion barriers, thus mitigating LeTID, as expected from studies on B-doped material. We observe no significant dependence of LeTID susceptibility on the doping concentration. Most interestingly, it appears that modifying the peak firing temperature, which has the greatest effect on the extent of LeTID in B-doped silicon, has a much smaller effect on the Ga-doped material, with LeTID being observed even when firing at 700 °C.