Laser processing for back-contacted silicon solar cells

We use laser ablation of Si and laser ablation of organic coatings on Si wafers for locally processing solar cells. We present experimental investigations of a variety of pulsed lasers, such as Nd:YAG laser and frequency-converted solid state lasers concerning their applicability of laser structuring silicon solar cells. The laser-induced Si crystal damage is investigated by means of contact-less minority carrier lifetime measurements. With our optimized laser parameters for structuring monocristalline Si we find the depth of the laser-induced damage to be 3 µm for the frequency-tripled (λ = 355 nm), 4 µm for the frequency-doubled (λ = 532 nm), and above 20 µm for the Nd:YAG (λ = 1064 nm) laser. One-dimensional simulation results show the influence of a lowered minority carrier lifetime in the silicon absorber on the performance of a back junction solar cell. With an optimized laser process we fabricate solar cells with a Rear Interdigitated contact scheme that is metallized by one Single vacuum Evaporation step (RISE). The so-called RISE process aims at highest efficiencies in combination with low process complexity.