Extended study on short pulse laser ablation of dielectric layers with UV and VIS laser wavelength and pulse durations from fs to ns

A wide range laser pulse duration experiment is carried out including pulse durations from 250 femtoseconds (fs) to 30 nanoseconds (ns) based on four different laser systems, two capable of visible (VIS) and ultra-violet (UV) wavelength. All laser systems are used to ablate PECVD SiO2/SiNX and PECVD-based nitride passivation stacks. Test structure samples for photoluminescence (PL) and scanning electron microscopy (SEM) analysis are ablated as well as typical line patterns for PERC solar cells and fluence test samples for all laser systems. In addition standard multi-crystalline (mc) solar cells are ablated on the front side as proposed in [1] to study laser damage effects due to the reduction of the pseudo fill factor (pFF). Thus a comparison of four different evaluation methods (SEM, pFF, PL, IV) for laser damage is carried out showing a good correlation between PL measurements and VOC and pseudo fill factor values from the IV characteristics on solar cell level. The pFF based method, although it is very reliable, does not provide full information for PERC rear side openings which is attributed to the dependence of the aluminum alloy formation on the surface structure remaining after laser ablation.