Laser Ablation of SiO2/SiNx and AlOx/SiNx Back Side Passivation Stacks for Advanced Cell Architectures

In this paper, we investigate laser ablation of stacks used for back side passivation of PERC and PERL solar cells. The objective of this work is to define laser conditions for a complete and damage-free ablation process of two stacks: the standard SiO2/SiNx PERC passivation stack and AlOx/SiNx layers. For this, we have developed a characterization procedure based on optical microscopy and photoluminescence allowing us to find optimal laser parameters for a soft ablation process. Ablation of SiO2/SiNx and AlOx/SiNx stacks have been performed with UV lasers with either ns or ps pulse lengths. Once the optimal laser ablation parameters have been found, PERC cells have been processed with different laser conditions. The comparison of the PERC cell performances confirms that the optimal laser conditions for the ablation process gives better cell performances. This work allowed us to determine optimal laser parameters for ablation of backs side passivation stacks of PERC cells. This almost damage-free laser process is promising for its implementation in PERL cell processing.