Novel approach to short-pulse and ultra-short pulse laser ablation of silicon nitride passivation layers

Laser ablation of passivation layers is one of the most promising processes for high efficiency cell concepts in high throughput solar cell production. Especially on the front side a depth- or material-selective ablation process is required to avoid damage to the sensitive emitter. To develop a fast and reliable laser ablation process with a minimum amount of damage to the emitter it is vital to use the most suitable laser source and to optimize the processing parameters. For identification of the influence of pulse duration on cell performance after ablation a new experimental approach is chosen, where full crystalline solar cells are used as samples. In an iterative experimental sequence ablation of lines between the fingers is alternated with Suns-Voc measurements. The measurements reveal the impact of the laser ablation process on the electrical properties of the solar cell, like pseudo fill factor and open circuit voltage. The method has two decisive advantages com pared to other approaches presented in earlier works: a) the preparation of special samples (e.g. full cells without front metallization) is not required and reliable commercially available standard cells can be used instead; b) the iterative nature of the approach allows an extrapolation to larger ablated areas.