Impact of scribe width reduction on the back-contact insulation process for the series connection of thin-film silicon solar cells

Abstract

The loss of active area due to the integrated series connection of thin-film solar cells is one of the major reasons for reduced cell-to-module efficiencies. Therefore, it is crucial to reduce the dead area losses to increase the module efficiency. In this work, the back-contact insulation process (P3) for thin-film silicon modules was evaluated for substrate side laser scribing with 532 nm. A special emphasis was placed on the influence of the P3 scribe width reduction on the electrical properties of the solar module. A strong dependence of the ablation behavior on the processing beam radius and absorber thickness was observed. Calculations of the laser beam intensity distribution predict a decrease in heat-affected zone formation when the processing beam radius decreases. However, due to an increased ablation threshold fluence, measurements showed severe deterioration of the module properties for reduced beam radii. Raman microscopy revealed good agreement between extent/degree of absorber modification at the direct scribe edge, electrical evaluation, and scribe morphology for a-Si:H solar cells, while for a-Si:H/μc-Si:H tandem cells the P3 process evaluation remains challenging.