Laser ablation compatible substoichiometric SiO_x/SiN_y passivating rear side mirror for passivated emitter and rear thin-film crystalline silicon solar cells

Fabrication of industrial thin-film crystalline silicon solar cells remains challenging because of the high level of light trapping and surface passivation required to achieve a good conversion efficiency, while reducing the process cost. This work proposes a solution of rear side reflector supplying both passivation and light trapping, and guaranteeing compatibility with a laser process for local opening in order to use the passivated emitter and rear cell architecture. The key element is the use of substoichiometric silicon oxide deposited by plasma-enhanced chemical vapor deposition with a higher silicon concentration than the usual nearly stoichiometric oxide. This material is absorbent at usual ultraviolet laser wavelengths, and thus allows laser ablation with limited substrate heat, greatly reducing substrate damage after ablation. A layer of this oxide is incorporated into a SiO_x/SiN_y dielectric stack, which shows the expected qualities in term of passivation and reflectivity.