Roll-to-roll flexible back-contacted c-Si PV modules: performance analysis and impact of mechanical and thermal stress

Flexible crystalline-silicon photovoltaics (Fc-SiPV) have recently attracted attention, because they enable solar energy production in applications where lightweight and bendable panels are preferred. However, the lamination process for glass-free solar cells must be carefully optimized, to prevent cracking; in addition, the impact of cracks that form after lamination needs to be investigated, to fully understand how field-induced damage may affect performance and reliability. In this study, we propose a glass-free module architecture with polyethylene terephthalate (PET) as front cover resulting in lightweight modules with crystalline silicon solar cells. We focused on the effectiveness of the roll-to-roll lamination process, on the evaluation of cell performance before and after lamination, and on the role of cracked cells in series-connected mini-modules under different operating conditions. We found that: i) the main efficiency losses are optical in nature, resulting from increased reflections; ii) the lamination does not induce new cracks or electrical damage, but can promote the propagation of pre-existing cracks, typically originating from stress-concentrated regions such as soldering pads; iii) we analyzed mini-modules with damaged (cracked) cells in order to assess what would be the impact of cell damage on module performance when installed outdoor on curved surfaces. These results demonstrate how a low-cost roll-to-roll process can be adopted to fabricate mechanical resilient flexible c-Si mini-modules, while providing new insights into dynamic hot spot formation and current re-distribution governed by crack propagation.