Abstract
Cracks in silicon wafer solar cells are a major concern in the photovoltaics (PV) industry. Because of the way they are manufactured, silicon (Si) wafer solar cells often contain microcracks that may grow into larger cracks during their integration into a PV module. These cracks could be further propagated by external loads during the transportation and installation of the modules or during field operation when the modules are subjected to snow loads. The implications of large cell cracks are tremendous as they represent module failure and replacement costs to the manufacturer. Even if the propagation of cracks does not result in the catastrophic fracture of cells, they will give rise to significant power loss over time. Thus, the objective of this thesis is to understand the evolution of stresses in silicon cells during the entire manufacturing cycle of a conventional wafer-based PV laminate. This is mainly achieved through the use of finite element methods. Experiments are also performed to validate and verify the fundamental understanding of how these stresses arise. The scope of this thesis is categorised into 3 sections. In the first part, numerical simulations are performed to study the maximum stresses generated in the cells as they undergo the entire manufacturing cycle. New insights into the evolution of stresses in the cells during the manufacturing cycle are presented and it was found that the end of the pressure ramping step contributed to the most critical instance of stress. The next part investigated the effect of geometry and material properties, in particular the thickness of the interconnect and the encapsulant stiffness. Parametric numerical models are performed and the underlying physics of the problem is presented. Experimental techniques are also performed to verify the simulation results. In the last part, the scientific understanding obtained from the stress evolution in PV laminates is used to look into the feasibility of a novel PV design that enhances the mechanical reliability of silicon cells through a careful selection of material cover. The results based on an analytical solution indicate the possibility of enhancing the fracture strength of silicon cells. In conclusion, the research evaluates the critical steps of the PV laminate manufacturing cycle and the findings are be further used to perform optimisation studies in improving the mechanical reliability of PV modules.