Thermo-mechanical stress modelling and fracture analysis on ultra-thin silicon solar cell based on super multi-busbar PV modules

Thinning of crystalline silicon (c-Si) wafers will reduce material cost and improve productivity, which significantly impacts the development of solar photovoltaic (PV) industry. However, this process leads to reduction in mechanical strength of the cell and increased solar cell fracture during the manufacturing process. This study investigates the mechanical property of full wafers and half wafers with varying thicknesses, both before and after the slicing process. Thermo- mechanical stress in half cells was analyzed using finite element modeling (FEM) to clarify the origin of cracks, the influence of Si thickness on cracking and the process impacts on eventual cell breakage. Fracture analysis was implemented not only in soldering process but also during lamination and dynamic mechanical loading (DML) tests. Our findings reveal that the thinner solar cells become even more fragile and susceptible to fracture or power attenuation during the module manufacturing process and operation as well. FEM simulations also verify that the highest stress occur in the thinnest Si wafers after soldering, lamination and DML processes, respectively. However, the choice of 16 Cu ribbons with a diameter of 0.26 mm, which is verified and confirmed as the optimal super multi-busbar (SMBB) technology for the ultra-thin solar cells based PV module, can help to reduce the cell stress and improve the module reliability in mass production.