Simulation of Spalling with a Non-planar Bi-layered Interface Due to the Reuse of the Substrate

Kerfless wafering techniques have the potential to reduce the cost of crystalline silicon (Si) in photovoltaics by saving material and production costs. Thermomechanical spallation from thick wafers with aluminium (Al) in the double function as stressor layer and contacting layer in the final solar cell is one attractive option. In principle this technique might allow to produce multiple thin film solar cells via thermo-mechanical exfoliation, which is essential to be ascertaining for the technique in an industrial context. The aim of this study concerns the feasibility to reuse the parental Si substrate in the presence of non-planar Si-Al interface originated by the first exfoliation. A numerical method based on the Finite Element Method (FEM) and Linear Elastic Fracture Mechanics (LEFM) is used to simulate the evolution of the non-planar Si-Al interface after successive exfoliations. We find a partial reduction in the amplitude of the transferred groove on the Si-Al interface for grooves having typical realistic dimension. The numerical results are confirmed by the reduction of the amplitude of the groove observed in the experimental tests. These results are promising for the repeated exfoliation from one substrate, inasmuch as the possible roughness on the parental substrate after the first use does not significantly affect the subsequent exfoliations.