Enabling curvable silicon photovoltaics technology using polycarbonate-sandwiched laminate design

Abstract

Cracks in brittle silicon solar cells (wafers) are a major concern in the solar photovoltaics (PV) industry. Because of the slicing of the wafers from large ingots and further stressing during subsequent operations such as soldering and laser cutting, silicon (Si) solar cells often contain microcracks that may grow into larger cracks during cell integration into a PV module. Through our previous works on residual stress probing using synchrotron scanning X-ray microdiffraction (μSXRD) experiments, finite-element modelling of the manufacturing sequences (from cells to laminate) have been validated to predict the stresses highly accurately in the conventional PV module design (glass-cell-backsheet). In the present work, we use those validated finite element methodologies to predict the residual stresses in a novel PV module design in which silicon cells are sandwiched between polycarbonate (PC) sheets – the lightweight PC-cell-PC module. It is shown that the post-lamination residual stresses in the cells are highly compressive, which is good for inhibiting crack growth. This feature also enables the novel PV modules to be curved without the cells cracking, which favors its application to building-integrated or automotive-integrated PV modules. We demonstrate the basic feasibility of the concept – with mini curved PC-sandwiched laminates, showing the upper bounds of the achievable curvature (and their associated stress levels) without any observable cracks in the cells as determined by electroluminescence imaging. The curving here is utilized to demonstrate the larger extent of mechanical stresses the same silicon solar cells could withstand with the PC-PC design.