Fabrication of singulated c-Si solar cells for semi-flexible photovoltaic modules

Abstract

The decreasing cost of photovoltaics over the last decade has resulted in a rapid proliferation of solar cells into the energy portfolio of countries like China, the United States, and Germany. Despite great reductions in the levelized cost of electricity for silicon-based photovoltaics, residential- and commercial-scale PV projects are still dominated by soft costs incurred through the distribution, permitting, and installation of panels. Part of this cost can be attributed to the weight of the panels, on the order of 30 kilograms per 300 watt panel, primarily caused by the thick glass protective layer and aluminum framing on the front and edges of the panel, respectively. These materials are necessary to prevent flexure or impacts on the fragile and thin silicon wafers in the solar module. In this thesis, I detail a method called "singulation", whereby intentional cracks are introduced in a grid pattern across the surface of the silicon by laser etching. A thin polyimide coating is then applied to the front of the cells, and an electrode layer is printed on top of this polymer layer. The polyimide acts as a crack termination layer which functions to prevent the intentional cracks from splitting the electrodes. The intentional crack lines then function as small length flexural pivot points about which the smaller silicon sections can bend. The increase in mechanical robustness of this technique was assessed primarily through bending and impact tests. Singulated cells were found to be able to sustain 77.8% greater bending strain before unintentional fracture versus their non-singulated counterparts, and they also were able to achieve a 93.8% reduction in non-functional area versus non-singulated cells in an impact test.