Mechanical strength and reliability of a novel thin monocrystalline silicon solar cell

Abstract

Thin crystalline silicon solar cells, on the order of a few to tens of μm thick, are of interest due to significant material cost reduction and potentially high conversion efficiency. These thin silicon films impose stringent mechanical strength and handling requirements during wafer transfer, cell processing and module integration. Quantitative mechanical and fracture analyses to address reliability issues become necessary. Based on a bi-material foil composed of thin monocrystalline silicon and a supporting substrate fabricated from a novel SOM® (Semiconductor on Metal) kerf-less exfoliation process, closed-form mechanical analyses are introduced and developed to evaluate their strength and fracture behaviors. These analyses include the thermal stress field in the device silicon layer and supporting substrate, the fracture behavior and effects of pyramid structures from surface texturing and the energy release rate at the silicon-substrate interface. It is shown that the introduction of the intrinsic compressive residual strain in the SOM® substrate expands the processing temperature spectrum. The developed analysis and methodology can be readily extended to other thin film solar cell structures with various configurations of device layers and supporting substrates.