Quantitative Photoelastic Characterization of Residual Strains in Grains of Multicrystalline Silicon

摘要

The residual strain and its variation in multicrystalline Si substrates for solar cells have been quantitatively characterized. The strain was evaluated from the absolute difference of refractive indices |Δn| and the principal direction ψ of strain-induced birefringence measured by scanning infrared polariscope, and the effective photoelastic coefficients calculated numerically at each grain, the crystallographic orientation of which was determined by the electron backscatter diffraction technique. It has been shown that the residual strain increases at grains with multitwin boundaries and in the vicinity of small-angle grain boundaries, reaching the order of 10−4, corresponding to 10 MPa in terms of stress.