This article reports on a method for the measurement of residual stress in multicrystalline silicon ribbons, based on the infrared photoelastic technique. This self-calibrating method allows the in situ determination of the photoelastic coefficients and can thus be used for any crystal orientation. The method was validated by the experimental determination of the photoelastic coefficient of monocrystalline (100) silicon wafers and by comparison with strain measurements using asymmetrical x-ray diffraction. The distribution of residual stress in multicrystalline silicon ribbons was also measured. The results showed strong evidence for tensile stress in the central region and compressive stress near the edges of the ribbons. Both the measured residual stress and the photoelastic coefficient distributions are correlated to grain boundaries.

In this paper, we report on the first solar cells fabricated on silicon foils employing the stress-induced liftoff methodcut technique and using an epoxy stress-inducing layer. The latter is a 900-μm-thick epoxy layer, which was manually dispensed on the surface of a monocrystalline silicon sample and cured at 150 °C for 1 h. The crack propagation is then activated by cooling down the sample to room temperature on an aluminum plate. The structural and electrical properties of the resulting silicon foils are presented. The thickness of the silicon foil and the maximum roughness height after this process are found to be around 130 and 37.4 μm, respectively. Tensile and compressive regions present in the foil were detected by the birefringence technique and indicate the formation of structural defects such as dislocations during the process. Average minority carrier lifetimes around 28 μs were measured on n-type silicon foils after surface passivation by an iodine-ethanol solution. Photon conversion efficiencies of 12.6% and 13.4% are measured using conventional sun simulator (1-sun AM1.5G) and SINTON Suns-Voc setup systems, respectively.

We investigate the relationships between growth rate, time-temperature profile, residual stress, dislocation density, and electrical performance of silicon ribbons grown via optical zone melting. The time-temperature profiles of ribbons grown at different velocities were investigated using direct measurements and computational fluid dynamics (CFD) modeling. Residual stresses up to 20 MPa were measured using infrared birefringence imaging. The effect of crystallization speed on dislocation density and residual stress is discussed from the context of thermal stresses during growth. More broadly, we demonstrate the usefulness of combining spatially resolved stress and microstructure measurements with CFD simulations toward optimizing kerfless silicon wafer quality.