Growth velocity and grain size of multicrystalline solar cell silicon

Growth rates, grain size and orientation in solar cell silicon has been analyzed in order to study nucleation and growth mechanisms. Samples solidified in an in situ furnace at two different cooling rates, with variations in impurity levels and substrate were analyzed with EBSD. A correlation between cooling rate and growth undercooling was found. Samples with a high cooling rate displayed fast growing crystal needles, while the slower cooled samples did not reach the same growth rates. The solidified samples with the lowest cooling rate, 10 K/min, were dominated by one or a few large grains, while the samples with the higher cooling rate, 30 K/min, had a more uniform and smaller grain distribution, indicating that the highest cooling rate gave a higher nucleation rate. The dominating crystal surface planes were near-{112} for the samples with the largest grains. Variations in crucible substrate such as roughness, coating/no coating did not alter nucleation conditions.

► The growth velocity and grain size of Si on Si3N4 coated SiO2 have been investigated. ► Substrate properties, silicon and cooling rate have been altered. ► Variations in growth velocity, average size and orientations were found to be linked to cooling rate for these small scale experiments.