The effect of substrate material on nucleation behavior of molten silicon for photovoltaics

To manufacture crystalline silicon for photovoltaic applications, molten silicon is often solidified while in physical contact with a crucible or substrate, where nucleation of new grains should be minimized. This study aims to determine the propensity of silicon to nucleate in contact with different materials. Differential scanning calorimetry is used to measure the undercooling below the melting temperature of molten silicon in contact with these materials. Dry thermal oxide shows up to 141 °C of undercooling before nucleation occurs, while silicon nitride consistently shows less than 20 °C. Noticeable variation in the level of undercooling may be related to sample deformations or coating thickness. Greater undercooling indicates a lower driving force for the coating material to nucleate heterogeneously, thus promoting growth of larger grains, which will be useful in designing crystal growth processes for photovoltaics.