Modeling of gettering of precipitated impurities from Si for carrier lifetime improvement in solar cell applications
The liquid aluminum layer method for gettering metallic impurities in multicrystalline Si wafers used for solar cell fabrication is modeled. Aspects modeled include impurity atom diffusion and segregation, and precipitate dissolution using Fe as the impurity. The carrier capture cross section of impurity precipitates is derived. Based on the model, a variable temperature scheme is proposed for faster and more efficient gettering. The gettering efficiency is estimated based on the recombination coefficient of the minority carriers diffusing through the wafer across surfaces, taking into account both dissolved and precipitated impurity.