Minority Carrier Diffusion Lengths in Multi-Crystalline Silicon Wafers and Solar Cells

Abstract

In the present contribution the effect of the processing steps on the characteristics of ribbon-, cast-multicrystalline and Cz monocrystalline Si is investigated by SPV (Surface PhotoVoltage) analyses. The minority carrier diffusion length L D has been measured by SPV in noncontact and non-destructive mode at the different processing steps employed in solar cell processing. The diffusion length, related to the material recombination properties, increases after the emitter diffusion process and increases after the subsequent process steps. The comparison between the characteristics of the starting material and the properties of the final devices allowed us to understand the role of the gettering phenomena occurred during the processing steps and their efficiency in impurity removal. This analysis shows that the increase in the diffusion length after the processing steps strongly depends on the quality of the starting material and thus on the material defect content.