EXPERIMENTAL OF THE OPTICAL-ABSORPTION COEFFICIENT OF THE MULTICRYSTALLINE P-TYPE SOLAR GRADE SILICON

The minority carrier diffusion length L characterizes the electrical quality of multicrystalline silicon wafers used for photovoltaics. Its determination before and after different treatments (impurity diffusion, passivation, metallisation) is needfull and requires the accurate knowledge of the optical absorption coefficient alpha in the near infrared. We have determinated the spectral variation of alpha in the range between 0.86 and 1.06 mum and we propose an analytic expression which is very close to those proposed for solar grade single crystals. In addition we have verified that the values of alpha are not affected by long phosphorus diffusion needed to getter metallic impurities.