Study of the crystal features of mc-Si PV cells by laser beam induced current (LBIC)



In this work we present LBIC measurements of a set of commercial multicrystalline silicon samples manufac-tured by different suppliers. The LBIC measurements were obtained with a home-made system, using several excitation wavelengths, equipped with an autofocus system, and controlling the reflected light. This system keeps constant the distance between the microscope objective and the sample, despite the bowing and the surface roughness characteristic of this type of samples. For the calculation of the Leff maps one needs to consider the distribution of the reflected light, which the maps usually show contrasts corresponding to the different grain orientations. The LBIC maps present networks of dark lines, corresponding to regions with high carrier capture rates. The dark line network does not necessarily match the grain boundaries (GB) revealed in the optical images, but many of them are intragarin defects. The trapping activity of the GB is known to depend on the GB angle. Usually, small angle GBs are decorated with defects that make them electrically active, while the large angles GBs are less decorated, and present a weak electrical activity. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)