Capillarity in the processing of photovoltaic silicon

Processing of photovoltaic quality silicon (PV Si) starting from metallurgical Si involves contact between liquid silicon and the refractory materials used as crucibles for melting and crystallisation. The interactions (i.e. wetting, infiltration and sticking) between silicon and two types of crucible used in the course of PV Si processing, namely graphite and coated silica, are described and interpreted. A model of the wetting and infiltration phenomena, coupling thermodynamics and kinetics, is used to analyse the influence of the main parameters of the material (microstructure, chemistry) and the process (temperature and atmosphere). Examples are given of the ways to use the understanding of elementary processes at silicon/crucible interfaces in order to select crucible material and determine the desired process parameters.