Improved P-Type or Raw N-Type Multicrystalline Silicon Wafers for Solar Cells

Abstract

In this paper it is shown that the metallic impurities are the main harmful defect in multicrystalline silicon (mc-Si) and that extended defects have only poor recombination strength when they are not decorated, like in float zone silicon wafers or in Cz tricrystals. In n-type mc-Si wafers, the capture cross sections of metallic impurities are neatly smaller than in p-type material and that induce a marked decrease of the influence of dissolved and precipitated impurities and also of the impurity-defect interactions. As a consequence the diffusion lengths and the lifetimes of minority carriers are very high, although the material contains grain boundaries and dislocations. Raw n-type mc-Si wafers appear to be very suited for stable high efficiency solar cells.