N-type multicrystalline silicon wafers for solar cells

In n-type silicon the capture cross sections of metallic impurities, are neatly smaller than in p-type. So, lifetime and also diffusion length of minority carriers should be neatly higher. This is of a paramount interest for multicrystalline silicon wafers, in which the impurity-defects interaction governs the recombination strength of minority carriers. In 1.2 Ωcm wafer, lifetime is found around 200 μs and diffusion lengths around 220 μm, These values increase strongly after gettering treatments like phosphorus diffusion or AI-Si alloying. Scan maps reveal that extended defects are poorly active, even when the density of dislocation is higher than 10⁵ cm^-2. High quality abrupt p⁺n junctions are obtained by Al-Si alloying and annealing at 850 or 900 °C, which could be used for rear junction cells.