Control of metal impurities in “dirty” multicrystalline silicon for solar cells

The rapid growth of the global photovoltaics (PV) industry is increasingly limited by the availability of suitable Si feedstock material. Therefore, it is very important to explore new approaches that might allow processing of solar cells with satisfactory energy conversion efficiency based on inexpensive feedstock material with less stringent impurity control, i.e., “dirty” silicon. Our detailed studies of the distribution of metal impurity clusters in multicrystalline Si have demonstrated that cells with the same total impurity content can have widely different minority carrier diffusion lengths based on the distribution of the metals, i.e., whether they are dispersed throughout the material or concentrated in a few, large clusters. Possible approaches to defect engineering of metal clusters in silicon are discussed.