Solar cells from upgraded metallurgical grade (UMG) and plasma-purified UMG multi-crystalline silicon substrates

High impurity concentrations do not allow the direct use of upgraded metallurgical grade (UMG) Si for PV production. A newly developed prototype inductive plasma-purification system andprocess allowedthe significant reduction of the elements B, C, O, P, Al, Ca, Fe and Ti, depending on the duration of the treatment. Based on this type of purification, it is shown that subsequent appropriate low-cost cell-processing yields homogeneously distributed energyconversion efficiencies throughout the cast ingots. Stabilisedcell efficiencies of up to 14.7% were already experimentally shown to be attainable on highly B-doped (ro0:1O cm) 102 cm 2 multi-crystalline Si substrates of high purity. On plasma-purifiedUMG p-type 0.1–0.2 O cm ingots, efficiencies of up to 12.38% are reached, to be compared with about 10.12% on the same material without prior plasma treatment. Some light-induced degradation is present on processedsamples, which is most likely linkedto the presence of metastable boron–oxygen complexes in the material, andresults in stabilisedefficiencies of, respectively, 12.19% and 10.00%. r 2002 Elsevier Science B.V. All rights reserved.