Trace elements and charge recombination in polycrystalline photovoltaic materials

Trace element contamination and other defects trap photo-induced charge in photovoltaic materials and devices. With few exceptions, trace elements have a strongly degrading influence on device performance at concentrations below the minimum detectable limit for even the most sensitive ion beam analytical techniques. However, grain boundaries in polycrystalline silicon solar cells may getter trace impurities form surrounding grains and may achieve detectable concentration levels. By combining Proton Induced X-ray Emission (PIXE) to image impurities with Ion Beam Induced Charge (IBIC) to image the charge collection efficiency the existence of spatial correlations between impurity distributions and charge collection efficiency may be investigated. Using these methods we find that the distribution of impurities in a commercial polycrystalline solar cell suggests a correlation between some elements and the variations in charge collection efficiency. (C) 1998 Elsevier Science B.V.