Influence and passivation of extended crystallographic defects in polycrystalline siliconReport as inadecuate

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Abstract : Influence and passivation of extended crystallographic defects are investigated in large grained polycrystalline silicon wafers and N+ P solar cells. When the mean grain size exceeds 1 mm, the influence of intragrain defects becomes predominant. It was found that the defects have not by themselves a noticeable recombination activity and that the segregation of impurities oxygen

., could be the main source of trap centres. Two techniques of passivation by hydrogenation are used : ion implantation and anneal in gas flow. The improvements of minority carrier diffusion lengths, and the increase of light beam induced currents at A = 940 nm, indicate that hydrogen effects are essentially bulk effects. Nevertheless, the material is improved up to a depth of about 30 μm only after ion implantation or annealing in gas flow. As desorption of hydrogen occurs at temperatures lower than 500 °C, it is assumed that the passivation is more related to chemical effects with impurities segregated at extended crystallographic defects than the result of the saturation of dangling bonds.

Keywords : p solar cells n sup carrier lifetime crystal defects elemental semiconductors minority carriers passivation silicon solar cells semiconductor extended crystallographic defects polycrystalline wafers grain size intragrain defects segregation impurities trap centres hydrogenation ion implantation minority carrier diffusion lengths light beam induced currents bulk effects annealing desorption chemical effects dangling bonds Si:O

Author: S. Martinuzzi



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