Electrical and structural properties of twin planes in dendritic web silicon

The electrical and structural properties of dendritic silicon have been measured and compared with solar cell efficiencies. The twin planes in the web and their effect on minority carrier diffusion length were of particular interest. The starting material and the cells were always from the same web strips. Cross-sectional electron-beam-induced current (EBIC) analysis was used to identify differences in the electrical behavior of low- and high-efficiency web material, both in the as-grown state and after solar-cell processing. High-efficiency cells exhibit flat EBIC linescans across the web cross sections, high minority-carrier diffusion lengths, few dislocations, and no defect clusters. Low-efficiency cells show EBIC linescans of reduced amplitude near the twin planes, low diffusion lengths, many dislocations, and electrically active defect clusters at the twin planes. Excessive recombination at the twin planes seems to limit the efficiency of these cells. In both high- and low-efficiency material, DLTS (deep-level transient spectroscopy) peaks present in the as-grown material disappear upon cell processing.<
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