DLTS study of EFG solar cells

Deep levels in processed edge-defined film-fed-grown (EFG) silicon solar cells were investigated using deep-level transient spectroscopy (DLTS). Several deep levels were observed in the polycrystalline solar cells, typically at concentrations near 10¹² cm^-3. The trap signatures of many of these levels corresponded with those reported for polycrystalline silicon grown by other methods, and therefore tentative trap identifications were made. These levels were associated with iron, aluminum, and other impurities and were often coupled with dislocations or grain boundaries. Deep-level spectra taken in a high-temperature range, extending up to 450 K, revealed a novel feature which appears to be trap related. This feature showed a strong correspondence with bulk lifetime, as determined by the infrared photoconductivity method, for samples fabricated from different crystal growth conditions. A possible explanation for this surprising high-temperature feature is presented