IRON CONCENTRATION IN CZOCHRALSKI SILICON WAFERS AFTER GETTERING BY SCREEN-PRINTED EMITTERS

摘要

Single-sided solar cell emitters created by phosphorus dopant pastes are an alternative to theconventional double-sided POCl_3 emitters. Thereby, during the emitter formation gettering of impurities such as ironis essential to improve the solar grade wafer quality. In this paper, we demonstrate single-sided screen-printedemitters in monocrystalline Czochralski silicon (Cz-Si) wafers with an improved gettering of iron compared toconventional double-sided POCl_3 emitters due to process induced extended gettering time. The phosphorus dopantpastes used had to be chosen carefully to provide a sufficiently suitable emitter sheet resistance and to avoid any ironcontamination from the phosphorus dopant paste, which is observed in turn. The iron concentration is determinedfrom the minority carrier lifetime obtained by quasi-steady-state photoconductance measurements, down to very lowlevels for solar cell material. In addition, the well-known metastable boron-oxygen complexes in Cz-Si have beentransferred into a stable state by light-induced degradation prior to these measurements. Therefore, this work showsthe correct way how to determine the iron concentration [Fe], when p-type Cz-Si wafers are used.