Comparing improved state-of-the-art to former EFG Si-ribbons with respect to solar cell processing and hydrogen passivation

Abstract

Recently, the ASE Company succeeded in enhancing the material quality of their octagon edge-defined film-fed growth (EFG) silicon ribbons resulting in a higher average cell efficiency in the manufacturing line of ASE Americas. In order to quantify and characterize these improvements in material quality, lifetime measurements have been performed on state-of-the-art and, for comparison reasons, also on older EFG material. Moreover, these wafers were subjected to a laboratory solar cell process. Consequently, it has been possible to perform laser beam induced current (LBIC) mappings and to compare the resulting internal quantum efficiency (IQE) mappings to the lifetime measurements performed before cell processing. As a result we found typical, different distributions of lifetime and IQE for the two materials. Further on, the solar cells have been hydrogen passivated using a microwave-induced hydrogen plasma and characterized again so that the impact of this passivation technique on the materials in different states of development could have been investigated. In this way, an appropriate hydrogen defect passivation turned out to reduce the differences between the different kinds of EFG ribbons.