Advanced Characterization Methods for PV

Freiburg, Fraunhofer ISE - Thursday, January 14th 2016

Session I: Materials

1.5 V. Jordi, CEA INES (F), “Characterization of oxygen-related defects in high-efficiency Czochralski silicon wafers”

Abstract: Oxygen is by far the most abundant impurity in nowadays monocrystalline silicon wafers obtained by the Czochralski process. If harmful as such, Oxygen can however form a plurality of defects during ingot/cell processing, leading to unacceptably large efficiency drops at the solar cell level (up to 4% absolute). As ever higher efficiencies are targeted, the Oxygen content as well as the concentration of the related defects (precipitates, boron-oxygen complexes, thermal donors etc) have to be accurately measured. This is required for instance for quality control purposes, or pulling/cell process optimization. However current non-destructive techniques such as FTIR are not easy transferable to thin as-cut wafers, and do not provide a global picture of oxygen-related populations. In this context, we developed a technique named Oxymap together with AET Technologies (France), based on contactless resistivity measurements and appropriate wafer anneals, which has proven non-destructive and independent of surface state and thickness. We present an overview of the latest results obtained on large measurement volumes, in the frame of the technique developments.