Boron-Oxygen Defect Activation Kinetics along the Height of Cz Ingots–Correlation with the Compositional Properties

The present study focuses on the kinetics of the boron-oxygen defect activation in solar cells fabricated from two Czochralski silicon ingots having different compositional properties (particularly various carbon and germanium contents). We show first that the difference between the experimental and the expected time constants associated with the degradation of the cells performances under illumination due to the boron-oxygen activation is higher in the last solidified part of the ingots. Secondly at such locations a pronounced slowing down of the long-term kinetics is observed. Possible explanations are proposed and discussed among which the segregation of some impurities which could interact with oxygen or oxygen dimers. Particularly a clear correlation is highlighted between the carbon content and the amplitude of this slowing down. Eventually this work shows that the experimental conditions generally used for evaluating the amplitude of the light-induced degradation effects have to be reconsidered.