Characterization of the initial rapid decay on light-induced carrier lifetime and cell performance degradation of Czochralski-grown silicon

The rapid initial degradation of Czochralski-grown silicon (Cz-Si) solar cell performance has been investigated. The initial rapid degradation occurs at the beginning of the degradation process and is followed by a second slower degradation. The surface effect due to interface state degradation between the passivation layer and the Si substrate was investigated on several kinds of Cz- and float zone Si (FZ-Si), wafers. Carrier lifetime degradation induced by an illumination for 30 s was observed on every Cz-Si wafer, but no degradation was observed on FZ-Si wafers. Moreover, only the decrease of IR response of a cell was observed as a result of the initial degradation. The results suggest that the degradation occurs in the bulk. The magnitude and decay time of the degradation appear to depend on the wafer resistivity. Defects very similar to boron-oxygen complexes specific to Cz-Si were considered to be responsible. The distinctly small activation energy of 0.19 eV was obtained for the initial degradation, which suggests a fundamentally different defect reaction process. The activation energy of 1.6 eV for the defect annihilation process was obtained for both defects as well.