Boron-oxygen related light-induced degradation of Si solar cells: Transformation between minority carrier traps and recombination active centers

Abstract

Light-induced degradation (LID) has a considerable impact on solar cells made from boron-doped Czochralski (Cz) grown silicon wafers. Thus, a great effort has been made to investigate this type of degradation. Recently, it has been suggested that minority carrier traps are acting as precursors to the LID-related defects and that the enhanced recombination might occur through a trap-assisted Auger process. In this study, we investigate the former suggestion using photoconductance measurement of boron-doped Cz wafers in the course of LID. A clear anti-correlation between minority carrier trap density and LID extent has been found. We detect minority carrier traps in the dark annealed state which disappear upon LID. A time constant of $55\pm 5$ min for trap annihilation under 1 sun illumination at 60 °C has been determined, in agreement with previous findings regarding the LID-related defects' formation rate. Additionally, the kinetic of the traps is studied at different temperatures ranging from 25 °C to 100 °C. This study highlights the fact that despite decades of LID-related research, new insights can be obtained when using new approaches, such as those presented in this paper.