Atomic structure of light-induced efficiency-degrading defects in boron-doped Czochralski silicon solar cells

• Published in: Energy & environmental science Vol. 2021; no. 14
• Main Authors: Meyer, Abigail R., Taylor, P. Craig, Venuti, Michael B., Eley, Serena, LaSalvia, Vincenzo, Nemeth, William, Page, Matthew R., Young, David L., Stradins, Paul, Agarwal, Sumit
• Format: Journal Article
• Language: English
• Published: United States Royal Society of Chemistry 13.08.2021
• Subjects: boron doped; Cz Si; Czochralski; electron paramagnetic resonance; EPR; LID; light induced degradation; photovoltaic; SOLAR ENERGY
• ISSN: 1754-5692; 1754-5706

Boron-doped Czochralski (Cz) Si is the most commonly used semiconductor in the fabrication of solar cells. The minority carrier lifetime of boron-doped Cz Si decreases upon exposure to light due to B–O-related defects, which reduce the performance of ~109 solar modules worldwide. Using electron paramagnetic resonance (EPR), we have identified the spin-active paramagnetic signatures of this phenomenon and gained insights into its microscopic mechanism. We found a distinct defect signature, which diminished when the degraded sample was annealed. The second signature, a broad magnetic field spectrum, due to the unionized B acceptors, was present in the annealed state but vanished upon light exposure. These observations show that, on degradation, nearly all the ~1016 cm–3 B atoms in Cz Si complexed with interstitial O atoms, whereas only ~1012 cm–3 of these complexes created defects that were recombination-active. The formation rate of these recombination-active defects correlated with the decay of the minority carrier lifetime. Furthermore, the line shape parameters linked these defects to both B and O impurities in Cz Si.