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

• Published in: Energy & environmental science 2021-10, Vol.14 (1), p.5416-5422
• 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: Article
• Language: English
• Subjects: Annealing; Atomic structure; Boron; Carrier lifetime; Defects; Electron paramagnetic resonance; Electron spin resonance; Fabrication; Impurities; Line shape; Magnetic fields; Minority carriers; Photodegradation; Photovoltaic cells; Recombination; Silicon; Solar cells
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d1ee01788h

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 ∼10 9 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 ∼10 16 cm −3 B atoms in Cz Si complexed with interstitial O atoms, whereas only ∼10 12 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. The line shape parameters linked these defects to both B and O impurities in Cz Si. Using electron paramagnetic resonance, we show that under light exposure, nearly all the 10 16 boron doping sites in Si degrade to form shallow traps. Of these 10 16 traps, only 10 12 -10 13 cm −3 are spin-active and responsible for light-induced degradation.