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Title: Potential-induced degradation in solar cells: Electronic structure and diffusion mechanism of sodium in stacking faults of silicon

Sodium decorated stacking faults (SFs) were recently identified as the primary cause of potential-induced degradation in silicon (Si) solar-cells due to local electrical short-circuiting of the p-n junctions. In the present study, we investigate these defects by first principles calculations based on density functional theory in order to elucidate their structural, thermodynamic, and electronic properties. Our calculations show that the presence of sodium (Na) atoms leads to a substantial elongation of the Si-Si bonds across the SF, and the coverage and continuity of the Na layer strongly affect the diffusion behavior of Na within the SF. An analysis of the electronic structure reveals that the presence of Na in the SF gives rise to partially occupied defect levels within the Si band gap that participate in electrical conduction along the SF.
Authors:
;  [1] ;  [2] ; ;  [1]
  1. Fraunhofer Institut für Werkstoffmechanik IWM, Wöhlerstr. 11, 79108 Freiburg (Germany)
  2. (IAM-ZBS), Engelbert-Arnold-Str. 4, 76131 Karlsruhe (Germany)
Publication Date:
OSTI Identifier:
22314377
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ATOMS; DENSITY FUNCTIONAL METHOD; ELECTRICAL FAULTS; ELECTRONIC STRUCTURE; LAYERS; P-N JUNCTIONS; SILICON; SODIUM; SOLAR CELLS; STACKING FAULTS