Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

Journal Article · Sun Aug 07 00:00:00 EDT 2016 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4959988· OSTI ID:22597738

Ballif, Christophe; De Wolf, Stefaan ^[1]; Menda, Deneb; Özdemir, Orhan ^[2]; Descoeudres, Antoine; Barraud, Loris ^[3]

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1. Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de la Maladière 71b, CH-2002 Neuchâtel (Switzerland)
2. Department of Physics, Yıldız Technical University, Davutpasa Campus, TR-34210 Esenler, Istanbul (Turkey)
3. CSEM, PV-Center, Jaquet-Droz 1, CH-2002 Neuchâtel (Switzerland)

Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers—inserted between substrate and (front or rear) contacts—since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation of such films as window layers—without degraded carrier collection—demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.

• OSTI ID: 22597738
• Journal Information: Journal of Applied Physics, Vol. 120, Issue 5; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ASYMMETRY
COMPARATIVE EVALUATIONS
ELECTRIC POTENTIAL
ELECTRONS
FIELD EMISSION
FILL FACTORS
FILMS
HETEROJUNCTIONS
HOLES
IMPLEMENTATION
INTERFACES
LAYERS
PASSIVATION
PERFORMANCE
SILICON OXIDES
SILICON SOLAR CELLS
SUBSTRATES
SURFACES
TOPOLOGY
DARK CURRENT