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Proceedings Paper

Simulation, modeling, and comparison of III-V tunnel junction designs for high efficiency metamorphic multi-junction solar cells
Author(s): Alexandre W Walker; Jeffrey F. Wheeldon; Christopher E. Valdivia; Gitanjali Kolhatkar; Karin Hinzer
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Paper Abstract

Simulations of AlxGa1-xAs/GaAs (x = 0.3) and AlxGa1-xAs/AlxGa1-xAs (x < 0.2) tunnel junction J-V characteristics are studied for integration into a 2D metamorphic multi-junction solar cell model composed of GaInP/GaAs/InGaAs. A comparison of the simulated solar cell J-V characteristics under AM1.5D spectrum is discussed in terms of short circuit current density (Jsc), open circuit voltage (VOC), fill factor (FF) and efficiency (η) for both tunnel junction designs. Using AlxGa1-xAs/GaAs top and bottom tunnel junctions, the metamorphic solar cell obtained values of Jsc = 12.3 mA/cm2, VOC = 2.56 V, FF = 0.81 and η = 25.5%, whereas the solar cell with the AlxGa1-xAs/AlxGa1-xAs top and bottom tunnel junctions reported values of Jsc = 12.3 mA/cm2, VOC = 2.22 V, FF = 0.81 and η = 22.1%. At open circuit voltage, energy band diagrams show minimal curvature in the electron and hole quasi Fermi levels; furthermore, the difference between the top sub-cell electron quasi Fermi level and the bottom sub-cell hole quasi Fermi level is shown to be equal to qVOC for both designs. The energy band diagram of the complete structure is compared for both tunnel junction designs, showing the difference in energy levels that correspond to the difference in measured open circuit voltage. The observed decrease in open circuit voltage was ΔVOC = 0.34 V, which was attributed to the difference in tunnel junction material band parameters such as bandgap, valence and conduction band offsets at heterojunctions and Fermi level degeneracies due to doping concentration differences.

Paper Details

Date Published: 22 September 2010
PDF: 9 pages
Proc. SPIE 7750, Photonics North 2010, 77502X (22 September 2010); doi: 10.1117/12.872882
Show Author Affiliations
Alexandre W Walker, Univ. of Ottawa (Canada)
Jeffrey F. Wheeldon, Univ. of Ottawa (Canada)
Christopher E. Valdivia, Univ. of Ottawa (Canada)
Gitanjali Kolhatkar, Univ. of Ottawa (Canada)
Karin Hinzer, Univ. of Ottawa (Canada)

Published in SPIE Proceedings Vol. 7750:
Photonics North 2010
Henry P. Schriemer; Rafael N. Kleiman, Editor(s)

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