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Research Papers

Optical and Electronic Simulation of Silicon/Germanium Tandem Four Terminal Solar Cells

[+] Author and Article Information
Vishnuvardhanan Vijayakumar

e-mail: vishnuvv@eden.rutgers.edu

Dunbar P. Birnie, III

e-mail: dunbar.birnie@rutgers.edu
Department of Materials Science
and Engineering,
Rutgers—State University of New Jersey,
Piscataway, NJ 08854

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received February 3, 2013; final manuscript received May 18, 2013; published online July 18, 2013. Assoc. Editor: Santiago Silvestre.

J. Sol. Energy Eng 136(1), 011009 (Jul 18, 2013) (7 pages) Paper No: SOL-13-1043; doi: 10.1115/1.4024744 History: Received February 03, 2013; Revised May 18, 2013

A tandem solar cell architecture of silicon and germanium solar cells in a mechanical (stack like) arrangement is evaluated to increase the efficiency of light absorption in the far infrared region from 1107 nm to 1907 nm wavelength, which constitutes about 14.5% of the power intensity in the solar AM 1.5 spectrum. In this work, the technical feasibility of tandem solar cells is investigated. Here, we report on detailed electrical and optical simulations of this structure quantifying the various theoretical and practical loss mechanisms in the encapsulation, interfaces, and in the device and indicate that a relative efficiency improvement of 20% may be attainable with silicon and germanium solar cells in this configuration. The optical and electrical parameters for silicon and germanium simulation models were extracted from experimental devices and material vendors. The developed simulation models were validated by comparing the performance of stand-alone silicon and germanium solar cells with experimental devices reported in the literature.

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Figures

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Fig. 1

(a) Theoretical conversion efficiencies based on Shockley and Queisser limit and (b) two junction (mechanical stack) solar cells under AM 1.5 solar spectrum

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Fig. 2

Illustration of the proposed Si/Ge tandem solar cell

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Fig. 3

Illustration of the modeled silicon solar cells. On the left is the HIT and on the right is the bifacial solar cell architecture.

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Fig. 4

Illustration of the modeled germanium solar cell

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Fig. 5

Extinction coefficient of the materials used in the tandem device

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Fig. 6

Refractive index of the materials used in the tandem device

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Fig. 7

Optical loss due to various layers in the top cell before the light gets absorbed by the silicon layer

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Fig. 8

Light spectrum incident on the tandem device, absorbed by silicon cell and light incident on germanium cell

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Fig. 9

Optical loss due to various layers in the bottom cell before the light gets absorbed by the germanium layer

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Fig. 10

Illustration of the light intensity available at silicon and germanium surfaces and the various optical losses in the device

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Fig. 11

Simulated and theoretical maximum current-voltage curves for silicon solar cells

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Fig. 12

External quantum efficiency of simulated silicon and germanium solar cells

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Fig. 13

Simulated and theoretical maximum current-voltage curves for germanium solar cells

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