Multi-Junction Solar Cell

by Michael Bonitatibus

Submitted : Fall 2008

This report covers the topic of acquiring the best efficiency of multi-cell solar panels using combinations of different semi-conductor materials. Using the irradiance values of the solar spectrum at the surface and through the use of numerical integration, the current for a square centimeter of sunlight can be derived. Using the band gap values of various semi-conductor materials, the minimum wavelength to be absorbed for energy can be found for each material. The solar panel with the best rating of efficiency can be made using the correct combination of material for each layer. The current that can be gained by each square centimeter of material limits how much current the other layers can have flowing through them, as each panel is wired as one circuit. As a result of this, a careful selection of material to absorb the spectrum for each layer must be carefully chosen. This report will analyze two, three, four, and five junction solar cells. The expected results of these calculations are a noticeable increase in efficiency of each cell as the number of junctions is increased. The calculated values gained from this project agree with the expected results as the efficiency of a cell increases as the number of junctions is increased. The return of this efficiency, however, decreases as each junction is further added. This plays an important role of the economical efficiency of multi-junction solar systems as they are very expensive in terms of their use of multiple semiconductor materials as well as complex design.

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