The Junction Producing The Lowest Current Essay

1513 Words Dec 9th, 2014 7 Pages
junction producing the lowest current. Therefore, current density, which has an inverse relationship with bandgap energy, should ideally be equal between the junctions. However, multijunction designs are intrinsically based on a range of bandgaps, so material selection involves a compromise between matched current densities and ideal coverage of bandgaps. Layer thickness can be optimized to minimize losses [7]. Power conversion efficiency is defined as the ratio of electrical power output from the cell to the power of the sunlight striking the surface of the cell. This can be visualized as the ratio of areas under the absorbance spectra and AM1.5G sunlight spectrum (Figure 2). The ultimate achievable efficiency between a theoretical system of the sun (a blackbody at a temperature of 6000K) and a receiver on earth (at an approximate temperature of 300K) is the 95% Carnot efficiency. For a single-junction solar cell under the non-concentrated AM1.5G spectrum, efficiency is limited to approximately 31% (37% at a concentration factor of 1000), as derived in Shockley and Queisser’s detailed balance limit calculation. Because this is the best-case efficiency with one semiconductor junction, this limit can be increased only through the use of concentrator optics and other cell architectures. A three-junction GaInP/GaInAs/Ge cell, as described previously, has a Shockley-Queisser efficiency of 41.4% (50.1% at 1000 sun concentration), indicating a significant improvement over the one-…

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