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The Shockley–Queisser limit, zoomed in near the region of peak efficiency. In a traditional solid-state semiconductor such as silicon, a solar cell is made from two doped crystals, one an n-type semiconductor, which has extra free electrons, and the other a p-type semiconductor, which is lacking free electrons, referred to as "holes."
The band gap (1.34 eV) of an ideal single-junction cell is close to that of silicon (1.1 eV), one of the many reasons that silicon dominates the market. However, silicon's efficiency is limited to about 30% (Shockley–Queisser limit). It is possible to improve on a single-junction cell by vertically stacking cells with different bandgaps ...
The Shockley–Queisser limit for the efficiency of a single-junction solar cell under unconcentrated sunlight at 273 K. This calculated curve uses actual solar spectrum data, and therefore the curve is wiggly from IR absorption bands in the atmosphere. This efficiency limit of ~34% can be exceeded by multijunction solar cells.
Thermodynamic efficiency limit is the absolute maximum theoretically possible conversion efficiency of sunlight to electricity. Its value is about 86%, which is the Chambadal-Novikov efficiency , an approximation related to the Carnot limit , based on the temperature of the photons emitted by the Sun's surface.
The theoretical studies are of practical use because they predict the fundamental limits of a solar cell, and give guidance on the phenomena that contribute to losses and solar cell efficiency. Band diagram of a solar cell, corresponding to very low current (horizontal Fermi level ), very low voltage (metal valence bands at same height), and ...
The numbers are normally not similar as you suggest. But in any case, f c cannot be more than 1, and the upper limit (the Shockley-Queisser limit) requires taking f c = 1. Eric Kvaalen 19:05, 6 September 2016 (UTC) Yes, virtually all above-gap photons come from recombination, but not all recombinations create above-bandgap photons.
Such a cell can have a maximum theoretical power conversion efficiency of 33.7% – the solar power below red (in the infrared) is lost, and the extra energy of the higher colors is also lost. For a two layer cell, one layer should be tuned to 1.64 eV and the other at 0.94 eV, with a theoretical performance of 44%.
These effects produce an upper limit on the efficiency of silicon solar cells, currently around 20% for common modules and up to 27.1% [8] for the best laboratory cells (33.16% is the theoretical maximum efficiency for single band gap solar cells, [9] see Shockley–Queisser limit.).