[6][7][8] In addition, another emerging technology, concentrator photovoltaics (CPV), uses high-efficient, multi-junction solar cells in combination with optical lenses and a tracking system.
It is possible to build a solar cell identical to a radio, a system known as an optical rectenna, but to date these have not been practical.
On the downside it is energetically and economically expensive to produce silicon in bulk, and great efforts have been made to reduce the amount required.
According to the Shockley–Queisser limit, the majority of a cell's theoretical efficiency is due to the difference in energy between the bandgap and solar photon.
Thin-films of amorphous silicon have been employed instead, notably Uni-Solar's products, but other issues have prevented these from matching the performance of traditional cells.
[10] Numerical analysis shows that the "perfect" single-layer solar cell should have a bandgap of 1.13 eV, almost exactly that of silicon.