As semiconductor lithography heads towards 1 nm, a whole new opportunity opens up for solar cells using "quantum dots". Quantum dots in the 2-6 nm size range cover the visible light spectrum. By using feature *size*, rather than feature *composition* through exotic chemicals, quantum dots will enable the efficient capture of light energy in this spectral range w/o using rare chemicals. https://en.wikipedia.org/wiki/Quantum_dot At 06:12 PM 5/18/2016, Brent Meeker wrote:
Germanium is more common than cadmium and indium is about the same as cadmium in the Earth's crust. They are not rare relative to the quantities needed for PV. Using a different semi-conductor to capture photons of different energy wouldn't depend on directionality. The gain in efficiency comes from (a) capturing more photons and (b) capturing a photon with just enough energy to boost the electron into the conduction band with little or no excess.
On 5/18/2016 10:34 AM, Warren D Smith wrote:
In any event, it seems to me this whole approach probably is totally uneconomical because Ge and In are rare.