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. Brent On 5/18/2016 10:34 AM, Warren D Smith wrote:
35.4% energy conversion (sun->electric) efficiency achieved. The light was split into 4 spectral bands each handled with a different semiconductor: Ge: 0.67eV Si: 1.1eV GaInAs: 1.41eV GaInP: 1.88eV I don't understand their splitting scheme. Can it be used with scattered sunlight, i.e. which is not coming from just one direction? In any event, it seems to me this whole approach probably is totally uneconomical because Ge and In are rare. http://newsroom.unsw.edu.au/news/science-tech/milestone-solar-cell-efficienc...
(Even greater efficiency has been achieved by the same team but using concentrated sunlight.)