http://www.scientificamerican.com/article.cfm?id=the-solar-cell-that-turns-1-photon-into-2-electrons (http://www.scientificamerican.com/article.cfm?id=the-solar-cell-that-turns-1-photon-into-2-electrons)
Another tehnology that will not come to market soon. :-\
This only increases the total conversion efficiency by 5%.
Gravock
check what happens in a betavoltaic cell,you get one beta particle tunnelling into silicon wafer knocking out thousands of electrons in its ballistic path.same with alphavoltaics,gammavoltaics