Novel solar cell concentrator photovoltaic converter system. Final report, April 1979

Attainment of photovoltaic conversion efficiencies greater than 25% to 30%, thought necessary to make concentrator photovoltaics economical, seems possible if the solar spectrum is more efficiently used by splitting the spectrum and using solar cells of different bandgaps. For initial work on multi-bandgap concentrator solar cells, the spectrum has been split by an optical filter which transmits light above 1.6 eV and below 1.1 eV and reflects light between 1.1 and 1.6 eV. Theoretical modeling of possible conversion efficiencies led to the choice of the filter bandpass energies and practical solar cell fabrication considerations have led to the choice of silicon and the Al/sub x/Ga/sub 1-x/As system for initial develoment work. Special silicon concentrator solar cells with a p/sup +/:n-:n/sup +/ structure have been designed for this application and have attained apparent cell converson efficiencies of 16.2% at a current ratio of 455 suns. An Al/sub 0/ /sub 93/Ga/sub 0/ /sub 07/As/Al/sub 0/ /sub 17/Ga/sub 0/ /sub 83/As solar cell with a bandgap near 1.6 eV has attained a cell converson efficiency of 20.4% at a flux concentration of 525 suns. These cells have been packaged and combined with the spectrum splitting filter to give conversion efficiencies at 50/sup 0/C,more » including the filter and the cells, of 27.0% at 113 suns and 26.0% at 489 suns.« less