Radiation-hard, lightweight 12% AM0 BOL InP/Si solar cells

Indium phosphide (InP) space solar cells were made by Spire on lightweight Si wafers to greatly increase the cell end-of-life (EOL) power density. A NASA-measured best cell efficiency of 12.5% was obtained at one-sun AM0 beginning-of-life (BOL) for a 2/spl times/4 cm cell. Average efficiency for fifteen 2/spl times/2 cm InP heteroepitaxial cells on 16 mil Si wafers tested by NASA was 12.3%. Data are presented comparing 1 MeV electron and 3.9 MeV alpha particle irradiation showing relatively little cell power output degradation out to a very high fluence (less than 20% after a fluence of about 4/spl times/10/sup 16/ 1 MeV electrons/cm/sup 2/, about 40/spl times/ the "standard" fluence). Calculations are presented which show that in very high radiation environments (e.g. van Allen proton belts), these cells can provide over twice as much EOL power density than GaAs/Ge or Si cells.