Comparison of windows for P-on-N InGaP solar cells

Indium gallium phosphide (In/sub 0.49/Ga/sub 0.51/P, /spl ap/1.9 eV) lattice matched to GaAs and Ge is useful as a top cell material for tandem solar cells. The authors present the first measured data on P-on-N InGaP cells. Quantum efficiency is compared for InGaP cells grown with: (1) (/spl ap/2.4 eV) InAlP windows; (2) (/spl ap/2 eV) AlGaAs windows; and (3) no windows and thin emitters (500-5000 /spl Aring/). The best efficiency is for a windowless 500 /spl Aring/ emitter cell (11.4% AM0, 13.5% AM1.5G one-sun at 25/spl deg/C). Conclusions are: (1) AlGaAs windows have a high interface recombination (/spl ap/10/sup 6/ cm/s) with InGaP; (2) InAlP windows have low interface recombination with InGaP, but InAlP cannot be doped heavily P-type (at least with zinc), leading to heterojunction rectification and poor AM0 efficiency in P-on-N designs (but not N-on-P); and (3) at this time the best design for a one-sun P-on-N InGaP cell is a windowless thin emitter (500 /spl Aring/).