Improvements in InP solar cells

Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metal-organic chemical vapor deposition. Air mass zero efficiencies as high as 18.8% (NASA measurement) have been achieved. The best cells, which were those made by ion implantation, show an open-circuit voltage of 873 mV, short-circuit current of 35.7 mA/cm², and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90% in the red end of the spectrum, but drops to 54% in the blue end. Other cells have achieved 74% in the blue end. A preliminary investigation of InP solar cells on foreign substrates has been carried out. Although problems have been encountered with doping of the InP by the substrate, cells of 7.1% efficiency on silicon and cells of 9.4%, efficiency on GaAs have been made.