High volume production of rugged, high efficiency GaAs/Ge solar cells

The authors describe progress in replacing gallium arsenide substrates with germanium substrates in the high-volume production of GaAs solar cells. The Ge substrates provide the option of larger, stronger, and thinner cells, with all the electrical advantages of GaAs cells. Early optimization procedures enhanced the GaAs/Ge cell output, using the enhanced photovoltage generated at the GaAs/Ge interface. More detailed measurements showed that these optimized efficiency values were obtained under simulated AM0 spectra which had excess output in the near-infrared region. The enhanced V_oc led to higher V_oc temperature coefficients. Present efforts to scale-up GaAs/Ge cell production have concentrated on achieving passive-Ge conditions, for operation under true AM0 conditions. This produces cells with properties of GaAs/GaAs cells with all the mechanical advantages of Ge substrates. AM0 efficiency up to 18.2% has been demonstrated for 4 cm*2 cm passive-Ge GaAs/Ge solar cells.