High-efficiency gallium-arsenide solar cells

Gallium-arsenide solar cells which exhibit conversion efficiencies up to 13 percent have been made. A brief description of the cell geometry and the fabrication processes is given. A typical current-voltage (I-V) curve for such GaAs solar cells is shown and compared to a theoretical curve based on an experimentally determined space-charge-recombination junction current and zero series resistance in the cell. It is shown that internal power dissipation is a small fraction of the energy delivered to the load. Although the junction depth in the final cell is less than a micron, the surface concentration is sufficiently high to keep series-resistance power losses negligible. The effect of the resultant high built-in drift field is to increase the apparent minority-carrier diffusion length, and thus permit a design with high collection efficiency despite the low minority-carrier lifetimes observed in GaAs.