Increased performance of thin-film GaAs solar cells by rear contact/mirror patterning

Current thin-film GaAs solar cells typically have a completely metal covered rear side that functions as back contact, rear mirror and stable carrier to the solar cell. However, the bottom contact layer, that typically remains whole in this configuration, absorbs a large amount of photons that would otherwise be reflected back into the cell structure. This work identifies and quantifies the performance limits by non-optimal rear contact reflectance in the standard configuration of thin-film GaAs solar cells and proposes a design solution. In this study we show that the total reflectance at the back of the solar cell is increased from 63.5% to 93.2% by partially etching the absorbing GaAs contact layer and applying a dielectric material in the etched regions. Both shallow junction and deep junction cells were produced, and for deep junction solar cells the patterning resulted in a more than linear increase in the open circuit voltage and a linear increase in the short circuit current, which is in good agreement with previously reported numerical models.