Improved energy conversion efficiency of GaAs solar cells for space based on multilayer top contacts

Abstract

The use of optimized multilayer top contact metallization rather than single-thickness contacts can improve the efficiency of optimized n-p GaAs solar cells by 3.3% for a 4 cm × 4cm geometry and by 1.3% for a 2 cm × 2 cm geometry. Multilayer top contacts are also more tolerant of variations in semiconductor layer thickness and doping levels. There is a 3.4% efficiency gain for the 4 cm × 4 cm solar cell and a 1.5% gain for the 2 cm × 2 cm solar cell if a worst case model is assumed where the collector layer and window layer sheet resistivities are ten times greater than desired. It is also demonstrated that the optimized multilayer contacts on the n-p device are more efficient than those on similarly optimized p-n devices (1.1% for the 2 cm × 2 cm solar cell and 1.0% for the 4 cm × 4 cm solar cell). A description of the power losses due to the top contacts is developed from first principles. An optimization process follows which minimizes the losses for multilayer top contacts. The optimized multilayer contacts are then analyzed for various semiconductor layer thickness and doping level changes for both the 4 cm × 4 cm and 2 cm × 2 cm solar cells as well as the n-p and p-n structures.