High Efficiency GaInP/GaAs Tandem Solar Cells

GaInP/GaAs tandem solar cells have achieved new record efficiencies, specifically 25.7% under air-mass 0 (AMO) illumination and 29.5% under AM1.5 global (AM1.5G) illumination. These values are the “highest efficiencies achieved by any solar cell under these illumination conditions. The monolithic, series-connected design of the tandem cells allows them to be substituted for silicon or gallium arsenide cells in photovoltaic panel systems with minimal design changes. The advantages of using GaInP/GaAs tandem solar cells in space and terrestrial applications are discussed primarily in terms of the reduction in balance-of-system costs that accrues when using a higher efficiency cell. The new efficiency values represent significant improvement over previous efficiencies for this materials system, and we identify grid design, back interface passivation and top interface passivation as the three key factors leading to the improvement. In producing the high-efficiency cells, we have addressed nondestructive diagnostics and materials growth reproducibility as well as peak cell performance.