High-efficiency GaAs/CuInSe2 and AlGaAs/CuInSe2 thin-film tandem solar cells

Tandem cell throughput has been increased, and quantities of cells that produce tens of watts of power in total were fabricated. An improved efficiency of 23.1% AM0/one sun at 28°C has been obtained for 4 cm² tandem cells. The mechanically stacked tandem cells consist of an n+:AlGaAs/n:GaAs/p:GaAs/p+:A thin-film top cell and an n+:CdZnS/p:CuInSe₂ thin-film bottom cell. In addition to being highly efficient, the cells are light in weight and radiation resistant. Large numbers of tandem cells have been completed, and individual cell performances exceeded 20% for the GaAs top cell and 3% for the CuInSe₂ (CIS) bottom cell. To attain increased radiation resistance and even higher end-of-life efficiencies, the use of an AlGaAs high-bandgap cell for the upper cell was investigated. Large areas of thin-film AlGaAs were produced using the CLEFT process and filters to simulate AlGaAs cell structures to be used over the CIS cells were fabricated. CIS cells have been tested under these filters. Results of these measurements indicate that significantly higher efficiencies can be expected from the lower cell in this configuration, and very high end-of-life efficiencies are possible with this approach