Concentrator tandem solar cells based on AlGaAs/GaAs-InP/InGaAs(or GaSb) structures

We have developed high-efficiency IR-transparent AlGaAs/GaAs top cells as well as InP/InGaAs and GaSb bottom cells for mechanically stacked tandem solar cells designed for space application. AlGaAs/GaAs and InP/InGaAs structures are prepared by liquid phase epitaxy, GaSb structures-by Zn-diffusion process. The highest top cell efficiency is 23.8% (AMO, 100 suns, 25/spl deg/C). The infrared-sensitive InP/InGaAs cell efficiency measured under a GaAs IR-filter is 5.9%. The maximum GaSb cell efficiency under GaAs-filter is 5.1%. Mechanically stacked four-terminal tandem solar cells have been fabricated and tested as well. The reached efficiency of an AlGaAs/GaAs-InP/InGaAs tandem cell is 28.2% (AMO, 70 suns, 25/spl deg/C).