Developments in GaAs solar cells

The progress in space photovoltaics is reviewed with emphasis on GaAs based solar cells. The maximum practicable efficiency for a single junction device is probably 23-24% under AMO 1 sun illumination. There are two ways to achieve higher efficiency, namely concentrating the incident solar flux or splitting the solar spectrum by utilising multijunction cells to convert energy more effectively over a larger fraction of the solar spectrum. The prospects for the realisation of solar cells which employ these concepts to achieve efficiencies approaching 30% AMO are discussed