This paper reports results about aluminium gallium indium phosphide (AlGaInP) based solar cells, in order to define their physical properties for applications in high efficiency devices. In fact, used as top junction, AlGaInP is a promising material for the realization of high efficiency solar cells with more than three junctions. Here AlGaInP single junction solar cells grown on germanium substrates with aluminium concentration varying from 0% to 12% were studied in detail by optical and electrical methods. (C) 2010 Elsevier B.V. All rights reserved.