Aiming at the improvement of the conversion efficiency of a monolithic high-efficiency multi-junction solar cell based on the lattice constant of InP different types of low-band gap n/p solar cells were prepared on the lattice constant of InP via metal organic chemical vapor deposition (MOCVD) using only non-gaseous, so-called alternative precursors like tertiarybutylphosphine (TBP). Employing this less-toxic precursor compared to phosphine an InP single n/p solar cell was prepared as reference yielding the highest internal quantum efficiency reported in the literature. New materials were introduced on the lattice constant of InP, in particular GaAsSb (E-gap = 0.75 eV) and InAlGaAs (E-gap 1.03 eV). The new absorber materials were compared to more established materials like InGaAs (E-gap = 0.75 eV) and InGaAsP (E-gap 1.03 eV). It will be shown that the latter cell with 18% Al reached an internal quantum efficiency close to that of the InGaAsP cell. (c) 2005 Elsevier B.V. All rights reserved.