There is agreement in the literature that Cu(In(1-x)Ga(x))Se(2) (CIGSe) absorber used in solar cells has an optimum composition (x approximate to 0.3) corresponding to a band gap (1.1-1.2 eV) far below the theoretical value giving the maximum (1.4-1.5 eV). This paper presents a re-investigation of the crystal structure of bulk CIGSe compounds for both stoichiometric and Cu-poor compositions. Regardless of the gallium content, all the stoichiometric compounds are found to adopt the well-known chalcopyrite structure (space group 1-42d) while a modification of the structure is evidenced for the high Ga-content Cu-poor compounds. The X-ray diffraction analyses demonstrate that the crystal structure Of Cu(0.743)In(0.543) Ga(0.543)Se(2) is derived from that of the stannite structure (space-group 1-42m). Ab-initio calculations show a strong dependence of the electronic structure near the Fermi level with the copper content. Such modifications are expected to significantly change the optical properties of Cu-poor CIGSe materials. (C) 2008 Elsevier B.V. All rights reserved.