Effect of Stoichiometric Deviations on the Structural Properties of CuInSe2, CuIn0.5Ga0.5Se2 and CuGaSe2.

Ingots of CuInSe2, Culn(0.5)Ga(0.5)Se(2), and CuGaSe2 were synthesized under similar fusion at 1150 degrees C in silisa ampoule, cut into slices and determined their composition by energy dispersive analysis of X-Rays. The structural properties, including the occupation fraction of each atomic sublattice, were studied by X-ray powder diffraction and Rietveld refinement. The Cu occupation number, N(Cu), is lower than one The complex of two Cu vacancies and a substitutional cation, 2V(Cu)+B-Cu(3+) (B-Cu(3+) =In, Ga+In and Ga in CIS, CIGS and CGS respectively in a Cu site) is assumed and would explain the presence of Cu vacancies and allow an estimate of the B3+ concentration in its sublattice. When this increases a decrease in concentration of both Cu in its sublattice and the complex 2V(Cu)+B-Cu(3+) are found. The strucutrual parameters depend on Cu and B3+ sublattice occupancy fractions for all compounds. .In CuGaSe2, the lattice parameters increase as does Ga3+(subl) while the opposite arrives in CuInSe2 for In3+(subl). The distance of Se atom to z axis depends on Cu(subl) for all the compounds increasing in the case of CuInSe2 with V(Cu) and In-cu antisites, decreasing the InSe bond distance. The opposite effect is observed in CuIn0.5Ga0.5Se2, and CuGaSe2.