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

Abstract

Ingots of CuInSe2, CuIn0.5Ga0.5Se2 and CuGaSe2 were synthesized under similar fusion at 1150°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 catio, 2V(Cu)+B3+Cu (B3+Cu= 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)+B3+Cu 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 InCu antisites, decreasing the InSe bond distance. The opposite effect is observed in CuIn0.5Ga0.5Se2, and CuGaSe2.