Study on the properties of CuInSe2 ingots grown from the melt using stoichiometric and non-stoichiometric charges

CuInSe2 (CIS) ingots have been prepared by direct reaction of stoichiometric and non-stoichiometric proportions of high-purity Cu, In and Se. Two approaches, namely the one-ampoule process (quartz crucible) and two-ampoule process (graphite crucible) were investigated to grow the crystals, using starting charges with excess copper, and (nearly stoichiometric and with excess indium), respectively. The effect of deviation from stoichiometry in the charge on the physical properties of the resulting polycrystals is presented. Compositional analysis of the best part of the ingots with starting metals ratio (Cu/In) greater than or equal to 1 showed that the matrix preserved the original character of the charge and evidenced that the CIS chalcopyrite structure, α-CIS, tolerates well a large In excess. In contrast, the composition of the crystal prepared with a 10% Cu excess was nearly-stoichiometric, with chemical images revealing the formation of heterogeneous phases besides α-CIS. The inclusions precipitation was found to increase toward the ingot base. Interestingly, powder X-ray diffraction measurements revealed the presence of secondary phases rather in all the samples. The corresponding diffraction peaks were however few and very weak, with intensities of less than 3% the maximum value recorded for the CIS (1 1 2) plane.