Structural investigation of the Cu2Se–In2Se3–Ga2Se3 phase diagram, X-ray photoemission and optical properties of the Cu1−z(In0.5Ga0.5)1+z/3Se2 compounds

Abstract

Structures of compounds in the Cu 2 Se-In 2 Se 3-Ga 2 Se 3 system have been investigated through X-ray diffraction. Single crystal structure studies for the so-called stoichiometric compounds Cu(In,Ga)Se 2 (CIGSe) confirm that the chalcopyrite structure (space group I4¯ 2d) is very flexible and can adapt itself to the substitution of Ga for In. On the other hand a structure modification is evidenced in the Cu 1Àz (In 0.5 Ga 0.5) 1+z/3 Se 2 series when the copper vacancy ratio (z) increases; the chalcopyrite structure turns to a modified-stannite structure (I4¯ 2m) when zZ0.26. There is a continuous evolution of the structure from Cu 0.74 (In 0.5 Ga 0.5) 1.09 Se 2 to Cu 0.25 (In 0.5 Ga 0.5) 1.25 Se 2 ((i.e. Cu(In 0.5 Ga 0.5) 5 Se 8), including Cu 0.4 (In 0.5 Ga 0.5) 1.2 Se 2 (i.e. Cu(In 0.5 Ga 0.5) 3 Se 5). From this single crystal structural investigation, it is definitively clear that no ordered vacancy compound exists in that series. X-ray photoemission spectroscopy study shows for the first time that the surface of powdered Cu 1Àz (In 0.5 Ga 0.5) 1+z/3 Se 2 compounds (za0) is more copper-poor than the bulk. The same result has often been observed on CIGSe thin films material for photovoltaic applications. In addition, optical band gaps of these nonstoichiometric compounds increase from 1.2 to 1.4 eV when z varies from 0 to 0.75.

Deep surface Cu depletion induced by K in high‐efficiency Cu(In,Ga)Se2 solar cell absorbers

“…This leads to a compound close to Cu 2 (In,Ga) 5 Se x . The shoulders visible in the grazing incidence XRD (noted Ψ) indicate the presence of this Cu‐depleted phase, as previously observed by Szaniawski and Souilah . Using the pseudo‐ternary diagram from the latter to estimate the corresponding amount of Se in the second phase, we obtain a stoichiometry of 2:5:8.5.…”

Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process

“…ODC-related phases, comparing to that of the chalcopyrite structure. 15,16 This finding is consistent with results of several authors: a continuous decrease of the tetragonal unit cell parameter as a function of Cu-deficiency in the film has been reported for the Cu(In,Ga)Se 2 single crystal 17 and also for physical vapor deposited Cu(In, Ga)Se 2 thin film. 18 The reduction of the lattice parameter was attributed to the structural modification to more Cu-poor phases.…”

“…Of course, the degree of the Cu-depletion strictly depends on the order of the Cu-deficiency at the bulk region of the film. The presence of the Cu-depleted surface layer has already been detected by the modeling of the grazing incidence x-ray diffraction for the polycrystalline Cu(In,Ga)Se 2 thin film 18 and also for the Cu(In,Ga)Se 2 powder compound, 17 as evidenced by the x-ray photoemission spectroscopy study. Therefore, the Cu-poor surface region appears to be a general phenomenon in CIGSbased material.…”

Thermal expansion of CuInSe2 in the 11–1,073 K range: an X-ray diffraction study

“…Table 1 presents the structural data of monocrystalline CuInSe 2 [29,[43][44][45][46], Table 2 shows data obtained by powder diffraction structure refinement using Rietveld or Le Bail method [15,23,[47][48][49][50][51][52][53][54], Table 3 provides data obtained by powder and single crystal diffraction using traditional methods [16,27,28,55,56] and Table 4 provides data for thin films and nanocrystals [57][58][59][60][61][62][63]; more data for comparison can be found in [15,48,64] (in the last reference, theoretical values have also been considered). In Fig.…”