Local structure ofCuIn3Se5:X-ray absorption fine structure study and first-principles calculations

Abstract

A detailed extended x-ray absorption fine structure ͑EXAFS͒ study of CuInSe 2 and CuIn 3 Se 5 on Cu-K, InK , and Se-K edges was performed. It was found that CuInSe 2 and CuIn 3 Se 5 have well-defined local structure with the same average Cu-Se and In-Se bond lengths. They can be best described by structures containing weighted local tetrahedral cationic clusters around each Se: 2Cuϩ2In (kϭ8), and equal number of V Cu ϩCuϩ2In (k ϭ7) and V Cu ϩ3In (kϭ9), where k denotes the nominal number of valence electrons of the cation clusters. CuInSe 2 consists of 100% kϭ8 clusters and CuIn 3 Se 5 consists of 20% kϭ8 and 40% kϭ7 and 40% kϭ9 clusters. First-principles band structure calculations of various CuInSe 2 , CuIn 3 Se 5 and CuIn 5 Se 8 compounds confirmed that the average Cu-Se and In-Se bond lengths in various ordered vacancy structures are identical to within the calculation uncertainty, in agreement with the present EXAFS measurements. The first-principles calculations also find that the formation energy of several possible crystal structures for CuIn 3 Se 5 and CuIn 5 Se 8 are very similar, which explains why the long-range order of CuIn 3 Se 5 is not uniquely determined.

Structural diversity and electronic properties of Cu2SnX3(X=S, Se): A fir

“…In previous studies of ternary CuInSe 2 and quaternary Cu 2 ZnSnS 4 structures, the valence octet rule was found to play an important role in determining the energy stability of different structures. 7,25,29 The octet rule states that if the sum of the valence electrons of the cations surrounding the anion atom divided by the coordination number (four for tetrahedral structure) plus the number of the anion valence electrons is equal to eight, then the structure has low energy because the anion is in an eight-electron closed-shell state. For tetrahedral Cu 2 ZnSnS 4 , this requires the sum of the cation valence electrons surrounding each anion is equal 8 since S has 6 valence electrons.…”

“…The situation is similar to the CuInSe 2 -derived ordered vacancy compounds. 29 Ordered vacancy compounds are formed by creating ordered (In Cu + 2V Cu ) defect pairs in CuInSe 2 , 30 whereas Cu 2 SnS 3 can be considered as formed by creating ordered (Sn Zn + 2Cu Zn ) defect pairs in Cu 2 ZnSnS 4 .…”

Predicted roles of defects on band offsets and energetics at CIGS (Cu(In,Ga)Se2/CdS) solar cell interfaces and implications for improving performance

“…Experimentally, the structure of the commonly observed Cu deficient phase CuIn 3 Se 5 has been interpreted in terms of several quite different structural models, 28 with no consensus. However, some theoretical models have been proposed to investigate this phase.…”

“…Density functional theory (DFT) 25,26 methods of QM are widely used to investigate the relationship between chemistry and functionality of materials, and some DFT efforts have previously been applied toward such aspects of CIGS solar cells, as defect formation 19,[27][28][29][30][31][32] and levels. [33][34][35] The most important aspect of CIGS solar cells is the CIGS/CdS interface, where the essential physics of photovoltaics takes place.…”

Structural investigation of CuIn5Se8 single crystals by optical second harmonic generation, ellipsometry, and photoluminescence

“…First-principles calculations demonstrated that the total energies of all these models are extremely close: the difference between them not exceeding 4 meV/atom. 6 This explains why the long-period ordering of defects/vacancies cannot be determined experimentally without ambiguity. The structure of CuIn 3 Se 5 depends considerably on the crystal growth conditions and annealing history.…”