Layered Quaternary Compounds in the Cu2S-In2S3-Ga2S3 system.

Several new materials with four structure-types (e.g., Cu0.32In1.74Ga0.84S4 (CIGS4), Cu0.65In1.75Ga1.4S5 (CIGS5), Cu1.44In2.77Ga0.76S6 (CIGS6), and Cu1.1In2.49Ga1.8S7 (CIGS7)) have been evidenced in the Cu2S-In2S3-Ga2S3 pseudo-ternary system. All of them present a 2D structure built upon infinite 2/∞[InS2] layers ((InS6) octahedra sharing edges) on which condense on both sides mono-, bi-, or tri-2/∞[MS] layers ((MS4) tetrahedra (M = Cu, In, Ga) sharing corners). (M(Td))n-2(In(Oh))Sn slabs are separated from each other by a van der Waals gap, and subscript n refers to the number of sulfur layers within the building block. These compounds have the propensity to display stacking faults but also polymorphic forms. Their optical gap (ca. 1.7 eV) is quite similar to the one of the Cu(In0.7Ga0.3)S2 chalcopyrite absorbers used in tandem solar cells, and the major charge carriers are holes. This suggests that they might be very attractive for photovoltaic applications in thin film devices but also for photocatalysis.

Crystal Chemistry, Optical-Electronic Properties, and Electronic Structure of Cd1- xIn2+2 x/3S4 Compounds (0 ≤ x ≤ 1), Potential Buffer in CIGS-Based Thin-Film Solar Cells.

CdIn2S4 and In2S3 compounds were both previously studied as buffer layers in CIGS-based thin-film solar cells, each of them exhibiting advantages and disadvantages. Thus, we naturally embarked on the study of the CdIn2S4-In2S3 system, and a series of Cd1- xIn2+2 x/3S4 (0 ≤ x ≤ 1) materials were prepared and characterized. Our results show that two solid solutions exist. The aliovalent substitution of cadmium(II) by indium(III) induces a structural transition at x ≈ 0.7 from cubic spinel Fd3̅ m to tetragonal spinel I41/ amd that is related to an ordering of cadmium vacancies. Despite this transition, the variation of optical gap is continuous and decreases from 2.34 to 2.11 eV going from CdIn2S4 to In2S3 while all compounds retain an n-type behavior. In contrast with the Al xIn2-xS3 solid solution, no saturation of the gap is observed. Moreover, XPS analyses indicate a difference between surface and volume composition of the grains for Cd-poor compounds. The use of Cd1- xIn2+2 x/3S4 compounds could be a good alternative to CdIn2S4 and In2S3 to improve CIGS/buffer interfaces with a compromise between photovoltaic conversion efficiency and cadmium content.

Cationic and Anionic Disorder in CZTSSe Kesterite Compounds: A Chemical Crystallography Study.

The cationic and anionic disorder in the Cu2ZnSnSe4-Cu2ZnSnS4 (CZTSe-CZTS) system has been investigated through a chemical crystallography approach including X-ray diffraction (in conventional and resonant setup), 119Sn and 77Se NMR spectroscopy, and high-resolution transmission electron microscopy (HRTEM) techniques. Single-crystal XRD analysis demonstrates that the studied compounds behave as a solid solution with the kesterite crystal structure in the whole S/(S + Se) composition range. As previously reported for pure sulfide and pure selenide compounds, the 119Sn NMR spectroscopy study gives clear evidence that the level of Cu/Zn disorder in mixed S/Se compounds depends on the thermal history of the samples (slow cooled or quenched). This conclusion is also supported by the investigation of the 77Se NMR spectra. The resonant single-crystal XRD technique shows that regardless of the duration of annealing step below the order-disorder critical temperature the ordering is not a long-range phenomenon. Finally, for the very first time, HREM images of pure selenide and mixed S/Se crystals clearly show that these compounds have different microstructures. Indeed, only the mixed S/Se compound exhibits a mosaic-type contrast which could be the sign of short-range anionic order. Calculated images corroborate that HRTEM contrast is highly dependent on the nature of the anion as well as on the local anionic order.

The stability domain of the selenide kesterite photovoltaic materials and NMR investigation of the Cu/Zn disorder in Cu2ZnSnSe4 (CZTSe).

Bulk compounds, prepared via the ceramic route, related to Cu2ZnSnSe4 (CZTSe), a material considered for use in photovoltaic devices, were investigated using NMR spectroscopy, electron-probe microanalyses and X-ray diffraction. These materials adopt the kesterite structure regardless of the Cu and Zn contents. It is also shown that the stability domain of the copper-poor quaternary phases is wider for selenide derivatives than for sulphides. Finally, the Cu/Zn disorder level in CZTSe is found to be higher when the samples are quenched, which is reminiscent of the behaviour of the parent sulphide compounds CZTS.

Solid-state NMR and Raman spectroscopy to address the local structure of defects and the tricky issue of the Cu/Zn disorder in Cu-poor, Zn-rich CZTS materials.

The material Cu2ZnSn(S,Se)4 (CZTS) offers a promising indium-free alternative to Cu(In,Ga)Se2 for the absorber layer in thin-film solar cells. It is known that the highest solar energy conversion efficiencies are reached for Cu-poor, Zn-rich CZTS compositions and that too much disorder at the Cu and Zn sites can have a negative impact on the device performance. In this article, we investigate the structures of [VCu + ZnCu] A-type and [2ZnCu + ZnSn] B-type defect complexes and their impact on the long-range Cu/Zn disorder. To that end, we use (119)Sn, (65)Cu, and (67)Zn solid-state NMR and Raman spectroscopy to characterize powdered CZTS samples. For both A- and B-type substitutions, our NMR investigations demonstrate the clustering of the complexes. Moreover, we show that (A+B)-type compounds should be considered as A-type and B-type compounds, since no interaction seems to exist between [VCu + ZnCu] and [2ZnCu + ZnSn] defect complexes. In addition, it is worth noting that [2ZnCu + ZnSn] complexes have only a minor impact on the level of disorder at the Cu and Zn sites. In contrast, [VCu + ZnCu] complexes seem to restrain the random distribution of Cu at the Zn site and of Zn at the Cu site; i.e., the long-range Cu/Zn disorder. Raman characterization of the CZTS samples was also conducted. The Q = I287/I303 and the newly introduced Q' = I338/(I366 + I374) ratios determined from Raman spectra collected at 785 nm turn out to be very sensitive to the level of Cu/Zn disorder. Moreover, they can be used to differentiate the nature of the substitution in slow-cooled materials.

X-ray resonant single-crystal diffraction technique, a powerful tool to investigate the kesterite structure of the photovoltaic Cu2ZnSnS4 compound.

Cu/Zn disorder in the kesterite Cu2ZnSnS4 derivatives used for thin film based solar cells is an important issue for photovoltaic performances. Unfortunately, Cu and Zn cannot be distinguished by conventional laboratory X-ray diffraction. This paper reports on a resonant diffraction investigation of a Cu2ZnSnS4 single crystal from a quenched powdered sample. The full disorder of Cu and Zn in the z = 1/4 atomic plane is shown. The structure, namely disordered kesterite, is then described in the I42m space group.

Multinuclear (67Zn, 119Sn and 65Cu) NMR spectroscopy--an ideal technique to probe the cationic ordering in Cu2ZnSnS4 photovoltaic materials.

For the very first time, (67)Zn, (119)Sn and (65)Cu NMR investigations have been carried out on Cu2ZnSnS4 derivatives (CZTS) for photovoltaic applications. NMR spectroscopy is shown to be sensitive enough to probe the Cu/Zn disorder within the kesterite structure of the studied compounds. In addition, reference spectra of Cu2ZnSnS4 are provided, and experimental (67)Zn and (65)Cu parameters are compared with ab initio calculations.

New three-dimensional thiostannates composed of linked Cu8S12 clusters and the first example of a mixed-metal Cu7SnS12 cluster.

Three new compounds (enH)(6+n)Cu(40)Sn(15)S(60) (1), (enH)(3)Cu(7)Sn(4)S(12) (2), and (trenH(3))Cu(7)Sn(4)S(12) (tren = tris(2-aminoethyl)amine) (3) containing Cu(8)S(12) and Cu(7)SnS(12) clusters have been prepared from direct solvothermal reaction of the elements in amine solvents. In 1, the cubic close-packed arrangement of Cu(8)S(12) clusters, interconnected by capping SnS(4) tetrahedra and CuS(3) triangles, form two interpenetrating channel networks that are presumably filled with disordered solvent molecules. Structures 2 and 3 contain well-ordered, protonated amine molecules and Cu(7)SnS(12) clusters. The clusters are connected by SnS(4) tetrahedra to form a three-dimensional structure with ReO(3) topology. (119)Sn Mössbauer measurement is consistent with Sn(IV) atoms linking, and Sn(II) atoms within, the mixed-metal Cu(7)SnS(12) clusters.

In situ XRD, XAS, and magnetic susceptibility study of the reduction of ammonium nickel phosphate NiNH4PO4 x H2O into nickel phosphide.

The reduction of the ammonium nickel phosphate NiNH(4)PO(4) x H(2)O precursor into nickel phosphide (Ni(2)P), a highly active phase in hydrotreating catalysis, was studied using a combination of magnetic susceptibility and in situ X-ray diffraction and X-ray absorption spectroscopy (XAS) techniques. The transformation of NiNH(4)PO(4) x H(2)O into Ni(2)P could be divided into three distinguishable zones: (1) from room temperature to 250 degrees C, the NiNH(4)PO(4) x H(2)O structure was essentially retained; (2) from 300 to 500 degrees C, only an amorphous phase was observed; (3) above 500 degrees C, a crystallization process occurred with the formation of Ni(2)P. An in situ XAS study and magnetic susceptibility measurements clearly revealed for the first time that the amorphous region corresponds to the nickel pyrophosphate phase alpha-Ni(2)P(2)O(7). The phosphate reduction into phosphide did not start before 550 degrees C and led to the selective formation of Ni(2)P at 650 degrees C.

Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta).

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0

A new lanthanum titanium oxysulfide, La(16)Ti(5)S(17+x)O(17), with x = 0.75 (9).

The title compound, hexadecalanthanum pentatitanium heptadecasulfide heptadecaoxide, La(16)Ti(5)S(17+x)O(17) [x = 0.75 (9)], has been obtained as a by-product in the preparation of new oxychalcogenide compounds in the La/Ti/Ag/S/O system. La(16)Ti(5)S(17+x)O(17) crystallizes in the tetragonal system (space group I4/m) and is isostructural with Nd(16)Ti(5)S(17)O(17). The structure of the title compound consists of an [La(2)S(2)] rock-salt-type framework, which delimits [001] square channels containing two types of chains of corner-sharing Ti(O,S)(6) octahedra. These chains are connected through La(O,S)(n) polyhedra.