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CdSe semiconductor thin films were grown on indium tin oxide (ITO) coated glass substrates by co-electrochemical deposition method. Deposition potential was kept at - 0.95 V vs. Ag/AgCl reference electrode for ten minutes. Deposition electrolyte includes an aqueous solution of 10 mM CdCl2, 20 mM H(2)SeO(3 )as precursors, 200 mM LiCl as complexing agent, and HCl for adjusting of pH. Deposited CdSe thin film was annealed at 500 degrees C for 30 min in air medium. Precursor and annealed CdSe thin films were characterized using a number of techniques, including SEM, EDX, XRD, UV-vis spectroscopy, and electrochemical impedance spectroscopy. SEM studies show that annealing alters the surface of precursor CdSe film from smooth to granular appearance. According to EDX analyses, the ratio of Cd/Se is close to 1.07 and 1.04 for the precursor and annealed CdSe thin film, respectively. XRD analysis shows that each film has polycrystalline structure. Precursor film has only cubic structure of CdSe, while annealed film has hexagonal structure of CdSe and cubic crystal phase of CdO. Optical energy band gap of the as-deposited CdSe film increases from 1.64 to 1.71 eV after annealing due to the mixture of the two phases. Refractive index against wavelength changes between 2.0 and 3.3. Calculations performed by using the data of Mott-Schottky measurements show that precursor CdSe film has 1.72 x 10(16 )cm(-3), while annealed film is of 3.65 x 10(17 )cm(-3 )carrier concentration. The prepared films exhibit n-type semiconductor character. The study reports energy level diagrams of the produced semiconductor CdSe thin films by using the Mott-Schottky and Tauc's approximations. The carrier transport properties in the interface between active CdSe thin film and electrolyte are discussed based on an equivalent electronic circuit simulated to the Nyquist data of the CdSe/electrolyte system.

The structure and mobility of dislocations in the layered semiconductor InSe is studied within a multiscale approach based on generalized Peierls--Nabarro model with material-specific parametrization derived from first principles. The plasticity of InSe turns out to be attributed to peculiarities of the generalized stacking fault relief for the interlayer dislocation slips such as existence of the stacking fault with a very low energy and low energy barriers. Our results give a consistent microscopic explanation of recently observed [Science {\bf 369}, 542 (2020)] exceptional plasticity of InSe., Comment: 7 pages, 5 figures

Tin diselenide (SnSe2) is a van der Waals semiconductor, which spontaneously forms a subnanometric SnO2 skin once exposed to air. Here, by means of surface-science spectroscopies and density functional theory, we have investigated the charge redistribution at the SnO2-SnSe2 heterojunction in both oxidative and humid environments. Explicitly, we find that the work function of the pristine SnSe2 surface increases by 0.23 and 0.40 eV upon exposure to O2 and air, respectively, with a charge transfer reaching 0.56 e-/SnO2 between the underlying SnSe2 and the SnO2 skin. Remarkably, both pristine SnSe2 and defective SnSe2 display chemical inertness toward water, in contrast to other metal chalcogenides. Conversely, the SnO2-SnSe2 interface formed upon surface oxidation is highly reactive toward water, with subsequent implications for SnSe2-based devices working in ambient humidity, including chemical sensors. Our findings also imply that recent reports on humidity sensing with SnSe2 should be reinterpreted, considering the pivotal role of the oxide skin in the interaction with water molecules. © PID2019-109525RB-I00; Horizon 2020 Framework Programme, H2020: 730872; Ministerio de Economía y Competitividad, MINECO: CEX2018-000805-M, E12H1800010001; Ministero dell’Istruzione, dell’Università e della Ricerca, MIUR; Ministry of Education and Science of the Russian Federation, Minobrnauka: FEUZ-2020-0060 This work has been partially supported by the Spanish Ministerio de Ciencia e Innovación under Project PID2019-109525RB-I00. D.F. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M). D.F. and A.A.T. acknowledge the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. A.P. and G.D. acknowledge the CERIC–ERIC Consortium for the access to the Nanospectroscopy facility and financial support. G.D. acknowledges funding of a Ph.D. fellowship from PON Ricerca e Innovazione 2014–2020 (Project E12H1800010001) by the Italian Ministry of University and Research (MIUR). D.W.B. acknowledges the support by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, Project No. FEUZ-2020-0060).

This is an author-created, un-copyedited version of an article published in 2D Materials. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2053-1583/ab0113, We theoretically study the formation of single-particle bound states confined by strain at the center of bubbles in monolayers of transition-metal dichalcogenides (TMDs). Bubbles ubiquitously form in two-dimensional crystals on top of a substrate by the competition between van der Waals forces and the hydrostatic pressure exerted by trapped fluid. This leads to strong strain at the center of the bubble that reduces the bangap locally, creating potential wells for the electrons that confine states inside. We simulate the spectrum versus the bubble radius for the four semiconducting group VI TMDs, MoS2, WSe2, WS2 and MoSe2, and find an overall Fock-Darwin spectrum of bubble bound states, characterised by small deviations compatible with Berry curvature effects. We analyse the density of states, the state degeneracies, orbital structure and optical transition rules. Our results show that elastic bubbles in these materials are remarkably efficient at confining photocarriers, We acknowledge funding from the Graphene Flagship, contract CNECTICT-604391, from the Comunidad de Madrid through Grant MAD2D-CM, S2013/MIT-3007, from the Spanish Ministry of Economy and Competitiveness through Grants No. RYC-2011-09345, RYC-2016-20663, FIS2015-65706-P, FIS2016-80434-P (AEI/FEDER, EU) and the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377)

International audience; Functionalizing the surface of chalcogenide films is of major interest due to the wide use of these materials in infrared integrated optics. A functionalization route via short peptides that has been already used for silicon, ZnSe and other semiconductors is applied to amorphous films of the ternary Ge-Se-Te system. The biotinylated 12-mer peptides LLADTTHHRPWT and SVSVGMKPSPRP were chosen and used to capture streptavidin. High-resolution atomic force microscopy images highlight that the 12-mer peptide LLADTTHHRPWT provides better interface layers for streptavidin molecule detection.

Recent studies have shown that arsenic can form single-layer phases in buckled honeycomb as well as symmetric washboard structures, named as arsenene. These structures are stable even in freestanding form and are nonmagnetic semiconductors in the energy range which is suitable for various electronic applications. In this study we investigated the adsorption of selected adatoms (H, Li, B, C, N, O, Al, Si, P, Cl, Ti, Ga, Ge, As, Se, and Sb) and physisorption of molecules (H2, O2, and H2O) to these two arsene phases. Since the interaction of these adspecies with arsenene are studied using large supercells, the coupling between adspecies is minimized, and hence our results can be interpreted to mimic the effects of isolated adatom or physisorbed molecule. It is found that the adatoms form strong chemisorption bonds and hence modify the atomic structure and physical properties locally. Some of the adatoms give rise to significant local reconstruction of the atomic structure. Electronic states of some adatoms become spin polarized and attain net magnetic moments; they may even display half-metallic character at high coverage. A majority of adsorbed atoms give rise to localized states in the fundamental band gap. We showed that the interactions between H2, O2, and H2O molecules and single-layer arsenene are rather weak and do not cause any significant changes in the physical properties of these molecules, as well as those of arsenene phases. However, some of these molecules can be dissociated at the edges of the flakes of arsenene structures; their constituents are adsorbed to the edge atoms and cause local reconstructions.

Cu2ZnSnSe4 (CZTSe) is a semiconductor used as the absorber layer in highly promising sustainable thin film solar cells. The authors study the effect of Ar+ etching of copper deficient and zinc excess CZTSe thin films deposited on Mo/glass substrates on the surface elemental composition, measured by x-ray photoelectron spectroscopy, and photoluminescence (PL) spectra. Low temperature PL spectra reveal a broad asymmetrical band at 0.95 eV. The temperature and excitation intensity dependencies of this band suggest that it is a free-to-bound (FB) recombination of electrons from the conduction band with holes localized at an acceptor affected by potential fluctuations. The surface composition of the as grown films demonstrates a strong copper deficiency: [Cu]/[Zn + Sn] = 0.33. The etching of the film surface using Ar+ beam increases [Cu]/[Zn + Sn] to 0.51, which is significantly smaller than that of 0.78 in the bulk, measured by wavelength dispersive x-ray analysis, demonstrating the presence on the surface of a copper-depleted layer. The Ar+ etching drastically reduces the FB band intensity by a factor of 4.5, broadens it and develops a low energy tail. Ar ions displace atoms in CZTSe lattice creating primary radiation defects, vacancies, and interstitials, which recombine at room temperature forming antisite defects with deep energy levels. Some of them generate the observed low energy tail and increase the mean depth of potential fluctuation γ, determined from the shape of the low energy side of FB band, from 24 meV before Ar+ etching to 35 meV after. Other deep defects work as nonradiative recombination centers reducing the intensity of the FB band. © 2018 Author(s).

Sb2Se3 is a highly interesting semiconductor with high absorption coefficient in the visible range and is composed of non-toxic and earth-abundant elements. To overcome the challenge of intrinsic low electrical conductivity of Sb2Se3 crystals, tin-doped (SnxSb1−x)2Se3 semiconductors (x = 0.00, 0.03, 0.05, 0.07 and 0.10) have been synthesized by a conventional melt-quenching method in a vacuum sealed silica tube. With increasing Sn doping concentration, the (SnxSb1−x)2Se3 crystals exhibited a great improvement in electrical conductivity by several orders of magnitude thanks to the great increase of carrier concentration reaching almost 2 × 1016 cm−3. Compared to undoped Sb2Se3, the dark current density of a representative (Sn0.10Sb0.90)2Se3 increased by approximately 10 times and the photocurrent density with essentially visible illumination increased by approximately 14 times. In addition, the doped sample showed a faster, reversible and stable photoresponse. These excellent performances combined with a simple and easily scalable synthesis method pave the way for using this semiconductor for highly efficient photoelectric devices.

International audience; Sb2Se3 is a highly interesting narrow band gap semiconductor with promising applications in new-generation electronic and photoelectronic devices. However, it has intrinsically low electrical conductivity, which limits its broader scope of applications. To overcome this challenge, Sn-doped Sb2Se3 ((SnxSb1−x)2Se3) nanorods with enhanced electrical conductivity are firstly synthesized via a facile hot-injection method. With increasing the doping concentration of Sn4+, the (SnxSb1−x)2Se3 nanorods exhibit several orders of magnitude improvement in electrical conductivity, which originates from the increase of carrier concentration. The photodetector based on the (SnxSb1−x)2Se3 nanorod film shows a higher responsivity (6.21 A W−1) and external quantum efficiency (906%), a lower noise equivalent power (3.14 × 10−13 W Hz−1/2), and a fast response time (0.04 s), surpassing the performance of the Sb2Se3 nanorod film photodetector. In addition, the (SnxSb1−x)2Se3 nanorod film photodetector also displays a broadband spectral response ranging from UV to IR. Those excellent performances unambiguously demonstrate that the (SnxSb1−x)2Se3 nanorods are promising for utilization as highly efficient broadband photodetectors. © The Royal Society of Chemistry.

The nature and dynamics of acceptor states in solution-processed Cu2ZnSn(S,Se)4 (CZTSSe) thin films are investigated by variable temperature photoluminescence (PL) and electrical impedance spectroscopy. Highly pure I-4 phase CZTSSe with the composition Cu1.6ZnSn0.9(S0.23Se0.77)4 is synthesized by sequentially spin coating of dimethyl-formamide/isopropanol solutions containing metal salts and thiourea onto Mo coated glass, followed by annealing in an Se atmosphere at 540 °C. As-annealed films are highly compact with a thickness of 1.3 μm and grain sizes above 800 nm, with a band gap of 1.18 eV. Photovoltaic devices of 0.25 cm2 with the architecture glass/Mo/CZTSSe/CdS/i-ZnO/Al:ZnO demonstrate a power conversion efficiency reaching up to 5.7% in the absence of an anti-reflective coating. Under AM 1.5G illumination at 296 K, the best device shows a 396 mV open-circuit voltage (VOC), 27.8 mA cm-2 short-circuit current (JSC) and 52% fill factor (FF). The overall dispersion of these parameters is under 15% for a total of 20 devices. In the near IR region, PL spectra are dominated by two broad and asymmetrical bands at 1.14 eV (PL1) and 0.95 eV (PL2) with characteristic power and temperature dependences. Analysis of the device electrical impedance spectra also reveals two electron acceptor states with the same activation energy as those observed by PL. This allows assigning PL1 as a radiative recombination at localized copper vacancies (VCu), while PL2 is associated with CuZn antisites, broadened by potential fluctuations (band tails). The impact of these states on device performance as well as other parameters, such as barrier collection heights introduced by partial selenization of the back contact, are discussed. © 2017 The Royal Society of Chemistry. Engineering and Physical Sciences Research Council, EPSRC: EP/L017792/1 Institute of Advanced Studies, University of Bristol, IAS: EP/K035746/1 DT, JWB and DJF are indebted to the Engineering and Physical Sciences Research Council (EPSRC) funded PVTEAM grant (EP/L017792/1). DJF acknowledges Institute of Advanced Studies of the University of Bristol support of a University Research Fellowship 2016. Impedance analysis was performed with a Solartron analyzer procured under EPSRC CDT Capital grant EP/K035746/1. Microscopic imaging and analysis were done at the Chemical Imaging Facility, University of Bristol, with equipment funded by EPSRC Grant ‘‘Atoms to Applications’’ (EP/K035746/1). The authors are grateful for measurement facilities provided at CREST, Loughborough University and the Department of Physics, SUPA, Strathclyde University.

Synthesis and high temperature transport properties of NaCu1+xMn1-xSe2, (x=0-0.75) a new quaternary layered selenide, are reported. NaCuMnSe2 crystallizes in a trigonal unit cell with space group of P-3m1 (a=4.1276 �, c=7.1253 �). The isovalent substitution of Mn2+ by Cu2+ is carried out. All the compositions show semiconducting nature, whereas the Seebeck coefficient increases gradually over the entire measured temperature range. Compositions with x=0 and 0.025 follow thermally activated behavior. With increase in copper concentration the conduction mechanism transforms to 2D variable range hopping (VRH) for x=0.05 and 0.075. � 2014 Elsevier Inc.

Boundary conditions and ranges of the formation of indium(III) sulfide and selenide upon precipitation by thiocarbamide and selenocarbamide are determined. Potentiometric titration of indium chloride (InCl3) in the concentration range of 0.0001 to 0.100 mol/L by a solution of sodium hydroxide is performed. It is found that the following pH ranges are optimal for In 2S3 and In2Se3 film precipitation: from 3.0 to 4.5 and from 9.0 to 14.0. Indium selenide layers 100 to 300 nm thick are prepared on vitroceramic by hydrochemcial precipitation. © 2013 Pleiades Publishing, Ltd.

Starting from its measured structure, the electronic structures and optical absorptions of CdSe single source precursor, cadmium bis(diselenophosphinate) (CSP), have been studied by means of density functional theory calculations. In contrast to covalent bonding in ligand-free cadmium selenide, the Cd–Se bonds in CSP are featured by the coordination of the 4 p electrons of Se atoms, resulting in low net charge on Cd and blue shifted electron transitions. The ligands not only stabilize the CdSe core but also affect the HOMO–LUMO transition. Computations were extended to the corresponding ZnSe and CdS complexes and came to similar conclusions.

A micro-sensor based on selenide glasses for evanescent wave detection in mid-infrared spectral range was designed and fabricated. Ge-Sb-Se thin films were successfully deposited by radio-frequency magnetron sputtering. In order to characterize them spectroscopic ellipsometry, atomic force microscopy and contact angle measurements were employed to study near and middle infrared refractive index, surface roughness and the wettability, respectively. Selenide sputtered films were micro-patterned by means of reactive ion etching with inductively coupled plasma process enabling single-mode propagation at a wavelength of 7.7 µm for a waveguide width between 8 and 12 µm. Finally, optical waveguide surface was functionalized by deposition of a hydrophobic polymer, which will permit detection of organic molecules in water. Thus, the optical transducer is a ridge waveguide composed by cladding and guiding Ge-Sb-Se sputtered layers exhibiting a tailored refractive index contrast and a polymer layer onto its surface ready for environmental detections in middle infrared.

The photoresponse of Cd-doped CuInSe2 (CIS) epitaxial thin films on GaAs(100) was studied using x-ray photoelectron spectroscopy under illumination from a 532 nm laser between sample temperatures of 28-260 degrees C. The initial, air-exposed surface shows little to no photoresponse in the photoelectron binding energies, the Auger electron kinetic energies or peak shapes. Heating between 50 and 130 degrees C in the analysis chamber results in enhanced n-type doping at the surface and an increased light-induced binding energy shift, the magnitude of which persists when the samples are cooled to room temperature from 130 degrees C but which disappears when cooling from 260 degrees C. Extra negative charge trapped on the Cu and Se atoms indicates deep trap states that dissociate after cooling from 260 degrees C. Analysis of the Cd modified Auger parameter under illumination gives experimental verification of electron charging on Cd atoms thought to be shallow donors in CIS. The electron charging under illumination disappears at 130 degrees C but occurs again when the sample is cooled to room temperature. (C) 2016 American Vacuum Society.

Stimulated emission and lasing in Cu(In,Ga)Se2 thin films have been demonstrated at a temperature of 20 K using excitation by a nanosecond pulsed N2 laser with power densities in the range from 2 to 100 kW cm-2. Sharp narrowing of the photoluminescence band, superlinear dependence of its intensity on excitation laser power, as well as stabilization of the spectral position and of the full-width at half-maximum of the band were observed in the films at increasing excitation intensity. The stimulated emission threshold was determined to be 20 kW cm-2. A gain value of 94 cm-1 has been estimated using the variable stripe length method. Several sharp laser modes near 1.13 eV were observed above the laser threshold of I thr ∼ 50 kW cm-2. © 2016 IOP Publishing Ltd.

WOS: 000379457000010, Group II-VI semiconductor honeycomb monolayers have a noncentrosymmetric crystal structure and therefore are expected to be important for nano piezoelectric device applications. This motivated us to perform first principles calculations based on density functional theory to unveil the piezoelectric properties (i.e., piezoelectric stress (e(11)) and piezoelectric strain (d(11)) coefficients) of these monolayer materials with chemical formula MX (where M = Be, Mg, Ca, Sr, Ba, Zr, Cd and X = S, Se, Te). We found that these two-dimensional materials have peculiar piezoelectric properties with d(11) coefficients 1 order of magnitude larger than those of commercially utilized bulk materials. A clear trend in their piezoelectric properties emerges, which, Flemish Science Foundation (FWO-Vl); Methusalem foundation of the Flemish government; Scientific and Technological Research Council of Turkey [TUBITAK-115F024, TUBITAK-113F333]; Hercules foundation; Anadolu University [BAP-1407F335, -1505F200]; Turkish Academy of Sciences (TUBA-GEBIP), This work was supported by the Flemish Science Foundation (FWO-Vl), the Methusalem foundation of the Flemish government and the Bilateral program FWO-TUBITAK between Flanders and Turkey. We acknowledge the support from the Scientific and Technological Research Council of Turkey (TUBITAK-115F024). Computational resources were provided by TUBITAK ULAKBIM, High Performance and Grid Computing Center (TR-Grid e-Infrastructure), and HPC infrastructure of the University of Antwerp (Cal-cUA) a division of the Flemish Supercomputer Center (VSC), which is funded by the Hercules foundation. C.S. acknowledges the support from the Scientific and Technological Research Council of Turkey (TUBITAK-113F333) and the support from Anadolu University (BAP-1407F335, -1505F200), and the Turkish Academy of Sciences (TUBA-GEBIP).

In this manuscript we present the first successful application of a spatial atomic-layer-deposition process to thin film solar cells. Zn(O,S) has been grown by spatial atomic layer deposition (S-ALD) at atmospheric pressure and applied as buffer layer in rigid and flexible CIGS cells by a lab-scale (15×15 cm2) S-ALD set-up. We achieved values of cell efficiency (16 %) higher than the reference cells on glass substrate. © 2017 IEEE. Newport

International audience; Amorphous chalcogenide thin films were fabricated by the pulsed laser deposition technique. Thereafter, the stacks of multilayered thin films for reflectors and microcavity were designed for telecommunication wavelength. The prepared multilayered thin films for reflectors show good compatibility. The microcavity structure consists of Ge25Ga5Sb10S65 (doped with Er3+) spacer layer surrounded by two 5-layer As40Se60/Ge25Sb5S70 reflectors. Scanning/transmission electron microscopy results show good periodicity, great adherence and smooth interfaces between the alternating dielectric layers, which confirms a suitable compatibility between different materials. The results demonstrate that the chalcogenides can be used for preparing vertical Bragg reflectors and microcavity with high quality. © 2016, Tianjin University of Technology and Springer-Verlag Berlin Heidelberg.

In this manuscript we present the first successful application of a spatial atomic-layer-deposition process to thin film solar cells. Zn(O,S) has been grown by spatial atomic layer deposition (S-ALD) at atmospheric pressure and applied as buffer layer in rigid and flexible CIGS cells by a lab-scale (15x15 cm2) S-ALD set-up. We achieved values of cell efficiency (16 %) higher than the reference cells on glass substrate.

Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced self-assembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H(2)O)(4)](NO(3))(2), HNO(3), and Ti(OC(4)H(9))(4) and then aging the samples under 50% humidity at 30 degrees C (denoted as meso-xCd(II)-yTiO(2)). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H(2)S (or H(2)Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H(2)S (or H(2)Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H(2)S or H(2)Se gas). However, this problem can be overcome by further aging the samples at 130 degrees C for a few hours before H(2)S (or H(2)Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO(2). However, the H(2)Se reaction, additionally, needs to be carried at lower H(2)Se pressures in an N(2) atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-yTiO(2). Otherwise, an excessive number of Se(8) particles form in the film samples.

Modification of the absorber surface properties by Cd2+ treatment (Cd2+ partial electrolyte) results in the following: formation of Cd(OH)2 on the absorber surface, deposition of thinner chemical bath-deposited CdS buffer layer, and a smaller space charge region. The impact on electrical performances is as follows: decrease of the series resistance (RS), increase of the fill factor, increase of the efficiency (η), and reduction of the crossover between the dark and light current density-voltage curves. The present contribution aims at determining the impact of modifying the properties of the absorber/buffer layer interface on the electrical performance of Cu2ZnSnSe4 (CZTSe) thin-film solar cells, by using a Cd2+ partial electrolyte (Cd PE) treatment of the absorber before the buffer layer deposition. In this work, CZTSe/CdS solar cells with and without Cd PE treatment were compared with their respective Cu(In,Ga)Se2 (CIGSe)/CdS references. The Cd PE treatment was performed in a chemical bath for 7 min at 70 °C using a basic solution of cadmium acetate. X-ray photoemission spectroscopy measurements have revealed the presence of Cd at the absorber surface after the treatment. The solar cells were characterized using current density-voltage (J-V), external quantum efficiency, and drive-level capacitance profiling measurements. For the CZTSe-based devices, the fill factor increased from 57.7% to 64.0% when using the Cd PE treatment, leading to the improvement of the efficiency (η) from 8.3% to 9.0% for the best solar cells. Similar observations were made on the CIGSe solar cell reference. This effect comes from a considerable reduction of the series resistance (RS) of the dark and light J-V, as determined using the one-diode model. The crossover effect between dark and light J-V curves is also significantly reduced by Cd PE treatment.

International audience; Single crystals of the new ternary selenide Ba0.5Cr5Se8 were synthesized using a self-flux method in fused silica tubes. This new phase was first considered to crystallize in the usual monoclinic symmetry for pseudo-hollandite compounds. However, single-crystal X-ray diffraction study showed unambiguously that Ba0.5Cr5Se8 crystallizes in the P1¯ triclinic space group with cell parameters a = 9.5084(4) Å, b = 7.1788(3) Å, and c = 8.9296(4) Å and α = 89.9979(16)°, β = 104.3958(22)°, γ = 100.8869(17)°, and Z = 2. Bulk samples were prepared by solid-state reaction and sintered using a spark-plasma sintering device. A combination of powder X-ray diffraction and transmission electron microscopy was used to perform structural analysis on spark plasma sintering prepared samples. Ba0.5Cr5Se8 orders antiferromagnetically with TN = 58 K and shows a semiconducting behavior with ρ300K = 0.35 Ω·cm and S300K = 230 μV·K-1. A maximum of the Seebeck coefficient of 315 μV·K-1 occurs at 635 K with ρ635K = 0.14 Ω·cm, while the thermal conductivity remains low and constant at about 0.8 W·m-1·K-1 from room temperature up to 873 K, leading to a maximum ZT of 0.12 around 800 K. A remarkably large increase of thermal conductivity is observed in the antiferromagnetic state. © 2015 American Chemical Society.

Kesterite Cu2ZnSn(S,Se)4 absorber layers with different [S]/([S]+[Se]) ratios were studied using XPS, UPS, Hard X-ray (HIKE) photoemission and the Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS). The samples were prepared by IREC using sequentially sputtered metallic precursor stacks with metal ratios of [Cu]/([Zn]+[Sn])=0.80, [Zn]/[Sn]=1.20 followed by annealing under S+Se+Sn atmosphere. Different etching procedures were used depending on the sample's composition. It is shown that the surface composition varies from that of the bulk, especially for the Se-rich samples. Contamination with sulfur is detected after using a Na2S etching solution for the pure Se kesterite. A Cu-depleted surface was found for all samples before and after etching. HIKE measurements show a higher [Zn]/[Sn] ratio in the near surface region than on the very surface. This is explained by the fact, the etching procedure removes secondary phases from the very few surface layers, while some of ZnS(e) is still buried underneath. In order to investigate the band gap transition from the pure sulfide (1.5 eV) to the pure selenide (1eV), the valence and conduction band of the respective absorbers were probed. According to UPS and HIKE measurements, the relative distance between Fermi level (Ef) and valance band maximum (VBM) for sulfide sample was 130 meV larger than for selenide. Using NEXAFS on the copper, zinc and tin edges, the development of the conduction band with increasing [S]/([S]+[Se]) ratios was studied. Stoichiometric powder samples were used as reference materials. © 2015 Published by Elsevier Ltd.

Modification of the absorber surface properties by Cd2+ treatment (Cd2+ partial electrolyte) results in the following: formation of Cd(OH)2 on the absorber surface, deposition of thinner chemical bath-deposited CdS buffer layer, and a smaller space charge region. The impact on electrical performances is as follows: decrease of the series resistance (RS), increase of the fill factor, increase of the efficiency (η), and reduction of the crossover between the dark and light current density-voltage curves. The present contribution aims at determining the impact of modifying the properties of the absorber/buffer layer interface on the electrical performance of Cu2ZnSnSe4 (CZTSe) thin-film solar cells, by using a Cd2+ partial electrolyte (Cd PE) treatment of the absorber before the buffer layer deposition. In this work, CZTSe/CdS solar cells with and without Cd PE treatment were compared with their respective Cu(In,Ga)Se2 (CIGSe)/CdS references. The Cd PE treatment was performed in a chemical bath for 7 min at 70 °C using a basic solution of cadmium acetate. X-ray photoemission spectroscopy measurements have revealed the presence of Cd at the absorber surface after the treatment. The solar cells were characterized using current density-voltage (J-V), external quantum efficiency, and drive-level capacitance profiling measurements. For the CZTSe-based devices, the fill factor increased from 57.7% to 64.0% when using the Cd PE treatment, leading to the improvement of the efficiency (η) from 8.3% to 9.0% for the best solar cells. Similar observations were made on the CIGSe solar cell reference. This effect comes from a considerable reduction of the series resistance (RS) of the dark and light J-V, as determined using the one-diode model. The crossover effect between dark and light J-V curves is also significantly reduced by Cd PE treatment.

In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated. © Published under licence by IOP Publishing Ltd.

The electron structure of CuIn1 − x Ga x Se2 single crystals is determined via resonant photoemis-sion and the main regularities of its transformation upon varying concentration x from 0 to 1 are established. The dependence of the shape of valence band spectra on the photon energy is studied. Integral photoemission intensities are shown to be determined by atomic photoionization cross sections. Processes of the direct and two-step creation of photoelectrons accompanying photoemission and the participation of internal states in the spectra of electrons from valence bands are studied. Two-hole final states in photoemission are obtained upon threshold excitation of the Cu 2p level. The strong interaction of holes leads to the multiplet splitting of these states. Partial densities of the components’ states are determined using the energy dependence of atomic photoionization cross sections.

New synthetic strategies are needed for the assembly of porous metal titanates and metal chalcogenite-titania thin films for various energy applications. Here, a new synthetic approach is introduced in which two solvents and two surfactants are used. Both surfactants are necessary to accommodate the desired amount of salt species in the hydrophilic domains of the mesophase. The process is called a molten-salt-assisted self-assembly (MASA) because the salt species are in the molten phase and act as a solvent to assemble the ingredients into a mesostructure and they react with titania to form mesoporous metal titanates during the annealing step. The mesoporous metal titanate (meso-Zn 2TiO4 and meso-CdTiO3) thin films are reacted under H2S or H2Se gas at room temperature to yield high quality transparent mesoporous metal chalcogenides. The H2Se reaction produces rutile and brookite titania phases together with nanocrystalline metal selenides and H2S reaction of meso-CdTiO3 yields nanocrystalline anatase and CdS in the spatially confined pore walls. Two different metal salts (zinc nitrate hexahydrate and cadmium nitrate tetrahydrate) are tested to demonstrate the generality of the new assembly process. The meso-TiO2-CdSe film shows photoactivity under sunlight. High quality mesoporous metal titanate thin films are synthesized using a molten-phase-assisted self-assembly (MASA) method. The metal salts are used as a non-volatile solvent in the new assembly process. The films are converted into mesoporous titania-metal chalcogenides (TiO2-CdS, TiO 2-CdSe, and TiO2-ZnSe) under H2S or H 2Se at room temperature and may find applications in solar cells, catalysis, photocatalysis, electronics, and optoelectronics. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mesoporous silica metal oxide (ZnO and CdO) thin films have been used as metal ion precursors to produce the first examples of mesoporous silica metal sulfide (meso-SiO 2@ZnS, meso-SiO 2@CdS) or silica metal selenide (meso-SiO 2@ZnSe, meso-SiO 2@CdSe) thin films, in which the pore walls are made up of silica and metal sulfide or metal selenide nanoflakes, respectively. A gentle chemical etching with a dilute HF solution of the meso-SiO 2@CdS (or meso-SiO 2@CdSe) produces mesoporous cadmium sulfide (meso-CdS) (or cadmium selenide, meso-CdSe). Surface modified meso-CdS displays bright blue photoluminescence upon excitation with a UV light. The mesoporous silica metal oxides are formed as metal oxide nanoislands over the silica walls through a self-assembly process of a mixture of metal nitrate salt-two surfactants-silica source followed by calcination step. The reactions, between the H 2S (or H 2Se) gas and solid precursors, have been carried out at room temperature and monitored using spectroscopy and microscopy techniques. It has been found that these reactions are: 1) taking place through the diffusion of sulfur or selenium species from the top metal oxide layer to the silica metal oxide interface and 2) slow and can be stopped at any stage to obtain mesoporous silica metal oxide metal sulfide or silica metal oxide metal selenide intermediate thin films. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heterometallic cubane-type clusters were synthesized from the reaction of group 6 and 8 metallaboranes using transition-metal carbonyl compounds. Structural and spectroscopic study revealed the existence of novel “capped-cubane” geometry. In addition, the crystal structure of these clusters distinctly confirms the presence of boride unit as one of the vertices. These clusters possess 60 cluster valence electrons (cve) and six metal–metal bonds. A plausible pathway for the formation of ruthenium-capped cubane has been described.

The thermolysis of [(Cp*Mo)2B4H 4S2], 1 with [Fe2(CO)9] yielded eleven vertex dimolybdathiaborane cluster [(Cp*Mo)2B 4H2S2Fe4(CO)9(?-CO)], 2 together with cubane-type [(Cp*Mo)2(?3-S) 2B2H(?-H){Fe(CO)2}2Fe(CO) 3], 3 and a fused cluster [(Cp*Mo)2B 4H4S2 Fe2(CO)5], 4. In a similar fashion, thermolysis of [(Cp*Mo)2B4H 4Se2], 5 with [Fe2(CO)9] yielded tetracapped pentagonal bipyramidal [(Cp*Mo)2B3H 3Se2{Fe(CO)2}2{Fe(CO) 3}2], 6, and an incomplete cubane-type cluster [(Cp*Mo)2BH(?3-Se)2Fe 2(CO)7], 7. In parallel with the formation of 6 and 7, clusters [(Cp*Mo)2(?3-Se)2B 2H(?-H){Fe(CO)2}2Fe(CO)3], 8 and [(Cp*Mo)2B4 H4Se2Fe 2(CO)5], 9 were obtained albeit in low isolated yields. Cluster 6 exhibits tetracapped pentagonal bipyramidal geometry, having 98 cluster valence electrons, appropriate for its geometric structure. The thermolysis of 9 in presence of [Co2(CO)8] led to the isolation of [(Cp*Mo)2B3H2Se 2Co(CO)(?-CO)3{Fe4(CO)7}], 10. The structure analysis shows that both of the clusters 2 and 10 are based on 11-vertex closo-cage geometry and the core geometry of them can be derived from tricapped square antiprism by performing diamond-square-diamond (dsd) rearrangement. All new metallaheteroborane compounds have been fully characterized by various spectroscopic techniques and elemental analyses and the geometric structures were unequivocally established by crystallographic analysis of 2, 6, 7 and 10. � 2012 Elsevier B.V. All rights reserved.

WOS: 000308769000034, We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb2S3 and Sb2Se3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. (C) 2012 Elsevier Masson SAS. All rights reserved.

International audience; Atom Probe Tomography (APT) technique is the only nano-scale-sensitive analytic tool allowing 3D chemical analysis with atomic scale resolution. For long restricted to conductive samples, implementation of ultra fast laser pulsing extend now the field of applications to the analysis of semiconductor materials. In the present study, high efficiency Cu(In, Ga)Se 2 (CIGSe) thin films have been investigated by APT in order to solve interrogations about grain boundaries (GBs) composition. The analyzed CIGSe layers have been grown by co-evaporation on Mo-coated soda-lime glass substrates following the standard 3-stage process and the atom probe tips prepared using a focused ion beam (FIB) equipment. In order to ensure the presence of GB in the small APT investigated volume, location and misorientation of GBs have been determined by electron backscattering scanning diffraction (EBSD) and one GB interface placed close to the edge of the tip. From APT analyses, spatial distribution of CIGSe elements can be imaged at atomic scale; particular attention has been devoted to the composition profiles at the vicinity of the CIGSe GB interface. New results are compared with usual CIGSe GB passivation models. © 2011 IEEE.

In this work, CuInSe 2 based flexible photovoltaic cells have been fabricated completely using non-vacuum low-cost techniques. Thin films were deposited on molybdenum thin foil substrates by electrodeposition using a buffered aqueous electrolyte with the deposition of subsequent layers performed by spray pyrolysis. In addition, the buffer layer CdS was replaced with a wider bandgap ZnS (3.7 eV) and analysis undertaken of the fabrication pathway, morphological and compositional changes resulting from the different precursor route. The deposited films were annealed in a Se atmosphere at 450 °C. The influence of annealing temperature and time on the properties of the films are briefly discussed. Characterisation of thin films was performed using aqueous electrolyte contacts. Capacitance measurements were made as a function of applied bias on thin films deposited on metal substrates with blocking electrolyte contacts where analysis of the impedance gave values of the space charge capacitance from which the doping density and flat band potential were derived. The structural characterisation was carried out using X-ray diffraction and Raman spectroscopy. The structure and device properties of Mo (SS)/CuInSe 2/ZnS/n +-ZnO/Ni were characterized using current-voltage technique and photocurrent spectroscopy. © 2011 Elsevier B.V., This work was supported by the Spanish Government through MEC grant MAT2009-14625-C03-03 and the Fundacao para a Ciencia e a Tecnologia (FCT) in Portugal.