References of "Valle, Nathalie"
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See detailThe effect of KF post-deposition treatments on the optoelectronic properties of Cu(In,Ga)Se2 single crystals
Ramirez Sanchez, Omar UL; Bertrand, Maud; Debot, Alice UL et al

in Solar RRL (2021)

The power conversion efficiency boost of Cu(In,Ga)Se2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through post-deposition treatments results in an ... [more ▼]

The power conversion efficiency boost of Cu(In,Ga)Se2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through post-deposition treatments results in an improvement of the open-circuit voltage, which origin has been associated with grain boundaries. The present work discusses the effect of potassium fluoride post-deposition treatments on the optoelectronic properties of a series of sodium-free Cu(In,Ga)Se2 single crystals with varying Cu and Ga content. Results suggest that improvement of the quasi-Fermi level splitting can be achieved despite the absence of grain boundaries, being greater in low-gallium Cu-poor absorbers. Secondary ion mass spectrometry reveals the presence of potassium inside the bulk of the films, suggesting that transport of potassium can occur through grain interiors. In addition, a type inversion from n to p in KF-treated low-gallium Cu(In,Ga)Se2 is observed, which along a carrier lifetime study demonstrates that potassium can act as a dopant. The fact that potassium by its own can alter the optoelectronic properties of Cu(In,Ga)Se2 single crystals demonstrates that the effect of post-deposition treatments goes beyond grain boundary passivation. [less ▲]

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See detailCritical field anisotropy in the antiferroelectric switching of PbZrO3 films
Milesi-Brault, Cosme; Godard, Nicolas; Girod, Stephanie et al

in APPLIED PHYSICS LETTERS (2021), 118(4),

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the ... [more ▼]

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the possibility to induce a phase transition to a polar phase by an electric field. Here, we investigate the switching behavior of the model antiferroelectric perovskite PbZrO3 using thin films processed by chemical solution deposition in different geometries and orientations. Both out-of-plane and in-plane switching configurations are investigated. The critical field is observed to be highly dependent on the direction of the electric field with respect to the film texture. We show that this behavior is qualitatively consistent with a phase transition to a rhombohedral polar phase. We finally estimate the importance of crystallite orientation and film texturation in the variations observed in the literature. [less ▲]

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See detailElucidating the growth mechanism of ZnO films by atomic layer deposition with oxygen gas via isotopic tracking
Nguyen, Tai; Valle, Nathalie; Guillot, Jerome et al

in JOURNAL OF MATERIALS CHEMISTRY C (2021), 9(12), 4307-4315

The growth process of zinc oxide (ZnO) thin films by atomic layer deposition (ALD) accompanied by the presence of oxygen gas pulsing is investigated by means of the isotopic tracking of oxygen O-18 from ... [more ▼]

The growth process of zinc oxide (ZnO) thin films by atomic layer deposition (ALD) accompanied by the presence of oxygen gas pulsing is investigated by means of the isotopic tracking of oxygen O-18 from the water precursor and oxygen O-16 from the gas. In a previous study [T. Nguyen et al., Results Mater., 2020, 6, 100088, DOI: 10.1016/j.rinma.2020.100088], by means of structural, electrical, and optical characterizations, we identified key growth parameters of this unusual ALD process. Unexpectedly, the influence of molecular oxygen on the crystallography, microstructure, and morphology of the hundred-nanometer- to micrometer-thick ZnO films was significant. In this study, we present an unprecedented methodology by combining isotopic tracers with mass spectrometry to elucidate the role of the two different sources of oxygen atoms during the evolution of the growth. Notably, the use of in situ quartz crystal microbalance (QCM) and Secondary Ion Mass Spectrometry (SIMS) reveals new insights into the reaction mechanism for ZnO thin film growth. On the one hand, the non-negative mass change during the ZnO growth without O-2 gas is attributed to the presence of bare zinc atoms on the surface due to the reaction between monoethyl zinc and hydroxyl groups of the water precursor after the diethyl zinc pulse. On the other hand, the detection of ZnxOyC2H5- ions by Time-of-Flight SIMS (TOF-SIMS) and the mass increase during the O-2 pulse suggest a new reaction mechanism for the ZnO thin film growth in the presence of gaseous O-2 where the ethyl ligand of the zinc precursor can react with O-2 to form ethylperoxy radicals. The formations of the ethylperoxy zinc and/or zinc atoms lead to more adsorption of water to form ethylhydroperoxide during the water pulse, inducing the positive mass change. The use of an isotopic substitution allowed us to unambiguously associate the mass gain with the gradual incorporation of gaseous oxygen throughout the growth process and thereby support the chemical reaction. [less ▲]

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See detailWaste- and Cd-Free Inkjet-Printed Zn(O,S) Buffer for Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells
Chu, van Ben UL; Siopa, Daniel UL; Debot, Alice UL et al

in ACS Applied Materials and Interfaces (2021), 13

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See detailChemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface
Colombara, Diego UL; Elanzeery, Hossam UL; Nicoara, Nicoleta et al

in Nature Communications (2020)

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See detailSingle crystal growth of BaZrO3 from the melt at 2700 degrees C using optical floating zone technique and growth prospects from BaB2O4 flux at 1350 degrees C
Xin, Cong; Veber, Philippe; Guennou, Mael UL et al

in CRYSTENGCOMM (2019), 21(3), 502-512

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single ... [more ▼]

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single crystals were obtained with a mirror furnace without the need for post-treatment annealing. Its properties are determined and compared with those of two commercial crystals grown by the tri-arc Czochralski method. The chemical composition was investigated using glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS), which indicate minor impurities of Sr, Hf, Ca and Ti, with maximal concentrations for Sr and Hf in the range of 0.3-0.5 at. The optical band gap determined by UV-visible spectroscopy is found to be similar to 4.8 eV and indicates the high quality of the BaZrO3 crystals grown by the optical floating zone technique. Raman spectroscopy at ambient conditions and at low temperatures down to 4.2 K reveals a relatively sharp second-order spectrum and does not reveal any structural phase transition. Prospective high-temperature solution growth using BaB2O4 self-flux was investigated and led to 150-200 mu m BaZrO3 crystals. This solvent opens the way to grow BaZrO3 at half its melting point by the flux method. [less ▲]

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See detailFreshwater pearl mussels as a stream water stable isotope recorder
Pfister, Laurent UL; Thielen, Frank; Deloule, Etienne et al

in Ecohydrology (2018), 11:e2007

For several decades, stable isotopes have been a commonly used and effective tool for flow path analysis, stream water source apportionment, and transit time analysis. The Global Network of Isotopes in ... [more ▼]

For several decades, stable isotopes have been a commonly used and effective tool for flow path analysis, stream water source apportionment, and transit time analysis. The Global Network of Isotopes in Precipitation repository now has monthly precipitation isotope time series extending over several years and even decades in some settings. However, stream water isotope composition time series remain rather short with only very few data sets spanning over more than a few years. A critical challenge in this respect is the collection of stream water isotope data sets across a wide variety of headwater streams and for long durations. We rely on a new approach for stream signal reconstruction based on freshwater mussels, specifically the freshwater pearl mussel Margaritifera margaritifera. We use secondary ion mass spectrometry (SIMS) to quantify oxygen isotope ratios in pearl mussel shell growth bands. In our study area, the observed seasonal variability in precipitation δ18O values ranges between −15‰ and −3‰. This input signal is strongly damped in stream water, where observed values of δ18O range between −10‰ and −6.5‰. These values are consistent with our measured average shell‐derived stream water δ18O of −7.19‰. Along successive growth bands, SIMS‐based stream water δ18Ow values varied within a seasonal range of −9‰ to −5‰. The proposed SIMS‐based shell analysis technique is obviously well suited for analysing isotopic signatures of O in shell material—especially from the perspective of reconstructing historical series of in‐stream isotope signatures. [less ▲]

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See detailSodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers
Colombara, Diego UL; Werner, Florian UL; Schwarz, Torsten et al

in Nature Communications (2018)

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See detailDeliberate and Accidental Gas-Phase Alkali Doping of Chalcogenide Semiconductors: Cu(In,Ga)Se2
Colombara, Diego UL; Berner, Ulrich; Ciccioli, Andrea et al

in Scientific Reports (2017), 7

Alkali metal doping is essential to achieve highly efficient energy conversion in Cu(In,Ga)Se2 (CIGSe) solar cells. Doping is normally achieved through solid state reactions, but recent observations of ... [more ▼]

Alkali metal doping is essential to achieve highly efficient energy conversion in Cu(In,Ga)Se2 (CIGSe) solar cells. Doping is normally achieved through solid state reactions, but recent observations of gas phase alkali transport in the kesterite sulfide (Cu2ZnSnS4) system (re)open the way to a novel gas-phase doping strategy. However, the current understanding of gas-phase alkali transport is very limited. This work (i) shows that CIGSe device efficiency can be improved from 2% to 8% by gas-phase sodium incorporation alone, (ii) identifies the most likely routes for gas-phase alkali transport based on mass spectrometric studies, (iii) provides thermochemical computations to rationalize the observations and (iv) critically discusses the subject literature with the aim to better understand the chemical basis of the phenomenon. These results suggest that accidental alkali metal doping occurs all the time, that a controlled vapor pressure of alkali metal could be applied during growth to dope the semiconductor, and that it may have to be accounted for during the currently used solid state doping routes. It is concluded that alkali gas-phase transport occurs through a plurality of routes and cannot be attributed to one single source. [less ▲]

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See detailPost-deposition treatment of Cu2ZnSnSe4 with alkalis
Rey, Germain UL; Babbe, Finn UL; Weiss, Thomas UL et al

in Thin Solid Films (2016), 633

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor ... [more ▼]

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor (from 0.58 to 0.61 and 0.62), open-circuit voltage (Voc) (from 314 mV to 337 mV and 325 mV) and short-circuit current density (from 35.3 mA⋅cm −2 to 38.3 mA⋅cm −2 and 38.6 mA⋅cm −2). Voc improvement was higher for solar cells with NaF treatment due to an increase in radiative efficiency at room temperature and shallower defect activation energy as determined by photoluminescence (PL) and temperature dependent admittance spectroscopy, respectively. In the case of KF treatment, red-shift of the PL, higher band tail density of state and donor activation energy deeper in the band gap were limiting further improvement of the Voc compared to NaF treatment. [less ▲]

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See detailDoping mechanism in pure CuInSe2
Werner, Florian UL; Colombara, Diego UL; Melchiorre, Michele UL et al

in JOURNAL OF APPLIED PHYSICS (2016), 119

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See detail13.3% efficient solution deposited Cu(In,Ga)Se 2 solar cells processed with different sodium salt sources
Berner, Ulrich; Colombara, Diego UL; De Wild, Jessica UL et al

in Progress in Photovoltaics (2015)

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See detailVapour phase alkali species for Cu(In,Ga)Se2 solar cells
Berner, Ulrich; Colombara, Diego UL; Bertram, Tobias UL et al

Scientific Conference (2015, September)

Alkalis are essential in Cu(In,Ga)Se2 absorber layers for efficient solar cells. Current doping methods rely on solid state diffusion of an alkali through to the absorber layer, e.g. a thin NaF layer on ... [more ▼]

Alkalis are essential in Cu(In,Ga)Se2 absorber layers for efficient solar cells. Current doping methods rely on solid state diffusion of an alkali through to the absorber layer, e.g. a thin NaF layer on Mo or NaCl dissolved in a metal precursor ink[1]. The apparent concentration of alkali in the final absorber is determined by the initial alkali dosing and the use of an interfacial barrier to stop alkali diffusion from the substrate. Until now the vapor–absorber interface as a source or sink of alkali doping has been largely ignored. We show that device efficiency improves from 2 to 8% by gas phase Na adsorption alone. Conversely initial results show that Na can also be desorbed to the gas phase. Although these efficiencies are lower than those obtained by including Na directly in the precursor (device efficiency 13.3% [1]), the findings are relevant to all chalcogenide growers as they show that exact doping, and thus control of device efficiency, is only possible when gas phase adsorption/desorption processes are controlled. [less ▲]

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See detailAlternative etchning for improved Cu-rich CuInSe2 solar Cells
Depredurand, Valérie UL; Bertram, Tobias UL; Thevenin, Maxime UL et al

in Materials Research Society Symposia Proceedings (2015), 1771

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See detailHCl and Br2-MeOH etching of Cu2ZnSnSe4 polycrystalline absorbers
Mousel, Marina UL; Redinger, Alex UL; Djemour, Rabie UL et al

in Thin Solid Films (2013), 535

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See detailCu2ZnSnSe4 thin film solar cells produced via coevaporation and annealing including a SnSe2 capping layer
Redinger, Alex UL; Mousel, Marina UL; Djemour, Rabie UL et al

in Progress in Photovoltaics (2013), 22(1), 51-57

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been ... [more ▼]

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been evaporated onto the absorber prior to the high-temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1 could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red-kink effect, has also been observed in the closely related Cu(In,Ga)Se-2 thin film solar cells. Copyright (c) 2013 John Wiley Sons, Ltd. [less ▲]

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See detailDetection of a ZnSe secondary phase in coevaporated Cu2ZnSnSe4 thin films
Redinger, Alex UL; Hönes, Katja UL; Fontané, Xavier et al

in Applied Physics Letters (2011), 98(101907), 1019071-1019073

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See detailRoute Toward High-Efficiency Single-Phase Cu2ZnSn(S,Se)4 Thin-Film Solar Cells: Model Experiments and Literature Review
Redinger, Alex UL; Berg, Dominik M.; Dale, Phillip UL et al

in IEEE Journal of Photovoltaics (2011)

Detailed reference viewed: 190 (5 UL)