Synthesis and Optical Properties of Cu2CoSnS4 Colloidal Quantum Dots

Monodisperse quaternary chalcopyrite Cu2CoSnS4 colloidal quantum dots have been synthesized by acid peptization of a tailored Cu2CoSnS4 precursor displaying loosely packed, ultrafine primary crystallites. Well-defined peaks shifted to higher energy compared to the Cu2CoSnS4 bulk band gap value were observed on the UV-Vis absorption curve consistent with a quantum confinement behavior. First investigations by room temperature time resolved photoluminescence (TRPL) spectroscopy suggest that the photoluminescence emission does not arise from a donor–acceptor recombination.

Highly-crystallized quaternary chalcopyrite nanocrystals via a high-temperature dissolution–reprecipitation route

Quaternary chalcopyrite (Cu2CoSnS4, Cu2ZnSnS4) nanocrystals displaying high crystallization and controlled morphology were synthesized via a high-temperature growth regime achieved by dissolution–reprecipitation of tailored ultrafine precursors in the temperature range 400–500 °C

A high temperature route to the formation of highly pure quaternary chalcogenide particles

A process route to the fabrication of quaternary chalcogenides (Cu2CoSnS4, Cu2ZnSnS4) particles is proposed in molten KSCN at 400 °C. This high temperature route allows the formation of highly pure and highly crystallized quaternary chalcogenides particles. Control of primary crystallites size is demonstrated by altering the chemical homogeneity of the precursors. This method could be exploited to prepare building blocks for the fabrication of low-cost solar cell absorbers

Surfactant-free CZTS nanoparticles as building blocks for low-cost solar cell absorbers

A process route for the fabrication of solvent-redispersible, surfactant-free Cu2ZnSnS4 (CZTS) nanoparticles has been designed with the objective to have the benefit of a simple sulfide source which advantageously acts as (i) a complexing agent inhibiting crystallite growth, (ii) a surface additive providing redispersion in low ionic strength polar solvents and (iii) a transient ligand easily replaced by an carbon-free surface additive. This multifunctional use of the sulfide source has been achieved through a fine tuning of((Cu2+)a(Zn2+)b(Sn4+)c(Tu)d(OH?)e)t+, Tu = thiourea) oligomers, leading after temperature polycondensation and S2- exchange to highly concentrated (c > 100 g l-1), stable, ethanolic CZTS dispersions. The good electronic properties and low-defect concentration of the sintered, crack-free CZTSe films resulting from these building blocks was shown by photoluminescence investigation, making these building blocks interesting for low-cost, high-performance CZTSe solar cells

Surfactant-free CZTS nanoparticles as building blocks for low-cost solar cell absorbers

A process route for the fabrication of solvent-redispersible, surfactant-free Cu2ZnSnS4 (CZTS) nanoparticles has been designed with the objective to have the benefit of a simple sulfide source which advantageously acts as (i) a complexing agent inhibiting crystallite growth, (ii) a surface additive providing redispersion in low ionic strength polar solvents and (iii) a transient ligand easily replaced by an carbon-free surface additive. This multifunctional use of the sulfide source has been achieved through a fine tuning of((Cu2+)a(Zn2+)b(Sn4+)c(Tu)d(OH?)e)t+, Tu = thiourea) oligomers, leading after temperature polycondensation and S2- exchange to highly concentrated (c > 100 g l-1), stable, ethanolic CZTS dispersions. The good electronic properties and low-defect concentration of the sintered, crack-free CZTSe films resulting from these building blocks was shown by photoluminescence investigation, making these building blocks interesting for low-cost, high-performance CZTSe solar cells

A gas-templating strategy to synthesize CZTS nanocrystals for environment-friendly solar inks

A high-temperature gas-templating strategy is proposed to synthesize Cu2ZnSnS4 (CZTS) nanocrystals for all-aqueous solar inks. Our gas templating process route involves the in-situ generation and stabilization of nanosized gas bubbles into a molten KSCN-based reaction mixture at 400 °C. Chemical insights of the templating gas process are provided such as the simultaneous formation of gas bubbles and CZTS nuclei highlighting the crucial role of the nucleation stage on the sponge and resulting nanocrystals properties. The high porosity displayed by the resulting CZTS nanocrystals facilitates their further post-fragmentation, yielding individualized nanocrystals. The advantages of our high temperature gas templating route are illustrated by the following: (i) the low defect concentration displayed by the highly crystalline nanocrystals, (ii) the synthesis of CZTS nanocrystals displaying S2− polar surfaces after ligand exchange. The good photoluminescence properties recorded on the pure CZTS nanocrystals reveal potential for exploration of new complex chalcogenide nanocrystals useful for various applications including photovoltaics and water splitting. Here we demonstrate that using these building blocks, a CZTS solar cell can be successfully fabricated from an environment-friendly all-aqueous ink

Patch-like, two dimensional WSe2-based hetero-structures activated by a healing catalyst for H2 photocatalytic generation

2D photoactive materials may offer interesting opportunities in photocatalytic devices since they combine strong light absorption and shortening of charge carriers’ diffusion path. Because of their high surface defect concentration and the formation of a majority of edge/plane vs plane/plane contacts between the anisotropic building blocks, surface defect passivation and improvement of charge carrier transport are critical for the large development of high surface area, 2D photo-catalysts. Here, we propose a hetero-structure nanoporous network with a patch-like coating as high performance 2D photo-catalysts. The hetero-structured building blocks are composed of a photo-active WSe2 nanoflake in direct contact with both a conducting rGO nanosheet and an ultrathin layer of healing catalyst. The resulting nanoporous film achieves a H2 evolution photocurrent density up to 5 mA cm−2 demonstrating that the patch-like hetero-structures represent an effective strategy to simultaneously improve hole collection, defect passivation and charge transfer. These hetero-structures made of an ultrathin healing catalyst layer represent promising building blocks for the bottom-up fabrication of high surface area photocathodes particularly for 2D photo-catalysts displaying high defect concentration

Mo thio and oxo-thio molecular complexes film as self-healing catalyst for photocatalytic hydrogen evolution on 2D materials

2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm−2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties

Spin dependent recombination in dilute nitride semiconductors

Ce travail de thèse est une contribution à l'étude des propriétés de spin dans les semiconducteurs par spectroscopie de photoluminescence et par photoconductivité en vue d applications possibles dans le domaine de l électronique du spin.Nous avons analysé les propriétés de spin des électrons de conduction dans les matériaux semiconducteurs nitrures dilués, massif et puits quantiques (GaAsN, GaAsN/GaAs). Nous avons étudié le mécanisme de recombinaison dépendante du spin des électrons de conduction sur les centres paramagnétiques induits par l introduction d azote dans GaAs. Nous avons mis en évidence l effet de filtrage de spin des électrons de conduction que ce mécanisme peut induire ; en particulier, nous avons mené des études détaillées en fonction de la concentration d azote, de la puissance excitatrice, d un champ magnétique externe et, pour les hétérostructures, de l épaisseur des puits quantiques. L origine chimique des centres paramagnétiques a été, de plus, identifiée par des études de résonance paramagnétique détectée optiquement (ODMR).Nous avons également complété ces études purement optiques sur la recombinaison dépendante du spin, par des expériences de photoconductivité en vue d applications possibles liées à l électronique du spin. Nous avons montré que la photoconductivité des matériaux nitrures dilués peut être contrôlée par la polarisation de la lumière incidente. Un détecteur électrique de la polarisation de la lumière à base de GaAsN a été ainsi fabriqué et testé.Ces résultats ont été également interprétés et simulés grâce à un système d équations dynamiques pouvant rendre compte à la fois des résultats de photoluminescence et de transportThis thesis work is a contribution to the investigation of the spin properties of semiconductors by photoluminescence and photoconductivity spectroscopy with the aim of future applications in the spintronic field. We have studied the conduction band electron spin properties of dilute nitride semiconductors in epilayers and quantum wells (GaAsN, GaAsN/GaAs). In particular, we have investigated the spin dependent recombination of conduction band electrons on deep paramagnetic centers induced by the introduction of nitrogen into GaAs. We have also evidenced the spin filtering effect made possible by this spin dependent recombination mechanism. More precisely, we have carried out a systematic study of the spin filtering effect as a function of the nitrogen concentration, excitation power, external magnetic field and, for the hetero-structures, as well as a function of the quantum well thickness. The chemical origin of the deep paramagnetic centers has been also determined by optically detected magnetic resonance (ODMR). We have completed these all-optical studies on the spin dependent recombination by photoconductivity experiments in order to demonstrate a proof of concept system for spintronic applications. We have shown that the photoconductivity in dilute nitride semiconductors can be controlled by the polarization of the incident light: an electrical detector of the light polarization has therefore been built. These results have been as well modeled thanks to a rate equation system able to reproduced both the photoluminescence and photoconductivity experimental resultsTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Mise en forme et frittage de couches minces Cu2ZnSnS4 pour la conversion photovoltaïque à partir de nanoparticules déposées par voie liquide

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF