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Narrow band gap tin(II) chalcogenide (SnS, SnSe, SnTe) nanocrystals are of high interest for optoelectronic applications such as thin film solar cells or photo- detectors. However, charge transfer and charge transport processes strongly depend on nanocrystals' surface quality. Using 119Sn-Mössbauer spectroscopy, which is the most sensitive tool for probing the Sn oxidation state, we show that SnS nanocrystals exhibit a Sn(IV)Sn(II) ratio of around 20:80 before and 40:60 after five minutes exposure to air. Regardless of the tin or sulfur precursors used, similar results are obtained using six different synthesis protocols. The Sn(IV) content before air exposure arises from surface related SnS2 and Sn2S3 species as well as from surface Sn atoms bound to oleic acid ligands. The increase of the Sn(IV) content upon air exposure results from surface oxidation. Full oxidation of the SnS nanocrystals without size change is achieved by annealing at 500 °C in air. With the goal to prevent surface oxidation, SnS nanocrystals are capped with a cadmium-phosphonate complex. A broad photoluminescence signal centered at 600 nm indicates successful capping, which however does not reduce the air sensitivity. Finally we demonstrate that SnSe nanocrystals exhibit a very similar behavior with a Sn(IV)/Sn(II) ratio of 43:57 after air exposure. In the case of SnTe nanocrystals, the ratio of 55:45 is evidence of a more pronounced tendency for oxidation. These results demonstrate that prior to their use in optoelectronics further surface engineering of tin chalcogenide nanocrystals is required, which otherwise have to be stored and processed under inert atmosphere. [ABSTRACT FROM AUTHOR]

In recent years the treatment of thin films of nanocrystals (NCs) with short monofunctional or bifunctional bridging ligands has commonly been used to improve the conductivity within the NCs' assemblies. How does this surface ligand exchange in the solid state influence the electronic energy levels of the system? We show that electrochemical studies and in particular differential pulse voltammetry (DPV) can be used to give an answer to this question. Combined UV-vis, DPV and cyclic voltammetry data reveal that a shift of several tens of meV of the NCs' HOMO and LUMO levels takes place upon surface ligand exchange. As objects of our study we have selected thin solid films of stearic acid and oleylamine capped CdSe NCs, which were treated with acetonitrile solutions of 1,2-ethanedithiol, butylamine, phenylenediamine, benzenedithiol and pyridine to induce the ligand exchange in the solid state, confirmed by FTIR spectroscopy. The resulting modified films exhibit strongly enhanced conductivity as compared to the films constituted of pristine NCs. [ABSTRACT FROM AUTHOR]

Abstract: Coral reef lagoons are under the growing influence of anthropogenic activities, leading to increasing loads of nutrients and various contaminants. Modelling approaches are a useful tool for studying such a complex coastal environment. In this study, we carried out the development of a three-dimensional coupled hydrodynamical-biogeochemical model of the south-west lagoon of New Caledonia. The biogeochemical model presented in was dynamically coupled with a hydrodynamical model (MARS3D) in order to study the short-term variability of the ecosystem. Two simulations (in winter and summer) were then performed from measured initial conditions using realistic wind and irradiance conditions and river inputs. Examinations of the biogeochemical response to these transient meteorological conditions were presented and compared with temporal field data corresponding to the considered periods. Results highlighted the ecosystem functioning, based on the balance of hydrodynamical and biogeochemical processes. Influence of urban and terrigeneous inputs were limited to the coastal zone. The model accurately reproduced the measured Chl.a and bacterial production, highlighting the improvement made on the biogeochemical model. However, the underestimation of some variables in model outputs, in particular nutrients, led us to focus on different inputs, such as sediment inputs which were not taken into account or properly estimated. Moreover, the role of boundary waters appeared crucial and suggested a calibration effort. Last, the final aim of our modelling study will help the development of a useful tool for studying the key processes of the ecosystem of the south-west lagoon of New Caledonia, as well as the examination of the biogeochemical response under different scenarios. [ABSTRACT FROM AUTHOR]

Abstract: This work is an extension and improved version of the biogeochemical model of the South-West lagoon of New Caledonia, presented by . This new ecological model was developed to include an explicit description of the microbial loop. Additional variables included bacterial production and dissolved organic matter and a better description of organic matter recycling. A particular effort was made to calibrate parameters of the model for the studied area, using representative field measurements and experiments. The biogeochemical model described the nitrogen and carbon cycles relating the variable stoichiometry of the elements in each biological compartment. Several lagoon surveys demonstrated that, on average, the water column is nearly homogenous. We chose therefore to present in this paper non dimensional model outputs in order to study the behaviour of the new model. The addition of a microbial loop modified the simulated functioning of the lagoon and the fluxes of carbon and nitrogen between the different compartments: it allowed a better description of the recycling of organic matter, recognized as important processes in oligotrophic ecosystems like in the SW lagoon of NC. A sensitivity analysis was performed in order to identify the most sensitive parameters and variables of the model. The different results emphasised the importance of the dissolved inorganic and organic compartment. Preliminary comparisons with field data showed that the model reproduced realistic values. However, the next important step of this work was to dynamically couple this new biogeochemical model in a 3D hydrodynamical model in order: (1) to perform a realistic validation with in situ data (2) to achieve an analysis of the spatial and temporal variability of the ecosystem. This study is presented in the companion paper (). [ABSTRACT FROM AUTHOR]

Abstract: We assessed the temporal variability of nutrients, phytoplankton and bacterioplankton at two sites of different trophic status in New Caledonia’s South-West lagoon, a tropical coastal ecosystem. During stable meteorological conditions, Chl.a, bacterial production and nutrient concentrations experience weak but consistent daily variation. Short-term (1–2week interval) fluctuations of planktonic variables are in the same range as annual variations at both sites. A part of these short term variations is linked to local meteorological events (wind in the main channel, precipitation at the coastal station). Although annual variations are weak compared to short term variations, phytoplankton and bacterioplankton production show consistent temporal patterns, with maxima in December–January and April–May and minima in August. Annual bacterial production represents 21% and 34% of particulate primary production at the oligotrophic and mesotrophic sites, respectively. Mineral nutrient availability indicates that nitrogen is probably the primary limiting factor of phytoplankton throughout the year. [ABSTRACT FROM AUTHOR]

Abstract: Single-crystal magnetic tunnel junctions employing bcc (1 0 0) Fe electrodes and MgO(1 0 0) insulating barrier are elaborated by molecular beam epitaxy. Two extreme regimes have been investigated. First, for extremely thin MgO thickness we show that the equilibrium tunnel transport in Fe/MgO/Fe systems leads to antiferromagnetic interactions, mediated by the tunneling of the minority spin interfacial resonance state. Second, for large MgO barrier thickness, the tunnel transport validates specific spin filtering effect in terms of symmetry of the electronic Bloch function and symmetry-dependent wave function attenuation in the single-crystal barrier. Within this framework, we present giant tunnel magnetoresistive effects at room temperature (125–150%). Moreover, we illustrate that the interfacial chemical and electronic structure plays a crucial role in the filtering. We show that the insertion of carbon impurities at the Fe/MgO interface changes radically the voltage response of the tunnel magnetoresistance. Moreover, we provide experimental evidence for the electronic interfacial resonance states contribution to the spin polarized tunnel transport. [Copyright &y& Elsevier]

High conductive carbon nanotube (CNT) yarns are a near challenge to be an alternative to metal in electrical wiring. In this work, we largely improve carbon nanotube yarn electrical conductivity by chemical doping, annealing treatments (above 2000 °C) and combination of both. We present a new efficient CNT p-type dopant based on platinum chloride IV. It decreases the resistivity by a factor of 3 and is stable over half a year. The annealing treatments above 2000 °C dramatically improve the CNT structural quality by a decade. In addition, we show that the CNT yarn electrical resistivity decreases linearly with the CNT structural quality increase and we report the world record resistivity for an undoped CNT yarn spun from CNT array (0.76 mΩ cm). We reveal that the CNT structural quality is not the only factor needed to reach high electrical conductivities. The increase in CNT structural quality significantly improves the doping efficiency by a factor of 2. By systematic measurements of the CNT yarn and web resistance from 3 K to 300 K, we are able to explain the influence of the doping, annealing, compaction and CNT length on the electrical charge transport. Image 1 [ABSTRACT FROM AUTHOR]

Geminate recombination of bound polaron pairs at the donor/acceptor interface is one of the major loss mechanisms in organic bulk heterojunction solar cells. One way to overcome Coulomb attraction between opposite charge carriers and to achieve their full dissociation is the introduction of high dielectric permittivity materials such as nanoparticles of narrow band gap semiconductors. We selected CuInS2 nanocrystals of 7.4 nm size, which present intermediate energy levels with respect to poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). Efficient charge transfer from P3HT to nanocrystals takes place as evidenced by light-induced electron spin resonance. Charge transfer between nanocrystals and PCBM only occurs after replacing bulky dodecanethiol (DDT) surface ligands with shorter 1,2-ethylhexanethiol (EHT) ligands. Solar cells containing in the active layer a ternary blend of P3HT:PCBM:CuInS2-EHT nanocrystals in 1:1:0.5 mass ratio show strongly improved short circuit current density and a higher fill factor with respect to the P3HT:PCBM reference device. Complementary measurements of the absorption properties, external quantum efficiency and charge carrier mobility indicate that enhanced charge separation in the ternary blend is at the origin of the observed behavior. The same trend is observed for blends using the glassy polymer poly(triarylamine) (PTAA). [ABSTRACT FROM AUTHOR]

Donor–acceptor (D–A) small molecules are regarded as promising hole-transporting materials for perovskite solar cells (PSCs) due to their tunable optoelectronic properties. This paper reports the design, synthesis and characterization of three novel isomeric D-π-A small molecules PY1, PY2 and PY3. The chemical structures of the molecules consist of a pyrazolo[1,5-a]pyrimidine acceptor core functionalized with one 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole (3,6-CzDMPA) donor moiety via a phenyl π-spacer at the 3, 5 and 7 positions, respectively. The isolated compounds possess suitable energy levels, sufficient thermal stability (Td > 400 °C), molecular glass behavior with Tg values in the range of 127–136 °C slightly higher than that of the reference material Spiro-OMeTAD (126 °C) and acceptable hydrophobicity. Undoped PY1 demonstrates the highest hole mobility (3 × 10−6 cm2 V−1 s−1) compared to PY2 and PY3 (1.3 × 10−6 cm2 V−1 s−1). The whole isomers were incorporated as doped HTMs in planar n-i-p PSCs based on double cation perovskite FA0.85Cs0.15Pb(I0.85Br0.15)3. The non-optimized device fabricated using PY1 exhibited a power conversion efficiency (PCE) of 12.41%, similar to that obtained using the reference, Spiro-OMeTAD, which demonstrated a maximum PCE of 12.58% under the same conditions. The PY2 and PY3 materials demonstrated slightly lower performance in device configuration, with relatively moderate PCEs of 10.21% and 10.82%, respectively, and slight hysteresis behavior (−0.01 and 0.02). The preliminary stability testing of PSCs is also described. The PY1-based device exhibited better stability than the device using Spiro-OMeTAD, which could be related to its slightly superior hydrophobic character preventing water diffusion into the perovskite layer. [ABSTRACT FROM AUTHOR]

Abstract: All-inorganic 12-nm CuInSe2 nanocrystals, surface functionalized with metal chalcogenide complex ligands, were prepared via phase transfer ligand exchange in a biphasic (anhydrous hydrazine/hexane) mixture. I–V characteristics of thin films of these nanocrystals showed a four order of magnitude increase in current density as compared to nanocrystals capped with initial oleylamine ligands. [Copyright &y& Elsevier]

Abstract: We have studied hole transport in triarylamine based dendrimer using space-charge-limited current transient technique. A mobility of 8×10−6 cm2/(Vs) and a characteristic detrapping time of about 100ms have been obtained. We found that quasi-ohmic contact is formed with gold. The obtained mobility differs from the apparent one given by the analysis of stationary current–voltage characteristics because of a limited contact efficiency. The comparison between transients obtained from fresh and aged samples reveals no change in mobility with aging. The deterioration of electrical properties is exclusively caused by trap formation and accumulation of ionic conducting impurities. Finally, repeated transient measurements have been applied to analyze the dynamics of charge trapping process. [Copyright &y& Elsevier]

Since the late '80s, a highly stable conductive polymer has been developed, that is poly(3,4-ethylene dioxythiophene), also known as PEDOT. Its increasing conductivity throughout the years combined with its intrinsic stability have aroused great attention both in the academic and industrial fields. The growing importance of PEDOT, can be easily acknowledged through the numerous applications in thermoelectricity, photovoltaics, lighting, sensing, technical coatings, transparent electrodes, bioelectronics, and so forth. Although its high electrical conductivity is strongly established in the literature, the wide range of data shows that disorder, as the limiting factor in charges' transport, hinders the design of materials with optimal performances. The aim of this article is to review and discuss recent progresses dealing with the electrical conductivity and transport properties in PEDOT materials, with special attention on morphological and structural features. Particular emphasis is given to the commercial PEDOT:PSS as well as other PEDOT-based materials stabilized with smaller counter-anions. It appears that the electrical conductivity and the transport mechanisms are closely related to the fabrication process, the crystallinity of the material and the choice of the counter-anions. With the tunable electrical properties, new functionalities appear accessible and add up to the already existing applications that are concisely highlighted. [ABSTRACT FROM AUTHOR]

Two simple carbazole-based hole-transporting materials (HTMs) substituted with fused aromatic rings (Cz-N and Cz-Pyr) were synthesized in high yield and tested in perovskite solar cells (PSC). Cz-Pyr appears as a very promising HTM owing to its easy synthesis, relatively high Tg and high efficiency, outperforming the reference HTM Spiro-OMeTAD in PSCs. [ABSTRACT FROM AUTHOR]

Three new carbazole-based twin molecules with non-conjugated linear alkyl chains of various length as linker were synthesized in a one-step reaction. The new hole-transporting materials TCz-C3 , TCz-C6 , and TCz-C12 exhibit molecular glass behavior and the glass transition temperature can be tuned via the length of the linker. The optical and electrochemical properties are not significantly altered by the twin molecular structure, while the glass transition temperature increases and the hole mobility is strongly increased with reduced chain length by up to almost one order of magnitude, as determined from OFET measurements in saturation regime, demonstrating that conjugated linkers are not necessarily required in the design of twin molecules. The molecule with the shortest chain length (C 3 ), namely TCz-C3 , exhibited a promising power conversion efficiency of 2.21% in solid-state DSSC using the D102 dye as organic sensitizer. [ABSTRACT FROM AUTHOR]