Structure et Propriétés d'Architectures Moléculaires

Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Todays strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.

Lithium-ion batteries are becoming increasingly important for electrifying the modern transportation system and, thus, hold the promise to enable sustainable mobility in the future. However, their large-scale application is hindered by severe safety concerns when the cells are exposed to mechanical, thermal, or electrical abuse conditions. These safety issues are intrinsically related to their superior energy density, combined with the (present) utilization of highly volatile and flammable organic-solvent-based electrolytes. Herein, state-of-the-art electrolyte systems and potential alternatives are briefly surveyed, with a particular focus on their (inherent) safety characteristics. The challenges, which so far prevent the widespread replacement of organic carbonate-based electrolytes with LiPF6 as the conducting salt, are also reviewed herein. Starting from rather "facile" electrolyte modifications by (partially) replacing the organic solvent or lithium salt and/or the addition of functional electrolyte additives, conceptually new electrolyte systems, including ionic liquids, solvent-free, and/or gelled polymer-based electrolytes, as well as solid-state electrolytes, are also considered. Indeed, the opportunities for designing new electrolytes appear to be almost infinite, which certainly complicates strict classification of such systems and a fundamental understanding of their properties. Nevertheless, these innumerable opportunities also provide a great chance of developing highly functionalized, new electrolyte systems, which may overcome the afore-mentioned safety concerns, while also offering enhanced mechanical, thermal, physicochemical, and electrochemical performance.

We review the field of multinary metal chalcogenide nanocrystals, which has gained strongly increasing interest in the quest for novel narrow band gap semiconductors. Small (2–4 nm) CuInS2 and CuInSe2 nanocrystals, for example, exhibit size dependent luminescence in the visible and near infrared range. Their quantum yield can exceed 50% after growth of a ZnS shell, which makes them appealing emitters for lighting, displaying and biological imaging applications. Cu2ZnSnS4 (CZTS) nanocrystals, on the other hand, can be used as solution processed absorbing materials in thin film solar cells showing high power conversion efficiencies (currently around 8–10%). These examples illustrate that multinary metal chalcogenide nanocrystals have high potential for replacing classical cadmium and lead chalcogenide quantum dots in many fields. We give an overview of the chemical synthesis methods of the different systems reported to date, classifying them according to the obtained crystal structure. Next, we discuss their photophysical properties and give a brief description of the main fields of application. Finally, we conclude by outlining current challenges and related future directions of this exponentially growing domain.

We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III-V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors' view on the perspectives in this field is given.

Abstract A new method for the preparation of active layers of polymeric solar cells without the need for thermal post‐treatment to obtain optimal performance is presented. Poly(3‐hexylthiophene) (P3HT) nanofibers are obtained in highly concentrated solutions, which enables the fabrication of nanostructured films on various substrates. Here, the preparation of these fibers along with their characterization in solution and in the solid state is detailed. By mixing these nanofibers with a molecular acceptor such as [6,6]‐phenyl C 61 ‐butyric acid methyl ester (PCBM) in solution, it is possible to obtain in a simple process a highly efficient active layer for organic solar cells with a demonstrated power conversion efficiency (PCE) of up to 3.6 %. The compatibility of the room‐temperature process developed herein with commonly used plastic substrates may lead to applications such as the development of large‐area flexible solar cells.

This critical review discusses specific chemical and physicochemical requirements which must be met for organic compounds to be considered as promising materials for applications in organic electronics. Although emphasis is put on molecules and macromolecules suitable for fabrication of field effect transistors (FETs), a large fraction of the discussed compounds can also be applied in other organic or hybrid (organic-inorganic) electronic devices such as photodiodes, light emitting diodes, photovoltaic cells, etc. It should be of interest to chemists, physicists, material scientists and electrical engineers working in the domain of organic electronics (423 references).

InP/ZnS core/shell nanocrystals are prepared using a single-step heating-up method relying on the difference in reactivity of the applied InP and ZnS precursors. The obtained particles exhibit size-dependent emission in the range of 480-590 nm, a fluorescence quantum yield of 50-70%, and high photostability.

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The invasiveness of cells is correlated with the presence of dynamic actin-rich membrane structures called invadopodia, which are membrane protrusions that are associated with localized polymerization of sub-membrane actin filaments. Similar to focal adhesions and podosomes, invadopodia are cell-matrix adhesion sites. Indeed, invadopodia share several features with podosomes, but whether they are distinct structures is still a matter of debate. Invadopodia are built upon an N-WASP-dependent branched actin network, and the Rho GTPase Cdc42 is involved in inducing invadopodial-membrane protrusion, which is mediated by actin filaments that are organized in bundles to form an actin core. Actin-core formation is thought to be an early step in invadopodium assembly, and the actin core is perpendicular to the extracellular matrix and the plasma membrane; this contrasts with the tangential orientation of actin stress fibers anchored to focal adhesions. In this Commentary, we attempt to summarize recent insights into the actin dynamics of invadopodia and podosomes, and the forces that are transmitted through these invasive structures. Although the mechanisms underlying force-dependent regulation of invadopodia and podosomes are largely unknown compared with those of focal adhesions, these structures do exhibit mechanosensitivity. Actin dynamics and associated forces might be key elements in discriminating between invadopodia, podosomes and focal adhesions. Targeting actin-regulatory molecules that specifically promote invadopodium formation is an attractive strategy against cancer-cell invasion.

Abstract Regioregular head‐to‐tail (HT)‐coupled poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with a weight‐average molecular weight ( M w ) in the 7.3–69.6 kDa range is crystallized by directional epitaxial solidification in 1,3,5‐trichlorobenzene (TCB) to yield highly oriented thin films. An oriented and periodic lamellar structure consisting of crystalline lamellae separated by amorphous interlamellar zones is evidenced by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both the overall crystallinity as well as the orientation of the crystalline lamellae decrease significantly with increasing M w . The total lamellar periodicity is close to the length of “fully extended” chains for M w = 7.3 kDa (polystyrene‐equivalent molecular weight, eq. PS) and it saturates to a value of ca. (25–28) ± 2 nm for M w ≥ 18.8 kDa (eq. PS). This behavior is attributed to a transition from an oligomeric‐like system, for which P3HT chains are essentially in a fully extended all‐trans conformation and do not fold, to a semicrystalline system that involves a periodic alternation of crystalline lamellae separated by extended amorphous interlamellar zones, which harbor chain folds, chain ends, and tie molecules. For P3HT with M w of ca. 7.3 kDa (eq. PS), epitaxial crystallization on TCB allows for the growth of both “edge‐on” and “flat‐on” oriented crystalline lamellae on the TCB substrate. The orientation of the lamellae is attributed to 1D epitaxy. Because of the large size of the “flat‐on” crystalline lamellae, a characteristic single‐crystal electron diffraction pattern corresponding to the [001] zone was obtained by selected area electron diffraction (SAED), indicating that P3HT crystallizes in a monoclinic unit cell with a = 16.0 Å, b = 7.8 Å, c = 7.8 Å, and γ = 93.5°.

Abstract Neutrons and x‐rays were extensively used to study the microstructure of the polymeric membranes for fuel cells. The small‐angle x‐ray and neutron scattering (SAXS and SANS resp.) data for Nafion® and alternative membranes present specific features. The different analyses and proposed models to interpret these data are reviewed. A special emphasis is devoted to the recent elongated polymer particle model which appears as the most efficient model for Nafion® to interpret not only the numerous scattering data but also the transport swelling and mechanical properties. Neutrons can also be used to study the water management in situ in an operating fuel cell either to visualise the water accumulation in the gas distributors or to determine the water concentration profiles through the membrane and during operation.

This critical review discusses specific preparation and characterization methods applied to hybrid materials consisting of π-conjugated polymers (or oligomers) and semiconductor nanocrystals. These materials are of great importance in the quickly growing field of hybrid organic/inorganic electronics since they can serve as active components of photovoltaic cells, light emitting diodes, photodetectors and other devices. The electronic energy levels of the organic and inorganic components of the hybrid can be tuned individually and thin hybrid films can be processed using low cost solution based techniques. However, the interface between the hybrid components and the morphology of the hybrid directly influences the generation, separation and transport of charge carriers and those parameters are not easy to control. Therefore a large variety of different approaches for assembling the building blocks--conjugated polymers and semiconductor nanocrystals--has been developed. They range from their simple blending through various grafting procedures to methods exploiting specific non-covalent interactions between both components, induced by their tailor-made functionalization. In the first part of this review, we discuss the preparation of the building blocks (nanocrystals and polymers) and the strategies for their assembly into hybrid materials' thin films. In the second part, we focus on the charge carriers' generation and their transport within the hybrids. Finally, we summarize the performances of solar cells using conjugated polymer/semiconductor nanocrystals hybrids and give perspectives for future developments.

This article provides the first comprehensive review of the most recent class of lithium-ion battery materials, hosting lithium by a combined conversion/alloying mechanism.

Poly(3,4-ethylenedioxythiophene) (PEDOT) is certainly the most known and most used conductive polymer because it is commercially available and shows great potential for organic electronic, photovoltaic, and thermoelectric applications. Studies dedicated to PEDOT films have led to high conductivity enhancements. However, an exhaustive understanding of the mechanisms governing such enhancement is still lacking, hindered by the semicrystalline nature of the material itself. In this article, we report the development of highly conductive PEDOT films by controlling the crystallization of the PEDOT chains and by a subsequent dopant engineering approach using iron(III) trifluoromethanesulfonate as oxidant, N-methyl pyrrolidone as polymerization rate controller and sulfuric acid as dopant. XRD, HRTEM, Synchrotron GIWAXS analyses and conductivity measurements down to 3 K allowed us to unravel the organization, doping, and transport mechanism of these highly conductive PEDOT materials. N-methyl pyrrolidone promotes bigger crystallites and structure enhancement during polymerization, whereas sulfuric acid treatment allows the replacement of triflate anions by hydrogenosulfate and increases the charge carrier concentration. We finally propose a charge transport model that fully corroborates our experimental observations. These polymers exhibit conductivities up to 5400 S cm–1 and thus show great promise for room temperature thermoelectric applications or ITO alternative for transparent electrodes.

Abstract This Full Paper focuses on the preparation of single‐walled or multi‐walled carbon nanotube solutions with regioregular poly(3‐hexylthiophene) (P3HT) and a fullerene derivative 1‐(3‐methoxycarbonyl) propyl‐1‐phenyl[6,6]C 61 (PCBM) using a high dissolution and concentration method to exactly control the ratio of carbon nanotubes (CNTs) to the P3HT/PCBM mixture and disperse the CNTs homogeneously throughout the matrix. The CNT/P3HT/PCBM composites are deposed using a spin‐coating technique and characterized by absorption and fluorescence spectroscopy and by atomic force microscopy to underline the structure and the charge transfer between the CNTs and P3HT. The performance of photovoltaic devices obtained using these composites as a photoactive layer mainly show an increase of the short circuit current and a slight decrease of the open circuit voltage which generally leads to an improvement of the solar cell performances to an optimum CNT percentage. The best results are obtained with a P3HT/PCBM (1 : 1) mixture with 0.1 wt % multi‐walled carbon nanotubes with an open circuit voltage ( V oc ) of 0.57 V, a current density at the short‐circuit ( I sc ) of 9.3 mA cm –2 and a fill factor of 38.4 %, which leads to a power conversion efficiency of 2.0 % (irradiance of 100 mW cm –2 spectroscopically distributed following AM1.5).

The semicrystalline structure of regioregular head-to-tail- (HT-) coupled poly(3-hexylthiophene-2,5-diyl) (Rr-P3HT) thin films grown by directional epitaxial solidification (DES) has been studied by high-resolution transmission electron microscopy (HR-TEM). A 10-fold increase of the weight-average molecular weight of the Rr-P3HT leads to several major structural changes: (i) an increase of the fluctuations of the lamellar thickness while preserving the average length of the polymer stems in the crystalline domains; (ii) an increase of the disorder in the crystalline packing of Rr-P3HT chains; (iii) an enhanced interconnectivity between crystalline lamellae via tie-crystallites and tie-chains; (iv) for Mw ≥ 18.8 kDa equiv PS, preferential tilt angles of the polymer chains in the crystalline lamellae. Similar to stiff-chain polymers like poly(etheretherketone), the concomitant increase of the interchain distance (i.e., the a parameter in the unit cell) and the tilting of Rr-P3HT chains in the crystalline lamellae are attributed to chain folding exerting stress on the crystal packing because of the stiffness of comb-shaped Rr-P3HT chains.

We report a QENS study of the molecular motions in a perfluorinated ionomer membrane, Nafion, under increasing hydration levels from almost dry to fully saturated. Combined experiments performed on time-of-flight and backscattering spectrometers have been used to investigate the picosecond to the nanosecond dynamic behavior of water. The experimental spectra have been simulated over the whole Q range from 0.34 to 2.25 Å-1 by a single theoretical model taking into account the localized motions within confining domains, the microscopic features of the elementary jump process, and the long-range diffusion mechanism. The diffusion in a restricted geometry with ill-defined boundaries has been described by Gaussian statistics, contrary to the popular diffusion inside an impermeable sphere model where the boundaries are well defined. Evaluation of the spectra reveals the existence of two populations of protons in Nafion at all hydrations that are nonexchangeable on the nanosecond time-scale. A first population of three protons per ionic group is involved in a slow jump mechanism on characteristic length-scales of 2 to 4 Å and typical times ranging from 500 to 150 ps when increasing the water content in the membrane. This slow population, already present in the dried state, is presumably composed of the protons of the hydronium ions. The second fast population is composed of the additional hydrating water molecule protons. Between low hydration (3 H2O/SO3-) and saturation (17.5 H2O/SO3-), these protons are involved in a faster localized motion on roughly the same length scale, i.e., in the same water droplet as the hydronium ion. Long-range diffusion of these protons between neighboring domains of restricted motions is observed, even at very low hydration. As the number of water molecules in the membrane increases, a general finding is that the characteristic sizes increase and the characteristic times decrease, approaching asymptotic values at saturation. This is further reflected by the behavior of the local diffusion coefficient (inside a droplet) and the long-range diffusion coefficient (from one droplet to another) that vary, respectively, from 0.45 to 2 (10-5 cm2/s), and 0.1 to 0.58 (10-5 cm2/s), for λ ∼ 3 to 17.5. Overall, a molecular scenario for the proton motions among the different hydration steps has been proposed on the basis of the quantification of the dynamics on different length scales and time scales: below 10 H2O/SO3- the hydration protons diffuse faster and faster in ionic clusters of growing size. Above this first hydration regime, the asymptotic upper limit with increased hydration is reached: the water molecules locally display a bulk-like behavior within the hydrophilic domains. The long-range diffusion appears to be correlated to the enhancement of hydronium mobility with water loading. These findings, that qualitatively confirm the results of a previous similar study, bring a significant improvement to the description of the experimental data and new quantitative information concerning the nature of the molecular motions in hydrated Nafion.

Among the new photovoltaic technologies, the Dye-Sensitized Solar Cell (DSC) is becoming a realistic approach towards energy markets such as BIPV (Building Integrated PhotoVoltaics). In order to improve the performances of DSCs and to increase their commercial attractiveness, cheap, colourful, stable and highly efficient ruthenium-free dyes must be developed. Here we report the synthesis and complete characterization of a new purely organic sensitizer (RK1) that can be prepared and synthetically upscaled rapidly. Solar cells containing this orange dye show a power conversion efficiency of 10.2% under standard conditions (AM 1.5G, 1000 Wm(-2)) using iodine/iodide as the electrolyte redox shuttle in the electrolyte, which is among the few examples of DSC using an organic dyes and iodine/iodide red/ox pair to overcome the 10% efficiency barrier. We demonstrate that the combination of this dye with an ionic liquid electrolyte allows the fabrication of solar cells that show power conversion efficiencies of up to 7.36% that are highly stable with no measurable degradation of initial performances after 2200 h of light soaking at 65°C under standard irradiation conditions. RK1 achieves one of the best output power conversion efficiencies for a solar cell based on the iodine/iodide electrolyte, combining high efficiency and outstanding stability.

Diagnostic sensing device using exhaled breath of human have critical advantages due to the noninvasive diagnosis and high potential for portable device with simple analysis process. Here, we report ultrafast as well as highly sensitive bumpy WO3 hemitube nanostructure assisted by O2 plasma surface modification with functionalization of graphene-based material for the detection of acetone (CH3COCH3) and hydrogen sulfide (H2S) which are biomarkers for the diagnosis of diabetes and halitosis, respectively. 0.1 wt % graphene oxide (GO)- and 0.1 wt % thin layered graphite (GR)- WO3 hemitube composites showed response times of 11.5 ± 2.5 s and 13.5 ± 3.4 s to 1 ppm acetone as well as 12.5 ± 1.9 s and 10.0 ± 1.6 s to 1 ppm of H2S, respectively. In addition, low limits of detection (LOD) of 100 ppb (Rair/Rgas = 1.7 for acetone and Rair/Rgas = 3.3 for H2S at 300 °C) were achieved. The superior sensing properties were ascribed to the electronic sensitization of graphene based materials by modulating space charged layers at the interfaces between n-type WO3 hemitubes and p-type graphene based materials, as identified by Kelvin Probe Force Microscopy (KPFM). Rapid response and superior sensitivity of the proposed sensing materials following cyclic thermal aging demonstrates good potential for real-time exhaled breath diagnosis of diseases.