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Hybrid photovoltaic structures made of P3HT and branched CdSe nanocrystals (NCs) with 50–90 wt% ratio were investigated. Charge Extraction by Linearly Increasing Voltage (CELIV) mobility and temperature dependent (photo-)conductivity measurements were used to analyze the charge transport. The samples with 50 wt% were photosensitive, but just a minor PV effect was observed. The photovoltaic phenomenon was pronounced in the samples containing 75 wt% or more of NCs. The Open Circuit Voltages up to 1 V were obtained. The recombination of the generated carriers was fast and could be a limiting factor of the cell current. Carrier mobility was up to (3–4) × 10−4 cm2/V s. From the fitting of mobility data the best carrier transport conditions were found in the samples with 75 wt% and 83 wt% of NCs.

International audience; Electrical transport properties of multiwalled carbon nanotube (MWCNT) polymer nanocomposites based on epoxy and high density polyethylene (HDPE) as matrices have been studied. The composites have been prepared from masterbatches by dilution. Low electrical percolation thresholds of 0.05 and 0.4 vol.% of carbon nanotubes in epoxy and HDPE matrices were found respectively. The analysis of the temperature dependence of dc-conductivity shows that the charge transport is fully described as the combination in series of one-dimensional (1-D) and three-dimensional (3-D) variable range hopping (VRH) regimes. The transport is limited by the 1-D VRH regime in the low temperatures limit and by the 3-D VRH regime at room temperature. The analysis of the VRH parameters when the overall volume fraction of MWCNT decreases reveals two distinct situations. In the epoxy the local characteristics of the masterbatch remain practically unchanged and a percolating network is maintained even at very low volume fractions; in the HDPE matrix, the density of the MWCNT bundles packing decreases as revealed by the strong variation of the Mott temperature parameter. Our results indicate that amorphous polymers matrices give lower percolation thresholds than semicrystalline ones when a masterbatch dilution process is used.

Tin sulfide (SnS), having a direct band gap of 1.3 eV, is a promising absorber material for solar energy conversion. We synthesized colloidal SnS nanocrystals with a size tuneable from 5 to 20 nm and low size dispersion. These nanocrystals can be processed as thin films using low-cost solution phase methods. They also offer the possibility of controlling the crystalline phase before deposition. With the goal to obtain dense and crack-free films of high conductivity, we used a layer-by-layer deposition technique. In the first step, the substrate was dipped in the nanocrystal colloidal solution (“ink”). Next, exchange of the nanocrystal surface ligands (oleylamine, trioctylphosphine, oleic acid) was carried out by dipping the substrate into a solution of small cross-linking molecules (1,4-benzenedithiol). This exchange enhances the electronic coupling and charge carrier mobilities by reducing the interparticle distance. At the same time it assures the immobilization of the nanocrystals to avoid their removal during subsequent depositions. The thickness of the nanocrystal thin films was controlled in a range of 100–250 nm by varying the number of the alternating nanocrystal deposition and ligand exchange steps. Scanning electron microscopy and atomic force microscopy investigations show that the obtained films are dense and homogeneous with a surface roughness as low as 3 to 4 nm root mean square. Using an inverted structure, the heterojunction of a SnS nanocrystals film with n-type ZnO nanocrystals shows a strongly increased current density under white light irradiation with respect to the dark.

It is shown that highly conducting films of polyaniline protonated with di-esters of sulfosuccinic and sulfophthalic acids which contain alkyl- or alkoxy-type substituents exhibit highly anisotropic structural, electrical and magnetic properties. The layered-like structure of these films can be described as consisting of polyaniline chains which are mainly oriented parallel to the plane of the film and form regular out-of-plane stacks. These stacks are separated by bilayers of the dopant anions. Accordingly, the main anisotropy observed for solution cast films implies in-plane and out-of-plane measurements. An electrical anisotropy of about 80 is found for the in-plane and out-of-plane electronic conductivities at 5 K. The temperature dependences of the in-plane and out-of-plane conductivities are qualitatively similar and have been fitted as a series combination of variable-range-hopping-type and power law contributions. A maximum is observed in the temperature dependence of the electrical anisotropy at low temperature. The films also show a clear anisotropy of magnetization whose temperature and field characteristics depend on the chemical structure of the dopant anion.

We have studied hole transport in triarylamine based dendrimer using space-charge-limited current transient technique. A mobility of 8 × 10 −6 cm 2 /(V s) and a characteristic detrapping time of about 100 ms 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.

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.