Toward a better understanding of the doping mechanism involved in Mo(tfd-COCF3)3_3)_3 doped PBDTTT-c

In this study, we aim to improve our understanding of the doping mechanism involved in the polymer PBDTTT-c doped with(Mo(tfd-COCF3)3. We follow the evolution of the hole density with dopant concentration to highlight the limits of organic semiconductor doping. To enable the use of doping to enhance the performance of organic electronic devices, doping efficiency must be understood and improved. We report here a study using complementary optical and electrical characterization techniques, which sheds some light on the origin of this limited doping efficiency at high dopant concentration. Two doping mechanisms are considered, the direct charge transfer (DCT) and the charge transfer complex (CTC). We discuss the validity of the model involved as well as its impact on the doping efficiency.Comment: Accepted manuscript, J. Appl. Phy

Effect of the semi-conductive properties of the passive layer on the current provided by stainless steel microbial cathodes

Geobacter sulfur reducens biofilms were formed under constant polarisation at −0.6 V vs. Ag/AgCl on stainless steel cathodes to catalyse the reduction of fumarate. The time-evolution of the current strongly depended on the quality of the inoculum. Inoculating with young cells significantly shortened the initial lag-phase and using the same inoculum improved the reproducibility of the current–time curves. The whole set of experiments showed that 254SMO stainless steel provided higher current densities (on average 14.1 A/m2) than biofilms formed on 316L stainless steel (on average 4.5 A/m2). Biofilm coverage assessed by epifluorescent microscopy showed that coverage ratios were generally higher for 316L than for 254SMO. It must be concluded that 254SMO is more efficient in transferring electrons to bacterial cells than 316L. Mott–Schottky diagrams recorded on both materials under conditions of electrolysis in the absence of microorganisms showed that the surface oxide layers had similar n-type semi-conductive behaviour for potential values higher than the flat band potential. In contrast, 316L exhibited slight p-type behaviour at potential lower than the flat band potential, while 254SMO did not. The higher electrochemical performances of biocathodes formed on 254SMO are explained by semi-conductive properties of its passive layer, which prevented the p-type behaviour occurring in cathodic electrolysis conditions

Space–charge theory applied to the grain boundary impedance of proton conducting BaZr0.9Y0.1O3−δ.

The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr0.9Y0.1O3−δ as a function of pO2 and temperature. pO2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space–charge layers in the grain boundaries. A grain boundary core–space–charge layer model is therefore applied to interpret the data. Using a Mott–Schottky approximation, a Schottky barrier height of 0.5–0.6 V and an effective grain boundary width of 8–10 nm (=2× space–charge layer thickness) is obtained at 250 °C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space–charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra

Activating cobalt nanoparticles via the Mott-Schottky effect in nitrogen-rich carbon shells for base-free aerobic oxidation of alcohols to esters

Heterogeneous catalysts of inexpensive and reusable transition-metal are attractive alternatives to homogeneous cat-alysts; the relatively low activity of transition-metal nanoparticles has become the main hurdle for their practical ap-plications. Here, the de novo design of a Mott-Schottky-type heterogeneous catalyst is reported to boost the activity of a transition-metal nanocatalyst through electron transfer at the metal/nitrogen-doped carbon interface. The Mott-Schottky catalyst of nitrogen-rich carbon-coated cobalt nanoparticles (Co@NC) was prepared through direct polycon-densation of simple organic molecules and inorganic metal salts in the presence of g-C3N4 powder. The Co@NC with controllable nitrogen content and thus tunable Fermi energy and catalytic activity exhibited a high turnover frequency (TOF) value (8.12 mol methyl benzoate mol-1 Co h-1) for the direct, base-free, aerobic oxidation of benzyl alcohols to methyl benzoate; this TOF is 30-fold higher than those of the state-of-the-art transition-metal-based nanocatalysts reported in the literature. The presented efficient Mott-Schottky catalyst can trigger the synthesis of a series of alkyl esters and even diesters in high yields

Earth-Abundant Tin Sulfide-Based Photocathodes for Solar Hydrogen Production.

Tin-based chalcogenide semiconductors, though attractive materials for photovoltaics, have to date exhibited poor performance and stability for photoelectrochemical applications. Here, a novel strategy is reported to improve performance and stability of tin monosulfide (SnS) nanoplatelet thin films for H2 production in acidic media without any use of sacrificial reagent. P-type SnS nanoplatelet films are coated with the n-CdS buffer layer and the TiO2 passivation layer to form type II heterojunction photocathodes. These photocathodes with subsequent deposition of Pt nanoparticles generate a photovoltage of 300 mV and a photocurrent density of 2.4 mA cm-2 at 0 V versus reversible hydrogen electrode (RHE) for water splitting under simulated visible-light illumination (λ > 500 nm, Pin = 80 mW cm-2). The incident photon-to-current efficiency at 0 V versus RHE for H2 production reach a maximum of 12.7% at 575 nm with internal quantum efficiency of 13.8%. The faradaic efficiency for hydrogen evolution remains close to unity after 6000 s of illumination, confirming the robustness of the heterojunction for solar H2 production

Quantification of Ion Migration in CH3NH3PbI3 Perovskite Solar Cells by Transient Capacitance Measurements

Solar cells based on organic-inorganic metal halide perovskites show efficiencies close to highly-optimized silicon solar cells. However, ion migration in the perovskite films leads to device degradation and impedes large scale commercial applications. We use transient ion-drift measurements to quantify activation energy, diffusion coefficient, and concentration of mobile ions in methylammonium lead triiodide (MAPbI3) perovskite solar cells, and find that their properties change close to the tetragonal-to-orthorhombic phase transition temperature. We identify three migrating ion species which we attribute to the migration of iodide (I-) and methylammonium (MA+). We find that the concentration of mobile MA+ ions is one order of magnitude higher than the one of mobile I- ions, and that the diffusion coefficient of mobile MA+ ions is three orders of magnitude lower than the one for mobile I- ions. We furthermore observe that the activation energy of mobile I- ions (0.29 eV) is highly reproducible for different devices, while the activation energy of mobile MA+ depends strongly on device fabrication. This quantification of mobile ions in MAPbI3 will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells