Reaction dynamics during the testing of polymerization catalyst

The olefins polymerization process in a slurry reactor is discussed. The reaction rate dynamics was analyzed and the contributions of feed flow, gas-liquid mass transfer, polymerization reaction, and catalyst deactivation were estimated. The propylene solubility in a solvent mixture “heptane” was calculated using Soave-Redlich-Kwong equation of state. These data were then approximated by Henry-like equation and the results were verified in experiments. The influence of propylene dissolving in ”heptane which was examined in special experiments without catalyst has provided the independent estimation of gas-liquid mass transfer coefficient. It has been shown that the reaction rate during the first 20-30 min of test is much lower (or higher) than total monomer consumption, depending on reactant addition sequence. The method of kinetic experiments interpretation and corresponding mathematical model are proposed. The method enables to estimate the kinetic parameter of monomer dissolution, the reaction rate constant of polymerization, as well as the parameters of active centers transformation – activation, deactivation and self-regeneration. An adequacy of model was proved by the description of experiments at two different pressures but with the same parameters values

Diamond-based electrodes for organic photovoltaic devices

The present paper demonstrates the possibility of replacing indium–tin oxide (ITO) with heavily boron-doped diamond (BDD). Plasma Enhanced Chemically Vapor Deposited BDDs layers of various thicknesses were prepared containing various boron concentrations in a gas phase. The dependence of the above-mentioned parameters on the optical and electrical properties of each BDD was studied in order to achieve optimal conditions for the effective application of diamond electrodes in organic electronics as a replacement for ITO. Bulk-heterojunction polymer–fullerene organic solar cells were fabricated to test the potency of BDD application in photovoltaic devices. The obtained results demonstrated the possibility of the aforementioned application. Even though the efficiency of BDD-based devices is lower compared to those using regular ITO-based architecture, the relevant issues were explained

Diamond/Porous Titanium Nitride Electrodes With Superior Electrochemical Performance for Neural Interfacing

Robust devices for chronic neural stimulation demand electrode materials which exhibit high charge injection (Qinj) capacity and long-term stability. Boron-doped diamond (BDD) electrodes have shown promise for neural stimulation applications, but their practical applications remain limited due to the poor charge transfer capability of diamond. In this work, we present an attractive approach to produce BDD electrodes with exceptionally high surface area using porous titanium nitride (TiN) as interlayer template. The TiN deposition parameters were systematically varied to fabricate a range of porous electrodes, which were subsequently coated by a BDD thin-film. The electrodes were investigated by surface analysis methods and electrochemical techniques before and after BDD deposition. Cyclic voltammetry (CV) measurements showed a wide potential window in saline solution (between −1.3 and 1.2 V vs. Ag/AgCl). Electrodes with the highest thickness and porosity exhibited the lowest impedance magnitude and a charge storage capacity (CSC) of 253 mC/cm2, which largely exceeds the values previously reported for porous BDD electrodes. Electrodes with relatively thinner and less porous coatings displayed the highest pulsing capacitances (Cpulse), which would be more favorable for stimulation applications. Although BDD/TiN electrodes displayed a higher impedance magnitude and a lower Cpulse as compared to the bare TiN electrodes, the wider potential window likely allows for higher Qinj without reaching unsafe potentials. The remarkable reduction in the impedance and improvement in the charge transfer capacity, together with the known properties of BDD films, makes this type of coating as an ideal candidate for development of reliable devices for chronic neural interfacing

Morphology versus Vertical Phase Segregation in Solvent Annealed Small Molecule Bulk Heterojunction Organic Solar Cells

The deep study of solvent annealed small molecules bulk heterojunction organic solar cells based on DPP(TBFu)2 : PC60BM blend is carried out. To reveal the reason of the solvent annealing advantage over the thermal one, capacitance-voltage measurements were applied. It was found that controlling the vertical phase segregation in the solar cells a high fullerene population in the vicinity of the cathode could be achieved. This results in increase of the shunt resistance of the cell, thus improving the light harvesting efficiency

Studium ultrarychlé dynamiky nosičů v polovodičích pomocí časově rozlišené terahertzové spektroskopie

Matematicko-fyzikální fakultaFaculty of Mathematics and Physic

Materials for Solar Cells Based on Thin Silicon Films

Thin lm microcrystalline silicon is the most promising materiál for large area PN junction solar cells. As microcrystalline silicon is a heterogenous material composed of two phases (amorphous silicon tissue from which crystalline grains of micrometric dimension grow). The Raman spectra are commonly used to determine the crystallinity of mixed phase silicon thin lms by analyzing the contributions of amorphous and crystalline phase to TO phonon band. Many dierent empirical or semi-empirical methods of evaluating crystallinity from the Raman spectra exist. In this master's thesis the microcrystalline Raman spectra were studied and a better way of evaluating crystallinity was searched for. The decomposition of the microcrystalline spectra of the series of the samples, where a single deposition parameter was changing,by tting them with Gaussian bands was performed. We also report on the development of a special software for the band decomposition by non-linear least-squares tting based on Marquardt-Levenberg algorithm and demonstrate its use for a series of lms with structure changing from amorphous to fully microcrystalline