The Influence of Charge Transport and Recombination on the Performance of Dye‐Sensitized Solar Cells

Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic‐hole conductors as hole transport materials (HTM). Nano‐crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4‐carboxylic acid‐4′‐carboxylate) (4,4′‐dinonyl‐2,2′‐bipyridyl)(NCS)₂ , coded Z‐907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO₂ film and charge recombination across the dye sensitized heterojunction is obtained.     

Functional analysis of type II thioesterase of Streptomyces lydicus AS 4.2501

Constructing a mutant strain of single gene disruption is the basis for the study of gene function and metabolomics. Systematic and complete genome sequencing is the basis of genetic manipulation. In the case of a little knowledge about the Streptomyces lydicus genome and the speculation that polyketide synthases (type I) might be responsible for the polyketide side chain biosynthesis of streptolydigin, a 588-bp fragment was amplified by polymerase chain reaction (PCR) according to the homology existing in the same functional genes among Streptomyces. A mutant strain of this gene was constructed by single crossover homologous recombination. The results of sequence analysis as well as the metabolite analysis of the mutant and the original strain by liquid chromatography/mass spectroscopy indicated that this fragment was part of type II thioesterase (TE) gene, which was required for streptolydigin biosynthesis like other type II TEs function in related antibiotics biosynthesis. Furthermore, targeted gene manipulation based on PCR was a powerful tool for studying gene function and metabolomics, especially when little was known about the genomic sequence of streptomyces.     

Atomic oxygen recombination on the ODS PM 1000 at high temperature under air plasma

High temperature materials are necessary for the design of primary heat shields for future reusable space vehicles re-entering atmospheric planet at hypersonic velocity. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic oxygen and this phenomenon is more or less catalyzed by the material of the heat shield. PM 1000 is planned to be use on the EXPERT capsule to study in real conditions its catalycity. Before the flight, it is necessary to perform measurements on ground test facility. Experimental data of the recombination coefficient of atomic oxygen under air plasma flow were obtained in the diffusion reactor MESOX on pre-oxidized PM 1000, for two total pressures 300 and 1000 Pa in the temperature range (850-1650 K) using actinometry and optical emission spectroscopy. In this investigation, the evolution of the recombination coefficient is dependent of temperature, pressure level and also of the chemical composition of the surface leading to one order of magnitude for a given temperature. The recombination coefficient is increasing with temperature and also dependent on the static pressure. The surface change due to the plasma exposure is inspected with SEM, XRD and XPS. As chromium oxide is the main part of the oxide layer formed during the oxidation in air plasma conditions, a sintered Cr₂O₃ sample was elaborated from powders to compare the data of the recombination coefficient obtained on PM 1000. Pre- and post-test analyses on the several materials were carried out using SEM, WDS, XRD and XPS.     

Effects of chain transfer and recombination/disproportionation of inhibitor radicals on inhibited oxidation of lipids

The kinetics of inhibited oxidation of lipids was studied by computer simulation to evaluate the contributions of the recombination/disproportionation of inhibitor radicals and chain transfer to retardation effects. The influence of inhibitor regeneration on the induction periods and inhibited oxidation rate was demonstrated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1915–1920, October, 1999.     

A Silicon Plasma-Based Wideband Modulator

Theoretical and experimental analysis has been performed for surface oriented silicon plasma-based p,i,n structures used to control high power level, broadband devices. It is shown that these structures are very promising for their use as modulators in the millimeter and submillimeter wave range.     

Improved Conductivity Induced by Photodesorption in SnO2 Thin Films Grown by a Sol-Gel Dip Coating Technique

Thin films of undoped and Sb-doped SnO2 have been prepared by a sol-gel dip-coating technique. For the high doping level (2–3 mol% Sb) n-type degenerate conduction is expected, however, measurements of resistance as a function of temperature show that doped samples exhibit strong electron trapping, with capture levels at 39 and 81 meV. Heating in a vacuum and irradiation with UV monochromatic light (305 nm) improves the electrical characteristics, decreasing the carrier capture at low temperature. This suggests an oxygen related level, which can be eliminated by a photodesorption process. Absorption spectral dependence indicates an indirect bandgap transition with Eg 3.5 eV. Current-voltage characteristics indicate a thermionic emission mechanism through interfacial states.     

Mass spectrometric study of NF3 plasma etching of silicon

NF₃ plasma etching is used for dry cleaning of reactors after plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon from SiH₄. The NF₃ plasma chemistry, in a closed isothermal plasma box with silicon coated walls, is analyzed by mass spectrometry of gases. Silicon is etched as SiF₄ by F atoms produced in the NF₃ dissociation into F+NF₂, or 2F+NF. The NF radicals recombine as N₂ +2F whereas the long-lived NF₂ radicals do not react with Si, but recombine as N₂F₄ This is the main limitation (or fluorine conversion into SiF₄. The pressure increase at the end point of etching is attributed to the sudden increase of F atom concentration in the gas phase and the consequent recombination q( F atoms as F₂.     

Photoluminescence of boron carbide

The excitation of B_4.3C with an Ar-laser () yields a photoluminescence spectrum between about 1.56 and 1.58 eV with its main maximum at 1.563 eV and a weaker maximum at 1.572 eV. It is attributed to the indirect-allowed recombination of free excitons.     

Absolute Calibration of TALIF of Atomic Nitrogen by NO Titration—Experimental and Theoretical Analysis

The method of absolute calibration of the TALIF signal of atomic nitrogen by NO titration in the afterglow of a flow tube reactor has been analyzed using TALIF and emission spectroscopy. An increase in production of atomic nitrogen at titration beginning and an asymmetric parabolic curve for emission of NObands have been observed. Of three possible explanations of these effects the model of wall recombination was favored: it led to fitted wall recombination coefficients referring to wall loss factors, which where in the same dimension as literature values and was able to simulate a hysteresis effect, which has been observed experimentally. According to the observations the titration end point cannot be used to determine the atomic nitrogen density in the afterglow before any NO has been added into the system as the titer produces part of this density itself. But for absolute calibration purposes referring to the wall recombination model the linear decrease of the TALIF signal with increasing titer concentration can still be used as straight line of calibration. Only a correction of the calibration factor by a factor of 0.59 for 5 mbar titrations has to be taken into account as the titer shows wall interaction not only in a catalytic way, but is partly consumed.     

条形靶激光等离子体复合特性的理论研究

报导一个条形靶激光等离子体的计算程序JLULP1,并首次用此程序研究了条形Si靶激光等离子体的空间和时间分布特性及其与靶形状之间的关系.结果表明,条形靶产生的激光等离子体比圆柱形靶产生的激光等离子体更有利于三体复合.