Electrical properties of CdTe near the melting point

A new experimental setup for the investigation of electrical conductivity (σ) in liquid and solid CdTe was built for a better understanding of the properties near the melting point (MP). The temperature dependence of σ was studied, within the interval 1,050-1,130°C, at defined Cd-partial pressures 1.3-1.6 atm, with special attention to the liquid-solid phase transition. We found that the degree of supercooling decreases with increasing Cd overpressure and reaches the lowest value at 1.6 atm without change of the melting temperature during heating

Water Splitting Photovoltaic-Photoelectrochemical GaAs/InGaAsP - WO3/BiVO4 Tandem Cell with Extremely Thin Absorber Photoanode Structure

We demonstrate highly efficient solar hydrogen generation via water splitting by photovoltaicphotoelectrochemical (PV-PEC) tandem device based on GaAs/InGaAsP (PV cell) and WO3/BiVO4 core/shell nanorods (PEC cell). We utilized extremely thin absorber (ETA) concept to design the WO3/BiVO4 core/shell heterojunction nanorods and obtained the highest efficiencies of photo-induced charge carriers generation, separation and transfer that are possible for the WO3/BiVO4 material combination. The PV-PEC tandem shows stable water splitting photocurrent of 6.56 mA cm-2 under standard AM1.5G solar light that corresponds to the record solar-to-hydrogen (STH) conversion efficiency of 8.1%

Green fabrication of stable lead-free bismuth based perovskite solar cells using a non-toxic solvent

The very fast evolution in certified efficiency of lead-halide organic-inorganic perovskite solar cells to 24.2%, on par and even surpassing the record for polycrystalline silicon solar cells (22.3%), bears the promise of a new era in photovoltaics and revitalisation of thin film solar cell technologies. However, the presence of toxic lead and particularly toxic solvents during the fabrication process makes large-scale manufacturing of perovskite solar cells challenging due to legislation and environment issues. For lead-free alternatives, non-toxic tin, antimony and bismuth based solar cells still rely on up-scalable fabrication processes that employ toxic solvents. Here we employ non-toxic methyl-acetate solution processed (CH3NH3)3Bi2I9 films to fabricate lead-free, bismuth based (CH3NH3)3Bi2I9 perovskites on mesoporous TiO2 architecture using a sustainable route. Optoelectronic characterization, X-ray diffraction and electron microscopy show that the route can provide homogeneous and good quality (CH3NH3)3Bi2I9 films. Fine-tuning the perovskite/hole transport layer interface by the use of conventional 2,2′,7,7′-tetrakis (N,N′-di-p-methoxyphenylamino)−9,9′-spirbiuorene, known as Spiro-OMeTAD, and poly(3-hexylthiophene-2,5-diyl - P3HT as hole transporting materials, yields power conversion efficiencies of 1.12% and 1.62% under 1 sun illumination. Devices prepared using poly(3-hexylthiophene-2,5-diyl hole transport layer shown 300 h of stability under continuous 1 sun illumination, without the use of an ultra violet-filter

HP-HT sintering, microstructure, and properties of B6O- and TiC-containing composites based on cBN

The article presents a study of the potential for the use of B6O superhard boron suboxide as a binder in composite materials with a low cBN content. Superhard B6O is characterized by higher mechanical properties than TiC widely used in commercial materials today. Composites containing 60 vol % cBN and different binder compositions that included B6O and TiC have been sintered in a toroid-type high-pressure apparatus at a pressure of 7.7 GPa in a temperature range from 1500 to 2000 A degrees C. The microstructure, phase and elemental composition of the sintered materials have been examined via electron microscopy and X-ray diffraction analysis. Mechanical properties have been analyzed via indentation techniques. The performance of the cutting tools produced from the sintered composites has been evaluated in turning hardened cold work tool steel

Superhard pcBN tool materials with Ti₃SiC₂ MAX-phase binder: structure, properties, application

Superhard cutting tool materials were sintered in cBN–(Ti₃SiC₂–TiC) system via high pressure–high temperature method. Sintering was performed under the pressure 8 GPa in the 1400–2400 °C temperature range. The initial mixtures of three compositions were chosen with 90, 80 and 60 vol % cBN. The mixtures were prepared by mixing cBN (1–3 μm) and Ti₃SiC₂–TiC (< 2 μm). It was found, that upon sintering, the compositions of the obtained samples differed from the initial mixtures in all cases as a result of chemical reactions. Microstructure observations, phase composition estimation, and mechanical properties of the obtained tool materials were carried out. The results indicate that both the varying cBN content and the applied sintering conditions have a direct effect on the structure, properties, and kinetics of reactions.Надтверді матеріали системи cBN–(Ti₃SiC₂–TiC) при високому тиску і високій температурі. Спікання проводили при тиску 8 ГПа в температурному діапазоні 1400–2400 °С. Вихідні суміші трьох композицій були обрані з вмістом cBN 90, 80 і 60 % (за об’ємом). Суміші були приготовані шляхом змішування cBN (1–3 мм) и Ti₃SiC₂–TiC (< 2 мм). Було встановлено, що після спікання в результаті хімічних реакцій склад отриманих зразків відрізняється від складу вихідних сумішей. Проводили спостереження мікроструктури, оцінку фазового складу і механічних властивостей отриманих інструментальних матеріалів. Результати вказують на те, що різний зміст cBN і застосовані умови спікання чинять прямий вплив на структуру, властивості і кінетику реакцій.Сверхтвердые инструментальные материалы системы cBN–(Ti₃SiC₂–TiC) были спечены при высоком давлении и высокой температуре. Спекание проводили при давлении 8 ГПа в температурном диапазоне от 1400 до 2400 °С. Исходные смеси трех композиций были выбраны с содержанием cBN 90, 80 и 60 % (по объему). Смеси были приготовлены смешиванием порошков cBN (1–3 мм) и Ti₃SiC₂–TiC (< 2 мм). Было установлено, что после спекания в результате химических реакций состав полученных образцов во всех случаях отличается от состава исходных смесей. Проводили наблюдения микроструктуры, оценка фазового состава и механических свойств полученных инструментальных материалов. Результаты указывают на то, что разное содержание cBN и применяемые условия спекания оказывают прямое влияние на структуру, свойства и кинетику реакций

Studies of self organization processes in nanoporous alumina membranes by small angle neutron scattering

We performed studies of the self organization processes in nanoporous alumina membranes at initial and late stages of aluminum anodization by using scanning electron microscopy SEM and small angle neutron scattering SANS . SEM observations indicated three stages in the self organization of nanopores in alumina 1 nucleation of random nanopores with a broad radius distribution, 2 narrowing the radius distribution and 3 slow evolution of the nanoporous structure towards ordering of nanopores into large domains. SANS studies revealed orientational correlation between ordered domains of nanopores, which is characterized by a small misorientation angle. For the samples with high aspect ratios of nanopores, the SANS patterns showed azimuthal smearing, which was attributed to the redistribution of nanopores between the domains during their growt

Semiinsulating CdTe

Experimental conditions for the growth of near stoichiometric high-resistivity CdTe single crystals with a minimal concentration of point defects are investigated. The position of the stoichiometric line in the pressure-temperature (P-T) phase diagram is evaluated from high-temperature in situ galvanomagnetic measurements. Calculations based on a model of two major native defects (Cd vacancy and Cd interstitial) show, that a very small variation of Cd pressure P(Cd) results in a strong generation of uncompensated native defects. Modelling of room temperature carrier density dependence on the deep defect density NDD, PCd, and annealing temperature T shows, that the range of optimal PCd, at which high resistivity can be reached, broadens with increasing NDD or decreasing T. It is shown that at low T &lt;450°C the deep defect density &lt; 1015 cm-3 is sufficient to grow the high-resistivity CdTe. © 2002 Elsevier Science B.V. All rights reserved

The influence of growth conditions on the quality of CdZnTe single crystals

Experimental conditions were investigated for growth of inclusion-free near-stoichiometric CdZnTe single crystals with a minimized concentration of native point defects. The positions of the stoichiometric line pS = 8 � 105 exp(-1.76 � 104/T) (atm) and the room-temperature and high-temperature p-n lines were evaluated from high-temperature in situ galvanomagnetic measurements. The Cd pressure at the congruent melting point was estimated at � 1.15-1.20 atm from analysis of the total inclusion volume of five single crystals fabricated at Cd pressures in the range of 1-1.3 atm. An inclusion-free single crystal was prepared at PCd � 1.2 atm. Calculations based on a model of two major defects, the Cd vacancy and the Cd interstitial, show that a very small deviation of PCd from PS results in a large generation of the native defects. Thus a reproducible production of a high-resistivity material by a slow cooling along the PS seems to be very difficult