Double-Layer TiO2 Electrodes with Controlled Phase Composition and Morphology for Efficient Light Management in Dye-Sensitized Solar Cells

The light-scattering effect in the dye-sensitized solar cells (DSCs) was studied by controlling TiO₂ phase composition and morphology by fabrication of double-layer cells with different arrangement modes. The starting material for preparation of TiO₂ cells was synthesized by an aqueous sol–gel process. X-ray diffraction and field emission scanning electron microscopic analyses revealed that TiO₂ nanoparticles had particle size ranging between 18 and 44 nm. The optical property and band gap energy of TiO₂ nanoparticles were studied through UV–Vis absorption. The indirect optical band gap energy of anatase and rutile nanoparticles was found to be 3.47 and 3.41 eV, respectively. The double-layer DSC made of nanostructured TiO₂ film with phase composition of 78 % anatase and 22 % rutile as the under-layer and mixtures of anatase-nanoparticles and anatase-microparticles as the over-layer (i.e., NM solar cell) was shown the highest power conversion efficiency (PCE) of 6.04 % and open circuit voltage of 795 mV. This was achieved due to the optimal balance between the light scattering effect and dye sensitization parameters. Optimum light scattering of photoanode led to improve the PCE of NM double-layer solar cell which was demonstrated by diffuse reflectance spectroscopy.     

Sensor Performance of Nanostructured TiO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> Films Prepared by an Aqueous Sol–Gel Process

Nanostructured TiO₂–SnO₂ thin films and powders were prepared by a facile aqueous particulate sol–gel route. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range 17.2–19.3 nm. Moreover, the sols were stable over 5 months, since the constant zeta potential was measured during this period. The effect of Sn:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction analysis revealed that the powders were crystallised at the low temperature of 400 °C containing anatase-TiO₂, rutile-TiO₂ and cassiterite-SnO₂ phases, depending on annealing temperature and Sn:Ti molar ratio. Furthermore, it was found that SnO₂ retarded the anatase to rutile transformation up to 800 °C. The activation energy of crystallite growth was calculated in the range 0.96–6.87 kJ/mol. Transmission electron microscope image showed that one of the smallest crystallite sizes was obtained for TiO₂–SnO₂ binary mixed oxide, being 3 nm at 600 °C. Field emission scanning electron microscope analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20–40 nm at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption.     

Electrochemical insertion into and the detection of hydrogen in amorphous silicon solid electrolytes

The specific features of amorphous silicon are mainly contributed by the incorporation of hydrogen into the silicon during the vapour deposition process but, in spite of the considerable progress in the development of amorphous silicon cells, two major problems exist - light induced degradation and hydrogen evolution. As a result, there is a need to be able to measure and adjust the hydrogen content of the amorphous silicon. It is shown that this can be achieved using a potentiometric sensor, based on a proton conductor, and electrochemical tritation. Experiments show that it is possible to detect changes in hydrogen at all temperatures, using solid electrolytes, but that it is only possible to titrate hydrogen into the amorphous silicon at elevated temperatures. Paper presented at the 1st Euroconference on Solid State Ionics in Zakynthos, Greece, 11–18 Sept. 1994     

Use of strontium β-alumina based composite electrolyte in phosphorus concentration cells

A composite electrolyte based upon Sr β-alumina and strontium phosphate(s) has been developed for the measurement of phosphorus activities. The Sr β-alumina solid electrolyte and the composite electrolyte have been characterised for structural, physical and chemical properties using techniques such as X-ray diffraction, impedance spectroscopy, scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). Reversibility to metal/metal phosphides in concentration cells have been demonstrated. Thermodynamic data for metal (e.g. Cu and Co) phosphides and strontium phosphates, obtained by this method is considerably more accurate than the published data. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept, 13–19, 1997     

Immobilised molten salt membrane based magnesium sensor for aluminium-magnesium melts

Magnesium sensitive probes were constructed and tested in different melts of commercial aluminium-magnesium alloys. The probes were composed of a porous magnesium oxide one closed end tube or thimble to which a magnesium conducting salt is impregnated. The activity of magnesium in the aluminium-magnesium melt was determined with report to a pure magnesium reference contained in the inside of the thimble and sealed from the surrounding atmosphere and melt by zirconia based cement. Measurements were conducted in various commercial aluminium-magnesium alloys under inert atmosphere as well as in air. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994     

Binary codes and partial permutation decoding sets from the odd graphs

For k ≥ 1, the odd graph denoted by O(k), is the graph with the vertex-set Ω^{k}, the set of all k-subsets of Ω = {1, 2, …, 2k +1}, and any two of its vertices u and v constitute an edge [u, v] if and only if u ∩ v = /0. In this paper the binary code generated by the adjacency matrix of O(k) is studied. The automorphism group of the code is determined, and by identifying a suitable information set, a 2-PD-set of the order of k ⁴ is determined. Lastly, the relationship between the dual code from O(k) and the code from its graph-theoretical complement $\overline {O(k)} $ , is investigated.     

Van der Waals effects on structure and optical properties in organic photovoltaics

We have recently reported that dispersion forces can have drastic effects on the structure and charge separation in organic photovoltaics (OPVs) (Martinez et al., J. Phys. Chem. C 121, 20 134 [2017]). Here we investigate dimer complexes formed by the polymer P3HT and the fullerene derivative PCBM. We show how van der Waals (vdW) interactions affect the geometrical structure, which has strong effects on the electronic structure and UV-Vis absorption spectrum. Time-dependent density functional theory calculations demonstrate that the experimentally observed blue-shift of the absorption maximum of P3HT/PCBM OPV cells with respect to pure P3HT results mainly from distortions in P3HT due to vdW interactions between donor and acceptor fragments. Reduced absorption in the red region of the UV-Vis spectrum results from distortions of P3HT and small charge transfer between P3HT and PCBM. These results are in qualitative agreement with experiments and recent theoretical results on the corresponding solid-state films.     

The diels-alder dimerisation of 2,3-dichlorocyclopentadienone and of 2,3,8,9-tetrachlorobicyclo[4.3.0]nona-2,4,8-trien-7-one

The Diels-Alder dimer of 2,3-dichlorocyclopentadienone, shown to be endo-4,5,7,8-tetrachlorotricyclo[5.2.1.0^2,6]deca-4,8-dien-3,10-dione 1, forms 2,3,8,9-tetrachlorobicyclo[4.3.0]nona-2,4,8-trien-7-one 3 on thermal extrusion of carbon monoxide. The trienone 3 itself dimerises at ca. 160°, with loss of hydrogen chloride, affording two stereoisomeric aromatic derivatives 8 and 9.     

A three carbon intercalation of an enediol silyl ether; a short entry to the bicyclo[5.3.1]undecyl system of taxanes

A three step synthesis of 11-methylene-bicyclo[5.3.1]undecan-2,6-dione is described.