TOWARD A MORE EFFICIENT UTILISATION OF BETALAINS AS PIGMENTS FOR DYE-SENSITIZED SOLAR CELLS

We report on the use of natural dyes, betalains, as pigments for Dye-Sensitized Solar Cells (DSSC). Time-Dependent Density Functional Theory calculations provide the electronic spectra of the various types of betalain dyes and allow a discussion of their matching to the solar spectrum. Experimentally, we vary parameters such as the nature of the extracting solvent, the pH and the composition of the extract, to optimize the fabrication of DSSCs using betalains. Based on UV-Vis spectra correlated with electro-optic measurements providing the photovolatic conversion efficiency under standard AM1.5 conditions we find that the decrease of the pH of the dye solution leads to an increase of the DSSC performance, likely due to the increasing ratios of betacyanins with respect to betaxanthins in the extracts as well as the possible hydrolysis of betanin to betanidin. In order to fabricate better DSSCs using betalain natural dyes, we propose to use water as extracting solvent, to increase the content in betacyanins on the photoanode by a preliminary purification and to raise the stability of the dyes preferably by using anti-oxidizing copigments that do not interact with the substrate

Critical properties of random anisotropy magnets

The problem of critical behaviour of three dimensional random anisotropy magnets, which constitute a wide class of disordered magnets is considered. Previous results obtained in experiments, by Monte Carlo simulations and within different theoretical approaches give evidence for a second order phase transition for anisotropic distributions of the local anisotropy axes, while for the case of isotropic distribution such transition is absent. This outcome is described by renormalization group in its field theoretical variant on the basis of the random anisotropy model. Considerable attention is paid to the investigation of the effective critical behaviour which explains the observation of different behaviour in the same universality class.Comment: 41 pages, 10 figure

Discrete space-time by means of the weyl-dirac theory

A connection between the Weyl-Dirac theory and scale relativity theory through the hydrodynamic models (relativistic and non-relativistic approaches) is established. In such conjecture, considering that the motions of the microparticles take place on continuous but non-differentiable curves i.e. on fractals, a Weyl-Dirac type equation was found. Some correspondences with known hydrodynamic models, particularly Bialynicki-Birula's approach, are analyzed. All these results reflect the fractal structure of the space-time (a concept in agreement with the new ideas on the space-time)

Discrete Space-Time by Means of the Weyl-Dirac Theory

A connection between the Weyl-Dirac theory and scale relativity theory through the hydrodynamic models (relativistic and non-relativistic approaches) is established. In such conjecture, considering that the motions of the microparticles take place on continuous but non-differentiable curves i.e. on fractals, a Weyl-Dirac type equation was found. Some correspondences with known hydrodynamic models, particularly Białynicki-Birula's approach, are analyzed. All these results reflect the fractal structure of the space-time (a concept in agreement with the new ideas on the space-time

Discrete Space-Time by Means of the Weyl-Dirac Theory

A connection between the Weyl-Dirac theory and scale relativity theory through the hydrodynamic models (relativistic and non-relativistic approaches) is established. In such conjecture, considering that the motions of the microparticles take place on continuous but non-differentiable curves i.e. on fractals, a Weyl-Dirac type equation was found. Some correspondences with known hydrodynamic models, particularly Białynicki-Birula's approach, are analyzed. All these results reflect the fractal structure of the space-time (a concept in agreement with the new ideas on the space-time

Some framed f-structures on transversally Finsler foliations

Some problems concerning to Liouville distribution and framed $f$-structures are studied on the normal bundle of the lifted Finsler foliation to its normal bundle. It is shown that the Liouville distribution of transversally Finsler foliations is an integrable one and some natural framed $f(3,\varepsilon)$-structures of corank 2 exist on the normal bundle of the lifted Finsler foliation

Density Functional Theory (DFT) Study of Coumarin-based Dyes Adsorbed on TiO2 Nanoclusters—Applications to Dye-Sensitized Solar Cells

material

DFT Study of Binding and Electron Transfer from a Metal-Free Dye with Carboxyl, Hydroxyl, and Sulfonic Anchors to a Titanium Dioxide Nanocluster

We report results of density functional theory (DFT) calculations of a metal-free dye, 5-(4-sulfophenylazo)salicylic acid disodium salt, known as Mordant Yellow 10 (MY-10), used as sensitizer for TiO2 dye-sensitized solar cells (DSSCs). Given the need to better understand the behavior of the dyes adsorbed on the TiO2 nanoparticle, we studied various single and double deprotonated forms of the dye bound to a TiO2 cluster, taking advantage of the presence of the carboxyl, hydroxyl, and sulfonic groups as possible anchors. We discuss various binding configurations to the TiO2 substrate and the charge transfer from the pigment to the oxide by means of DFT calculations. In agreement with other reports, we find that the carboxyl group tends to bind in bidentate bridging configurations. The salicylate uses both the carboxyl and hydroxyl substituent groups for either a tridentate binding to adjacent Ti(IV) ions or a bidentate Ti-O binding together with an O-H-O binding, due to the rotation of the carboxyl group out of the plane of the dye. The sulfonic group prefers a tridentate binding. We analyze the propensity for electron transfer of the various dyes and find that for MY-10, as a function of the anchor group, the DSSC performance decreases in the order hydroxyl + carboxyl > carboxyl > sulfonate