New approach to the reduction of recombination in dye-sensitised solar cells via complexation of oxidised species.

Although dye-sensitised solar cells (DSSCs) have received great attention as low-cost and clean energy conversion devices, their conversion efficiency still lags behind that of inorganic solar cells. One of the reasons is due to the recombination of injected electrons with the oxidised species of the redox couple that are present in the electrolyte near the surface of the bare TiO2 particles. While most research has focused on blocking the bare surface of the TiO2 nanoparticles, we have introduced a new approach that can directly reduce the concentration of the oxidised species of the redox couple present in the electrolytes through complex formation. Recombination was reduced by the addition of cyclodextrins (CDs) to a polyethyleneglycol dimethyl ether (PEGDME) electrolyte containing iodide/triiodide redox couples that can form a complex with the triiodide. Experimental and theoretical investigation of the complex formation between triiodide and the CD in PEGDME matrix was performed. Increase in total power conversion efficiency was achieved using the alpha-CD as an additive in a low volatile PEGDME based electrolyte. Electrochemical impedance spectra and intensity modulated photovoltage spectroscopy measurements showed that the increase in the short-circuit current density is due to the suppression of surface recombination by the complex formation between the CDs and the triiodide ions.

Effects of basis set superposition error on optimized geometries and complexation energies of organo-alkali metal cation complexes.

Theoretical studies were performed to study the binding of alkali metal cations, X(+) (X = Li, Na, K), to poly(ethylene oxide) (PEO, I), poly(ethylene amine) (PEA, II), and poly(ethylene N-methylamine) (PEMA, III) by the Hartree-Fock (HF) and B3LYP methods using the 6-31G(d) and 6-311+G(d,p) basis sets. Two types of complex were considered in this study: a singly coordinated system (SCS) and a doubly coordinated system (DCS). Complexation energies were calculated both without and with basis set superposition error (BSSE). Because of the strong charge-dipole interactions, the complexation energies were largely negative and decreased in the order Li(+) > Na(+) > K(+). Three possible counterpoise (CP) approaches were examined in detail. In the case of the function CP (fCP) correction, the complexation energies exhibited an unusual trend because of the deformation of the subunits. This problem was solved by including geometry relaxation in the CP-corrected (GCP) interaction energies. The effects on the structures and vibrational frequencies were small when the complexes were reoptimized on the CP-corrected potential energy surface (PES).

Roles of terminal groups of oligomer electrolytes in determining photovoltaic performances of dye-sensitized solar cells.

The effect of terminal groups of oligomer electrolytes on the photovoltaic performance of dye-sensitized solar cells (DSSCs) have been systematically investigated to show that the terminal group plays a critical role in determining the concentration of I(3)(-), ionic conductivity, flatband potential and consequently the energy conversion efficiency.

Dye-sensitized solar cells based on composite solid polymer electrolytes.

The ionic conductivity of polymer electrolytes and their interfacial contact with dye-attached TiO2 particles were enhanced markedly by the addition of amorphous oligomer into polymer electrolytes, resulting in very high overall energy conversion efficiency.

Excellent optical and interfacial performance of a PEDOT-b-PEG block copolymer counter electrode for polymer electrolyte-based solid-state dye-sensitized solar cells.

A poly(3,4-ethylenedioxythiophene)-b-poly(ethylene glycol) (PEDOT-b-PEG) block copolymer doped with perchlorate on FTO shows excellent optical and interfacial performance as a counter electrode (CE), such as low charge transfer resistance and low reflectivity for polymer electrolyte-based solid-state dye-sensitized solar cells (DSCs), resulting in 8.45% energy conversion efficiency, greater than the common Pt CE, via a facile room-temperature process.

Coordination structure of various ligands in crosslinked PVA to silver ions for facilitated olefin transport.

The most effective ligand among -OH, -O- and -CHO for facilitated olefin transport by silver ions in room temperature crosslinked poly(vinyl alcohol) membrane has been evaluated.

Enhancement of facilitated olefin transport by amino acid in silver-polymer complex membranes.

Silver ions dissolved in a polymer matrix are additionally coordinated by carbonyl oxygens of asparagines and their counter anions interact with cationic sites, resulting in the enhanced activity of the silver ion as an olefin carrier for facilitated olefin transport.

Dye-sensitized nanocrystalline solar cells based on composite polymer electrolytes containing fumed silica nanoparticles.

We report remarkably high energy conversion efficiency (4.5% at 100 mW cm(-2)) of a dye-sensitized solar cell in the solid state, using composite polymer electrolytes containing fumed silica nanoparticles.

Barrier effect of dendrons on TiO2 particles in dye sensitized solar cells.

The short circuit current of dye sensitised solar cells increased significantly by the simple addition of polyester hydroxyl acetylene bis(hydroxymethyl)propanoic acid dendrons on TiO(2) nanoparticles, resulting in a very high overall energy conversion efficiency.

Synergistic catalytic effect of a composite (CoS/PEDOT:PSS) counter electrode on triiodide reduction in dye-sensitized solar cells.

Inorganic/organic nanocomposite counter electrodes comprised of sheetlike CoS nanoparticles dispersed in polystyrenesulfonate-doped poly(3,4-ethylenedioxythiophene (CoS/PEDOT:PSS) offer a synergistic effect on catalytic performance toward the reduction of triiodide for dye-sensitized solar cells (DSSCs), yielding 5.4% power conversion efficiency, which is comparable to that of the conventional platinum counter electrode (6.1%). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements revealed that the composite counter electrodes exhibited better catalytic activity, fostering rate of triiodide reduction, than that of pristine PEDOT: PSS electrode. The simple preparation of composite (CoS/PEDOT:PSS) electrode at low temperature with improved electrocatalytic properties are feasible to apply in flexible substrates, which is at most urgency for developing novel counter electrodes for lightweight flexible solar cells.

Organic-inorganic hybrid compounds containing polyhedral oligomeric silsesquioxane for conservation of stone heritage.

Alkoxysilane solutions based on tetraethoxysilane (TEOS) have been widely used for the consolidation of decaying heritage stone surfaces. TEOS-based products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the grains of stone components. However, they suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developing capillary force and dense gel fractures left inside of the stone. In this study, a TEOS-based stone consolidant containing functional (3-glycidoxypropyl)trimethoxysilane (GPTMS) and polyhedral oligomeric silsesquioxane (POSS) has been prepared in order to reduce gel crack formation during the drying phase. The addition of nanometer-sized POSS and/or GPTMS having a flexible segment reduces the capillary force developed during solvent evaporation. The properties of the TEOS/GPTMS/POSS composite solutions were compared with those of commercial products (Wacker OH and Unil sandsteinfestiger OH 1:1). The gelation time was similar to that of commercial consolidants, and the TEOS/GPTMS/POSS solution was stable over a period of up to 6 months. The addition of POSS and GPTMS provided a crack-free gel, while the gel from the commercial consolidants exhibited cracks after drying. The surface hydrophobicity of the treated decayed granite increased with the addition of POSS and GPTMS, and it was higher than that of the commercial product, implying the possibility of POSS and GPTMS as barriers to the penetration of water. This result implies that the TEOS/GPTMS/POSS solution showed a high suitability for the consolidation of granite heritage.

Complexation mechanism of olefin with silver ions dissolved in a polymer matrix and its effect on facilitated olefin transport.

Remarkable separation performance of olefin/paraffin mixtures was previously reported by facilitated olefin transport through silver-based polymer electrolyte membranes. The mechanism of facilitated olefin transport in solid membranes of AgCF3SO3 dissolved in poly(N-vinyl pyrrolidone) (PVP) is investigated. In silver polymer electrolyte membranes, only free anions are present up to the 2:1 mole ratio of [C=O]:[Ag], and ion pairs start to form at a ratio of 1:1, followed by higher-order ionic aggregates above a ratio of 1:2. At silver concentrations above 3:1, the propylene permeance increases almost linearly with the total silver concentration, unexpectedly, regardless of the silver ionic constituents. It was also found that all the silver constituents, including ion pairs and higher order ionic aggregates, were completely redissolved into free anions under the propylene environment; this suggests that propylene can be a good ligand for the silver cation. From these experimental findings, a new mechanism for the complexation reaction between propylenes and silver salts in silver-polymer electrolytes was proposed. The new mechanism is consistent with the linearity between the propylene permeance and the total silver concentration regardless of the kind of the silver constituents. Therefore, the facilitated propylene transport through silver-polymer electrolytes may be associated mainly with the silver cation weakly coordinated with both carbonyl oxygen atoms and propylene.