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A hybrid system in which the counter electrode is exchanged with a redox couple dissolved in the electrolyte is an alternative to a “sandwich” type electrochromic (EC) device. We have developed a solid redox (tetramethylthiourea/tetramethylformaminium disulfide dication TMTU/[TMFDS]2+) electrolyte based on organically modified silane matrix. The EC device employing a solid electrolyte colors homogeneously, visible transmittance (Tvis) changes from 60% to 5%, at −1.5 V within less than 5 min when 240 nm cubic WO3 layer is employed. The results show that solidification of the electrolyte does not affect coloring kinetic, but the reduction of [TMFDS]2+ to TMTU at the Pt electrode significantly slows bleaching and reduces the self-bleaching of the device. Moreover, the EC device employing solid electrolyte colors homogeneously and is colorless in the bleached state (C, a and b values are below 10).

We report on the development of WO3 layers with increased symmetry induced by the incorporation of titanium into a crystalline WO3 matrix. The atomic ratio between W and Ti was varied stepwise from 100:1 to 100:20 with pure WO3 layers, made using peroxo sol–gel synthesis, as a reference. Layers were then formed by dip-coating from the corresponding sols. IR spectroscopy and XRD analysis of layers and powders heat-treated at 450 °C proved that the presence of titanium ions induces ordering and increases the symmetry of WO6 octahedra in the WO3 crystalline matrix leading to the transformation of the cell symmetry from monoclinic through tetragonal up to the cubic. Cyclic voltammetry confirmed that this increased symmetry leads to an up-shift in redox potential, which favors the coloration of the layers in photochromic devices. According to our knowledge, this is the first report of colorless cubic WO3 layers, which have potential applications in optoelectronic devices and sensors.

High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO2 paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO2 nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO2 layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO2 nanoparticles P25 acting as an interconnecting network within TiO2 layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO2 nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO2 layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO2 layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m2, AM1.5, 25 °C) were realized.

The influence that the degree of polyesterification has on a titanium sol (Ti-sol) prepared via the Pechini method that acts as a matrix in TiO2 pastes used for dye sensitized solar cells is reported. The different content of the polyester in the Ti-sol was realized by varying the heating time of the Ti-sol. Titanium dioxide pastes were prepared by introducing a commercial TiO2 nanopowder into the Ti-sols. The TiO2 layers were tested as photoanodes in dye-sensitized solar cells (DSSCs). The most appropriate degree of polyesterification was achieved by heating the Ti-sol for 0.5 and 1 h, while longer heating deteriorates the TiO2 layer morphology. The highest efficiency of the DSSCs based on an ionic liquid electrolyte was 6.3% measured under standard test conditions (100 mW/cm2, AM 1.5, 25 °C).

A titanium oxide layer used in a dye-sensitized solar cell (DSSC) has to meet two opponent properties to enable high conversion efficiency: a large surface area (for high dye loading) and good connection between TiO2 grains (for efficient extraction of electrons toward the front contact). In order to meet a trade-off between these criteria a preparation method for TiO2 paste formulation based on Pechini sol–gel method and commercial nanocrystalline TiO2 powder has been developed. A series of TiO2 pastes with different molar ratios between titanium isopropoxide, citric acid and ethylene glycol (1:X:4X) in the paste have been examined. The structure and morphology as well as cross-cut tests of deposited and sintered TiO2 layers have been analyzed. Results reveal that the paste with X = 8 exhibits the best properties, resulting in an overall conversion efficiency of DSSC under standard test conditions (100 mW/cm2, 25 °C, AM 1.5G) up to 6.6% for ionic liquid based electrolyte.

The performance of dye-sensitized solar cells, based on pure and binary ionic liquid electrolyte with different iodine concentrations, have been evaluated under 1 sun illumination and different cells temperature between 5 and 55 °C. At lower temperatures a short-circuit current ( J SC ) may be limited by the diffusion of tri-iodide. In this situation J SC increases with increasing temperature, while at higher temperatures the J SC decreases due to more pronounced recombinations. We find a maximum for J SC at intermediate temperatures. This maximum shifts to lower temperatures by increasing iodine concentration. At a certain temperature different iodine concentration is optimal for different ionic liquids employed in the electrolyte. The open circuit voltage monotonically decreases with temperature while the conversion efficiency is basically dominated by temperature dependence of J SC .

A novel titanium oxide paste based on Pechini sol–gel method and nanocrystalline titanium oxide powder have been successfully developed. Titanium oxide layers possess high inner surface area assuring high dye loading and well-connected nanocrystalline grains assuring good electron transport within the layer. The dye-sensitized layers have been used to assemble dye-sensitized solar cells with acetonitrile- and ionic liquid-based electrolyte. Overall conversion efficiencies of dye-sensitized solar cells (DSSCs) determined under standard test conditions (100 mW/cm 2 , 25 °C and AM 1.5 G) are 10.2% for acetonitrile and 7.3% for ionic liquid-based electrolyte.

Dye-sensitized solar cells (DSSCs) are recognized as one of the world's leading innovation in nanosciences and photovoltaic technology. In contrast to the conventional silicon-based solar cells the demand on purity of materials for DSSC is lower and forecasted manufacturing costs are approximately halved which make the DSSCs attractive alternative. Nowadays the conversion efficiency of DSSCs exceeds 10% which makes it competitive with other thin film solar cells. In this chapter the structure and the fundamental operation of the DSSC are presented. Afterwards the properties and requirements for each individual component used in a DSSC are given. In addition advanced hybrid DSSC systems also are presented. In overall, the emphasis of this chapter is given to the involvement of sol-gel chemistry in the preparation of the individual DSSCs components, primarily of TiO2 layers and electrolytes.

The performance of dye-sensitized solar cells (DSSC) based on the propyl-methyl-imidazolium iodide (PMII) ionic liquid (IL) with and without the addition of SiO 2 nanoparticles is studied. Results confirm that the presence of SiO 2 nanoparticles in PMII electrolyte improves the charge transport of iodide/tri-iodide redox couple in the electrolyte and consequently increases the efficiency of DSSC up to 20%, relatively. Short circuit current density ( J SC ) of the DSSC under illumination may be limited by the charge transport of the redox couple in the IL-based electrolytes and a theoretical maximum of J SC can be evaluated from the cyclic voltammetry measurements of simple symmetric cells (TCO-Pt electrolyte Pt-TCO). The results show a strong temperature dependence of the DSSC performance if the PMII/I 2 -based electrolytes are used.