Recent Developments in the desing of dye sensitized solar cell components

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Recent Development in the Design of Dye Sensitized Solar Cells Components

Recent developments in the development of new materials for dye sensitized solar cells mainly concerning novel electron mediators and new types of catalytic counter electrodes are reviewed

Photoelectrochemical behaviour of sensitized tiO2 photoanodes in aqueous solutions: application to hydrogen production

The use of TiO2 photoanodes sensitized with ruthenium(II) polypyridine complexes bearing phosphonic acid anchoring groups has been investigated in the context of photoinduced hydrogen generation. The photoanodes sustained 240 h of irradiation without undergoing appreciable hydrolysis and decomposition in an aqueous environment at pH 3. While the use of organic sacrificial donors, like ascorbic acid, considerably enhanced the photoanodic response, the exploitation of iodide was more problematic because the adsorption of photogenerated I3 - from aqueous media favored charge recombination with conduction band electrons, thus limiting the efficiency of the photoelectrosynthetic device. However, experiments performed in a three-compartment cell, where the photolectrode was in contact with an organic solvent, showed a remarkable photocurrent, with an electrolysis yield close to 87%. Introduction The use of sunlight to drive thermodynamically unfavorable reactions is the primary goal of any artificial photochemical system aimed to produce electricity or valuable materials such as fuels. The growing demand of a sustainable and renewable alternative to fossil fuels has aroused interest in photodriven hydrogen production on semiconductor substrates. A semiconductor with a band gap higher than 1.23 eV would be required to photogenerate electron-hole pairswith sufficient driving force to carry out the two redox reactions for water splitting: 4H2Oþ4e- f 2H2 þ4OH- 4OH- f O2 þ4e- þ2H2O These reactions are multi-electron-transfer processes that can efficiently occur on the surface of a semiconductor provided that (a) the band edges match the redox potentials for water reduction and oxidation, (b) the charge-transfer processes at the interface are fast, and (c) the stability requirements under irradiation are met. The simplest method to use sunlight to produce hydrogen and oxygen fromwater consists of the direct electrolysis of an aqueous solution by means of a solid-state photovoltaic device (e.g., silicon solar cells appropriately connected in series to reach the required overpotential for wate

Modified Tungsten Oxide and Process for its Preparation

The present invention relates to a modified tungsten oxide having an atomic concentration of 0.5 to 7.0%, preferably from 2.0 to5.0%,of nitrogen atoms in lattice posi-tion, with respect to the total number of atoms of the oxide, having a surface morphology,detectable by means of a scanning electron microscope, characterized by nanostructures in the form of vermiform or branched open swellings, preferably having a length ranging from 200to2,000nm, and a width ranging from 50 to 300nm, having an appearance similar to Rice Krispies.The present invention also relates to a process for the preparation of the above oxide by the anodization of metallic tungsten, and also a photoanode comprising the above oxide

Nanostructured photoelectrodes based on WO3: applications to photooxidation of aqueous electrolytes

Some recent studies mainly addressing the preparation and the modification of nanostructured thin films based on WO3 and their application to photoelectrolysis of aqueous electrolytes are reviewed with the aim of rationalizing the main factors at the basis of an efficient photoanodic response. WO3 represents one of the few materials which can achieve efficient water photo-oxidation under visible illumination, stably operating under strongly oxidizing conditions; thus the discussion of the structurerelated photoelectrochemical properties of WO3 thin films and their optimization for achieving almost quantitative photon to electron conversion constitutes the core of this contribution

The role of transition metal complexes in dye sensitized solar devices

This article focuses on the progress obtained in the design of metal complexes which find application as sensitizers for dye-sensitized solar cells, DSSCs, and as electron shuttles in substitution of the triiodide/ iodide redox couple. Coupling of sterically hindered dyes with mobile shuttles, based on a transition metal complex, represents the most advanced innovation which has allowed to reach on a single device the record efficiency of 12%. Issues which require further research are also discusse

Process for the synthesis of precursor complexes of titanium dioxide sensitization dyes based on ruthenium polypyridine complexes

The present invention concerns a process for the synthesis of precurs complexes for tio2 sensitization based on the microwave assisted procedure in aqueous solvent

Substituted Polypyridine Complexes of Cobalt(II/III) as Efficient Electron-Transfer Mediators in Dye-Sensitized Solar Cells

A number of cobalt complexes of substituted polypyridine ligands were synthesized and investigated as possible alternatives to the volatile and corrosive iodide/triiodide redox couple commonly used as an electron-transfer mediator in dye-sensitized solar cells (DSSCs). The extinction coefficients in the visible spectrum are on the order of 102 M-1 cm-1 for the majority of these complexes, diminishing competition with the light-harvesting dye. Cyclic voltammetric studies revealed a dramatic surface dependence of the heterogeneous electron-transfer rate, which is surprisingly different for gold, carbon, and platinum electrodes. DSSCs were assembled using a mediator that consisted of a mixture of Co(II) and Co(III) complexes in a 10:1 ratio. DSSCs containing these mediators were used to characterize incident photon-to-current conversion efficiency and photoelectrochemical responses. The best performing of these mediators were identified and subjected to further study. As suggested by electrochemical results, gold and carbon are superior cathode materials to platinum, and no evidence of corrosion on any cathode material was observed. Addition of lithium salts to the mediator solution resulted in a dramatic improvement in cell performance. The observed Li+ effect is explained in terms of the recombination of injected electrons in the photoanode with the oxidized mediator. The best mediator, based on tris(4,4¢-di-tert-butyl-2,2¢-dipyridyl)- cobalt(II/III) perchlorate, resulted in DSSCs exhibiting efficiencies within 80% of that of a comparable iodide/ triiodide-mediated DSSC. Due to the commercial availability of the ligand and the simplicity with which the complex can be made, this new mediator represents a nonvolatile, noncorrosive, and practical alternative as an efficient electron-transfer mediator in DSSCs

A viable surface passivation approach to improve efficiency in cobalt based dye sensitized solar cells

A successful general strategy for improving the electron collection efficiency in Dye Sensitized Solar Cells based on common Ru(II) complexes like Z907 and kinetically fast redox mediators based on the [Co(bpy)3]3+/2+ couples was investigated. The post-treatment of the dyed photoanode with commercially available tri-alkoxy silanes was effective in screening the TiO2 surface by electron recapture involving Co(III), but, interestingly, silanes endowed with relatively short propyl chains like aminopropyl-triethoxysilane (APTS) and trimethylammoniumpropyl- trimethoxysilane (TMAS) bearing a cationic charge, proved to be more effective than longer and more sterically hindered C16 chains in suppressing the dark current. In the best cases (TMAS and APTS), the siloxane treatment resulted in overall improvements of the cell efficiency of the order of respectively 600% and 500% by comparison with the untreated photoanode based on the Z907 Ru(II) Dye. This approach may represent a viable procedure for improving the electron collection efficiency in cobalt mediated DSSCs even without the use of highly sterically hindered dyes specifically designed to work in conjunction with kinetically fast metal based mediators

Efficient solar water oxidation using photovoltaic devices functionalized with earth-abundant oxygen evolving catalysts

Indium tin oxide (ITO) surfaces of triple junction photovoltaic cells were functionalized with oxygen evolving catalysts (OECs) based on amorphous hydrous earth-abundant metal oxides (metal = Fe, Ni, Co), obtained by straightforward Successive Ionic Layer Adsorption and Reaction (SILAR) in an aqueous environment. Functionalization with Fe(III) oxides gave the best results, leading to photoanodes capable of efficiently splitting water, with photocurrent densities up to 6 ± 1 mA cm−2 at 0 V vs. the reversible hydrogen electrode (RHE) under AM 1.5 G simulated sunlight illumination. The resulting Solar To Hydrogen (STH) conversion efficiencies, measured in two electrodes configuration, were in the range 3.7–5%, depending on the counter electrode that was employed. Investigations on the stability showed that these photoanodes were able to sustain 120 minutes of continuous illumination with a < 10% photocurrent loss at 0 V vs. RHE. Pristine photoanodic response of the cells could be fully restored by an additional SILAR cycle, evidencing that the observed loss is due to the detachment of the more weakly surface bound catalyst