Dye-sensitized metal oxide

Heimer, T.A. Heilweil, E.J. Bignozzi, C.A. Meyer, G.J. (2000) Electron injection, recombination, and halide oxidation dynamics at dye-sensitized metal oxide interfaces. J Phys Chem A 104 4256-4262... 

The structural studies discussed here deal specifically with the interactions of molecules anchored with carboxylic acids to transition metal oxide surfaces. Bi-isonicotinic acid interacting with metal oxide surfaces combines interest in local carboxylic acid binding, and aromatic interaction with the surfaces. Electronic interactions have been investigated quantum-chemically for several aromatic molecules, including benzoic acid, bi-isonicotinic acid and catechol, all strongly anchored to TiC>2 substrates. Together, these systems represent a significant step towards studies of dye-sensitized metal oxide surfaces in photoelectrochemical devices. 

Figure 15 Electron transfer schemes for dye-sensitized metal oxides. Scheme 1 is the standard excitation-injection scheme, while Scheme 2 is a direct photoinjection, consistent with the calculated absorption threshold of catechol sensitized TiC>2...

Organic CTMs Applied to Nanoporous Dye-sensitized Metal Oxide Electrodes... 

Many laboratories have built transient absorption spectroscopic systems to investigate the electron injection process in dye-sensitized metal oxide semiconductors. However, because of the often observed complicated reaction... 

There are some advantages of IR probe transient absorption for investigating dye-sensitized metal oxide semiconductors. Since the absorption of injected electrons does not usually overlap other absorption bands of the dye molecule, it is easy to analyze the electron injection process. It is easy to compare electron injection processes in different kinds of dye molecule, because the reaction product is always the same, the conductive electron, unless one changes the metal oxide nanocrystalline film. Then not only the reaction rates but also the reaction yields can be compared by measuring the absorption intensities in the timescale just after the reactions are completed. This information is important especially when discussing the relation between the electron injection process and solar cell performance such as the photocurrent generation yield. It is hard to evaluate and compare electron injection yields for... 

In this session, some representative results of interfacial electron injection studies at metal oxide surface using time-revolved IR spectroscopy will be presented. The effects of metal oxide materials, sensitizer dyes, solvents and additive ions on dye-sensitized metal oxides will be discussed. Also, a recent result regarding electron injection from a photoexcited gold nanoparticle into a Ti02 nanoparticle will be shown and its characteristics will be discussed. 

First, the p-type material needs to have electronic levels into which holes can be injected from the oxidized or excited state of the dye. The redox levels of the dye and the p-type material therefore have to be adapted carefully. An intimate contact between the sensitized metal oxide and the p-type material is vital to assure fast injection and regeneration processes (Fig. 1). This implies either the growth or deposition of one semiconductor inside a preformed, sensitized porous film of its counterpart or the in situ formation of the sensitized composite. Direct formation of the sensitized junction would be appreciable however, charge collection within the two independent semiconductor networks, in which at least one semiconductor is formed from nanometer-sized inorganic semiconductor particles, demands intimate contact between the particles. Reduced... 

Another approach for designing biofuel cells is to combine the bioelectrocata-lytic properties of enzymes and light-harvesting nanomaterials such as metal oxide nanoparticles. Seeking for an efficient photoelectrolytic hydrogen production cell, hydrogenases were coupled to dye-sensitized titanium oxide nanoparticles. Two... 

E. Palomares, J.N. Clifford, S.A. Haque, T. Lutz, J.R. Durrant, Control of charge recombination dynamics in dye sensitized solar cells by the use of conformally deposited metal oxide blocking layers,... 

Dye-sensitized solar cells (DSSCs) are photoelectrochemical solar devices, currently subject of intense research in the framework of renewable energies as a low-cost photovoltaic device. DSSCs are based upon the sensitization of mesoporous nanocrystalline metal oxide films to visible light by the adsorption of molecular dyes.5"7 Photoinduced electron injection from the sensitizer dye (D) into the metal oxide conduction band initiates charge separation. Subsequently, the injected electrons are transported through the metal oxide film to a transparent electrode, while a redox-active electrolyte, such as I /I , is employed to reduce the dye cation and transport the resulting positive charge to a counter electrode (Fig. 17.4). 

DSSCs efficiencies up to 10.4%8 have been reported for devices employing nanocrystalline Ti02 films. Several studies have addressed the use of alternative metal oxides including SnCU,9 10 ZnO,11,12 and Nb205.13 The performance of dye-sensitized solar cells can be understood in view of the kinetic competition among the various redox processes involved in the conversion of light into electricity. Ultrafast electron injection (k2) has been observed in the femtosecond-picosecond (10 l5-... 

The details of die operating principles of the dye-sensitized solar cell are given in Figure. 3. The photoexcitation of the metal-to-ligand charge transfer of the adsorbed sensitizer [Eq. (1)] leads to injection of electrons into the conduction band of the oxide [Eq. (2)]. The oxidized dye is subsequently reduced by electron donation from an electrolyte containing the iodide/triiodide redox system [Eq. 

In Dr. M. Gratzel s plenary lecture at IPS-2000,103 he presented the following research topics to improve DSC. 1) Mastering the interfaces, electron transfer dynamics, control of dark current. 2) Charge transport in nanocrystalline films. 3) Panchromatic sensitizers, dye cocktail, quantum dot charge injection. 4) Light management, mixed metal oxide films, core-shell metal oxide films. 5) New... 

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