THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production

Electron transfer from the excited electronic singlet state of chemisorbed ruthenium(II) cis-di(isothiocyanato)bis(2,2‘-bipyridyl-4,4‘-dicarboxylate) into empty electronic states in a colloidal anatase TiO2 film was measured as a transient absorption signal of the injected hot electrons with a rise time <25 fs. Optical absorption of the anchored dye molecules led to the excited singlet state of the dye with a small admixture of charge transfer states. The electron transfer reaction reported here did not involve redistribution of vibrational excitation energy and was thus completely different from the well-known Marcus−Levich−Jortner−Gerischer type of electron transfer in the case of weak electronic interaction. It was also not a direct optical charge transfer transition from the donor to the acceptor level but rather an electron transfer reaction with an ultrashort but finite reaction time.

Measurement of Ultrafast Photoinduced Electron Transfer from Chemically Anchored Ru-Dye Molecules into Empty Electronic States in a Colloidal Anatase TiO2 Film

The essential role of the dark equilibrium potential is discussed for charge separation and the photovoltaic functioning of the title cell. A quantitative model is presented for the potential distribution in the sponge-type title cell. The unique screening process for the photogenerated electrons is discussed that facilitates their extremely long lifetime since the screening ions cannot function as recombination centers. A general analogy is pointed out for the photovoltaic functioning of the sponge-type electrochemical solar cell and of a conventional single-crystal solid-state solar cell.

Origin of Photovoltage and Photocurrent in the Nanoporous Dye-Sensitized Electrochemical Solar Cell

By application of 20 fs laser pulses, vibrational wave packets of low-energy modes (mainly 357 and 421 cm-1) were generated in the perylene chromophore that gave rise to periodic beats that lasted ...

Experimental fingerprints of vibrational wave-packet motion during ultrafast heterogeneous electron transfer.

Bis(ammonium lactato)titanium dihydroxide decomposes in neutral aqueous solution at temperatures above 100 °C to produce anatase nanocrystals of preferentially oblate habitus, and with a very narrow size distribution There is almost no dependence of size on precursor concentration, and a time dependence is observed only in the very beginning of crystal growth The crystal size is mainly determined by the reaction temperature, increasing from ca 2 nm at 120 °C to about 20 nm at 300 °C We assume the temperature dependent formation of a layer of byproduct ammonium lactate at the crystallite surface where it interferes with growth reactions After removal of this layer, continued heating yields larger crystallites in typical anatase shapes, indicating that Ostwald ripening has now become effective

Frank Willig

Papers

Measurement of Ultrafast Photoinduced Electron Transfer from Chemically Anchored Ru-Dye Molecules into Empty Electronic States in a Colloidal Anatase TiO2 Film

Origin of Photovoltage and Photocurrent in the Nanoporous Dye-Sensitized Electrochemical Solar Cell

Experimental fingerprints of vibrational wave-packet motion during ultrafast heterogeneous electron transfer.

Formation of uniform size anatase nanocrystals from bis(ammonium lactato)titanium dihydroxide by thermohydrolysis

Ultrafast electron injection from excited dye molecules into semiconductor electrodes