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 surface science of titanium dioxide

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.

TiO2 photocatalysis and related surface phenomena

During the past five years, the authors have developed in their laboratory a new type of solar cell that is based on a photoelectrochemical process. The light absorption is performed by a monolayer of dye (i.e., a Ruthenium complex) that is adsorbed chemically at the surface of a semiconductor (i.e., titanium oxide (TiO{sub 2})). When excited by a photon, the dye has the ability to transfer an electron to the semiconductor. The electric field that is inside the material allows extraction of the electron, and the positive charge is transferred from the dye to a redox mediator that is present in solution. A respectable photovoltaic efficiency (i.e., 10%) is obtained by the use of mesoporous, nanostructured films of anatase particles. The authors show how the TiO{sub 2} electrode microstructure influences the photovoltaic response of the cell. More specifically, they focus on how processing parameters such as precursor chemistry, temperature for hydrothermal growth, binder addition, and sintering conditions influence the film porosity, pore-size distribution, light scattering, and electron percolation and consequently affect the solar-cell efficiency.

Nanocrystalline titanium oxide electrodes for photovoltaic applications

Nanocrystalline titanium dioxide colloids have been synthesized using a sol−gel technique followed by growth under hydrothermal conditions in a basic environment at temperatures between 190 and 270 °C. Thin films have been made from aqueous suspensions of these colloids. X-ray analysis showed the colloids to be primarily the anatase crystal phase. Scanning electron microscopy (SEM) revealed a predominantly rodlike particle morphology after growth at lower temperatures and the formation of principally truncated tetragonal or tetrahydral bipyramidal nanocrystallites following growth at higher temperatures. The rodlike particles self-organize into regular cubic arrays with the long axis of the rods aligned perpendicular to the film surface. This self-organization is dependent upon the base used in colloidal synthesis and also upon the dielectric constant of the medium used during film formation.

Self-Organization of TiO2 Nanoparticles in Thin Films

Ionic liquid electrolytes are prepared using sulfolane as a plasticizer for eutectic melts to realize highly stable and efficiently performing dye-sensitized solar cells (DSCs) in hot climate conditions. Variations in the viscosity of the formulations with sulfolane content are measured and performance in DSCs is investigated using the ruthenium dye C106 as a sensitizer. A power conversion efficiency (PCE) of 8.2% is achieved under standard reporting conditions. Apart from lowering the viscosity, the addition of sulfolane induces a negative shift of the TiO2 conduction band edge. Strikingly the device performance increases to 8.4% at 50 degrees C due to higher short circuit photocurrent and fill factor, over-compensating the loss in open circuit voltage with increasing temperature. The PCE increases also upon decreasing the light intensity of the solar simulator, reaching up to 9% at 50 mW cm(-2). Devices based on these new electrolyte formulations show excellent stability during light soaking for 2320 h under full sunlight at 60 degrees C and also during a 1065 h long heat stress at 80 degrees C in the dark. A detailed investigation provides important information about the factors affecting the principal photovoltaic parameters during the aging process and the first results from a series of outdoor measurements are reported.

Francine Arendse

Papers

Nanocrystalline titanium oxide electrodes for photovoltaic applications

Self-Organization of TiO2 Nanoparticles in Thin Films

Ionic Liquid–Sulfolane Composite Electrolytes for High‐Performance and Stable Dye‐Sensitized Solar Cells

Mesoporous nanocrystalline thin films for electrochemical applications