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

TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Applications of hybrid organic–inorganic nanocomposites

The dye-sensitized solar cell (DSC) provides a technically and economically credible alternative concept to present day p–n junction photovoltaic devices. In contrast to the conventional silicon systems, where the semiconductor assumes both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a wide band gap oxide semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption band in conjunction with oxide films of nanocrystalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to current conversion efficiencies of 10.6% have been reached. New electrolytes based on ionic liquids have been developed that show excellent stability both under prolonged light soaking and high temperature stress. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, and discuss the importance of mastering the interface of the mesoporous films by assisting the self-assembly of the sensitizer at the surface of the oxide nanocrystals.

Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells

Highly efficient dye-sensitized solar cells were produced using single-crystalline TiO 2 nanotubes as a thin-film semiconductor because of the very high electron transfer through single-crystalline TiO 2 nanotubes when compared to that through nanoporous TiO 2 films composed of nanoparticles. The dye-sensitized solar cells with single-crystalline TiO 2 nanotubes showed more than double the short-circuit current density than those made of titania nanoparticles Degussa P-25 in the thin-film thickness region. Titania nanotubes were synthesized using molecular assemblies composed of surfactant molecules, i.e., laurylamine hydrochloride, and titanium alkoxide, i.e., tetraisopropylorthotitanate modified with acetylacetone, as a template. They have outer and inner diameters of about 10 and 5 nm, respectively, a length in the range from 30 nm to several hundred nanometers, and have a single-crystalline structure of anatase, as confirmed on lattice images observed by high-resolution transmission electron microscopy. The light to electricity conversion of the titania nanotube cells was around 5%. They also showed the highest photocatalytic activity when compared to the commercially available nanocrystalline titania.

https://iopscience.iop.org/article/10.1149/1.1589763/pdf

Issei Okada

Papers

Formation of Titania Nanotubes and Applications for Dye-Sensitized Solar Cells

Dye-sensitized Solar Cells Using Semiconductor Thin Film Composed of Titania Nanotubes