Nanocrystalline surfaces semiconductors

The convoluted, high-surface-area interface between the Ti02 and the electrolyte solution is an essential characteristic of DSSCs [1-3,5,17,18]. The photoconversion process begins at this interface when the adsorbed dye, D, absorbs a photon and the resulting excited state, D, injects an electron, 2, into the nanocrystalline Ti02 semiconductor ... 

Nanocrystalline Ti02 surfaces are prepared by coating conducting glass with a paste containing colloidal semiconductor particles, followed by a sintering process. For the solar cell type applications of nanocrystalline surfaces under discussion here,... 

The structure and composition of a nanocrystalline surface may have a particular importance in terms of chemical and physical properties because of their small size. For instance, nanocrystal growth and manipulation relies heavily on surface chemistry [261]. The thermodynamic phase diagrams of nanocrystals are strongly modified from those of the bulk materials by the surface energies [262]. Moreover, the electronic structure of semiconductor nanocrystals is influenced by the surface states that He within the bandgap but are thought to be affected by the surface reconstruction process [263]. Thus, a picture of the physical properties of nanocrystals is complete only when the structure of the surface is determined. 

In this communication we would like to report the synthesis and characterization of a new heteroleptic rutheni-um(II) complex with one of the bipyridine ligands replaced by a more conjugated ligand such as the 5,6-dimethyl-l,10-phenanthroline. Scheme 1 illustrates the molecular structure of the ruthenium(II) heteroleptic complex. Moreover, we have also carried out a study of the interfacial charge-transfer kinetics of the molecule when anchored onto the surface of nanocrystalline Ti02 semiconductor particles. 

Thin film coatings of nanocrystalline semiconductors, as collections of quantum dots (QD or Q-dot) attached to a solid surface, resemble in many ways semiconductor colloids dispersed in a liquid or solid phase and can be considered as a subsection of the latter category. The first 3D quantum size effect, on small Agl and CdS colloids, was observed and correctly explained, back in 1967 [109]. However, systematic studies in this field only began in the 1980s. 

An important aspect of semiconductor films in general with regard to electronic properties is the effect of intrabandgap states, and particularly surface states, on these properties. Surface states are electronic states in the forbidden gap that exist because the perfect periodicity of the semiconductor crystal, on which band theory is based, is broken at the surface. Change of chemistry due to bonding of various adsorbates at the surface is often an important factor in this respect. For CD semiconductor films, which are usually nanocrystalline, the surface-to-volume ratio may be very high (several tens of percent of all the atoms may be situated at the surface for 5 mn crystals), and the effects of such surface states are expected to be particularly high. Some aspects of surface states probed by photoluminescence studies are discussed in the previous section. 

Semiconductor photochemistry and photophysics play an important role in the broad field of supramolecular photochemistry. The unique properties of nanocrystalline semiconductor particles—which include quantum size effects on the band-gap, high surface area which is optimal for interfacial reactions, good photo- and thermal stability, and compatibility with the environment (i.e., green chemistry)—have led to an explosion of interest in the field. This volume of the Molecular and Supramolecular Photochemistry series provides chapters, authored by experts in the field, that discuss the area of semiconductor photochemistry and photophysics and highlight recent important advances in the area. 

Solar cells, or photovoltaic devices, have been studied for many years [3], Most of the current work is focused on dye-sensitized nanocrystalline solar cells. These provide a technical and economically viable alternative to present-day photovoltaic devices. In contrast to conventional systems, in which the semiconductor assumes both the task of light absorption and charge carrier transport, the two functions are separated in dye-sensitized nanocrystalline solar cells [54] (cf. OPCs). Light is absorbed by the dye sensitizer, which is anchored to the surface of a wide-band-gap semiconductor. Charge separation takes place at the interface via photoinduced electron injection from the dye into the conduction band of the... 

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