Nanocrystalline surfaces charge separation

Coordination Complexes Gerfin, T., Gratzel, M., and Walder, L., Molecular and Supramolecular Surface Modification of Nanocrystalline Ti02 Films Charge-Separating and 1 381... 

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... 

The competition between molecular-based and molecule-substrate interactions is one of the features that make supramolecular assemblies based on the combination of molecular components and solid substrates so exciting and also potentially useful from the applications point of view. The control issue is whether can one achieve long-lived charge separation between molecular components when immobilized on a surface, and from the fundamental perspective, can the interactions between the surface and molecular components be manipulated In this section, the immobilization of molecular components consisting of at least two electroactive and/or photoactive units will be discussed. The intramolecular interactions within these dyads in solution, as well as their behavior as interfacial supramolecular triads when immobilized on nanocrystalline TiC>2, will be compared. 

The results obtained for the solar cell discussed above suggest a strong interaction between the chromophore and the metal oxide layer, a large surface area, thus yielding large absorbances, and an efficient charge-separation upon injection. Several studies have indeed been carried out in an attempt to utilize the potential of nanocrystalline metal oxides as substrates for electrochromic devices. A particularly interesting approach has been reported by Fitzmaurice and co-workers [17]. These authors have constructed an electrochromic device based on the combination of... 

Qian Y, Sturchio NC, Chiarello RP, Lyman PF Lee T-L, Bedzyk MJ (1994) Lattice location of trace elements within minerals and at their surfaces with X-ray standing waves. Science 265 1555-1557 Rajh T, Nedeljkovic JM, Chen LX, Poluektov O, Thumauer MC (1999) Improving optical and charge separation properties of nanocrystalline 2 by surface modification with vitamin C. J Phys Chem ... 

The only way to rationalize the transport data for nanocrystalline ionic materials is to consider the systems separately, from the viewpoint of the level of defects in the crystals and the nature ofthe samples. In the case of lowly defective systems, such as the alkaline earth fluorides, there is good evidence for a conductivity enhancement, and the data can be explained in terms of models based on the space-charge layer. A key experiment here was the observation of enhanced conductivity in very thin alternating Cafb/Bafb layers when measured perpendicular to the layers [298]. This was explained as being due to the space-charge layers overlapping and saturating the layers. However, this observation is difficult to explain in terms of a model based on surface mismatch. 

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