Semiconductors mesoporous film

Figure 9.7. Illustration of the usage of mesoporous films of transparent conducting oxides for novel types of solar cells. The dark gray areas correspond to ITO, the brighter ones to an oxide deposited onto the TCO matrix. The sphere symbolizes a dye. For instance, such films can be used as porous electrodes to include dyes and to deposit semiconductors such as ZnO. 

To detail DSSC technologies, Fig. 18.1 illustrates the modus operandi of DSSCs. Initially, light is absorbed by a dye, which is anchored to the surface of either n- or p-type semiconductor mesoporous electrodes. Importantly, the possibility of integrating both types of electrodes into single DSSCs has evoked the potential of developing tandem DSSCs, which feature better overall device performances compared to just n-or p-type based DSSCs [19-26]. Briefly, n-type DSSCs, such as TiOz or ZnO mesoporous films, are deposited on top of indium-tin oxide (ITO) or fluorine-doped tin oxide (FTO) substrates and constitute the photoanodes. Here, charge separation takes place at the dye/electrode interface by means of electron injection from the photoexcited dye into the conduction band (cb) of the semiconductor [27,28]. A different mechanism governs p-type DSSCs, which are mainly based on NiO electrodes on ITO and/or FTO substrates... 

However, to the best of my knowledge, no magnetic materials based on mesoporous solids are ready for any reliable application similar to magnetic fluids or magnetic polymer films although thin magnetic mesoporous films can be obtained similar to mesoporous films with semiconductor particles. 

As naturally abundant and low-cost semiconductor, NiO is widely used in electrochromic windows [20], batteries [21], supercapacitors [22], and sensors [23], While all these applications benefit from an interconnected, three-dimensional NiO nanostructure that combines a high specific surface area with a good electric conductivity, the performance enhancement becomes vividly evident as an increased coloration contrast and improved switching behavior when applied in electrochromic devices. NiO nanomaterials recently employed in electrochromic studies include nanocomposites [24], inverse opals [25], macroporous [26] and mesoporous films [27-29],... 

Of the various semiconductors tested to date, Ti02 is the most promising photocatalyst because of its appropriate electronic band structure, photostability, chemical inertness and commercial availability. But currently, a variety of nanostmctured Ti02 with different morphologies including nanorods, nanowires, nanostmctured films or coatings, nanotubes, and mesoporous/nanoporous structures have attracted much attention. 

Review of literature concerning the photochemistry of inorganic compounds shows us that a substantial progress was achieved during the past two decades in understanding the photophysical and photochemical properties of nanometer semiconductor particles [1-4] and structurally organized semiconductor materials, including the nanostructured semiconductor films, mesoporous molecular sieves [5 - 10] etc., and, also in the elaboration of physical and chemical techniques for their synthesis and examination of their photocatalytic activity in various chemical and electrochemical redox-processes. 

Photovoltaic cells based on the sensitization of mesoporous titanium dioxide by Ru(II) complex dyes in conjunction with the I.3 /U redox couple as a mediator have proved very efficient at exploiting this principle. In such systems, the ionic mediator travels back and forth by diffusion from the working electrode to the counterelectrode, to shuttle to the sensitizer the electrons that have gone through the electrical circuit [18, 21, 84]. Recently, solid-state devices have been described where the liquid electrolyte present in the pores of the nanocrystalline oxide film is replaced by a large-bandgap p-type semiconductor acting as a hole-transport medium [85 88]. 

Figure 8.1 Schematic of a liquid electrolyte dye-sensitised solar cell. Photoexcitation of the sensitiser dye is followed by electron injection into the conduction band of the mesoporous oxide semiconductor, and electron transport through the metal oxide film to the TCO-coated glass working electrode. The dye molecule is regenerated by the redox system, which is itself regenerated at the platinised counter electrode...

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