Sensitized hole generation

The elementary cell of the single crystals is monoclinic with 4 or 2 molecules per unit cell for a-perylene and chrysene or anthracene and phenanthrene respectively 70,71,72,73). Until now the sensitized hole generation has only been studied at the 001 plane of these crystals. The planar area of the organic molecules is turned away by a large angle from the 001 plane. The molecules in the crystal are facing the adsorbed dye molecule with their rims. Thus, no sandwich arrangement can be formed between the dye molecule and a crystal molecule at the ideal 001 surface of the crystal as shown later in Fig. 30. 

Sensitized hole generation in the organic crystals involves the ionisation energies at the surface of the organic crystals shown in Table 1 which have been derived from thermally activated electron transfer to redox ions 79>. 

The corresponding injection currents for sensitized hole generation are almost independent of the applied voltage. The remaining increase in the quantum efficiency (holes per incident photon) with rising external field strength (Fig. 27) corresponds to a relative linear increase of the current with a coefficient of 10-6... 

We can now discuss the quantum yield W for sensitized hole generation. With sufficient regeneration of the dye Cox A et > crJW we can write for the sensitized current ... 

Fig. 31. Quantum yield (filled circles) of rhodamine sensitized hole generation at the surface of organic crystals relative to perylene W/Wpe versus the ionisation energies 7C of the organic crystals (lower abcissa). The range of the estimate for the value at phenanthrene is indicated by the wiggled arrow. The activation times for electron transfer and back electron transfer Tjg are also shown (compare Section IV 7)...

Very early studies of dye sensitization have been on metal electrodes and aromatic hydrocarbon crystals [6,7]. On metal electrodes, the excited states of dye molecules are rapidly deactivated (by energy transfer to the broad continuum states of the metal) and there are no evidences of electron transfer quenching. Organic crystals are insulators with a wide bandgap (> 3eV) and narrow conduction and valence bands. Hole injection in the fully occupied valence bands of organic crystals such as anthracene, perylene or phenanthrene through excited dye molecules (e.g, Rhodamine B) was discovered in 1963 and the process has been examined extensively. The efficiency of sensitized hole generation in these cases is directly related to the... 

Fig. 26. General reaction scheme for dye sensitized hole injection in organic crystals. The scheme shows the excitation of the adsorbed dye ( ... ) in the first row at the left hand side. Through electron transfer the "reduced dye-hole pair" (2D. . , 2C+) is generated with its singlet and triplet spin state (2. row). The dissociated "reduced dye-hole pair is shown in the third row, and finally the hole contributing to the injection current in the fourth row. The regeneration of the dye molecules can be seen on the left hand side of the third row and the generation of sensitized delayed crystal fluorescence in the first row on the right hand side. Details are explained in Section IV 4 of the text...

Regensburger5 suggested that photosensitization by selenium involves hole generation and migration in selenium, injection across the interface and transport through the sensitized material. He also suggested that sensitization by dyes may involve the same type of mechanism. 

To facilitate a self-contained description, we will start with well-estahlished aspects related to the semiconductor energy hand model and the electrostatics at semiconductor-electrolyte interfaces in the dark . We shall then examine the processes of light absorption, electron-hole generation, and charge separation at these interfaces. The steady state and dynamic aspects of charge transfer are then briefly considered. Nanocrystalline semiconductor films and size quantization are then discussed as are issues related to electron transfer across chemically modified semiconductor-electrolyte interfaces. Finally, we shall introduce the various types of photoelectrochemical devices ranging from regenerative and photoelectrolysis cells to dye-sensitized solar cells. 

These include lasers, plasma etching, and chemical etching. Unfortunately, the reliability of micro-hole generation processes has not been established exactly, and a suitable inspection system should be used.IVaditional hole checkers do not work on blind holes. An AOI system is sensitive to the low contrast of copper foil surfaces. 

One of the strategies is to minimize the diffusion path of exitons (botmd states between an electron and electron hole) generated by photons hitting the active material in a photovoltaic cell. Once separated, holes and electrons should reach anode and cathode electrodes, respectively. During the process, recombination of holes and electrons lead to energy losses via thermal dissipation. In order to reduce such losses, minimizing the diffusion paths of exitons by means of BCP-derived nanostructures may be beneficial. To this end, a thin solid-state dye-sensitized solar cell (ssDSSC) with a 3D gyroidal titania network was fabricated (see Fig. 12) [37]. In contrast to typical disordered nanoparticle networks, the ordered mesoporous... 

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