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Intrinsic photogeneration

Figure 16. Schematic energy diagram for intrinsic photogeneration in an azo pigment and extrinsic photogeneration in the presence of a donor hole transport molecule. (Reprinted with permission from Ref. [34b].)... Figure 16. Schematic energy diagram for intrinsic photogeneration in an azo pigment and extrinsic photogeneration in the presence of a donor hole transport molecule. (Reprinted with permission from Ref. [34b].)...
We initially restrict ourselves to the simplest process the linear intrinsic photogeneration of charge-carrier pairs. Their production rate is proportional to the absorbed intensity of photons of the excitation light in the crystal, and requires neither excitonic processes at the crystal surface nor at the contacts, nor does it involve biexcitonic processes. [Pg.239]

Fig. 8.16 Scheme of the individual steps in the process of intrinsic photogeneration of charge-carrier pairs, Mp - M, in a molecular C7stal. The charge carriers are polarons (p). a Sq = neutral ground state S], S2, S3 are singlet excitons. Rate constants k/ i for autoionisation, kn for radiationless and kr for radiative intramolecular recombination (fluorescence), b bound charge-carrier pairs... [Pg.242]

A review is given on generation and transport of charge carriers in crystalline polydiacetylenes. Emphasis is placed on separating experimental facts related to both intrinsic photogeneration and time dependent transport from model considerations. The problem of crystal doping is briefly addressed. [Pg.135]

Fig. 8.3 Mechanism of intrinsic photogeneration of charges in amorphous photoconductors D = electron donor site A = electron acceptor site. (From [6].)... Fig. 8.3 Mechanism of intrinsic photogeneration of charges in amorphous photoconductors D = electron donor site A = electron acceptor site. (From [6].)...
Random walk theory is able to rationalize the experimental observation that (1) in conjugated polymers or related disordered organic solids intrinsic photogeneration... [Pg.25]

Amorphous selenium is a typical intrinsic photogenerator. The quantum yield of photogeneration was shown to have a strong dependence on the excitation wavelength, temperature and electric field [277]. A difiusion model based on the Onsager theory [278,279] has successfully been applied to analyze the diffiisive motion of opposite charges in the presence of an applied field Figure (10.27a). The model assumes that there is an activation barrier for the ionization process. If the excitation does not result in ionization, the... [Pg.530]

In conclusion, nanorods are a potentially interesting material, but present results still do not allow understanding of whether the nanostructure leads to an improvement of the intrinsic photocatalytic behaviour, or whether other factors (accessible surface area, enhanced adsorption, etc) are responsible for the observed differences. In ZnO nanorods have been shown quite recently by surface photovoltage spectroscopy that the built-in electrical field is the main driving force for the separation of the photogenerated electron-hole pairs.191 This indicates that the nano-order influences the photophysical surface processes after photogeneration of the electron-hole pairs. A similar effect could be expected for Titania nanorods. However, present data do not support this suggestion, mainly due to the absence of adequate photo-physical and -chemical characterization of the materials and surface processes. [Pg.374]

The diffusion length of photogenerated charge carriers is one of the important parameters governing the efficiency of a solar cell. In conventional cells, this is an intrinsic property of the semiconductor and its purity [34]. However, in DSSCs, the diffusion length is a function of the rate of reaction (4) and, thus, varies with different redox couples, surface treatments, and so forth. When the oxidation of R [reaction (2)] is chemically irreversible, the diffusion length of electrons is effectively infinite, whereas with kinetically fast, reversible redox couples (see Section VI), it approaches zero with unpassivated interfaces. [Pg.56]

Photogeneration of Charge Pairs and Intrinsic Properties of Semiconductors... [Pg.4]


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