Photogeneration polymers

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Having established the tendency of TBMS to undergo acid catalyzed depolymerization, the propensity for photochemically generated acid to effect the same phenomenon was evaluated. The resistance of TBS and TBSS to acid catalyzed depolymerization was also evaluated. Onium salts are well known photogenerators of acid, (16,17) while 2,6-dinitrobenzyl tosylate has been shown recently (15) to efficiently generate acid upon irradiation. Unirradiated samples of all the polymers... 

Zhang J, Xu S, Kumacheva E (2005) Photogeneration of fluorescent silver nanoclusters in polymer microgels. Adv Mater 17 2336-2340... 

Note 3 An example of chemical amplification is the transformation of [(fert-butoxy-carbonyl)oxy]phenyl groups in polymer chains to hydroxyphenyl groups catalyzed by a photogenerated acid. 

Fig. 7.7 Percentage of photogenerated holes that contribute to anodic decomposition versus O2 evolution from naked (no catalyst), Pt-coated, and polymer-Pt coated n-CdS photoanode in 0.5 M Na2S04 solution (pH = 8.6) [14].

Muller JG, Lupton JM, Feldmann J, Lemmer U, Scharber MC, Sariciftci NS, Brabec CJ, Scherf U (2005) Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer fullerene solar cells. Phys Rev B 72 195208... 

Photoconducting polymers such as poly (JV-vinylcarbazole) are used in xerography or electrophotography, since the photogenerated charge carriers can travel through the polymer film with relative facility before getting immobilized or trapped (Roberts,... 

Photoconductivity of polymers will be reviewed within the framework of semiconductor physics. The focus of attention will be the photogeneration and transport of the charge carriers, the relation between chemical structure and photoelectrical properties, and sensitization processes involving dyes and dopant molecules. 

For positive lit electrodes one can register the drift of holes, and for negative ones- the drift of the electrons. The photosensitizer (for example Se) may be used for carrier photoinjection in the polymer materials if the polymer has poor photosensitivity itself. The analysis of the electrical pulse shape permits direct measurement of the effective drift mobility and photogeneration efficiency. The transit time is defined when the carriers reach the opposite electrode and the photocurrent becomes zero. The condition RC < tlr and tr > t,r should be obeyed for correct transit time measurement. Here R - the load resistance, Tr -dielectric relaxation time. Usually ttras 0, 1-100 ms, RC < 0.1 ms and rr > 1 s. Effective drift mobility may be calculated from Eq. (4). The quantum yield (photogenerated charge carriers per absorbed photon) may be obtained from the photocurrent pulse shape analysis. 

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