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The photoconductivity of films of amorphous molecular semiconductors increases upon simultaneous photogeneration of singlet electron–hole pairs (EHPs) and triplet excitons and decreases upon photogeneration of triplet EHPs and triplet excitons. An increase in external electric field strength leads to a decrease in the effect of triplet excitons on the film photoconductivity caused by EHP dissociation. It is concluded that under increasing external electric field strength the mobility of charge carriers increases and the velocity of EHP dissociation becomes comparable with the velocity of spin conversion of EHPs interacting with triplet excitons. © 1997 John Wiley & Sons, Ltd.

The paper is devoted to the investigation of multiplicity and evolution of multiplicity in the course of life of electron-hole pairs in the films of poly-N-epoxypropylcarbazole, containing the CT-complexes as the electron-hole pairs photogeneration centers. The main results were obtained from the analysis of the effects of external magnetic and electric fields influence on photoconductivity.

Polymer composition films based on polystyrene and containing electron donors, viz., substituted tetrathiafulvalenes, an electron acceptor, viz., 2,4,5,7 tetranitrofluoren 9 one, and sensitizers, viz., a cationic polymethine dye, 1,3,3 trimethyl 2 [3 (1,3 dihydro 1,3,3 trimethyl 2H indol 2 ylidene)prop 1 en 1 yl] 3H indolium tetrafluoroborate, and a neutral mero cyanine dye, 5 {3 [(1,3 dihydro 1,3,3 trimethyl 2H indol 2 ylidene)ethylidene] 2 phenyl cyclopent 1 en 1 ylmethylene} 2 thioxodihydropyrimidine 4,6(1H,5H ) dione, were prepared. The internal photoeffect upon film irradiation in the near IR range is provided by low ioniza tion potentials of the donors and the high electron affinity of the acceptor. The photoconduc tivity increases upon replacement of a cationic dye by a neutral one, mainly because of photogeneration of mobile charge carriers of both signs and a decrease in the activation energy for the photoconduction current. The decrease in the activation energy for the photocurrent is due to the fact that in the case of a neutral dye, the mobile charge carriers move away from each other during their separation, while in the case of a cationic dye, the colorless counterion strongly helds the photogenerated charge carrier.The design of the materials that conduct electric cur rent on exposure to near IR radiation is a fairly topical task for photoelectric solar energy converters. 1-3 Along with inorganic semiconductors, the use of organic poly mers and their compositions for this purpose appears promising. 1,4-6 These are selected or developed with al lowance for the requirements to their films placed be tween the electrical contacts in the sandwich structures of photoelectric converters. 7 Generally, the photoconduc tivity of polymer films is provided by the presence of three types of molecules: donors, acceptors, and photo generation centers of charge carriers. 8 If the donor mol ecules are characterized by the ionization potential E i,d (proportional to the HOMO energy) and the acceptor molecules, by the electron affinity A e,a (proportional to the LUMO energy), 9 the molecules of the photogeneration centers are selected to meet the conditions |E i,c | > |E i,d | and |A e,c | < |A e,a |, where E i,c and A e,c are the ionization potential and the electron affinity of the photogeneration center molecule, respectively. If these conditions are ful filled, the absorption of a light quantum gives an elec tron-hole pair (EHP). Dissociation of the EHP results in free charge carriers.An important condition for the photoconduction is the transport of charge carriers within the bulk of the polymer film toward the electrical contacts without cap ture or recombination. 10-15 These structural features and properties of polymeric materials have already been imple mented in films based on carbazolyl containing polymers and polymers with conjugated bonds, 5 which use either intermolecular charge transfer complexes (CTC) or or ganic dyes and their aggregates as IR absorption and charge carrier photogeneration centers.How...

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