Time-resolved study of polaron pairs in conjugated polymers by two-correlated-pulses technique

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Abstract
Formation of polaron pairs is studied in photoconducting conjugated polymers such as substituted polythiophenes. The polaron pairs show themselves in the second order processes that were the main supplier of free charge carrier at high excitation density provided by femtosecond laser pulses. Two-correlated-pulses technique are used, and permitted to resolve kinetics of the free charge carrier formation within the picosecond time domain. The external electrical field is shown to change a relative amount of free charge carriers formed in the first and second order processes (i.e., by dissociation of primarily formed polaron pairs and by dissociation of the pairs formed as a result of recombination of primary pairs). A method of estimation of intercharge distances in the pairs based on the action of the electrical field is suggested and shows that polaron pairs of two intercharge distances (about 4 and 10 nm) are formed at the photoexcitation of polythiophenes studied.