On the mechanism of electrical conduction in some new quaternary salts of bipyridine and indolizine pyridine in thin films

The temperature dependences of dc electrical conductivity, sigma, and Seebeck coefficient, S, for six recently synthesized quaternary salts of bipyridine and indolizine pyridine (GAL compounds) in thin films, have been investigated. The thin-film samples (d = 0.06-0.60 mu m) were deposited by spin-coating using dimethylformamide solutions, onto glass. XRD was used for structure investigations, while AFM technique, corroborated to optical microscopy, was used for the examination of surface morphology of samples. The present compounds behave as typical n-type polycrystalline semiconductors. The activation energy of electrical conduction, Delta E, ranged between 1.61 and 1.73 eV, while the ratio of charge carrier mobilities, b, laid in the range 1.08-1.14. By studying optical absorption direct band gaps ranged between 3.78 and 4.00 eV have been found. Some correlations between semiconducting parameters and molecular structure of the compounds were established. The model based on band gap representation can be conveniently used for the explanation of electronic transport in investigated compounds. The investigated compounds are also suitable for applications in thermistor manufacture. (c) 2007 Elsevier B.V. All rights reserved.