Electronic transport properties of some new monoquaternary salts of 4,4′-bipyridine in thin films

Abstract

The dc electrical conductivity and thermoelectric power of some recently synthesized monoquaternary salts of 4,4′-bipyridine in thin films have been investigated as a function of temperature. Thin-film samples ( d = 0.30–0.95 μm) were deposited from dimethylformamide solutions, by an immersion technique, onto glass. Their heat treatment within temperature range of 291–617 K leads to stable structure and reproducible electronic transport properties.The crystalline structure of organic samples was investigated by XRD, while AFM technique, corroborated to optical microscopy, was used for the examination of surface morphology.The temperature dependences of the electrical conductivity and thermoelectric power are typical for n-type polycrystalline semiconductors. The activation energy of electrical conduction ranges between 1.56 and 1.86 eV, while the ratio of charge carrier mobilities lies in the range of 1.08–1.33.Some correlations between semiconducting parameters and molecular structure of the compounds were established. In the higher temperature range (415–617 K), the model based on band gap representation is suitable for the explanation of electronic transfer in investigated compounds. The examined compounds are also promising for thermistor applications.