On the electronic transport properties of pyrrolo[1,2-a][1,10]phenanthroline derivatives in thin films

The temperature dependences of electrical conductivity, sigma, and Seebeck coefficient, S, for six new synthesized pyrrolo[1,2-a][1,10]phenanthroline compounds, have been investigated. Thin film samples (d = 0.05-0.66 mu m) deposited by an immersion method (with dimethylformamide as solvent) onto glass were used. The crystalline structure of as-prepared organic films was investigated by XRD. The sample surface was examined by means of AFM and optical microscopy techniques. The ln sigma =f(10(3)/T) and S=f(10(3)/T) experimental curves are quite typical for polycrystalline semiconducting materials. The examined organic compounds show a p-type electrical conduction. The activation energy of electrical conduction ranged between 1.42 and 2.04 eV, while the ratio of charge carrier mobilities was in the range 0.76-0.90. The study of optical absorption evidenced direct bandgaps ranged between 4.06 and 4.11 eV, as well bandgaps of 2.69-3.58 eV for amorphous phases. Some relationships between materials parameters and molecular structure of the compounds are established. The model based on band gap representation is suitable for the explanation of charge transport in the studied compounds. (C) 2005 Elsevier B.V. All rights reserved.