Influence of polar molecular chain orientation on optical and carrier transport properties of polymer blends

We report investigation of optical and electrical properties of poly(9-vinylcarbazole) (PVK) doped with 30 wt% 4-dibutylamino-4′-nitrostilbene (DBANS), depending on the molecular chain orientation of polar DBANS molecules. Orientation of dopant diode-like DBANS dye molecules was achieved by application of a static electric field through the polymer film, while heating the material near its glass transition temperature (Tg). Modification of optical properties due to the orientation was evidenced by the spectral dependencies of absorption coefficient. Appearance of the orientation-induced built-in electrical field was proven optically by the solid electric field induced second harmonic generation (SEFISHG) and electrically by current–voltage (IV) characterization. Measurement of the thermally stimulated currents (TSC) spectra demonstrated that carrier transport and trapping are affected, too. Changes of the TSCs induced by orientation were expressed best in the temperature range of 280–290 K. They could be attributed to the thermally activated process with activation energy of about 0.38 eV.