Mechanism of charge transport in anisotropic layers of a phthalocyanine polymer

Solid samples of phthalocyaninato-polysiloxanes (PcPS) have been analyzed b y electrical dark conductivity experiments and by pulse-radiolysis time-res olved microwave conductivity (PR-TRMC) measurements. The in-plane conductiv ity of anisotropic PcPS Langmuir-Blodgett assemblies on gold surface-comb e lectrodes reveals an ohmic dependence at low voltages followed by a space-c harge-limited current regime at higher electric fields. The conductivity di splays a close to Arrhenius-type temperature dependence, with activation en ergies of 0.33-0.36 eV. The analysis of the space-charge limited currents ( SCLC) experiments yields charge carrier mobilities of approximately 10(-7)- 10(-6) cm(2)V(-1) s(-1) at room temperature. The conductivity perpendicular to the polymer chains was investigated by performing dielectric experiment s on sandwich devices. These measurements reveal conductivities which are l ower by several orders of magnitude than the corresponding in-plane values but the activation energy agrees quite well with that of the ohmic currents in the in-plane conductivity experiments. This result indicates that the s ame processes such as the hopping of charges in an energetically disordered material are involved in the transport. The intrachain mobility, as determ ined by PR-TRMC, is temperature-independent with a value of ca. 2 x 10(-2) cm(2)/Vs. The lack of any pronounced temperature dependence of the PR-TRMC mobility supports our conclusion that the electrical conductivities in the de-surface-comb and ac-dielectric spectroscopy experiments are limited by t emporary trapping or hindrance of motion of the charge carriers on particul ar sites during their transport over macroscopic distances.