Solid samples of phthalocyaninato-polysiloxanes (PcPS) have been analyzed by electrical dark conductivity experiments and by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) measurements. The in-plane conductivity of anisotropic PcPS Langmuir−Blodgett assemblies on gold surface-comb electrodes reveals an ohmic dependence at low voltages followed by a space-charge-limited current regime at higher electric fields. The conductivity displays a close to Arrhenius-type temperature dependence, with activation energies 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 cm2/V-1 s-1 at room temperature. The conductivity perpendicular to the polymer chains was investigated by performing dielectric experiments on sandwich devices. These measurements reveal conductivities which are lower 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 same processes such as the hopping of charges in an energetically disordered material are involved in the transport. The intrachain mobility, as determined by PR-TRMC, is temperature-independent with a value of ca. 2 × 10-2 cm2/Vs. The lack of any pronounced temperature dependence of the PR-TRMC mobility supports our conclusion that the electrical conductivities in the dc-surface-comb and ac-dielectric spectroscopy experiments are limited by temporary trapping or hindrance of motion of the charge carriers on particular sites during their transport over macroscopic distances.

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The photoinduced generation and the transport of charge carriers have been investigated in sandwich structures of Langmuir–Blogdett films of phthalocyaninato-polysiloxane between aluminum and gold electrodes. The diodelike current–voltage characteristics as well as the photovoltaic properties are directly related to the asymmetric electrode configuration. Under short-circuit conditions the photoactive region is located close to the aluminum electrode. By applying an external bias, the photoactive region is enlarged throughout the whole film thickness, and collection efficiencies of up to 0.3% are observed. Recombination effects have been studied by investigating the intensity dependence of the photocurrent. Nearly square root behavior under short circuit conditions is due to efficient charge carrier recombination whereas a linear intensity dependence is observed under reverse bias, indicating charge carrier diffusion to the electrodes. The transition between these two regimes is analyzed with respect to the charge carrier mobility yielding a value as small as 10−11 cm2/V s. The anisotrope molecular orientation in the film causes a photoconductivity clearly depending on the polarization of the incident light. The formation of a microcavity in these structures strongly influences the spectral properties and it allows, in agreement with theoretical calculations, to obtain an improved efficiency in a selected region of low film absorption. Atmospheric oxygen doping results in clear increase in the dark current, but the charge generation process remains nearly unaffected.

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The dark electrical conductivity of Langmuir−Blodgett assemblies of phthalocyaninato−polysiloxane (PcPS) has been measured at room temperature as a function of the degree of electrochemical oxidation. The conductivity is observed to increase from <10-6 S/cm for unoxidized PcPS to 10-5 S/cm at an oxidation level of 20%, and to decrease upon further oxidation. The initial increase in conductivity upon oxidative doping is believed to arise from the introduction of charge carriers with mobilities of approximately 10-6 cm2/Vs, while the subsequent decrease in conductivity at higher oxidation levels is attributed to reduced charge carrier mobility in the highly charged polymer.