Molecular
dynamics of a low-band gap polymer, poly{[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]} (PTB7), and its 1:1.5 wt blend with a
fullerene derivative, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM),
accessible for organic photovoltaics was studied with the broadband
dielectric spectroscopy (BDS) technique in a wide range of frequency
(from 10–1 to 106 Hz) and temperature
(from −130 to 150 °C). In the BDS spectra, three types
of molecular mobility of the polymer chains designated as γ-,
β1-, and β2-relaxations, along with
conductivity and electrode polarization processes, were recognized,
separated, and analyzed. The relaxation processes in PTB7 and PTB7:PC71BM
were described with Arrhenius-type equations and related parameters
were found. Their analysis allowed us to reveal the influence of the
PC71BM molecules on the dynamics of the polymer chains. Based on dc
conductivity data, the Cole–Cole diagrams for PTB7 and PTB7:PC71BM
were plotted. They allowed for estimating the hole lifetime and its
comparison with the hole extraction time.
Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5 cm2/(V s) at an electric field of (1–7)×105 V/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account.
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