A study of charge transport in a novel electroluminescent poly(phenylene vinylene-co-fluorenylene vinylene) based π-conjugated polymer

The charge transport properties in a novel electroluminescent poly{[2-(4',5'-bis(3-methylbutoxy)-2'-p-methoxy-phenyl)phenyl-1,4-phenylene vinylene]-co-(9,9-dioetyl-2,7-fluorenylene vinylene)} (BPPPV-PF) have been studied using a time-of-flight (TOF) photoconductivity technique. The TOF transients for holes were recorded over a range of temperatures (207-300 K) and electric fields (1.5 x 10(5)-6.1 x 10(5) V/cm). The hole transport in this polymer was weakly dispersive in nature with a mobility at 300 K of 5 x 10(-5) cm(2)/V s at 2.5 x 10(5) V/cm. This increased to 8.4 x 10(-5) cm(2)/V s at 6.1 x 10(5) V/ cm. The temperature and field dependence of charge mobility has been analyzed using the disorder formalisms (Bassler's Gaussian disorder model (GDM) and correlated disorder model (CDM)). The fit with Gaussian disorder (GDM) model yielded the mobility pre-factor mu(infinity) = 1.2 x 10(-3) cm(2)/V s, energetic disorder parameter sigma = 82 meV and positional disorder parameter Sigma = 1.73. The average inter-site separation (a = 7 angstrom) and the charge localization length (L = 3.6 angstrom) was estimated by assuming the CDM type charge transport. The microscopic charge transport parameters derived for this polymer are almost identical to the reported values for fully conjugated polymers with high chemical purity. The results presented indicate that the charge transport parameters can be controlled and optimized for organic optoelectronic applications. (C) 2006 Elsevier B.V. All rights reserved.