Carrier transport properties of poly(substituted phenylacetylene)s

Abstract

The u.v./vis. and i.r. spectra, current-voltage characteristics, carrier trapping levels and carrier mobilities of three poly(substituted phenylacetylene)s, one having an acceptor group o-CF 3, one having a donor group o-SiMe 3 and one having a 2,6-dimethyl-4-t-butyl group, have been studied. All three polymers show rather low conductivity, with the donor substitution leading to much higher conductivity than the acceptor substitution. Both holes and electrons take part in the severely trap-modulated conduction. In the case of poly(2,6-dimethyl-4-t-butylphenylacetylene) two trap levels with Gaussian distributions of trap energies have been found by isothermal decay current measurement. These trap energies agree closely with the apparent activation energy observed for conduction, consequently the dark conduction has its origin in thermal detrapping. In the case of poly( o-trimethylsilylphenylacetylene) and poly(2,6-dimethyl-4-t-butylphenylacetylene) hole and electron drift mobilities have been determined by the time-of-flight method using Scher-Montroll treatment of data to be 4 × 10 −7 and 1.7 × 10 −5 cm 2 V −1, respectively, for both carriers. Donor substitution to the phenyl ring of poly(phenylacetylene) significantly enhances the photoconduction of the poly(phenylacetylene).