Morphology and charge transport in poly(2-methoxy-5-(2 '-ethylhexyloxy)-1,4-phenylenevinylene) films

Jeng, U and Hsu, C H and Sheu, H S and Lee, H.Y. and Inigo, A R and Chiu, H C and Fann, W S and Chen, S H and Su, A C and Lin, T L and Peng, K.Y. and Chen, S A (2005) Morphology and charge transport in poly(2-methoxy-5-(2 '-ethylhexyloxy)-1,4-phenylenevinylene) films. Macromolecules, 38 (15). pp. 6566-6574. ISSN 0024-9297

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Abstract

Structural characteristics of optical quality poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) films drop-cast from toluene solutions have been examined by use of wide-angle (WAXS) and small-angle X-ray scattering (SAXS) as well as field-emission scanning electron microscopy. For the as-cast film SAXS and WAXS patterns clearly suggest existence of nanodomains of mesomorphic order. Under grazing incidence, both SAXS and WAXS patterns of the as-cast film exhibit impressive uniaxial symmetry with strong scattering along the film normal; however, the corresponding normal-incidence patterns are circularly isotropic, implying in-plane random orientation. A structural model consisting of preferentially uniaxial-oriented nanodomains and disordered matrix is therefore proposed for the as-cast film. Annealing at 210 degrees C results in disorientation of nanodomains: this decrease in structural asymmetry upon heat treatment correlates well with concomitant changes in charge transport behavior determined from time-of-flight measurements, manifesting dramatically decreased charge mobility as well as transition from nondispersive to dispersive modes.