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New functionalized soluble poly(p-phenylene vinylene) derivative bearing polar molecules was designed and synthesized in order to investigate effects of molecular orientation in polymer photovoltaic devices. The active polar molecule is the 4-(N-butyl-N-2-hydroxyethyl)-1-nitro-benzene group. The grafting of the push-pull molecule with a donor/transmitter/acceptor structure, possessing a large ground state dipole moment, enables the molecular orientation by a dc electric field. An internal electric field stored in such system facilitates exciton dissociation and improves charge transport in single-layer devices. In our systems an increase in the external quantum efficiency by a factor of about 1.5 to 2 is estimated. The associated effects of orientation on the carrier injection and transport properties were evidenced.