Improvement of photovoltaic efficiency by polar molecule orientation in a newly developed semiconducting polymer

We report investigations of a new purposefully designed and synthesized functionalized soluble poly(p-phenylene vinylene) (ppv) derivative bearing polar diode-like molecules (nlo-ppv). The active polar molecule is the 4-(n-butyl-n-2-hydroxyethyl)-1-nitro-benzene group on the copolymer. The grafting of the push–pull molecule with a donor/transmitter/acceptor structure, possessing a large ground state dipole moment, enables the efficient molecular orientation by a dc-electric field. An internal electric field could be stored in such system, facilitating exciton dissociation and improving charge transport in polymer photovoltaic single-layer devices, resulting in increased efficiency. In the test systems an increase of the external quantum efficiency by a factor of about 1.5 to 2 took place upon orientation of the polar molecules. The effect of orientation on the carrier injection and transport properties depending on the chain orientation direction was evidenced.