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

Abstract

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)-l-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. (c) 2007 Elsevier B.V. All rights reserved.