Extraordinary conduction increase in model conjugated/insulating polymer system induced by surface located electric dipoles

Abstract

The simple junction between the organic semiconductor and insulator possesses fascinating properties. The increase of the conductivity of conjugated material is one of the effects that is well documented in the literature. However, to-this-day there is no consistent explanation for this phenomenon. Herein, a lamellar system based on the regioregular poly(3-hexylthiophene) (R-P3HT), and the recently developed poly(4-vinylpyridine) (P4VP) cross-linked with d-block metal complexes is studied. Bilayer samples, mimicking organic Field Effect Transistors, are fabricated in a three-step procedure: (i) R-P3HT thin film casting, (ii) subsequent P4VP film casting on top of the R-P3HT, and (iii) cross-linking of the P4VP surface. The Cobalt and Zinc complexes exist only on the surface of the bilayer and do not penetrate the semiconductor. The conductivity of the system increases with each preparation step, to reach a value four orders higher as compared to the as-cast R-P3HT. Additional experiments show that the described effect is a consequence of the contact of R-P3HT and P4VP. Observed increase in the system's conductivity is attributed to the electric field induced in the semiconductor area by the pyridine dipole moments directed by surface-oriented metal complex. These findings open up new possibilities in tuning the performance of organic electronic devices.