Dielectric Relaxation and Electrical Conductivity of Poly(3-hexyltiophene) and its blends with fullerene: from bulk to thin films

9th International Conference on Broadband Dielectric Spectroscopy and its Applications; University of Pisa and National Research Council, Pisa, Italy; September 11-16, 2016; http://the-dielectric-society.org/?q=9th-bds-conference-pisa-2016Organics photovoltaics (OPV) is one of the leading technologies aiming to transform solar light into electrical energy. The organic bulk heterojunction (BHJ) is one of the most promising material architectures consisting of an interpenetrating network of an organic donor semiconductor blended with an acceptor one. Blends of poly(3-hexylthiophene) (P3HT), as donor polymer, and a fullerene derivative as acceptor system are among the most promising photovoltaic blends. In this contribution the relaxational behavior and the electrical conductivity of a series of P3HT/phenyl-C71-butyric acid methyl ester (PC71BM) blends as revealed by dielectric spectroscopy will be presented. The results show that hexyl lateral chains of the polymer exhibit a low temperature/high frequency relaxation that presents similar features as that observed in polyethylene. This relaxation is not affected by the presence of PC71BM in the blends. Another high temperature/low frequency process associated to electrical conduction is also observed. The dependence with temperature of the electrical conductivity can be separated into two regions. At lower temperature the conductivity exhibits an Arrhenius behavior whereas at high temperature the conductivity can be described by the Gaussian Disorder model. In the low temperature region, the activation energy decreases when increasing the PC71BM content. The electrical conductivity of thin films of P3HT, as revealed by Conducting Atomic Force Microscopy (C-AFM), will be discussed and the effect of surface patterning by means of Laser Induced Periodic Surface Structures (LIPSS) will be described. This method enables the formation of well-ordered ripple nanostructures. C-AFM reveals a higher electrical conduction in the trenches than in the ridges regions. The effect of molecular order on this effect will be further discussedPeer Reviewe