Relaxation and Conductivity in P3HT/PC71BM Blends As Revealed by Dielectric Spectroscopy

The conduction mechanism and the molecular dynamics on the paradigmatic bulk heterojunction formed by poly(3-hexylthiophene) (P3HT) and phenyl-C71-butyric acid methyl ester (PCBM) blends have been characterized by dielectric spectroscopy. The results show that hexyl lateral chains of the polymer exhibit a high frequency local motion, similar to a polyethylene-like relaxation. By dielectric spectroscopy the dependence with temperature of the conductivity has also been studied. The results in the low temperature region provide a method to estimate the energy offsets of the system due to the presence of the C71 derivative. In the high temperature region, the temperature dependence of the conductivity can be described by the Gaussian disorder model, and we have observed that the energetic disorder in this region does not depend upon the content of PCBM in the blends.This work has been supported by Spanish Ministry of Economy under the project MAT2014-59187-R, MAT2012-33517, and CTQ 2013-43086-P. J.C. acknowledges the China Scholarship Council for funding her research. E.R. thanks MINECO for the tenure of a Ramón y Cajal contract (No. RYC-2011-08069).Peer Reviewe