Effect of External Electric Field on Reorganization Energy in Poly(3-Hexylthiophene): An Investigation Based on Density Functional Theory

Abstract

In this work, we study the influence of an external electric field on the structural properties of Poly(3-hexylthiophene) (P3HT). P3HT is an interesting organic semiconductor used as a donor material in many bulk heterojunction-based semiconductor devices. Raman and infrared spectroscopy generally yield valuable information about the structural properties of molecules. For P3HT, we have been interested in the effect of an external electric field on structural properties and their influence on electronic properties. We have performed a vibration-mode analysis, for which we have used density functional theory (DFT) to compute Raman spectra. It appears from our computational study that external electric field strengths well above the range of practically useful values would have to be applied in order to induce a significant effect on the structural properties of P3HT. The results show field-induced changes not only in the bandgap but also in the reorganization energy. Hence, we have calculated the Huang–Rhys factors, which provide insights into the electron–phonon coupling in P3HT and reveal that in presence of an external electric field, the electron–phonon coupling increases, resulting in bound polaron generation.