Theoretical and Experimental Raman Investigation of Mechanical Strain and Electric Field Effects on Conductive Polymers

Abstract

Mechanical strain and electric field affect the performance of conductive polymer devices, for which the underlying mechanism should be investigated at the molecular level. This study combines theoretical and experimental Raman approaches to explore the changes in the molecular structure of poly(3-hexylthiophene) (P3HT) and poly(3,4-ethylenedioxythiophene) (PEDOT) under the influence of mechanical strain and external electric fields. Theoretical calculations reveal the pronounced shifts in the main Raman peak if the conjugating length is changed by the mechanical strain, while in experiments, the peak position is unaffected under tensile and bending strain. Under an external electric field, the theoretical results predict a continuous red shift of the main Raman peak accompanied by the change in bond lengths, while in experiments, the same peak exhibits a red shift at an initial increase of the electric field strength and then becomes almost unchanged at a stronger electric field. The discrepancies between calculation and experimental results are attributed to the complex nature of the conjugated chains and noncrystalline domain present in the organic semiconductors, which limits the effectiveness of strain and electric field on the conjugated chains. The results of this study help to bridge the gap between the theoretical study and the actual response of conductive polymers for flexible and electronic device applications.