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

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