On the mechanism of conductivity enhancement in PEDOT/PSS film doped with sorbitol

Abstract

The mechanism of conductivity enhancement in PEDOT/PSS film doped with sorbitol is investigated by X-ray diffraction (XRD), Fourier transform Raman spectroscopy (FT-RM), Atomic force microscopy (AFM), Scanning electron microscopy (SEM). The XRD show that the amorphous state of sorbitol-doped films is not changed and the FT-RM indicate that the main characteristic absorption peak of PEDOT shifts to red. These observations indicate that the increase in conductivity is not attributed to the crystallization behavior of PEDOT, but to the change of the resonant structure of PEDOT chain from a 'benzoid' to a 'quinoid' structure, which increase the rigidity of PEDOT chain. In addition, there is a conformational conversion of the PEDOT chains from the coil structure to expanded-coil or linear structure. These chains changes are helpful to charge transport through the PEDOT chains and conductivity enhancement of composite films. The increased inter-molecule interactions were investigated by the morphological changes of films as observed in AFM and SEM images, which further confirmed the change of the resonant structure of PEDOT chain.