Effect of Secondary Doping Using Sorbitol on Structure and Transport Properties of PEDOT–PSS Thin Films

Poly(3,4-ethylene dioxythiophene):poly(styrenesulphonate) (PEDOT–PSS) in the recent past has emerged as one of the most fascinating conducting polymers for many device applications. The unique feature of PEDOT–PSS is its transparency in the entire visible spectrum with excellent thermal stability. The PEDOT–PSS as prepared as an aqueous dispersion has very low conductivity, and it hinders the performance of a device. In this work we report the conductivity enhancement of PEDOT–PSS thin films through secondary doping using a polar organic solvent such as sorbitol. The mechanism of conductivity enhancement was studied through various physical and chemical characterizations. The effect of sorbitol concentration on structure and transport properties of PEDOT–PSS thin films was investigated in detail. The structural and morphological modifications in PEDOT–PSS due to the addition of sorbitol was studied through Fourier transform spectroscopy, Ultra Violet–visible spectroscopy, theromogravimetric analysis, scanning electron microscopy and atomic force microscopy. The interactions resulting from conformational changes of PEDOT chains that changes from coiled to linear structure due to the sorbitol treatment significantly improves the conductivity of PEDOT–PSS films. The secondary doping of sorbitol reduces the energy barrier that facilitates the charge carrier hopping leading to enhanced conductivity. We have observed that the conductivity of PEDOT–PSS thin films was increased by two fold due to sorbitol treatment when compared to conductivity of pure PEDOT–PSS. We have carried out detailed analysis of dielectric parameters of sorbitol-treated PEDOT–PSS films and found that sorbitol treatment has a significant effect on various dielectric attributes of PEDOT–PSS films. Hence, secondary doping using sorbitol could be a useful way to effectively tailor the conductivity and dielectric properties of PEDOT–PSS thin films that can be used as flexible electrodes in optoelectronic devices.