Pulse electropolymerization of high performance PEDOT/MWCNT counter electrodes for Pt-free dye-sensitized solar cells

Abstract

High performance poly(3,4-ethylenedioxythiophene) (PEDOT) nano-meadows were electropolymerized onto multi-wall carbon nanotube (MWCNT) as counter electrodes (CEs) for Pt-free dye-sensitized solar cells (DSCs) for the first time. This composite film was fabricated using an electrophoresis of MWCNTs onto a fluorinated tin oxide glass substrate and then subjected to PEDOT electropolymerization by using the pulse potentiostatic method. The surface of MWCNTs was wrapped with nano-meadows PEDOT thin film of ∼55 nm in thickness. The extensive cyclic voltammograms (CV) showed PEDOT/MWCNT CE with excellent electrocatalytic activity for I₃⁻ reduction. Moreover, the peak current densities of the PEDOT/MWCNT CE showed no sign of degradation after consecutive 200 CV tests, suggesting the great electrochemical stability of the PEDOT/MWCNT CE. The electrochemical impedance spectroscopy demonstrated that the PEDOT/MWCNT CE had the lowest charge-transfer resistance among all CEs tested in this study. The DSC assembled with the PEDOT/MWCNT composite CE demonstrated an enhanced photovoltaic conversion efficiency of 7.03% compared to that using conventional Pt CE (5.88%) under full sunlight illumination (100 mW cm⁻², AM1.5 G) due to the intrinsic superior electrocatalytic activity of the nano-meadows PEDOT material, highly specific surface area and high electrical conductivity of the MWCNTs. Therefore, the PEDOT/MWCNT CE can be considered as a promising alternative CE for use in Pt-free DSCs.