Polypyrrole-coated multi-walled carbon nanotubes for the simple preparation of counter electrodes in dye-sensitized solar cells

Abstract

Polypyrrole-coated multi-walled carbon nanotubes (PPy/MWCNT) were synthesized using a three-step chemical oxidative polymerization and were simply deposited by an ex situ method from n-butyl alcohol dispersions onto conducting FTO glasses to be used as a low-cost replacement for Pt counter electrodes (CE) in dye-sensitized solar cells (DSSCs). PPy/MWCNT CEs, compared to PPy CEs, have significantly higher interlayer cohesion and adhesion to the FTO substrate, which increases with the MWCNT ratio. The network structure of PPy/MWCNT CEs, with a larger surface area compared to PPy CEs (characterized by SEM), has a positive effect on the charge transfer resistance (Rct), and the PPy/MWCNT CE sample with a ratio of 70:30 reaches a lower Rct than the standard Pt CE, as measured by electrochemical impedance spectroscopy. PPy/MWCNT CEs have reasonable catalytic activities and good stability in the presence of an iodide/triiodide electrolyte, as measured by cyclic voltammetry. The conversion efficiency of the DSSC with PPy/MWCNT (70:30) CEs reaches a ∼10× higher value (η=4.9%) than the DSSC with pristine PPy CEs (η=0.5%) and a ∼30% lower value than the standard DSSC with Pt CEs (η=7.1%).