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

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 Fro 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 (R-ct), and the PPy/MWCNT CE sample with a ratio of 70:30 reaches a lower R-ct 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 similar to 10 x higher value (eta = 4.9%) than the DSSC with pristine PPy CEs (eta = 0.5%) and a similar to 30% lower value than the standard DSSC with Pt CEs (eta = 7.1%). (C) 2015 Elsevier B.V. All rights reserved.