Water-Soluble Polyelectrolyte-Grafted Multiwalled Carbon Nanotube Thin Films for Efficient Counter Electrode of Dye-Sensitized Solar Cells

Abstract

Water-soluble, polyelectrolyte-grafted multiwalled carbon nanotubes (MWCNTs), MWCNT-g-PSSNa, were synthesized using a “grafting to” route. MWCNT-g-PSSNa thin films fabricated by an electrostatic spray (e-spray) technique were used as the counter electrode (CE) for dye-sensitized solar cells (DSSCs). The e-sprayed MWCNT-g-PSSNa thin-film-based CEs (MWCNT-CE) were uniform over a large area, and the well-exfoliated MWCNTs formed highly interconnected network structures. The electrochemical catalytic activity of the MWCNT-CE at different thicknesses was investigated. The MWCNT-g-PSSNa thin film showed high efficiency as a CE in DSSCs. The power conversion efficiency (PCE) of the DSSCs using the MWCNT-g-PSSNa thin-film-based CE (DSSC-MWCNT) was >6% at a CE film thickness of ∼0.3 μm. The optimum PCE was >7% at a film thickness of ∼1 μm, which is 20−50 times thinner than conventional carbon-based CE. The charge transfer resistance at the MWCNT-CE/electrolyte interface was 1.52 Ω cm² at a MWCNT-CE thickness of 0.31 μm, which is lower than that of a Pt-CE/electrolyte interface, 1.78 Ω cm². This highlights the potential for the low-cost CE fabrication of DSSCs using a facile deposition technique from an environmentally “friendly” solution at low temperatures.