Rapid fabrication and photovoltaic performance of Pt-free carbon nanotube counter electrodes of dye-sensitized solar cells

We fabricated uniform multiwalled carbon nanotube (MWCNT) thin films on fluorine-doped tin oxide (FTO) glass substrates with controlled thickness by an easy and versatile spin-coating process (SCP). Aqueous dispersions of MWCNTs were dropped on the FTO glass substrates and spin-coated to form uniform MWCNT thin films, which were then used as the catalytic medium on the counter electrodes (CEs) of dye-sensitized solar cells (DSCs). For the DSC with an optimized MWCNT-thin-film thickness coated on the CE, the short circuit current density (Jsc) was more than that of the conventional Pt-based DSC (10.97 ± 0.13 mA cm−2 vs 9.58 ± 0.17 mA cm−2), while its power conversion efficiency (PCE) was comparable to that of conventional DSC (∼4.41 ± 0.14% and ∼4.69 ± 0.22%, respectively). This suggests that the accumulation of MWCNTs on the CE increases the interfacial contact area between the MWCNTs and liquid electrolyte in the DSC, allowing the rapid reduction of I3−. Simultaneously, it decreases the charge transfer resistance owing to rapid electron transport through the MWCNT medium with its relatively high electrical conductivity. Thus, the precisely controlled rapid accumulation of MWCNT thin films by the SCP on the CEs of DSCs is a very promising approach for replacing the expensive Pt metal that is currently used in DSC applications.