Investigation of carbon nanotube webs as counter electrodes in a new organic electrolyte based dye sensitized solar cellElectronic supplementary information (ESI) available. See DOI: 10.1039/c1jm15055c

A new organic electrolyte system composed of 1-methyl-3-propylimidazole-2-thione (T) and 2,2-dithiobis(1-methyl-3-propyl-2-imidazolinium) ditriflate (DT) has been formulated and used in dye sensitized solar cells (DSSCs). The electroactivity of different counter electrodes (CEs) has been evaluated by means of measuring J V curves, Tafel plots and impedance spectroscopy. The CEs investigated were thin films of Pt and CoS on FTO, where CoS showed much better electroactivity towards the regeneration of the electrolyte at the cathode. In addition, electroactive layers of multi-walled carbon nanotube webs (MWCNT webs) have been investigated, for the first time, as CEs in a DSSC. CEs made with 20 layers of the webs showed great performance towards the reduction of DT. An efficiency of = 4.12% has been attained in a DSSC with 20 layers of MWCNT webs, whereas by using a CoS based CE a slightly lower efficiency ( = 3.99%) was measured. These results were attributed to the high surface area and electrocatalytic activity of the MWCNT webs. Multi-walled carbon nanotube webs have been investigated, for the first time, as counter electrodes in a dye sensitized solar cell incorporating an organic based electrolyte.