Electro-polymerization of polypyrrole/multi-wall carbon nanotube counter electrodes for use in platinum-free dye-sensitized solar cells

In the development of the dye-sensitized solar cell (DSSC), it is critically important, but remains challenging to discover new counter electrode (CE) materials to replace the expensive and precious platinum (Pt). Herein we electro-polymerize the polypyrrole (PPy) on the multi-wall carbon nanotube (MWCNT)-coated F-doped tin oxide substrate by a facile cyclic voltammetry method to obtain the PPy/MWCNT composite CE. The resultant composite CE shows that the MWCNT is wrapped with 15 nm thickness of PPy nanoparticles, which takes advantage of the high surface area and good conductivity of the MWCNT and good catalytic activity of the PPy for the reduction of triiodide to iodide, providing the fast electron transport and diffusion channels and plenty of interfacial catalytic active sites. The DSSC based on the PPy/MWCNT composite CE shows an excellent photoelectric conversion efficiency of 7.15% under full sunlight illumination (100 mW cm (2), AM 1.5 G), which is much higher than that of the MWCNT (1.72%) and PPy (5.72%) based DSSCs, and 92.14% that of the Pt-based DSSC (7.76%). (C) 2016 Elsevier Ltd. All rights reserved.