Spherical polypyrrole nanoparticles as a highly efficient counter electrode for dye-sensitized solar cells

Discrete spherical polypyrrole (PPy) nanoparticles with a uniform diameter of similar to 85 nm and electrical conductivity of similar to 10 S cm(-1) were fabricated by chemical oxidative polymerization within micelles composed of myristyl trimethyl ammonium bromide (MTAB) and decyl alcohol as the nanoreactors. A methanol-based colloidal dispersion containing 5 wt% PPy was dropcast directly onto fluorine-doped tin oxide (FTO) glass to use as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The surface resistivity of the PPy layer on the FTO glass decreased from 624 to 387 U sq(-1) after post-doping with concentrated HCl vapor for 1 min. The DSSCs made of PPy/FTO and HCl-doped PPy/FTO CEs exhibited power conversion efficiencies of similar to 5.28 and similar to 6.83%, respectively under standard AM 1.5 sunlight illumination. The post-doped and highly oxidized PPy allowed the electrons to move into the PPy layer readily and facilitated the electrocatalytic reaction of the I-3(-)/I- redox couple, giving enhanced cell performance. Moreover, the cell efficiency was enhanced to similar to 7.73% with further fine tuning of the electrolyte composition, which is comparable to the value (similar to 8.2%) using conventional Pt CEs.