A novel TCO- and Pt-free counter electrode for high efficiency dye-sensitized solar cells

A novel polymer based TCO- and Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs) was fabricated by employing conductivity enhanced PEDOT:PSS film as conductive substrate and electrodeposited PEDOT layer as the catalytic layer. Through an ethylene glycol (EG) treatment, the conductivity of the spray-coated PEDOT:PSS film on glass substrate was significantly enhanced with a low sheet resistance of 17.2 Omega square(-1), very close to that of fluorine doped tin oxide (FTO) glass. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements showed that the phase separation between PEDOT and PSS, and the depletion of PSS during the EG-treatment process contributed to enhanced conducting pathways for carriers. After electrodeposition of an extra PEDOT catalytic layer, the polymer based CE showed a very low sheet resistance of 15.5 Omega square(-1) and good catalytic activity towards the I-/I-3(-) redox reaction compared to the pyrolyzed Pt CE. A DSSC based on this TCO- and Pt-free (PEDOT/PEDOT:PSS/Glass) CE showed a high energy conversion efficiency of 8.33% accompanied by a fill factor of 0.64 under 1 sun illumination (100 mW cm(-2) AM 1.5), which was comparable to that of the Pt/FTO CE based cell (8.75%).