Pyrolytic carbon from an aromatic precursor and its application as a counter electrode in dye-sensitized solar cells.

Pyrolytic carbon thin films were deposited on quartz plates through a chemical vapor deposition process, by using a biphenyl precursor, 4,4'-bis(chloromethyl-1,1'-biphenyl). The pyrolytic carbons were microporous and catalytic toward reduction of tri-iodide, and the films thus obtained possessed a metallic appearance with good mirror reflections, hydrophilic surfaces, and low sheet resistances. The pyrolytic carbon-coated quartz plates were used, in place of the commonly used Pt-coated fluorine-doped tin oxide glass, as the counter electrode for dye-sensitized solar cells (DSSCs). The light to electricity conversion efficiency of the cell thus obtained was reasonably high, achieving 78% of that obtained by using the conventional but much more expensive Pt counter electrode. From the electrochemical impedance spectroscopic analysis, one found that the minor reduction in the conversion efficiency came from the relatively higher resistance and lower catalytic activity of the pyrolytic carbon. This work demonstrates that the newly developed pyrolytic carbon films may be a promising alternative to Pt as the counter electrode material for DSSCs.