Vertically-aligned carbon nanotube counter electrodes for dye-sensitized solar cells

Vertically-aligned carbon nanotube forests can be used as counter electrodes for triiodide reduction in dye-sensitized solar cells. It is desirable to use a highly conductive substrate for nanotube growth that can serve as a mechanical and electrical support for the nanotube forest in the operating cell. Unfortunately, the high temperatures and harsh atmospheres required for nanotube growth preclude the use of many common substrates. Fluorine doped tin oxide coated glass, stainless steel and aluminum have been investigated as counter electrode substrates using a variety of common chemical vapour deposition techniques for carbon nanotubes. Changes in the chemical, electrical and morphological properties of the substrates have been studied using X-ray photoelectron spectroscopy, resistance measurements and scanning electron microscopy. Under all growth conditions, fluorine doped tin oxide was reduced to tin which subsequently de-wets the surface, forming isolated islands of tin on glass. Aluminum and stainless steel were successfully used as growth substrates, and DSSCs constructed using the resulting nanotube forests had efficiencies comparable to those constructed using Pt counter electrodes. The nanotube DSSCs were found to have a higher series resistance, due to the lower catalytic activity of the nanotube surface compared to Pt.

► Pt-free dye sensitized solar cells.
► Vertically aligned carbon nanotube counter electrodes.
► Direct growth of VACNTs on counter electrode substrate.
► Fluorine-doped tin oxide is not a suitable substrate for VACNT growth.