High electrocatalytic activity of low-loaded transparent carbon nanotube assemblies for CoII/III-mediated dye-sensitized solar cells

Abstract

The development of low-loaded electrocatalysts that can act as alternatives to platinum has been a long standing challenge for use in energy-related devices. Here we report that ultrashort carbon nanotube assemblies with a loading of <5 μg cm⁻² exhibit notably high optoelectrochemical and photovoltaic performances, similar to those of conventional platinum, in dye-sensitized solar cells (DSCs) employing the redox mediator cobalt(II/III)tris(2,2′-bipyridine). The electrochemical activity of the densely packed open-end-rich nanotube assemblies is strongly influenced by the redox-active species used in the organic electrolyte. The extremely high transparency (∼97.5%) of the assembly allowed us to successfully fabricate Co^II/III-mediated bifacial DSCs. The power conversion efficiencies for front- and rear-side irradiation were ∼4.7% and were almost insensitive to which face of the cell was irradiated.