Bamboo-like nitrogen-doped carbon nanotubes formed by direct pyrolysis of Prussian blue analogue as a counter electrode material for dye-sensitized solar cells

Abstract

Nitrogen-doped carbon materials were prepared by direct pyrolysis of nanostructured Prussian blue analogue (metal hexacyanoferrates) without additional carbon sources and metal catalysts. The pyrolysis temperature played a crucial role in determining the structure of resultant carbon materials. Bamboo-like nitrogen-doped carbon nanotubes (NCNTs) could be formed at a pyrolysis temperature of 700°C, while only the nitrogen-doped carbon spheres (NCNSs) were obtained at 500°C. After removal of metal catalysts, the bamboo-like NCNTs exhibited superior electrocatalytic behavior towards I−/I3− than the hollow NCNSs, primarily due to their higher surface area and electrical conductivity in comparison with NCNSs. The photoelectron conversion efficiency of dye-sensitized solar cell (DSC) using NCNT counter electrode reached 7.48%, which was even better than that using Pt counter (7.12%) and much higher than that using NCNS counter (5.53%). The improved photovoltaic performance of DSC employing metal-free NCNT counter electrode was primarily attributed to the significantly reduced diffusion and charge-transfer resistances in porous NCNT catalyst layer in comparison with the compact NCNS electrode.