Hierarchical porous carbons as a metal-free electrocatalyst of triiodide reduction for dye-sensitized solar cells

Hierarchical porous carbons (HPCs) are prepared by a one-step hydrothermal route using soluble resols as a carbon source, polystyrene spheres and Pluronic F127 as macroporous and mesoporous templates, respectively. The resulting HPCs comprise continuous macro-meso-micropore networks on the carbon blocks, simultaneously exhibiting large surface areas (501-709 m(2) g(-1)), which are particularly evaluated as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Electrochemical impedance spectra (EIS), Tafel polarization curves, and cyclic voltammograms (CVs) demonstrate that the hierarchical pore system plays a crucial role in promoting the catalytic activities of the HPC CEs. In comparison with other porous carbon CEs, the HPC CEs with various macropores and appropriate micro/mesopores present better catalytic behaviors due to the easier accessibility for electrolyte ions and better utilization of the catalytically active sites, resulting in the higher photovoltaic conversion efficiencies of DSSCs. The optimum photovoltaic conversion efficiency of DSSCs based on HPC CEs is 7.22%, which can even match up to that of the cell with Pt CE (7.25%). (C) 2014 Elsevier B.V. All rights reserved.