Incorporation of plasma-functionalized carbon nanocapsules into a nanocrystalline TiO2 photoanode for use in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated using TiO2 nanoparticles incorporating different amounts of plasma functionalized carbon nanocapsules (CNCs) as the photoanode. The functionalization was obtained by grafting maleic anhydride (MA) onto the walls of CNCs immediately after the in situ argon plasma treatment. Nanocrystalline semiconductor film electrodes were prepared by sintering TiO2 with added MA-CNCs on a conducting glass substrate. Capacitance measurements obtained from electrochemical impedance spectroscopy (EIS) analysis in an aqueous electrolyte are fitted using the Mott-Schottky relationship and demonstrate the variation of flatband potential (V-fb) for the composite with MA-CNC content. The potential chronoamperometric and cyclic voltammetric data supports the argument that the increased V-fb minimizes the defect state for trapping/detrapping of electrons within the MA-CNC/TiO2. As a result of higher film capacitance and electron accumulation, the MA-CNC/TiO2 shows increased conversion efficiency and photocurrent density when used as the photoanode in DSSCs. EIS measurement further demonstrates that charge recombination at the interface of MA-CNC/TiO2 and electrolyte is suppressed with increasing electron lifetime and is in good agreement with the photovoltaic performance. The amount of MA-CNCs added, however needs to be optimized due to the unavoidable issue of aggregation. (C) 2011 Elsevier Ltd. All rights reserved.