Dye sensitized solar cell based on platinum decorated multiwall carbon nanotubes as catalytic layer on the counter electrode Ambily Mathew a , G. Mohan Rao a, *, N. Munichandraiah b a Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012 India b Department of Inorgonic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 India 1. Introduction Dye-sensitized solar cells (DSSC) have been regarded as potential candidates for the next generation solar cells owing to their high energy conversion efficiency, low cost materials and facile fabrication methods [1,2]. DSSC consists of a photoanode made of nanocrystalline semiconductor sensitized with a dye, an electrolyte and a counter electrode. Upon illumination, electrons are generated from the dye and injected into the conduction band of TiO 2 , while holes move towards the counter electrode through iodide/tri-iodide I  /I 3  redox couple electrolyte. After flowing through external load, electrons reach the counter electrode; reduce the tri-iodide ions, and the electrical circuit gets completed. Counter electrode (CE) is one of the most important components in dye sensitized solar cell. The function of the counter electrode is to perform the reduction of I 3  ions generated by the oxidation of iodide ions in the electrolyte by the oxidized dye. Commonly used transparent conducting oxide coated glass substrate cannot be used directly as counter electrode due to the less catalytic activity towards tri-iodide reduction, as well as, due to the high charge transfer over potential. Usually a catalytic layer such as platinum is employed on the counter electrode [3–5]. Though platinum shows excellent catalytic activity and electronic conductivity, the high cost imposes a limitation to the fabrication of cost effective DSSCs. Several other materials such as carbon materials, conducting polymers and composites made of carbon based materials and polymers [6–13] have been introduced. Of all the materials so far investigated, carbon nanotubes have been found to be a good alternative to platinum due to their high electrical conductivity, high aspect ratio and good mechanical strength. Both single walled nanotubes (SWNT) and multiwaled nanotubes (MWNT) have shown promising results as a catalytic layer on the counter electrode [14,15]. In a recent report, Huang et al. have used a composite electrode made of platinum nanoparticles supported on MWCNTs by using poly (oxyethy- lene)-segmented imide polymer as a dispersant and achieved almost 1% higher energy conversion efficiency than that of a DSSC made with platinum CE [16]. In another report Li et al. employed a platinum carbon black composite electrode and achieved an enhanced efficiency [17]. In the present study we have synthe- sized multiwalled carbon nanotubes by pyrolysis method, which is a low cost method compared to other techniques. This will again reduce the cost of DSSC. We have prepared Pt/MWCNT by simple chemical reduction method without using any polymer and investigated its performance as a catalytic layer on the counter electrode of DSSC. The dispersion of platinum on the surface of MWNTs enhances the catalytic activity of platinum due to the maximum utilization of platinum nanoparticles. Here multi- walled carbon nanotubes serve not only as a catalyst support to ensure the full exposure of platinum but also act as a catalyst. Thus the concept of hybrid catalyst is employed for the efficiency enhancement of DSSC. Materials Research Bulletin 46 (2011) 2045–2049 A R T I C L E I N F O Article history: Received 22 February 2011 Received in revised form 24 May 2011 Accepted 1 July 2011 Available online 7 July 2011 Keywords: A. Nanostructures B. Chemical synthesis C. Electron microscopy C. Impedance spectroscopy A B S T R A C T In this study we have employed multiwall carbon nanotubes (MWCNT), decorated with platinum as catalytic layer for the reduction of tri-iodide ions in dye sensitized solar cell (DSSC). MWCNTs have been prepared by a simple one step pyrolysis method using ferrocene as the catalyst and xylene as the carbon source. Platinum decorated MWCNTs have been prepared by chemical reduction method. The as prepared MWCNTs and Pt/MWCNTs have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In combination with a dye adsorbed TiO 2 photoanode and an organic liquid electrolyte, Pt/MWCNT composite showed an enhanced short circuit current density of 16.12 mA/cm 2 leading to a cell efficiency of 6.50% which is comparable to that of Platinum. ß 2011 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 80 22932349; fax: +91 80 23600135. E-mail address: gmrao@isu.iisc.ernet.in (G.M. Rao). Contents lists available at ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2011.07.001