Application of microporous polyaniline counter electrode for dye-sensitized solar cells Qinghua Li, Jihuai Wu * , Qunwei Tang, Zhang Lan, Pinjiang Li, Jianming Lin, Leqing Fan Institute of Materials Physical Chemistry, Huaqiao University, Fengze Area, Quanzhou, Fujian 362021, China article info Article history: Received 20 May 2008 Received in revised form 27 June 2008 Accepted 27 June 2008 Available online 5 July 2008 Keywords: Dye-sensitized solar cells Polyaniline Counter electrode Microporousity Cyclic voltammogram abstract An inexpensive microporous polyaniline (PANI) is used as a substitute for platinum to construct the coun- ter electrode in dye-sensitized solar cells (DSSCs). The PANI counter electrode with microporosity and a size diameter of about 100 nm possesses lower charge-transfer resistance and higher electrocatalytic activity for the I  3 =I  redox reaction than Pt electrode does. The overall energy conversion efficiency of the DSSC with PANI counter electrode reaches 7.15%, which is higher than that of the DSSC with Pt coun- ter electrode. The excellent photoelectric properties, simple preparation procedure and inexpensive cost allow PANI electrode to be a credible alternative for DSSCs. Ó 2008 Published by Elsevier B.V. 1. Introduction Since the first report of a dye-sensitized solar cell (DSSC) in 1991 by O’Regan and Gratzel [1], this system has aroused a lot of interests over the last decade due to its high efficiency, low cost and simple preparation procedure [2–4]. In general, the DSSC con- sists of a dye-sensitized porous nanocrystalline TiO 2 film electrode, a redox electrolyte, and a platinized counter electrode to collect electrons and catalyze the redox couple regeneration. Platinized counter electrode is an expensive component in DSSC [5]. Recently, in order to reduce the production cost of DSSCs, attempts on vari- ous carbon materials have been made to replace Pt [6,7]. However, the conversion efficiency of the DSSCs based on the carbon elec- trode was relatively low due to the poor catalytic activity for I  3 reduction and lower carbon conductivity. Conducting polymers are promising candidates for counter electrode materials used in DSSCs, because of their unique proper- ties, such as inexpensiveness, high-conductivity, good stability, and catalytic activity for I  3 reduction [8,9]. However, there are few reports about using conducting polymers as counter electrode materials in DSSCs. The polyaniline (PANI) is one of the most inten- sively studied conducting polymers during the last decade, due to its easy synthesis, high-conductivity, good environmental stability and interesting redox properties [10,11]. Up to now, no publication has reported on using PANI as counter electrode for DSSC. In this paper, PANI nanoparticles are used to construct counter electrodes for DSSCs and it is expected that the photoelectric performances of DSSC with PANI electrode could be improved. 2. Experimental 2.1. Preparation of PANI The PANI was synthesized by an aqueous oxidative polymeriza- tion reaction with perchloride acid as a dopant in the presence of ammonium persulfate [11]. About 50 mL of aniline monomer, puri- fied by a vacuum distillation, was added into 100 mL of perchloride acid solution and 100 mL of 1 M ammonium persulfate was added slowly into. Keep the whole system in the dark at 0 °C for at least 4 h, the solution’s color changed gradually to dark green. The emer- ald sediment was filtered, collected, and rinsed adequately with an enough amount of methanol, perchloride acid and distilled water. Then, it was subjected to ultrasonic irradiation with a power of 100 W for 2 h. After sonication, the emerald material was filtered and dried at 85 °C to remove residue solvent. The resultant emer- ald material was obtained with a yield of 60%. Scheme 1 shows the polymerization reaction equation. 2.2. Assembling of DSSCs 0.5 g of PANI was slowly added into 50 mL of 10 wt.% Triton X-100 solution. And the mixture was subjected to ultrasonic irradi- ation for 15 min to form an even suspension. The PANI was depos- ited on the surface of the pretreated FTO glass (sheet resistance 10 X cm 2 , Hartford Glass Co. USA) [12] by the ‘‘dip-tugging” 1388-2481/$ - see front matter Ó 2008 Published by Elsevier B.V. doi:10.1016/j.elecom.2008.06.029 * Corresponding author. Tel.: +86 595 22693899; fax: +86 595 22693999. E-mail address: jhwu@hqu.edu.cn (J. Wu). Electrochemistry Communications 10 (2008) 1299–1302 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom