Journal of Power Sources 196 (2011) 5792–5796 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Down-converting lanthanide doped TiO 2 photoelectrodes for efficiency enhancement of dye-sensitized solar cells H. Hafez a , M. Saif b,∗ , M.S.A. Abdel-Mottaleb c a Environmental Studies and Research Institute (ESRI), Minoufiya University, Sadat Branch, Sadat City, Egypt b Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt c Nano-Photochemistry and Solarchemistry Lab., Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia, 11566 Cairo, Egypt article info Article history: Received 18 December 2010 Received in revised form 3 February 2011 Accepted 13 February 2011 Available online 21 February 2011 Keywords: Dye-sensitized solar cells Lanthanide ions Down-conversion abstract Lanthanide (Ln 3+ ) doped TiO 2 down-conversion photoelectrodes (Ln 3+ = Eu 3+ and Sm 3+ ions) are used to enhance the photovoltaic efficiency of dye-sensitized solar cells (DSSC). We report on achieving fill fac- tors of 0.67 and 0.69 and efficiencies of 5.81% and 5.16% for Sm 3+ and Eu 3+ , respectively. This is compared to the 4.23% efficiency for the undoped-titania photoelectrodes. This enhancement is probably due to the improved UV radiation harvesting via a down-conversion luminescence process by the lanthanide ions. The structure, optical and photoluminescence properties of the down-converting photoelectrode are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and room temperature photoluminescence excitation and emission spectrofluorimetric measurements. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Recently, clean renewable energy utilization has been proposed as one of the main potential solutions for global warming [1]. Silicon-based solar cell technology is the most dominate technol- ogy in the current market of solar energy. Due to its relatively high cost and complicated fabrication methodology, developing a low-cost and highly efficient alternative technology has received a great deal of attention in the past decade [2]. In 1991, O’Reagan and Grätzel designed the first dye-sensitized solar cell (DSSC) [3]. Because of its low cost and simple fabrication methodology, improving DSSC efficiency has become of significant importance for many research groups worldwide. In DSSCs, TiO 2 films with mesoscopic texture are widely used as the photoanode onto which dye-sensitizers are adsorbed. Under illumination, excited dye-molecules inject electrons into the conduction band of the semiconductor. Injected electrons are then transported to the con- ducting glass substrate [4]. Generally, DSSCs have maximum absorption up to 800 nm of the total incident solar irradiation [5,6]. This represents a major issue for this technology, since 50% of solar irradiation is in the ultraviolet and infrared regions, and thus is not utilized. This limits the solar energy conversion efficiency for DSSCs. Therefore, attempting to extend the spectral response range of a DSSC to the UV region rep- ∗ Corresponding author. Tel.: +20 109542296; fax: +20 22581243. E-mail address: mona saif1@yahoo.com (M. Saif). resents an extremely important approach to increasing the DSSC efficiency. Preliminary encouraging results in our laboratory encouraged us to carry out further investigations to explore the possibility of mod- ifying the spectral response of DSSCs by the use of down-conversion lanthanide-doped TiO 2 photoelectrodes. Lanthanide-derived compounds have been widely used as highly efficient light conversion molecular devices (LCMD), mag- nets and catalysts based on the electronic, optical, and chemical characteristics arising from their 4f electrons [6,7]. Among the many lanthanide ions, europium (Eu 3+ ) and samarium (Sm 3+ ) ions have been recognized as the most efficient down-converting materials that convert the ultraviolet light to red and orange-red emissions, respectively [7,8]. Intermolecular energy transfer pro- cess from the host material, which absorbs the UV energy to the central lanthanide cation results in the observed visible light emis- sion [8]. Moreover, doping of titania electrode with lanthanide ions provide complexation centers on the TiO 2 surface, thus enhancing its dye adsorption ability [9]. In the current work, we have investigated the role of new down-converter Eu 3+ or Sm 3+ -doped TiO 2 photoelectrode on the photovoltaic efficiency enhancement of dye-sensitized solar cells. 2. Experimental 2.1. Materials Chemical agents including tetraisopropyl titanate Ti[OCH(CH 3 ) 2 ] 4 , samarium nitrate Sm(NO 3 ) 3 and europium 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.02.031