Journal of Photochemistry and Photobiology A: Chemistry 181 (2006) 226–232 Solid-state dye-sensitized solar cell: Improved performance and stability using a plasticized polymer electrolyte Viviane C. Nogueira, Claudia Longo, Ana Fl´ avia Nogueira, Mauro A. Soto-Oviedo, Marco-A. De Paoli ∗ Laborat´ orio de Pol´ ımeros Condutores e Reciclagem, Instituto de Qu´ ımica, UNICAMP. C. Postal 6154, 13084-971 Campinas, SP, Brazil Received 14 September 2005; received in revised form 29 November 2005; accepted 30 November 2005 Available online 6 January 2006 Abstract The addition of the plasticizer poly(ethylene glycol)methyl ether to the polymer electrolyte based on poly(epichlorohydrin-co-ethylene oxide), NaI and I 2 increased the ionic conductivity by one order of magnitude (1.7 × 10 -4 S cm -1 ) without compromising its electrochemical, thermal and dimensional stabilities. The plasticized polymer electrolyte presented an estimated diffusion coefficient of 2 × 10 -6 cm -2 s -1 , ca. five times higher than the diffusion coefficient estimated for the polymer electrolyte without plasticizer. Solid-state dye-sensitized TiO 2 solar cells (1 cm 2 ) were assembled with the plasticized polymer electrolyte and presented an open circuit potential of 0.64 V, short-circuit current of 0.60 mA cm -2 and an energy conversion efficiency of 1.75% under light intensity of 10 mW cm -2 . This efficiency remained unchanged for 30 days, showing that cell efficiency and stability can be improved using a plasticized polymer electrolyte. © 2005 Elsevier B.V. All rights reserved. Keywords: Polymer electrolyte; Ionic conductivity; Plasticizer; Solid-state dye-sensitized TiO 2 solar cell; Stability 1. Introduction Dye-sensitized TiO 2 solar cells (DSSC) have been intensively investigated as potential alternatives to photovoltaic devices due to the low energy consumption for their production, low cost of raw materials and high integrated efficiency of solar energy conversion (∼10%) [1,2]. The working principle of these cells is based on electron injection from a photoexcited sensitizer dye into the conduction band of the nanocrystalline TiO 2 semicon- ductor. The original state of the dye is subsequently restored by electron donation from the electrolyte, usually an organic solvent containing a redox couple, such as iodide/triiodide. Regener- ation of iodide ions is achieved at the counter-electrode by electrons from the external circuit [1,2]. The use of a liquid electrolyte still remains a critical issue in view of the practical applications of DSSC. The liquid electrolyte demands a perfect sealing of the devices in order to avoid leakage and evaporation of the solvent, which might result in low long-term stability and performance [3]. Many efforts have been made to overcome this ∗ Corresponding author. Tel.: +55 19 3788 3075; fax: +55 19 3788 3023/3022. E-mail address: mdepaoli@iqm.unicamp.br (Marco-A.D. Paoli). drawback, replacing the liquid electrolytes by room temperature ionic liquids [4,5], organic and inorganic hole-transport materi- als [6–8], gel [9,10] and polymer electrolytes [2,11,12]. Polymer electrolytes are composed by alkaline salts (e.g. lithium or sodium salts) dissolved in a high molecular weight polymer host such as poly(ethylene oxide) (PEO) or poly(propylene oxide) (PPO) [2]. In general, DSSC assembled with polymer electrolytes exhibit lower efficiency than cells employing liquid electrolytes due to the lower ionic mobility of the I - /I 3 - species in the polymeric medium, which affects the kinetics of all the transfer processes involved in cell oper- ation. However, in spite of the lower performance, the benefits obtained by replacement of liquid electrolytes can be worthwhile in achieving cells with improved stability [13]. Since 1996, our group has been working on DSSC using a polymer electrolyte based on poly(epichlorohydrin-co-ethylene oxide), P(EPI-EO), and the first results were published in 1999 [14]. The best energy conversion efficiency that we have obtained for a solid-state DSSC (active area of 1 cm 2 ) was 2.6% under 10 mW cm -2 [11]. However, our results indicate that we have already reached the limit of the cells efficiency for a system based only on polymer and salt. Other components must be added to the system in order to ensure cells with a 1010-6030/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2005.11.028