Journal of Power Sources 196 (2011) 2410–2415 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Novel agarose polymer electrolyte for quasi-solid state dye-sensitized solar cell Ying Yang a,∗ , Hao Hu b , Cong-Hua Zhou c , Sheng Xu b , Bobby Sebo b , Xing-Zhong Zhao b,∗∗ a School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China b Department of Physics and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan University, Wuhan 430072, China c School of Physical Science and Technology, Central South University, Changsha 410083, China article info Article history: Received 8 July 2010 Received in revised form 20 August 2010 Accepted 22 October 2010 Available online 29 October 2010 Keywords: Dye-sensitized solar cell Polysaccharide Inorganic filler Electrochemical impedance analysis Electron lifetime abstract Quasi-solid state dye-sensitized solar cells (DSSCs) are fabricated with a novel polysaccharide gel elec- trolyte composed of agarose in 1-methyl-2-pyrrolidinone (NMP) as polymer matrix, lithium iodide (LiI)/iodine (I 2 ) as redox couple and titania nanoparticles as fillers. The polysaccharide electrolyte with different agarose concentrations (1–5 wt%) and various inorganic filler TiO 2 concentrations (0–10 wt%) are studied systematically by differential scanning calorimetry (DSC) and the AC impedance spectra. The electrochemical and photoelectric performances of DSSCs with these electrolytes are also investigated. It is found that increasing agarose and inorganic filler concentration leads to a decrease in T g in the range of 1–2 wt% for agarose and 0–2.5 wt% for TiO 2 changed electrolytes, which results in high conductivity in these electrolytes. From the electrochemical analysis, it is observed that the electron lifetime in TiO 2 of DSSCs increases with agarose, while decreases with inorganic filler contents. The prolonged electron lifetime in DSSCs is advantageous to improve open-circuit voltage (V oc ). Based on these results, the cell with the electrolyte of 2 wt% agarose shows the optimized energy conversion efficiency of 4.14%. The optimized efficiency of the DSSC with added titania is 4.74% at 2.5 wt% titania concentration. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Dye-sensitized solar cells (DSSCs) have been attracting intensive interest for scientific research and industrial applications because of their high photon-to-electricity conversion efficiency and low cost [1,2]. However, it is a challenge to use them outdoors due to their hard hermetic sealing requirements. Much effort has been directed to developing nonvolatile electrolytes meeting the sta- bility requirements for outdoor applications [3–5]. One strategy attracting particular interest is to replace the liquid electrolyte with polymer gel [6] or solid electrolyte [7,8]. Due to the absence of solvent in the solid electrolyte, there are several serious problems existing, such as crystallization of the iodide salt, low ionic conductivity and poor ability to penetrate into the nanocrystalline TiO 2 films, all of which consequently dete- riorate the cell performance and stability [9]. However, quasi-solid state polymer gel electrolyte has as high ionic conductivity as liquid electrolyte and also suppresses the solvent leakage, thus showing good stability. Recent researches on polymer gel electrolyte proved that the incorporation of inorganic nanoparticle filler in polymer electrolyte ∗ Corresponding author. Tel.: +86 731 88877863; fax: +86 731 88836207. ∗∗ Corresponding author. Tel.: +86 27 87642784; fax: +86 27 68752569. E-mail addresses: muyicaoyang@hotmail.com (Y. Yang), xzzhao@whu.edu.cn (X.-Z. Zhao). yields higher ionic conductivity [10]. The filler provides a solid like support matrix, allowing the amorphous polymer to main- tain its liquid-like characteristics in terms of fast ionic mobility at the microscopic level. This could help in enhancing the cell perfor- mance, and further could increase the stability and lifetime of these devices [11]. Polysaccharide, such as agarose and -carrageenan is con- sidered to be good and environment-friendly polymer matrix for forming cross-linking networks with other components in the polymer electrolyte because of their rich hydroxyl groups in molecule structure. Meanwhile, polysaccharide shows much lower crystallinity at room temperature compared to traditional PEO matrix. These may lead to high ionic conductivity, and excel- lent thermal and chemical stability of polysaccharide electrolyte [12–14], making it suitable for use as heterogeneous medium in photoenergy conversion [15–17]. Although excellent achieve- ments have been reached in studying polysaccharide electrolyte, until now there are seldom studies which make systematic report- ing on the ionic or electronic transport process in DSSCs with polysaccharide electrolyte. On the other hand, few attempts have been made to investigate quasi-solid-state electrolytes prepared from agarose directly dissolved in organic solvents. This is because solubility of polysaccharides in an organic solvent is generally much lower than that in water as we generally know. Herein, the electrochemical and photovoltaic performances of agarose elec- trolyte based DSSCs with different agarose and inorganic filler TiO 2 concentrations are systematically studied. Also, a simple method 0378-7753/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2010.10.067