Journal of Photochemistry and Photobiology A: Chemistry 173 (2005) 1–6 Electrophoretically deposited TiO 2 photo-electrodes for use in flexible dye-sensitized solar cells Jun-Ho Yum a , Seok-Soon Kim a , Dong-Yu Kim a , Yung-Eun Sung b,∗ a Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea b School of Chemical & Biological Engineering and Research Center for Energy Conversion and Storage, Seoul National University, Seoul 151-744, Republic of Korea Received 17 September 2004; received in revised form 25 November 2004; accepted 20 December 2004 Available online 21 January 2005 Abstract The preparation of an electrophoretically deposited film composed of wide band gap nanocrystalline TiO 2 without the use of a surfactant or any post-thermal treatments is described. The resulting film was examined with reference to applications in a flexible dye-sensitized solar cell. The packing densities of the films could be controlled through electrophoretic deposition parameters, such as the applied electric field or the concentration of electrolyte. The fill factor and efficiency of energy conversion of the flexible dye-sensitized solar cell employing electrophoretically deposited TiO 2 film was 50% and 1.03%, respectively. To increase the efficiency of energy conversion of the flexible dye-sensitized solar cell, compression was employed and, as a result, the fill factor and efficiency of energy conversion increased to 56.3% and 1.66%, respectively. Thus, the fabrication of a flexible dye-sensitized cell by electrophoretic deposition without the need for any thermal treatment and surfactant is possible. © 2004 Elsevier B.V. All rights reserved. Keywords: Electrophoretic deposition; Flexible solar cell; Dye-sensitization; Packing density; TiO 2 1. Introduction Nanocrystalline semiconducting films comprised of wide band-gap oxides are known to show extraordinary optical and electronic properties and are applicable for use in photo- voltaics [1–3], photocatalysis [4], electrochromic [5–7], and batteries [8]. Nanocrystalline TiO 2 for use in photoelectro- chemical cells based on dye-sensitized solar cells (DSCs) that were pioneered by O’Regan and Gr¨ atzel, have been the fo- cus of numerous investigations during the last decade [1–3]. One of the current issues associated with DSCs is the fab- rication of flexible DSCs, in which flexible transparent con- ductive substrates are used. The use of such substrates such as poly(ethylene terephthalate) coated with tin-doped indium oxide (ITO-PET) are known to have advantages in that they ∗ Corresponding author. Tel.: +82 2 880 1889; fax: +82 2 888 1604. E-mail address: ysung@snu.ac.kr (Y.-E. Sung). are not fragile, have a versatile shape, and their use is techno- logically advantageous. A porous network of nanocrystalline TiO 2 serves as the basis for many optoelecrical and electri- cal devices. Typically, a porous network of nanocrystalline TiO 2 in photovoltaic cells using glass can be readily prepared by sintering at 450–500 ◦ C, a process that removes additives including organic surfactants [1–3]. However, this thermal treatment cannot be used in the preparation of a porous net- work of TiO 2 in flexible DSCs because of the susceptibil- ity of the flexible substrates to degradation followed loos- ing their transparency and inducing distortion. Alternative routes, such as a thermal treatment at a temperature of around 130 ◦ C [9–11] or compression [12,13] are employed for this purpose. Pichot et al. examined a surfactant-free coating of nanocrystalline TiO 2 with a thermal treatment of 100 ◦ C and obtained a fill factor of 69% and an energy conversion effi- ciency of 1.2% [9]. De Paoli and coworkers demonstrated a flexible DSCs employing polymer electrolyte and obtained 1010-6030/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2004.12.023