A Flexible plastic-stainless steel dye-sensitized solar cell based on organic T À /T 2 electrolyte Samuk Pimanpang 1,2,3 , Madsakorn Towannang 1 , Anongnad Thiangkaew 1 , Wasan Maiaugree 1 , Pikaned Uppachai 1 , Wirat Jarernboon 4 and Vittaya Amornkitbamrung 1,2,3, * ,† 1 Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand 2 Nanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Khon Kaen 40002, Thailand 3 The Integrated Nanotechnology Center, Khon Kaen University, Khon Kaen 40002, Thailand 4 College of Nanotechnology, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road, Ladkrabang, Bangkok 10520, Thailand SUMMARY Flexible dye-sensitized solar cells (DSSCs) were fabricated using a TiO 2 film coated on stainless steel (TiO 2 /SS) as the working electrode and a Pt film coated on conductive plastic (Pt/plastic) as the counter electrode. Thin Pt film was deposited on conductive plastic specimens for four different deposition times (30, 60, 90 and 120 s) using an electrochemical deposition process. Scanning electron micrographs of the resulting Pt films showed that Pt nanoparticles formed on conductive plastic. The DSSC characteristics were analyzed by illuminating light on the counter electrode. The performance of the cell with 30 s of Pt deposition (30 s-Pt) showed the highest DSSC efficiency, ~2.72%. Cell efficiency decreased with the duration of Pt deposition (or Pt thickness). This is attributed to the reduced transmittance through the thicker Pt films, which is supported by UV-visible spectroscopic measurements. Copyright © 2013 John Wiley & Sons, Ltd. KEY WORDS flexible dye-sensitized solar cell; conductive plastic; stainless steel; electrochemical deposition; Pt nanoparticle Correspondence *Vittaya Amornkitbamrung, Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand. † E-mail: vittaya@kku.ac.th Received 25 November 2012; Revised 30 September 2013; Accepted 3 October 2013 1. INTRODUCTION Dye-sensitized solar cells (DSSCs) have received world attention since O’Regan and Grätzel’s breakthrough study in 1991 [1]. This interest is due to their simple structure, low production costs and promising energy conversion efficiency. A DSSC consists of three main parts. These are the working electrode, electrolyte and counter electrode. Working electrodes are commonly made from TiO 2 nanoparticles. Counter electrodes normally used a thin Pt film, and the electrolyte most often used an iodide/triiodide (I À /I 3 À ) solution. Recently, Wang et al. used an organic disulfide/thiolate (T 2 /T À ) solution as a DSSC electrolyte [2]. They obtained a very promising efficiency of ~6.44% under 1 sun. In another study, Wang et al. obtained a moderately good efficiency of ~3.68% based on using T 2 /T À electrolyte and a Pt counter electrode [3]. The special advan- tages of this organic electrolyte over inorganic I À /I 3 À electrolyte are its low corrosiveness and high transparency. Figure 1(a) compares the optical images of the inorganic (I À /I 3 À ) and organic (T 2 /T À ) electrolytes. It is seen that the organic electrolyte has a lighter color than the inorganic electrolyte. UV-visible spectra in Figure 1(a) show the higher transmittance of the T À /T 2 electrolyte than that of I À /I 3 À electrolyte in the range of 475–657 nm. This high electrolyte transparency allows the possibility of operating DSSC in an inverted orientation, that is, light illuminates the top of the counter electrode surface as presented in Figure 2(a). The low corrosiveness of this organic electrolyte also widens the choices of possible conductive substrates, including conducting metal, flexible foil or flexible stainless steel. Flexible metal is an interested substrate because of its low price, high conductivity, high flexibility and high temperature stability [4]. In this study, we used flexible stainless steel (SS) as the conductive substrate. This is because SS substrate has a low price and high conductivity, which will reduce the DSSC production cost while enhancing the cell flexibility, durability and efficiency. However, there is a challenge in coating TiO 2 film on conductive plastic because of the low melting temperature of plastic. The screen printing method and the doctor blade method are not usable because of the high annealing temperature of ~450–550 °C for removing polymer binder and connecting TiO 2 nanoparticles. By altering the cell architecture to one where light illuminates INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. 2014; 38:429–435 Published online 6 November 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/er.3131 Copyright © 2013 John Wiley & Sons, Ltd. 429