Nanostructured platinum counter electrodes by self-assembled nanospheres for dye-sensitized solar cells Yuan-Hsuan Jhang a , Yu-Tang Tsai a , Chih-Hung Tsai c,⇑ , Sui-Ying Hsu a , Tsung-Wei Huang a , Chun-Yang Lu a , Ming-Che Chen a , Yan-Fang Chen a , Chung-Chih Wu a,b,⇑ a Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC b Innovative Photonics Advanced Research Center (i-PARC), National Taiwan University, Taipei 10617, Taiwan, ROC c Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401, Taiwan, ROC article info Article history: Received 29 March 2012 Received in revised form 23 May 2012 Accepted 24 May 2012 Available online 16 June 2012 Keywords: DSSCs Counter electrode Nanosphere lithography Nanostructure abstract We report a method to fabricate nanostructured Pt counter electrodes for DSSCs using self- assembly nanosphere monolayers. The spin-coating in combination with the water transfer technique was adopted to produce low-defect, large-area and close-packed (hexagonal) self-assembly nanosphere monolayers on glass substrates. By vacuum deposition of SiO 2 through pores of self-assembly nanosphere monolayers, arrays of SiO 2 nanodots were formed on glass substrates. Further blanket deposition of Pt on such nanostructured sub- strates gave nanostructured Pt counter electrodes for DSSCs. DSSCs using such nanostruc- tured Pt electrodes showed enhanced short-circuit currents, spectral responses, and power conversion efficiencies, compared to DSSCs using unstructured Pt counter electrodes. Investigations by electrochemical impedance spectroscopy revealed the reduction of charge-transfer resistances for the Pt/electrolyte interface in using nanostructured Pt coun- ter electrodes, due to increase of the active surface areas and thus the electro-catalytic abil- ity (activity). Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Energy and environment are becoming more and more important issues and concerns of human beings in recent years, and scientists have been devoted to development of renewable energy to mitigate such issues. One of the most promising renewable energies is dye-sensitized solar cells (DSSCs) [1], which has attracted much attention due to their potential cost and fabrication advantages [2–5].A dye-sensitized solar cell device typically consists of a transparent conductive substrate, a porous thin-film pho- toelectrode composed of TiO 2 nanoparticles, dyes, an elec- trolyte, and a counter electrode [6]. The counter electrode as the conductive layer is critical in DSSC operation since it is to catalyze the reduction of the I  3 ions in the electro- lyte produced during the regeneration of the oxidized dyes [7]. Among various materials used for counter electrodes of DSSCs [8–16], Pt is most effective due to its excellent elec- trocatalytic activity for reduction of triiodide. Researchers had thus investigated various deposition of Pt counter electrodes in order to enhance the performance of DSSCs [17–20]. Recently, we have reported a method to produce nano- textures in Pt electrodes for DSSCs by depositing Pt on tex- tured fluorine-doped tin oxide (FTO) substrates [21]. Yet textured FTO substrates are expensive and the growth of textured FTO requires high temperatures (thus not com- patible with plastic substrates). Here we report an 1566-1199/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.orgel.2012.05.048 ⇑ Corresponding authors. Address: Department of Electrical Engineer- ing, Graduate Institute of Photonics and Optoelectronics and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC (C.-C. Wu). Tel.: +886 2 33663636; fax: +886 2 33669404. E-mail addresses: cht@mail.ndhu.edu.tw (C.-H. Tsai), chungwu@cc.ee. ntu.edu.tw (C.-C. Wu). Organic Electronics 13 (2012) 1865–1872 Contents lists available at SciVerse ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel