The optical properties of nanoporous structured

Materials Chemistry and Physics 122 (2010) 284–289

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The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC Yeji Lee, Misook Kang ∗ Department of Chemistry, College of Science, Yeungnam University, 214-1 Dae-dong, Gyeongsan, Gyeongbuk 712-749, South Korea

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Article history: Received 5 June 2009 Received in revised form 22 January 2010 Accepted 20 February 2010 Keywords: Nanoporous TiO2 Nano-sized TiO2 Dye-sensitized solar cell (DSSC) N719 dye

a b s t r a c t This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO2 was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO2 prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO2 was approximately 8.71% with the N719 dye under 100 mW cm−2 simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO2 than on the nano-sized TiO2 particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO2 film. © 2010 Elsevier B.V. All rights reserved.

1. Introduction DSSCs (dye-sensitized solar cells) consist of a sensitizing dye, a transparent conducting substrate (F-doped tin oxide), a nanometer sized TiO2 film, iodide electrolyte, and a counter electrode (Pt or carbon). The absorption of light by dye molecules leads to the excitation of electrons on the HOMO orbital to an electronically excited state, the LUMO orbital. The excited dye molecule injects an electron into the conducting band of the TiO2 film. The oxidized dye is restored by electron donation from reducing ions in the electrolyte, usually an organic solvent containing redox system. The donated electron is in turn regenerated by the reduction of conjugated ions in the electrolyte. The circuit is completed by electron migration through an external load [1–3]. One drawback with DSSCs is the high band gap of the core materials, e.g. TiO2 particles