Electrochimica Acta 54 (2008) 714–719 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Polymer-sensitized photoelectrochemical solar cells based on water-soluble polyacetylene and -In 2 S 3 nanorods Wonjoo Lee a , Sun-Ki Min a , Gangri Cai a , Rajaram S. Mane a , T. Ganesh a , Gumae Koo a , Jinho Chang a , Su-Jin Baek b , Soo-Hyoung Lee b,∗ , Sung-Hwan Han a,∗ a Department of Chemistry, Hanyang University, Haengdang-dong 17, Sungdong-ku, Seoul 133-791, Republic of Korea b School of Semiconductor and Chemical Engineering, Chonbuk National University, Duckjin-dong 664-14, Jeonju 561-756, Republic of Korea article info Article history: Received 22 April 2008 Received in revised form 25 June 2008 Accepted 30 June 2008 Available online 12 July 2008 Keywords: Polymer photosensitizer Solar cells Chemical bath deposition Interfacial contact In2S3 abstract In this paper, we present a method for preparing polymer-sensitized photoelectrochemical solar cells (PECs) using water-soluble acetylene polymer photosensitizers and -In 2 S 3 nanorods. Since water-soluble acetylene polymers are hydrophilic, they were able to overcome the problems associated with the adhe- sion of hydrophobic polymers and were well matched with the hydrophilic -In 2 S 3 surface. The polymer layers were easily prepared by dipping the -In 2 S 3 nanorods films in an aqueous polymer solution, and the resulting polymer-sensitized PECs showed a power conversion efficiency of 1.63% under air mass 1.5 conditions (I = 80 mW/cm 2 ). © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Recently, dye-sensitized photoelectrochemical solar cells (PECs) have attracted a great deal of interest, as they provide high energy- conversion efficiency at a low cost [1–6]. Generally, Ru-complex sensitizers are used in dye-sensitized PECs, which exhibit a high solar energy-to-electricity conversion efficiency of 10% [1,4–6]. However, when compared to Ru-complex sensitizers, metal-free organic photosensitizers have many advantages, such as low cost, high extinction coefficients, and easy purification. For these rea- sons, extensive research has been conducted on metal-free organic photosensitizers [7–22], with the highest overall power conversion efficiency achieved thus far at an impressive 8% [22]. Due to their versatile optical and semiconductor properties, conjugated polymers are strong candidates for improving the prop- erties of dye-sensitized PECs by their incorporation into the cells as sensitizers [23–30]. With their high extinction coefficient, broad visible absorption spectrum, and tunable band gap, conjugated polymers serve as alternative high-harvesting and charge-transfer materials in PECs, and many of these polymer-sensitized PECs have recently been demonstrated [23–28]. For example, poly(2- ∗ Corresponding authors. Tel.: +82 2 2220 0934; fax: +82 2 2299 0762. E-mail addresses: shlee66@chonbuk.ac.kr (S.-H. Lee), shhan@hanyang.ac.kr (S.-H. Han). thiophene acetic acid) was used to sensitize TiO 2 in devices with power conversion efficiencies up to 1.5% [28–30]. Although the performance of polymer-sensitized PECs has thus far been lower than that of conventional organometallic photosensitizer cells, the prospects are high for rapid improvement. However, it is impor- tant to note that there is a critical problem between inorganic semiconductors and conducting polymers when layering polymers on the semiconductor surface: hydrophilicity [31]. Most inorganic semiconductors have hydrophilic surface characteristics, while conjugated polymers are generally hydrophobic in nature. This mismatch in hydrophilicity raises the problem of heterogeneous interfacial contact between the semiconductor and the polymer, which eventually leads to a decrease in efficiency [31]. Therefore, the ultimate target for high efficiency polymer-sensitized PECs should be the design of hydrophilic polymer photosensitizers for layering on a hydrophilic inorganic surface. In this paper, our approach is to make polymer-sensitized PECs that circumvent the interfacial contact problem. We report polymer-sensitized PECs based on water-soluble conjugated poly- mer photosensitizers and -In 2 S 3 nanorods. The -In 2 S 3 nanorods in thin film form were obtained using a chemical bath deposition method. The polyacetylene photosensitizers are hydrophilic and even water-soluble, as they contain quaternary pyridinium salts with different functional groups, such as an amine or carboxyl group. The hydrophilic nature of the conducting polymer is well matched with the hydrophilic -In 2 S 3 nanorods, and the polymers 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.06.072