Use of High Surface Area TiO 2 Nanosheet in Dye-sensitized Solar Cell

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0951-E06-30

Use of High Surface Area TiO2 Nanosheet in Dye-sensitized Solar Cell Sorapong Pavasupree, Supachai Ngamsinlapasathian, Yoshikazu Suzuki, and Susumu Yoshikawa Institute of Advanced Energy, Kyoto University, Uji, 611-0011, Japan

ABSTRACT High surface area nanosheet TiO2 with mesoporous structure were synthesized by hydrothermal method at 130 oC for 12 h. The samples characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50-100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO2 had average pore diameter about 3-4 nm. The BET surface area and pore volume of the sample were about 642 m2/g and 0.774 cm3/g, respectively. The solar energy conversion efficiency (η) of the cell using nanorods/nanoparticles TiO2 (from the nanosheet calcined at 450 oC for 2 h) with mesoporous structure was about 7.08 % with Jsc of 16.35 mA/cm2, Voc of 0.703 V and ff of 0.627; while η of the cell using P-25 reached 5.82 % with Jsc of 12.74 mA/cm2, Voc of 0.704V and ff of 0.649. INTRODUCTION TiO2 has been widely used for various applications such as a semiconductor in dyesensitized solar cell, water treatment materials, catalysts, gas sensors, and so on [1-11]. In the view point of surface area, nanosheet and nanotubes (from nanosheet rolling technique) TiO2 (or titanate) offered high surface area (about 100-400 m2/g) [1-2]. In our previous works, nanofibers TiO2 were synthesized by hydrothermal and post heat-treatments from natural rutile sand, however, nanofibers TiO2 had rather low surface area (10-20 m2/g) [3-4]. The author’s group preliminary reported that the mesoporous nanorods or nanowires/nanoparticles composite structure (hydrothermal method at 150 oC for 20-72 h) showed better photovoltaic conversion effect in dye-sensitized solar cell [5-6]. In this study, high surface area nanosheet TiO2 with mesoporous structure (with much higher surface area, 642 m2/g) has been synthesized, which shows high performance in dyesensitized solar cell. The detail microstructure and photovoltaic properties will be reported. THEORY (OR EXPERIMENT) 2.1 Synthesis Titanium (IV) butoxide (Aldrich) was mixed with the same mole of acetyacetone (ACA, Nacalai Tesque, Inc., Japan) to slowdown the hydrolysis and the condensation reactions. Subsequently, distilled water 40 ml was added in the solution, and the solution was stirred at room temperature for 5 min. After kept stirring, ammonia aqueous solution 28 % (Wako Co., Ltd., Japan) 30 ml was added in the solution, then the solution was put into a Teflon-lined stainless steel autoclave and heated at 130 oC for 12 h with stirring condition. After the autoclave

was naturally cooled to room temperature, the obtained product was washed with HCl aqueous solution, 2-propanal and distilled water for several times, followed by drying at 100 oC for 12 h. 2.2 Characterization The crystalline structure of the samples was evaluated by X-ray diffraction (XRD, RIGAKU RINT 2100). The microstructure of the prepared m