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1113-F09-20

TiO2 Nanotube Arrays by using ZnO Nanorod Template through Liquid Phase Deposition for Organic- Inorganic Hybrid Photovoltaic Cells Thitima Rattanavoravipa, Takashi Sagawa, and Susumu Yoshikawa Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan.

ABSTRACT TiO2 nanotube arrays had been selected as electron transport material incorporate with P3HT:PCBM blended polymer to fabricate the hybrid organic-inorganic solar cells. Well aligned TiO2 nanotube arrays has been synthesized though the liquid phase deposition by using ZnO nanorod arrays as templates. Three types of dyes (viz. NKX-2677, D149, N719) were adsorbed onto the surface of TiO2 nanotube arrays to increase the interfacial contacts between the organic polymer and inorganic metal oxide. Surface modification with NKX-2677 exhibited remarkable improvement of the cell efficiencies in terms of current density, open circuit voltage, and fill factor as compared with those of other dyes. INTRODUCTION Recently, polymer based solar cells have attracted a great interest in terms of lightweight, printable and flexible photovoltaic devices [1-2]. In order to improve the cell efficiencies, the combination of organic semiconductor and inorganic semiconductor as hybrid organic-inorganic solar cells recently have been reported [3-4]. On the other hand, 1D nanostructured metal oxides are promising electrodes for photovoltaic devices due to their high conductivity as a direct path for charge transport [5-6]. Among these various nanostructured metal oxides, TiO2 is an attractive oxide because of appropriate band gap and processability in addition to the conductivity [7-8]. We report herein a simple and controllable fabrication of TiO2 nanotube arrays through liquid phase deposition method by using ZnO nanorod template and its application to the electron transporting layer for hybrid organic-inorganic solar cells. Particularly, modification of the surface of the metal oxide with various kinds of dyes as been investigated in the organic-inorganic hybrid solar cells in order to improve the light-harvesting properties and electron injection at the interface between the inorganic and organic semiconductors since the net areas of the interfacial contacts between the organic polymer and inorganic metal oxides are generally small [9-10]. EXPERIMENTAL DETAILS ZnO nanorod arrays were hydrothermally prepared on the FTO conducting glass substrate. FTO substrate was seeded by zinc acetate in ethanol and the substrate was annealed in order to form the crystal seeds aligned on the substrate. The seeded substrate was immersed into an aqueous solution of Zn(NO3)2 and NaOH at 110 oC for 20 min. After the the growth of ZnO, sample was washed by deionized water and dried in the air. Secondly, the process for deposition of TiO2 –covered ZnO nanorods array was performed through the liquid phase deposition

technique [11] with slight modification. The template of ZnO nanorod arrays on FTO substrate was immersed into aqueous solution of ammonium hexafluorot