The Optimization of InP/ZnS core/shell Nanocrystals and TiO 2 Nanotubes for Quantum Dot Sensitized Solar Cells
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The Optimization of InP/ZnS core/shell Nanocrystals and TiO 2 Nanotubes for Quantum Dot Sensitized Solar Cells
Seungyong Lee, Rick Eyi, Mahmood Khan, Scott Little, and Omar Manasreh Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701, U.S.A.
ABSTRACT The synthesis of InP/ZnS core/shell nanocrystals and TiO 2 nanotubes and the optimization study to couple them together were explored for quantum dot sensitized solar cells. InP/ZnS nanocrystals have advantages of tunable optical properties and intrinsic nontoxicity. Highly luminescent InP/ZnS nanocrystals were produced by precursor-based colloidal synthesis for a photosensitizer. In order to improve on air stability, ZnS shell was grown on InP core. The emission peak was observed at 550 nm. Transmission electron microscopy (TEM) image shows that the nanocrystals highly crystalline and monodisperse. TiO 2 nanotube is main inorganic material which is capable of harvesting light as well as being a prominent anode electrode in solar cells. The nanotubular form of TiO 2 enhances charge transfer and reduces interfacial charge recombination. Free-standing TiO 2 nanotubes were produced by anodization using ammonium fluoride. The free-standing nanotubes were formed under the condition that chemical dissolution speed which depends on fluoride concentration was faster than the speed of Ti oxidation. Electrophoretic deposition was carried out to couple the InP/ZnS nanocrystals with the TiO 2 nanotubes. Under an optimized applied voltage condition, the current during the electrophoretic deposition decreased continuously with time. The amount of the deposited nanocrystals was estimated by calculation and the deposited nanocrystals on the TiO 2 nanotubes were observed in the TEM.
INTRODUCTION While silicon junction devices have dominated the solar cell industry, dye or quantum dot sensitized solar cells based on mesoscopic inorganic semiconductors have drawn interest due to their potential development [1-3]. Quantum dot sensitized solar cells use quantum dots as sensitizers instead of dye material, benefiting from tuning absorption range by controlling its size [4-6]. Among all II-VI and III-V semiconductor nanocrystals, InP nanocrystal is expected to be the most promising one with a wide coverage range of photon absorption and a non-toxic advantage [7]. In quantum dot sensitized solar cells, mesoporous TiO 2 is usually employed to couple quantum dots since it is photostable, cheap, and non-toxic [8-10]. Porous TiO 2 film which is prepared from nanocrystalline TiO 2 particles is most widely used. In the nanoparticle system, numerous trapping sites as well as long travel distance causes more charge recombination and reduced mobility [11]. In comparison with the nanocrystalline form, TiO 2 nanotubes have advantages of large surface area and high electron mobility with a highly ordered tubular structure [12-13].
In this article, the synthesis of InP/ZnS core/shell nanocrystals and highly ordered TiO 2 nanotubes, and coupling these materials are repo
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