Synthesis of two-dimensional ZnO nanosheet-structures for the application in dye-sensitized solar cells
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Synthesis of two-dimensional ZnO nanosheet-structures for the application in dye-sensitized solar cells Yongming Meng • Yu Lin • Yibing Lin
Received: 27 August 2013 / Accepted: 3 October 2013 / Published online: 12 October 2013 Ó Springer Science+Business Media New York 2013
Abstract A large amount of nano-ZnO with a thin sheetlike morphology has been manufactured by a simple citric acid assisted hydrothermal route. The influences on the morphologies and structures of ZnO products for the introduction of citric acid in the reaction system have been investigated. A dye-sensitized solar cell assembled by the ZnO nanosheets as photoanode shows an efficiency of 1.82 % with a short-circuit current density of 7.48 mA cm-2 which is over 1.5 times higher than the one without adding citric acid during the synthetic process. This result is mainly connected to the unique superiority of the two-dimensional sheet-like ZnO nanostructures for light scattering and dye loading.
1 Introduction Energy crisis has been an eager issue to be solved in the world. Consequently the development and utilization of new energy is a valid way to remedy the shortage of energy. Solar energy, a type of clean and abundant natural power source, is regarded as the most promising energetic resource for the solution of energy problems currently. Dye-sensitized solar cell (DSSC), a novel photoelectric conversion device firstly reported by Gra¨tzel in 1991 [1], has attracted more and more concentrations due to its facile assembly and low-cost production. It is well-known that the dye-sensitized photoanodes constituted by semiconductor materials play a key role to realize the lightto-electric conversion procedure of DSSCs [2–4].
In contrast with traditional TiO2 electrode layers commonly used in DSSCs, ZnO is a peculiar kind of semiconductive metal oxide with a 3.37 eV wide band gap similar to TiO2 and a much higher electronic mobility rate than that of TiO2 [5–7], which furnishes a significant possibility for its application in DSSC. DSSCs based on one-dimensional (1D) ZnO nanostructures such as nanorods [8, 9], nanotubes [10] and nanowires [11, 12] have aroused extensive interests for scientists in recent years. Although the 1D-ZnO nanomaterials provide a structural advantage for the straight electronic transportation to reduce the chance of charge recombination [13–15], the efficiencies of 1D-ZnO-DSSCs still stay at relatively low levels just because of their insufficient surface area for dye loading and poor ability for solar light trapping [16, 17]. Compared with 1D nanomaterials, two-dimensional (2D) nanostructures like nanosheets or nanoplates with large exposed surface area and some specific crystal facets [18, 19] could offer more space for dye adsorption and electron transmission undoubtedly, which is a possible approach to elevate the photovoltaic properties of ZnO-based DSSCs. In this article, a simple citric acid (C6H8O7) assisted hydrothermal method is used to fabricate large scales of 2D ZnO nanosheet-structures with high surface area and
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