Oxido De Zinc

Chu et al. Nanoscale Res Lett 2011, 6:38 http://www.nanoscalereslett.com/content/6/1/38

NANO EXPRESS

Open Access

Flexible Dye-Sensitized Solar Cell Based on Vertical ZnO Nanowire Arrays
Sheng Chu1, Dongdong Li1,2, Pai-Chun Chang1, Jia G Lu1*
Abstract Flexible dye-sensitized solar cells are fabricated using vertically aligned ZnO nanowire arrays that are transferred onto ITO-coatedpoly(ethylene terephthalate) substrates using a simple peel-off process. The solar cells demonstrate an energy conversion efficiency of 0.44% with good bending tolerance. This technique paves a new route for building large-scale cost-effective flexible photovoltaic and optoelectronic devices. Introduction Flexible solar cells have attracted tremendous interest because of its potential for wearableelectronics and other versatile applications [1]. Dye-sensitized solar cell (DSSC) is well known as one competitive alternative to conventional inorganic photovoltaic cells due to its simplicity, low cost, and good power conversion efficiency [2]. Typically, the photoanodes of flexible DSSCs consist of titanium oxide nanocrystals on a plastic substrate that are produced by utilizing low-temperatureprocesses, such as sintering [3], mechanical pressing [4], hydrothermal crystallization [5], electrophoretic deposition [6], microwave irradiation [7], or film transfer [8]. However, low-temperature treatments usually result in poor material crystallinity and fragile characteristic, thus limit the potential of DSSCs as flexible electronics. Recently, significant progress in photovoltaics has beenachieved based on one-dimensional materials owing to the improved crystalline quality, efficient charge separation/transport process, and mechanical flexibility [9-15]. ZnO, an n-type semiconductor, is known for its high electric conduction and carrier mobility [16]. ZnO has demonstrated as a good photoanode in DSSCs since its energy band structure is similar to that of TiO2 [17,18]. Additionally,the syntheses of one-dimensional ZnO materials with controllable structures have been well developed by using either vapor or solution phase growth methods [11,19]. In this work, vertically aligned ZnO nanowire arrays with high aspect ratio are
* Correspondence: jia.grace.lu@usc.edu 1 Department of Physics and Department of Electrical Engineering, University of Southern California, Los Angeles,CA 90089-0484, USA. Full list of author information is available at the end of the article

synthesized by vapor phase growth. A robust peel-off technique is employed to transfer vertically aligned nanowire arrays onto indium tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) flexible substrate. Bendable ZnO nanowire-based DSSCs are then assembled following polymer packaging with nanowiresas electrodes. The fabricated device shows good tolerance under strong mechanical bending.

Experimental Methods Aligned ZnO nanowire arrays are synthesized via seed growth scheme [20]. A ~500 nm ZnO seed layer is first deposited onto an n-type Si (100) substrate (resistivity in the range of 1–10 Ω cm) in a molecular beam epitaxy system. Pure zinc powder is then placed at the center of ahorizontal tube furnace for the ZnO nanowire array growth. Oxygen carried by Ar (1:1000) is kept flowing during the synthesis. The typical growth and characterization of ZnO nanowires can be found in our previous reports [19,21,22]. Polydimethylsiloxane (PDMS) solution, made by mixing the base and curing agent (10:1 w/w) (Sylgard 184), is diluted (5:1 w/w) by a hexamethylcyclotrisiloxane solution inmethylene chloride (Alfa Aesar). The solution is subsequently dropped onto the nanowire film and spun at a rate of 2,000 rpm for 1 min to allow uniform distribution of a thin PDMS layer at the bottom of ZnO nanowire arrays. After a heat treatment at 150°C for 1 h, the PDMS layer is cured at the bottom of the ZnO nanowire array forming a matrix. This PDMS matrix together with the embedded ZnO wires...