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ed Single-Crystal Rutile TiO2 Nanowires

ed Single-Crystal Rutile TiO2 Nanowires

Solar Cells DOI:10.1002/anie.201108076Rapid Charge Transport in Dye-Sensitized Solar Cells Made from Vertically Aligned Single-Crystal Rutile TiO 2Nanowires**

Xinjian Feng, Kai Zhu, Arthur J. Frank, Craig A. Grimes, and Thomas E. Mallouk*

Over the past two decades, dye-and quantum dot-sensitized TiO 2are attractive for solar cell and other optoelectronic solar cells and polymer/inorganichybrid solar cells have applications.

emerged as promising alternatives to solid-state p-n junction Figure 1a,b show, respectively, cross-sectional field-emis-cells for addressing the urgent need for inexpensive, efficient sion scanning electron microscope (FE-SEM;JEOL 6300) solar power. [1]At the heart of these solar cells is a mesoporous images taken at low and high magnification, which show TiO 2nanoparticle (NP)electrode, which not only provides

a high surface area for accommodating the light-absorbing

sensitizer but also serves as the stable conductor for photo-

generated electrons. Fast charge transport in the network is

essential for effective charge collection, particularly in solid-

state cells in which recombination is very fast. [2]To increase

the electron mobility, TiO 21D polycrystalline nanotube

arrays [3]and single-crystalline nanowire (NW)arrays [4,5]

have recently been proposed and studied as electrode

materials for solar cells. However, there is little experimental

evidence of substantially enhanced electron transport in these

TiO 21D nanostructure-based solar cells. For example, there is

no substantial difference in electron transport between 1D

TiO 2nanotube and NP-based dye-sensitized solar cells

(DSSCs).[3c]

Herein, we report a ketone–HClsolvothermal process for

the growth of single-crystal rutile TiO 2NW arrays on F-doped

tin oxide (FTO)substrates. The TiO 2NWs begin to grow

within 15min and lengths up to 10m m can be obtained within

2h. Using these NW films, we show for the first time that the Figure 1. a and b) FE-SEM cross-sectional images of NW arrays on electron diffusion coefficient of single-crystal rutile TiO FTO-coated glass substrate at low and high magnifications, respec-

2NWs

is more than two orders of magnitude higher than that of tively. c) HR-TEM image of the as-synthesized single NW.

rutile NP films at the same photoelectron density. In light of

the findings reported here, arrays of 1D single-crystal rutile

arrays of uniform and well-separated NWs. NWs grow

vertically from the substrate to an average length of about

1.6m m and a diameter of 40nm during a reaction time of [*]Dr. X. Feng, [+]Prof. C. A. Grimes, Prof. T. E. Mallouk

Department of Chemistry, Materials Research Institute 30min. From the grazing angle X-ray diffraction (GAXRD)The Pennsylvania State University patterns (FigureS1in the Supporting Information), the University Park, PA 16802(USA)crystal phase of the thin base layer and nanowire arrays E-mail:tem5@psu.eduwere identified as tetragonal rutile (JCPDSfile number 21-Dr. K. Zhu, [+]Dr. A. J. Frank 1276). High-resolution transmission electron microscope National Renewable Energy Laboratory (HR-TEM)images (Figure1c) confirm that the NWs are 1617Cole Boulevard, Golden, CO 80401(USA)single crystalline and have a (110)interplanar distance of

[+]These authors contributed equally to this work. 0.327nm. The NWs grow with a preferred [001]orientation.

[**]Work at Penn State was supported by the U.S. Department of The length of NWs increases almost linearly with the reaction

Energy, Office of Science, Office of Basic Energy Sciences under time. For example, growth of 15min results in around 260nm grant number DE-SC0001087. Work at NREL was supported by the

U.S. Department of Energy, under grant number DEAC36-long NWs and a two hour reaction gives around 9.6m m long

08GO28308. The Penn State Nanofabrication facility is supported NWs (seeFigure S2in the Supporting Information). The NW by the National Science Foundation under grant number ECS-length can also be adjusted by using different amounts of 0335765. We would like to thank Dr. Bangzhi Liu at the Penn State precursor. For example, for a reaction temperature of 2008C Nanofabrication facility for his help with FE-SEM, TEM, and HR-and a duration of 45min NWs with lengths of around 1.1and TEM

ed Single-Crystal Rutile TiO2 Nanowires

analyses. around 4.4m m can be obtained by using 0.4and 0.8mL of Supporting information for this article is available on the WWW tetrabutyl titanate, respectively (seeFigure S3in the Support-under http://www.sodocs.net/doc/d09726c4650e52ea541898b7.html /10.1002/anie.201108076.

ed Single-Crystal Rutile TiO2 Nanowires

ing

ed Single-Crystal Rutile TiO2 Nanowires

Information).

Angew. Chem. Int. Ed. 2012, 51, 2727–2730 2012Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 2727

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