Enhanced Electron Collection Efficiency Observed in Dye-Sensitized Solar Cells with Hollow TiO 2 Nanofiber Photoanodes
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Enhanced Electron Collection Efficiency Observed in DyeSensitized Solar Cells with Hollow TiO2 Nanofiber Photoanodes Dye-sensitized solar cells (DSSCs) are fabricated and studied in an attempt to replace current solar cell technologies with cheaper and more efficient devices to better utilize solar energy. DSSCs have been presented as a cost-effective alternative to conventional silicon solar cells, employing mesoporous, anatase TiO2 films. The TiO2 photoanode has been previously fabricated as interconnected, spherical nanoparticle films and more recently using TiO2 nanotube arrays. Now E. Ghadiri and N. Taghavinia of Sharif University of Technology, Iran; and S.M. Zakeeruddin, M. Grätzel, and J.-E. Moser of the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, have employed nanostructured, TiO 2 hollow fibers as photoanodes in DSSCs which demonstrate improved electron transport properties as compared to mesoporous, spherical nanoparticle films. In the May 12 issue of Nano Letters (DOI: 10.102/nl904125q; p. 1632), Ghadiri and coworkers described their facile and novel preparation of TiO2 nanofibers using lowcost cellulose fibers as a template. Aqueous solutions of (NH4)2TiF6 and boric acid at a temperature of 50°C were used to deposit titania on cotton fibers. The samples are heated to 500°C for 3 h in air to remove the cellulose template. TiO2 nanofibers were employed in conjunction with the ruthenium complex Na–RuII (4,4’-bis(5-hexylthiophen-2-yl)2,2’-bipyridine)(4-carboxylic acid-4’carboxylate-2,2’-bipyridine)(NCS)2 (C101) to produce 6 μm films for DSSCs. The volatile redox-active electrolyte used was comprised of 1.0 M 1,3-dimethylimidazolium iodide, 0.05 M LiI, 0.1 M guanidinium thiocyanate, 0.03 M I2, and 0.5 M tertbutylpyridine in a mixture of acetonitrile and valeronitrile (85/15,v/v). In the blue-green region of the spectrum (λ = 400–550 nm), the absorptance (α) of the film was close to α = 0.8 and peaked at α = 0.81 at λmax = 550 nm. At λ = 550 nm, the incident photon-to-current conversion efficiency of the photovoltaic device was 0.77 and the absorbed photon-tocurrent efficiency exceeded 90% in the 550–650 nm range of the spectrum. The highest photovoltaic power conversion efficiency of η = 7.15% was measured with TiO 2 nanofiber films of 9 μm thickness. Carrier trapping was observed to be reduced in the designs employing hollow
SNAPSHOT Perspectives on Future Nanowire Technologies Semiconductor nanowires became one of the most active nanoscience research areas in the late 1990s. Since then, semiconductor nanowire research activity, as measured by the number of publications, has increased exponentially. Discovery and hypothesis-driven research have emerged in several subfields, including nanowire electronics, nanowire photonics, energy conversion and storage, and interfacing nanowires with living cells. Extensive worldwide research activities quickly followed the publication of research papers that introduced the original ideas and concepts in these subfields. Recently, in a short perspectiv
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