High surface area nanocrystalline zinc oxide material is fabricated using mesoporous nanostructured carbon as a sacrificial template through combustion process. The resulting material is characterized by XRD, N2 adsorption, HR-SEM, and HR-TEM. The nitrogen adsorption measurement indicates that the materials possess BET specific surface area ca. 30？m2/g. Electron microscopy images prove that the zinc oxide spheres possess particle size in the range of 0.12？μm–0.17？μm. The nanocrystalline zinc oxide spheres show 1.0% of energy conversion efficiency for dye-sensitized solar cells. 1. Introduction Dye-sensitized solar cells (DSCs) have attracted great attention, due its advantages such as low cost, easy fabrication, and high energy conversion efficiency over traditional Si-solar cells [1, 2]. DSCs are composed of porous nanostructured oxide film with adsorbed dye molecules as a dye-sensitized anode, an electrolyte containing iodide/triiodide redox couple, and a platinized fluorine-doped tin oxide (FTO) glass as the counter electrode [3–5]. In DSCs high-internal-surface-area and wide-band-gap semiconductor material with adsorbed dye as a photoanode plays an important role. The choice of semiconductor depends on its conduction band, density state that allows efficient electronic coupling with the dye energy level to facilitate charge separation and minimize recombination. Additionally, the semiconductor material must have high internal surface area to maximize light absorption by the dye monolayer with good electrical conductivity to the substrate. In general, anatase titania nanocrystals are used as recipient of injected electrons from optically excited dye and provide the conductive pathway to the circuit. To complete the cycle the redox species in electrolyte solution transport the hole from oxidized dye to counter electrode [6]. However, titania has low electron mobility and transport properties, which trigger electron recombination rate. Recently, zinc oxide materials have been paid great interest as an alternative for titania in DSCs as its energy band gap is similar to that of titania with higher electron mobility [7, 8]. Moreover, zinc oxide possesses tunable structural properties more than any other semiconductor materials. Recently, several researchers have been using mesoporous silica as a template to prepare different transition metal oxides [9–14]. But removal of silica from the composite is a relatively difficult task which requires either strong acid or strong base conditions. Recent research work of Srinivasu et al. has demonstrated first
References
[1]
M. K. Nazeeruddin, A. Kay, I. Rodicio et al., “Conversion of light to electricity by cis-X2 bis(2, -bipyridyl-4, -dicarboxylate)ruthenium(II) charge-transfer sensitizers (X = Cl？, Br？, I？, CN？, and SCN？) on nanocrystalline TiO2 electrodes,” Journal of the American Chemical Society, vol. 115, no. 14, pp. 6382–6390, 1993.
[2]
Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide, and L. Y. Han, “Dye-sensitized solar cells with conversion efficiency of 11.1%,” Japanese Journal of Applied Physics, vol. 45, no. 24–28, pp. L638–L640, 2006.
[3]
M. Gr？tzel, “Photoelectrochemical cells,” Nature, vol. 414, no. 6861, pp. 338–344, 2001.
[4]
J. Bisquert, D. Cahen, G. Hodes, S. Ruhle, and A. Zaban, “Physical chemical principles of photovoltaic conversion with nanoparticulate, mesoporous dye-sensitized solar cells,” Journal of Physical Chemistry B, vol. 108, no. 24, pp. 8106–8118, 2004.
[5]
A. B. F. Martinson, T. W. Hamann, M. J. Pellin, and J. T. Hupp, “New architectures for dye-sensitized solar cells,” Chemistry, vol. 14, no. 15, pp. 4458–4467, 2008.
[6]
A. Hagfeld and M. Gratzel, “Light-induced redox reactions in nanocrystalline systems,” Chemical Reviews, vol. 95, no. 1, pp. 49–68, 1995.
[7]
M. Law, L. E. Greene, J. C. Johnson, R. Saykally, and P. Yang, “Nanowire dye-sensitized solar cells,” Nature Materials, vol. 4, no. 6, pp. 455–459, 2005.
[8]
E. M. Kaidashev, M. Lorenz, H. Von Wenckstern et al., “High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition,” Applied Physics Letters, vol. 82, no. 22, pp. 3901–3903, 2003.
[9]
B. Tian, X. Liu, H. Yang et al., “General synthesis of ordered crystallized metal oxide nanoarrays replicated by microwave-digested mesoporous silica,” Advanced Materials, vol. 15, no. 16, pp. 1370–1374, 2003.
[10]
H. Yang, Q. Shi, B. Tian et al., “One-step nanocasting synthesis of highly ordered single crystalline indium oxide nanowire arrays from mesostructured frameworks,” Journal of the American Chemical Society, vol. 125, no. 16, pp. 4724–4725, 2003.
[11]
J. -H. Smatt, B. Spliethoff, J. B. Rosenholm, and M. Linden, “Hierachically porous nanocrystalline cobalt oxide monoliths through nanocasting,” Chemical Communications, vol. 10, no. 19, pp. 2188–2189, 2004.
[12]
J. -H. Smatt, C. Weidenthaler, J. B. Rosenholm, and M. Linden, “Hierarchically porous metal oxide monoliths prepared by the nanocasting route,” Chemistry of Materials, vol. 18, no. 6, pp. 1443–1450, 2006.
[13]
Y. Wang, C. -M. Yang, W. Schmidt, B. Spliethoff, E. Bill, and F. Schuth, “Weakly ferromagnetic ordered mesoporous Co3O4 synthesized by nanocasting from vinyl-functionalized cubic Ia3d mesoporous silica,” Advanced Materials, vol. 17, no. 1, pp. 53–56, 2005.
[14]
C. Dickinson, W. Zhou, R. P. Hodgkins, Y. Shi, D. Zhao, and H. He, “Formation mechanism of porous single-crystal Cr2O3 and Co3O4 templated by mesoporous silica,” Chemistry of Materials, vol. 18, no. 13, pp. 3088–3095, 2006.
[15]
P. Srinivasu, S. P. Singh, A. Islam, and L. Han, “Metal-Free Counter Electrode for Efficient Dye-Sensitized Solar Cells through High Surface Area and Large Porous Carbon,” International Journal of Photoenergy, vol. 2011, Article ID 066901.
[16]
Y. Tachibana, K. Hara, K. Sayama, and H. Arakawa, “Quantitative analysis of light-harvesting efficiency and electron-transfer yield in ruthenium-dye-sensitized nanocrystalline TiO2 solar cells,” Chemistry of Materials, vol. 14, no. 6, pp. 2527–2535, 2002.
[17]
I. M. Arabatzis, T. Stergiopoulos, M. C. Bernard, D. Labou, S. G. Neophytides, and P. Falaras, “Silver-modified titanium dioxide thin films for efficient photodegradation of methyl orange,” Applied Catalysis B, vol. 42, no. 2, pp. 187–201, 2003.
[18]
R. E. Mistler, “Tape casting-the basic process for meeting the needs of the electronics industry,” American Ceramic Society Bulletin, vol. 69, no. 6, pp. 1022–1026, 1990.
