由於染料敏化太陽能電池之電子電洞對是由受光激發之染料所產生，因此增加染料敏化太陽能電池之光電轉換效率最有效的方法即為增加其陽極之導電性及可用的表面積。為了增加染料的吸附面積，本實驗利用垂直配向之奈米碳管具有大表面積、良好導電性、化學穩定性佳、電子傳輸路徑短之優點，結合氧化鋅奈米結構，完成一個具有大表面積之陽極結構。本實驗之垂直配向奈米碳管使用熱化學氣相沉積法成長於不鏽鋼基板上，隨後同樣利用熱化學氣相沉積法以氧化鋅奈米結構直接披覆於奈米碳管表面。垂直成長之奈米碳管不僅能增加氧化鋅奈米結構與不鏽鋼基板間的導電性，同時也能增加染料吸附於氧化鋅之表面積。為了得到最佳的染料敏化程度與最適合染料吸附之氧化鋅附著於奈米碳管之直徑，本研究以陽極浸泡染料的時間與氧化鋅的厚度為參數，得到一最佳浸泡染料時間為15小時和氧化鋅附著於奈米碳管之直徑133 nm。其最佳光電特性之短路電流(Jsc)、開路電壓(Voc)、填充因子(FF)與光電轉換效率(η)分別為6.00 mA、0.48 V、0.65與2.73%。

To improve the photoelectric conversion efficiency (η) of dye-sensitized solar cells (DSSCs), the most effective method is to enhance the anode with electrical conductivity and usable surface area because electron-hole pairs are produced from the dye after illumination. Carbon nanotubes (CNTs) have many advantages such as a large surface area, good electric conduction, and good chemical stability. To increase the effective surface area of dye absorption, we combined vertically aligned CNTs with ZnO nanostructures to fabricate an anode with a larger surface area. This study reports the synthesis of the vertically aligned CNTs on stainless steel sheets and the direct coating of ZnO nanostructures on all the vertically aligned CNTs using thermal chemical vapor deposition (CVD). The resultant vertically aligned CNTs not only serve as a template to provide good electric connection between the ZnO nanostructures and the stainless steel sheet but also result in an increased surface area of ZnO for dye absorption. We adjusted the dye immersion time and ZnO thickness to obtain the efficiency of the DSSCs and determined the optimal sensitization of the anode and the most suitable diameter of ZnO-coated vertically aligned CNTs for dye absorption. The optimum immersion time and ZnO-coated vertically aligned CNTs diameter were found to be 15 h and 133 nm, respectively. We presented the optimum photoelectric characteristics as a short circuit current density (Jsc) of 6.00 mA, open circuit voltage (Voc) of 0.48 V, fill factor (FF) of 0.65, and η of 2.73%.

[1] M. Matsumura, S. Matsudaira, and H. Tsubomura, “Dye sensitization and surface structures of semiconductor electrodes,” Ind. Eng. Chem. Prod. Res. Dev., vol. 19, pp. 415-421, Apr. 1980.
[2] N. Vlachopoulos, P. Liska, J. Augustynski, and M. Grätzel, “Very efficient visible light energy harvesting and conversion by spectral sensitization of high surface area polycrystalline titanium dioxide films,” J. Am. Chem. Soc., vol. 110, no. 4, pp. 1216-1220, Feb. 1988.
[3] B. O'Regan and M. Grätzel, “A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films,” Nature, vol. 353, pp. 737-740, Oct. 1991.
[4] C. Y. Jiang, X. W. Sun, G. Q. Lo, and D. L. Kwong, “Improved dye-sensitized solar cells with a ZnO-nanoflower photoanode,” Appl. Phys. Lett., vol. 90, pp. 26350-1-26350-3, June 2007.
[5] D. Kuang, C. Klein, Z. Zhang, S. Ito, J.-E. Moser, S. M. Zakeeruddin, and M. Grätzel, “Stable, high-efficiency ionic-liquid-based mesoscopic dye-sensitized solar cells,” Small, vol. 3, no. 12, pp. 2094-2102, Nov. 2007.
[6] K.-M. Lee, C.-W. Hu, H.-W. Chen, and K.-C. Ho, “Incorporation carbon nanotubes in a low-temperature fabrication process for dye-sensitized TiO2 solar cells,” Sol. Energy Mater. Sol. Cells, vol. 92, pp. 1628-1633, Aug. 2008.
[7] M. K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Müller, P. Liska, N. Vlachopoulos, and M. Grätzel, “Conversion of light to electricity by cis-X2Bis(2,2’-bipyridyl-4,4’-dicarboxylate)ruthenium(II) charge-transfer sensitizers (X=Cl-, Br-, I-, CN-, and SCN-) on nanocrystalline TiO2 electrodes,” J. Am. Chem. Soc., vol. 115, no. 14, pp. 6382-6390, July 1993.
[8] W. Kubo, T. Kitamura, K. Hanabusa, Y. Wada, and S. Yanagida, “Quasi-solid-state dye-sensitized solar cells using room temperature molten salts and a low molecular weight gelator,” Chem. Commun., vol. 374, pp. 374-375, Jan. 2002.
[9] M. Grätzel, “Dye-sensitized solar cells,” J. Photochem. Photobiol. C: Photochem. Rev., vol. 4, pp. 145-153, July 2003.
[10] M. Grätzel, “Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells,” J. Photochem. Photobiol. A: Chem., vol. 164, pp. 3-14, Feb. 2004.
[11] S.-R. Jang, R. Vittal, and K.-J. Kim, “Incorporation of functionalized single-wall carbon nanotubes in dye-sensitized TiO2 solar cells,” Langmulr, vol. 20, pp. 9807-9810, Sep. 2004.
[12] Md. K. Nazeeruddin, C. Klein, P. Liska, and M. Grätzel, “Synthesis of novel ruthenium sensitizers and their application in dye-sensitized solar cells,” Coord. Chem. Rev., vol. 249, pp. 1460-1467, Apr. 2005.
[13] K. Suzuki, M. Yamaguchi, M. Kumagai, N. Tanabe, and S. Yanagida, “Dye-sensitized solar cells with ionic gel electrolytes prepared from imidazolium salts and agarose,” C. R. Chimie, vol. 9, pp. 611-616, May 2006.
[14] D. Wei, H. E. Unalan, D. Han, Q. Zhang, L. Niu, G. Amaratunga, and T. Ryhanen, “A solid-state dye-sensitized solar cell based on a novel ionic liquid gel and ZnO nanoparticles on a flexible polymer substrate,” Nanotechnology, vol. 19, pp. 424006-1-424006-5, Sep. 2008.
[15] N. Robertson, “Optimizing dyes for dye-sensitized solar cells,” Angew. Chem. Int. Ed., vol. 45, pp. 2338-2345, Mar. 2006.
[16] A. Hagfeldt and M. Grätzel, “Light-induced redox reactions in nanocrystalline systems,” Chem. Rev., vol. 95, pp. 49-68, Jan. 1995.
[17] K. Kalyanasundaram and M. Grätzel, “Applications of functionalized transition metal complexes in photonic and optoelectronic devices,” Coord. Chem. Rev., vol. 77, pp. 347-414, July 1998.
[18] M. Grätzel, “Mesoporous oxide junctions and nanostructured solar cells,” Curr. Opin. Colloid Interface Sci., vol. 4, pp. 314-321, Aug. 1999.
[19] X.-T. Zhang, H.-W. Liu, T. Taguchi, Q.-B. Meng, O. Sato, and A. Fujishima, “Slow interfacial charge recombination in solid-state dye-sensitized solar cell using Al2O3-coated nanoporous TiO2 films,” Sol. Energy Mater. Sol. Cells, vol. 81, pp. 197-203, Feb. 2004.
[20] K. Fujihara, A. Kumar, R. Jose, S. Ramakrishna, and S. Uchida, “Spray deposition of electrospun TiO2 nanorods for dye-sensitized solar cell,” Nanotechnology, vol. 18, pp. 365709-1-365709-5, Aug. 2007.
[21] K. Zhu, N. R. Neale, A. Miedaner, and A. J. Frank, “Enhanced charge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO2 nanotubes arrays,” Nano Lett., vol. 7, no. 1, pp. 69-74, Jan. 2007.
[22] M. S. Akhtar, M. A. Khan, M. S. Jeon, and O-B. Yang, “Controlled synthesis of various ZnO nanostructured materials by capping agents-assisted hydrothermal method for dye-sensitized solar cells,” Electrochim. Acta, vol. 53, pp. 7896-7874, May 2008.
[23] N. N. Dinh, M.-C. Bernard, A. H.-L. Goff, T. Stergiopoulos, and P. Falaras, “Photoelectrochemical solar cells based on SnO2 nanocrystalline films,” C. R. Chimie, vol. 9, pp. 676-683, May 2006.
[24] D. B. Menzies, R. Cervini, Y.-B. Cheng, and G. P. Simon, “Nanostructured ZrO2-coated TiO2 electrodes for dye-sensitised solar cells,” J. Sol-Gel Sci. Technol., vol. 32, pp. 363-366, Dec. 2004.
[25] R. Katoh, A. Furube, T. Yoshihara, K. Hara, G. Fujihashi, S. Takano, S. Murata, H. Arakawa, and M. Tachiya, “Efficiencies of electron injection from excited N3 dye into nanocrystalline semiconductor (ZrO2, TiO2, ZnO, Nb2O5, SnO2, In2O3) films,” J. Phys. Chem. B, vol. 108, pp. 4818-4822, Mar. 2004.
[26] X. Chen and S. S. Mao, “Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications,” Chem. Rev., vol. 107, pp. 2891-2959, June 2007.
[27] G. P. Smestad and M. Grätzel, “Demonstrating electron transfer and nanotechnology: A natural dye-sensitized nanocrystalline energy converter,” J. Chem. Educ., vol. 75, pp. 752-756, June 1998.
[28] M. Grätzel, “Photoelectrochemical cells,” Nature, vol. 414, pp. 338-344, Nov. 2001.
[29] M. A. Fox and M. T. Dulay, “Heterogeneous photocatalysis,” Chem. Rev., vol. 93, pp. 341-357, Jan. 1993.
[30] A. L. Linsebigler, G. Lu, and J. T. Yates, “Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results,” Chem. Rev., vol. 95, no. 3, pp. 735-758, May 1995.
[31] 劉茂煌，"奈米光電池"，工業材料雜誌，203期，pp. 91-97，2003。
[32] C.-Y. Yen, Y.-F. Lin, S.-H. Liao, C.-C. Weng, C.-C. Huang, Y.-H. Hsiao, C.-C. M. Ma, M.-C. Chang, H. Shao, M.-C. Tsai, C.-K. Hsieh, C.-H. Tsai, and F.-B. Weng, “Preparation and properties of a carbon nanotubes-based nanocomposite photoanode for dye-sensitized solar cells,” Nanotechnology, vol. 19, pp. 375305-1-375305-9, Aug. 2008.
[33] T. Y. Lee, P. S. Alegaonkar, and J.-B. Yoo, “Fabrication of dye sensitized solar cell using TiO2 coated carbon nanotubes,” Thin Solid Films, vol. 515, pp. 5131-5135, Apr. 2007.
[34] S. L. Kim, S.-R. Jang, R. Vittal, J. Lee, and K.-J. Kim, “Rutile TiO2-modified multi-wall carbon nanotubes in TiO2 film electrodes for dye-sensitized solar cells,” J. Appl. Electrochem., vol. 36, pp. 1433-1439, Sep. 2006.
[35] P. Brown, K. Takechi, and P. V. Kamat, “Single-walled carbon nanotube scaffolds for dye-sensitized solar cells,” J. Phys. Chem. C, vol. 112, pp. 4776-4782, Mar. 2008.
[36] C. Liu, K. S. Kim, J. Baek, Y. Cho, S. Han, S.-W. Kim, N.-K. Min, Y. Choi, J.-U. Kim, and C. J. Lee, “Improved field emission properties of double-walled carbon nanotubes decorated with Ru nanoparticles,” Carbon, vol. 47, pp. 1158-1164, Jan. 2009.
[37] W. Zhu, C. Bower, G. P. Kochanski, and S. Jin, “Electron field emission from nanostructured diamond and carbon nanotubes,” Solid-State Electron., vol. 45, pp. 921-928, July 2001.
[38] Y. Tu, Z. P. Huang, D. Z. Wang, J. G. Wen, and Z. F. Ren, “Growth of aligned carbon nanotubes with controlled site density,” Appl. Phys. Lett., vol. 80, no. 21, pp. 4018-4020, May 2002.
[39] K. L. Chopra, S. Major, and D. K. Pandya, “Transparent conductors-a status review,” Thin Solid Films, vol. 102, pp. 1-46, Apr. 1983.
[40] S.-S. Lin, J.-L. Huang, and D.-F. Lii, “Effect of substrate temperature on the properties of Ti-doped ZnO films by simultaneous rf and dc magnetron sputtering,” Mater. Chem. Phys., vol. 90, pp. 22-30, Mar. 2005.
[41] D. Song, A. G. Aberle, and J. Xia, “Optimisation of ZnO: Al films by change of sputter gas pressure for solar cell application,” Appl. Surf. Sci., vol. 195, pp. 291-296, June 2002.
[42] R. S. Mane, W. J. Lee, H. M. Pathan, and S.-H. Han, “Nanocrystalline TiO2/ZnO thin films: fabrication and application to dye-sensitized solar cells,” J. Phys. Chem. B, vol. 109, pp. 24254-24259, Oct. 2005.
[43] P. Wagner and R. Helbig, “Halleffekt und anisotropie der beweglichkeit der elektronen in ZnO,” J. Phys. Chem. Solids., vol. 35, pp. 327-335, Mar. 1974.
[44] S. Iijima, “Helical microtubules of graphitic carbon,” Nature, vol. 354, pp. 56-58, Nov. 1991.
[45] H.-M. Cheng, Q.-H. Yang, and C. Liu, “Hydrogen storage in carbon nanotubes,” Carbon, vol. 39, pp. 1447-1454, June 2001.
[46] G. S. Choi, K. H. Son, and D. J. Kim, “Fabrication of high performance carbon nanotube field emitters,” Microelectron. Eng., vol. 66, pp. 206-212, Apr. 2003.
[47] B. J. Landi, R. P. Raffaelle, S. L. Castro, and S. G. Bailey, “Single-wall carbon nanotube-polymer solar cells,” Prog. Photovolt: Res. Appl., vol. 13, pp. 165-172, Feb. 2005.
[48] 成會明，奈米碳管，奈米研究與應用系列，第12冊，台北，五南圖書出版公司，2004年2月。
[49] J. K. Jian, C. Wang, Z. H. Zhang, X. L. Chen, L. H. Xu, and T. M. Wang, “Necktie-like ZnO nanobelts grown by a self-catalytic VLS process,” Mater. Lett., vol. 60, pp. 3809-3812, May 2006.
[50] L. Jiang and L. Gao, “Fabrication and characterization of ZnO-coated multi-walled carbon nanotubes with enhanced photocatalytic activity,” Mater. Chem. Phys., vol. 91, pp. 313-316, June 2005.
[51] V. A. Fonoberov, K. A. Alim, and A. A. Balandin, “Photoluminescence investigation of the carrier recombination processes in ZnO quantum dots and nanocrystals,” Phys. Rev. B, vol. 73, pp. 165317-1-165317-9, Apr. 2006.
[52] K. Vanheusden, W. L. Warren, C. H. Seager, D. R. Tallant, and J. A. Voigt, “Mechanisms behind green photoluminescence in ZnO phosphor powders,” J. Appl. Phys., vol. 79, no. 10, pp. 7983-7990, May 1996.
[53] H. Horiuchi, R. Katoh, K. Hara, M. Yanagida, S. Murata, H. Arakawa, and M. Tachiya, “Electron injection efficiency from excited N3 into nanocrystalline ZnO films: effect of (N3-Zn2+) aggregate formation,” J. Phys. Chem. B, vol. 107, pp. 2570-2574, Jan. 2003.
[54] C.-H. Ku and J.-J. Wu, “Chemical bath deposition of ZnO nanowire-nanoparticle composite electrodes for use in dye-sensitized solar cells,” Nanotechnology, vol. 18, pp. 505706-1-505706-9, Nov. 2007.