本研究利用串級結構提升染料敏化太陽能電池之電子傳輸效率及光捕獲能力。以不同厚度的二氧化鈦薄膜作為光電極，並利用N719/N719與Mercurochrome/SQ2兩個染料系統進行串級結構的探討。在N719/N719系統中，任何串級電池因光捕獲能力的提升，使其電池的效能呈現比組成的單電池佳。此外，高厚度光電極單電池分成兩個低厚度光電極單電池再以串級結構組合可以讓電池效率從5.81%提升到6.84%。主要是因為串級結構改善電子傳輸的阻力。這部分由電化學交流阻抗分析得到輔助證明。
在Mercurochrome/SQ2系統中，由紫外光-可見光吸收光譜度發現兩種染料在吸光波長範圍上有明顯差異，且將吸收短波長的Mercurochrome置於串級結構的上層而SQ2置於下層可得較佳的光捕獲效率。此系統最佳的串級電池效率為3.68% 與Mercurochrome及SQ2單電池最佳效率2.36% 和2.62% 相比明顯提升約40% ~ 50%。本研究探討的兩個系統皆可藉由串級結構的應用，使效率提升。

In this research, the tandem structure is applied on the dye-sensitized solar cell (DSSC) for improving the light-harvesting ability and electron transport efficiency. The two dye systems, N719/N719 and Mercurochrome/SQ2, were studied in this research. For the N719/N719 system, because of the enhancement in light-harvesting ability, the tandem cell can get the better efficiency than the single cells. In addition, dividing a single cell with high TiO2 thickness into two cells can promote efficiency from 5.81% to 6.84%. This enhancement is attributed to the reducing of electron transport resistance in the tandem cell. The analysis of electrochemical impedance is utilized to confirm the inference.
For Mercurochrome/SQ2 system, the UV-Vis absorbance spectra indicate that the two dyes have different absorption ranges. The best tandem structure is obtained by using Mercurochrome-sensitized cell as the top cell and SQ2-sensitized cell as the bottom cell. In this research, in order to get the optimum tandem structure and efficiency, changing the thickness of TiO2 photo electrodes is the way that be used in this research. Compared the efficiency of tandem cell (3.68%) and Mercurochrome (2.36%)、SQ2 (2.62%) single cells. The efficiency gets the 40% ~ 50% enhancement. In a word, the tandem structure can improve the efficiency of dye-sensitized solar cell.

[1] N. Tanaka, World Energy Outlook 2009, 2009.
[2] M. Grätzel, "Power the Plant," Nature, vol. 403, p. 363, 2000.
[3] M. Grätzel, "Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells," inorg. chem., vol. 44, pp. 6841-6851, 2005.
[4] M. Grätzel, "Conversion of Sunlight to Electric Power by Nanocrystalline Dye-sensitized Solar Cells," Journal of Photochemistry and Photobiology A: Chemistry, vol. 164, pp. 3-14, 2004.
[5] M. Grätzel, "Photoelectrochemical Cells," Nature, vol. 414, pp. 338-344, 2001.
[6] W. Shockley and H. J. Queisser, "Detailed Balance Limit of Efficiency of p-n Junction Solar Cell," J. Appl. Phys., vol. 32, p. 510, 1961.
[7] M. Grätzel, "Recent Advances in Sensitized Mesoscopic Solar Cells," ACCOUNTS of chemical research, vol. 42, p. 11, 2009.
[8] Q. Yu, et al., "High-Efficiency Dye-Sensitized Solar Cells: The Influence of Lithium Ions on Exciton Dissociation, Charge Recombination, and Surface States," ACSNANO, vol. 4, pp. 6032-6038, 2010.
[9] S. Ito, et al., "High-conversion-efficiency Organic Dye-sensitized Solar Cells with A Novel Indoline Dye," Chemical Communications, p. 5194, 2008.
[10] D. Bi, et al., "Device Performance Related to Amphiphilic Modification at Charge Separation Interface in Hybrid Solar Cells with Vertically Aligned ZnO Nanorod Arrays," The Journal of Physical Chemistry C, vol. 115, pp. 3745-3752, 2011.
[11] J.-H. Yum, et al., "Efficient Far Red Sensitization of Nanocrystalline TiO2Films by an Unsymmetrical Squaraine Dye," Journal of the American Chemical Society, vol. 129, pp. 10320-10321, 2007.
[12] G. Wolbauer, et al., "A Channel Flow Cell System Specifically Designed to Test the Efficiency of Redox Shuttles in Dye Sensitized Solar Cells," Solar Energy Materials & Solar Cells, vol. 70, pp. 85-101, 2001.
[13] C. A. Kelly, et al., "Cation-Controlled Interfacial Charge Injection in Sensitized Nanocrystalline TiO2," Langmuir, vol. 15, pp. 7047-7054, 1999.
[14] Y. Liu, et al., "Investigation of Influence of Redox Species on The Interfacial Energetics of A Dye-sensitized Nanoporous TiO2 Solar Cell," Solar Energy Materials and Solar Cells, vol. 55, pp. 267-281, 1998.
[15] S. Pelet, et al., "Cooperative Effect of Adsorbed Cations and Iodide on the Interception of Back Electron Transfer in the Dye Sensitization of Nanocrystalline TiO2," J. Phys. Chem. B, vol. 104, pp. 1791-1795, 2000.
[16] S. Kambe, et al., "Influence of the Electrolytes on Electron Transport in Mesoporous TiO2-Electrolyte Systems," J. Phys. Chem. B, vol. 106, pp. 2967-2972, 2002.
[17] Y. Cao, et al., "Dye-Sensitized Solar Cells with Solvent-Free Ionic Liquid Electrolytes," J. Phys. Chem. C, vol. 112, pp. 13775-13781, 2008.
[18] P. Wang, et al., "A New Ionic Liquid Electrolyte Enhances the Conversion Efficiency of Dye-Sensitized Solar Cells," J. Phys. Chem. B, vol. 107, pp. 13280-13285, 2003.
[19] S. Zhang, et al., "Effect of 4-tert-Butylpyridine on the Quasi-Fermi Level of Dye-Sensitized TiO2Films," Applied Physics Express, vol. 4, p. 042301, 2011.
[20] M. K. Nazeeruddin, et al., "Conversion of Light to Electricity by cis-XzBis(2,2’-bipyridyl-4,4’-dicarboxylate)ruthenium(II) Charge-Transfer Sensitizers (X = C1-, Br-, I-, CN-, and SCN-) on Nanocrystalline Ti02 Electrodes," J. AM. CHEM. SOC., vol. 115, pp. 6382-6390, 1993.
[21] Y.-L. Lee and C.-H. Chang, "Efficient Polysulfide Electrolyte for CdS Quantum Dot-sensitized Solar Cells," Journal of Power Sources, vol. 185, pp. 584-588, 2008.
[22] M.-S. Kang, et al., "Quasi-solid-state Dye-sensitized Solar Cells Employing Ternary Component Polymer-gel Electrolytes," Journal of Power Sources, vol. 180, pp. 896-901, 2008.
[23] X. Liu, et al., "An Efficient Organic-Dye-Sensitized Solar Cell with in situ Polymerized Poly(3,4-ethylenedioxythiophene) as a Hole-Transporting Material," Advanced Materials, vol. 22, pp. E150-E155, 2010.
[24] J. Xia, et al., "Influence of Doped Anions on Poly(3,4-ethylenedioxythiophene) as Hole Conductors for Iodine-Free Solid-State Dye-Sensitized Solar Cells," J. AM. CHEM. SOC., vol. 130, pp. 1258-1263, 2008.
[25] U. Bach, et al., "Solid-state Dye-sensitized Mesoporous TiO2 Solar Cells with High Photon-to-electron Conversion Efficiencies," Letter to nature, vol. 395, pp. 583-585, 1998.
[26] H. J. Snaith, et al., "Efficiency Enhancements in Solid-State Hybrid Solar Cells via Reduced Charge Recombination and Increased Light Capture," Nano Letters, vol. 7, pp. 3372-3376, 2007.
[27] K. Tennakone, et al., "A Dye-Sensitized Nano-porous Solid-state Photovoltaic Cell," Semicond. Sci. Technol., vol. 10, pp. 1689-1693, 1995.
[28] G. Kumara, "Dye-sensitized Solid-state Solar Cells Made from Magnesiumoxide-coated Nanocrystalline Titanium Dioxide Films: Enhancement of The Efficiency," Journal of Photochemistry and Photobiology A: Chemistry, vol. 164, pp. 183-185, 2004.
[29] I. K. Ding, et al., "Pore-Filling of Spiro-OMeTAD in Solid-State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device Performance," Advanced Functional Materials, vol. 19, pp. 2431-2436, 2009.
[30] Y.-L. Lee, et al., "A Platinum Counter Electrode with High Electrochemical Activity and High Transparency for Dye-sensitized Solar Cells," Electrochemistry Communications, vol. 12, pp. 1662-1665, 2010.
[31] H. Tsubomura, et al., "Dye Sensitized Zinc Oxide : Aqueous Electrolyte : Platinum Photocell," Nature, vol. 261, pp. 402-403, 1976.
[32] B. O'Regan and M. Grätzel, "A Low-cost, High-efficiency Solar Cell Based on Dye-sensitized Colloial TiO2 Films," Letter to nature, vol. 353, pp. 737-740, 1991.
[33] A. Hangeldt and M. Grätzel, "Molecular Photovoltaics," Acc. Chem. Res., vol. 33, pp. 269-277, 2000.
[34] M. K. Nazeeruddin, et al., "Combined Experimental and DFT-TDDFT Computational Study of Photoelectrochemical Cell Ruthenium Sensitizers," J. AM. CHEM. SOC., vol. 127, pp. 16835-16847, 2005.
[35] C. Y. Chen, et al., "Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells," ACS nano vol. 3, pp. 3103-3109, 2009.
[36] K. Sayama, et al., "Efficient Sensitization of Nanocrystalline TiO2 Films with Cyanine and Merocyanine Organic Dyes " Solar Energy Materials & Solar Cells, vol. 80, p. 47, 2003.
[37] K. Hara, et al., "Highly Efficient Photon-to-electron Conversion with Mercurochrome-sensitized Nanoporous oxide semiconductor Solar Cells," Solar Energy Materials & Solar Cells, vol. 64, p. 115, 2000.
[38] T. Horiuchi, et al., "Highly Efficiency of Dye-sensitized Solar Cell Based on Metal-free Indoline Dyes " J. AM. CHEM. SOC., vol. 126, p. 12218, 2004.
[39] S. Ito, et al., "High-Efficiency Organic-Dye- Sensitized Solar Cells Controlled by Nanocrystalline-TiO2 Electrode Thickness," Advanced Materials, vol. 18, pp. 1202-1205, 2006.
[40] M. Dürr, et al., "Tandem Dye-Sensitized Solar Cell for Improved Power Conversion Efficiencies," Applied Physics Letters, vol. 84, p. 3397, 2004.
[41] M. Murayama and T. Mori, "Novel Tandem Cell Structure of Dye-sensitized Solar Cell for Improvement in Photocurrent," Thin Solid Films, vol. 516, pp. 2716-2722, 2008.
[42] M. Murayama and T. Mori, "Dye-sensitized Solar Cell Using Novel Tandem Cell Structure," Journal of Physics D: Applied Physics, vol. 40, pp. 1664-1668, 2007.
[43] F. Inakazu, et al., "Dye-Sensitized Solar Cells Consisting of Dye-bilayer Structure Stained with Two Dyes for Harvesting Light of Wide Range of Wavelength," Applied Physics Letters, vol. 93, p. 093304, 2008.
[44] K. Uzaki, et al., "Tandem Dye-sensitized Solar Cells Consisting of Floating Electrode in One Cell," Journal of Photochemistry and Photobiology A: Chemistry, vol. 216, pp. 104-109, 2010.
[45] M. Yanagida, et al., "Optimization of Tandem-structured Dye-sensitized Solar Cell," Solar Energy Materials and Solar Cells, vol. 94, pp. 297-302, 2010.
[46] T. Yamaguchi, et al., "Series-connected Tandem Dye-sensitized Solar Cell for Improving Efficiency to More Than 10%," Solar Energy Materials and Solar Cells, vol. 93, pp. 733-736, 2009.
[47] A. Nattestad, et al., "Highly Efficient Photocathodes for Dye-sensitized Tandem Solar Cells," Nature materials, vol. 9, pp. 31-35, 2010.
[48] M. Wang, et al., "The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar Cells," ChemPhysChem, vol. 10, pp. 290-299, 2009.
[49] F. Fabregat-Santiago, et al., "Electron Transport and Recombination in Solid-State Dye Solar Cell with Spiro-OMeTAD as Hole Conductor," J. AM. CHEM. SOC., vol. 131, pp. 558-562, 2009.
[50] J. Bisquert, "Theory of the Impedance of Electron Diffusion and Recombination in a Thin Layer," J. Phys. Chem. B, vol. 106, pp. 325-333, 2002.
[51] M. Adachi, et al., "Determination of Parameters of Electron Transport in Dye-Sensitized Solar Cells Using Electrochemical Impedance Spectroscopy," J. Phys. Chem. B, vol. 110, pp. 13872-13880, 2006.