如何使染料敏化太陽能電池(Dye-sensitized solar cells,DSSC)中的電子傳輸單向化是達到高光電轉換效率的關鍵之一，但是事實上卻會有相反方向的電子再結合損失，主要的損失位置在TiO2/電解質界面和FTO/電解質界面，本研究致力於探討後者，以Nb2O5阻隔層來抑制該界面的再結合反應，利用Nb2O5的導帶位置具有些微高於TiO2的特性，可形成能階障礙抑制電子的再結合反應。
本研究中，阻隔層的製備方式為使用5mM的鈮前驅物(Nb ethoxide)以旋轉塗佈法沉積Nb2O5於FTO導電基材上，經過XRD、XPS和TEM鑑定為Nb2O5，並呈現少部分的TT相結晶態，以光學顯微鏡和SEM初步判別阻隔層較佳的均勻性為使用旋轉塗佈使用轉速3000rpm和塗佈5層，經由紫外/可見光譜儀檢測其不影響光線的穿透度，接著透過紫外/可見光譜儀量測半導體能隙和XPS量測半導體價帶，得到Nb2O5的導帶位置高於TiO2，能形成能階障礙於FTO/電解質界面；經由暗電流檢測，阻隔層具有抑制暗電流的功用；阻隔層的厚度有其最佳值，過厚反而會使得電子擴散係數下降，本研究的最佳厚度約在68~80nm左右。
交流阻抗法中傳輸線模組分析可量測DSSC內部的再結合電阻變化，使用揮發性電解質時，於低施加偏壓時(等同照射弱光)，再結合反應主要發生在FTO/電解質界面，阻隔層使得再結合電阻約增加3倍，於弱光(0.05sun)下，光電轉換效率由11.1%上升至11.8%；使用非揮發性電解質時，阻隔層使得再結合電阻約增加14倍於低施加偏壓下，增加範圍延伸至中高偏壓，隨著施加偏壓上升，增加幅度會下降，於弱光(0.05sun)下，使得光電轉換效率由7.87%上升至8.53%。
結果可知，Nb2O5阻隔層能夠抑制FTO/電解質界面的再結合反應，於弱光下顯示出阻隔層的重要性，而使用非揮發性電解質之光電轉換效率增加的比例為8.4%多於揮發性電解質的6.3%於照度0.05sun，因此於更弱光的室內環境下，配合使用低揮發性的電解質，氧化鈮阻隔層能夠抑制再結合反應使得DSSC的光電換效率提升。

Creating a unidirectional electron transport is one of the key factors of reaching high power energy conversion efficiency in dye-sensitized solar cell. Unfortunately, undesired electron pathway called recombination exists in real devices. The recombination causes photocurrent loss and mainly occurs at TiO2/electrolyte as well as FTO/electrolyte interface. Herein we focus on retarding the recombination at latter interface by using Nb2O5 blocking layer. Owing to slightly higher conduction band position of Nb2O5 comparing to TiO2, which can suppress charge recombination and enhance power conversion efficiency.
In this study, the Nb2O5 blocking layer was prepared by the spin coating 5mM niobium ethoxide ethanol solution on FTO substrate. The film was then characterized by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS) and transmission electron microscopy (TEM), which indicated a small part of TT-phase crystalline was formed. The uniformity of such blocking layer was scrutinized by optical microscope (OM) and scanning electron microscope (SEM). UV/Vis spectroscope was used to determine the transmittance of so-prepared Nb2O5 thin film on FTO. Band structure was positioned by XPS and UV/Vis spectroscope.
In order to evaluate the recombination extent, the electrochemical impedance spectroscopy with transmission line model was employed and the recombination resistance (Rct) can be obtained. At low forward bias, considering the same condition as low-sun irradiation, recombination takes place primarily at FTO/electrolyte interface. In the case of volatile electrolyte based devices, the Rct with the Nb2O5 blocking layer increases 3 times higher than the blank one. As non-volatile electrolyte was applied, more significant effect could be observed for 14 times improvement in Rct value in the device fabricated with this Nb2O5 blocking layer.
As the result, the Nb2O5 blocking layer could suppress the recombination at FTO/electrolyte interface, especially under low-sun condition. An increase in power conversion efficiency from 11.1% to 11.8% and 7.87% to 8.53% were obtained in volatile and non-volatile electrolyte based devices, respectively. This research reveals the importance of blocking effect under low illumination, which is the crucial issue of indoor application for DSSC and this niobium oxide thin film acts as a remarkable blocking layer.

摘要 I
Abstract II
致謝 IV
總目錄 V
表目錄 IX
圖目錄 XI
第一章 緒論 1
1-1 前言 1
1-2 染料敏化太陽能電池的發展 3
1-3 染料敏化太陽電池基本結構與工作原理 4
第二章 文獻回顧 7
2-1 DSSC界面阻隔層的發展 7
2-1-1 噴霧熱解法(Spray Pyrolysis) 10
2-1-2 網印法(Screen-Printed) 18
2-1-3 濺鍍法(Sputter) 21
2-1-4 旋轉塗佈法(Spin Coating) 23
2-2 研究動機與目的 28
第三章 實驗步驟與分析方法 30
3-1 實驗藥品 30
3-1-1 藥品簡介 30
3-1-2 藥品配製 31
3-2 實驗儀器 33
3-2-1 實驗儀器與設備 33
3-2-2 操作與分析儀器簡介 35
3-4 實驗步驟 54
3-4-1 組裝DSSC元件之步驟 54
3-4-2 導電玻璃清洗 56
3-4-3 光陽極製備 56
3-4-4 旋轉塗佈氧化鈮薄層 58
3-4-5 對電極製備 59
3-4-6 組裝電池 60
3-5 半導體能隙(band gap)量測分析 61
3-6 半導體價帶(valance band)量測分析 63
3-7 傳輸線模組(Transmission Lined Model)分析 66
3-7-1 DSSC內部電子傳輸 66
3-7-2 傳輸線模組阻抗數學式推導 67
3-7-2.1 電子擴散通式 67
3-7-2.2 分佈式電子密度表示式與邊界條件 67
3-7-2.3 元件阻抗方程式推導 69
3-7-2.4 傳輸線表示元件阻抗方程式 70
3-7-2.5 傳輸線模組圖的轉換 72
3-7-3 傳輸線模組圖的應用於DSSC元件性能分析 75
第四章 結果與討論 87
4-1 表面型態分析 87
4-2 氧化鈮成分分析 95
4-3 氧化鈮能階位置分析 104
4-3-1 半導體能隙量測 104
4-3-2 半導體價帶量測 105
4-4 沉積Nb2O5薄層於玻璃基材之光學性質探討 107
4-5 DSSC光電性能量測 109
4-5-1 暗電流量測 109
4-5-2 比較TiO2薄膜有無經過TiCl4浸鍍處理之效率差異 112
4-5-3 非揮發性(NVE)與揮發性電解質(VE)之DSSC元件效率差異 113
4-5-4 有無使用Nb2O5阻隔層於DSSC之元件效率差異 114
4-5-4.1 TiO2薄膜未經TiCl4浸鍍處理下，比較有無Nb2O5阻隔層之效率差異 114
4-5-4.2 使用揮發性電解質(VE)，比較有無Nb2O5阻隔層之效率差異 115
4-5-4.3 使用非揮發性電解質(NVE)，比較有無Nb2O5阻隔層之效率差異 119
4-6 交流阻抗法中傳輸線模組分析 122
4-6-1 傳輸線模組實際應用量測 122
4-6-2 比較有無TiCl4浸鍍處理之電子傳輸行為分析 128
4-6-3 比較非揮發性(NVE)與揮發性電解質(VE)之電子傳輸行為分析 132
4-6-4 比較有無使用Nb2O5阻隔層於DSSC之電子傳輸行為 138
4-6-4.1 使用揮發性電解質(VE)，比較有無Nb2O5阻隔層之電子傳輸行為 138
4-6-4.2 使用非揮發性電解質(NVE)，比較有無Nb2O5阻隔層之電子傳輸行為 143
第五章 結論 148
參考文獻 151
附錄 160

[1] Vogel, H. W., "Lehrbuch der photographie." R. Oppenheim. (1878).
[2] Meier, H. and W. Albrecht., "Zum Ausseren Lichtelektrischen Effekt Organischer Farbstoffe." Berichte Der Bunsen-Gesellschaft Fur Physikalische Chemie 69(9-10): 917-&(1965).
[3] Tributsc.H and M. Calvin., "Electrochemistry of Excited Molecules - Photo-Electrochemical Reactions of Chlorophylls." Photochemistry and Photobiology 14(2): 95-&(1971).
[4] Memming, R. and Tributsc. H., "Electrochemical Investigations on Spectral Sensitization of Gallium Phosphide Electrodes." Journal of Physical Chemistry 75(4): 562-&(1971).
[5] Gerische, H., "Electrochemical Techniques for Study of Photosensitization." Photochemistry and Photobiology 16(4): 243-&(1972).
[6] Tang, C. W., "2-Layer Organic Photovoltaic Cell." Applied Physics Letters 48(2): 183-185(1986).
[7] Tsubomura, H., et al., "Dye Sensitized Zinc-Oxide - Aqueous-Electrolyte - Platinum Photocell." Nature 261(5559): 402-403(1976).
[8] Oregan, B. and M. Gratzel., "A Low-Cost, High-Efficiency Solar-Cell Based on Dye-Sensitized Colloidal TiO2 Films." Nature 353(6346): 737-740(1991).
[9] Yella, A., et al., "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency." Science 334(6056): 629-634(2011).
[10] Xia, J., et al., "Importance of Blocking Layers at Conducting Glass/TiO2 Interfaces in Dye-sensitized Ionic-liquid Solar Cells." Chemistry Letters 35(3): 252-253(2006).
[11] Zaban, A., et al., "Bilayer nanoporous electrodes for dye sensitized solar cells." Chemical Communications(22): 2231-2232(2000).
[12] Yang, S. M., et al., "Enhanced energy conversion efficiency of the Sr2+-modified nanoporous TiO2 electrode sensitized with a ruthenium complex." Chemistry of Materials 14(4): 1500-1504(2002).
[13] Diamant, Y., et al., "Core-shell nanoporous electrode for dye sensitized solar cells: the effect of the SrTiO3 shell on the electronic properties of the TiO2 core." Journal of Physical Chemistry B 107(9): 1977-1981(2003).
[14] Taguchi, T., et al., "Improving the performance of solid-state dye-sensitized solar cell using MgO-coated TiO2 nanoporous film." Chemical Communications(19): 2480-2481(2003).
[15] Palomares, E., et al., "Control of charge recombination dynamics in dye sensitized solar cells by the use of conformally deposited metal oxide blocking layers." Journal of the American Chemical Society 125(2): 475-482(2003).
[16] Perera, V. P. S. and K. Tennakone., "Recombination processes in dye-sensitized solid-state solar cells with CuI as the hole collector." Solar Energy Materials and Solar Cells 79(2): 249-255(2003).
[17] Levy, B., et al., "Directed photocurrents in nanostructured TiO2/SnO2 heterojunction diodes." Journal of Physical Chemistry B 101(10): 1810-1816(1997).
[18] Zaban, A., et al., "Electric potential distribution and short-range screening in nanoporous TiO2 electrodes." Journal of Physical Chemistry B 101(40): 7985-7990(1997).
[19] Pichot, F. and B. A. Gregg., "The photovoltage-determining mechanism in dye-sensitized solar cells." Journal of Physical Chemistry B 104(1): 6-10(2000).
[20] Cahen, D., et al., "Nature of photovoltaic action in dye-sensitized solar cells." Journal of Physical Chemistry B 104(9): 2053-2059(2000).
[21] van de Lagemaat, J., et al., "Influence of electrical potential distribution, charge transport, and recombination on the photopotential and photocurrent conversion efficiency of dye-sensitized nanocrystalline TiO2 solar cells: A study by electrical impedance and optical modulation techniques." Journal of Physical Chemistry B 104(9): 2044-2052(2000).
[22] Fabregat-Santiago, F., et al., "Mott-Schottky analysis of nanoporous semiconductor electrodes in dielectric state deposited on SnO2(F) conducting substrates." Journal of the Electrochemical Society 150(6): E293-E298(2003).
[23] Kavan, L. and M. Gratzel., "Highly Efficient Semiconducting TiO2 Photoelectrodes Prepared by Aerosol Pyrolysis." Electrochimica Acta 40(5): 643-652(1995).
[24] Gregg, B. A., et al., "Interfacial recombination processes in dye-sensitized solar cells and methods to passivate the interfaces." Journal of Physical Chemistry B 105(7): 1422-1429(2001).
[25] Cameron, P. J. and L. M. Peter., "Characterization of titanium dioxide blocking layers in dye-sensitized nanocrystalline solar cells." Journal of Physical Chemistry B 107(51): 14394-14400(2003).
[26] Cameron, P. J., et al., "How important is the back reaction of electrons via the substrate in dye-sensitized nanocrystalline solar cells?" Journal of Physical Chemistry B 109(2): 930-936(2005).
[27] Ito, S., et al., "Dye-sensitized photocells with meso-macroporous TiO2 film electrodes." Bulletin of the Chemical Society of Japan 73(11): 2609-2614(2000).
[28] Ito, S., et al., "Control of dark current in photoelectrochemical (TiO2/I--I3-)) and dye-sensitized solar cells." Chem Commun (Camb)(34): 4351-4353(2005).
[29] Liu, X. Z., et al., "Recombination reduction in dye-sensitized solar cells by screen-printed TiO2 underlayers." Chinese Physics Letters 23(9): 2606-2608(2006).
[30] Hattori, R. and H. Goto., "Carrier leakage blocking effect of high temperature sputtered TiO2 film on dye-sensitized mesoporous photoelectrode." Thin Solid Films 515(20-21): 8045-8049(2007).
[31] Hart, J. N., et al., "TiO2 sol-gel blocking layers for dye-sensitized solar cells." Comptes Rendus Chimie 9(5-6): 622-626(2006).
[32] Yoo, B., et al., "Chemically deposited blocking layers on FTO substrates: Effect of precursor concentration on photovoltaic performance of dye-sensitized solar cells." Journal of Electroanalytical Chemistry 638(1): 161-166(2010).
[33] Manca, M., et al., "Charge recombination reduction in dye-sensitized solar cells by means of an electron beam-deposited TiO2 buffer layer between conductive glass and photoelectrode." Thin Solid Films 518(23): 7147-7151(2010).
[34] Sayama, K., et al., "Photoelectrochemical properties of a porous Nb2O5 electrode sensitized by a ruthenium dye." Chemistry of Materials 10(12): 3825-3832(1998).
[35] Xia, J. B., et al., "Fabrication and characterization of thin Nb2O5 blocking layers for ionic liquid-based dye-sensitized solar cells." Journal of Photochemistry and Photobiology a-Chemistry 188(1): 120-127(2007).
[36] Morita, S., et al., "Tri-functional Nb2O5 nano-islands coated on an indium tin oxide layer for a highly efficient dye-sensitized plastic photoanode." Journal of Power Sources 240: 753-758(2013).
[37] Cho, T. Y., et al., "Efficiency enhancement of flexible dye-sensitized solar cell with sol-gel formed Nb2O5 blocking layer." Current Applied Physics 13(7): 1391-1396(2013).
[38] Kikuchi, N., et al., "Electrical and mechanical properties of SnO2 : Nb films for touch screens." Vacuum 66(3-4): 365-371(2002).
[39] Xia, J. B., et al., "Sputtered Nb2O5 as an effective blocking layer at conducting glass and TiO2 interfaces in ionic liquid-based dye-sensitized solar cells." Chemical Communications(2): 138-140(2007).
[40] Xia, J. B., et al., "Sputtered Nb2 O5 as a novel blocking layer at conducting Glass/TiO2 interfaces in dye-sensitized ionic liquid solar cells." Journal of Physical Chemistry C 111(22): 8092-8097(2007).
[41] Chun, J. H. and J. S. Kim., "Comparison of Different Structures of Niobium Oxide Blocking Layer for Dye-Sensitized Solar Cells." Journal of Nanoscience and Nanotechnology 14(8): 6226-6230(2014).
[42] Wessels, K., et al., "Efficiency improvement of dye-sensitized solar cells based on electrodeposited TiO2 films by low temperature post-treatment." Electrochimica Acta 55(22): 6352-6357(2010).
[43] Nazeeruddin, M. K., et al., "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." Journal of the American Chemical Society 115(14): 6382-6390(1993).
[44] Lan, J.-L., et al., "Effects of Iodine Content in the Electrolyte on the Charge Transfer and Power Conversion Efficiency of Dye-Sensitized Solar Cells under Low Light Intensities." The Journal of Physical Chemistry C 116(49): 25727-25733(2012).
[45] Zhang, Q. F. and G. Z. Cao., "Nanostructured photoelectrodes for dye-sensitized solar cells." Nano Today 6(1): 91-109(2011).
[46] Duong, T. T., et al., "Enhancing the efficiency of dye sensitized solar cells with an SnO2 blocking layer grown by nanocluster deposition." Journal of Alloys and Compounds 561: 206-210(2013).
[47] "Spin Coating Theory." Brewer Science Inc. From the World Wide Web: http://www.brewerscience.com/research/processing-theory/spin-coating-theory (2013)
[48] 黃文雄, "儀器總覽-化學分析儀器" 行政院國家科學委員會精密儀器發展中心, 89年
[49] 林智仁, "場發射式掃瞄式電子顯微鏡簡介", 工業材料雜誌181期, 91年1月
[50] 日本株式會社東京精密, "表面粗度膜厚量測儀使用手冊", 103年
[51] 林裕閔, "太陽光電系統原理介紹" 工研院光電科技中心, 97年
[52] "Incident Photon to Charge Carrier Efficiency of Solar Cells." From the World Wide Web: http://www3.nd.edu/~pkamat/pdf/ipce.pdf (2013).
[53] Siegbahn, K.M., "X-Ray Photoelectron Spectroscopy (XPS)." From the World Wide Web: http://memo.cgu.edu.tw/sykuo/Mat-6.pdf (2004).
[54] Wang, Q., et al., "Electrochemical impedance spectroscopic analysis of dye-sensitized solar cells." Journal of Physical Chemistry B 109(31): 14945-14953(2005).
[55] Reddy, K. M., et al., "Bandgap studies on anatase titanium dioxide nanoparticles." Materials Chemistry and Physics 78(1): 239-245(2003).
[56] Liu, J., et al., "Single-crystalline nanoporous Nb2O5 nanotubes." Nanoscale Research Letters 6(2011).
[57] Chen, X. B., et al., "Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals." Science 331(6018): 746-750 (2011).
[58] Wong, Y. H. and K. Y. Cheong., "Band alignment and enhanced breakdown field of simultaneously oxidized and nitrided Zr film on Si." Nanoscale Research Letters 6(2011).
[59] Goldfarb, I., et al., "Band offsets in transition-metal oxide heterostructures." Journal of Physics D-Applied Physics 46(29)(2013).
[60] Smart, R., et al., "X-ray Photoelectron Spectroscopy." From the World Wide Web: http://mmrc.caltech.edu/SS_XPS/XPS_PPT/XPS_Slides.pdf (2013).
[61] Surface & Materials Group., "X-ray Photoelectron Spectroscopy." From the World Wide Web: http://chemlabs.nju.edu.cn/cai/Physical_Chemistry/ solid%
20phys%20chem/XPS.pdf (2005).
[62] Greiner, M. T., et al., "Universal energy-level alignment of molecules on metal oxides." Nature Materials 11(1): 76-81(2012).
[63] Bisquert, J., "Influence of the boundaries in the impedance of porous film electrodes." Physical Chemistry Chemical Physics 2(18): 4185-4192(2000).
[64] Bisquert, J., "Theory of the impedance of electron diffusion and recombination in a thin layer." Journal of Physical Chemistry B 106(2): 325-333(2002).
[65] Fabregat-Santiago, F., et al., "Influence of electrolyte in transport and recombination in dye-sensitized solar cells studied by impedance spectroscopy." Solar Energy Materials and Solar Cells 87(1-4): 117-131(2005).
[66] Wang, Q., et al., "Characteristics of high efficiency dye-sensitized solar cells." Journal of Physical Chemistry B 110(50): 25210-25221(2006).
[67] Miettunen, K., et al., "Dye Solar Cells on ITO-PET Substrate with TiO2 Recombination Blocking Layers." Journal of the Electrochemical Society 156(8): B876(2009).
[68] Barea, E., et al., "Origin of efficiency enhancement in Nb2O5 coated titanium dioxide nanorod based dye sensitized solar cells." Energy & Environmental Science 4(9): 3414(2011).
[69] Fabregat-Santiago, F., et al., "Correlation between photovoltaic performance and impedance spectroscopy of dye-sensitized solar cells based on ionic liquids." Journal of Physical Chemistry C 111(17): 6550-6560(2007).
[70] Shi, J., et al., "Synthesis, characterization and electrochemical properties of a compact titanium dioxide layer." Solid State Sciences 11(2): 433-438(2009).
[71] Ozer, N., et al., "Characterization of Sol-Gel Deposited Niobium Pentoxide Films for Electrochromic Devices." Solar Energy Materials and Solar Cells 36(4): 433-443(1995).
[72] Aegerter, M. A., "Sol-gel niobium pentoxide: A promising material for electrochromic coatings, batteries, nanocrystalline solar cells and catalysis." Solar Energy Materials and Solar Cells 68(3-4): 401-422(2001).
[73] Aegerter, M. A., et al., "Sol-gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism." International Journal of Photoenergy 4(1): 1-10(2002).
[74] Ueno, S. and S. Fujihara., "Effect of an Nb2O5 nanolayer coating on ZnO electrodes in dye-sensitized solar cells." Electrochimica Acta 56(7): 2906-2913 (2011).
[75] Ou, J. Z., et al., "Elevated Temperature Anodized Nb2O5: A Photoanode Material with Exceptionally Large Photoconversion Efficiencies." Acs Nano 6(5): 4045-4053(2012).
[77] Salvador, P., et al., "Illumination intensity dependence of the photovoltage in nanostructured TiO2 dye-sensitized solar cells." Journal of Physical Chemistry B 109(33): 15915-15926(2005).
[76] Bisquert, J. and I. Mora-Sero., "Simulation of Steady-State Characteristics of Dye-Sensitized Solar Cells and the Interpretation of the Diffusion Length." Journal of Physical Chemistry Letters 1(1): 450-456(2010).
[78] Gonzalez-Pedro, V., et al., "Modeling High-Efficiency Quantum Dot Sensitized Solar Cells." Acs Nano 4(10): 5783-5790(2010).