臺灣博碩士論文加值系統

由於Squaraine (SQ) 染料在近紅外光區域具有強烈的吸光特性，且跟太陽光的吸收光
譜高度吻合，因而Squaraine (SQ)染料在染料敏化太陽能電池發展中，市集具有發展潛
力的。在本篇研究中，利用了密度泛函理論(DFT)及time-dependent 密度泛函理論
(TD-DFT)計算了6 個SQ 衍生的染料分子，探討染料分子在溶劑中，以及吸附在鋭鈦
礦相(TiO2)38 cluster (101)面兩種狀態下，其分子結構、光學性質及電賀轉移的性質的
變化。從計算結果中可以得知，分別以carboxylic acid (CA) 及cyanoacrylic acid (CAA)，
作為SQ 染料分子的acceptor/anchor 時，SQ 染料分子會具有不同的吸附及躍遷性質。
以CAA 為anchor 的SQ 染料分子，不僅比以CA 作為anchor 的SQ 染料分子具有較紅
位移的吸收性質，且其轉移至anchor/TiO2 的電荷密度也較多。除此之外，以CAA 分
子取代CA 分子的SQ 染料，還有著另一根有著明顯電荷轉移性質的吸收峰(2)。另一
方面，以dicyanovinyl group a 及 ethyl cyanoacetate group 加入 squarate 部分形成
cis-HSQ2-CA/CAA 和cis-HSQ3-CA/CAA 的官能基化的SQ 染料分子，其轉移至
anchor/TiO2 的電荷密度相較於trans-SQ1-CA/CAA 分子具有著較少比率。除此之外，
在本篇研究中還有探討在D--A 類型的染料中，改變acceptor 對其的影響。我們認為
不同的acceptor 會影響LUMO 的能階，但對HOMO 的能階卻不會造成太大的影響。
在溶劑中，有著拉電子官能基acceptor 的DPA-Th2-AA(NO2)分子，其有著最強的最大
吸收波長(max)及明顯轉移至acceptor 的電荷轉移性質。另一方面AA(H) 及有著推電
子官能基acceptor 的AA(NH2) 分子，其擁有較低的電荷轉移性質。然而DPA–
Th2-AA(NO2)/(TiO2)轉移至TiO2 的電荷密度卻十分少。預計的原因可能為，在被光激
發後，較低的LUMO 能階會和較低能量的TiO2 的conduction band 作用。由於較低能
量的TiO2 的conduction band 有著較低的態密度(density of states)，因此導致了較少的
電荷密度轉移至TiO2。本篇研究提供了染料敏化太陽能電池設計新染料分子的依據。

Squaraine (SQ) dye is one of the most promising dyes for dye-sensitized solar cell (DSSC) due to its intense absorption in the red/near-infared (NIR) region closely matches with the solar spectra. In this study, we employed density functional theory (DFT) and time-dependent DFT (TD-DFT) to investigate the structural, optical, and electron transfer properties of six SQ-derived dyes in solution and adsorbed on a (TiO2)38 cluster having an anatase (101) surface, as a model for corresponding DSSCs. We found that SQ dyes using carboxylic acid (CA) as acceptor/anchoring group and SQ dyes using cyanoacrylic acid (CAA) as acceptor/anchoring group have different absorption properties and transition characters. The CAA-based SQ dyes not only own more red-shifted absorption properties but also have enhanced charge transfer (CT) character with electron density transferred to the anchor/TiO2 in relative to those of corresponding CA-based SQ dyes. Moreover, substituent of CA by CAA results in CAA-based SQ dyes having an additional absorption (2), which also have significant CT character. On the other hand, functionalized SQs with dicyanovinyl group and ethyl cyanoacetate group into squarate moiety yielded cis-HSQ2-CA/CAA and cis-HSQ3-CA/CAA are less capable for electron transfer to the anchor/TiO2 in relative to that of corresponding trans-SQ1-CA/CAA. In addition, we also investigate various acceptors of D--A dyes. We identified that different acceptors affect the LUMO energy levels and they have less effect for the energy level of HOMO. In solution, the DPA-Th2-AA(NO2) with electron-withdrawing acceptor has the largest max and its absorption has significant CT character to the acceptor. On the other hand, the AA(H) and electron-donating AA(NH2) groups generate the lowest CT character. However, DPA–Th2-AA(NO2)/(TiO2) have less electron density transferred to TiO2. It is expected that the lower energy LUMOs of dyes (red-shifted absorption) will couple with the lower-energy TiO2 conduction band, which has lower density of states leading to less electron density redistributed to TiO2 upon excitation. This study provides clues for designing new sensitizer for DSSC applications.

摘要 i
Abstract ii
Acknowledgements iv
Contents vi
List of Figures viii
List of Tables ix
Chapter 1. Introduction 1
Chapter 2. Computational Methods 7
Chapter 3. A Density Functional Theory Investigation of the Photo-physical
Properties of Squaraine Dyes with Cis and Trans Configurations in Dye-Sensitized
Solar Cells 9
3.1 Studied Systems and Molecular Conformations 10
3.2 Absorption Spectra and Transition Characters of Free Dyes 17
3.3 Absorption Properties of Dye Molecules Adsorbed on TiO2 Cluster 28
3.4 Transition Properties of Dye Molecules Adsorbed on TiO2
Clusters upon Photo-Excitation 31
Chapter 4. Acceptor Effects of D--A dyes on their Photo-physical Properties
in Dye Sensitized Solar Cells 48
4.1 Studied Systems and Molecular Geometries 49
4.2 Absorption Spectra of Free Dyes 52
4.3 Charge-Transfer Character of Free Molecules 66
4.4 Absorption Properties and Electron Transfer of Molecules
Adsorbed on TiO2 Cluster 69
Chapter 5. Conclusion and Summary 79
References 81
Appendix A 86
Appendix B 87

1. O’Regan, B.; Grätzel, M., A low-Cost, High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353 (6346), 737-740.
2. Anothumakkool, B.; Agrawal, I.; Bhange, S. N.; Soni, R.; Game, O.; Ogale, S. B.; Kurungot, S., Pt- and TCO-Free Flexible Cathode for DSSC from Highly Conducting and Flexible PEDOT Paper Prepared via in Situ Interfacial Polymerization. ACS Appl. Mater. Interfaces 2016, 8, 553−562.
3. (a) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H., Dye-Sensitized Solar Cells. Chem. Rev. 2010, 110 (11), 6595-663; (b) Andrea Listorti, B. O. R., and James R Durrant, Electron Transfer Dynamics in Dye-Sensitized Solar Cells. Chem. Mater. 2011, 23, 3381–3399; (c) Rocca, D.; Gebauer, R.; De Angelis, F.; Nazeeruddin, M. K.; Baroni, S., Time-Dependent Density Functional Theory Study of Squaraine Dye-Sensitized Solar Cells. Chem. Phys. Lett. 2009, 475 (1-3), 49-53.
4. (a) Huang, W.-K.; Wu, H.-P.; Lin, P.-L.; Lee, Y.-P.; Diau, E. W.-G., Design and Characterization of Heteroleptic Ruthenium Complexes Containing Benzimidazole Ligands for Dye-Sensitized Solar Cells: The Effect of Fluorine Substituents on Photovoltaic Performance. J. Phys. Chem. Lett. 2012, 3, 1830−1835; (b) Hsu, H.-Y.; Cheng, C.-W.; Huang, W.-K.; Lee, Y.-P.; Diau, E. W.-G., Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye Sensitized Solar Cells. J. Phys. Chem. C 2014, 118, 16904−16911.
5. Chen, C.-Y.; Wang, M.; Li, J.-Y.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C.-h.; Decoppet, J.-D.; Tsai, J.-H.; Grätzel, C.; Wu, C.-G.; Zakeeruddin, S. M.; Grätzel, M., Highly Efficient Light-Harvesting Ruthenium Sensitizer for Thin-Film Dye-Sensitized Solar Cells. ACS Nano 2009, 3 (10), 3103-3109.
6. Andersen, A. R.; Halme, J.; Lund, T.; Asghar, M. I.; Nguyen, P. T.; Miettunen, K.; Kemppainen, E.; Albrektsen, O., Charge Transport and Photocurrent Generation Characteristics in Dye Solar Cells Containing Thermally Degraded N719 Dye Molecules. J. Phys. Chem. C 2011, 115, 15598–15606.
7. Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M., Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency. Science 2011, 334 (6056), 629-634.
8. Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Gratzel, M., Dye-Sensitized Solar Cells with 13% Efficiency Achieved Through the Molecular Engineering of Porphyrin Sensitizers. Nat Chem 2014, 6 (3), 242-247.
9. (a) Zeng, W.; Cao, Y.; Bai, Y.; Wang, Y.; Shi, Y.; Zhang, M.; Wang, F.; Pan, C.; Wang, P., Efficient Dye-Sensitized Solar Cells with an Organic Photosensitizer Featuring Orderly Conjugated Ethylenedioxythiophene and Dithienosilole Blocks. Chem. Mater. 2010, 22 (5), 1915-1925; (b) Gupta, A.; Kelson, M. M. A.; Armel, V.; Bilic, A.; Bhosale, S. V., N-Alkyl- and N-Aryl-Dithieno[3,2-b:2′,3′-d]Pyrrole-Containing Organic Dyes for Efficient Dye-Sensitized Solar Cells. Tetrahedron 2014, 70 (12), 2141-2150.
10. He, J.; Wu, W.; Hua, J.; Jiang, Y.; Qu, S.; Li, J.; Long, Y.; Tian, H., Bithiazole-Bridged Dyes for Dye-Sensitized Solar Cells with High Open Circuit Voltage Performance. J. Mater. Chem. 2011, 21 (16), 6054.
11. Kakiage, K.; Aoyama, Y.; Yano, T.; Otsuka, T.; Kyomen, T.; Unno, M.; Hanaya, M., An Achievement of over 12 Percent Efficiency in an Organic Dye-Sensitized Solar Cell. Chem. Commun. 2014, 50 (48), 6379-81.
12. (a) Baheti, A.; Thomas, K. R. J.; Li, C.-T.; Lee, C.-P.; Ho, K.-C., Fluorene-Based Sensitizers with a Phenothiazine Donor: Effect of Mode of Donor Tethering on the Performance of Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 2249−2262; (b) Katono, M.; Bessho, T.; Meng, S.; Humphry-Baker, R.; Rothenberger, G.; Zakeeruddin, S. M.; Kaxiras, E.; Grätzel, M., D-π-A Dye System Containing Cyano-Benzoic Acid as Anchoring Group for Dye-Sensitized Solar Cells. Langmuir 2011, 27, 14248–14252; (c) Ganesan, P.; Chandiran, A.; Gao, P.; Rajalingam, R.; Grätzel, M.; Nazeeruddin, M. K., Molecular Engineering of 2‑Quinolinone Based Anchoring Groups for Dye-Sensitized Solar Cells. J. Phys. Chem. C 2014, 118, 16896−16903.
13. Ren, X.; Jiang, S.; Cha, M.; Zhou, G.; Wang, Z.-S., Thiophene-Bridged Double D-π-A Dye for Efficient Dye-Sensitized Solar Cell. Chem. Mater. 2012, 24 (17), 3493-3499.
14. Namuangruk, S.; Fukuda, R.; Ehara, M.; Meeprasert, J.; Khanasa, T.; Morada, S.; Kaewin, T.; Jungsuttiwong, S.; Sudyoadsuk, T.; Promarak, V., D－D－π－A-Type Organic Dyes for Dye-Sensitized Solar Cells with a Potential for Direct Electron Injection and a High Extinction Coefficient: Synthesis, Characterization, and Theoretical Investigation. J. Phys. Chem. C 2012, 116, 25653-25663.
15. (a) Ying, W. J.; Guo, F. L.; Li, J.; Zhang, Q.; Wu, W. J.; Tian, H.; Hua, J. L., Series of New D-A-p-A Organic Broadly Absorbing Sensitizers Containing Isoindigo Unit for Highly Efficient Dye-Sensitized Solar Cells. ACS Appl Mater Interfaces 2012, 4 (8), 4215-24; (b) Wu, Y.; Zhu, W. H.; Zakeeruddin, S. M.; Gratzel, M., Insight into D-A-p-A Structured Sensitizers: A Promising Route to Highly Efficient and Stable Dye-Sensitized Solar Cells. ACS Appl Mater Interfaces 2015, 7 (18), 9307-18.
16. Jradi, F. M.; Kang, X.; Pajares, D. O. N. G.; Getmanenko, Y. A.; Szymanski, P.; Parker, T. C.; El-Sayed, M. A.; Marder, S. R., Near-Infrared Asymmetrical Squaraine Sensitizers for Highly Efficient Dye Sensitized Solar Cells: The Effect of π‑Bridges and Anchoring Groups on Solar Cell Performance. Chemistry of Materials, ACS 2015.
17. (a) Tsai, H.-H.; Tan, C. J.; Hu, J. C., DSC Research: Ideas, Assignments, Notes and Others 2014; (b) Li, J.-Y.; Chen, C.-Y.; Ho, W.-C.; Chen, S.-H.; Wu, C.-G., Unsymmetrical Squaraines Incorporating Quinoline for Near Infrared Responsive Dye-Sensitized Solar Cells. Org. Lett. 2012, 14, 5420-5423; (c) Maeda, T.; Arikawa, S.; Nakao, H.; Yagi, S.; Nakazumi, H., Linearly p-Extended Squaraine Dyes Enable the Spectral Response of Dye-Sensitized Solar Cells in the NIR Region over 800 nm. New J. Chem. 2013, 37, 701-708.
18. Qin, C.; Numata, Y.; Zhang, S.; Islam, A.; Yang, X.; Sodeyama, K.; Tateyama, Y.; Han, L., A Near-Infrared cis-Configured Squaraine Co-Sensitizer for High-Efficiency Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2013, 23.
19. Paek, S.; Choi, H.; Kim, C.; Cho, N.; So, S.; Song, K.; Nazeeruddin, M. K.; Ko, J., Efficient and Stable Panchromatic Squaraine Dyes for Dye-Sensitized Solar Cells. Chem. Commun. 2011, 47 (10), 2874-2876.
20. Li, J.; Yang, X.; Cheng, M.; Wang, M.; Sun, L., Phenoxazine-Based Panchromatic Organic Sensitizers for Dye-Sensitized Solar Cells. Dyes Pigments 2015 116, 58-64.
21. Wei, T.; Sun, X.; Xin Li; Ågren, H.; Xie, Y., Systematic Investigations on the Roles of the Electron Acceptor and Neighboring Ethynylene Moiety in Porphyrins for Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, A-J.
22. (a) Surakhot, Y.; Rattanawan, R.; Ronyhut, K.; Mangsachart, P.; Sudyoadsuk, T.; Promarak, V.; Namuangruk, S.; Kungwand, N.; Jungsuttiwong, S., The Number Density Effect of N-substituted Dyes on the TiO2 Surface In Dye Sensitized Solar Cells: A Theoretical Study. RSC Adv. 2015, 5, 11549–11557; (b) Wu, T.-Y.; Tsao, M.-H.; Chen, F.-L.; Su, S.-G.; Chang, C.-W.; Wang, H.-P.; Lin, Y.-C.; Ou-Yang, W.-C.; Sun, I.-W., Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors. Int. J. Mol. Sci. 2010, 11, 329-353; (c) Sekar, M. S. R.; Palani, E.; Sambandam, A., One-Pot Synthesis of Metal Free Organic Dyes Containing Different Acceptor Moieties for Fabrication of Dye-Sensitized Solar Cells. Tetrahedron Lett. 2013, 54, 3132–3136.
23. An, M.; Sarker, A. K.; Jung, D.-C.; Hong, J.-D., An Organic Nitrile Dye with Strong Donor and Acceptor Groups for Dye-Sensitized Solar Cells Bull. Korean Chem. Soc.
2011, 32, 2083-2086.
24. (a) Yamazaki, E.; Murayama, M.; Nishikawa, N.; Hashimoto, N.; Shoyama, M.; Kurita, O., Utilization of Natural Carotenoids as Photosensitizers for Dye-Sensitized Solar Cells. Solar Energy 2007 81, 512–516; (b) Zhou, H.; Wu, L.; Gao, Y.; Ma, T., Dye-sensitized solar cells using 20 natural dyes as sensitizers. Journal of Photochemistry and Photobiology A: Chemistry 2011, 219, 188–194.
25. Cai, S.; Tian, G.; Li, X.; Su, J.; Tian, H., Efficient and Stable DSSC Sensitizers Based on Substituted Dihydroindolo[2,3-B] Carbazole Donors with High Molar Extinction Coefficients. J. Mater. Chem. A 2013, 1, 11295–11305.
26. Baldoli, C.; Bertuolo, S.; Licandro, E.; Viglianti, L.; Mussini, P.; Marotta, G.; Salvatori, P.; Angelis, F. D.; Manca, P.; Manfredi, N.; Abbotto, A., Benzodithiophene Based Organic Dyes for DSSC: Effect of Alkyl Chain Substitution on Dye Efficiency. Dyes Pigments 2015, 121, 351-362.
27. Jradi, F. M.; Kang, X.; O’Neil, D.; Pajares, G.; Getmanenko, Y. A.; Szymanski, P.; Parker, T. C.; El-Sayed, M. A.; Marder, S. R., Near-Infrared Asymmetrical Squaraine Sensitizers for Highly Efficient Dye Sensitized Solar Cells: The Effect of π-Bridges and Anchoring Groups on Solar Cell Performance. Chem. Mater. 2015, 27 (7), 2480-2487.
28. Shivashimpi, G. M.; Pandey, S. S.; Watanabe, R.; Fujikawa, N.; Ogomi, Y.; Yamaguchi, Y.; Hayase, S., Novel Unsymmetrical Squaraine Dye Bearing Cyanoacrylic Acid Anchoring Group and Its Photosensitization Behavior. Tetrahedron Lett. 2012 53, 5437–5440.
29. (a) Puyada, A. L.; Chaitanya, G. K.; Thomas, A.; Paramasivam, M.; Bhanuprakash, K., DFT Studies of Squarylium and Core-Substituted Squarylium Dye Derivatives: Understanding the Causes of the Additional Shorter Wavelength Absorption in the Latter. J. Phys. Org. Chem. 2012, 26, 37–46; (b) Pastore, M.; Mosconi, E.; Angelis, F. D.; Grätzel, M., A Computational Investigation of Organic Dyes for Dye-Sensitized Solar Cells: Benchmark, Strategies, and Open Issues. J. Phys. Chem. C 2010, 114, 7205–7212.
30. (a) Lu, X.; Wu, C.-M. L.; Wei, S.; Guo, W., DFT/TD-DFT Investigation of Electronic Structures and Spectra Properties of Cu-Based Dye Sensitizers. J. Phys. Chem. A 2010, 114, 1178–1184; (b) Angelis, M. P. a. F. D., Computational Modeling of Stark Effects in Organic Dye-Sensitized TiO2 Heterointerfaces. J. Phys. Chem. Lett. 2011, 2, 1261–1267; (c) Rocca, D.; Gebauer, R.; Angelis, F. D.; Nazeeruddin, M. K.; Baroni, S., Time-Dependent Density Functional Theory Study of Squaraine Dye-Sensitized Solar Cells. Chem. Phys. Lett. 2009, 475, 49–53.
31. Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A., Cheeseman, J. R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G. A., Nakatsuji, H., Caricato, M., Li, X., Hratchian, H. P., Izmaylov, A. F., Bloino, J., Zheng, G., Sonnenberg, J. L., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Montgomery, J. A., Jr., Peralta, J. E., Ogliaro, F., Bearpark, M., Heyd, J. J., Brothers, E., Kudin, K. N., Taroverov, V. N., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A., Burant, J. C., Iyengar, S. S., Tomasi, J., Cossi, M., Rega, N., Millam, N. J., Klene, M., Knox, J. E., Cross, J. B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R. E., Yazyev, O., Austin, A. J., Cammi, R., Pomelli, C., Ochterski, J. W., Martin, R. L., Morokuma, K., Zakrzewski, V. G., Voth, G. A., Salvador, P., Dannenberg, J. J., Dapprich, S., Daniels, A. D., Farkas, Ö., Foresman, J. B., Ortiz, J. V., Cioslowski, J., Fox, D. J. , Gaussian, Inc., Wallingford CT 2009.
32. Cossi, M.; Rega, N.; Scalmani, G.; Barone, V., Energies, Structures, and Electronic Properties of Molecules in Solution with the C-PCM Solvation Model. J. Comput. Chem. 2003, 24 (6), 669-81.
33. Yanai, T.; Tew, D. P.; Handy, N. C., A New Hybrid Exchange–Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393 (1-3), 51-57.
34. Steiner, E., Density-Difference Maps in Quantum Chemistry. Theoretica chimica acta 1982, 60 (6), 561-572.
35. O'Boyle, N. M.; Tenderholt, A. L.; Langner, K. M., cclib: A Library for Package-Independent Computational Chemistry Algorithms. J. Comput. Chem. 2008, 29 (5), 839-45.
36. Qin, C.; Numata, Y.; Zhang, S.; Yang, X.; Islam, A.; Zhang, K.; Chen, H.; Han, L., Novel Near-Infrared Squaraine Sensitizers for Stable and Efficient Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2014, 24, 3059–3066.
37. Wu, C. G.; Chung, M. F.; Tsai, H.-H. G.; Tan, C. J.; Chen, S. C.; Chang, C. H.; Shih, T. W., Fluorene-Containing Organic Photosensitizers for Dye-Sensitized Solar Cells. ChemPlusChem 2012, 77 (9), 832-843.
38. Srinivas, K.; Prabhakar, C.; Devi, C. L.; Yesudas, K.; Bhanuprakash, K.; Rao, V. J., Enhanced Diradical Nature in Oxyallyl Derivatives Leads to Near Infra Red Absorption: A Comparative Study of the Squaraine and Croconate Dyes Using Computational Techniques. J. Phys. Chem. A 2007, 111 (17), 3378-3386.
39. (a) Beverina, L.; Ruffo, R.; Salamone, M. M.; Ronchi, E.; Binda, M.; Natali, D.; Sampietro, M., Panchromatic Squaraine Compounds for Broad Band Light Harvesting Electronic Devices. J. Mater. Chem. 2012, 22 (14), 6704; (b) Mayerhoffer, U.; Gsanger, M.; Stolte, M.; Fimmel, B.; Wurthner, F., Synthesis and Molecular Properties of Acceptor-Substituted Squaraine Dyes. Chemistry 2013, 19 (1), 218-32.
40. (a) De Angelis, F.; Fantacci, S.; Mosconi, E.; Nazeeruddin, M. K.; Grätzel, M., Absorption Spectra and Excited State Energy Levels of the N719 Dye on TiO2 in Dye-Sensitized Solar Cell Models. J. Phys. Chem. C 2011, 115 (17), 8825-8831; (b) Pastore, M.; Fantacci, S.; De Angelis, F., Modeling Excited States and Alignment of Energy Levels in Dye-Sensitized Solar Cells: Successes, Failures, and Challenges. J. Phys. Chem. C 2013, 117 (8), 3685-3700.
41. Chen, B.-S.; Chen, D.-Y.; Chen, C.-L.; Hsu, C.-W.; Hsu, H.-C.; Wu, K.-L.; Liu, S.-H.; Chou, P.-T.; Chi, Y., Donor–Acceptor Dyes with Fluorine Substituted Phenylene Spacer for Dye-Sensitized Solar Cells. J. Mater. Chem. 2011, 21 (6), 1937.