中文摘要

Ru錯合物因其具有高光電流轉換效率與高穩定性而經常被作為染料敏化太陽能電池的敏化劑。一些Ru錯合物，例如，以DX1為基底的錯合物，表現出有效的自旋-軌道（Spin-Orbit, SO）交互作用，因此對於染料敏化太陽能電池應用能提供更長波長的吸收；然而，有些Ru錯合物的SO交互作用非常弱。因此，有必要研究Ru錯合物的SO相互作用的性質。在這論文研究中，我們探究通過輔助配位基強化的SO交互作用以激活Ru/Os錯合物的長波長吸收和spin-forbidden triplet transitions。藉由TDDFT包含SO交互作用研究具有不同輔助配位基的兩個Ru/Os配合物系列：（I）以DX1為基底的Ru/Os染料和類Black dye的Ru/Os染料，並以三個相同的滷素和NCS陰離子作為輔助配位基，和（II）Ru/Os錯合物（由Wu和Chen團隊合成的Os-3，CYC-33R和CYC-33O）結合了高度共軛的2-thiohexyl-3,4-ethylenedioxythiophene官能化聯吡啶基部分作為輔助配位基。我們發現輔助配位基顯著影響最長波長的spin-allowed 吸收並且影響SO交互作用的強度。
對於以DX1為架構的Ru/Os染料和類Black-dye的Ru/Os染料，具有NCS配位基的Ru/Os錯合物比以鹵素作為配位基的對應物具有更長波長的S1躍遷。另一方面，以碘離子為配位基的Ru/Os錯合物比其他對應物具有最短的波長S1躍遷。Os錯合物的波長S1躍遷比Ru對應物更長。輔助配位基對電子躍遷的軌道貢獻對於以SO交互作用激活spin-forbidden triplet 躍遷相當重要。 較輕的NCS- 配位基的DX-Ru-2NCS錯合物對電子躍遷有更多軌域貢獻，因此減少了Ru重原子的貢獻，從而使SO交互作用更弱。另一方面，具有來自碘配位基顯著軌域貢獻的DX-Ru-2I增強了SO交互作用。苯二甲氧基膦衍生的配位基改變了以DX1為基底Ru錯合物的S1狀態與低價三重態之間的能量差，可以對其進行修飾與調節SOC強度。與相應的Ru錯合物相比，Os錯合物中的Os原子促使SOC矩陣元素增強的自旋禁態三重態。
為了研究Os-3，CYC-33R和CYC-33O，CYC-33O的強化1MLCT和3MLCT躍遷主要是從Os 至4,4’,4”-tricarboxy-2,2’:6’,2’’-terpyridine錨定配位基，增加CYC-33O和TiO2之間的異質電子轉移。以CYC-33O敏化的器件在1000 nm以上具有全色轉換現象，產生的光電流密度為19.38 mA cm-2，遠高於基於Rh類似物（CYC-33R）和模型錯合物（Os-3）敏化劑。本研究提供了幾種激活Ru/Os配合物的spin-forbidden長波長躍遷的新策略。

Abstract

Ru complexes have been often employed as sensitizers for DSCs applications because of their high photon-to-current conversion efficiency and long-term stability. Some of Ru complexes such as DX1-based complexes exhibit effective spin–orbit (SO) interactions and thus give longer wavelength absorption for DSCs applications; however, other Ru complexes show very weak SO interactions. Therefore, it is necessary to investigate the nature of SO interactions for Ru complexes. In this study, we explore the long wavelength absorptions and spin-forbidden triplet transitions activated for ruthenium (Ru)/osmium (Os) complexes by SO interactions strengthened by ancillary ligands. Two series of Ru/Os complexes with different ancillary ligands were studied by TDDFT with SO interactions: (I) DX1-based Ru/Os dyes and black dye-like Ru/Os dyes with three identical halogens and NCS anions as ancillary ligands, and (II) Ru/Os complexes (Os-3, CYC-33R and CYC-33O synthesized by Wu and Chen group) incorporating highly-conjugated 2-thiohexyl-3,4-ethylenedioxythiophene functionalized bipyridyl moiety as ancillary ligand. We found ancillary ligands significantly affect the longest wavelength spin-allowed absorption and influence the strength of SO interactions.
For DX1-based and black dye-like Ru/Os dyes, Ru/Os complexes with NCS ligands exhibit longer wavelength S1 transition than their corresponding counterparts with halogens as ligands. On the other hand, Ru/Os complexes with iodide ligands give the shortest wavelength S1 transition than the other counterparts. The Os-complex has longer wavelength S1 transition than its Ru-counterpart. Orbital contribution of ancillary ligands to the electronic transition is crucial to activate the spin-forbidden triplet transition by SO interactions. DX-Ru-2NCS complex, which has more orbital contribution from light NCS ligands to the electronic transitions, and therefore, reduces the contribution from heavy Ru atom, gives weaker SO interactions. On the other hand, DX-Ru-2I, which has significant orbital contribution from heavy iodide ligands, enhances SO interactions. The phenyldimethoxyphosphine-derived ligands alter the energy difference between the S1 state and the low-lying triplet states for DX1-based Ru-complexes, which can be modified to tune the SOC (spin-orbit coupling) strength. The Os atom in Os-complexes promotes the SOC matrix elements which strengthens the spin-forbidden triplet states than those of corresponding Ru-complexes.
For the Os-3, CYC-33R, and CYC-33O dyes, the reinforced 1MLCT and 3MLCT transitions of CYC-33O are mainly from osmium to the 4,4’,4”-tricarboxy-2,2’:6’,2’’-terpyridine anchoring ligand, increasing the heterogeneous electron transfer between CYC-33O and TiO2. The device sensitized with CYC-33O exhibits panchromatic conversion beyond 1000 nm, yielding a photocurrent density of 19.38 mA cm-2, which is much higher than those of the cells based on the ruthenium analogue (CYC-33R) and model osmium complex (Os-3) sensitizers. This study offers several new approaches for activating spin-forbidden long wavelength transitions for Ru and Os complexes.

References

1. 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 (20), 3059-3066.
2. Nazeeruddin, M. K.; Baranoff, E.; Grätzel, M., Dye-sensitized solar cells: A brief overview. Solar Energy 2011, 85 (6), 1172-1178.
3. Yang, L.-N.; Sun, Z.-Z.; Li, Q.-S.; Chen, S.-L.; Li, Z.-S.; Niehaus, T. A., Unsymmetrical squaraine dye containing dithieno[3,2-b:2′,3′-d]pyrrole as a π-spacer: A potential photosensitizer for dye-sensitized solar cells. J. Power Sources 2014, 268, 137-145.
4. Ozawa, H.; Yamamoto, Y.; Kawaguchi, H.; Shimizu, R.; Arakawa, H., Ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand for dye-sensitized solar cells: synthesis, photo- and electrochemical properties, and adsorption behavior to the TiO2 surface. ACS Appl Mater Interfaces 2015, 7 (5), 3152-3161.
5. Liu, S.-H.; Fu, H.; Cheng, Y.-M.; Wu, K.-L.; Ho, S.-T.; Chi, Y.; Chou, P.-T., Theoretical study of N749 dyes anchoring on the (TiO2)28 surface in DSSCs and their electronic absorption properties. J. Phys. Chem. C 2012, 116 (31), 16338-16345.
6. Nazeeruddin, M. K.; De Angelis, F.; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.; Gratzel, M., Combined experimental and DFT-TDDFT computational study of photoelectrochemical cell ruthenium sensitizers. J. Am. Chem. Soc. 2005, 127 (48), 16835-16847.
7. Chen, C. Y.; Chen, J. G.; Wu, S. J.; Li, J. Y.; Wu, C. G.; Ho, K. C., Multifunctionalized ruthenium-based supersensitizers for highly efficient dye-sensitized solar cells. Angew. Chem. Int. Ed. 2008, 47 (38), 7342-7345.
8. Yin, N.; Wang, L.; Lin, Y.; Yi, J.; Yan, L.; Dou, J.; Yang, H.-B.; Zhao, X.; Ma, C.-Q., Effect of the π-conjugation length on the properties and photovoltaic performance of A–π–D–π–A type oligothiophenes with a 4,8-bis(thienyl)benzo[1,2-b:4,5-b']dithiophene core. Beilstein J. Org. Chem. 2016, 12, 1788-1797.
9. Lee, D.; Ma, X.; Jung, J.; Jeong, E. J.; Hashemi, H.; Bregman, A.; Kieffer, J.; Kim, J., The effects of extended conjugation length of purely organic phosphors on their phosphorescence emission properties. Phys. Chem. Chem. Phys. 2015, 17 (29), 19096-19103.
10. Tsai, H.-H. G.; Tan, C.-J.; Tseng, W.-H., Electron transfer of squaraine-derived dyes adsorbed on TiO2 clusters in dye-sensitized solar cells: A density functional theory investigation. J. Phy. Chem. C 2015, 119 (9), 4431-4443.
11. Kanno, S.; Imamura, Y.; Hada, M., Design of spin-forbidden transitions for polypyridyl metal complexes by time-dependent density functional theory including spin-orbit interaction. Phys. Chem. Chem. Phys. 2016, 18 (21), 14466-14478.
12. Juwita, R.; Lin, J.-Y.; Lin, S.-J.; Liu, Y.-C.; Wu, T.-Y.; Feng, Y.-M.; Chen, C.-Y.; Gavin Tsai, H.-H.; Wu, C.-G., Osmium sensitizer with enhanced spin–orbit coupling for panchromatic dye-sensitized solar cells. J. Mater. Chem. A 2020, 8 (25), 12361-12369.
13. McClure, D. S., Spin‐orbit interaction in aromatic molecules. J. Chem. Phys. 1952, 20 (4), 682-686.
14. Xiaoyi Zhang, M. P., Klaus B. Møller, Jianxin Zhang and Sophie E. Canton, Characterizing the solvated structure of photoexcited [Os(terpy)2]2+ with x-ray transient absorption spectroscopy and DFT calculations. Molecules 2016, 21, 235.
15. Jia Zhang, B. H., Revealing photoinduced bulk polarization and spin-orbit coupling effects in high-efficiency 2D/3D Pb–Sn alloyed perovskite solar cells Nano Energy 2020, 76, 104999.
16. Kinoshita, T.; Fujisawa, J.; Nakazaki, J.; Uchida, S.; Kubo, T.; Segawa, H., Enhancement of near-IR photoelectric conversion in dye-sensitized solar cells using an osmium sensitizer with strong spin-forbidden transition. J Phys Chem Lett 2012, 3 (3), 394-398.
17. Rodriguez-Serrano, A.; Rai-Constapel, V.; Daza, M. C.; Doerr, M.; Marian, C. M., Internal heavy atom effects in phenothiazinium dyes: enhancement of intersystem crossing via vibronic spin-orbit coupling. Phys. Chem. Chem. Phys. 2015, 17 (17), 11350-11358.
18. Swetha, T.; Reddy, K. R.; Singh, S. P., Osmium polypyridyl complexes and their applications to dye-sensitized solar cells. Chemical record 2015, 15 (2), 457-74.
19. Ayman A. Abdel-Shafi, D. R. W. a. A. Y. E. c., Photosensitized generation of singlet oxygen from ruthenium(II) and osmium(II) bipyridyl complexes. Dalton Trans. 2004, 30-36.
20. Zhang, X.; Canton, S. E.; Smolentsev, G.; Wallentin, C. J.; Liu, Y.; Kong, Q.; Attenkofer, K.; Stickrath, A. B.; Mara, M. W.; Chen, L. X.; Warnmark, K.; Sundstrom, V., Highly accurate excited-state structure of [Os(bpy)2dcbpy]2+ determined by x-ray transient absorption spectroscopy. J. Am. Chem. Soc. 2014, 136 (24), 8804-8809.
21. Ronca, E.; De Angelis, F.; Fantacci, S., Time-dependent density functional theory modeling of spin–orbit coupling in ruthenium and osmium solar cell sensitizers. J. Phy. Chem. C 2014, 118 (30), 17067-17078.
22. Wu, K. L.; Ho, S. T.; Chou, C. C.; Chang, Y. C.; Pan, H. A.; Chi, Y.; Chou, P. T., Engineering of osmium(II)-based light absorbers for dye-sensitized solar cells. Angew. Chem. Int. Ed. 2012, 51 (23), 5642-5646.
23. G. Te Velde, F. M. B., E. J. Baerends, C. Fonseca Guerra, S. J. A. Van Gisbergen, J. G. Snijders, T. Zieglers, Chemistry with ADF. J. Comput. Chem. 2001, 22, 931-967.
24. Fantacci, S.; Ronca, E.; De Angelis, F., Impact of spin-orbit coupling on photocurrent generation in ruthenium dye-sensitized solar cells. J. Phys. Chem. Lett 2014, 5 (2), 375-380.
25. van Lenthe, E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G., Relativistic regular two-component Hamiltonians. Int. J. Quantum Chem 1996, 57 (3), 281-293.
26. Lenthe, E. v.; Snijders, J. G.; Baerends, E. J., The zero‐order regular approximation for relativistic effects: The effect of spin–orbit coupling in closed shell molecules. J. Chem. Phys. 1996, 105 (15), 6505-6516.
27. Wang, F.; Ziegler, T., A simplified relativistic time-dependent density-functional theory formalism for the calculations of excitation energies including spin-orbit coupling effect. J. Chem. Phys. 2005, 123 (15), 154102.
28. Becke, A. D., Density‐functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98 (7), 5648-5652.
29. Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.; Pederson, M. R.; Singh, D. J.; Fiolhais, C., Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B: Condens. Matter 1992, 46 (11), 6671-6687.
30. Schott, E.; Zarate, X.; Arratia-Perez, R., Substituents effects on two related families of dyes for dye sensitized solar cells: [Ru(4,4'-R,R-2,2'-bpy)3]2+ and [Ru(4,4'-COOH-2,2'-bpy)(4,4'-R,R-2,2'-bpy)2]2+. J. Phys. Chem. A 2012, 116 (27), 7436-7442.
31. S. P. McGlynn, S. M. G., T. Azumi, M. Kinoshita, Molecular spectroscopy of the triplet state. Prentice-Hall 1969.
32. Takumi Kinoshita, J. T. D., Satoshi Uchida, Takaya Kubo and Hiroshi Segawa, Wideband dye-sensitized solar cells employing a phosphine-coordinated ruthenium sensitizer. Nat. Photon 2013, 7, 535-539.
33. Slovenski, Photovoltaic devices - Part 3: Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data. IEC 2016, 3, 219.
34. Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H., Dye-sensitized solar cells. Chem. Rev. 2010, 110 (11), 6595-6663.
35. Nazeeruddin, M. K.; Pechy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Gratzel, M., Engineering of efficient panchromatic sensitizers for nanocrystalline TiO2-based solar cells. J. Am. Chem. Soc. 2001, 123 (8), 1613-1634.
36. Zhang, L.; Cole, J. M., Dye aggregation in dye-sensitized solar cells. J. Mater. Chem. A 2017, 5 (37), 19541-19559.
37. Nguyen, T. D.; Lin, C. H.; Wu, C. G., Effect of the CF3 substituents on the charge-transfer kinetics of high-efficiency cyclometalated ruthenium sensitizers. Inorg. Chem. 2017, 56 (1), 252-260.
38. Li, C.; Wu, S. J.; Wu, C. G., Structural design of ruthenium sensitizer compatible with cobalt electrolyte for a dye-sensitized solar cell. J. Mater. Chem. A 2014, 2 (41), 17551-17560.
39. Kruger, J.; Plass, R.; Gratzel, M.; Cameron, P. J.; Peter, L. M., Charge transport and back reaction in solid-state dye-sensitized solar cells: A study using intensity-modulated photovoltage and photocurrent spectroscopy. J. Phys. Chem. B 2003, 107 (31), 7536-7539.
40. Pazoki, M.; Cappel, U. B.; Johansson, E. M. J.; Hagfeldt, A.; Boschloo, G., Characterization techniques for dye-sensitized solar cells. Energ Environ. Sci. 2017, 10 (3), 672-709.