發展新型異配位釕金屬光敏染料於高效能染料敏化太陽能電池之應用

Development of New Heteroleptic Ruthenium Photosensitizers for Use in Efficient Dye-Sensitized Solar Cells

呂宗展(Zong-Zhan Lu)

指導教授 ： 林英智

共同指導教授 ： 呂光烈(Kuang-Lieh Lu)

國立臺灣大學/理學院/化學研究所/博士(2016年)

https://doi.org/10.6342/NTU201610291

摘要

染料敏化太陽能電池被視為一種高效能的綠色能源元件，它甚至可以在陽光低照度或室內燈具的照明下運作，因此，可以安裝在各式各樣的位置，作多樣性的應用。本論文成功地設計與合成出五個釕金屬光敏染料JF-2t，Z1，Z2，Z3，Z4，並將之應用於染料敏化太陽能電池。另外，也對染料做基本光物理與電化學性質的探討以及理論計算其軌域分佈及吸收光譜。含多併噻吩類單元的光敏染料Z1與Z2相對於含單一噻吩的染料JF-2t與市售染料N3有較強的光收成能力。在標準的AM1.5G光照下，Z1 (8.70%)與Z2 (8.15%)所製成的電池元件比JF-2t (7.85%)與N3 (7.40%)的元件光電轉換效率高。Z1電池元件的光電表現優於Z2電池元件，主要來自於Z2染料分子在光電極的二氧化鈦膜上的吸附量較低，因此元件的二氧化鈦表面包覆度不好以及暗電流較高的緣故，此可藉由電化學阻抗數據來證明。從比較多併噻吩單元於釕金屬光敏染料的最佳長度，發現多併噻吩單元可適用於設計與發展高效能染料敏化太陽能電池。因此進一步以鄰二氮菲為輔助配位基底，再接上多聯噻吩單元，再以多電子己烷硫為末端基的吸光團合成出兩個光敏染料Z3與Z4。從兩者理論計算所得的電子吸收光譜，發現Z3染料吸收較長波長光的能力比Z4強，能有效將電子由金屬中心轉移到錨固配位基上，再注入到二氧化鈦光電極。Z4染料的輔助基底鄰二氮菲聯接較長多聯噻吩單元時，會有較嚴重的不共平面情況，使得無法有效的延伸π共軛系統，因此吸光波段較短。由此，我們可以合理的推測Z3染料所製成的染敏元件，其光電轉換效率會優於以Z4為染料所之元件。

關鍵字

染料 ； 太陽能電池 ； 釕金屬 ； 異配位錯合物 ； 噻吩 ； 多併噻吩 ； 光電轉換效率最佳化 ； 阻抗測量儀

並列摘要

Dye-sensitized solar cells (DSSCs) have recently emerged as efficient green energy sources that can operate even under conditions of limited sunlight or indoor lighting, and, hence, can be installed at a wide variety of locations for various applications. Five new ruthenium photosensitizers, Ru(Hdcbpy)(otip)(NCS)2]-•0.5[H]+• 0.5[N(C4H9)4]+ (JF-2t, H2dcbpy = 4,4'-dicarboxy-2,2'-bipyridine, otip = 2-(5-octyl-thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(Hdcbpy)(ottip)(NCS)2]-•0.5[H]+•0.5[N(C4H9)4]+ (Z1, ottip = 2-(5-octyl- thieno[3,2-b]thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(Hdcbpy)(odttip)(NCS)2]-•0.5[H]+•0.5[N(C4H9)4]+ (Z2, odttip = 2-(6-octyl- dithieno[3,2-b:2′,3′]thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(H2dcbpy)(bhttp)(NCS)2]-•0.6[H]+•0.4[N(C4H9)4]+ (Z3, bhttp = 4,7-bis(2- hexylthiothiophen-5-yl)-1,10-phenanthroline, and [Ru(H2dcbpy)(bhtbtp)(NCS)2]-•0.67[H]+•0.33[N(C4H9)4]+ (Z4, bhtbtp = 4,7-bis(5-hexylthio-2,2′-bithiophen-5′-yl)-1,10-phenanthroline, for use in DSSCs applications were synthesized. The compounds were photophysically and electrochemically characterized and density functional theory investigations were carried out. The fused-thiophene-based Z1 and Z2 had stronger light-harvesting capabilities compared to the nonfused-thiophene analogue, JF-2t, and a standard N3 dye. The power-conversion efficiency of the Z1- and Z2-sensitized solar cells were superior (8.70% and 8.15%) to the JF-2t and N3-sensitized solar cells (7.85% and 7.40%, respectively) under standard AM1.5G full sunlight irradiation. The photovoltaic performance of Z1 was better than Z2, primarily due to the fact that the level of dye loading of the Z1-based cells was higher and charge recombination was less, as evidenced by EIS data. This study not only demonstrates the excellent power-conversion efficiency of such fused-thiophene-incorporated ruthenium sensitizers but also points to the promise that fused-thiophene antennas might be useful molecules for use in the engineering of ruthenium dyes for DSSCs. Moreover, two new heteroleptic phenanthroline-based ruthenium dyes, Z3 and Z4, incorporating two light-harvesting oligothiophene antennas with electron-rich hexylthio-terminal chains were designed and synthesized. In the calculated electronic spectra, Z3 exhibited a red-shift and the MLCT transition for efficient electron injection was lower than Z4, in which longer oligothiothiophene antennas had been incorporated. This outcome can be attributed to the noncoplanar link between a phenanthroline base and the oligothiophene antennas in the computed molecular structure. Therefore, Z3-based cells can be expected to have superior power-conversion efficiency than Z4-based cells.

並列關鍵字

Dyes ； Solar cells ； Ruthenium ； Heteroleptic complexes ； Thiophene ； Fused-thiophene ； Optimization of the power-conversion efficiency ； Impedance spectroscopy

參考文獻

(2) Grätzel, M. Nature 2003, 421, 586.

(3) Mitchinson, A. Nature 2008, 455, 9.

(4) Grätzel, M. Acc. Chem. Res. 2009, 42, 1788.

(5) Hurd, F.; Livingston, R. J. Phys. Chem. 1940, 44, 865.

(11) Grätzel, M. Nature 2001, 414, 338.