含噻吩吸光基團之高效能釕金屬光敏染料於染料敏化太陽能電池之應用

Abstract

本論文中成功的設計與合成出七個一系列的新型釕金屬光敏染料JF-1□7。從比較釕金屬光敏染料JF-1與JF-2可知，JF-2相對於JF-1具有較高的光電轉換效率。由於含有噻吩的JF-2在吸收光譜中具有較寬廣的金屬到配子電荷轉換（MLCT）分佈、較強的電荷注入與再生驅動力，並且其最高佔有分子軌域（HOMO）與最低未佔分子軌域（LUMO）分別分佈於NCS□及酸根，有利於電子的轉移，因此將噻吩用於光敏染料的結構修飾上可大幅的提升其光電轉換效率。而比較釕金屬光敏染料JF-3與JF-4可知，若在結構上加入良好的推電子基團，如JF-3（在JF-2的結構中加入硫二苯銨），則可增強與加寬吸收光譜中的莫耳吸收係數、降低電池中的電阻、提升電子的生命期與增加染料分子的光電轉換效率。在釕金屬光敏染料JF-5□7中，染料JF-5具有直線並共平面的聯噻吩吸光基團，染料分子於二氧化鈦表面的吸附量與吸收光譜中MLCT的吸收強度可達最佳化，因此JF-5具有最佳的光電轉換效率。以上的討論中顯示噻吩與推電子基團可用於提升光敏染料的光電轉換效率，並且最佳化了吸光基團的共軛長度，提供了直接有效的方式來設計具有高效能的釕金屬光敏染料。

A series of seven new ruthenium photosensitizers, [Ru(dcbpy)(opip)(NCS)2] (JF-1, dcbpy = 4,4'-dicarboxylic acid-2,2'-bipyridine, opip = 2-(4-octylphenyl)-1H-imidazo [4,5-f][1,10]phenanthroline), [Ru(dcbpy)(otip)(NCS)2] (JF-2, otip = 2-(5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(dcbpy)(potip)(NCS)2] (JF-3, potip = 2-(4-(10H-phenothiazin-10-yl)-5-octyl- thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(dcbpy)(dpotip)(NCS)2] (JF-4, dpotip = 2-(4-(N,N-diphenylamino)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f] [1,10]phenanthroline), [Ru(dcbpy)(obtip)(NCS)2] (JF-5, obtip = 2-(5-octyl-(2,2'- bithiophen)-5'-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(dcbpy)(ottip)(NCS)2] (JF-6, ottip = 2-(5-octyl-2,2',5',2''-terthiophene-5''-yl)-1H-imidazo[4,5-f][1,10] phenanthroline) and [Ru(dcbpy)(dottip)(NCS)2] (JF-7, dottip = 2-(2,3-di- (5-octylthiophen-2-yl)thiophen-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), were designed and synthesized in a typical one-pot reaction. The power-conversion efficiency of JF-2 was 20% higher than that of JF-1, due to modification of the ancillary ligand with a thiophene moiety. The greater device performance of JF-2 compared to JF-1 was caused from the broader MLCT distribution, the appropriate localization of the frontier orbitals and the stronger driving force of the charge injection and regeneration. The multifunctionalized ruthenium dye JF-3 incorporating an excellent electron-donating phenothiazine shows the superior DSCs performance (9.1%) compared to N3 (8.8%) and JF-4 (7.9%). The comparison of electron-donating phenothiazine and N,N-diphenylamino groups utilized in multifunctionalized molecular architecture for ruthenium dyes demonstrated that the phenothiazine group can efficiently increase and broaden the molar extinction coefficient of band II in the UV□vis absorption spectrum, reduce the device resistances, rise the electron lifetime, and enhance the power-conversion efficiency. The ruthenium sensitizer JF-5 incorporating a linear and planar 2,2'-bithiophene antenna showed the best DSCs performance (9.5%) compared to N3 (8.8%), JF-6 (8.7%), and JF-7 (6.4%). The difference in the performance of these sensitizers demonstrated that elongating the linear and planar light-harvesting antenna results in an enhancement in MLCT intensity, but a reduction in the quantity of dye-loading. The findings in the structural comparision of these ruthenium photosensitizers, JF-1□7, not only open an alternative strategy for the design of sophisticated 1,10-phenanthroline-based ligands and multifunctionalized ancillary ligands for improving the photovoltaic performance of ruthenium sensitizers, but also optimize light-harvesting antennas and point to a promising direction for molecule engineering in DSCs.