可交聯型釕金屬錯合物在染料敏化太陽能電池上的 合成與應用

Abstract

染料敏化太陽能電池為各類有機太陽能電池中，目前效率最好的一種。染料的開發正是其中最關鍵的一環，在本研究中，利用在釕金屬錯合物之雙吡啶配位基上修飾以可進行聚合或交聯反應之不同官能基，在染料吸附後反應，使其能成為一穩定且減低脫附機率的染料層。 在第一部分中，合成了帶有乙烯基長碳鏈取代的釕金屬錯合物染料Ru-C (Ru(4,4’-dicarboxylic acid)(4,4’-bis(diundec-1-ene)-2-2’-bipyridine) -(NCS)2 ) ，除了利用NMR、IR、UV-Vis光譜等方式鑑定其結構外，並藉用DLS與AFM觀察染料吸附行為，發現染料分子先以類似微胞顆粒或是大顆粒聚集的型態分散吸附在TiO2上，之後染料分子會慢慢均勻吸附到TiO2未被覆蓋的表面，當達到平衡穩定之後，最後可觀察出染料完全覆蓋TiO2，形成高度約一個染料分子的均勻表面。再進一步使用UV-Vis光譜分析比較N3與Ru-C吸附於TiO2之吸附量。 結果發現，Ru-C在12-24小時達單層染料分子，為直立於TiO2表面上的奈米結構，因N3帶有四個羧基化吡啶配位鍵，容易平躺於TiO2表面上，使單一分子表面積較Ru-C為大，在吸附24小時內可達單層吸附。 接著利用UV-Vis與IR光譜來進行證明Ru-C與methyacrylic acid( MAA)或自行合成的帶丙烯酸基離子液體單體(AMImI)在吸附上TiO2後的反應性研究。 Ru-C在染料敏化太陽能電池上除了在使用一般乙腈液態電解質可達5.94%外，使用MAA讓Ru-C染料更可以在二氧化鈦表面聚合，不易從二氧化鈦表面脫附而有不錯的長期穩定性。至於Ru-C與N3染料的元件表現差異也可以利用IMVS/IMPS等分析來與其吸附型態做連結。

第二部分是合成另一帶有可進行聚合反應之苯乙烯官能基的釕金屬染料Ru-S (Ru (4,4’-dicarboxylic acid) (4,4'-bis((4-vinylbenzyloxy)methyl) -2,2'-bipyridine-(NCS)2 )。同樣地利用NMR、IR、UV-Vis光譜等方式鑑定其結構外，也進一步經由研究吸附在TiO2表面後帶有氧乙烷鏈段的的triethyleneglyco- dimethacrylate (TGDMA)與帶有丙烯酸基的離子液體AMImI進行共聚合反應後的UV-Vis光譜脫附實驗，證明其增進與TiO2鍵結的穩定性。 在太陽能電池元件的表現上，以3-methoxypropyl -nitrile (MPN)為溶劑的液態電解質時以不同濃度的TGDMA與AMImI進行表面聚合改質後，可以將原本7.53%的效率分別提升至8.32%與8.28%。而在以polymethacrylate膠態電解質製備的元件時則能將效率從6.96%分別增加至7.53%與7.4%。 另一部分則以變化液態電解質中Li+ (LiClO4或LiI)的濃度來觀察Ru-S染料元件的開環電壓(Voc)、短路電流(Jsc)與效率表現。 而Voc隨Li+濃度的變化，從吸附在TiO2上Ru-S染料的IR光譜實驗可證明Ru-S染料本身即具有螯合Li+減緩因提高Li+造成Voc下降的能力。 IMVS/IMPS與EIS的技術可以分別說明charge recombination的機率增加對於改質前後Voc的影響，而IPCE圖譜與charge extraction 的分析則支持了改質後元件的Jsc上升的結果。

Dye sensitized solar cells are generally agreed to have the highest power efficiency among the organic solar cells in the present time. Notably, the ruthenium dyes play the most important role for their high efficiency. In this research, by modifying the bipyridine ligand on the ruthenium complex with reactive functional groups for polymerization or crosslink, we are able to stabilize the ruthenium dye on the TiO2 surface in service. In the first part of this research, Ru(2,2’-bipyridine-4,4’-bicarboxylic acid)(4,4’-bis(11-dodecenyl)-2,2’-bipyridine)(NCS)2, denoted as Ru-C, for titanium oxide nanocrystalline based solar cells was synthesized. The structure characterization of Ru-C was conducted by NMR, IR, and UV-Vis spectroscopies and its adsorption mechanism on TiO2 was studied by atomic force microscopy. The results revealed that the adsorption of dye molecules onto TiO2 surface began in vesicle form, followed by the dissolution of the condensed dyes located away from TiO2, resulting the center-hollowed vesicle configuration. With the increase of time, the dye molecules adsorbed onto the uncovered TiO2 surface, leading to a homogeneous surface with an approximate height of one dye molecule. Then, we measured the adsorptive amount of Ru-C and N3 on the TiO2 at different adsorbing time interval with UV-vis absorption spectrascopy. Through calculation, 12-24 hr adsorption could cover a monolayer with the Ru-C molecules tilted vertically with respect to the TiO2 surface. Because N3 had four carboxylic acid groups, it easily lied in flat form on the surface of TiO2. This is the reason why the surface coverage of N3 on TiO2 is larger than that of Ru-C. The adsorptive amount of N3 on TiO2 surface reached a monolayer within 24 h. The crosslinking properties of Ru-C by itself and with MAA and 1-methyl-3-[2-[(1-oxo-2-propenyl)oxy] -ethyl]-imidazilium iodide (denoted as AMImI) were investigated by Fourier-transform infrared and UV-Vis absorption spectroscopies. For the performance of DSSCs, Ru-C with ACN liquid electrolyte attained 5.94% power conversion efficiency. By further copolymerizing with MAA or AMImI, a longer storage life could be achieved. The polymerized AMImI was then used to gel the MPII ionic liquid electrolyte systems to fabricate the gel-type DSSC with the conversion efficiency reaching 5.34%. The difference of device performance between Ru-C and N3 can also be correlated to the morphology difference during the adsorption process on the basis of the electrochemical analysis, such as IMVS/IMPS and EIS etc. In the second part, another crosslinkable ruthenium complex with styryl groups on the bipyridine ligand, denoted as Ru-S was synthesized and characterized by NMR, IR, and UV-Vis spectroscopies. Its copolymerization or crosslink properties with AMImI and triethyleneglycodimethacrylate (TGDMA) were measured by UV-Vis spectroscopy. By using MPN based liquid electrolyte, the efficiency of DSSCs using Ru-S to crosslink with optimized amounts of TGDMA and AMImI increased from 7.53% to 8.32% and 8.28%, respectively. However, using the PMA-gelled electrolyte system, the device performance was raised from 6.96% to 7.53% and 7.4%. On the other hands, these DSSC systems with various Li+ concentrations in liquid electrolytes were studied. The Li+-coordination capability of Ru-S was then investigated by IR spectroscopy, which was used to explain the slow decreasing trend of Voc as the Li+ concentration was increased. The IMVS/IMPS and EIS techniques were used to realize the relationship between the charge recombination and the Voc difference of devices before and after cross-linked with functional crosslinkers and the improvement of Jsc in devices was further supported by the IPCE spectras and charge extraction experiments.