Synthesis and Applications of Crosslinkable Ruthenium Complex on Dye-sensitized Solar Cells
Date Issued
2011
Date
2011
Author(s)
Liu, Ken-Yen
Abstract
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.
Subjects
dye-sensitized soalr cell
crosslinkable ruthenium complex
adsorption behavior
Li+-coordination capability
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