Multifunctionalized Ruthenium‐Based Supersensitizers for Highly Efficient Dye‐Sensitized Solar Cells

Abstract

Dye-sensitized solar cells (DSCs) have been explored for photovoltaic applications because of their low cost and impressive conversion efficiency.[1] A DSC with 10 % efficiency was first demonstrated by Grätzel and co-workers using N3 (cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4-dicarboxylate) ruthenium(II)) as a sensitizer.[2] Progress in optimizing ruthenium-based sensitizers for DSCs has been focused primarily on enhancing the light-harvesting ability, and redshifting the metal-to-ligand charge transfer (MLCT) band. [3][4][5][6][7][8][9][10] These results can be achieved by extending the conjugation length of the anchoring or ancillary ligand. [11][12][13][14][15] Furthermore, retaining the photoinduced interfacial charge separation between the dye molecules and TiO 2 is also a crucial strategy to enhance the performance of DSCs. [16] This strategy is beautifully demonstrated by adding a hole-transport segment on the dye molecule in all-solid-state DSCs. [17,18] However, this concept could not be applied to liquid-state DSCs, [19,20] probably because the ruthenium sensitizers have relatively low light-harvesting capacity and large molecular size.We have shown [21,22] that thiophene-derived units are the good candidates for increasing the conjugation length of the ancillary ligand to increase the light-harvesting ability and red-shift the MLCT band of a ruthenium complex. Herein we reveal that thiophene-derived species can be functionalized easily with a alkyl-substituted hole-transport moiety, such as bis(heptyl)carbazole. Ruthenium complexes with ligands functionalized by thiophene, carbazole, and alkyl chains can be regarded as supersensitizers. The efficiency of a liquidstate DSC based on one of these supersensitizers is 9.72 %, which is 1.2 % higher than that (8.51 %) of the N3-based cell at the same fabrication and efficiency measuring conditions. This is the first demonstration that a carbazole moiety in the dye can enhance the performance of a liquid-state DSC. Furthermore, the terminal alkyl chains on the ancillary ligand were also modulated to explore the impact of the sensitizer size on the cell performance in the DSC. In situ photoelectrochemical measurements were used for the first time to study the intramolecular electron-transfer processes of the oxidized dye.The structures of the supersensitizers CYC-B6S and CYC-B6L are depicted in Figure 1. The electronic absorption spectra of these supersensitizers and N3 measured in DMF are displayed in Figure 2, and the optical data are summarized in Table 1. The absorption spectra of the supersensitizers show that the band centered at around 550 nm (which is the characteristic metal-to-ligand charge-transfer (MLCT) transition) is stronger and more red-shifted than that for N3. These results indicate that the spectral response of ruthenium

Kinetic pathway for interfacial electron transfer from a semiconductor to a molecule

“…Density functional theory (DFT) indicated that the methyl substituents in the xylyl bridge destabilized the planar configuration of the arylthiophene moiety by about 40 kJ mol -1 relative to the phenyl bridge. The extinction coefficients of the xylyl-bridged compounds were about half those with phenyl bridges, a behaviour that is also consistent with decreased conjugation 36,37 . Marcus-Hush analysis of the absorption spectra of the one-electron oxidized forms of these molecules revealed an approximate tenfold decrease in electronic coupling (H AB ) through the xylyl bridge.…”

Ultrafast dynamics at the zinc phthalocyanine/zinc oxide nanohybrid interface for efficient solar light harvesting in the near red region

“…In most cases, polypyridyl ruthenium complexes are likely choices for such applications [1][2][3][4]. While the complexes work reasonably well in visible light, the main drawback of such complexes is a lack of reasonable absorption in the near-IR region.…”

Novel organic dyes with anchoring group of barbituric/thiobarbituric acid and their application in dye-sensitized solar cells

“…After the successful exploration by Grätzel and co-worker [1,10], DSSCs based on Ru-photosensitizers, such as N3 and N719, have been extensively investigated and developed [11,12]. So far, the impressive solar-toelectrical power conversion efficiency values of $11% have been reported for the Ru sensitizers [11][12][13][14][15][16]. However, in addition to high cost of rare Ru metal, the ruthenium dyes featuring relatively low molar extinction coefficients and tedious purification processes [12].…”