Synthesis and Application of New Ruthenium Complexes Containingβ-Diketonato Ligands as Sensitizers for Nanocrystalline TiO₂Solar Cells

Abstract

Five heteroleptic ruthenium complexes having differentβ-diketonato ligands, [Ru(tctpy)(dppd)(NCS)] (1), [Ru(tctpy)(pd)(NCS)] (2), [Ru(tctpy)(tdd)(NCS)] (3), [Ru(tctpy)(mepd)(NCS)] (4), and [Ru(tctpy)(tmhd)(NCS)] (5), where tctpy = 4,4′,4′′-tricarboxy-2,2′:6′,2′′-terpyridine, pd = pentane-2,4-dione, mepd = 3-methylpentane-2,4-dione, tmhd = 2,2,6,6-tetramethylheptane-3,5-dione, tdd = tridecane-6,8-dione, and dppd = 1,3-diphenylpropane-1,3-dione, were synthesized and characterized. These heteroleptic complexes exhibit a broad metal-to-ligand charge transfer absorption band over the whole visible range extending up to 950 nm. The low-energy absorption bands and theE (Ru3+/2+) oxidation potentials in these complexes could be tuned to about 15 nm and 110 mV, respectively, by choosing appropriateβ-diketonate ligands. Molecular orbital calculation of complex1shows that the HOMO is localized on the NCS ligand and the LUMO is localized on the tctpy ligand, which is anchored to the TiO2nanoparticles. Theβ-diketonato-ruthenium(II)-polypyridyl sensitizers, when anchored to nanocrystalline TiO2films for light to electrical energy conversion in regenerative photoelectrochemical cells, achieve efficient sensitization to TiO2electrodes with increasing activity in the order5<4<3≈2<1. Under standard AM 1.5 sunlight, the complex1yielded a short-circuit photocurrent density of 16.7 mA/cm2, an open-circuit voltage of 0.58 V, and a fill factor of 0.64, corresponding to an overall conversion efficiency of 6.2%. A systematic tuning of HOMO energy level shows that an efficient sensitizer should possess a ground-state redox potential value of >+.53 V versus SCE.

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

“…A series of β-diketonate ligands ( 31 in Figure 25 ) was investigated by Islam et al [ 119 , 120 , 121 , 122 , 123 , 124 , 125 ] as ancillary ligands alternative to thiocyanates in the BD structure. The strong σ-donating nature of the negatively-charged oxygen donor atom destabilizes the ground-state energy level of the dye compared to BD, leading to a shift of the MLCT transitions to lower energies.…”

“…A very efficient sensitization ( η = 9.1%; TiO 2 : 20 μm, dye: 0.2 mM CH 3 CN / t -butanol 1:1 with 20 mM DCA, electrolyte: 0.6 M DMPII, 0.05 M I 2 , 0.1 M LiI, 0.07 M t-bupy in CH 3 CN), with an IPCE greater than 80% in the whole visible range extending up to 950 nm was obtained. Further substituted β-diketonate ligands were tested in 2011 [ 119 ] showing a great potential to tune the photochemical properties.…”

Organometallic Compounds for Dye‐Sensitized Solar Cells (DSSC)

“…Moreover, whether iodine regenerates the dye practically at 100% yield is another challenge [48]. The synthesis of a series of ruthenium polypyridyl complexes allowing the systematic tuning of the LUMO sensitizer for easy injection of the excited electrons to the semiconductor oxide and HOMO energy level of the sensitizer for efficient dye regeneration has been reported in the literature [49]. The possibility of tuning the MLCT energy has led to the preparation of many different organocompounds that have been investigated for semiconductor sensitization.…”

A New Heteroleptic Biquinoline Ruthenium(II) Sensitizer for Near‐IR Sensitization of Nanocrystalline TiO2

“…(1) and reported that these solar cells have an enhanced red response in the near-IR region, but the solar cell performance was decreased due to the poor electron injection efficiency on to TiO 2 [8]. As a part of our research program in the development of new photosensitizers [9][10][11][12][13][14], we have strategically designed a heteroleptic dye SPS-02 ( Figure 1) having both 4,4 ′ -di-tert-butyl-2-2 ′ -dipyridyl and 4,4 ′ -dicarboxy-2,2 ′ -biquinoline in the same molecule, which exhibits better performance in the IR region.…”