HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 291
C148 - New Efficient and Tunable Ruthenium Photosensitizer for Dye Sensitized Solar
Cells
Robson Raphael Guimarães, André Luis Araújo Parussulo, Henrique Eisi Toma, Koiti Araki
Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, BR
Dye sensitized solar cells (DSSCs) 1 are one of the most interesting alternative renewable
energy sources because delivers relatively high energy conversion efficiency and its simple
fabrication. However, among all dyes tested for such purpose [Ru(dcbH2)2L2] complex
derivatives, where dcbH2= 2,2’-bipyridine-4,4’-dicarboxilic acid and L are π-donor ligands show
the highest performance. In fact, the derivatives where L = SCN – and different degrees of
deprotonation were shown to be the best photosensitizers. Benzotriazol attracted our
attention because is a strong donor ligand and exhibits an additional acid-base site that can be
used to tune its properties and adequate the complex excited state energy 2 .
Figure 1 Absorbance spectrum of the [Ru(4,4'-dicarboxy-2,2'-piridine)2(benzotriazole)2](PF6) and two successive
deprotonation products (a) and photoaction spectrum compared with the N719 dye (b).
Thus, we describe in this work the synthesis, characterization and photosensitizing
properties of the [Ru(dcbH2)2(btzH)2] complex, where btz= benzotriazole, in DSSCs. Elemental
analysis for C36H36F6O8N10PRu·4H2O, Exp. (Calc.): %C 41,88(41,39); %H 3,41(3,28); %N 12,46
(13,41). Only the molecular peak with the characteristic isotopomeric distribution was
observed in the mass spectrum at m/z 827.1, consistent with the
[Ru(dcbpyH)(dcbpyH2)(btzH)2] + species. Its UV-vis spectrum was sensitive to the solution pH,
exhibiting three acid-base equilibria in aqueous solution whose pKa’s were determined to be
3.1, 6.4 and 12. The [Ru(dcbH2)2(btzH)2] species exhibits metal-to-ligand charge-transfer bands
(MLCT bands) at 488 and 359 nm, in addition to a band at 309 nm with a shoulder at 297 nm
assigned to 4,4’-dicarboxy-2,2’-bipyridine ligand p(pi)→p(pi)* transition. 3 The deprotonation of
the btzH ligands (pKa = 6.4 and 12.0) led to the batochromic shifts (Figure 1a) of the MLCT
bands as a consequence of the enhanced π-donor properties and rise of the HOMO.
The cyclic voltammograms of the complex in aqueous solution at pH 9.5 presented a
reversible pair of waves at E1/2 = 0.8, assigned to the Ru(III/II) redox pair. The IPCE pattern of all
cells showed a maximum around 500 nm and a shoulder at 600 nm, covering all the visible
range from 400 to 650 nm. Interestingly the IPCE curves were only slightly lower than the
results obtained with cells prepared with the N719 dye, suggesting that both have similar solar
energy conversion efficiencies. However, it is important to remember at this point that the
electron injection properties of the new ruthenium complex dye can be tuned by
deprotonation, enhancing the electron injection kinetics and hole transfer properties,
improving the solar light harvesting efficiency.
© SEFIN 2012