Ru complexes of thienyl-functionalized dipyrrins as NCS-free sensitizers for the dye-sensitized solar cell

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
Chemical Communications (Impact Factor: 6.83). 07/2012; 48(70):8790-2. DOI: 10.1039/c2cc34311h
Source: PubMed


We report the first case of Ru(II) dipyrrinates employed as dyes in dye-sensitized solar cells. These complexes exhibit panchromatic light harvesting that results in significant DSSC current densities, rendering them promising for photovoltaic applications. Adjustment of the lowest excited state energy is required to boost the power conversion efficiency.

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    ABSTRACT: Two ruthenium complexes featuring bulky ancillary ligands, XS48 and XS49, were synthesized and studied as dyes in dye-sensitized solar cells (DSCs). Both dyes exhibit higher solar-to-electrical energy conversion efficiency when compared to a commonly used N3 sensitizer under the same conditions. To examine the influence of the bulky ancillary ligands and alleviate the electron recombination in cells, we have developed a dual functioned truxene-based co-adsorbent (MXD1) as an alternative candidate to chenodeoxycholic acid (CDCA). This co-adsorbent not only effectively shields the back electron transfer from the TiO2 to I3- ions, but also enhances the light harvesting ability in the short wavelength regions. The photovoltaic performance of XS48-sensitized DSC was independent of the co-adsorbents, whilst XS49 with large bulky ancillary ligand presented better performance when co-adsorbent was employed. Interestingly, the simultaneous adsorption-to-sequential adsorption of XS48/49 and MXD1 has caused a notably improved photovoltage, which can be primarily ascribed to the enhanced dye adsorption and retardation of charge recombination. These results not only provide a new vision on how ancillary ligands affect the performance of ruthenium complexes but also open up a new way to achieve further efficiency enhancement of ruthenium complexes.
    No preview · Article · Dec 2012 · ACS Applied Materials & Interfaces
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    ABSTRACT: While they may have been overshadowed by the brightness of their BODIPY analogues, dipyrrin based metal complexes have recently appeared as novel interesting luminescent species owing to the development of various synthetic strategies for the preparation of such coordination compounds with appreciable quantum yields and tuneable emission wavelength. Not only the rigidification brought by functionalization of the dipyrrin backbone either at position 5 or positions 1 and 9, but also a careful choice of the ligands present in the complex coordination sphere have been key in these developments leading to bright and stable emitters. At position 5, equivalent to the meso position of a porphyrin, introduction of peripheral groups, such as the mesityl moiety hindering the rotational freedom of this unit, has been particularly targeted, hence limiting a favourable non-radiative deactivation pathway. Regarding positions 1 and 9, their proximity to the metal center has prompted their use for the introduction of additional coordinating units, thus providing a pseudo-macrocyclic character to the ligands. In this perspective article, the different types of modification of dipyrrin as well as the resulting metal complexes incorporating these derivatives, their photophysical properties and their applications in sensing and materials science are reviewed.
    No preview · Article · Apr 2013 · Dalton Transactions
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    ABSTRACT: Three Ru(II) dipyrrinate complexes, [Ru(bpy)2(3-TDP)](PF6) (1), [Ru(H2dcbpy)(Hdcbpy)(3-TDP)] (2), and [Ru(H2dcbpy)(Hdcbpy)(TPADP)] (3) (bpy = 2,2′-bipyridine; dcbpy = 4,4′-dicarboxylato-2,2′-bipyridine; 3-TDP = 3-thienyl-dipyrrinate; TPADP = triphenylamino-dipyrrinate), have been synthesized and characterized by electrochemical and photophysical methods as well as by theoretical electronic structure calculations on the DFT level. The complexes exhibit panchromatic light harvesting due to complementary ligand-based absorption around 450 nm and metal-to-ligand charge transfer (MLCT) absorption around 530 nm. Complexes 2 and 3 have been investigated as potential sensitizers for the dye-sensitized solar cell (DSSC). Time-dependent DFT calculations reveal the preferential localization of an excited-state electron on the H2dcbpy ligands, leading to a favorable scenario for electron injection from these anchoring ligands into TiO2. Solution-phase transient absorption spectroscopy was used to follow the excited state dynamics of methyl-ester derivatives of 2 and 3. Excitation with a 400-nm laser pulse resulted in two bleaches centered at 460 and 540 nm and corresponding to the ligand-based and MLCT transitions, respectively. A rapid 2 ps loss of the ligand based bleach corresponded with a growth of the MLCT bleach that were interpreted as the result of vibrational relaxation between metal-centered and ligand-centered frontier orbitals. The electron-injection kinetics were studied on dyes 2 and 3 anchored on the TiO2 surface. The excited state electron-injection yield and incident photon-to-current efficiency were dramatically suppressed by addition of tert-butylpyridine (TBP), indicating that the lowest excited state was positioned close in energy to the TiO2 acceptor states. Nevertheless, the injection yield measured with 416-nm excitation was less sensitive to the TBP concentration than that measured with 532-nm excitation, thus suggesting the possibility of hot-electron injection from the upper excited states generated by the ligand-based excitations. Based on the findings of this study, a pathway is proposed for improving the electron-injection yield of Ru-dipyrrinate dyes and increasing the power-conversion efficiency of the DSSC incorporating these dyes.
    No preview · Article · Aug 2013 · The Journal of Physical Chemistry C
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