Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Publication date: 1st March 2014
The quest for carbon neutral energy sources has recently focused on the great potential of solar energy;1–4 hence it has unchained a development in research and optimization of the different components of photovoltaic devices.5–10 Iodide-triiodide (I-/I3-) is currently the electrolyte system of choice in dye-sensitized solar cells (DSSCs), attributable to its conduction mechanism allowing quick regeneration of the dye, and also its complex charge transfer that translates in slow recombination kinetics and lower current dissipation; 7,8,11–13 despite the benefits there are also challenges to overcome regarding the practical incompatibility with several materials because of its corrosive character, loss of material and efficiency over time due to inherent volatility, competitive absorption of the solar radiation, and limitations in the dark current potential (VOC).14–20 In response to the I-/I3- disadvantages there has been several attempts to attain a viable alternative, one of the most successful approach falling into the field of organometallic-cobalt chemistry;21–25 following this development the objective of the present work is to synthetize and evaluate two cobalt complexes as a redox mediator for DSSCs: one tridentate ligand similar to the more traditional poly-pyridine systems, and the second one based on a β-diketiminate tetradentate ligand that introduces a six-membered chelate ring.
Both shuttles will be characterized by FT-IR, UV-Vis and NMR spectroscopy. Moreover, photoelectrochemical properties (Voc, IPCE, and Jsc) and electrochemical impedance will be measured for further comparison by theoretical calculations of shuttle redox potentials.
Development of alternative systems could open new venues for electrolyte-dye pairs with optimal energy-level pairing, improving stability and efficiencies, as demonstrated by several more positive redox potential reported in the literature.21,24,26–28
Figure 1. Scheme of general working principle of DSSCs.
(1) Ondersma, J. W.; Hamann, T. W. Recombination and Redox Couples in Dye-Sensitized Solar Cells. Coord. Chem. Rev. 2013, 257, 1533–1543. (2) Feldt, S. Alternative Redox Couples for Dye-Sensitized Solar Cells, Uppsala Universitet, 2013, pp. 13–21. (3) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Dye-Sensitized Solar Cells. Chem. Rev. 2010, 110, 6595–6663. (4) U.S. Department of Energy. SunShot Vision Study; 2012. (5) Hamann, T. W. The End of Iodide? Cobalt Complex Redox Shuttles in DSSCs. Dalton Trans. 2012, 41, 3111–3115. (6) Xie, Y.; Hamann, T. W. Fast Low-Spin Cobalt Complex Redox Shuttles for Dye-Sensitized Solar Cells. J. Phys. Chem. Lett. 2013, 4, 328–332. (7) Boschloo, G.; Hagfeldt, A. Characteristics of the Iodide/triiodide Redox Mediator in Dye-Sensitized Solar Cells. Acc. Chem. Res. 2009, 42, 1819–1826. (8) Yu, Z. Liquid Redox Electrolytes for Dye-Sensitized Solar Cells, École Polytechnique Fédérale de Lausanne, 2012, pp. 1–12. 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Efficient Non-Corrosive Electron-Transfer Mediator Mixtures for Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2006, 128, 9996–9997. (15) Hernández Redondo, A. Copper ( I ) Polypyridine Complexes : the Sensitizers of the Future for Dye-Sensitized Solar Cells ( DSSCs ), University of Basel, 2009, pp. 8–32. (16) Daeneke, T.; Kwon, T.-H.; Holmes, A. B.; Duffy, N. W.; Bach, U.; Spiccia, L. High-Efficiency Dye-Sensitized Solar Cells with Ferrocene-Based Electrolytes. Nat. Chem. 2011, 3, 211–215. (17) Xiang, W.; Huang, F.; Cheng, Y.-B.; Bach, U.; Spiccia, L. Aqueous Dye-Sensitized Solar Cell Electrolytes Based on the cobalt(II)/(III) Tris(bipyridine) Redox Couple. Energy Environ. Sci. 2013, 6, 121–127. (18) Spokoyny, A. M.; Li, T. C.; Farha, O. K.; Machan, C. W.; She, C.; Stern, C. L.; Marks, T. J.; Hupp, J. T.; Mirkin, C. A. Electronic Tuning of Nickel-Based Bis(dicarbollide) Redox Shuttles in Dye-Sensitized Solar Cells. Angew. Chem. Int. Ed. Engl. 2010, 49, 5339–5343. (19) Aribia, K. Ben; Moehl, T.; Zakeeruddin, S. M.; Grätzel, M. Tridentate Cobalt Complexes as Alternative Redox Couples for High-Efficiency Dye-Sensitized Solar Cells. Chem. Sci. 2013, 4, 454–459. (20) Hardin, B. E.; Snaith, H. J.; McGehee, M. D. The Renaissance of Dye-Sensitized Solar Cells. Nat. Photonics 2012, 6, 162–169. (21) Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency. Science 2011, 334, 629–634. (22) Kavan, L.; Yum, J.-H.; Graetzel, M. Optically Transparent Cathode for Co(III/II) Mediated Dye-Sensitized Solar Cells Based on Graphene Oxide. ACS Appl. Mater. Interfaces 2012, 4, 6999–7006. (23) Feldt, S. M.; Lohse, P. W.; Kessler, F.; Nazeeruddin, M. K.; Grätzel, M.; Boschloo, G.; Hagfeldt, A. 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