Alkoxy-substituted ZnII tetraarylporphyrinates with improved power conversion efficiency in DSSCs

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, Alessio Orbelli Biroli, 324
Publication date: 5th February 2015

The introduction of long alkoxy chains at the ortho-positions of the two opposite phenyl rings into the structure of meso-disubstituted push-pull Zn^II diarylporphyrinates, has been proved to be an efficient-design strategy to improve the power conversion efficiencies of this kind of dyes in DSSCs.¹< However, despite the interesting light-conversion efficiencies displayed by this series of meso push-pull Zn^II diarylporphyrinates,² a multistep synthesis is required reducing overall yields. On the contrary, tetraarylporphyrins are easy to achieve and functionalize in β-pyrrolic position by relatively few synthetic steps.³ Recently, some of us developed a straightforward synthetic route, which improves the overall yields of Zn^II-tetraarylporphyrinate dyes monosubstituted in β-pyrrolic position.⁴ Moreover, under the same DSSC fabrication conditions, these porphyrinic dyes have shown comparable or better light-conversion efficiencies compared to those of some correlated meso-disubstituted push-pull Zn^II diarylporphyrinates.⁵ Therefore, in this work we have introduced such design strategy, i. e. the introduction of long alkoxy chains, into the molecular structure of tetraarylporphirinates substituted in in β-pyrrolic position. In particular, we synthesized, characterized and investigated as sensitizers for DSSCs a series of β-substituted Zn^II-tetraarylporphyrinate dyes, bearing octyloxy chains at the ortho,ortho-, ortho,para- or ortho-positions of the four phenyl groups respectively.⁵ The alkoxy group position strongly influences their electronic absorption and electrochemical features. Improvements in power conversion efficiency ranging from 40% to 80% were obtained compared to a reference dye characterized by the presence of sterically bulky t-butyl groups in the meta-positions. The presence of relatively extended alkyloxy chains can prevent aggregation phenomena, but may also produce a lipophilic sphere around the pophyrinic core which makes dye loading difficult. In fact, a large amount of CDCA was necessary to make the TiO₂ surface a more lipophilic environment, in order to support dye loading. This fact is probably reflected in the low J_SC values obtained. For this reason we are investigating alkoxy chains of different lengths and nature, in order to find the right balance to prevent the aggregation and to improve dye loading.

1. (a) Li, L. L.; Diau, E. W. G., Porphyrin-sensitized solar cells. Chem. Soc. Rev. 2013, 42, 291-304; (b) 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. 2. (a) Yella, A.; Mai, C.-L.; Zakeeruddin, S. M.; Chang, S.-N.; Hsieh, C.-H.; Yeh, C.-Y.; Grätzel, M. Molecular Engineering of Push–Pull Porphyrin Dyes for Highly Efficient Dye-Sensitized Solar Cells: The Role of Benzene Spacers. Angew. Chem. Int. Ed. 2014, 53, 2973-2977; (b) Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; CurchodBasile, F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; NazeeruddinMd, K.; Grätzel, M. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nat. Chem. 2014, 6, 242-247. 3. (a) Campbell, W. M.; Burrell, A. K.; Officer, D. L.; Jolley, K. W. Porphyrins as light harvesters in the dye-sensitised TiO2 solar cell. Coord. Chem. Rev. 2004, 248, 1363-1379; (b) Stephenson, A. W. I.; Wagner, P.; Partridge, A. C.; Jolley, K. W.; Filichev, V. V.; Officer, D. L. An alternative synthesis of β-pyrrolic acetylene-substituted porphyrins. Tetrahedron Lett. 2008, 49, 5632-5635. 4. Di Carlo, G.; Orbelli Biroli, A.; Pizzotti, M.; Tessore, F.; Trifiletti, V.; Ruffo, R.; Abbotto, A.; Amat, A.; De Angelis, F.; Mussini, P. R. Tetraaryl ZnII Porphyrinates Substituted at β-Pyrrolic Positions as Sensitizers in Dye-Sensitized Solar Cells: A Comparison with meso-Disubstituted Push–Pull ZnII Porphyrinates. Chem. Eur. J. 2013, 19, 10723-10740. 5. Orbelli Biroli, A.; Tessore, F.; Vece, V.; Di Carlo, G.; Mussini, P. R.; Trifiletti, V.; De Marco, L.; Giannuzzi, R.; Manca, M.; Pizzotti, M., Highly improved performance of ZnII tetraarylporphyrinates in DSSCs by the presence of octyloxy chains in the aryl rings. Journal of Materials Chemistry A 2015, 3, 2954-2959.

© FUNDACIO DE LA COMUNITAT VALENCIANA SCITO