On the Role of the Anchoring Unit in the Efficiency of Pyranoanthocyanin-based Dye-Sensitized Solar Cells

Ana Lucia Pinto^a, Luis Cruz^b, Vânia Gomes^b, Hugo Cruz^a, Giuseppe Calogero^c, Victor de Freitas^b, A. Jorge Parola^a, Fernando Pina^a, J. Carlos Lima^a

^aUniversidade NOVA de Lisboa, LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, 2829-516 Caparica, Portugal

^bLAQV-REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.

^cCNR, Instituto per i Processi Chimico-Fisici, Sede di Messina, Italy., Salita Sperone, C. da Papardo, I-98158 Faro Superiore Messina, Italy

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)

Roma, Italy, 2020 May 12th - 14th

Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo

Oral, Ana Lucia Pinto, presentation 050
DOI: https://doi.org/10.29363/nanoge.hopv.2020.050
Publication date: 6th February 2020

Dye-Sensitized Solar Cells (DSSCs) are photovoltaic devices based on the sensitization of wide band-gap semiconductor electrodes with dyes absorbing visible light. Following the work of Grätzel, several types of pigments such as the original ruthenium(II) complex,[1] and organic dyes,[2] have been used as light absorbers. The first reported DSSC using natural anthocyanin dyes extracted from blackberries displayed a conversion yield of 0.56%.[3] Anthocyanins are the main polyphenolic dyes found in young red wines, which are transformed into more stable structures such as pyranoanthocyanins, during wine ageing and maturation. While anthocyanins practically lose their red color between pH 1 and 5, as a result of the formation of colorless hemiketals, their relative compounds pyranoanthocyanins are more resistant to hydration and keep colour in the visible over a wide pH range.[4] Thus, they constitute a photosensitizer family with great potential for bio-inspired DSSCs. Still, the best known efficiency reported so far using this family of compounds is 0.006% for cyanidin-3-O-glucoside-pyruvic acid adduct.[5]

When considering naturally occurring dyes, betalains which contain carboxylates as anchoring groups show higher efficiencies compared to anthocyanins.[6] This led to the idea that carboxylic linkage was essential in order to have strong electronic coupling and rapid forward and reverse electron transfer reactions between the dye and the DSSC.[6] In this work, a series of bio-inspired pyranoanthocyanin derivatives were designed, synthesized and applied for the first time as dye sensitizers in DSSCs. Furthermore, both anchoring groups (carboxyl and catechol) were compared within closely related molecules with the same pyranoflavylium core. A relation was established between dye structure and cell efficiency. Specifically, the presence of the catechol unit was shown to increase electron injection to the TiO₂ semiconductor. An overall efficiency of 1.15% was obtained for the best performing compound, with no further optimization.

References:

[1] Wang, Q., Moser, J.-E. & Grätzel, M. Electrochemical impedance spectroscopic analysis of dye-sensitized solar cells. J. Phys. Chem. B. 2005, 109, 14945–14953.

[2] Calogero, G., Sinopoli, A., Citro, I., Di Marco, G., Petrov, V., Diniz, A. M., Parola, A. J. & Pina, F. Synthetic analogues of anthocyanins as sensitizers for dye-sensitized solar cells. Photochem. Photobiol. Sci. 2013, 12, 883–94.

[3] Cherepy, N. J., Smestad, G. P., Grätzel, M. & Zhang, J. Z. Ultrafast Electron Injection: Implications for a Photoelectrochemical Cell Utilizing an Anthocyanin Dye-Sensitized TiO2 Nanocrystalline Electrode. J. Phys. Chem. B. 1997, 101, 9342–9351.

[4] Cruz, L., Sousa, J. L. C., Marinho, A., Mateus, N. & de Freitas, V. Synthesis and structural characterization of novel pyranoluteolinidin dyes. Tetrahedron Lett. 58, 159–162 (2017).

[5] Santos, C. M., Gomes, B., Gonçalves, L. M., Oliveira, J., Rocha, S., Coelho, M., Rodrigues, J. A., Freitas, V. & Aguilar, H. Pyranoflavylium Derivatives Extracted from Wine Grape as Photosensitizers in Solar Cells. J. Braz. Chem. Soc. 2014, 25, 1029–1035.

[6] Calogero, G., Yum, J-H., Sinopoli, A., Di Marco, G., Grätzel, M. & Nazeeruddin, M. K. Anthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cells. Sol. Energy. 2012, 86, 1563–1575.

Acknowledgements:

This work was supported by the Associate Laboratory for Green Chemistry, LAQV-REQUIMTE which is financed by national funds from FCT/MCTES (UID/QUI/50006/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER - 007265). FCT/MCTES is acknowledged for Project PTDC/QEQ-QFI/1971/2014, grants PD/BD/135087/2017 (ALP), SFRH/BD/136556/2018 (VG) and, a research FCT contract (LC).

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