Expected and surprising effects observed in co-sensitized dye systems

Chinmai Mysorekar^a, Adam Glinka^a, Nur Izyan^b, Safalmani Pradhan^b, Shyam Sudhir Pandey^b, Marcin Ziółek^a

^aFaculty of Physics and Astronomy, Adam Mickiewicz University, 2 Uniwersytetu Poznańskiego, 61-614, Poznań, Poland

^bGraduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2,4-Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan

Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV25)

Roma, Italy, 2025 May 12th - 14th

Organizers: Filippo De Angelis, Francesca Brunetti and Claudia Barolo

Oral, Chinmai Mysorekar, presentation 144
Publication date: 17th February 2025

Dye-sensitized solar cells (DSSCs) have emerged as a promising solution for renewable energy, offering an affordable, efficient, and flexible way to convert sunlight into electricity[1]. Co-sensitization involves the use of multiple dyes is a promising approach to enhance light absorption and improve the overall device efficiency[2]–[4]. The synergistic interaction between these dyes leads to improved light harvesting by broadening the solar spectrum coverage, while minimizing dye aggregation. It also helps in reducing energy losses which thereby improves the device’s overall performance. Using photovoltaic characterization[5], stationary absorption, and ultrafast transient absorption (TA)[6], [7] techniques, we investigate the mechanisms driving performance of the systems.

In this study, we examine the systems featuring squaraine (SQ258)[8] and triphenylamine (D35, L1, XY1b) dyes in conjunction with cobalt- and copper-based electrolytes. The co-sensitization of dye pairs: XY1b with L1, and SQ258 with D35, which possess complimentary absorption spectra and unique electronic characteristics are selected. A key finding is the discovery of novel “co-Stark shift effect”, where the absorption of D35 shifts due to the electric field created by electron injection from SQ258 into titania, and the absorption of L1 shifts due to electron inject from XY1b. These interactions highlight the significant role of electron coupling in co-sensitized systems and can suggest a new method to directly estimate electron injection quantum yield from the co-sensitized dye. Co-sensitization for squaraine dyes shows substantial reduction in aggregation, thereby improving electron injection quantum yield. In contrast, no changes in the absorption of individual triphenylamine dyes were observed, resulting in their inherently stable behaviour.

TA studies further reveal that triphenylamine dyes demonstrate efficient electron injection due to the absence of fast internal conversion seen in squaraine dyes. However, they exhibit charge recombination on the hundreds-of-picoseconds timescale, whereas squaraine dye avoid such recombination, balancing the trade-off between injection efficiency and recombination suppression. Additionally, thin TiO₂ layers combines with these dye mixtures enable the construction of semi-transparent, bi-facial solar cells in various colours, offering both efficiency and aesthetic flexibility[9].

This study provides new insights into the interplay of dye interactions and their impact on DSSC performance, paving the way for the development of advanced co-sensitized systems with optimized efficiency and design potential.

References:

[1] B. O’Regan and M. Gratzel, “A Low-Cost, High-Efficiency Solar-Cell Based on Dye-Sensitized Colloidal TiO2 Films,” Nature, vol. 353, no. 6346, pp. 737–740, 1991.

[2] J. Watson, R. R. Rodrigues, and J. H. Delcamp, “Near-infrared unsymmetrical squaraine core-based sensitizers for co-sensitized high-photocurrent dye-sensitized solar cells,” Cell Reports Phys. Sci., vol. 3, no. 1, p. 100701, 2022.

[3] Y. Cao, Y. Liu, S. M. Zakeeruddin, A. Hagfeldt, and M. Grätzel, “Direct Contact of Selective Charge Extraction Layers Enables High-Efficiency Molecular Photovoltaics,” Joule, vol. 2, no. 6, pp. 1108–1117, 2018.

[4] H. Michaels et al., “Dye-sensitized solar cells under ambient light powering machine learning: Towards autonomous smart sensors for the internet of things,” Chem. Sci., vol. 11, no. 11, pp. 2895–2906, 2020.

[5] M. K. Nazeeruddin, E. Baranoff, and M. Grätzel, “Dye-sensitized solar cells: A brief overview,” Sol. Energy, vol. 85, no. 6, pp. 1172–1178, 2011.

[6] M. J. Marchena et al., “Real-time photodynamics of squaraine-based dye-sensitized solar cells with iodide and cobalt electrolytes,” J. Phys. Chem. C, vol. 117, no. 23, pp. 11906–11919, 2013.

[7] M. Gierszewski, A. Glinka, and M. Ziółek, “Co-Sensitization Effects of Indoline and Carbazole Dyes in Solar Cells and Their Neutral–Anion Equilibrium in Solution,” Materials (Basel)., vol. 15, no. 21, 2022.

[8] S. Pradhan, Y. Kurokawa, and S. S. Pandey, “Design and Synthesis of Novel NIR-Sensitive Unsymmetrical Squaraine Dyes for Molecular Photovoltaics,” Phys. Status Solidi Appl. Mater. Sci., vol. 220, no. 24, 2023.

[9] F. Grifoni et al., “Toward Sustainable, Colorless, and Transparent Photovoltaics: State of the Art and Perspectives for the Development of Selective Near-Infrared Dye-Sensitized Solar Cells,” Adv. Energy Mater., vol. 11, no. 43, 2021.

Acknowledgements:

The research was funded by the NCN (National Science Centre, Poland), grant number 2021/43/O/ST4/00017.

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