On the impact of side chains over the structural and optical properties of aqueous-processable PTQ10-based polymeric electron donors in solution

Rafael Ribeiro^a^,^b, Leandro Franco^c, Alexandre Holmes^c, Tárcius Ramos^d, Ergang Wang^c, Márcio Varella^a, Moysés Araujo^b^,^e

^aInstitute of Physics, University of São Paulo, Rua do Matão 1731, 05508-090 São Paulo, São Paulo, Brazil

^bDepartment of Engineering and Physics, Karlstad University, 65188 Karlstad, Sweden

^cDepartment of Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg SE-412 96, Sweden

^dTheoretical Chemistry Lab, Unit of Theoretical and Structural Physical Chemistry, Namur Institute of Structured Matter, University of Namur, Rue de Bruxelles, 61, B-5000 Namur, Belgium

^eMaterials Theory Division, Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden

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

Poster, Rafael Ribeiro, 234
Publication date: 17th February 2025

Developing aqueous-processable materials is crucial for the fabrication and commercialization of eco-friendly organic solar cells [1]. Although significant progress has been made in designing aqueous-processable electron donor and acceptor polymers by introducing polar side chains, the efficiencies of these environmentally friendly devices still limited in comparison to the state-of-the-art devices produced with halogenated solvents [2]. To explore how varying substituents influence structural and optical properties in solution, we examined the PTQ10 polymer [3] backbone with both alkyl and alkoxy side chains. Using classical molecular dynamics simulations, we studied oligomer chains at low and high concentrations in two solvent systems: a water/ethanol mixture and chloroform. By employing an unsupervised machine learning method combined with density functional theory calculations, we determined the optimal system size for performing quantum calculations and examined how side chain modifications affect the polymer's excited states. Employing a sequential QM/MM methodology [4], we computed absorption spectra for each polymer variant. Simulations at elevated concentrations revealed oligomer stacking behavior, indicating early-stage polymer aggregation in solution—a finding that aligns well with our experimental observations, where a red shift was detected in the PTQ(8bO2) spectrum upon transitioning from chloroform to the aqueous mixture.

References:

[1] Rech J. J., Neu J., Qin Y., Samson S., Shanahan J., Josey III R. F., Ade H., You W. Designing Simple Conjugated Polymers for Scalable and Efficient Organic Solar Cells. ChemSusChem 2021, 14(17), 3561-3568.

[2] Ren, H.; Chen, J.-D.; Zhang, Y.-F.; Zhang, J.-L.; Chen, W.-S.; Li, Y.-Q.; Tang, J.-X. 20.4% Power conversion efficiency from albedo-collecting organic solar cells under 0.2 albedo. Science Advances 2024, 10.

[3] Sun, C.; Pan, F.; Bin, H.; Zhang, J.; Xue, L.; Qiu, B.; Wei, Z.; Zhang, Z.-G.; Li, Y. A low cost and high performance polymer donor material for polymer solar cells. Nature Communications 2018, 9, 743.

[4] Coutinho, K.; Canuto, S.; Zerner, M. C. A Monte Carlo-quantum mechanics study of the solvatochromic shifts of the lowest transition of benzene. The Journal of Chemical Physics 2000, 112, 9874–9880.

Acknowledgements:

We thank the CAPES financial support from CAPES/PrInt exchange grant (88887.937407/2024-00). R. R. B. and M. T. do N. V. acknowledge financial support from São Paulo Research Foundation (FAPESP-2022/04379-3 and FAPESP-2024/22044-4). M. T. do N. V. also acknowledges financial support from CNPq (Grant no. 306285/2022-3). L. R. F. and C. M. A. acknowledge financial support from the Swedish Research Council (2020-05223) and from the STandUP for Energy collaboration. T. N. R. is a postdoctoral researcher of the Fonds de la Recherche Scientifique – FNRS. Computations were performed at NSC Tetralith provided by the National Academic Infrastructure for Supercomputing in Sweden (NAISS) funded by the Swedish Research Council through grant agreement no. 2022-06725 (NAISS).

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