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2023 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 11, no 27, p. 9316-9326Article in journal (Refereed) Published
Abstract [en]
In all-polymer solar cells, high performance is attributed to the fine-grained morphology of the film in the active layer. However, the mechanism by which this fine-grained morphology is achieved remains unknown. Polymeric non-fullerene acceptors have the potential to restrict the self-aggregation, typical of non-fullerene small molecule acceptors. Here we employed a blend of the polymeric acceptor PF5-Y5 and the donor polymer PBDB-T to investigate the balance between molecular interactions in solution. Temperature-dependent absorption spectra show evidence of temperature-induced disaggregation of both donor and acceptor polymers, where the donor polymer disaggregation depends on the solvent polarity. Concentration-dependent fluorescence spectra of blend solutions display blue-shifted acceptor emission upon dilution, similar to that observed in acceptor solutions, and a decreased tendency for charge transfer from donor to acceptor upon dilution. Excitation spectra of dilute blend solutions contain an increased contribution to the long-wavelength acceptor emission, as compared to pure acceptor solutions, from a chromophore that absorbs in a region where the donor does not absorb. These observations can be explained by donor-acceptor complexation in dilute blend solutions, that is stabilized in more polar solvents. Moreover, the near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. The results corroborate that the interaction between segments of the donor and acceptor polymer chains favours the formation of donor-acceptor charge transfer complexes, stabilized by hybridization of the molecular orbitals, which reduces the electronic energy. The proposed donor-acceptor complex formation competes with the donor and acceptor self-aggregation and is influenced by the solvent environment. These pre-formed donor-acceptor complexes in low-concentration solutions can be expected to have important consequences on the film morphology of all-polymer blends. The results from this joint experimental-theoretical spectroscopy study provide insights that can guide the design of compatible donor and acceptor polymers for future high-performance organic solar cells.
Place, publisher, year, edition, pages
Royal Society of Chemistry, 2023
National Category
Polymer Chemistry Theoretical Chemistry
Research subject
Chemistry; Materials Science
Identifiers
urn:nbn:se:kau:diva-94224 (URN)10.1039/d1tc03853b (DOI)001019691000001 ()2-s2.0-85164140693 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, 2016.0059Swedish Energy Agency, 48598-1Swedish National Space Board, 174/19 and 137/21Swedish Research Council, 2014-05984
Note
This paper was included as a manuscript in Ishita Jalan's PhD thesis entitled "Solution Chemistry and Morphological Properties for Organic Solar Cells: Exploring Alternative Solvents Using Microgravity and Modelling as Tools", 2023:13.
2023-04-102023-04-102023-08-09Bibliographically approved