EPR Characterization of the Light-Induced Negative Polaron in a Functionalized Dithienylthiazolo[5,4-d]thiazole Acceptor for Organic Photovoltaics
Functionalized 2,5-dithienylthiazolo[5,4-d]thiazole (DTTzTz) derivatives have attracted interest towards application as non-fullerene acceptors in solution-processed organic solar cells. Here, we present a combined high-field electron paramagnetic resonance and density functional theory study of the light-induced negative polaron on the novel acceptor 2,4-diCN-Ph-DTTzTz formed after charge transfer in bulk heterojunction blends with a donor polymer. Despite spectral overlap with the polymer cation, the g-anisotropy of the acceptor radical could be directly confirmed through detection of its unique 14N hyperfine couplings using electron–electron double resonance (ELDOR)-detected nuclear magnetic resonance (EDNMR) for spectral filtering. The spectral assignment is further underpinned by quantum-chemical calculations, which also provide detailed information about the spin density and charge distribution of the polaron in the DTTzTz acceptor.
The authors want to acknowledge the Research Foundation Flanders (FWO-Vlaanderen) for support of this work through the project G0B6715 N and the PhD fellowship of M. Van Landeghem.
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