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Fluorine substitution has been vital to the molecular design of π-conjugated polymers toward highly efficient polymer solar cells because it results in improved intermolecular contacts. However, the understanding of how regioselectivity impacts relevant optoelectronic properties in nonsymmetric fluorinated systems remains poorly developed. In response, we herein incorporated a single fluorine atom onto the π-bridge of 1,2,3triazolo4,5-fisoindole-5,7(2H,6H)-dione (TzBI)-polymers to construct two regioisomeric donors, denoted as PTzBI-dF and PTzBI-pF, and investigated how these subtle structural details impact the bulk properties of solar cells. We found that the fluorine substituent position has a profound effect on molecular conformations and thus the aggregated morphology, leading to notably different optical absorption and charge transport. The resulting polymer PTzBI-dF, with fluorine atom distal to the TzBI core, exhibited a power conversion efficiency of up to 17.3% that obviously outperforms the regioisomeric counterpart. These findings highlighted the strategic superiority of materials design toward high-performance solar cells.
Fan et al. (2020) studied this question.