The continued improvement in efficiency for organic photovoltaics (OPVs) is due in part to the development of new conjugated polymeric materials. We have reported a fluorination technique which yields a high efficiency polymer, PBnDT-FTAZ, (~7%) with phenyl-C61-butyric acid methyl ether (PCBM) and even higher efficiencies (~12%) when paired with non-fullerene acceptors. The addition of the fluorine substituent on the acceptor benzotriazole (TAZ) moiety increased all three major device characteristics (Voc, Jsc, and FF); however the fluorination strategy is not universal, as not all acceptor moieties have a location for fluorination. In this study, we created a new design motif to incorporate fluorine substituents into conjugated polymers using the common thiophene linkers which connect the donor and acceptor moieties of the polymer, rather than fluorinating directly on the acceptor moiety. This new design motif will allow for materials, previously with no fluorination location, to enjoy the benefits attributed to fluorination. We introduce a difluorinated thiophene (dFT) linker into the BnDT-TAZ system to create a new polymer, PBnDT-dFT-HTAZ. Compared with the nonfluorinated counterpart (PBnDT-HTAZ), a 50% improvement in the efficiency is seen when using the dFT linker. This increase is primarily attributed to the large increase in Voc (0.74V vs 0.99V), owed to the deeper HOMO level of the dFT containing polymer. This work illustrates a fluorination pathway which can be used to improve the performance of polymers for OPVs.

Utilizing fluorinated thiophene units to improve photovoltaic device performance

256th National Meeting (2018)

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