Structural correlations in the generation of polaronpairs in low-bandgap polymers for photovoltaics

摘要

Polymeric semiconductors are materials where unique optical and electronic propertiesoften originate from a tailored chemical structure. This allows for synthesizing conjugatedmacromolecules with ad hoc functionalities for organic electronics. In photovoltaics, donor–acceptor co-polymers, with moieties of different electron affinity alternating on the chain, haveattracted considerable interest. The low bandgap offers optimal light-harvesting characteristicsand has inspired work towards record power conversion efficiencies. Here we show for the firsttime how the chemical structure of donor and acceptor moieties controls the photogenerationof polaron pairs. We show that co-polymers with strong acceptors show large yields of polaronpair formation up to 24% of the initial photoexcitations as compared with a homopolymer(η=8%). π-conjugated spacers, separating the donor and acceptor centre of masses, have thebeneficial role of increasing the recombination time. The results provide useful input into theunderstanding of polaron pair photogeneration in low-bandgap co-polymers for photovoltaics.