Fluorinated Benzothiadiazole (BT) Groups as a Powerful Unit for High-Performance Electron-Transporting Polymers

다국어 초록 (Multilingual Abstract)

<P>Over the past few years, one of the most remarkable advances in the field of polymer solar cells (PSCs) has been the development of fluorinated 2,1,3-benzothiadiazole (BT)-based polymers that lack the solid working principles of previous designs, but boost the power conversion efficiency. To assess a rich data set for the influence of the fluorinated BT units on the charge-transport characteristics in organic field-effect transistors (OFETs), we synthesized two new polymers (<B>PDPP-FBT</B> and <B>PDPP-2FBT</B>) incorporating diketopyrrolopyrrole (DPP) and either single- or double-fluorinated BT and thoroughly investigated them via a range of techniques. Unlike the small differences in the absorption properties of <B>PDPP-FBT</B> and its nonfluorinated analogue (<B>PDPP-BT</B>), the introduction of doubly fluorinated BT into the polymer backbone induces a noticeable change in its optical profiles and energy levels, which results in a slightly wider bandgap and deeper HOMO for <B>PDPP-2FBT</B>, relative to the others. Grazing incidence X-ray diffraction (GIXD) analysis reveals that both fluorinated polymer films have long-range orders along the out-of-plane direction, and π–π stacking in the in-plane direction, implying semicrystalline lamellar structures with edge-on orientations in the solid state. Thanks to the strong intermolecular interactions and highly electron-deficient π-systems driven by the inclusion of F atoms, the polymers exhibit electron mobilities of up to 0.42 and 0.30 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> for <B>PDPP-FBT</B> and <B>PDPP-2FBT</B>, respectively, while maintaining hole mobilities higher than 0.1 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. Our results highlight that the use of fluorinated BT blocks in the polymers is a promising molecular design strategy for improving electron transporting performance without sacrificing their original hole mobility values.</P><P><B>Graphic Abstract</B>
<IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-22/am505925w/production/images/medium/am-2014-05925w_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am505925w'>ACS Electronic Supporting Info</A></P>