A low-bandgap alternating copolymer containing the dimethylbenzimidazole moiety

다국어 초록 (Multilingual Abstract)

<P>A new acceptor unit containing dimethyl-2<I>H</I>-benzimidazole was synthesized and utilized for the synthesis of a conjugated polymer containing electron donor–acceptor pairs for OPV devices. The dimethyl-2<I>H</I>-benzimidazole unit was designed to act as a substitute for the BT unit of <B>PCDTBT</B>. This novel dimethyl-2<I>H</I>-benzimidazole unit has two methyl groups which can supply higher solubility than those of the BT series. A thin film of <B>PCDTMBI</B>, containing the dimethyl-2<I>H</I>-benzimidazole unit, shows two broad absorption bands with maxima at 400 and 636 nm and an absorption onset of 756 nm, corresponding to a band gap of 1.64 eV. The oxidation onset of <B>PCDTMBI</B> was estimated to be 0.67 V, which corresponds to a HOMO energy level of −5.47 eV. The LUMO energy level of the polymer was thus determined to be −3.82 eV. A device with a <B>PCDTMBI</B>:PC<SUB>71</SUB>BM blend had a <I>V</I><SUB>OC</SUB> value of 0.65 V, a <I>J</I><SUB>SC</SUB> value of 10.0 mA cm<SUP>−2</SUP>, and a <I>FF</I> of 0.48, leading to an efficiency of 3.12%. The enhanced efficiency of <B>PCDTMBI</B> was caused by the higher IPCE value between 400 and 700 nm and high mobility (2.2 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>).</P> <P>Graphic Abstract</P><P>A new acceptor unit containing dimethyl-2<I>H</I>-benzimidazole was synthesized and utilized for the synthesis of a conjugated polymer containing electron donor–acceptor pairs for OPV devices.
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