Low-bandgap copolymers consisting of 2,1,3-benzoselenadiazole and carbazole derivatives with thiophene or selenophene π-bridges

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Two donor–acceptor-type alternating copolymers consisting of 2,1,3-benzoselenadiazole and carbazole derivatives with thiophene or selenophene π-bridges were synthesized by Suzuki cross-coupling polymerization, and their optical, electrochemical, and photovoltaic properties were compared. The selenophene π-bridged copolymer (PCz-DSeBSe) exhibited a smaller band-gap (1.82 eV) than the thiophene-bridged polymer (PCz-DTBSe; 1.89 eV). PCz-DSeBSe also showed a deeper highest occupied molecular orbital energy level (−5.36 eV) than PCz-DTBSe (−5.20 eV). Moreover, the PCz-DSeBSe thin film showed higher crystallinity and hole mobility than the PCz-DTBSe thin film. Organic photovoltaic devices were fabricated using the polymers as the donors and [6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester (PC<SUB>71</SUB>BM) as the acceptor. The device using PCz-DSeBSe showed a higher open circuit voltage (<I>V</I> <SUB>oc</SUB>), short circuit current density (<I>J</I> <SUB>sc</SUB>), and power conversion efficiency (<I>PCE</I>) than that using PCz-DTBSe. The fabricated indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/PCz-DSeBSe:PC<SUB>71</SUB>BM/LiF/Al device showed the maximum <I>PCE</I> of 2.88% with a <I>J</I> <SUB>sc</SUB> of 7.87 mA/cm<SUP>2</SUP>, an <I>V</I> <SUB>oc</SUB> of 0.80 V, and a fill factor of 0.50 under AM 1.5G irradiation (100 mW/cm<SUP>2</SUP>).</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>