Two newly developed narrow bandgap polymers containing benzobis(thiadiazole) (BBT) have been synthesized using the Stille coupling reaction. The polymers showed absorption in the near infrared region due to strong charge-transfer interactions in the donor-acceptor (D-A) units, suggesting a rigid planarized structure. Although both the HOMO-LUMO levels of the polymers lie close to the work function of gold electrodes, a BBT-quaterthiophene polymer showed only p-type semiconducting behavior. In addition, the dominant charge-carrier type is holes even in BBT-thiazole-thiophene polymers, which consists mainly of acceptor units, and indicates that the thiophene ring in these polymers has a strong influence on the charge transport properties.
2014 The Society of Photopolymer Science and Technology (SPST)