title: Effects of Regioregularity and Molecular Weight on the Growth of Polythiophene Nanofibrils and Mixes of Short and Long Nanofibrils To Enhance the Hole Transport.
abstract: Morphological control over polythiophenes has been widely studied; however the impacts of regioregularity (RR) and molecular weight (MW) on their structural development have not been investigated systematically. This study examined a representative polythiophene, poly(3-hexylthiophene) (P3HT), to reveal that small differences in the RR can produce a large difference in the growth of nanofibrils. Low-RR P3HTs generated neat long nanofibrils (LNFs), whereas high-RR P3HTs formed short nanofibrils (SNFs). This study identified a critical RR (96-98%) depending on their MW, below which P3HT grew into LNFs and above which P3HT grew into SNFs. This study also found that the mixing ratio between high-RR P3HT and a low-RR P3HT in the solution phase is strongly correlated with the relative populations of SNF and LNF in the coated film. This study suggested that mixing high-RR and low-RR polymers may be a good strategy to optimize the electrical properties of polythiophenes for target applications. As an example, a mixture of high-RR (75%) P3HT and low-RR P3HT (25%) improved considerably the power conversion efficiency of bulk heterojunction polymer solar cells compared with the values obtained from the pure high-RR P3HT and the pure low-RR P3HT.
authors.affiliation: Department of Materials Science and Engineering, Yonsei University , 50 Yonsei-Ro, Seodaemun-Gu, Seoul, Korea 120-749.
authors.forename: Yujeong
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Research Institute of Iron and Steel Technology, Yonsei University , Seoul 120-749, Korea.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Oh
authors.forename: Sung Yun
authors.initials: SY
authors.lastname: Son
authors.forename: Taiho
authors.initials: T
authors.lastname: Park
authors.forename: Unyong
authors.initials: U
authors.lastname: Jeong
keywords: nanofibril; organic solar cells; poly(3-hexylthiophene); polythiophenes; regioregularity