title: 3,4-Disubstituted polyalkylthiophenes for high-performance thin-film transistors and photovoltaics.
abstract: We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Sangwon
authors.initials: S
authors.lastname: Ko
authors.forename: Eric
authors.initials: E
authors.lastname: Verploegen
authors.forename: Sanghyun
authors.initials: S
authors.lastname: Hong
authors.forename: Rajib
authors.initials: R
authors.lastname: Mondal
authors.forename: Eric T
authors.initials: ET
authors.lastname: Hoke
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: Michael D
authors.initials: MD
authors.lastname: McGehee
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao