title: Naphthodithiophene-naphthobisthiadiazole copolymers for solar cells: alkylation drives the polymer backbone flat and promotes efficiency.
abstract: We show that rational functionalization of the naphthodithiophene core in copolymers based on naphthodithiophene and naphthobisthiadiazole improves the solubility without an alteration of the electronic structure. Surprisingly, the introduction of linear alkyl chains brings about a drastic change in polymer orientation into the face-on motif, which is beneficial for the charge transport in solar cells. As a result, the present polymers exhibit high power conversion efficiencies of up to ~8.2% in conventional single-junction solar cells.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan. itaru.osaka@riken.jp
authors.forename: Itaru
authors.initials: I
authors.lastname: Osaka
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kakara
authors.forename: Noriko
authors.initials: N
authors.lastname: Takemura
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Koganezawa
authors.forename: Kazuo
authors.initials: K
authors.lastname: Takimiya