title: High-crystalline medium-band-gap polymers consisting of benzodithiophene and benzotriazole derivatives for organic photovoltaic cells.
abstract: Two semiconducting conjugated polymers were synthesized via Stille polymerization. The structures combined unsubstituted or (triisopropylsilyl)ethynyl (TIPS)-substituted 2,6-bis(trimethylstannyl)benzo[1,2-b:4.5-b']dithiophene (BDT) as a donor unit and benzotriazole with a symmetrically branched alkyl side chain (DTBTz) as an acceptor unit. We investigated the effects of the different BDT moieties on the optical, electrochemical, and photovoltaic properties of the polymers and the film crystallinities and carrier mobilities. The optical-band-gap energies were measured to be 1.97 and 1.95 eV for PBDT-DTBTz and PTIPSBDT-DTBTz, respectively. Bulk heterojunction photovoltaic devices were fabricated and power conversion efficiencies of 5.5% and 2.9% were found for the PTIPSBDT-DTBTz- and PBDT-DTBTz-based devices, respectively. This difference was explained by the more optimal morphology and higher carrier mobility in the PTIPSBDT-DTBTz-based devices. This work demonstrates that, under the appropriate processing conditions, TIPS groups can change the molecular ordering and lower the highest occupied molecular orbital level, providing the potential for improved solar cell performance.
authors.affiliation: Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University , Busan 609-735, Republic of Korea.
authors.forename: Ji-Hoon
authors.initials: JH
authors.lastname: Kim
authors.forename: Chang Eun
authors.initials: CE
authors.lastname: Song
authors.forename: Nara
authors.initials: N
authors.lastname: Shin
authors.forename: Hyunbum
authors.initials: H
authors.lastname: Kang
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wood
authors.forename: In-Nam
authors.initials: IN
authors.lastname: Kang
authors.forename: Bumjoon J
authors.initials: BJ
authors.lastname: Kim
authors.forename: Bongsoo
authors.initials: B
authors.lastname: Kim
authors.forename: Ji-Seon
authors.initials: JS
authors.lastname: Kim
authors.forename: Won Suk
authors.initials: WS
authors.lastname: Shin
authors.forename: Do-Hoon
authors.initials: DH
authors.lastname: Hwang
mesh_terms: D055664:Electrochemical Techniques; D037741:Fullerenes / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D011789:Quantum Theory; D012993:Solar Energy; D013059:Spectrum Analysis, Raman; D013876:Thiophenes / Q000737:chemistry*; D017971:Tin Compounds / Q000737:chemistry; D014230:Triazoles / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D011108:Polymers; D011137:Polystyrenes; D013876:Thiophenes; D017971:Tin Compounds; D014230:Triazoles; C533756:poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate); C109984:indium tin oxide; C012771:benzotriazole