title: The Importance of End Groups for Solution-Processed Small-Molecule Bulk-Heterojunction Photovoltaic Cells.
abstract: End groups in small-molecule photovoltaic materials are important owing to their strong influence on molecular stability, solubility, energy levels, and aggregation behaviors. In this work, a series of donor-acceptor pentads (D2 -A-D1 -A-D2 ) were designed and synthesized, aiming to investigate the effect of the end groups on the materials properties and photovoltaic device performance. These molecules share identical central A-D1 -A triads (with benzodithiophene as D1 and 6-carbonyl-thieno[3,4-b]thiophene as A), but with various D2 end groups composed of alkyl-substituted thiophene (T), thieno[3,2-b]thiophene (TT), and 2,2'-bithiophene (BT). The results indicate a relationship between conjugated segment/alkyl chain length of the end groups and the photovoltaic performance, which contributes to the evolving molecular design principles for high efficiency organic solar cells.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Ruomeng
authors.initials: R
authors.lastname: Duan
authors.affiliation: State Key Laboratory of Polymer Physic and Chemistry, Institute of Chemistry, Chinese Academy of Science, Zhongguancun North First Street 2, 100190, Beijing, P.R. China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Polymer Physic and Chemistry, Institute of Chemistry, Chinese Academy of Science, Zhongguancun North First Street 2, 100190, Beijing, P.R. China.
authors.forename: Jianhui
authors.initials: J
authors.lastname: Hou
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Wagner
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Baumgarten
authors.affiliation: State Key Laboratory of Polymer Physic and Chemistry, Institute of Chemistry, Chinese Academy of Science, Zhongguancun North First Street 2, 100190, Beijing, P.R. China. hechang@iccas.ac.cn.
authors.forename: Chang
authors.initials: C
authors.lastname: He
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany. muellen@mpip-mainz.de.
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
mesh_terms: D011211:Electric Power Supplies; D012993:Solar Energy; D012996:Solutions; D013876:Thiophenes / Q000737:chemistry; D014298:Trimethyltin Compounds / Q000737:chemistry
chemical_list: D012996:Solutions; D013876:Thiophenes; D014298:Trimethyltin Compounds
keywords: benzodithiophene; bulk heterojunction; small molecule; solar cells; thienothiophene