title: Development of Spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene]-Based A-π-D-π-A Small Molecules with Different Acceptor Units for Efficient Organic Solar Cells.
abstract: Three acceptor-π-donor-π-acceptor (A-π-D-π-A) small molecules (STFYT, STFRDN, and STFRCN) with spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene] (STF) as the central donor unit, terthiophene as the π-conjugated bridge, indenedione, 3-ethylrhodanine, or 2-(1,1-dicyanomethylene)rhodanine as the acceptor unit are designed, synthesized, and characterized as electron donor materials in solution-processing organic solar cells (OSCs). The effects of the spiro STF-based central core and different acceptors on the molecular configuration, absorption properties, electronic energy levels, carrier transport properties, the morphology of active layers, and photovoltaic properties are investigated in detail. The three molecules exhibit desirable physicochemical features: wide absorption bands (300-850 nm) and high molar absorption coefficients (4.82 × 104to 7.56 × 104M-1cm-1) and relatively low HOMO levels (-5.15 to -5.38 eV). Density functional theory calculations reveal that the spiro STF central core benefits to reduce the steric hindrance effect between the central donor block and terthiophene bridge and suppress excessive intermolecular aggregations. The optimized OSCs based on these molecules deliver power conversion efficiencies (PCEs) of 6.68%, 3.30%, and 4.33% for STFYT, STFRDN, and STFRCN, respectively. The higher PCE of STFYT-based OSCs should be ascribed to its better absorption ability, higher and balanced hole and electron mobilities, and superior active layer morphology as compared to the other two compounds. So far, this is the first example of developing the A-π-D-π-A type small molecules with a spiro central donor core for high-performance OSC applications. Meanwhile, these results demonstrate that using spiro central block to construct A-π-D-π-A molecule is an alternative and effective strategy for achieving high-performance small molecule donor materials.
authors.affiliation: College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University , Xiangtan 411105, China.|Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Wengong
authors.initials: W
authors.lastname: Wang
authors.affiliation: College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University , Xiangtan 411105, China.
authors.forename: Ping
authors.identifier: http://orcid.org/0000-0003-0672-2410
authors.initials: P
authors.lastname: Shen
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Xinning
authors.initials: X
authors.lastname: Dong
authors.affiliation: College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University , Xiangtan 411105, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Weng
authors.affiliation: College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University , Xiangtan 411105, China.
authors.forename: Guo
authors.initials: G
authors.lastname: Wang
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Haijun
authors.initials: H
authors.lastname: Bin
authors.affiliation: School of Materials Science & Engineering, Jiangsu Collaborative Innovation Central of Photovoltaic Science & Engineering, Changzhou University , Changzhou 213164, China.
authors.forename: Jing
authors.identifier: http://orcid.org/0000-0001-8983-5757
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Zhi-Guo
authors.identifier: http://orcid.org/0000-0003-4341-7773
authors.initials: ZG
authors.lastname: Zhang
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Yongfang
authors.initials: Y
authors.lastname: Li
keywords: A-π-D-π-A small molecule; acceptor unit; organic solar cells; photovoltaic properties; spiro[cyclopenta[1,2-b:5,4-b′]dithiophene-4,9′-fluorene]