title: Effect of Heterocyclic Anchoring Sequence on the Properties of Dithienogermole-Based Solar Cells.
abstract: The synthesis and characterization of two new small molecular donor materials, DTGe(ThFBTTh2)2and DTGe(FBTTh3)2, are presented for application in organic solar cells. These two materials represent structural evolutions of the high-efficiency, dithienogermole (DTGe)-cored small molecule DTGe(FBTTh2)2, in which the conjugation length in the backbone was extended by incorporating additional thiophene units. Using the same molecular framework, we have evaluated how the anchoring sequence of heterocyclic units influences material properties and function in solar cell devices. It was found that incorporating additional thiophene units into the backbone, regardless of the position in the molecular platform, caused a small reduction in band gaps; however, both highest occupied molecular orbitals and lowest unoccupied molecular orbital energy bands were at lower energies when the thiophenes were incorporated near the terminus of the molecule. The film morphologies of both materials could be controlled by either thermal or solvent vapor annealing to yield phase separation on the order of tens of nanometers and improved crystallinity. Peak power-conversion efficiencies of 3.6% and 3.1% were obtained using DTGe(ThFBTTh2)2and DTGe(FBTTh3)2, after solvent vapor treatment and thermal annealing, respectively. Our study provides a detailed analysis of how the ordering sequence of heterocyclic building blocks influences the properties and function of organic solar cells.
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Low Dimensional Carbon Materials Center, Perovtronics Research Center, Ulsan National Institute of Science and Technology (UNIST) , Ulsan 44919, South Korea.
authors.forename: Bright
authors.initials: B
authors.lastname: Walker
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Perovtronics Research Center, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulju-gun, Ulsan 44919, South Korea.
authors.forename: Daehee
authors.initials: D
authors.lastname: Han
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Perovtronics Research Center, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulju-gun, Ulsan 44919, South Korea.
authors.forename: Mijin
authors.initials: M
authors.lastname: Moon
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Low Dimensional Carbon Materials Center, Perovtronics Research Center, Ulsan National Institute of Science and Technology (UNIST) , Ulsan 44919, South Korea.
authors.forename: Song Yi
authors.initials: SY
authors.lastname: Park
authors.affiliation: KIER-UNIST Advanced Center for Energy, Korea Institute of Energy Research , Ulsan 44919, South Korea.
authors.forename: Ka-Hyun
authors.identifier: http://orcid.org/0000-0002-4763-2713
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Low Dimensional Carbon Materials Center, Perovtronics Research Center, Ulsan National Institute of Science and Technology (UNIST) , Ulsan 44919, South Korea.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Kim
authors.affiliation: Department of Energy Engineering, School of Energy and Chemical Engineering, Perovtronics Research Center, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulju-gun, Ulsan 44919, South Korea.
authors.forename: Changduk
authors.identifier: http://orcid.org/0000-0001-7452-4681
authors.initials: C
authors.lastname: Yang
keywords: bulk heterojunction; dithienogermole; organic electronics; photovoltaic; small molecule; solar cell