title: Series of Multifluorine Substituted Oligomers for Organic Solar Cells with Efficiency over 9% and Fill Factor of 0.77 by Combination Thermal and Solvent Vapor Annealing.
abstract: We report the synthesis of a family of multifluorine substituted oligomers and the corresponding polymer that have the same backbones but different conjugation lengths and amounts of fluorine atoms on the backbone. The physical properties and photovoltaic performances of these materials were systematically investigated using optical absorption, charge mobility, atomic force microscopy, transmission electron microscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering methods, and photovoltaic devices. The power conversion efficiencies (PCEs) based on oligomers were much higher than that in the polymer. Moreover, the devices based on BIT6F and BIT10F, which have an axisymmetric electron-deficient difluorobenzothiadiazole as the central unit, gave slightly higher PCEs than those with centrosymmetric electron-rich indacenodithiophene (IDT) as the central unit (BIT4F or BIT8F). Using proper solvent vapor annealing (SVA), particularly using thermal annealing (TA) followed by SVA, the device performance could be significantly improved. Notably, the best PCE of 9.1% with a very high FF of 0.76 was achieved using the medium-sized oligomer BIT6F with the optimized film morphology. This efficiency is the highest value reported for organic solar cells from small-molecules without rhodanine terminal group. More excitingly, devices from the shortest oligomer BIT4F showed an impressively high FF of 0.77 (the highest FF value reported for solution-processed small-molecule organic solar cells). These results indicate that photovoltaic performances of oligomers can be modulated through successive change in chain-length and fluorine atoms, alternating spatial symmetric core, and combined post-treatments.
authors.affiliation: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology , 5 South Zhongguancun Street, Beijing 100081, China.
authors.forename: Jin-Liang
authors.initials: JL
authors.lastname: Wang
authors.affiliation: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology , 5 South Zhongguancun Street, Beijing 100081, China.
authors.forename: Kai-Kai
authors.initials: KK
authors.lastname: Liu
authors.affiliation: Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , 381 Wushan Road, Guangzhou 510640, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Yan
authors.affiliation: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology , 5 South Zhongguancun Street, Beijing 100081, China.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Materials Science Division, Lawrence Berkeley National Lab , Berkeley, California 94720, United States.
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.affiliation: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology , 5 South Zhongguancun Street, Beijing 100081, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Xiao
authors.affiliation: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology , 5 South Zhongguancun Street, Beijing 100081, China.
authors.forename: Zheng-Feng
authors.initials: ZF
authors.lastname: Chang
authors.affiliation: Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , 381 Wushan Road, Guangzhou 510640, China.
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Wu
authors.affiliation: Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , 381 Wushan Road, Guangzhou 510640, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Materials Science Division, Lawrence Berkeley National Lab , Berkeley, California 94720, United States.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Russell