TY - JOUR
T1 - Alkynyl-Functionalized Head-to-Head Linkage Containing Bithiophene as a Weak Donor Unit for High-Performance Polymer Semiconductors
AU - Wang, Yulun
AU - Liao, Qiaogan
AU - Wang, Gang
AU - Guo, Han
AU - Zhang, Xianhe
AU - Uddin, Mohammad Afsar
AU - Shi, Shengbin
AU - Su, Huimin
AU - Dai, Junfeng
AU - Cheng, Xing
AU - Facchetti, Antonio
AU - Marks, Tobin Jay
AU - Guo, Xugang
PY - 2017/5/9
Y1 - 2017/5/9
N2 - Building blocks having a high degree of backbone planarity, good solubilizing characteristics, and well-tailored physicochemical properties are highly desirable for constructing high-performance polymer semiconductors. Due to the detrimental steric hindrance created by alkyl chain substituents at the 3- and 3′-positions of bithiophene, "head-to-head" linkage containing 3,3′-dialkyl-2,2′-bithiophenes (BTR) are typically avoided in materials design. Replacing alkyl chains with less steric demanding alkynyl chains should greatly reduce steric hindrance by eliminating two H atoms at the sp-hybridized carbon center. Here we report the synthesis of a novel electron donor unit, 3,3′-dialkynyl-2,2′-bithiophene (BTRy), and its incorporation into conjugated polymer backbones. The alkynyl-functionalized head-to-head bithiophene linkage yields polymers with good solubility without sacrificing backbone planarity; the BTRy-based polymers show a high degree of conjugation with a narrow bandgap of ∼1.6 eV. When incorporated into organic thin-film transistors, the polymers exhibit substantial hole mobility, up to 0.13 cm2 V-1 s-1 in top-gated transistors. The electron-withdrawing alkynyl substituents lower the frontier molecular orbitals, imbuing the difluorobenzothiadiazole and difluorobenzoxadiazole copolymers with remarkable ambipolarity: electron mobility > 0.05 cm2 V-1 s-1 and hole mobility ∼0.01 cm2 V-1 s-1 in bottom-gated transistors. In bulk-heterojunction solar cells, the BTRy-based polymers show promising power conversion efficiencies approaching 8% with very large Voc values of 0.91-1.04 V, due to the weak electron-withdrawing alkynyl substituents. In comparison to the tetrathiophene-based polymer analogues based on the unsubstituted π-spacer design, the BTRy-based polymers have comparable light absorption but with 0.14 V larger open-circuit voltage, translating to enhanced optoelectronic properties for this attractive design strategy. Thus, alkynyl groups are versatile semiconductor substituents, offering good solubility, substantial backbone planarity, optimized optoelectronic properties, and film crystallinity, for materials innovation in organic electronics.
AB - Building blocks having a high degree of backbone planarity, good solubilizing characteristics, and well-tailored physicochemical properties are highly desirable for constructing high-performance polymer semiconductors. Due to the detrimental steric hindrance created by alkyl chain substituents at the 3- and 3′-positions of bithiophene, "head-to-head" linkage containing 3,3′-dialkyl-2,2′-bithiophenes (BTR) are typically avoided in materials design. Replacing alkyl chains with less steric demanding alkynyl chains should greatly reduce steric hindrance by eliminating two H atoms at the sp-hybridized carbon center. Here we report the synthesis of a novel electron donor unit, 3,3′-dialkynyl-2,2′-bithiophene (BTRy), and its incorporation into conjugated polymer backbones. The alkynyl-functionalized head-to-head bithiophene linkage yields polymers with good solubility without sacrificing backbone planarity; the BTRy-based polymers show a high degree of conjugation with a narrow bandgap of ∼1.6 eV. When incorporated into organic thin-film transistors, the polymers exhibit substantial hole mobility, up to 0.13 cm2 V-1 s-1 in top-gated transistors. The electron-withdrawing alkynyl substituents lower the frontier molecular orbitals, imbuing the difluorobenzothiadiazole and difluorobenzoxadiazole copolymers with remarkable ambipolarity: electron mobility > 0.05 cm2 V-1 s-1 and hole mobility ∼0.01 cm2 V-1 s-1 in bottom-gated transistors. In bulk-heterojunction solar cells, the BTRy-based polymers show promising power conversion efficiencies approaching 8% with very large Voc values of 0.91-1.04 V, due to the weak electron-withdrawing alkynyl substituents. In comparison to the tetrathiophene-based polymer analogues based on the unsubstituted π-spacer design, the BTRy-based polymers have comparable light absorption but with 0.14 V larger open-circuit voltage, translating to enhanced optoelectronic properties for this attractive design strategy. Thus, alkynyl groups are versatile semiconductor substituents, offering good solubility, substantial backbone planarity, optimized optoelectronic properties, and film crystallinity, for materials innovation in organic electronics.
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U2 - 10.1021/acs.chemmater.7b01052
DO - 10.1021/acs.chemmater.7b01052
M3 - Article
AN - SCOPUS:85019083615
VL - 29
SP - 4109
EP - 4121
JO - Chemistry of Materials
JF - Chemistry of Materials
SN - 0897-4756
IS - 9
ER -