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Wang, Yingfeng,Guo, Han,Harbuzaru, Alexandra,Uddin, Mohammad Afsar,Arrechea-Marcos, Iratxe,Ling, Shaohua,Yu, Jianwei,Tang, Yumin,Sun, Huiliang,Ló,pez Navarrete, Juan Teodomiro,Ortiz, Rocio Ponce American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.19
<P>Development of high-performance unipolar n-type organic semiconductors still remains as a great challenge. In this work, all-acceptor bithiophene imide-based ladder-type small molecules BTI<I>n</I> and semiladder-type homopolymers PBTI<I>n</I> (<I>n</I> = 1-5) were synthesized, and their structure-property correlations were studied in depth. It was found that Pd-catalyzed Stille coupling is superior to Ni-mediated Yamamoto coupling to produce polymers with higher molecular weight and improved polymer quality, thus leading to greatly increased electron mobility (μ<SUB>e</SUB>). Due to their all-acceptor backbone, these polymers all exhibit unipolar n-type transport in organic thin-film transistors, accompanied by low off-currents (10<SUP>-10</SUP>-10<SUP>-9</SUP> A), large on/off current ratios (10<SUP>6</SUP>), and small threshold voltages (∼15-25 V). The highest μ<SUB>e</SUB>, up to 3.71 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μ<SUB>e</SUB> drops by 2 orders to 0.014 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP> for PBTI5. This monotonic decrease of μ<SUB>e</SUB> was also observed in their homologous BTI<I>n</I> small molecules. This trend of mobility decrease is in good agreement with the evolvement of disordered phases within the film, as revealed by Raman spectroscopy and X-ray diffraction measurements. The extension of the ladder-type building blocks appears to have a large impact on the motion freedom of the building blocks and the polymer chains during film formation, thus negatively affecting film morphology and charge carrier mobility. The result indicates that synthesizing building blocks with more extended ladder-type backbone does not necessarily lead to improved mobilities. This study marks a significant advance in the performance of all-acceptor-type polymers as unipolar electron transporting materials and provides useful guidelines for further development of (semi)ladder-type molecular and polymeric semiconductors for applications in organic electronics.</P> [FIG OMISSION]</BR>
Usta, Hakan,Kim, Dojeon,Ozdemir, Resul,Zorlu, Yunus,Kim, Sanghyo,Ruiz Delgado, M. Carmen,Harbuzaru, Alexandra,Kim, Seonhyoung,Demirel, Gö,khan,Hong, Jongin,Ha, Young-Geun,Cho, Kilwon,Facchetti, American Chemical Society 2019 Chemistry of materials Vol.31 No.14
<P>The first example of an n-type [1]benzothieno[3,2-<I>b</I>][1]benzothiophene (BTBT)-based semiconductor, <B>D(Ph</B><SUB><B>F</B></SUB><B>CO)-BTBT</B>, has been realized via a two-step transition-metal-free process without using chromatographic purification. Physicochemical and optoelectronic characterizations of the new semiconductor were performed in detail, and the crystal structure was accessed. The new molecule exhibits a large optical band gap (∼2.9 eV) and highly stabilized (Δ<I>E</I><SUB>LUMO</SUB> = 1.54 eV)/π-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT π-core and in-plane carbonyl units. The effect of out-of-plane twisted (64°) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline <B>D(Ph</B><SUB><B>F</B></SUB><B>CO)-BTBT</B> thin films prepared by physical vapor deposition exhibited large grains (∼2-5 μm sizes) and “layer-by-layer” stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances ∼3.25-3.46 Å) to favor two-dimensional (2D) source-to-drain (S → D) charge transport. The corresponding TC/BG-OFET devices demonstrated high electron mobilities of up to ∼0.6 cm<SUP>2</SUP>/V·s and <I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB> ratios over 10<SUP>7</SUP>−10<SUP>8</SUP>. These results demonstrate that the large band gap BTBT π-core is a promising candidate for high-mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation unconventional (opto)electronics.</P> [FIG OMISSION]</BR>