Browsing by Author "Liu, Cheng-Liang"

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High performance solution-processable tetrathienoacene (TTAR) based small molecules for organic field effect transistors (OFETs)
(2017-05-28)
Vegiraju, Sureshraju
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Huang, Deng-Yi
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Priyanka, Pragya
;
Li, Yo-Shan
;
Luo, Xian-Lun
Three new organic semiconductors with alkyl chain-substituted tetrathienoacene (TTAR) as the central core and both ends capped with thiophene (DT-TTAR), thienothiophene (DTT-TTAR) and dithienothiophene (DDTT-TTAR) have been synthesized and characterized for organic field effect transistor (OFET) applications. A hole mobility of 0.81 cm(2) V-1 s(-1) was achieved for the DDTT-TTAR film, which represents the highest mobility yet found for a solution-processable p-type TTAR-based small molecular semiconductors.
Influences of Conjugation Length on Organic Field-Effect Transistor Performances and Thin Film Structures of Diketopyrrolopyrrole-Oligomers
(2018-03-14)
Huang, Yi-Fan
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Chang, Shu-Ting
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Wu, Kuan-Yi
;
Wu, San-Lien
;
Ciou, Guan-Ting
Here, two diketopyrrolopyrrole (DPP)-based oligomers, DPP-4T and DPP-6T, are studied to reveal the influences of conjugation length on thin-film morphology and organic field-effect transistor (OFET) performances. PDMS-assisted crystallization in a solvent-annealing chamber is applied to prepare crystal arrays of DPP-4T and DPP-6T to optimize the quality of charge channels for OFET characterizations. To deliver insights into microstructure and morphology of thin films, a characterization procedure for determining molecular packing in thin film and crystallinity of the crystal arrays is presented via grazing incidence wide-angle X-ray scattering, electron diffraction, and lattice simulation software package (Cerius2). With the lattice parameters derived from analyses of grazing incidence wide-angle X-ray scattering (GIWAXS) and electron diffraction (ED), the lattice modeling results indicate that the inferior organic field-effect transistor (OFET) performances of DPP-6T are attributed to longer pi-stacking distance. Also, less-ordered molecular arrangement and lower continuity of crystalline domains, both of which are revealed from crystallinity results, lead to lower mobility of DPP-6T. In this case, longer conjugated backbones with more conformational degrees of freedom thus cause inherent crystal defects during the crystal growth process, despite the potential to enhance intermolecular pi-orbital overlap. Therefore, to achieve better OFET performance, suitable backbone length makes conjugated oligomers give high intermolecular pi-orbital overlap and low density of structural disorder, which are the priorities for constructing good charge channel.
Intramolecular Locked Dithioalkylbithiophene-Based Semiconductors for High-Performance Organic Field-Effect Transistors
(2017-09-20)
Vegiraju, Sureshraju
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Chang, Bo-Chin
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Priyanka, Pragya
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Huang, Deng-Yi
;
Wu, Kuan-Yi
New 3,3-dithioalkyl-2,2-bithiophene (SBT)-based small molecular and polymeric semiconductors are synthesized by end-capping or copolymerization with dithienothiophen-2-yl units. Single-crystal, molecular orbital computations, and optical/electrochemical data indicate that the SBT core is completely planar, likely via S(alkyl)S(thiophene) intramolecular locks. Therefore, compared to semiconductors based on the conventional 3,3-dialkyl-2,2-bithiophene, the resulting SBT systems are planar (torsional angle <1 degrees) and highly -conjugated. Charge transport is investigated for solution-sheared films in field-effect transistors demonstrating that SBT can enable good semiconducting materials with hole mobilities ranging from approximate to 0.03 to 1.7 cm(2) V-1 s(-1). Transport difference within this family is rationalized by film morphology, as accessed by grazing incidence X-ray diffraction experiments.
Solution-Processable Quinoidal Dithioalkylterthiophene-Based Small Molecules Pseudo-Pentathienoacenes via an Intramolecular S center dot center dot center dot S Lock for High-Performance n-Type Organic Field-Effect Transistors
(2020-06-03)
Vegiraju, Sureshraju
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Torimtubun, Alfonsina Abat Amelenan
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Lin, Po-Shen
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Tsai, Hsin-Chia
;
Lien, Wei-Chieh
A new organic small-molecule family comprising tetracyanoquinodimethane-substituted quinoidal dithioalky(SR)terthiophenes (DSTQs) (DSTQ-6 (1); SR = SC6H13, DSTQ : 10 (2); SR = SC10H21, DSTQ14 (3); SR = SC10H21) was synthesized and contrasted with a nonthioalkylated analogue (DRTQ14 (4); R = C14H29). The physical, electrochemical, and electrical properties of these new compounds are thoroughly investigated. Optimized geometries obtained from density functional theory calculations and single-crystal X-ray diffraction reveal the planarity of the SR-containing DSTQ core. DSTQs pack in a slipped pi-pi stacked two-dimensional arrangement, with a short intermolecular stacking distance of 3.55 A and short intermolecular S center dot center dot center dot N contacts of 3.56 angstrom. Thin-film morphological analysis by grazing incident X-ray diffraction reveals that all DSTQ molecules are packed in an edge-on fashion on the substrate. The favorable molecular packing, the high core planarity, and very low lowest unoccupied molecular orbital (LUMO) energy level (-4.2 eV) suggest that DSTQs could be electron-transporting semiconductors. Organic field-effect transistors based on solution-sheared DSTQ : 14 exhibit the highest electron mobility of 0.77 cm(2) V-1 s(-1) with good ambient stability, which is the highest value reported to date for such a solution process terthiophene-based small molecular semiconductor. These results demonstrate that the device performance of solution-sheared DSTQs can be improved by side chain engineering.
Solution-Processed High-Performance Tetrathienothiophene-Based Small Molecular Blends for Ambipolar Charge Transport
(2018-07-11)
Vegiraju, Sureshraju
;
Lin, Chih-Yu
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Priyanka, Pragya
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Huang, Deng-Yi
;
Luo, Xian-Lun
Four soluble dialkylated tetrathienoacene (TTAR)-based small molecular semiconductors featuring the combination of a TTAR central core, pi-conjugated spacers comprising bithiophene (bT) or thiophene (T), and with/without cyanoacrylate (CA) end-capping moieties are synthesized and characterized. The molecule DbT-TTAR exhibits a promising hole mobility up to 0.36 cm(2) V-1 s(-1) due to the enhanced crystallinity of the microribbon-like films. Binary blends of the p-type DbT-TTAR and the n-type dicyanomethylene substituted dithienothiophene-quinoid (DTTQ-11) are investigated in terms of film morphology, microstructure, and organic field-effect transistor (OFET) performance. The data indicate that as the DbT-TTAR content in the blend film increases, the charge transport characteristics vary from unipolar (electron-only) to ambipolar and then back to unipolar (hole-only). With a 1:1 weight ratio of DbT-TTAR DTTQ-11 in the blend, well-defined pathways for both charge carriers are achieved and resulted in ambipolar transport with high hole and electron mobilities of 0.83 and 0.37 cm(2) V-1 s(-1), respectively. This study provides a viable way for tuning microstructure and charge carrier transport in small molecules and their blends to achieve high-performance solution-processable OFETs.