Browsing by Author "Kim, Myung-Gil"

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Design, synthesis, and characterization of alpha,omega-disubstituted indeno[1,2-b]fluorene-6,12-dione-thiophene molecular semiconductors. Enhancement of ambipolar charge transport through synthetic tailoring of alkyl substituents
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2016) Ozdemir, Mehmet; Choi, Donghee; Kwon, Guhyun; Zorlu, Yunus; Kim, Hyekyoung; Kim, Myung-Gil; Seo, SungYong; Sen, Unal; Citir, Murat; Kim, Choongik; Usta, Hakan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan; Ozdemir, Mehmet; Sen, Unal
A series of indeno[1,2-b]fluorene-6,12-dione-thiophene derivatives with hydrocarbon substituents at alpha,omega-positions as side groups have been designed and synthesized. The new compounds were fully characterized by H-1/C-13 NMR, mass spectrometry, cyclic voltammetry, UV-vis absorption spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and melting point measurements. The solid state structure of the indeno[1,2-b]fluorene-6,12-dione acceptor core has been identified based on single-crystal X-ray diffraction (XRD). The structural and electronic properties were also studied using density functional theory calculations, which were found to be in excellent agreement with the experimental findings and provided further insight. The detailed effects of alkyl chain size and orientation on the optoelectronic properties, intermolecular cohesive forces, thin-film microstructures, and charge transport performance of the new semiconductors were investigated. Two of the new solution-processable semiconductors, 2EH-TIFDKT and 2OD-TIFDKT, were deposited as thin-films via solution-shearing, drop-casting, and droplet-pinned crystallization methods, and their morphologies and microstructures were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The solution-processed thin-film transistors based on 2EH-TIFDKT and 2OD-TIFDKT showed ambipolar device operations with electron and hole mobilities as high as 0.12 cm(2) V-1 s(-1) and 0.02 cm(2) V-1 s(-1), respectively, with Ion/Ioff ratios of 105 to 106. Here, we demonstrate that rational repositioning of the b-substituents to molecular termini greatly benefits the p-core planarity while maintaining a good solubility, and results in favorable structural and optoelectronic characteristics for more efficient charge-transport in the solid-state. The ambipolar charge carrier mobilities were increased by two-three orders of magnitude in the new indeno[1,2-b]fluorene-6,12-dione-thiophene core on account of the rational side-chain engineering.
Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020) Ozdemir, Resul; Ahn, Kyunghan; Deneme, Ibrahim; Zorlu, Yunus; Kim, Dojun; Kim, Myung-Gil; Usta, Hakan; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Diacene-fused thienothiophenes (DAcTTs) have provided an excellent pi-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transport characteristics remain largely unexplored. Herein, a series of functionalized low LUMO (lowest unoccupied molecular orbital) [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)(2)C-7, and D(C7CC(CN)(2))-BTBT, have been developed. Detailed structural, physicochemical, optoelectronic, and single-crystal characterization were performed. The new molecules exhibit large optical band gaps (similar to 2.8-3.1 eV) and highly stabilized (-Delta E-LUMO = 1.2-1.4 eV)/pi-delocalized LUMOs as compared to p-type DAcTTs. Symmetric functionalization is found to be important to enable strong intermolecular interactions in the solid-state. All molecules exhibit alternately stacked layers of "F-BTBT-F" and "S" (F: functional group/S: substituent) with strong herringbone-like interactions (2.8-3.6 angstrom distances) between pi-cores. While carbonyls, regardless of the substituent, adopt nearly coplanar pi-backbones with BTBT, dicyanovinylenes are found to be twisted (47.5 degrees). The conformational difference at the molecular level has unusual effects on the pi-electron deficiencies, frontier molecular orbital energetics, thermal/photophysical properties, and pi-electronic structures. Dicyanovinylenes at the 2,7 positions, despite twisted conformations, are shown for the first time to yield good electron transport in DAcTTs. The D(C7CC(CN)(2))-BTBT thin film exhibits large 2D plate-like crystalline grains (similar to 1-2 mu m sizes) of terraced islands and becomes a rare example of an n-type DAcTT in organic field-effect transistors (OFETs). Although a stabilized/pi-delocalized LUMO, largely governed by functional groups and intramolecular twists, is essential for electron transport, our findings suggest that it should be combined with proper substituents to yield a favorable three-dimensional BTBT/functional group pi-electronic structure and a low intramolecular reorganization energy. Combined with our first n-type DAcTT semiconductor D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs. The molecular engineering perspectives presented in this study may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.
High Electron Mobility in [1]Benzothieno[3,2-b][1]benzothiophene-Based Field-Effect Transistors: Toward n-Type BTBTs
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Usta, Hakan; Kim, Dojeon; Ozdemir, Resul; Zorlu, Yunus; Kim, Sanghyo; Ruiz Delgado, M. Carmen; Harbuzaru, Alexandra; Kim, Seonhyoung; Demirel, Gokhan; Hong, Jongin; Ha, Young-Geun; Cho, Kilwon; Facchetti, Antonio; Kim, Myung-Gil; 0000-0002-2891-5785; 0000-0003-2811-1872; 0000-0002-7957-110X; 0000-0002-8211-732X; 0000-0002-0618-1979; 0000-0002-9778-917X; 0000-0003-2434-3182; 0000-0001-8180-7153; 0000-0001-9632-3557; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The first example of an n-type [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based semiconductor, D-(PhFCO)-BTBT, 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 (similar to 2.9 eV) and highly stabilized (Delta E-LUMO = 1.54 eV)/pi-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT pi-core and in-plane carbonyl units. The effect of out-of-plane twisted (64 degrees) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline D(PhFCO)-BTBT thin films prepared by physical vapor deposition exhibited large grains (similar to 2-5 mu m sizes) and "layer-by-layer" stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances similar to 3.25-3.46 angstrom) 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 similar to 0.6 cm(2)/V.s and I-on/I-off ratios over 10(7)-10(8). These results demonstrate that the large band gap BTBT pi-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.
Microstructural modulation of organic passivation layers for metal oxide semiconductors to achieve high bias stability
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020) Ho, Dongil; Jeong, Ha-Yun; Minh Nhut Le; Usta, Hakan; Kwon, Hyuck-In; Kim, Myung-Gil; Kim, Choongik; 0000-0001-7494-0677; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Electrical properties of metal oxide thin-film transistors (TFTs) are tunedviathe microstructural control of organic back-channel passivation layers. In this study, organic semiconductor (OSC) passivation layers with various molecular and physicochemical properties are employed to identify the back-channel passivation mechanism in solution-processed amorphous indium gallium zinc oxide (a-IGZO) TFTs. The OSC microstructure influences the passivation of electrical defects ina-IGZO TFTs by compensating for acceptor-like trap states and dangling bonds in the back-channel. First, the distance between an n-type OSC (C-60) and thea-IGZO back-channel is controlled by employing phosphonic acid molecules with different carbon chain lengths. Positive bias stress stability is tuned by applying both the OSC and carbon chain effect, leading to stable, high-performance TFTs with the determination of subgap density of states to confirm the compensation effects on the total acceptor-like defect states. The n-doping of identical passivation layers is further investigated by using perylenedicarboximide derivatives to confirm the proposed n-doping mechanism. Finally, the semiconductor 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene is selected on the basis of our proposed passivation model and exhibited good passivation characteristics. This study demonstrates an ideal molecular design for organic passivation layers, which shows significant potential for the realization of stable, high-performance TFTs.
Optimized Activation of Solution-Processed Amorphous Oxide Semiconductors for Flexible Transparent Conductive Electrodes
(WILEY, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2018) Choi, Byung Doo; Park, Joohyung; Baeg, Kang-Jun; Kang, Minji; Heo, Jae Sang; Kim, Seonhyoung; Won, Jongkook; Yu, Seungwoo; Ahn, Kyunghan; Lee, Tae Hoon; Hong, Jongin; Kim, Dong-Yu; Usta, Hakan; Kim, Choongik; Park, Sung Kyu; Kim, Myung-Gil; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Here, the preparation of transparent amorphous oxide semiconductor (AOS) films with unprecedented conductivity via an optimized activation process under hydrogen atmosphere for applications in solution-processed large-area optoelectronics is reported. Owing to their high cost and mechanical vulnerability, conventional vacuum-processed indium-tin oxide (ITO) electrodes are inappropriate for use in next-generation flexible and wearable electronic devices and systems. As an alternative to the ITO electrodes, solution-processed AOS films, such as alpha-IZO and alpha-ZITO, with an optimized composition and postreduction treatment under hydrogen show the highest electrical conductivity of approximate to 300 S cm(-1) and a high optical transmittance of over 90% at 550 nm. The microstructures and electrical properties of these AOS films are also studied in order to determine the optimized chemical composition and postreduction conditions. It is found that a controlled hydrogen reduction treatment of AOS films is critical for achieving high electrical conductivity by suppressing the surface morphology degradation and grain boundary disconnection. Furthermore, the alpha-IZO transparent conductive electrodes are successfully implemented for high efficiency organic photovoltaic cells based on the PTB7/PC71BM active layers. This technique promises the low-cost fabrication of high mobility and/or conductive AOSs for their applications in large-area transparent and flexible optoelectronics.
Semiconducting Copolymers Based on meso-Substituted BODIPY for Inverted Organic Solar Cells and Field-Effect Transistors
(Advanced Electronic Materials, 2018) Ozdemir, Mehmet; Kim, Sang Woo; Kim, Hyungsug; Kim, Myung-Gil; Kim, Bumjoon J.; Kim, Choongik; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
The synthesis, physicochemical, and optoelectronic properties of a new class of low band-gap (?1.3 eV) donor–acceptor copolymers based on a highly electron-deficient meso-5-(2-octyldodecyl)thiophene-substituted BODIPY ?-unit are presented. The polymeric solutions exhibit strong aggregation-dependent excitonic properties indicating the presence of enhanced ?-coherence as a result of strong interchain interactions. The polymeric semiconductor thin films prepared by spin coating show isotropic nodule-like grains with essentially no ordering in the out-of-plane direction. Field-effect hole mobilities of 0.005 cm2 V-1·s-1 are observed in bottom-gate top-contact organic field-effect transistors, and inverted bulk-heterojunction organic photovoltaics employing the polymer:PC71BM active layer exhibit excellent power conversion efficiencies of 6.2% with a short-circuit current of 16.6 mA cm-2. As far as it is known, this is a record high value achieved to date for a boron-containing donor polymer in the photovoltaic literature indicating a significant enhancement in power conversion efficiency (>3–4 times). The findings clearly present that rationally designed BODIPY-based donor–acceptor copolymers can be a key player in photovoltaic applications.