Browsing by Author "Facchetti, Antonio"

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Design and development of functional organic small molecules and polymers for optoelectronics
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2016) Usta, Hakan; Demirel, Gokhan; Facchetti, Antonio; Muccini, Michele; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Design and development of functional organic small molecules and polymers for 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.
Indenofluorenes for organic optoelectronics: the dance of fused five- and six-membered rings enabling structural versatility
(Royal Society of Chemistry, 2022) Can, Ayse; Facchetti, Antonio; Usta, Hakan; 0000-0002-9398-3581; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Can, Ayse; Usta, Hakan
Polycyclic π-conjugated hydrocarbons (PCHs), either unfunctionalized or structurally modified derivatives, have attracted tremendous interest in the past few decades as high-performance semiconductors for use in new generations of organic (opto)electronic devices. Among several PCHs realized to date, the 6-5-6-5-6 π-fused-ring backbone of indenofluorene (IF) stands out as a unique semiconducting architecture with great structural and property versatility affording six different regioisomers, diverse functionalization/substitution positions, π-conjugation/delocalization patterns, aromatic behaviors, and electronic structures. In this review, we summarize and analyze the historical and recent advances in the design and implementation of IF-based semiconductors in organic transistor and solar cell devices, as well as in understanding the chemical structure-molecular property-semiconductivity relationships. Following an introduction to the fascinating properties of an IF π-framework that distinguishes this core among PCHs, we present IF-based semiconductors and discuss their properties by classifying them into four main families (IF-diones, IF-DCVs/IF-TTFs, π-IFs, and (un)substituted DH-IFs) considering whether methylene or methine C-bridges are present and how these positions are functionalized or substituted. For each family, design and synthetic approaches, molecular properties, and transistor/solar cell device applicability and/or performance are reviewed and discussed. At the end, we conclude with a section discussing the challenges and opportunities for future progress of IF-based semiconductor materials and related (opto)electronic technologies.
Insights Into Interface Treatments in p-Channel Organic Thin-Film Transistors Based on a Novel Molecular Semiconductor
(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC445 HOES LANE, PISCATAWAY, NJ 08855-4141, 2017) Liguori, Rosalba; Usta, Hakan; Fusco, Sandra; Facchetti, Antonio; Licciardo, Gian Domenico; Di Benedetto, Luigi; Rubino, Alfredo; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Organic thin-film transistors (OTFTs) were fabricated using a novel small molecule, C6-NTTN, as the semiconductor layer in several different architectures. The C6-NTTN layer was deposited via both vacuum evaporation at different substrate temperatures and via solution-processing, which yield maximum hole mobilities of 0.16 and 0.05 cm(2)/V . s, respectively. Surface treatments of the substrate, insulator, and metal contacts used for OTFT fabrication employing polymer films and different self-assembled monolayers were investigated. In particular, in bottom-gate devices, the insulator surface hydrophobicity was optimized by the deposition of poly(methyl methacrylate) or hexamethyldisilazane, while in the top-gate geometry, pentafluorobenzenethiol was efficiently used to modify the substrate surface energy and to change the contact work function. Atomic force microscopy analysis was exploited to understand the relationship between the semiconductor thin-film morphology and the device electrical performance. The results shown here indicate an inverse proportionality between the mobility and the interface trap density, with parameters depending especially on semiconductor-insulator interfacial properties, and a correlation between the threshold voltage and the characteristics of the semiconductor-metal interface.
Interplay between Charge Injection, Electron Transport, and Quantum Efficiency in Ambipolar Trilayer Organic Light-Emitting Transistors
(WILEY, 2022) Moschetto, Salvatore; Benvenuti, Emilia; Usta, Hakan; Özdemir, Resul; Facchetti, Antonio; Muccini, Michele; Prosa, Mario; Toffanin, Stefano; 0000-0003-4099-8664; 0000-0001-5533-1585; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
The fascinating characteristic of organic light-emitting transistors (OLETs) of being electrical switches with an intrinsic light-emitting capability makes them attractive candidates for a wide variety of applications, ranging from sensors to displays. To date, the OLET ambipolar trilayer heterostructure is the most developed architecture for maximizing device performance. However, a major challenge of trilayer OLETs remains the inverse correlation between external quantum efficiency and brightness under ambipolar conditions. The complex interconnection between electroluminescent and ambipolar charge transport properties, in conjunction with the limited availability of electron transport semiconducting materials, has indeed hampered the disruptive evolution of the OLET technology. Here, an in-depth study of the interplay of the key fundamental features that determine the device performance is reported by exploring electron transport semiconductors with different properties in ambipolar trilayer OLETs. Through the selection of compounds with tailored chemical structures, the relation between intrinsic optoelectronic characteristics of the electron transport semiconductor, energy level alignment within the structure, and morphological features is unraveled. Furthermore, the introduction of a suitable electron injector at the emissive/semiconducting layers interface sheds light into the bidimensional nature of OLETs that is a distinguishing factor of this class of devices with respect to prototypical organic light-emitting diodes.
Micro-/Nanostructured Highly Crystalline Organic Semiconductor Films for Surface-Enhanced Raman Spectroscopy Applications
(WILEY-V C H VERLAG GMBH, 2015) Yilmaz, Mehmet; Ozdemir, Mehmet; Erdogan, Hakan; Tamer, Ugur; Sen, Unal; Facchetti, Antonio; Usta, Hakan; Demirel, Gokhan; 0000-0003-3736-5049; 0000-0002-0618-1979; 0000-0001-5790-2943; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Usta, Hakan; Sen, Unal
The utilization of inorganic semiconductors for surface-enhanced Raman spectroscopy (SERS) has attracted enormous interest. However, despite the technological relevance of organic semiconductors for enabling inexpensive, large-area, and flexible devices via solution processing techniques, these p-conjugated systems have never been investigated for SERS applications. Here for the first time, a simple and versatile approach is demonstrated for the fabrication of novel SERS platforms based on micro-/nanostructured 2,7-dioctyl[1]benzothieno[3,2-b][1] benzothiophene (C8-BTBT) thin films via an oblique-angle vapor deposition. The morphology of C8-BTBT thin films is manipulated by varying the deposition angle, thus achieving highly favorable 3D vertically aligned ribbon-like micro-/nanostructures for a 90 degrees deposition angle. By combining C8-BTBT semiconductor films with a nanoscopic thin Au layer, remarkable SERS responses are achieved in terms of enhancement (approximate to 10(8)), stability (>90 d), and reproducibility (RSD < 0.14), indicating the great promise of Au/C8-BTBT films as SERS platforms. Our results demonstrate the first example of an organic semiconductor-based SERS platform with excellent detection characteristics, indicating that p-conjugated organic semiconductors have a great potential for SERS applications.
Molecular engineering of organic semiconductors enables noble metal-comparable SERS enhancement and sensitivity
(NATURE PUBLISHING GROUP, MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND, 2019) Demirel, Gokhan; Gieseking, Rebecca L. M.; Ozdemir, Resul; Kahmann, Simon; Loi, Maria A.; Schatz, George C.; Facchetti, Antonio; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
Nanostructured molecular semiconductor films are promising Surface-Enhanced Raman Spectroscopy (SERS) platforms for both fundamental and technological research. Here, we report that a nanostructured film of the small molecule DFP-4T, consisting of a fully pi-conjugated diperfluorophenyl-substituted quaterthiophene structure, demonstrates a very large Raman enhancement factor (>10(5)) and a low limit of detection (10(-9) M) for the methylene blue probe molecule. This data is comparable to those reported for the best inorganic semiconductor- and even intrinsic plasmonic metal-based SERS platforms. Photoluminescence spectroscopy and computational analysis suggest that both charge-transfer energy and effective molecular interactions, leading to a small but non-zero oscillator strength in the charge-transfer state between the organic semiconductor film and the analyte molecule, are required to achieve large SERS enhancement factors and high molecular sensitivities in these systems. Our results provide not only a considerable experimental advancement in organic SERS figure-of-merits but also a guidance for the molecular design of more sensitive SERS systems.
Nanostructured organic semiconductor films for molecular detection with surface-enhanced Raman spectroscopy
(NATURE RESEARCHHEIDELBERGER PLATZ 3, BERLIN 14197, GERMANY, 2017) Yilmaz, Mehmet; Babur, Esra; Ozdemir, Mehmet; Gieseking, Rebecca L.; Dede, Yavuz; Tamer, Ugur; Schatz, George C.; Facchetti, Antonio; Usta, Hakan; Demirel, Gokhan; 0000-0002-0618-1979; 0000-0001-5790-2943; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Usta, Hakan
pi-Conjugated organic semiconductors have been explored in several optoelectronic devices, yet their use in molecular detection as surface-enhanced Raman spectroscopy (SERS)-active platforms is unknown. Herein, we demonstrate that SERS-active, superhydrophobic and ivy-like nanostructured films of a molecular semiconductor, alpha,omega-diperfluorohexylquaterthiophene (DFH-4T), can be easily fabricated by vapour deposition. DFH-4T films without any additional plasmonic layer exhibit unprecedented Raman signal enhancements up to 3.4 x 10(3) for the probe molecule methylene blue. The combination of quantum mechanical computations, comparative experiments with a fluorocarbon-free alpha,omega-dihexylquaterthiophene (DH-4T), and thin-film microstructural analysis demonstrates the fundamental roles of the pi-conjugated core fluorocarbon substitution and the unique DFH-4T film morphology governing the SERS response. Furthermore, Raman signal enhancements up to similar to 10(10) and sub-zeptomole (< 10(-21) mole) analyte detection were accomplished by coating the DFH-4T films with a thin gold layer. Our results offer important guidance for the molecular design of SERS-active organic semiconductors and easily fabricable SERS platforms for ultrasensitive trace analysis.
Nanostructured superhydrophobic organic semiconductor films enable sub-zeptomole level molecular sensing in surface-enhanced Raman spectroscopy
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2017) Demirel, Gokhan; Usta, Hakan; Facchetti, Antonio; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Nanostructured superhydrophobic organic semiconductor films enable sub-zeptomole level molecular sensing in surface-enhanced Raman spectroscopy
Naphthalene diimide-based polymeric semiconductors. Effect of chlorine incorporation and n-channel transistors operating in water
(MRS COMMUNICATIONS, 2016) Ryu, Gi-Seong; Chen, Zhihua; Usta, Hakan; Noh, Yong-Young; Facchetti, Antonio; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
We demonstrate here the design, synthesis and characterization of two new chlorinated polymers, P(NDI2HD-T2Cl2) and P(NDI2OD-T2Cl2) based on N,N-difunctionalized naphthalene diimide (NDI) and 3,3-dichloro-2,2-bithiophene (T2Cl2) moieties. Our results indicate that organic thin-film transistors (OTFTs) based on these new chlorinated polymers exhibit electron mobilities approaching 0.1 cm(2)V(-1)s(-1) (I-on:I-off similar to 10(6)-10(7)), with far less ambipolarity due to their lower highest occupied molecular orbital energies, and they are more stable under deleterious high-humidity conditions (RH similar to 60%) and upon submersion in water, compared with those fabricated with the parent non-chlorinated polymers. In addition, OTFTs fabricated with the new chlorinated polymers exhibit excellent operational stabilities with <3% degradations upon bias-stress test.
Organic semiconductor based surface-enhanced Raman spectroscopy platforms
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2018) Demirel, Gokhan; Usta, Hakan; Facchetti, Antonio; 0000-0002-9778-917X; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Mühendislik Bilimleri Bölümü
Conference Conference: 256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond Location: Boston, MA Date: AUG 19-23, 2018 Sponsor(s):Amer Chem Soc
Paper-based substrates for sustainable (opto)electronic devices
(ELSEVIER, 2022) Usta, Hakan; Facchetti, Antonio; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Cellulose-based paper has been a convenient eco-friendly platform for storing and exchanging information for thousands of years. Amazingly, the studies and advancements in the past decade have demonstrated that paper and nanocellulose-based substrates are also attractive for fabricating flexible electronic circuits as well as optoelectronic components and devices. Paper and nanocellulose-based substrates have been considered for use in new generation green devices and optoelectronic applications based on their sustainable and inexpensive source, lightweight, and superior mechanical/optical properties, all factors that could also reduce manufacturing costs for producing these devices. In this chapter, we review functional materials and optoelectronic devices fabricated on paper or nanocellulose-based substrates including transistors and circuits, solar cells, light-emitting diodes, and other devices, such as sensors/actuators, batteries, supercapacitors/energy-harvesters, and breathalyzer/diagnosis devices. We also thoroughly discuss remaining challenges and promising research directions with paper-based substrates for future advancements in green optoelectronics.
Perfluoroalkyl-Functionalized Thiazole Thiophene Oligomers as N-Channel Semiconductors in Organic Field-Effect and Light-Emitting Transistors
(AMER CHEMICAL SOC, 2014) Sheets, William Christopher; Denti, Mitchell; Generali, Gianluca; Capelli, Raffaella; Lu, Shaofeng; Yu, Xinge; Muccini, Michele; Facchetti, Antonio; Usta, Hakan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Despite their favorable electronic and structural properties, the synthetic development and incorporation of thiazole-based building blocks into n-type semiconductors has lagged behind that of other π-deficient building blocks. Since thiazole insertion into π-conjugated systems is synthetically more demanding, continuous research efforts are essential to underscore their properties in electron-transporting devices. Here, we report the design, synthesis, and characterization of a new series of thiazole–thiophene tetra- (1 and 2) and hexa-heteroaryl (3 and 4) co-oligomers, varied by core extension and regiochemistry, which are end-functionalized with electron-withdrawing perfluorohexyl substituents. These new semiconductors are found to exhibit excellent n-channel OFET transport with electron mobilities (μe) as high as 1.30 cm2/(V·s) (Ion/Ioff > 106) for films of 2 deposited at room temperature. In contrary to previous studies, we show here that 2,2′-bithiazole can be a very practical building block for high-performance n-channel semiconductors. Additionally, upon 2,2′- and 5,5′-bithiazole insertion into a sexithiophene backbone of well-known DFH-6T, significant charge transport improvements (from 0.001–0.021 cm2/(V·s) to 0.20–0.70 cm2/(V·s)) were observed for 3 and 4. Analysis of the thin-film morphological and microstructural characteristics, in combination with the physicochemical properties, explains the observed high mobilities for the present semiconductors. Finally, we demonstrate for the first time implementation of a thiazole semiconductor (2) into a trilayer light-emitting transistor (OLET) enabling green light emission. Our results show that thiazole is a promising building block for efficient electron transport in π-conjugated semiconductor thin-films, and it should be studied more in future optoelectronic applications.
Photosensing Properties of Pentacene OFETs Based on a Novel PMMA Copolymer Gate Dielectric
(IEEE, 2015) Loffredo, Fausta; GRIMALDI, IMMACOLATAANGELICA; Miscioscia, Riccardo; Nenna, Giuseppe; Villani, Fulvia; Minarini, Carla; Petrosino, Mario; Rubino, Alfredo; Usta, Hakan; Facchetti, Antonio; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
In the present work, bottom-gate top-contact organic field effect transistors (OFETs) were fabricated by evaporating a pentacene semiconductor film on top of a new insulating poly(methyl methacrylate) (PMMA) copolymer containing methacrylate units. The PMMA copolymer was synthesized in order to combine the well-known insulating properties of PMMA with the possibility to be efficiently photocured enabling photopatterning-based organic circuitry integration processes. The properties of the pentacene layer deposited on ITO/PMMA copolymer stack were studied through morphological and structural analyses. Device photoresponses and photoexcitated transients were investigated and compared to reference devices based on standard PMMA gate dielectric.
pi-Conjugated donor-acceptor small molecule thin-films on gold electrodes for reducing the metal work-function
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2016) Azum, Naved; Taib, Layla Ahmad; Al Angari, Yasser Mohammed; Asiri, Abdullah M.; Denti, Mitchel; Zhao, Wei; Usta, Hakan; Facchetti, Antonio; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
This paper reports the design, facile synthesis and purification of four pi-conjugated donor-acceptor small molecules comprising heteroaromatic units, DA-1-DA-4, for surface and electronic structure modification of gold thin film. These molecules were characterized by H-1/C-13 nuclear magnetic resonance spectroscopy, cyclic voltammetry, UV-Vis spectroscopy, and single-crystal X-ray diffraction. Morphologically smooth thin-films (similar to 5 nm) of DA-1-DA-4 were deposited onto Au thin films via thermal evaporation and characterized by atomic force microscopy, theta-2 theta X-ray diffraction and ultraviolet photoelectron spectroscopy. The work functions of the small molecule coated Au electrodes are shifted to lower energies by similar to 0.1-03 eV, compared to that of the bare Au film measured as a reference. The vapor-deposition of structurally,simple small molecules developed here shows great promise as a facile approach to reduce gold work function for electron injection/extraction between organic semiconductors and Au contacts in various opto-electronic devices. (C) 2016 Elsevier B.V. All tights reserved.
Polymeric and Small-Molecule Semiconductors for Organic Field-Effect Transistors
(Wliey Online Library, 2015) Usta, Hakan; Facchetti, Antonio; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
This chapter reviews the achievements in the development of molecular and polymeric semiconductors for charge transport in thin-film transistors (TFTs). In particular, it introduces the basic concepts of organic semiconductor structure and organic thin-film transistor (OTFT) operation and then focuses on initial studies and works. Organic semiconductors for OTFTs must possess two essential structural features for their successful implementation in printed electronics. The first feature is a π-conjugated core/chain composed of linked unsaturated units. The second feature is core functionalization with solubilizing substituents, which is essential for inexpensive manufacture by solution methods as well as for enhancing solid-state core interactions. There are several advantages in using polymeric versus molecular p-conjugated semiconductors. Isoindigo has become a popular conjugated moiety in polymer semiconductor design because of its strong electron-withdrawing character. Polymeric p-channel TFTs have reached new heights, with hole mobilities unthinkable only few years back and surpassing 10 cm2V-1 s-1.
Selective Remanent Ambipolar Charge Transport in Polymeric Field-Effect Transistors For High-Performance Logic Circuits Fabricated in Ambient
(WILEY-V C H VERLAG GMBHPOSTFACH 101161, 69451 WEINHEIM, GERMANY, 2014) Fabiano, Simone; Usta, Hakan; Forchheimer, Robert; Crispin, Xavier; Facchetti, Antonio; Berggren, Magnus; 0000-0001-5154-0291; 0000-0001-7016-6514; 0000-0002-0618-1979; 0000-0002-8175-7958; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Ambipolar polymeric field-effect transistors can be programmed into a p- or n-type mode by using the remanent polarization of a ferroelectric gate insulator. Due to the remanent polarity, the device architecture is suited as a building block in complementary logic circuits and in CMOS-compatible memory cells for non-destructive read-out operations.
Solution-Processable BODIPY-Based Small Molecules for Semiconducting Microfibers in Organic Thin-Film Transistors
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2016) Ozdemir, Mehmet; Choi, Donghee; Kwon, Guhyun; Zorlu, Yunus; Cosut, Bunyemin; Kim, Hyekyoung; Facchetti, Antonio; Kim, Choongik; Usta, Hakan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Usta, Hakan
Electron-deficient pi-conjugated small molecules can function as electron-transporting semiconductors in various optoelectronic applications. Despite their unique structural, optical, and electronic properties, the development of BODIPY-based organic semiconductors has lagged behind that of other pi-deficient units. Here, we report the design and synthesis of two novel solution-proccessable BODIPY-based small molecules (BDY-3T-BDY and BDY-4T-BDY) for organic thin-film transistors (OTFTs). The new semiconductors were fully characterized by H-1/C-13 NMR, mass spectrometry, cyclic voltammetry, UV-vis spectroscopy, photoluminescence, differential scanning calorimetry, and thermogravimetric analysis. The single-crystal X-ray diffraction (XRD) characterization of a key intermediate reveals crucial structural properties. Solution-sheared top-contact/bottom-gate OTFTs exhibited electron mobilities up to 0.01 cm(2)/V center dot s and current on/off ratios of >10(8). Film microstructural and morphological characterizations indicate the formation of relatively long (similar to 0.1 mm) and micrometer-sized (1-2 mu m) crystalline fibers for BDY-4T-BDY-based films along the shearing direction. Fiber-alignment-induced charge-transport anisotropy (mu?/mu approximate to 10) was observed, and higher mobilities were achieved when the microfibers were aligned along the conduction channel, which allows for efficient long-range charge-transport between source and drain electrodes. These OTFT performances are the highest reported to date for a BODIPY-based molecular semiconductor, and demonstrate that BODIPY is a promising building block for enabling solution-processed, electron-transporting semiconductor films.
Ultrahigh Vacuum Self-Assembly of Rotationally Commensurate C8-BTBT/MoS2/Graphene Mixed-Dimensional Heterostructures
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Liu, Xiaolong; Balla, Itamar; Sangwan, Vinod K.; Usta, Hakan; Facchetti, Antonio; Marks, Tobin J.; Hersam, Mark C.; 0000-0002-0618-1979; 0000-0002-9358-5743; 0000-0002-5623-5285; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Mixed-dimensional van der Waals heterostructures combine the advantages of nanomaterials with qualitatively distinct properties such as the extended bandstructures and high charge carrier mobilities of inorganic two-dimensional materials and the discrete orbital energy levels and strong optical absorption of zero-dimensional organic molecules. The synergistic interplay between nanomaterials of distinct dimensionality has enabled a variety of unique applications such as antiambipolar transistors, sensitized photodetectors, and gate-tunable photovoltaics. Because the performance of mixed-dimensional heterostructure devices depends sensitively on the buried interfacial structure, it is of great interest to identify materials and chemistries that naturally form highly ordered heterointerfaces. Toward this end, here we demonstrate ultrahigh vacuum self-assembly of 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C8-BTBT) monolayers onto epitaxial MoS2/graphene heterostructures. With molecular-resolution scanning tunneling microscopy and spectroscopy, the resulting C8-BTBT/MoS2/graphene mixed-dimensional heterostructures are found to be rotationally commensurate with well-defined physical and electronic structures. It is further shown that the self-assembled C8-BTBT monolayers are insensitive to the structural defects and electronic perturbations of the underlying MoS2 substrate, which provides significant processing latitude. For these reasons, this work will facilitate ongoing efforts to utilize organic/MoS2/graphene mixed-dimensional heterostructures for electronic, optoelectronic, and photovoltaic applications.