WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 54Citation - Scopus: 57Ultralow Bandgap Molecular Semiconductors for Ambient-Stable and Solution-Processable Ambipolar Organic Field-Effect Transistors and Inverters(Royal Soc Chemistry, 2017) Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kwon, Guhyun; Kim, Hyekyoung; Sen, Unal; Usta, HakanThe design and development of novel ambipolar semiconductors is very crucial to advance various optoelectronic technologies including organic complementary (CMOS) integrated circuits. Although numerous high-performance ambipolar polymers have been realized to date, small molecules have been unable to provide high ambipolar performance in combination with ambient-stability and solution-processibility. In this study, by implementing highly p-electron deficient, ladder-type IFDK/IFDM acceptor cores with bithiophene donor units in D-A-D pi-architectures, two novel small molecules, 2OD-TTIFDK and 2OD-TTIFDM, were designed, synthesized and characterized in order to achieve ultralow band-gap (1.21-1.65 eV) semiconductors with sufficiently balanced molecular energetics for ambipolarity. The HOMO/LUMO energies of the new semiconductors are found to be -5.47/-3.61 and -5.49/-4.23 eV, respectively. Bottom-gate/top-contact OFETs fabricated via solution-shearing of 2OD-TTIFDM yield perfectly ambient stable ambipolar devices with reasonably balanced electron and hole mobilities of 0.13 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(3)-10(4), and 2OD-TTIFDK-based OFETs exhibit ambipolarity under vacuum with highly balanced (mu(e)/mu(h) similar to 2) electron and hole mobilities of 0.02 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(5)-10(6). Furthermore, complementary-like inverter circuits were demonstrated with the current ambipolar semiconductors resulting in high voltage gains of up to 80. Our findings clearly indicate that ambient-stability of ambipolar semiconductors is a function of molecular orbital energetics without being directly related to a bulk p-backbone structure. To the best of our knowledge, considering the processing, charge-transport and inverter characteristics, the current semiconductors stand out among the best performing ambipolar small molecules in the OFET and CMOS-like circuit literature. Our results provide an efficient approach in designing ultralow band-gap ambipolar small molecules with good solution-processibility and ambient-stability for various optoelectronic technologies, including CMOS-like integrated circuits.Article Citation - WoS: 25Citation - Scopus: 25Triisopropylsilylethynyl-Substituted Indenofluorenes: Carbonyl Versus Dicyanovinylene Functionalization in One-Dimensional Molecular Crystals and Solution-Processed N-Channel Ofets(Royal Soc Chemistry, 2018) Ozdemir, Resul; Park, Sangyun; Deneme, Ibrahim; Park, Yonghan; Zorlu, Yunus; Alidagi, Husniye Ardic; Usta, HakanThe design and synthesis of novel electron-deficient and solution-processable polycyclic aromatic hydrocarbons offers great opportunities for the development of low-cost and large-area (opto)electronics. Although (trialkylsilyl)ethynyl (R3Si-C?C-) has emerged as a very popular unit to solubilize organic semiconductors, it has been applied only to a limited class of materials that are mostly substituted on short molecular axes. Herein, two novel solution-processable indenofluorene-based semiconductors, TIPS-IFDK and TIPS-IFDM, bearing (triisopropylsilyl)ethynyl end units at 2,8-positions (long molecular axis substitution) were synthesized, and their single-crystal structures, optoelectronic properties, solution-sheared thin-film morphologies/microstructures, and n-channel field-effect responses were studied. In accordance with the DFT calculations, the HOMO/LUMO energies of the new compounds are found to be -5.77/-3.65 eV and -5.84/-4.18 eV for TIPS-IFDK and TIPS-IFDM, respectively, reflecting the high electron deficiency of the new -backbones. Both semiconductors exhibit slightly S-shaped molecular frameworks with highly coplanar IFDK/IFDM -cores, and they form slipped -stacked one-dimensional (1-D) columnar motifs in the solid state. However, substantial differences in the degree of - interactions and stacking distances (4.04 angstrom vs. 3.47 angstrom) were observed between TIPS-IFDK and TIPS-IFDM as a result of carbonyl vs. dicyanovinylene functionalization, which results in a three orders of magnitude variation in the charge carrier mobility of the corresponding thin films. Top-contact/bottom-gate OFETs fabricated via solution-shearing TIPS-IFDM yielded one of the best performances in the (trialkylsilyl)ethynyl literature ((e) = 0.02 cm(2) V-1 s(-1), I-on/I-off = 10(7)-10(8), and V-T approximate to 2 V under ambient atmosphere) for a 1-D polycrystalline semiconductor microstructure. To the best of our knowledge, the molecules presented here are the first examples of n-type semiconductors substituted with (trialkylsilyl)ethynyl groups on their long molecular axes.Article Citation - WoS: 16Citation - Scopus: 17Organic and Inorganic Semiconducting Materials-Based SERS: Recent Developments and Future Prospects(Royal Soc Chemistry, 2024) Ozdemir, Resul; Ozkan Hukum, Kubra; Usta, Hakan; Demirel, GokhanSurface-enhanced Raman spectroscopy (SERS) with high sensitivity/selectivity is a powerful analytical tool and has been widely used, particularly in the fields of chemistry, spectroscopy, molecular detection, food safety, anti-counterfeiting, and environmental monitoring. Conventional SERS detection relies on plasmonic materials (e.g., Au and Ag nanostructures) with exceedingly high enhancement factors up to 1012. However, these substrates encounter significant limitations, including poor reproducibility, high cost, lack of selectivity, limited SERS active area leading to inconsistent field enhancement and SERS signals, and the possibility of the photothermal decomposition of the analyte species. These drawbacks have the potential to impede detection accuracy and hinder large-scale practical applications. This review focuses on alternative approaches based on noble metal-free SERS substrates. Considering recent advancements in the field of SERS active platforms, we first introduce the implementation of inorganic compounds, including metal oxides, transition metal sulfides/-selenides/-tellurides, 2-D layered transition metal carbides and nitrides (Mxenes), metal-organic frameworks (MOFs), and single elemental inorganic materials for Raman signal enhancement applications. In the second part of the review, we highlight the fast-growing field of SERS-active organic platforms. Moreover, we discuss the promises and challenges for the future direction of organic and inorganic material-based SERS. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool and has been widely used, in different fields including molecular detection, food safety, anti-counterfeiting, and environmental monitoring.Article Citation - WoS: 16Citation - Scopus: 15Engineering Functionalized Low LUMO [1]Benzothieno[3,2-B][1]Benzothiophenes (BTBTs): Unusual Molecular and Charge Transport Properties(Royal Soc Chemistry, 2020) Ozdemir, Resul; Ahn, Kyunghan; Deneme, Ibrahim; Zorlu, Yunus; Kim, Dojun; Kim, Myung-Gil; Usta, HakanDiacene-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.Article Citation - WoS: 33Citation - Scopus: 34A Hybridized Local and Charge Transfer Excited State for Solution-Processed Non-Doped Green Electroluminescence Based on Oligo(p-Phenyleneethynylene)(Royal Soc Chemistry, 2020) Usta, Hakan; Alimli, Dilek; Ozdemir, Resul; Tekin, Emine; Alkan, Fahri; Kacar, Rifat; Can, AyseWe herein report a new highly efficient green emissive hot-exciton molecule, 1,4-bis((4'-diphenylamino3-cyano-[1,1'-biphenyl]-4-yl)ethynyl)-2,5-bis(2-ethylhexyloxy)benzene (2EHO-TPA-CNPE) that consists of an extended D'-pi'-A-pi-D-pi-A-pi'-D' molecular p-system with diphenylamino end units (D') and ethynylene/phenylene spacers (pi/pi'). The new molecule exhibits high photoluminescence (PL) quantum efficiencies (Phi(PL) = 0.95 (solution) and 0.45 (spin-coated neat thin-film)), and a strong PL solvatochromic behavior revealing significant changes in excited state energies/characteristics (locally excited (LE) -> hybridized local and charge transfer (HLCT) - charge-transfer (CT)) depending on solvent polarity. Highly efficient (radiative exciton yield (eta(r)) = 50-59% >> 25%) green-emitting OLEDs were fabricated in a conventional device architecture by employing (non-)doped thin-films reaching a maximum current efficiency (CEmax) of 12.0 cd A(-1) and a maximum external quantum efficiency (EQE(max)) of 5.5%. The emission profile of the non-doped OLED has CIE 1976 (u', v') chromaticity coordinates of (0.10, 0.55) corresponding to a night vision imaging system (NVIS) compatible Green A region. 2EHO-TPA-CNPE-based OLED devices of industrial relevance were also fabricated by ink-jet printing the emissive layer and by fabricating an inverted architecture, which possessed respectable device performances of 2.4-6.1 cd A(-1). The solid-state solvation effect in OLED devices yields HLCT electronic behavior resulting in high Zr's, which is confirmed by TDDFT to originate from energetically/spatially favorable reverse intersystem crossings (RISCs) (T-2/3 -> S-1). As a unique observation, delayed fluorescence due to this RISC was evident in the PL decay lifetime measurement with a ns-scale lifetime of similar to 10 ns. These results clearly allow a better understanding of the structure-photophysical property-electroluminescence relationships in this new class of oligo(p-phenyleneethynylene)-based hot-exciton molecules, and it could open up new opportunities for high-performance solution-processed optoelectronic/sensing applications.Article Citation - WoS: 39Citation - Scopus: 37A Dopant-Free 2,7-Dioctyl[1]Benzothieno[3,2 (C8-BTBT) Hole Transporting Layer for Highly Stable Perovskite Solar Cells With Efficiency Over 22%(Royal Soc Chemistry, 2022) Kaya, Ismail Cihan; Ozdemir, Resul; Usta, Hakan; Sonmezoglu, SavasIn this study, for the first time, n-i-p PSCs were fabricated using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL). The power conversion efficiency (PCE) of the optimized device with the C8-BTBT film that favored edge-on molecular alignment was 22.45% with negligible hysteresis. A thinner dopant-free C8-BTBT HTL effectively protected the perovskite layer from moisture resulting in better shelf-life stability for un-encapsulated PSCs, which maintained >80% of its initial PCE (after a period of 120 days) at a relative humidity level of 40-45%. In addition, the C8-BTBT-based PSCs kept their high performance with no obvious PCE loss at 60 degrees C for 20 days in the ambient atmosphere and retained 82% of their initial PCE at 85 degrees C for 10 days. Overall, our findings revealed that a thin solution-processed C8-BTBT HTL plays a critical role not only in hole extraction and transport but also in greatly improving the ambient and thermal stability of n-i-p PSCs.