Browsing by Author "Kara, Koray"

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Electroluminescence Performance of a Series of Fluorene/2,5-di(2-thienyl)-1h-pyrrole Polymers
(WILEY, 2020) Bilgili, Hakan; Kara, Koray; Yenel, Esma; Demiç, Şerafettin; Kuş, Mahmut; Koyuncu, Sermet
In this article, a series of fluorene/2,5-dithenyl-1H-pyrrole-based electroactive polymers (HS-X) with different feed ratio of SC12F/OF were synthesized via Suzuki coupling reactions. Chemical characterization of polymers was elucidated by(1)H NMR and Fourier-transform infrared spectroscopy. Electrochemical and electrophysical characterization of the synthesized polymers were investigated by cyclic voltammetry, UV-vis spectroscopy, and fluorescence spectroscopy. Thermal stability of polymers were studied with differential scanning calorimetry and manipulation of the Tg values of HS-X polymers was managed by increasing the numbers of the spiroalkylated fluorene (SAF) moieties incorporated into the polymer backbone. Five different conjugated polymers (HS-1, HS-2, HS-3, HS-4, and HS-5) were used as hole transport layer material in the fabrication of organic light-emitting diode (OLED) devices. The energy levels of the highest occupied molecular orbital as well as the lowest unoccupied molecular orbital and photoluminescence intensities were independent of the number of SAF units. OLED devices based on HS-X polymers were fabricated according to ITO/PEDOT:PSS/HS-X/Alq3/LiF:Al device configuration. Their electroluminescence performances were investigated and the best performance were obtained with the polymer containing 20% SC12F (HS-4) in an OLED device with a turn on voltage of 11.8 V, a maximum luminance of 1202 cd/m(2)and a maximum luminous efficiency of 0.30 cd/A compared to other polymers with different feed ratio.
Citation - WoS: 23
Citation - Scopus: 25
Improving the Performance of Inverted Polymer Solar Cells Through Modification of Compact Tio2 Layer by Different Boronic Acid Functionalized Self-Assembled Monolayers
(ELSEVIER SCIENCE BV, 2019) Kırbıyık, Çisem; Kara, Duygu Akın; Kara, Koray; Büyükçelebi, Sümeyra; Yiğit, Mesude Zeliha; Can, Mustafa; Kuş, Mahmut
In this study, we demonstrate the use of a series of boronic acid functionalized self-assembled monolayers (SAMs) to improve photovoltaic device performance P3HT and PCBM based solar cells. The SAMs treated compact TiO2 (c-TiO2) layer was utilized as an electron transport layer for inverted polymer solar cells (PSCs) with a configuration of FTO/c-TiO2/SAM/P3HT:PCBM/PEDOT:PSS/Ag. The modified with 3,4,5-methoxyphenylboronic acid (3-OMe) SAM shows the best improving due to the enhancement of J(sc) and V-oc. in device, which leads to a 26% improvement (2.8%) over non-modified device (2.2%). The enhancement in the modified devices is achieved by SAM modification reducing recombination of charges and improving charge selectivity. These results prove that the surface and electrical properties of compact TiO2 (c-TiO2) layer can be easily tuned as well as the upper layer morphology can be controlled by SAM modification.
Citation - WoS: 8
Citation - Scopus: 8
Molecular Engineering-Device Efficiency Relation: Performance Boosting of Triboelectric Nanogenerator Through Doping of Small Molecules
(Wiley, 2022) Yigit Arkan, Mesude Z.; Kinas, Zeynep; Arkan, Emre; Gökçe, Celal O.; Kara, Koray; Karabiber, Abdülkerim; Özel, Faruk; Kuş, Mahmut
Triboelectric nanogenerators (TENGs) are promising new generation systems with their basic motion-based working principle using both triboelectric and electrostatic effects. Today, the energy densities of TENGs are insufficient for many electronic devices and new strategies are needed to increase their power conversion efficiency. In this study, two different Perylene-based organic structures were added to the triboelectric layers as well as the electrochemical properties of these structures, and the device parameters related to these properties were investigated. A large variety of instrumental analyses, including cyclic voltammetry, contact angle, scanning electron microscopy, atomic force microscopy, and so on, have been used to identify the relationship between doped molecules, their doping ratios, and obtained fiber structures. Depending on molecular structure and even any small variations in side groups of molecules, different doping rates brought about various device outputs. Compared with undoped layers, doping of small molecules led to a similar to 3.3 times increase in the maximum power of the best-performed devices, and a very high voltage value of 500 V was obtained. The analysis of doping with small molecules undertaken here has extended our knowledge of how material design improves the electrical output and contributes to the device performance in TENGs.
Citation - WoS: 5
Citation - Scopus: 6
Rubrene Single Crystal Solar Cells and the Effect of Crystallinity on Interfacial Recombination
(Royal Soc Chemistry, 2022) Kara, Duygu Akın; Burnett, Edmund K.; Kara, Koray; Usluer, Özlem; Cherniawski, Benjamin P.; Barron, Edward J.; Briseno, Alejandro L.; Kuş, Mahmut
Single crystal studies provide a better understanding of the basic properties of organic photovoltaic devices. Therefore, in this work, rubrene single crystals with a thickness of 250 nm to 1000 nm were used to produce an inverted bilayer organic solar cell. Subsequently, polycrystalline rubrene (orthorhombic, triclinic) and amorphous bilayer solar cells of the same thickness as single crystals were studied to make comparisons across platforms. To investigate how single crystal, polycrystalline (triclinic-orthorhombic) and amorphous forms alter the charge carrier recombination mechanism at the rubrene/PCBM interface, light intensity measurements were carried out. The light intensity dependency of the J(SC), V-OC and FF parameters in organic solar cells with different forms of rubrene was determined. Monomolecular (Shockley Read Hall) recombination is observed in devices employing amorphous and polycrystalline rubrene in addition to bimolecular recombination, whereas the single crystal device is weakly affected by trap assisted SRH recombination due to reduced trap states at the donor acceptor interface. To date, the proposed work is the only systematic study examining transport and interface recombination mechanisms in organic solar cells produced by different structure forms of rubrene.