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    Conventional and inverted organic light emitting diodes based on bright green emmisive polyfluorene derivatives
    (Elsevier Sci Ltd, 2018) Mucur, Selin Piravadili; Kok, Cansu; Bilgili, Hakan; Canimkurbey, Betul; Koyuncu, Sermet
    Electro-active green light-emitting polymers based on polyfluorene derivatives (SF5 and SF6) were synthesized by Suzuki coupling reaction. Effect of fluorenone moiety on the main chain of the polyfluorene with allyl subunit was investigated against to performance of both inverted bottom emission and conventional organic light emitting diodes (IBOLEDs and OLEDs, respectively). 2,2',2-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H- benzimidazole) (TPBI) was then utilized as an electron transport layer (ETL) to analyze the change in transport characteristics of the devices with a structure of ITO/PEDOT:PSS/polyfluorene/TPBI/Ca/Al. The results showed that efficiency enhanced nearly four times while the light output values were lowered with the insertion of TPBI as an ETL. In addition, IBOLEDs were also fabricated with a device architecture of ITO/ZnO/polyfluorene/V2O5 /Al being keen on backwards charge injection behavior of the polymers. IBOLEDs were fabricated by using synthesized zinc oxide (ZnO) as the electron-injecting layer. Luminance and luminous efficiency were significantly low while turn on voltages were too low with respect to the conventional devices fabricated. Further, annealing treatment were optimized for light output characteristics of the fabricated OLEDs. This study revealed the importance of charge transport feature of the synthesized polyfluorene derivatives in electroluminescent devices with variant architecture. (C) 2018 Elsevier Ltd. All rights reserved.
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    Effect of thiophene linker addition to fluorene-benzotriazole polymers with the purpose of achieving white emission in OLEDs
    (Royal Soc Chemistry, 2020) Kok, Cansu; Doyranli, Ceylan; Canimkurbey, Betul; Mucur, Selin Piravadili; Koyuncu, Sermet
    With the purpose of obtaining white emission from single layer organic light emitting diodes (OLEDs), fluorene benzotriazole based polymers with double bond subunits (namely TP2 and SP3 with and without thiophene linker, respectively) were synthesized by a Suzuki cross-coupling polymerization reaction. SP3 and TP2 were used as an emissive layer of the OLED devices due to their outstanding solubility in organic solvents, photoluminescence intensity and morphological suitability for fine thin film-forming capability. The optical, electrochemical, light emission and electroluminescence characteristics, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on SP3 and TP2 were realized in detail to understand the effects of thiophene linker addition as a donor unit to the main chain of fluorene benzotriazole based polymers. As a result, TP2 emitted a bright yellow emission with a maximum brightness of 243 cd m(-2) at 40 mA cm(-2), and a maximum current efficiency of 1.38 cd A(-1) with more broad electroluminescence characteristics than SP3 polymer without the thiophene linker. SP3 emitted a greenish yellow emission with a maximum brightness of 1001 cd m(-2) at 845 mA cm(-2), and a maximum current efficiency of 0.33 cd A(-1). Carrier transport properties, charge carrier transit time and the equivalent circuit modelling studies were obtained through admittance spectroscopy. An equivalent circuit model with a combination of two resistors and one capacitor explained the charge conduction mechanism of SP3 and TP2 based OLEDs. SP3 and TP2 OLED devices represented typical p-type transporting characteristics with mobilities of 0.073 and 0.017 cm(2) V-1 s(-1), respectively with simplified device configuration. All the results indicate that thiophene addition to the main chain of fluorene benzotriazole based polymers with double bond subunits lead to a promising candidate for white emissive materials used in single layer white OLEDs.
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    Thermal annealing effect on light emission profile of polyfluorenes containing double bond subunit
    (Elsevier Science Bv, 2017) Mucur, Selin Piravadili; Kacar, Rifat; Meric, Cagla; Koyuncu, Sermet
    We presented comprehensive photoluminescence (PL) and electroluminescence (EL) studies of polyfluorene based electroactive polymer (SF4) containing double bond side chain to investigate its characteristics as a function of temperature. Annealing treatment was conducted for thin films on glass substrates and also for the organic light emitting diodes (OLEDs) at different temperatures. While polymer thin film coated on to glass substrate annealed at < 150 degrees C exhibited green color emission, OLEDs that annealed at > 150 degrees C shifted white color emission. It was implying that the emission was taking place interchain interaction. Phase modulation at higher annealing temperatures was occurred on the thin film as shown AFM images. Further, annealed polymer film with 120 degrees C exhibited the best performance in OLED device with luminance 5241 cd m (-2), a maximum efficiency 1.54 cd A (-1) and external quantum efficiency 0.54% compared to other polymer films annealed with different temperatures. (C) 2017 Elsevier B. V. All rights reserved.