Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Improving the Device Stability by Controlling the Morphology of Quantum Dot Emissive Layer Via a Coating Process in Blue Qleds(Wiley-v C H verlag Gmbh, 2024) Diker, Halide; Ozguler, Sahika; Unluturk, Secil Sevim; Ozcelik, Serdar; Varlikli, CananBlue light-emitting CdSe@ZnS/ZnS quantum dot (QD) nanoparticles (NPs) were synthesized and their photophysical properties in both solution and film phases were investigated. The morphological properties of films prepared by different coating methods i. e. single layer coating from low to high concentrations of QD solutions and layer-by-layer (multilayer) coating within constant low QD solution concentration, were also examined in detail. Varying the concentration (1-10 mg/mL) and the number of layers (from 1-16) did not essentially affect the photophysical properties of QD films, although it resulted in a direct increment in QD film thickness. The concentration and layer-dependent films were used as an emissive layer (EML) in QD light-emitting diodes (QLEDs). Although the "6 mg/ml(-1) Layer" QD EML-based device exhibited relatively high device efficiency compared to the "1 mg/ml(-10) Layers" based one at working voltage region, it had similar to 2-fold higher efficiency roll-off at high voltage region. The performance differences for both devices with the same QD EML thickness were attributed to the morphological variations for the QD layer in terms of surface roughness, void density, aggregates/clusters, and trap sites that were directly related to the charge injection balance and Auger recombination.Article Citation - WoS: 8Citation - Scopus: 8Reducing the Efficiency Roll Off and Applied Potential-Induced Color Shifts in Cdse@zns/Zns-based Light-Emitting Diodes(American Chemical Society, 2020) Özgüler, Şahika; Diker, Halide; Ünlütürk, Seçil Sevim; Özçelik, Serdar; Varlıklı, CananGreen light-emitting CdSe@ZnS/ZnS (QD) nano-particles were synthesized; the photophysical and morphological properties of their films, which were prepared by spin coating from six different concentrations, corresponding to absorbance values of 0.6, 1.1, 1.6, 2.1, 2.8, and 4.0, were determined. Increasing the absorbance value from 0.6 to 4.0 did not change the photophysical properties of QD films to a large extent, whereas it resulted in an increment in QD film thickness from 20 to 110 nm. The films were utilized as an emissive layer in QD light-emitting diodes with poly(9-vinylcarbazole) (PVK), PVK:2-(4-biphenyllyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and PVK:1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]-phenylene (OXD-7) hole-transport layers (HTLs). The presence of PBD or OXD-7 in PVK reduced the efficiency values but played a positive role in the color purity and efficiency roll off. The maximum color temperature and electroluminescence wavelength shifts obtained with applied potential were 109, 50, and 50 K and 11, 5, and 5 nm for pure-PVK, PVK:PBD, and PVK:OXD-7-based devices, respectively. Hole mobility, capacitance (at 10(3) Hz), and charge-transfer efficiency values were 9.0 x 10(-7), 6.8 x 10(-7), and 4.2 x 10(-7) cm(2) V s(-1), 1.7, 1, and 1 nF, and 6.90%, 15.50%, and 16.10% for pure-PVK, PVK:PBD, and PVK:OXD-7-based devices, respectively. Enhanced color purity and lowered efficiency roll off obtained with PVK:PBD and PVK:OXD-7 HTLs were attributed to decreased capacitance, increased charge-transfer efficiency, and reduced Joule heating.