Browsing by Author "Raveendra Kiran, M."

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Cyanopyridone-cored fluorophores with triphenylamine peripheries: From molecular design to OLED fabrication studies
(Elsevier B.V., 2023) Vishrutha, K.S.; Ulla, H.; Raveendra Kiran, M.; Badekai Ramachandra, B.R.; Vasudeva Adhikari, A.
Amongst many types of fluorescent organic materials, compounds with π-conjugation between an electron donor (D) and electron acceptor (A) have been intensively investigated as effective organic electroluminescence (EL) device components. Herein, we report the synthesis and structural characterization of a new series of D-A-D configured small molecule-based fluorophores (TPA-CyP1-7) having triphenylamine (TPA) as a donor unit and 3-cyanopyridine-2-one (CyP) as an acceptor core with different architects for use as efficient yellow light emitters in fluorescent organic light-emitting diodes (OLED). The detailed photophysical, solvatochromic, thermal, electrochemical, and EL properties, including quantum chemical calculations, were systematically investigated to study their relation between structure and properties. All the fluorophores show high fluorescent quantum yields in the solid film state and display high thermal stability with decomposition temperatures above 350 °C. The study reveals that they possess appropriate HOMO and LUMO energies level for effective charge injection. Finally, these yellow luminogens were employed to fabricate new OLED devices as sole emitters and dopants with CBP host materials. Interestingly, the host–guest devices doped with CBP host emitters show a remarkable improvement in the overall device performance. Among them, the TPA-CyP3-based doped device has achieved a maximum current efficiency (ηc), high power efficiency (ηp), and good external quantum efficiency (ηEQE) of 10.72 cd/A, 7.87 lm/W, and 5.32 %, respectively. © 2022 Elsevier B.V.
Effects of annealing temperature on the resistance switching behaviour of solution-processed ZnO thin films
(Academic Press, 2020) Raveendra Kiran, M.; Ulla, H.; Satyanarayan, M.N.; Umesh, G.
In this study, the resistance switching (RS) behaviour of the fabricated devices with the configuration: ITO/ZnO (x annealing temperature)/Al were investigated. It was observed that the area of a hysteresis loop in the Current-Voltage characteristics was reduced with increase in ZnO annealing temperature. Correspondingly, the on/off ratio of the RS also gets reduced. The hysteresis behaviour was highly consistent and repeatable for the films annealed at 150 °C. The films annealed at 450 °C did not show any RS behaviour. Under the high current condition, a reproducible RS behaviour was observed. This was attributed to the synergetic effects of lowering of the barrier height at electrode/ZnO interface and the increase in the grain size with the annealing temperatures. The RS behaviour is ascribed to the conduction mechanism at the ITO/ZnO interface. © 2020 Elsevier Ltd
Optoelectronic properties of hybrid diodes based on vanadyl- phthalocyanine and zinc oxide nanorods thin films
(Elsevier B.V., 2019) Raveendra Kiran, M.; Ulla, H.; Satyanarayan, M.N.; Umesh, G.
Herein, we report the optoelectronic properties of hybrid diodes fabricated using vanadyl phthalocyanine (VOPc) and zinc oxide nanorods (ZNR) with the configuration: ITO/ZNR/VOPc/MoO3/Al. Vertically aligned ZnO nanorods were grown using a simple aqueous solution (AS) method as a function of growth temperature. The correlation between the morphology of ZNR films and the optoelectronic properties of the ZNR/VOPc hybrid devices was investigated. The results show that the hybrid diodes with ZNR films grown at 120 °C offer the best optoelectronic properties. The higher photocurrent responsivity, Rph, (16.28 A/W) was achieved for devices with ZNR films grown at 120 °C. This value is 25 times higher than the Rph value obtained for the devices made with ZnO nanoparticle films that were reported earlier. © 2019
Utilization of newly configured carbazole-cyanopyridone structural hybrids towards achieving high-performance cyan fluorescent organic light-emitting diodes
(Royal Society of Chemistry, 2024) Vishrutha, K.S.; Ulla, H.; Raveendra Kiran, M.; Badekai Ramachandra, B.R.; Vasudeva Adhikari, A.V.
Herein, we report the synthesis, characterization, and device fabrication of novel D-A-D (donor-acceptor-donor) type cyanopyridone-based cyan light-emitting organic materials. These small molecules feature a strong electron-donating N-alkylated carbazole unit affixed to a powerful electron-withdrawing cyanopyridone core that is appended with varying secondary donor groups, producing bipolarity in their structures. All the synthesized molecules were well characterized by employing FT-IR, 1H NMR, and 13C NMR spectroscopy, followed by in-depth photophysical, thermal, electrochemical, and electroluminescent studies. Furthermore, we used the density functional theory (DFT) computational approach in the theoretical investigations to gain deeper insights into their electron cloud distributions and structural features. These fluorophores exhibit emission in the 489-510 nm range accompanied by high Stokes shift values, and their TGA data validate the excellent thermal stability (384 °C). As estimated by cyclic voltammetry, the HOMO and LUMO energy levels were found to be 5.35-5.69 eV and 2.92-3.02 eV, respectively, with band gaps of 2.36-2.74 eV. The optical and electrochemical properties of the luminogens have been successfully fine-tuned by varying the auxiliary donors at the carbazole-cyanopyridine hybrids. Electroluminescent studies proved the compatibility of the novel compounds to be an efficient cyan emissive layer with good performance characteristics. Interestingly, amongst the luminophores, Cz-CyP5 bearing a 4-hydroxyphenyl moiety exhibited a maximum current efficiency of 13.16 cd A−1, high power efficiency of 9.85 lm W−1, and good external quantum efficiency of 5.41%. © 2024 RSC.