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... solve this problem, aluminium or various alloys such as Mg/Ag as a cathode are used as cathode [37][38][39]. Figure 3 shows the evolution of OLED device structure. The electron and hole transport layers could help to high-speed movement of electrons and holes to meet each other in the emission layer. ...
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... Researchers are exploring distinct ideas to fabricate QDs with significant efficiency [10,11]. Among different varieties of QDs like perovskite quantum dots, InP and CdSe quantum dots contain different promising optical properties involving great color purity, a tunable emission wavelength, and a great photoluminescence quantum yield, which establish them as significant candidates for future cost-effective display device fabrication technology [12][13][14][15]. Applications, characterization, and synthesis of QDs are considered to be significant domains of investigation. ...
... Owing to the tiny size of these semiconducting QDs, they can produce high photoluminescence quantum yield when compared to their bulk materials [3]. Moreover, they can resist photobleaching for long time, and hence can be included in the design of optical biosensors [4][5][6], photovoltaic [7,8], bioimaging [9] and light emitting diode [10]. The most commonly utilized types of QDs are composed of semiconductors of periodic group II-VI (CdTe, CdSe, CdS, ZnSe, ZnS, PbS, PbSe, PbTe, SnTe) [11]. ...
Quantum dots (QDs) possess characteristic chemical and optical features. In this light, ZnS QDs capped with glutathione (GSH) were synthesized via an easy aqueous co-precipitation technique. Fabricated QDs were characterized in terms of X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Fourier transform infrared (FTIR) and Zeta potential analyses. Optical properties were examined using photoluminescence (PL) and ultraviolet–visible (UV–visible) spectroscopies. Moreover, GSH-capped ZnS QDs were evaluated as an optical probe for non-enzymatic detection of urea depending on the quenching of PL intensity of ZnS QDs in the presence of urea from concentration range of 0.5–5 mM with a correlation coefficient (R²) of 0.995, sensitivity of 0.0875 mM⁻¹ and LOD of 0.426 mM. Furthermore, GSH-capped ZnS QDs-urease conjugate was utilized as an optical probe for enzymatic detection of urea in the range from 1.0 µM to 5.0 mM. Interestingly, it was observed that urea has a good affinity towards ZnS QDs-urease conjugate with a linear relationship between the change of PL intensity and urea concentration. It was found that R² is 0.997 with a sensitivity of 0.042 mM⁻¹ for mM concentration (0.5–5 mM) and LOD of 0.401 mM. In case of µM concentration range (1–100 µM), R² was 0.971 with a sensitivity of 0.0024 µM⁻¹ and LOD of 0.687 µM. These data suggest that enzyme conjugation to capped QDs might improve their sensitivity and applicability.
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... The fundamental structure of QDs consists of three parts. The three basic characteristics of the structure of the QDs are core, shell, and ligand (Heydari et al. 2017;Ratnesh 2019). ...
... Additional steadiness is provided by the ligand layer. Protecting QDs from oxygen, moisture, and heating requires the installation of porous structures (Heydari et al. 2017;Steckel et al. 2006;Ippen et al. 2019). QDs are used in this method, which involves placing them in a sandwich with electron and hole transport layers. ...
... An electric field is applied to the QD layer in order to collect electrons and holes. Next, they merge to release a narrow band of light (Rahman et al. 2021;Heydari et al. 2017;Mitul 2017). ...
CdSe Quantum dots (QDs) are cytotoxic cadmium and selenide-based (II–VI) semiconductor nanocrystals with a few nanometer diameters and unique optical and electrical properties. The cytotoxicity of CdSe QDs should not be underestimated and has raised considerable concern. That toxicity is mostly determined by the surface characteristics and size of the particles. The core/shell configuration thus becomes a popular technique to modify the activity of quantum dots by enhancing biocompatibility and stability. The most common and effective synthesis method of those shell-free and core/shell-based CdSe QDs is organometallic and water-based synthesis. Those synthesis frequently requires high temperatures, an oxygen-free atmosphere, and highly poisonous substances like trioctylphosphane (TOP) or trioctylphosphane oxide (TOPO), which may be inefficient, harmful to the environment, and even deadly. Because of this, a biogenic synthesis method was made to get around its limits. Biosynthesis of quantum dots by microorganisms (bacteria, actinomycetes, fungus, and algae) is an environmentally friendly and cost-effective green technology where production may occur intracellularly or extracellularly. The enzyme NADH-dependent nitrate reductase has been reported to have an important role in reducing cadmium and selenide ions to CdSe QDs by several researchers. When synthesizing CdSe QDs, factors such as pH, temperature, synthesizing route, and substrate concentration affect the final product's size and form. They have attracted interest because of their potential usage in a wide range of applications, including photovoltaics, solar cells, LEDs, photocatalyst, optical sensors, medical, medicines, and optical amplifiers. In this review, we focus on the cytotoxicity of non-shell and core/shell-based CdSe QDs, the synthesis using a consortium of different microorganisms from both prokaryotes and eukaryotes, affecting factors, application, challenges, and future prospects of CdSe-based QDs.
... Each type of OLED is further divided into two categories, as shown in Fig. 8. The most commonly used OLEDs are shown in Fig. 9 [68,69]. ...
In the present time, organic light-emitting diode (OLED) is a very promising participant over light-emitting diodes (LEDs), liquid crystal display (LCD), and also another solid-state lighting device due to its low cost, ease of fabrication, brightness, speed, wide viewing angle, low power consumption, and high contrast ratio. The most prominent layer of OLED is the emissive layer because the device emission color, contrast ratio, and external efficiency depend of this layer’s materials. This review ruminates on the basics of OLEDs, different light emission mechanisms, OLEDs achievements, and different types of challenges revealed in the field of OLEDs. This review’s primary intention is to broadly discuss the synthesizing methods, physicochemical properties of conducting polymer polymethyl methacrylate (PMMA), and its polymeric nanocomposite-based emissive layer materials for OLEDs application. It also discusses the most extensively used OLED fabrication techniques. PMMA-based polymeric nanocomposites revealed good transparency properties, good thermal stability, and high electrical conductivity, making suitable materials as an emissive layer for OLED applications.
... Each element has its own function, core has to adsorb and re-emits the absorbed light, and shell does confine the emission and gives passivation to the defects occurring in the structure. The ligand layer has to maintain the stability in its performance over time 35 . ...
... Up till now researches could succeed in improving their EQE of above two order of magnitude 35 . ...
... FWHM of single sized QDs should be very small, but its broadening is unescapable because there are always different sized QDs. As the size of the QDs governs the wavelength of radiation and QDs of same size correspond to the radiation intensity, radiation spectrum indicates the QD size distribution directly116,35 . The emission spectrum describes the energy distribution of the LED emission over different wavelengths. ...
... The B-doped molecule have also sufficiently deep HOMO energy (-6.42 eV) to block holes in OLEDs. The HOMO and LUMO levels of B-doped molecule (HOMO= -6.42 eV and LUMO -2.94 eV) is similar to TAZ (HOMO= -6.4 eV and LUMO -2.8 eV) and TPBI (HOMO= -6.3 eV and LUMO -2.8 eV) molecules used in blue phosphorescent OLEDs [21]. In addition, one of the molecular design criteria, particularly for OLEDs, is large electron affinities and ionization potentials (>6.0 eV) to achieve high electron mobility [22]. ...
The aims of this study were to enhance electronic, photophysical and optical properties of molecular semiconductors. For this purpose, the isomers of the B-doped molecule (5,5′-Dibromo-2,2′-bithiophene) have been investigated by density functional theory (DFT) based on B3LYP/6-311++G** level of theory. The isomers were first calculated using kick algorithm. The most stable isomers of the B-doped molecule are presented depending on the binding energy, fragmentation energy, ionization potential, electron affinity, chemical hardness, refractive index, radial distribution function and HOMO-LUMO energy gap based on DFT. Ultraviolet-visible (UV–vis) spectra have been also researched by time-dependent (TD) DFT calculations. The value of a band gap for isomer with the lowest total energy decreases from 4.20 to 3.47 eV while the maximum peaks of the absorbance and emission increase from 292 to 324 nm and 392 to 440 nm with boron doped into 5,5′-Dibromo-2,2′-bithiophene. Obtained results reveal that the B-doped molecule has more desirable optoelectronic properties than the pure molecule.
Organic light-emitting diodes (OLEDs) are one of the leading, promising technologies for eco-friendly lighting sources and vivid color display panels owing to their low operating voltage, fast switching, wide viewing angle, lightweight flexibility, etc. This review reports the various synthesis techniques for optimizing the OLED device performance using polymeric nanocomposites, which provide lighting and display. The internal OLED device structure and its working mechanism have also been reviewed. Some of the processible conjugated polymeric nanocomposite materials exhibit unique electrical and optical properties that are of interest for OLEDs applications. Nanoparticles with conjugated polymer matrix make polymer nanocomposite, and that composite is used as an active layer between the structures of optoelectronic devices like OLEDs. The application of such polymeric nanocomposite materials is discussed, as well as their success and failure regarding their optical and electrical properties in making OLEDs. Various OLED device fabrication technologies have been reported. The quantum leap of solid-state flexible and rollable lighting and display devices as of OLED applications is also discussed. The exploration encompasses various aspects, including synthesis methods, internal device structures, working mechanisms, and the fabrication technologies involved in OLEDs. The insights obtained will contribute to the advancement of sustainable lighting and display technologies, fostering innovation in the field of organic electronics.
In this study, white organic light-emitting diodes (OLEDs) consisting of red quantum dots (RQD) and green quantum dots (GQD) were investigated. These are the most exciting new lighting technologies that have grown rapidly in recent years. The white OLED development processes used consisted of the following methods: (a) fabrication of a blue single-emitting layer OLED, (b) nanoimprinting into QD photoresists, and (c) green and red QD photoresists as color conversion layers (CCL) excited by blue OLEDs. To fabricate the blue OLED, the HATCN/TAPC pair was selected for the hole injection/transport layer on ITO and TPBi for the electron transport layer. For blue-emitting material, we used a novel polycyclic framework of thermally activated delayed fluorescence (TADF) material, ν-DABNA, which does not utilize any heavy metals and has a sharp and narrow (FWHM 28 nm) electroluminescence spectrum. The device structure was ITO/HATCN (20 nm)/TAPC (30 nm)/MADN: ν-DABNA (40 nm)/TPBi (30 nm)/LiF (0.8 nm)/Al (150 nm) with an emitting area of 1 cm × 1 cm. The current density, luminance, and efficiency of blue OLEDs at 8 V are 87.68 mA/cm2, 963.9 cd/m2, and 1.10 cd/A, respectively. Next, the bottom emission side of the blue OLED was attached to nanoimprinted RQD and GQD photoresists, which were excited by the blue OLED in order to generate an orange and a green color, respectively, and combined with blue light to achieve a nearly white light. In this study, two different excitation architectures were tested: BOLED→GQD→RQD and BOLED→RQD→GQD. The EL spectra showed that the BOLED→GQD→RQD architecture had stronger green emissions than BOLED→RQD→GQD because the blue OLED excited the GQD PR first then RQD PR. Due to the energy gap architectures in BOLED-GQD-RQD, the green QD absorbed part of the blue light emitted from the BOLED, and the remaining blue light penetrated the GQD to reach the RQD. These excited spectra were very close to the white light, which resulted in three peaks emitting at 460, 530, and 620 nm. The original blue CIE coordinates were (0.15, 0.07). After the excitation combination, the CIE coordinates were (0.42, 0.33), which was close to the white light position.
The serious threat that human beings face in near future will be shortage of fossil fuel reserves and abrupt changes in global climate. To prepare for these serious concerns, raised due to climate change and shortage of fuels, conversion of excessive atmospheric CO2 into valuable chemicals and fuels and production of hydrogen from water splitting is seen most promising solutions to combat the rising CO2 levels and energy crises. Amoung the various techniques that have been employed electrocatalytic conversion of CO2 into fuels and hydrogen production from water has gained tremendous interest. Hydrogen is a zero carbon-emitting fuel, can be an alternative to traditional fossil fuels. Therefore, researchers working in these areas are constantly trying to find new electrocatalysts that can be applied on a real scale to deal with environmental issues. Recently, colloidal nanocrystals (C-NCs)-based electrocatalysts have gained tremendous attention due to their superior catalytic selectivity/activity and durability compared to existing bulk electrodes. In this chapter, the authors discuss the colloidal synthesis of NCs and the effect of their physiochemical properties such as shape, size and chemical composition on the electrocatalytic performance and durability towards electrocatalytic H2 evolution reaction (EH2ER) and electrocatalytic CO2 reduction reactions (ECO2RR). The last portion of this chapter presents a brief perspective of the challenges ahead.
