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Graphene Quantum Dots Band Structure Tuned by Size for Efficient Organic Solar Cells
摘要： The electronic states of graphene quantum dots (GQDs) can be tuned by varying the lateral size and edge structure, which further influence their optoelectronic properties and the applications. In the work, three kinds of GQDs with different lateral size were prepared by photon-Fenton reaction and separated through gel column chromatography, and their effects on the photovoltaic performances of inverted organic solar cells based on the poly(3-hexylthiophene) (P3HT) and poly(3-hexylthiophene)/(6,6)-phenyl-C61 butyric acid methylester (PCBM) blend films were studied systematically. In comparing with P3HT:PCBM cells, the power conversion efficiency of the P3HT:PCBM solar cells containing 0.8% of GQDs-blue, GQDs-green, and GQDs-orange can be increased from 3.06 to 3.54, 4.43, and 3.73 % with a short-circuit current density of 10.3, 13.34, and 11.19 mA cm-2. It is illustrated also that the band structures (electronic energy states) tuned mainly by their lateral size of GQDs are the crucial factor to dominate their photovoltaic preferences as additives in conventional P3HT:PCBM solar cells.
关键词： power conversion efficiency,band structure,organic solar cells,graphene quantum dots
更新于2025-09-11 14:15:04
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Development of Graphene Quantum Dots-Based Optical Sensor for Toxic Metal Ion Detection
摘要： About 71% of the Earth’s surface is covered with water. Human beings, animals, and plants need water in order to survive. Therefore, it is one of the most important substances that exist on Earth. However, most of the water resources nowadays are insu?ciently clean, since they are contaminated with toxic metal ions due to the improper disposal of pollutants into water through industrial and agricultural activities. These toxic metal ions need to be detected as fast as possible so that the situation will not become more critical and cause more harm in the future. Since then, numerous sensing methods have been proposed, including chemical and optical sensors that aim to detect these toxic metal ions. All of the researchers compete with each other to build sensors with the lowest limit of detection and high sensitivity and selectivity. Graphene quantum dots (GQDs) have emerged as a highly potential sensing material to incorporate with the developed sensors due to the advantages of GQDs. Several recent studies showed that GQDs, functionalized GQDs, and their composites were able to enhance the optical detection of metal ions. The aim of this paper is to review the existing, latest, and updated studies on optical sensing applications of GQDs-based materials toward toxic metal ions and future developments of an excellent GQDs-based SPR sensor as an alternative toxic metal ion sensor.
关键词： metal ion,graphene quantum dots,surface plasmon resonance,optical sensor
更新于2025-09-11 14:15:04
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S, N co-doped graphene quantum dots decorated CdSe for enhanced photoelectric properties.
摘要： Cadmium selenide and S, N co-doped graphene quantum dots (CdSe/S, N-GQDs) nanocomposites were synthesized via a solvothermal method. The results show that S, N-GQDs have a grain size of around 5 nm and an average height of 0.5 nm, which contains only 1-2 layers of graphene sheets. The CdSe/S, N-GQDs composites exhibit distinct lattice fringes with a layer spacing of 0.24 and 0.35 nm, corresponding to (1120) and (111) crystal planes of S, N-GQDs and the cubic CdSe, respectively. The photoelectric properties of CdSe/S, N-GQDs were evaluated under ultraviolet light (365 nm) irradiation. Compared with CdSe and CdSe/GQDs, CdSe/S, N-GQDs composites have the largest photocurrent density of 4.286×10-5 A/cm2, which is about 10.5 times and 7.5 times as high as that of CdSe and CdSe/GQDs, respectively. The increase in photocurrent density of CdSe/S, N-GQDs can be attributed to the S, N-GQDs are nano-fragments of graphene, which can provide a larger specific surface area and greatly increase the contact surface with CdSe. In addition, the photoelectric properties of CdSe/S, N-GQDs composites can be adjusted by varying the doping ratio. When the doping ratio is 1:1, CdSe/S, N-GQDs have the best photoelectric performance.
关键词： graphene quantum dots,CdSe,photoelectric properties,doping ratio,co-doped
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - THz excited state level spacing in encapsulated graphene quantum dots
摘要： We report a high-quality encapsulated graphene quantum dot that exhibits stable Coulomb diamonds and excited states with a spacing of 0.4 THz. We performed the first transport spectroscopy measurement under THz illumination of a large quantum dot. The photocurrent map allows to measure with high precision a non-linear chemical potential renormalization of the graphene electrodes via the interaction with the quantum dot states.
关键词： graphene quantum dots,THz,transport spectroscopy,chemical potential renormalization,photocurrent
更新于2025-09-11 14:15:04
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One-pot microwave-assisted green synthesis of amine-functionalized graphene quantum dots for high visible light photocatalytic application
摘要： Nowadays, graphene quantum dots (GQDs) have gained a huge interest in the field of visible-range photocatalysts because of their tunable band gap and stable photochemical properties. In this work, amine-functionalized GQDs (AGQDs) were successfully prepared by one-step microwave-assisted conversion of glucose, H2O2, and NH3 solution. The obtained quantum dots possess the high quality of graphene structure with the average size of 3.78 nm as well as exhibit a strong green fluorescence with a high quantum yield. Interestingly, the amine-functionalized dots perform outstanding visible-light absorption. To further investigate photocatalytic properties, a composite of AGQDs and TiO2 was then prepared by a simple mixing route. The hybrid material showed high catalytic activity of dye degradation under visible light irradiation, which indicates the key role of AGQDs in enhancing light absorption and induced electron-hole separation. The current study may open a new way for construction of effective visible light photocatalytic systems with a cost-effective, simple approach.
关键词： Fluorescent visible light photocatalyst,Graphene quantum dots,Amine functionalized,Dyes photodegradation
更新于2025-09-11 14:15:04
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Investigation of photo-induced electron transfer between amino-functionalized graphene quantum dots and selenium nanoparticle and it's application for sensitive fluorescent detection of copper ions
摘要： Copper ions play an essential role in some biological processes. Currently, there is a need for the development of convenient and reliable analytical methods for the Cu2+ measurement. In the present work, a sensitive fluorescence method was developed for the determination of copper ions. Amino-functionalized graphene quantum dots (af-GQDs) and selenium nanoparticles (Se NPs) were synthetized, respectively, and they were characterized via transmission electron microscope, infrared spectrum analysis and X-ray photoelectron spectrum measurement. Photo-induced electron transfer (PET) between the prepared two nanomaterials could effectively quench the fluorescence of af-GQDs. Cu(II) was reduced to Cu(I) in the presence ascorbic acid and Cu2Se was finally generated on Se NPs surface, which led to the declined PET efficiency and inhibited the fluorescence quenching of af-GQDs. The change in fluorescence intensity was linearly correlated to the logarithm of the Cu2+ concentration from 1 nM to 10 μM, with a detection limit of 0.4 nM under the optimal conditions. The detections of copper ions in water samples were realized via standard addition method and the recovery values varied from 98.7% to 103%. The proposed fluorescence method was also employed to analyze the uptake of Cu2+ into human cervical carcinoma HeLa cells and cisplatin-resistant HeLa cells (HeLa/DDP cells). The experimental results indicate that the decreased hCTR1 expression level in HeLa/DDP cells weakened the uptake of copper ions into these drug-resistant tumor cells.
关键词： photo-induced electron transfer,selenium nanoparticles,cellular uptake,copper ions,fluorescence quenching,amino-functionalized graphene quantum dots
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Kerala, India (12–14 June 2019)] PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Insulator to semiconductor transition in graphene quantum dots
摘要： Zero dimensional graphene quantum dots (GQDs) exhibit interesting physical and chemical properties due to the edge effect and quantum confinement. As the number of carbon atoms in edge is more than on basal plane, GQDs are more reactive. Room temperature XRD pattern confirms the formation of the GQDs. UV-Visible spectra confirm that GQDs show optical absorption in the visible region. The emission peaks in the photoluminescence spectra are red shifted with the increase of excitation wavelength. Dynamic light scattering (DLS) analysis shows that the average size of the particles is found to be ~65 nm. The frequency dependent electrical transport properties of the GQDs are investigated in a temperature range from 300 to 500 K. Most interestingly, for the first time, the insulator to semiconductor transition of GQD is observed near 400K. The transition mechanism of GQD is discussed with detailed dielectric analysis. The effects of intercalated water on temperature dependent conductivity are clearly discussed. The dielectric relaxation mechanism is explained in the framework of permittivity, conductivity and impedance formalisms. The frequency dependent ac conductivity spectra follows the Jonscher's universal power law. Cole-Cole model is used to investigate the dielectric relaxation mechanism in the sample.
关键词： Graphene Quantum Dots,Insulator to Semiconductor Transition,Dynamic Light Scattering,Dielectric Relaxation,Photoluminescence
更新于2025-09-11 14:15:04
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Graphene quantum dot vertical cavity surface emitting lasers
摘要： Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. To date, there have only been a few reports on the realization of GQDs-based lasers. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors.
关键词： Vertical Cavity Surface Emitting Laser,Graphene Quantum Dots,Green Gap,Microwave-Assisted Hydrothermal Method,Distributed Bragg Reflectors (DBRs)
更新于2025-09-11 14:15:04
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Effects of Surface Passivation on Photoluminescence Properties and Biomedical Imaging of Graphene Quantum Dots
摘要： Owing to fluorescence properties and small size, graphene quantum dots (GQDs) have been investigated for biomedical imaging. Although GQDs demonstrate some desirable properties, their poor stability and low biocompatibility have applications in various aspects. Therefore, in this study, we synthesized surface-passivated GQDs and studied their properties. GQDs were prepared using thermal exfoliation of graphite oxide, followed by nitric acid refluxing. Then GQDs were passivated with polyethylene glycol (PEG) using hydrothermal at 120 ℃ for 72 h. Both GQDs and GQDs-PEG were characterized by transmission electron microscopy, UV-Vis absorption and photoluminescence spectroscopy. Compared with GQDs, GQDs-PEG exhibit higher fluorescence intensity and fluorescent quantum yield. Also, GQDs-PEG demonstrates less cytotoxicity than GQDs in terms of cell survival rate in MTT assay. Our findings demonstrate that both fluorescence characteristics and biocompatibility of GQDs can be improved by PEG surface passivation, and GQDs-PEG is desirable for biomedical imaging.
关键词： surface passivation,biomedical imaging,graphene quantum dots,photoluminescence,polyethylene glycol
更新于2025-09-10 09:29:36
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Amalgamation of N-graphene quantum dots with nanocubic like TiO2: an insight study of sunlight sensitive photocatalysis
摘要： In this work, a sunlight-sensitive photocatalyst of nanocubic-like titanium dioxide (TiO2) and N-doped graphene quantum dots (N-GQDs) is developed through a simple hydrothermal and physical mixing method. The successful amalgamation composite photocatalyst characteristics were comprehensively scrutinized through various physical and chemical analyses. A complete removal of bisphenol A (BPA) is attained by a synthesized composite after 30 min of sunlight irradiation as compared to pure TiO2. This clearly proved the unique contribution of N-GQDs that enhanced the ability of light harvesting especially under visible light and near-infrared region. This superior characteristic enables it to maximize the absorbance in the entire solar spectrum. However, the increase of N-GQDs weight percentage has created massive oxygen vacancies that suppress the generation of active radicals. This resulted in a longer duration for a complete removal of BPA as compared to lower weight percentage of N-GQDs. Hence, this finding can offer a new insight in developing effective sunlight-sensitive photocatalysts for various complex organic pollutants degradation.
关键词： Visible light,Near Infrared,Nanocubic-like TiO2,Bisphenol A,N-Graphene quantum dots,Sunlight
更新于2025-09-10 09:29:36