We report an atomically-thin passivation layer composed of a self-assembled alkane monolayer, that protects graphene from outside dopants and external contamination while retaining its transparency, flexibility and su-perior electron transfer ability. These advantages allowed successful fabrication of passivated graphene field-effect transistors (G-FETs) on a plastic substrate with ion-gel gate dielectrics for transparent and flexible elec-tronics. This highly transparent, flexible, and ultra-thin organic passivation layer has many possible applications in electronics that use graphene.

Transition metal dichalcogenides (TMDs) possess great potential for use in gas sensing applications because, in contrast to conventional metal oxides, they have unique semiconducting properties with band gaps that can be tuned by adjusting thickness and composition. However, one issue is that their recovery time at room temperature is too long for them to be used practically in sustainable sensing applications. We found that incorporating Se atoms weaken interactions with gas molecules compared to when S atoms are used alone, therefore, the responsivity, as well as the recovery properties, of MoSxSe2-x sensors were significantly enhanced by increasing the ratio of Se to S. Herein, we demonstrate high-performance gas sensors that are based on reduced graphene oxide (rGO) fibers coated with MoSxSe2-x, the fabricated sensor could efficiently refresh its surface to allow fast, complete recovery at room temperature. Furthermore, it was shown that the porosity of rGO fibers with their large surface-to-volume ratio leads to enhanced sensing at room temperature.

Taking a solution-based approach to obtain transition metal dichalcogenide monolayers affords a number of advantages, including processing that is scalable, cost effective, and enables tuning monol...

Two-dimensional materials have attracted great attention for their outstanding electronic properties. In particular, molybdenum disulfide (MoS2) shows great potential as a next-generation semiconductor due to its tunable direct bandgap with a high on-off ratio and extraordinary stability. However, the performance of MoS2 synthesized by physical vapor deposition has been limited by contact resistance between an electrode and MoS2, which determines overall device characteristics. Here, in order to reduce the contact resistance, we use in situ sulfurization of Mo by H2S gas treatment masked by a patterned graphene gas barrier, so that the Mo channel area can be selectively formed, resulting in a gradual edge contact between Mo and MoS2. Compared with field-effect transistors with a top contact between the Au/Ti electrode and the MoS2 channel, a gradual edge contact between the Mo electrode and the MoS2 channel provides a considerably enhanced electrical performance.

In the field of wastewater treatment, the advanced oxidation process (AOP) is a widely employed method. It uses reactive oxygen species (ROS) to degrade harmful organic and inorganic chemicals. Metal catalysts are the conventional standard when using these methods. However, they have drawbacks such as harsh activation conditions and poor recyclability. We previously suggested chemical vapor deposition (CVD) graphene film as an alternative metal-free catalyst. In this study, we enhanced the catalytic activity of the CVD graphene film by synergistically adding UV light irradiation. The result was complete degradation of phenol on a wafer-scale in a reduced timeframe. To further enhance the degradation process, we devised a graphene-based column for continuous in situ chemical oxidation and analyzed the intermediates over time, proving the potential of graphene-assisted AOP in industrial wastewater applications.

Recent development in mobile electronic devices and electric vehicles requires electrical wires with reduced weight as well as enhanced stability. In addition, since electric energy is mostly generated from power plants located far from its consuming places, mechanically stronger and higher electric power transmission cables are strongly demanded. However, there has been no alternative materials that can practically replace copper materials. Here, we report a method to prepare ultrastrong graphene fibers (GFs)-Cu core-shell wires with significantly enhanced electrical and mechanical properties. The core GFs are synthesized by chemical vapor deposition, followed by electroplating of Cu shells, where the large surface area of GFs in contact with Cu maximizes the mechanical toughness of the core-shell wires. At the same time, the unique electrical and thermal characteristics of graphene allow a ∼10 times higher current density limit, providing more efficient and reliable delivery of electrical energies through the GFs-Cu wires. We believe that our results would be useful to overcome the current limit in electrical wires and cables for lightweight, energy-saving, and high-power applications.

A new electron transport material (ETM) with two fluoranthene and a benzoquinoline moiety was synthesized for the fabrication of solution-processed phosphorescent organic light-emitting diodes (PHOLEDs).

The impact of anode buffer layers (ABLs) on the performance of CdSe quantum-dot light-emitting diodes (QLED) with a ZnO nanoparticle (NP) electron-transport layer and 4,4′-cyclohexylidenebis[ N , N -bis(4-methylphenyl)benzenamine] (TAPC) hole-transport layer was studied. Either MoO 3 or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) was used as the ABL. The QLED with a HAT-CN ABL exhibited better luminance performance, while the ultraviolet photoelectron spectroscopy and hole-only devices indicated that MoO 3 was a superior hole injector. These results suggest that the QLED with a MoO 3 ABL suffered from a severe charge carrier imbalance. Therefore, electron injection through the ZnO NP layer must be improved to further enhance the QLED performance.

New soluble host materials with benzocarbazole and triphenyltriazine moieties, 11-[3-(4,6-diphenyl-[1,3,5]triazin-2-yl)-phenyl]-11H-benzo[a]carbazole and 11-[3'-(4,6-diphenyl-[1,3,5]triazin-2-yl)-biphenyl-4-yl]-11H-benzo[a]carbazole, were synthesized for highly efficient red phosphorescent organic light-emitting diodes (PHOLED). Hole-transporting benzocarbazole moiety and electron transporting triphenyltriazine moiety, which are severely twisted each other enhance the solubility of those materials in common organic solvent. The improved solubility from this molecular design could be due to a reduced π-π stacking interaction, which gives a very uniform film morphology after spin coating of those materials. As a result, we obtained highly efficient soluble PHOLEDs combined with an evaporated blue common layer structure. The resultant red PHOLED exhibited the maximum current efficiency as well as external quantum efficiency values up to 23.7 cd/A and 19.0%.

The emerging carbon-based quantum dots have been attracting attention because of their tremendous potential for optoelectronic and biomedical applications, which is due to their unique and size-tunable optical properties, their ability to be functionalized, and their biocompatibility. Here, we report the facile one-step synthesis of highly fluorescent and amphiphilic n doped graphitic carbon dots (N-GCDs) using a fumaronitrile (FN) precursor. An interesting property of the prepared GCDs is their near pH neutral dispersibility without refinement, which stands in contrast to reported methods. This finding indicates that our approach could lead to low-cost and efficient processability that is scalable and environmentally friendly. In addition, we find that our N-GCDs have high density of graphitic structure such as sp(2)-hybridized carbon and tiny amounts of defect by near-edge X-ray absorption fine structure (NEXAFS) results. Finally, to confirm the electro-optical behavior of N-GCDs on photovoltaic devices, we fabricate iPSCs consisting of ITO/PEIE/PTB7:PC71BM (+ N-GCDs)/MoO3/Ag. Using this effective approach, we demonstrate the highest conversion efficiency of similar to 8.6% resulting from improved photoresponsibility and charge transport based on various charge and energy transfer dynamics. Also, we believe that the shape, size and functionality of these GCDs can be controlled using other chemical species to provide a variety opportunities for use in optoelectronics, biological applications, and sensors.

Interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Recently, polymer surface modifiers, such as poly(ethyleneimine) (PEI) and polyethylenimine ethoxylated (PEIE), were introduced to produce low WF electrodes and were reported to have good electron selectivity for inverted polymer solar cells (iPSCs) without an n-type metal oxide layer. To obtain more efficient solar cells, quantum dots (QDs) are used as effective sensitizers across a broad spectral range from visible to near IR. Additionally, they have the ability to efficiently generate multiple excitons from a single photon via a process called carrier multiplication (CM) or multiple exciton generation (MEG). However, in general, it is very difficult to prepare a bilayer structure with an organic layer and a QD interlayer through a solution process, because most solvents can dissolve and destroy the organic layer and QD interlayer. To present a more effective strategy for surpassing the limitations of traditional methods, we studied and fabricated the highly efficient iPSCs with mono-layered QDs as an effective multi-functional layer, to enhance the quantum yield caused by various effects of QDs monolayer. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer, which is verified by various analysis tools.

Field-effect graphene biosensors have in general relied on irreversible surface modification for the detection of biological entities. However, restoring a sensor to a pre-sensing-event state is highly desirable in securing sensor data integrity, especially in the case of an electrolyte-gated graphene FET which is prone to drift and degradation. We present a graphene FET biosensor array that mimics an SPR(surface plasmon resonance) system in its use of a microfluidic channel for restoration of the sensor equilibrium. A steady flow of PBS through a 20-micron wide channel provides calibration for FET conductance before and after introducing human Thrombin to the base flow, successfully isolating the protein-induced field-effect from permanent changes made to the graphene device. Graphene conductance shows exponential saturation and de-saturation curves as governed by the the Nernst Equation. The sensors show a sub-microMolar limit-of-detection which can be dynamically tuned by the flow rate. Sensor specificity is provided by electrophoretic functionalization of DNA aptamers onto the graphene surface. We confirm successful aptamer functionalization with fluorescence microscopy, amperometry, and scanning electron microscopy. The current method of sensor state restoration adds reliability to biosensor data without the necessity of a matching-device control group and also maximizes manufacturing efficiency through device recycling.

We have fabricated highly efficient green phosphorescent organic light-emitting diodes by solution process. Very interestingly, we found that the device efficiency is affected by interface between hole transport layer (HTL) and emission layer (EML). It was proved through spin cleaning process of cross-linkable HTL after curing which may affect the interface mixing. In addition, we tried to add complement layer to manipulate such effects. As a result, we significantly improved device efficiency (up to 72.7 cd/A) after spin cleaning process of the cross-linkable HTL material.

Electrical properties of graphene-based field effect transistors (G-FETs) can be degraded in ambient conditions owing to physisorbed oxygen or water molecules on the graphene surface. Passivation technique is one of a fascinating strategy for fabrication of G-FETs, which allows to sustain electrical properties of graphene in the long term without disrupting its inherent properties: transparency, flexibility and thinness. Ironically, despite its importance in producing high performance graphene devices, this method has been much less studied compared to patterning or device fabrication processes. Here we report a novel surface passivation method by using atomically thin self-assembled alkane layers such as C18NH2, C18-Br and C36 to prevent unintentional doping effects that can suppress the degradation of electrical properties. In each passivated device, we observe a shift in charge neutral point to near zero gate voltage and it maintains the device performance for 1 year. In addition, the fabricated PG-FETs on a plastic substrate with ion-gel gate dielectrics exhibit not only mechanical flexibility but also long-term stability in ambient conditions. Therefore, we believe that these highly transparent and ultra-thin passivation layers can become a promising candidate in a wide range of graphene based electronic applications.

Optical wireless channel has abundant available bandwidth and is suitable for high data rate, indoor communi- cations. In this paper, the performance of CDMA as a multiple access technique for optical wireless communication is examined. As the signature sequence, a (43,3,1,1) and a (63,3,1,1) optical orthogonal code (OOC) is used. Information data is modulated through a simple on-off keying (OOK) modulation scheme. Data rate of ZMbps is used and the bit error rate (BER) performance is simulated with respect to signal-to-noise ratio (SNR), number of users, and threshold values. It is possible to find the optimum number of users, the optimum threshold value from the results. It is seen that interference from other users actually helps to improve the BER performance, upto a certain number of users.