33 research outputs found
Flexible and Stretchable Optoelectronic Devices using Silver Nanowires and Graphene
No full textMany studies have accompanied the emergence of a great interest in flexible or/and stretchable devices for new applications in wearable and futuristic technology, including human-interface devices, robotic skin, and biometric devices, and in optoelectronic devices. Especially, new nanodimensional materials enable flexibility or stretchability to be brought based on their dimensionality. Here, the emerging field of flexible devices is briefly introduced using silver nanowires and graphene, which are famous nanomaterials for the use of transparent conductive electrodes, as examples, and their unique functions originating from the intrinsic property of these nanomaterials are highlighted. It is thought that this work will evoke more interest and idea exchanges in this emerging field and hopefully can trigger a breakthrough on a new type of optoelectronics and optogenetic devices in the near future
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim444911sciescopu
Moving beyond flexible to stretchable conductive electrodes using metal nanowires and graphenes
No full textStretchable and/or flexible electrodes and their associated electronic devices have attracted great interest because of their possible applications in high-end technologies such as lightweight, large area, wearable, and biointegrated devices. In particular, metal nanowires and graphene derivatives are chosen for electrodes because they show low resistance and high mechanical stability. Here, we review stretchable and flexible soft electrodes by discussing in depth the intrinsic properties of metal NWs and graphenes that are driven by their dimensionality. We investigate these properties with respect to electronics, optics, and mechanics from a chemistry perspective and discuss currently unsolved issues, such as how to maintain high conductivity and simultaneous high mechanical stability. Possible applications of stretchable and/or flexible electrodes using these nanodimensional materials are summarized at the end of this review. © The Royal Society of Chemistry 2016262711sciescopu
The effect of the dopant's reactivity for high-performance 2D MoS2 thin-film transistor
No full text© 2020 Springer Nature Switzerland AG. Part of Springer Nature. There are many studies on the solution-processed thin-film transistor (TFT) using transition metal dichalcogenide (TMD) materials. However, it is hard to control the electrical property of chemically exfoliated TMD materials compared to the chemical vapor deposition TMD. An investigation into the electrical modulation behavior of exfoliated two-dimensional (2D) material is important to fabricate well-modulated electronic devices via solution processing. Here, we report the effects of reactivity of organic dopants on MoS(2)and investigate how the chemical doping behavior influences the electrical properties of MoS2. The band state of dopants, which is related to the electron-withdrawing and donating behavior of chemical dopant, provides a proportional shift in the threshold voltages (V-th) of their field-effect transistors (FETs). However, on/off current ratio (I-on/I-off) and mobility (mu) are strongly influenced by the defect density depending on the reactivity of doping reaction, rather than the band state of organic dopants. Through the in-depth study on the doping reaction, we fabricate a FET and a TFT, having high mobility and a relatively high on/off ratio (10(4)) using a solution process.11Nsciescopu
Highly transparent and flexible supercapacitors using graphene-graphene quantum dots chelate
No full textNowadays, transparent and flexible energy storage devices are attracting a great deal of research interest due to their great potential as integrated power sources. In order to take full advantage of transparent and flexible devices, however, their power sources also need to be transparent and flexible. In the present work we fabricated new transparent and flexible micro-supercapacitors using chelated graphene and graphene quantum dots (GQDs) by a simple electrophoretic deposition (EPD) method. Through a chelate formation between graphene and GQDs with metal ions, the GQD materials were strongly adhered on an interdigitated pattern of graphene (ipG-GQDs) and its resulting porous ipG-GQDs film was used as the active material in the micro-supercapacitors. Amazingly, these supercapacitor devices showed high transparency (92.97% at 550 nm), high energy storage (9.09 μF cm-2), short relaxation time (8.55 ms), stable cycle retention (around 100% for 10,000 cycles), and high stability even under severe bending angle 45° with 10,000 cycles. © 2016 Elsevier Ltd263011sciescopu
Tunable Sub-nanopores of Graphene Flake Interlayers with Conductive Molecular Linkers for Supercapacitors
No full textAlthough there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a π-conjugated chemical carbon-carbon bond that can maintain high conductivity, which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 W h kg-1 and 30.3 kW kg-1, respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance. © 2016 American Chemical Society171911sciescopu
Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe
No full textA band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates. © The Author(s) 20166511sciescopu
Reducing the Photodegradation of Perovskite Quantum Dots to Enhance Photocatalysis in CO2 Reduction
No full text© 1996-2021 MDPI (Basel, Switzerland) unless otherwise stated. Solution-processed perovskite quantum dots (QDs) have been intensively researched as next-generation photocatalysts owing to their outstanding optical properties. Even though the intrinsic physical properties of perovskite QDs have been significantly improved, the chemical stability of these materials remains questionable. Their low long-term chemical stability limits their commercial applicability in photocatalysis. In this study, we investigated the photodegradation mechanisms of perovskite QDs and their hybrids via photoluminescence (PL) by varying the excitation power and the ultraviolet (UV) exposure power. Defects in perovskite QDs and the interface between the perovskite QD and the co-catalyst influence the photo-stability of perovskite QDs. Consequently, we designed a stable perovskite QD film via an in-situ cross-linking reaction with amine-based silane materials. The surface ligand comprising 2,6-bis(N-pyrazolyl)pyridine nickel(II) bromide (Ni(ppy)) and 5-hexynoic acid improved the interface between the Ni co-catalyst and the perovskite QD. Then, ultrathin SiO2 was fabricated using 3-aminopropyltriethoxy silane (APTES) to harness the strong surface binding energy of the amine functional group of APTES with the perovskite QDs. The Ni co-catalyst content was further increased through Ni doping during purification using a short surface ligand (3-butynoic acid). As a result, stable perovskite QDs with rapid charge separation were successfully fabricated. Time-correlated single photon counting (TCSPC) PL study demonstrated that the modified perovskite QD film exhibited slow photodegradation owing to defect passivation and the enhanced interface between the Ni co-catalyst and the perovskite QD. This interface impeded the generation of hot carriers, which are a critical factor in photodegradation. Finally, a stable red perovskite QD was synthesized by applying the same strategy and the mixture between red and green QD/Ni(ppy)/SiO2 displayed an CO2 reduction capacity for CO (0.56 mu mol/(g center dot h)).11Nsciescopu
Energy/Charge Transfer Modulation with Spacer Ligands for Highly Emissive Quantum Dot-Polymer Blend
No full text© 2021 American Chemical Society.A blend of perovskite quantum dots (QDs) and a hole transport layer (HTL) is a feasible candidate to solve the long-standing issues in light-emitting diodes (LEDs) such as charge injection, energy state matching, and defect passivation. However, QD:HTL blend structures for QD-based LEDs suffer from fast charge and energy transfers due to an inhomogeneous distribution of QDs and the HTL matrix. Here we report new cross-linkable spacer ligands between QDs and TFB that result in a highly emissive QD:TFB-blended LED device. We synthesize three representative spacer ligands to control the charge and energy transfers between QDs and the HTL. The first spacer ligand is used for controlling the molecular distance between QDs and TFB, and the second spacer ligand is designed to investigate how molecular interaction between QDs and the spacer ligand affects the optical property of the QD:TFB blend. Subsequently, the best spacer ligand, a 10-((2-benzoylbenzoyl)oxy)decanoic acid, is designed to anchor TFB (via a benzophenone group) and simultaneously bond to QDs (with a carboxylic acid functional group). The carboxylic acid group strongly interacts with QDs, dramatically improving the cross-linking rate between QDs and TFB. Due to the direct interaction between QDs and TFB, hole carriers can be effectively injected to perovskite QDs through the conductive backbone of TFB, resulting in the highest luminance values of 10917 cd/m2 at 7.4 V due to carrier injection balance. This is at least 10 times better LED performance compared with a pristine QD device.11Nsciescopu
Highly Efficient Thin-Film Transistor via Cross-Linking of 1T Edge Functional 2H Molybdenum Disulfides
No full textThin-film transistors (TFTs) have received great attention for their use in lightweight, large area, and wearable devices. However, low crystalline materials and inhomogeneous film formation limit the realization of high-quality electrical properties for channels in commercial TFTs, especially for flexible electronics. Here, we report a field-effect TFT fabricated via cross-linking of edge-1T basal-2H MoS2 sheets that are prepared by edge functional exfoliation of bulk MoS2 with soft organic exfoliation reagents. For edge functional exfoliation, the electrophilic 4-carboxy-benzenediazonium used as the soft organic reagent attacks the nucleophilic thiolates exposed at the edge of the bulk MoS2 with the help of an amine catalyst, resulting in 1T edge functional HOOC-benzene-2H basal MoS2 nanosheets (e-MoS2). The cross -linking via hydrogen bonding of the negatively charged HOOC of the e-MoS2 sheets with the help of a cationic polymer, polydiallyldimethylammonium chloride, results in a good film formation for a channel of the solution processing TFT. The TFT exhibits an extremely high mobility of 170 cm(2)/(V s) at 1 V (on/off ratio of 106) on SiO2/Si substrate and also a high mobility of 36.34 cm(2)/(V s) (on/off ratio of 10(3)) on PDMS/PET substrate. © 2017 American Chemical Society3311sciescopu
Improvement of Chemical Stability of Perovskite Nanocrystals as a Photoelectrochemical Catalyst for Hydrogen Evolution Reaction
No full textRecent advances in the synthesis and processing of perovskite materials have led to significant improvements in their stability under harsh conditions, making them increasingly attractive for use as photo and photoelectrochemical catalysts. In particular, core-shell structured perovskite nanocrystals have greatly enhanced chemical stability, enabling their use in aqueous environments; however, their low conductivity remains a challenge. To address this issue, this study developed two-time cross-linkable core-shell perovskite nanocrystals using two types of silanes, resulting in excellent chemical stability and high conductivity. The first cross-linking reaction was spontaneously initiated in the solution state, forming an ultrathin Si-O-Si amorphous matrix on the surface of the perovskite nanocrystals. The second cross-linking reaction was intentionally induced in the film state by exposing it to UV light. The resulting cross-linked perovskite/SiO2 nanocrystal films exhibited a high packing density, and among four different dopants, the Ag-doped film demonstrated the lowest onset potential for HER in a 0.5 M H2SO4 aqueous solution due to effective band modulation. These findings suggest that the two-time cross-linking approach can significantly enhance the performance of perovskite nanocrystals in photoelectrochemical applications
