The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from ...graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.
Abstract
Photophysical and photochemical properties of graphene quantum dots (GQDs) strongly depend on their morphological and chemical features. However, systematic and uniform manipulation of the ...chemical structures of GQDs remains challenging due to the difficulty in simultaneous control of competitive reactions, i.e., growth and doping, and the complicated post-purification processes. Here, we report an efficient and scalable production of chemically tailored N-doped GQDs (NGs) with high uniformity and crystallinity via a simple one-step solvent catalytic reaction for the thermolytic self-assembly of molecular precursors. We find that the graphitization of N-containing precursors during the formation of NGs can be modulated by intermolecular interaction with solvent molecules, the mechanism of wh ich is evidenced by theoretical calculations and various spectroscopic analyses. Given with the excellent visible-light photoresponse and photocatalytic activity of NGs, it is expected that the proposed approach will promote the practical utilization of GQDs for various applications in the near future.
Lead‐(Pb‐) halide perovskite nanocrystals (NCs) are interesting nanomaterials due to their excellent optical properties, such as narrow‐band emission, high photoluminescence (PL) efficiency, and wide ...color gamut. However, these NCs have several critical problems, such as the high toxicity of Pb, its tendency to accumulate in the human body, and phase instability. Although Pb‐free metal (Bi, Sn, etc.) halide perovskite NCs have recently been reported as possible alternatives, they exhibit poor optical and electrical properties as well as abundant intrinsic defect sites. For the first time, the synthesis and optical characterization of cesium ytterbium triiodide (CsYbI3) cubic perovskite NCs with highly uniform size distribution and high crystallinity using a simple hot‐injection method are reported. Strong excitation‐independent emission and high quantum yields for the prepared NCs are verified using photoluminescence measurements. Furthermore, these CsYbI3 NCs exhibit potential for use in organic–inorganic hybrid photodetectors as a photoactive layer. The as‐prepared samples exhibit clear on–off switching behavior as well as high photoresponsivity (2.4 × 103 A W−1) and external quantum efficiency (EQE, 5.8 × 105%) due to effective exciton dissociation and charge transport. These results suggest that CsYbI3 NCs offer tremendous opportunities in electronic and optoelectronic applications, such as chemical sensors, light emitting diodes (LEDs), and energy conversion and storage devices.
The rare‐earth element ytterbium (Yb) is substituted into the B site of a cubic ABX3 perovskite lattice in place of lead. The resulting CsYbI3 nanocrystals exhibit strong excitonic emission with high quantum yield and the potential for use in hybrid photodetectors as a photoactive layer. Such lead‐free CsYbI3 nanocrystals offer tremendous opportunities in optical and optoelectronic applications.
We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping ...processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters. Time-dependent temperature profiles and heat distribution analyses show that the performance of graphene-based heaters is superior to that of conventional transparent heaters based on indium tin oxide. In addition, we confirmed that mechanical strain as high as ∼4% did not substantially affect heater performance. Therefore, graphene-based, flexible, transparent heaters are expected to find uses in a broad range of applications, including automobile defogging/deicing systems and heatable smart windows.
We developed means to produce wafer scale, high-quality graphene films as large as 3 in. wafer size on Ni and Cu films under ambient pressure and transfer them onto arbitrary substrates through ...instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances. Transistors showed the hole and electron mobilities of the device of 1100 ± 70 and 550 ± 50 cm2/(V s) at drain bias of −0.75 V, respectively. The piezo-resistance gauge factor of strain sensor was ∼6.1. These methods represent a significant step toward the realization of graphene devices in wafer scale as well as application in optoelectronics, flexible and stretchable electronics.
Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural ...and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful is to direct stem cells’ proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate is comparable to the one achieved with common growth factors, demonstrating graphene’s potential for stem cell research.
Electronic fibres have been considered one of the desired device platforms due to their dimensional compatibility with fabrics by weaving with yarns. However, a precise connecting process between ...each electronic fibre is essential to configure the desired electronic circuits or systems. Here, we present an integrated electronic fibre platform by fabricating electronic devices onto a one-dimensional microfibre substrate. Electronic components such as transistors, inverters, ring oscillators, and thermocouples are integrated together onto the outer surface of a fibre substrate with precise semiconductor and electrode patterns. Our results show that electronic components can be integrated on a single fibre with reliable operation. We evaluate the electronic properties of the chip on the fibre as a multifunctional electronic textile platform by testing their switching and data processing, as well as sensing or transducing units for detecting optical/thermal signals. The demonstration of the electronic fibre suggests significant proof of concepts for the realization of high performance with wearable electronic textile systems.
For the application of graphene quantum dots (GQDs) to optoelectronic nanodevices, it is of critical importance to understand the mechanisms which result in novel phenomena of their light ...absorption/emission. Here, we present size-dependent shape/edge-state variations of GQDs and visible photoluminescence (PL) showing anomalous size dependences. With varying the average size (d a) of GQDs from 5 to 35 nm, the peak energy of the absorption spectra monotonically decreases, while that of the visible PL spectra unusually shows nonmonotonic behaviors having a minimum at d a = ∼17 nm. The PL behaviors can be attributed to the novel feature of GQDs, that is, the circular-to-polygonal-shape and corresponding edge-state variations of GQDs at d a = ∼17 nm as the GQD size increases, as demonstrated by high-resolution transmission electron microscopy.
Graphene quantum dots (GQDs) have been considered as a novel material because their electronic and optoelectronic properties can be tuned by controlling the size and the functional groups of GQDs. ...Here we report the synthesis of reduction-controlled GQDs and their application to bulk heterojunction (BHJ) solar cells with enhanced power conversion efficiency (PCE). Three different types of GQDsgraphene oxide quantum dots (GOQDs), 5 h reduced GQDs, and 10 h reduced GQDswere tested in BHJ solar cells, and the results indicate that GQDs play an important role in increasing optical absorptivity and charge carrier extraction of the BHJ solar cells. The enhanced optical absorptivity by rich functional groups in GOQDs increases short-circuit current, while the improved conductivity of reduced GQDs leads to the increase of fill factors. Thus, the reduction level of GQDs needs to be intermediate to balance the absorptivity and conductivity. Indeed, the partially reduced GQDs yielded the outstandingly improved PCE of 7.60% in BHJ devices compared to a reference device without GQDs (6.70%).
Short-chained, aromatic phenethylammonium bromide (PEABr) bulky cation engineering mitigate the surface defects and tune the optical refractive index (n) and the CsPbBr3 perovskite quantum dots that ...substantially improved the optoelectronic properties, PL stability, enabling perovskite light-emitting diode to boost external quantum efficiency from ~1% to ~7%.
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•CsPbBr3 PeQDs are passivated using PEABr cations via facile spin-coating methods.•PEABr passivation mitigates surface defects and tune the index n of CsPbBr3 PeQDs.•PEABr passivation improves the optical coupling and yield high luminescence.•The passivated CsPbBr3 PeQDs films deliver improved efficiency and stability.
All inorganic CsPbBr3 perovskite quantum dots (PeQDs) have emerged as great candidates for next-generation perovskite quantum dots light-emitting diodes (PeQLEDs) applications due to their excellent optoelectronic and light-emitting properties. However, the performance of CsPbBr3 based PeQLEDs is hindered by (i) the long-chain, synthetic insulating ligands on PeQDs surfaces and (ii) the inherently high refractive index (n) of the PeQDs that often leads to internal light confinement loss. These major shortcomings are addressed by introducing a short-chain ammonium moiety, namely phenethylammonium bromide (PEABr), via spin-coating to passivate the surface of the PeQDs films. PEABr passivation can effectively annihilate the intrinsic bromide vacancies of PeQDs and simultaneously tune the refractive index of the PeQDs films. The reduced n-mismatch between the emitter and the charge transporting layers suppresses the waveguide loss after PEABr passivation and significantly elevates the external quantum efficiency (EQE) and maximum luminance of the PeQLEDs from ~ 1.0% to ~ 6.85% and ~ 1300 cd m−2 to ~ 13000 cd m−2, respectively. More importantly, the environmental stability of the PeQDs also improves remarkably following PEABr passivation. The alky cation engineering demonstrated herein is a facile yet efficient approach to simultaneously boost the performance and stability of CsPbBr3 PeQDs.
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