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Homogeneously Bright, Flexible, and Foldable Lighting Devices with Functionalized Graphene Electrodes
Abstract
Alternating current electroluminescent technology allows the fabrication of large areas, flat and flexible lights. Presently the maximum size of a continuous panel is limited by the high resistivity of available transparent electrode materials causing a visible gradient of brightness. Here, we demonstrate that the use of the best known transparent conductor FeCl3-intercalated few-layer graphene (FeCl3-FLG) boosts the brightness of electroluminescent devices by 46% compared to pristine graphene. Intensity gradients observed for high aspect ratio devices are completely eliminated when using these highly conductive electrodes. Finally, we study devices supported on polymer substrates and their resilience to repeated, extreme flexural strains which surpass the requirements for a plethora of wearable electronics applications.
... This method leads to better device performance when compared to graphene patterning using reactive ion etching (RIE) (Fig. 1c). Light-emitting devices were fabricated using the graphene coating as electrode in an alternating current electroluminescent (ACEL) configuration 33 (Fig. 1c-e). ...
... The ACEL device configuration was chosen as this technology uniquely enables the realisation of large-area flexible and foldable graphene light sources, with good contrast and uniform brightness. 33 Furthermore, ACEL devices can display images with high resolution, can withstand mechanical shocks and a wide range of temperatures, 36 making this technology a valuable candidate for smart textiles. ACEL devices were fabricated on individual graphene-coated PP fibres which served as bottom electrode. ...
The true integration of electronics into textiles requires the fabrication of devices directly on the fibre itself using high-performance materials that allow seamless incorporation into fabrics. Woven electronics and opto-electronics, attained by intertwined fibres with complementary functions are the emerging and most ambitious technological and scientific frontier. Here we demonstrate graphene-enabled functional devices directly fabricated on textile fibres and attained by weaving graphene electronic fibres in a fabric. Capacitive touch-sensors and light-emitting devices were produced using a roll-to-roll-compatible patterning technique, opening new avenues for woven textile electronics. Finally, the demonstration of fabric-enabled pixels for displays and position sensitive functions is a gateway for novel electronic skin, wearable electronic and smart textile applications.
... Later, it was confirmed that FeCl 3 -intercalated graphene exhibits an outstanding thermal and humidity stability [43], as well as a high work function of 5.1 eV, which is promising for ITO replacement [44]. The technological applications of this material have diversified, as evidenced by the recent demonstration of extraordinary linear dynamic range photodetectors [45], novel position-sensitive photodetector technologies [46], and ultra-bright large-area flexible lighting devices [47]. [40]. ...
... Later, it was confirmed that FeCl3-intercalated graphene exhibits an outstanding thermal and humidity stability [43], as well as a high work function of 5.1 eV, which is promising for ITO replacement [44]. The technological applications of this material have diversified, as evidenced by the recent demonstration of extraordinary linear dynamic range photodetectors [45], novel position-sensitive photodetector technologies [46], and ultra-bright large-area flexible lighting devices [47]. The overlapped final data points mean that the doped graphene is thermally stable (annealed at 140 °C). ...
Nanostructured and chemically modified graphene-based nanomaterials possess intriguing properties for their incorporation as an active component in a wide spectrum of optoelectronic architectures. From a technological point of view, this aspect brings many new opportunities to the now well-known atomically thin carbon sheet, multiplying its application areas beyond transparent electrodes. This article gives an overview of fundamental concepts, theoretical backgrounds, design principles, technological implications, and recent advances in semiconductor devices that integrate nanostructured graphene materials into their active region. Starting from the unique electronic nature of graphene, a physical understanding of finite-size effects, non-idealities, and functionalizing mechanisms is established. This is followed by the conceptualization of hybridized films, addressing how the insertion of graphene can modulate or improve material properties. Importantly, it provides general guidelines for designing new materials and devices with specific characteristics. Next, a number of notable devices found in the literature are highlighted. It provides practical information on material preparation, device fabrication, and optimization for high-performance optoelectronics with a graphene hybrid channel. Finally, concluding remarks are made with the summary of the current status, scientific issues, and meaningful approaches to realizing next-generation technologies.
... Examples include an unforeseen stability to harsh environmental conditions [31], ease of large-area processing [32], the realization of allgraphene photodetectors [32] and the potential to enhance the efficiency of photovoltaic and organic light-emitting devices [32,33]. When used as a transparent electrode in electroluminescent devices, FeCl 3 -functionalized graphene also increases the brightness of the emitted light by up to 50% when compared with pristine graphene, and up to 30% compared with stateof-the-art commercial electrodes [34]. Furthermore, the record high charge density achieved in FeCl 3 -functionalized graphene [13,35] makes it an attractive platform for the production of high-responsivity, high-resolution photodetectors. ...
... Many of the above issues have been recently tackled using FeCl 3 -intercalated FLG [13,[31][32][33][34][35]42] (FeCl 3 -FLG), together with a new way to define optically active junctions [43]. As shown in figure 2a, a laser beam is used to control the [13,32] and consequent p-type doping of the graphene. ...
Graphene-based materials are being widely explored for a range of biomedical applications, from targeted drug delivery to biosensing, bioimaging and use for antibacterial treatments, to name but a few. In many such applications, it is not graphene itself that is used as the active agent, but one of its chemically functionalized forms. The type of chemical species used for functionalization will play a key role in determining the utility of any graphene-based device in any particular biomedical application, because this determines to a large part its physical, chemical, electrical and optical interactions. However, other factors will also be important in determining the eventual uptake of graphene-based biomedical technologies, in particular the ease and cost of manufacture of proposed device and system designs. In this work, we describe three novel routes for the chemical functionalization of graphene using oxygen, iron chloride and fluorine. We also introduce novel in situ methods for controlling and patterning such functionalization on the micro- and nanoscales. Our approaches are readily transferable to large-scale manufacturing, potentially paving the way for the eventual cost-effective production of functionalized graphene-based materials, devices and systems for a range of important biomedical applications.
... Graphene has attracted tremendous attention due to its large surface area, excellent mechanical strength, high electronic conductivity and good adsorption capacity [1,2].Graphene has a diverse range of applications in solar cells, hydrogen storage materials, electroluminescent devices and electrode materials [3][4][5]. In particular, graphene or reduced graphene oxide (rGO) and biopolymer (e.g., gellan gum, chitosan, and alginate) nano- composites have also gained growing interest in the develop- ment of advanced materials [6][7][8]. ...
... Electrodeposition of 2-hydroxypropyltri- methylammonium chloride chitosan- modified rGO (HACC-rGO) Graphene is attracting more attention due to its promising appli- cations in many fields [3][4][5]. However, its application is limited due to the fact that it aggregates and disperses poorly in sol- vents, which seriously limits its application [22,23]. ...
The electrodeposition of graphene has drawn considerable attention due to its appealing applications for sensors, supercapacitors and lithium-ion batteries. However, there are still some limitations in the current electrodeposition methods for graphene. Here, we present a novel electrodeposition method for the direct deposition of reduced graphene oxide (rGO) with chitosan. In this method, a 2-hydroxypropyltrimethylammonium chloride-based chitosan-modified rGO material was prepared. This material disperses homogenously in the chitosan solution, forming a deposition solution with good dispersion stability. Subsequently, the modified rGO material was deposited on an electrode through codeposition with chitosan, based on the coordination deposition method. After electrodeposition, the homogeneous, deposited rGO/chitosan films can be generated on copper or silver electrodes or substrates. The electrodeposition method allows for the convenient and controlled creation of rGO/chitosan nanocomposite coatings and films of different shapes and thickness. It also introduces a new method of creating films, as they can be peeled completely from the electrodes. Moreover, this method allows for a rGO/chitosan film to be deposited directly onto an electrode, which can then be used for electrochemical detection.
... As user demands for organic user interface (OUI) continues to grow in human-electronics interactions 1 , flexible displays play a crucial role in conveying information between device and user, driving the advancement of flexible electronic technologies. Therefore, shape-deformable displays such as foldable, bendable, rollable, and stretchable are emerging as the next generation of display technology, garnering significant research attention [2][3][4][5] , and some have already achieved commercial success. Exploiting the merits of flexible form factors, deformable displays are maximizing user convenience and form factor, and emphasizing thin, compact, and lightweight designs 6 . ...
... The Raman and PL spectra are, in fact, corrected in intensity to take into account the transmittance of all filters and optical parts, as well as the efficiencies of the grating and of the CCD. Such feature is usually not found in commercially-available Raman spectrometers.As an example of EL device characterization we use a ZnS 2 -based ACEL device with both graphene and functionalized graphene transparent electrodes37 .Figure9b shows the spectral emission of such device with graphene and FeCl 3 -intercalated graphene electrodes. The spectra can be decomposed into multiple Gaussian peaks, corresponding to the intraband transitions 38 in ZnS 2 . ...
Optoelectronic devices based on graphene and other two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs) are the focus of wide research interest. The characterization these emerging atomically thin materials and devices strongly relies on a set of measurements involving both optical and electronic instrumentation ranging from scanning photocurrent mapping to Raman and photoluminescence (PL) spectroscopy. Furthermore, proof-of-concept devices are usually fabricated from micro-meter size flakes, requiring microscopy techniques to characterize them. Current state-of-the-art commercial instruments offer the ability to characterize individual properties of these materials with no option for the in situ characterization of a wide enough range of complementary optical and electrical properties. Presently, the requirement to switch atomically-thin materials from one system to another often radically affects the properties of these uniquely sensitive materials through atmospheric contamination. Here, we present an integrated, multi-purpose instrument dedicated to the optical and electrical characterization of devices based on 2D materials which is able to perform low frequency electrical measurements, scanning photocurrent mapping, Raman, absorption and PL spectroscopy in one single set-up. We characterize this apparatus by performing multiple measurements on graphene, transition metal dichalcogenides (TMDs) and Si. The performance and resolution of each individual measurement technique is found to be equivalent to that of commercially available instruments. Contrary to nowadays commercial systems, a significant advantage of the developed instrument is that for the first time the integration of a wide range of complementary opto-electronic and spectroscopy characterization techniques is demonstrated in a single compact unit.
... In addition, the effects of transition metal chlorides as p-type dopants on the properties of graphene materials have also been extensively studied. Many studies have proven that transition metal chlorides can also effectively improve the conductivity of graphene materials [24,31,34,35,37,41]. However, most of these studies have focused on graphene prepared by chemical vapor deposition (CVD) and the total amount of intercalation is low. ...
The preparation of graphene-based conductive inks and their application in the field of flexible electronics have been extensively studied. However, improving the conductivity of the printed patterns always induces the neglect of the rheological properties of the graphene-based conductive inks or the mechanical properties of the as-printed patterns. In this study, the p-type doping of graphene with CuCl2 as the dopant is realized through liquid phase reaction, and the doped graphene powders are used to prepare the graphene-based conductive inks with a conductivity of 3.13 × 104 S m−1. Subsequently, to simplify the preparation of inks, CuCl2 is directly added into the graphene-based conductive inks, achieving the p-type doped graphene ink with the conductivity of 3.64 × 104 S m−1. The read range of ultrahigh-frequency radio frequency identification antenna and the temperature of the flexible electrothermal film printed with the CuCl2-doped graphene-based conductive inks can reach 7.15 m and 200°C, respectively when the equivalent isotropically radiated power is equal to 4 W and the input power density is 0.94 W cm−2. Moreover, good rheological properties of the conductive inks and high mechanical properties of the printed patterns are also obtained.
... Within these applications, graphene has been used as ITO replacement in traditional [24] and flexible [25] OLED display units. Graphene has likewise been used in flexible alternating current electroluminescent displays [26] and in LCDs [27]. ...
Transparent and conductive thin films are critical components in countless electronic devices and in solar energy generation. For nearly half a century these technologies have been founded on varying grades of highly transparent and conductive indium-doped tin oxide and its derivatives. Modern applications however demand mechanical properties that are unattainable with metal oxides, and those emerging needs have nudged nanomaterials with a superior strength and flexibility into the spotlight. With its exceptionally strong covalent structure and carrier mobility that can exceed conventional metals by many orders of magnitudes, graphene holds perhaps the greatest promise. This chapter will provide a review of the use of graphene transparent and conductive thin films in numerous applications and offer a comparison to similar technologies such as carbon nanotubes. A concise overview of the mechanism of conduction in polycrystalline graphene thin films will be given and, by reflecting on the established theoretical foundations, the prospects of boosting the optoelectric performance of graphene TCFs via optimized doping and synthesis will be discussed.
... However, AC-driven EL (ACEL) devices have recently gained considerable attention as promising alternatives to DC-driven devices, because they do not require of AC/DC converters and other costly switching devices which introduces power losses and complicated back-end electronics [11][12][13][14]. Furthermore, their intrinsic ability of flexible and straightforward device architecture with uniform large light-emitting areas with low heat generation and power consumption are further reasons of interest [15,16]. Among the different structures developed for ACEL devices, inorganic thin-film ACEL (ACTFEL) with a MISIM (metal-insulator-semiconductor-insulator -metal) architecture have been successfully used in monochromic flat panel displays for applications where it is required to stand extreme conditions, such as high temperatures, strong vibrations, and environments with high humidity [1,[17][18][19][20]. ...
In this work, white-emitting-alternating-current-thin film electroluminescent (w-ACTFEL) devices are demonstrated using europium-doped zinc sulfide (ZnS:Eu) and zirconium oxide (ZrO2) as the emissive and dielectric layers, respectively. These films were deposited by the ultrasonic spray pyrolysis technique on antimony-doped tin oxide glass substrates, forming a standard metal-insulator-semiconductor-insulator-metal (MISIM) architecture. 10 kHz sinusoidal voltages activated the white-EL of the devices. The colorimetric characteristics were investigated for three amplitudes of the applied voltage. The emission of the devices is made up of wide and narrow bands with peaks corresponding to violet, blue, green and red light, which together produce the resulting white light. According to the colorimetric analysis, this white light is close to the standard D65 CIE illuminant with a minimal dominant blue component. The variation in voltage amplitude induces small changes in the visual characteristics of the EL emission. The white-EL emission of these MISIM devices is attributed to the electron-impact excitation and subsequent relaxation of the excited levels of Eu²⁺ and Eu³⁺ impurities, and defect levels in the sublayer regions adjacent to the ZrO2–ZnS:Eu interfaces.
... In addition to these highly desirable traits, the i-FLG is stable to high levels of humidity across a wide range of temperatures (Wehenkel et al., 2015) and can be processed in large areas Walsh et al., 2018). i-FLG has so far been demonstrated as a transparent electrode in optoelectronic devices such as photodetectors (Withers et al., 2013;de Sanctis et al., 2017) and flexible lighting devices (Torres Alonso et al., 2016). ...
In this paper, we present the first organic photovoltaic (OPV) devices fabricated with FeCl3 intercalated few layer graphene (i-FLG) electrodes. i-FLG electrodes were first fabricated and characterized by electrical and spectroscopic means, showing enhanced conductive properties compared to pristine graphene. These electrodes were then used in the fabrication of OPV devices and tested against devices made with commercially available Indium Tin Oxide (ITO) electrodes. Both types of device achieved similar efficiencies, while the i-FLG based device exhibited superior charge transport properties due to the increase in work function characterizing i-FLG. Both types of device underwent a stability study using both periodic and continuous illumination measurements, which revealed i-FLG based OPVs to be significantly more stable than those based on ITO. These improvements are expected to translate to increased device lifetimes and a greater total energy payback from i-FLG based photovoltaic devices. These results highlight the potential benefits of using intercalated graphene materials as an alternative to ITO in photovoltaic devices.
... Graphene films grown by chemical vapor deposition (CVD) were used as the electrodes in ACEL devices. 38,39 Wang et al. demonstrated that single-layer graphene-based ACEL devices showed the optimum performance as the transparency decreased when increasing the stacked layers. 40 The as-fabricated device has a turn-on voltage of 80 V and a brightness of 1140 cd/m 2 at 480 V (16 kHz). ...
Since its first discovery by Destriau in oil dispersion of ZnS:Cu phosphors, alternating current electroluminescence (ACEL) has found enormous applications in lighting, full-color displays, and optoelectronics. ACEL materials are particularly useful for constructing flexible light-emitting devices owing to their low cost and easy integration with flexible electrodes and polymer substrates. ACEL devices utilizing the phosphor-elastomer composite as the emissive layer are intrinsically stretchable/deformable, in contrast to direct current light-emitting diodes that are often built on rigid panels. In this Research Update, we summarize recent advances in the design and preparation of various flexible-panel ACEL devices. Emerging applications enabled by these flexible ACEL devices are also highlighted.
... Graphene has been widely attempted to be used as one of the promising candidates for TCEs in various optical and electronic device applications owing to its high transmittance and high flexibility [12][13][14]. These properties are known to stem from the extremely thin, one-carbon-atom thickness, uniform absorption of light causing a zero-energy bandgap, and high carrier mobility because of its two-dimensional (2D) sp 2 electronic hybridization configuration [15][16][17]. ...
Demand for the fabrication of high-performance, transparent electronic devices with improved electronic and mechanical properties is significantly increasing for various applications. In this context, it is essential to develop highly transparent and conductive electrodes for the realization of such devices. To this end, in this work, a chemical vapor deposition (CVD)-grown graphene was transferred to both glass and polyethylene terephthalate (PET) substrates that had been pre-coated with an indium tin oxide (ITO) layer and then subsequently patterned by using a laser-ablation method for a low-cost, simple, and high-throughput process. A comparison of the results of the laser ablation of such a graphene/ITO double layer with those of the ITO single-layered films reveals that a larger amount of effective thermal energy of the laser used is transferred in the lateral direction along the graphene upper layer in the graphene/ITO double-layered structure, attributable to the high thermal conductivity of graphene. The transferred thermal energy is expected to melt and evaporate the lower ITO layer at a relatively lower threshold energy of laser ablation. The transient analysis of the temperature profiles indicates that the graphene layers can act as both an effective thermal diffuser and converter for the planar heat transfer. Raman spectroscopy was used to investigate the graphite peak on the ITO layer where the graphene upper layer was selectively removed because of the incomplete heating and removal process for the ITO layer by the laterally transferred effective thermal energy of the laser beam. Our approach could have broad implications for designing highly transparent and conductive electrodes as well as a new way of nanoscale patterning for other optoelectronic-device applications using laser-ablation methods.
... Within these technologies, graphene has been used as an ITO replacement in standard [230,231] and flexible [232][233][234] OLED displays. Graphene has also been used in flexible alternating-current electroluminescent displays [235][236][237], as well as in LCDs [238][239][240]. Other applications of graphene in display technologies include increasing standard ITO OLED performance [241] and using as electrodes for GaN micro-LEDs [242]. ...
Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes; it has low sheet resistance, high optical transmission and is flexible. Whereas the most common transparent electrode material, tin-doped indium-oxide (ITO) is brittle, less transparent and expensive, which limit its compatibility in flexible electronics as well as in low-cost devices. Here we review two large-area fabrication methods for graphene based transparent electrodes for industry: liquid exfoliation and low-pressure chemical vapor deposition (CVD). We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results. State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5, slightly over the minimum required for industry of 35, while CVD reaches as high as 419.
... ZnS-based materials are also potential for luminescence. ACELs are very promising due to their intrinsic ability of uniform light emission, flexible architecture, low heat generation, and low power consumption [26][27][28][29]. Paper-based electroluminescent device has been proposed [30] and in most cases the dielectric layer of ACELs is made of barium titanate or some other materials. ...
Humidity sensors are indispensable for various electronic systems and instrumentations. To develop a new humidity sensing mechanism is the key for the next generation of sensor technology. In this work, a novel flexible paper-based current humidity sensor is proposed. The developed alternating current electroluminescent devices (ACEL) consist of the electroless plating Ni on filter paper and silver nanowires (AgNWs) as the bottom and upper electrodes, and ZnS:Cu as the phosphor layer, respectively. The proposed humidity sensor is based on ACEL with the paper substrate and the ZnS:Cu phosphor layer as the humidity sensing element. The moisture effect on the optical properties of ACELs has been studied firstly. Then, the processing parameters of the paper-based ACELs such as electroless plated bottom electrode and spin-coated phosphor layer as a function of the humidity-sensitive characteristics are investigated. The sensing mechanism of the proposed sensor has been elucidated based on the Q ~ V analysis. The sensor exhibits an excellent linearity ( R 2 = 0.99965 ) within the humidity range from 20% to 90% relative humidity (RH) and shows excellent flexibility. We also demonstrate its potential application in postharvest preservation where the EL light is used for preservation and the humidity can be monitored simultaneously through the current.
... The polarization change is registered by a quarter wave plate (λ/4), a Wollaston prism (W) and a balanced photo detector (BPD). Lock-in amplifier (LA) and personal computer (PC) are used for signal processing work [30,31,[33][34][35][36][37][38][39][40][41][42]. In particular, high resolution scanning electron microsopy of intercalated samples is shown in [41]. ...
Abstract Time-resolved terahertz spectroscopy has become a common method both for fundamental and applied studies focused on improving the quality of human life. However, the issue of finding materials applicable in these systems is still relevant. One of the appropriate solution is 2D materials. Here, we demonstrate the transmission properties of unique graphene-based structures with iron trichloride FeCl3 dopant on glass, sapphire and Kapton polyimide film substrates that previously were not investigated in the framework of the above-described problems in near infrared and THz ranges. We also show properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions transferred to a polyimide and polyethylene terephthalate substrates. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow to control the transmission of samples for both the terahertz and infrared ranges, which can be used for creation of effective modulators and components for THz spectroscopy systems.
... Thus, p-type electrodes possessing low contact resistivity as well as high transmittance have been extensively studied. Several kinds of transparent conductive layer such as metal nanowires [13][14][15][16], graphene [17][18][19], carbon nanotubes [20,21], and conductive polymers [22][23][24] have been reported to improve the current spreading of LEDs. For top-emitting LEDs, indium-tin-oxide (ITO) has been widely used to increase current spreading uniformity over the entire active region due to its high optical transmittance and excellent electrical conductivity [25][26][27]. ...
A patterned double-layer indium-tin oxide (ITO), including the first unpatterned ITO layer serving as current spreading and the second patterned ITO layer serving as light extracting, was applied to obtain uniform current spreading and high light extraction efficiency (LEE) of GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Periodic pinhole patterns were formed on the second ITO layer by laser direct writing to increase the LEE of UV LED. Effects of interval of pinhole patterns on optical and electrical properties of UV LED with patterned double-layer ITO were studied by numerical simulations and experimental investigations. Due to scattering out of waveguided light trapped inside the GaN film, LEE of UV LED with patterned double-layer ITO was improved as compared to UV LED with planar double-layer ITO. As interval of pinhole patterns decreased, the light output power (LOP) of UV LED with patterned double-layer ITO increased. In addition, UV LED with patterned double-layer ITO exhibited a slight degradation of current spreading as compared to the UV LED with a planar double-layer ITO. The forward voltage of UV LED with patterned double-layer ITO increased as the interval of pinhole patterns decreased.
... The strong charge-transfer between graphene and FeCl 3 molecules [62] induces large p-doping of graphene [22], up to 10 14 cm −2 , and drastically changes the carriers dynamics [63]. The intercalation also results in a superior transparent conductor with a sheet resistance as low as 8 Ω/sq with 85 % transparency [18] highly sought for sensing and efficient lighting technologies [64]. Contrary to bulk graphite, the intercalation of FLG takes place at relatively low temperatures using a three-zones furnace, it does not require a carrier gas and the time-scale is reduced from tens of days to only 8 hrs. ...
Graphene and graphene-based materials exhibit exceptional optical and electrical properties with great promise for novel applications in light detection. However, several challenges prevent the full exploitation of these properties in commercial devices. Such challenges include the limited linear dynamic range (LDR) of graphene-based photodetectors, the lack of efficient generation and extraction of photoexcited charges, the smearing of photoactive junctions due to hot-carriers effects, large-scale fabrication and ultimately the environmental stability of the constituent materials. In order to overcome the aforementioned limits, different approaches to tune the properties of graphene have been explored. A new class of graphene-based devices has emerged where chemical functionalisation, hybridisation with light-sensitising materials and the formation of heterostructures with other 2D materials have led to improved performance, stability or versatility. For example, intercalation of graphene with FeCl 3 is highly stable in ambient conditions and can be used to define photo-active junctions characterized by an unprecedented LDR while graphene oxide (GO) is a very scalable and versatile material which supports the photodetection from UV to THz frequencies. Nanoparticles and quantum dots have been used to enhance the absorption of pristine graphene and to enable high gain thanks to the photogating effect. In the same way, hybrid detectors made from stacked sequences of graphene and layered transition-metal dichalcogenides enabled a class of devices with high gain and responsivity. In this work, we will review the performance and advances in functionalised graphene and hybrid photodetectors, with particular focus on the physical mechanisms governing the photoresponse, the performance and possible future paths of investigation.
... The strong charge-transfer between graphene and FeCl 3 molecules [64] induces large p-doping of graphene [22], up to 10 14 cm −2 , and drastically changes the carriers dynamics [65]. The intercalation also results in a superior transparent conductor with a sheet resistance as low as 8 Ω/sq with 85 % transparency [18] highly sought for sensing and efficient lighting technologies [66]. Contrary to bulk graphite, the intercalation of FLG takes place at relatively low temperatures using a three-zones furnace, it does not require a carrier gas and the time-scale is reduced from tens of days to Ref. ...
Graphene and graphene-based materials exhibit exceptional optical and electrical properties with great promise for novel applications in light detection. However, several challenges prevent the full exploitation of these properties in commercial devices. Such challenges include the limited linear dynamic range (LDR) of graphene-based photodetectors, the lack of efficient generation and extraction of photoexcited charges, the smearing of photoactive junctions due to hot-carriers effects, large-scale fabrication and ultimately the environmental stability of the constituent materials. In order to overcome the aforementioned limits, different approaches to tune the properties of graphene have been explored. A new class of graphene-based devices has emerged where chemical functionalisation, hybridisation with light-sensitising materials and the formation of heterostructures with other 2D materials have led to improved performance, stability or versatility. For example, intercalation of graphene with FeCl is highly stable in ambient conditions and can be used to define photo-active junctions characterized by an unprecedented LDR while graphene oxide (GO) is a very scalable and versatile material which supports the photodetection from UV to THz frequencies. Nanoparticles and quantum dots have been used to enhance the absorption of pristine graphene and to enable high gain thanks to the photogating effect. In the same way, hybrid detectors made from stacked sequences of graphene and layered transition-metal dichalcogenides enabled a class of detectors with high gain and responsivity. In this work we will review the performance and advances in functionalised graphene and hybrid photodetectors, with particular focus on the physical mechanisms governing the photoresponse in these materials, their performance and possible future paths of investigation.
... These results show FeCl 3 -FLG to be ideally suited for use as a transparent conducting electrode, with the versatility to be employed on flexible substrates with negligible detriment to its electrical or optical properties. 18 ...
... The emission wavelength from ZnS is determined primarily by the doping activators 26 . In the past decade, many efforts has been devoted to the functional construction of phosphor-based alternating current electroluminescent devices for flexible and stretchable light emission devices, owing to their simple fabrication procedure, low power consumption, large-area production as well as potential cost-effectiveness 31,32 . However, these EL devices exhibit relatively low luminance compared with organic light emitting devices 33 . ...
Building transient electronics are promising and emerging strategy to alleviate the pollution issues from electronic waste (e-waste). Although a variety of transient devices comprising organic and inorganic materials have been described, transient light emitting devices are still elusive but highly desirable because of the huge amount of lighting and display related consumer electronics. Here we report a simple and efficient fabrication of large-area flexible transient alternating current electroluminescent (ACEL) device through a full-solution processing method. Using transparent flexible AgNW-polymer as both electrodes, the devices exhibit high flexibility and both ends side light emission, with the features of controlled size and patterned structure. By modulating the mass ratio of blue and yellow phosphors, the emission color is changed from white to blue. Impressively, the fabricated ACEL device can be thoroughly dissolved in water within 30 min. Our strategy combining such advances in transient light emitting devices with simple structure, widely used materials, full solution process, and high solubility will demonstrate great potential in resolving the e-waste from abandoned light-emitting products and expand the opportunities for air-stable flexible light emitting devices.
Flexible alternating current electroluminescence (ACEL) devices integrated into textiles are gaining significant attention for their potential in lighting displays and health monitoring applications. Traditional challenges include high‐voltage “breakdown” and limited color output due to the inherent properties of ZnS:Cu. This study introduces a novel multi‐color ACEL device featuring a fluorescent dye color conversion layer alongside a robust protective layer designed to enhance device stability. The optimal ratio of dielectric layer concentration and protective layer thickness is systematically investigated to mitigate the risk of “breakdown”. Utilizing the principles of photoluminescence and electroluminescence, luminous electronic textile devices is successfully developed that exhibit both purple and green luminescence. Additionally, integration with a temperature sensor enables the device to serve as a health‐monitoring tool by signaling changes in body temperature. This research delineates the protective capabilities of the protective layer and the efficacy of the color conversion mechanism in maintaining consistent brightness under various conditions. The findings suggest a viable pathway for broadening applications and potentially accelerating the commercialization of wearable electroluminescent technologies.
Deformable alternating‐current electroluminescent (ACEL) devices are of increasing interest because of their potential to drive innovation in soft optoelectronics. Despite the research focus on efficient white ACEL devices, achieving deformable devices with high luminance remains difficult. In this study, this challenge is addressed by fabricating white ACEL devices using color‐conversion materials, transparent and durable hydrogel electrodes, and high‐k nanoparticles. The incorporation of quantum dots enables the highly efficient generation of red and green light through the color conversion of blue electroluminescence. Although the ionic‐hydrogel electrode provides high toughness, excellent light transmittance, and superior conductivity, the luminance of the device is remarkably enhanced by the incorporation of a high‐k dielectric, BaTiO3. The fabricated ACEL device uniformly emits very bright white light (489 cd m⁻²) with a high color‐rendering index (91) from both the top and bottom. The soft and tough characteristics of the device allow seamless operation in various deformed states, including bending, twisting, and stretching up to 400%, providing a promising platform for applications in a wide array of soft optoelectronics.
The development of stimuli‐interactive displays based on alternating current (AC)‐driven electroluminescence (EL) is of great interest, owing to their simple device architectures suitable for wearable applications requiring resilient mechanical flexibility and stretchability. AC‐EL displays can serve as emerging platforms for various human‐interactive sensing displays (HISDs) where human information is electrically detected and directly visualized using EL, promoting the development of the interaction of human–machine technologies. This review provides a holistic overview of latest developments in AC‐EL displays with an emphasis on their applications for HISDs. AC‐EL displays based on exciton recombination or impact excitations of hot electrons are classified into four representative groups depending upon their device architecture: (1) displays without insulating layers, (2) displays with single insulating layers, (3) displays with double insulating layers, and (4) displays with EL materials embedded in an insulating matrix. State‐of‐the‐art AC HISDs are discussed. Furthermore, emerging stimuli‐interactive AC‐EL displays are described, followed by a discussion of scientific and engineering challenges and perspectives for future stimuli‐interactive AC‐EL displays serving as photo‐electronic human–machine interfaces.
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Summary The most common technologies applied in flexible displays are adapted from the resistive and capacitive touch panels. The key components of a resistive panel are a conductive substrate, a liquid-crystal device front panel, and a transparent conductive film. For future optoelectronic devices, such as flexible displays, graphene and its derivatives seem to be promising candidates as they exhibit good transparency, conductivity, and stability. This chapter presents a comprehensive overview of the graphene/flexible polymer electrode characteristics, such as sheet resistance, transmittance, and mechanical robustness. The touch screen technology is expected to be revolutionized by flexible films consisting of single graphene stacks encapsulated within a thin transparent polymeric film. Although there is a very positive sentiment on the prospects of global graphene industry and graphene is being tested in numerous applications, graphene is not expected to enter into a product development trajectory within the very near future for a variety of reasons.
Super-hydrophobic and fire-retardant coatings have been applied to the bamboo surface. However, it remains a significant challenge to develop coating materials that perform multiple functions simultaneously. In this paper, a novel conductive bamboo timber ([email protected]), coated with reduced graphene oxide (RGO) and silver nanoparticles, was fabricated via a hydrothermal process and a silver mirror reaction process. The [email protected] composites had excellent photo-catalytic activity, meanwhile, the removal rate of rhodamine B (RhB), methylene blue (MB), and methyl orange (MO) after 60min photo-degradation were 77.6%, 88.8%, and 78.4%, respectively, superior to the raw bamboo timber (BT) and the bamboo timber coated with reduced graphene oxide (RGOBT). The [email protected] samples showed excellent antibacterial performance against Escherichia coli and Staphylococcus aureus. Additionally, the [email protected] samples exhibited improved thermal stability and fire-resistant property with a limiting oxygen index of 30.5%. Finally, the future directions of multifunctional bamboo research and opportunities for electronic industry application are prospected.
Graphene shows great promise as a replacement electrode material for flexible optoelectronic applications for its conductive, transparent and flexible properties. Here, we demonstrate the fabrication and application of functionalized graphene electrodes for flexible photovoltaics.
Alternating current‐driven electroluminescent (ACEL) devices have recently emerged as a potential candidate for next‐generation smart lighting, stretchable displays, and wearable electronics. Herein, a simple and efficient method is developed to fabricate high brightness, chromatic‐stable, and stretchable white ACEL devices through doping wide‐spectrum yellow photoluminescent phosphor into blue electroluminescent emissive layer. By tuning the ratio of electroluminescent to photoluminescent phosphors in the emissive layer, the optimized device achieved a maximum brightness of 3150 cd m⁻² for white emission with Commison Internationale de L'Eclairage coordinates of (0.28, 0.34), and manifested a more stable chromaticity than traditional ACEL devices. Moreover, a digital display and stretchable white ACEL device (with a tensile strain of 150%) are demonstrated to show the generality of this approach. The high brightness white ACEL devices proposed in this work offer a simplified architecture with facile fabrication process and large‐area compatibility, which may find broad range of applications in wearable optoelectronics.
Durable and extremely deformable electrodes play a significant role in the field of high‐strain flexible electronics, including wearable electronics and flexible tactile sensor. However, the existing flexible transparent electrodes hardly have a high strain limit and low square resistance simultaneously, like the combination of carbon‐based electrodes and metal electrodes. Herein, a semicovered silver nanotube (SC‐AgNT) network electrode is proposed. The SC‐AgNT network electrode consists of semicovered polymer nanofibers and a highly integrated Ag nanotube network for achieving high strain limit and low square resistance. Further, a tactile sensor based on this electrode is built, demonstrating the advance of the new electrodes. The strength enhancement layer consists of polyvinyl alcohol (PVA) nanofibers in the SC‐AgNT network electrode, making the electrode have the minimum bending radius of 0.1 mm and the maximum twist angle of 120° (0.9 Ω sq⁻¹ at 94% transmittance). A tactile sensing interface based on the SC‐AgNT network electrode displays highly stable electrical properties under multiple types and times of comprehensive deformation and touch deformation. The technical strategy for strengthening metal network electrodes and preparing integrated low‐resistance metal networks can be extended to enhance the performance of other metal‐based flexible electrodes and flexible devices.
Atomically thin two-dimensional (2D) materialsTwo-dimensional-(2D) materials has been reported in the International Technology Roadmap for SemiconductorsSemiconductors to be one of the potential technological enablers to achieve scaling sizes of 5 nm and lower, digressing away from the conventional silicon material. Given the uniqueness of these 2D materialsTwo-dimensional-(2D) materials, with properties ranging from semi-metalSemi-metal to semiconductors to insulating, research scale efforts have demonstrated promising new opportunities for both rigid and flexibleFlexiblenanoelectronicsFlexible-electronics and optoelectronics applicationsNanoelectronics, in numerous fields such as imaging and sensing, medicalMedical, industrial, environmental, biological, field-effect transistorsTransistors, solar cellsSolar cells, batteriesBatteries, thermoelectrics, lightLight emitting diodesLight-emitting diodes, lasers and ultra-fast optical communicationsUltra-fast optical communications. It is the focus of this chapter to provide an overall review of this fascinating world of atomically thin 2D novel materials, the physics underlying these materials, the recent applications surrounding these novel 2D materialsTwo-dimensional-(2D) materials and their devices, and the progressive efforts at large scale commercialization.
In these areas of flexible displays and wearable devices, double-sided light-emitting devices have huge commercial applications. Here, we provide a novel form of flexible double-sided light-emitting devices by designing and manufacturing different transparent interdigital electrodes for lighting the structural areas of composite emitting layers. The transparent interdigital electrodes are fabricated by embedding multiwalled carbon nanotubes (MWCNTs) into interdigital mesh-structured microcavities using a doctor-blading process and the emitting layers are fabricated by mixing copper-doped zinc sulfide (ZnS:Cu) phosphor particles into the transparent polydimethylsiloxane (PDMS) polymer. The fabricated double-sided light-emitting devices could be in the crimp state, exhibiting excellent flexibility. By designing the structure of the interdigital electrodes and the thickness of the emitting layers, the double-sided emission intensity of the light-emitting devices can be adjusted. Furthermore, based on the flexible double-sided light-emitting devices, various patterns can be successfully programmed, such as the digital, grayscale and ancient Chinese walls. The flexible and programmable double-sided light-emitting films provide a promising strategy for the next generation of customized flexible displays.
In this work, flexible electroluminescent devices (FELDs) are demonstrated using environmentally‐friendly cellulose nanocrystal (CNC) substrates with a silver nanowire conductive network. The CNC sheets with drop‐casted silver nanowires act as highly transparent conductive electrodes for an electroluminescent layer (a phosphorescent ink containing Cu/Br‐doped ZnS microparticles). This phosphorescent device requires operating voltages as low as 7 V and achieves high luminance of up to 43 Cd m⁻² (at 50 V). Furthermore, through impregnating the CNC host material with Rhodamine 6G or Thiazol Yellow G, different emission colors are achieved: blue, turquoise, green, and purple light emission having a broad (400–650 nm) luminescence spectrum are obtained. This device, which uses earth‐abundant, cost‐effective, and recyclable materials, is envisioned to lead to advancements in the areas of electronics and lighting technology.
While recent trends in flexible optoelectronic devices have led to a proliferation of studying transparent conductive electrodes (TCEs), maintaining the balance of high transmittance and high conductivity of TCEs remains a challenge. Herein, the collaboration of silver nanowires (AgNWs) network and new 2D Mxene nanosheets with excellent conductivity, hydrophilicity and mechanical flexibility contributes to a highly transparent and conductive hybrid electrode through a simple, scalable, low-cost solution-processing method. This AgNWs-Mxene electrode shows a low sheet resistance of 15.9 Ω sq-1 at ultra-high transmittance of 92.5%, and remarkable mechanical durability and chemical stability. As a proof of concept, the AgNWs-Mxene electrode is used in flexible alternating-current electroluminescent (ACEL) device, showing outstanding flexibility and stable illumination, which can maintain a constant illumination even under bending at 180°. This promising high-performance electrode will definitely provide a brand-new pathway for the development of flexible optoelectronic devices.
Reduced graphene oxide (rGO)-coated microfibers (GCMs) have been developed through a straightforward synthesis by soaking microfiber cloths in graphene oxide (GO) aqueous dispersions and followed by reduction with hydrazine vapors in autoclave at 80 °C. The produced GCMs show high hydrophobicity and oleophilicity, which can be used to recover crude oil from oil-in-water mixtures. The microscopic structures have been analyzed under optical microscopy and scanning electron microscopy; confirming the presence of rGO on the microfibers’ surface. Thermal gravimetric analysis measurements showed that GCMs are stable up to 300 °C. Raman spectroscopy indicated a strong quenching of the polymers’ peaks in GCMs and the appearance of graphene’s D and G peaks due to the rGO coating. The maximum uptake capacity of the GCMs is 6.78 g of oil per gram of material with a reduction of 13.5% after 10 adsorption-desorption cycles. Removals of 97.90% and 87.58% of crude oil have been achieved after a single application of GCMs in 1% (v/v) oil-water and oil-artificial seawater mixtures respectively. Oil concentrations below 35 ppm have been reached after the second and the fifth application of GCMs in oil-water and oil-artificial seawater mixtures respectively. The adhesion strength of the rGO coating has been assessed by different means such as sonication and vigorous mixing in water; the highest amount of rGO released in water was 8.3 ppm after 30 minutes of sonication. These properties suggest that GCMs can be used, as prepared or combined in filter devices, as a possible oil recovery method in case of oil spills.
Flexible alternating‐current electroluminescent (ACEL) devices have attracted considerable attention for their ability to produce uniform light emission under bent conditions and have enormous potential for applications in back lighting panels, decorative lighting in automobiles, and panel displays. Nevertheless, flexible ACEL devices generally require a high operating bias, which precludes their implementation in low power devices. Herein, solution‐processed La‐doped barium titanate (BTO:La) nanocuboids (≈150 nm) are presented as high dielectric constant (high‐k) nanodielectrics, which can enhance the dielectric constant of an ACEL device from 2.6 to 21 (at 1 kHz), enabling the fabrication of high‐performance flexible ACEL devices with a lower operating voltage as well as higher brightness (≈57.54 cd m−2 at 240 V, 1 kHz) than devices using undoped BTO nanodielectrics (≈14.3 cd m−2 at 240 V, 1 kHz). Furthermore, a uniform brightness across the whole panel surface of the flexible ACEL devices and excellent device reliability are achieved via the use of uniform networks of crossaligned silver nanowires as highly conductive and flexible electrodes. The results offer experimental validation of high‐brightness flexible ACELs using solution‐processed BTO:La nanodielectrics, which constitutes an important milestone toward the implementation of high‐k nanodielectrics in flexible displays. All solution‐processed La‐doped barium titanate nanocuboids are synthesized as high‐k nanodielectrics for high performance flexible alternating‐current electroluminescent devices with lower operating voltage as well as higher brightness. In addition, a uniform brightness across the whole panel surface of flexible alternating‐current electroluminescent devices and an excellent device reliability are demonstrated via the use of highly conductive and transparent electrodes with a uniform network of crossaligned silver nanowires.
Electroluminescence (EL): the light emission under an applied electrical potential is one of key light emitting techniques been applied over a vast range of applications. Alternative Current Electroluminescent (ACEL) is one of major light emitting technique discussed under EL. Even though it possesses some intrinsic advantages over Light Emitting Diodes (LEDs) and Light Emitting Cell (LEC), it has not been thoroughly discussed like LEDs and most of the time has kept under the shadow of LED. On the other hand, flexible light emitting devices have become an emerging trend in the field as they are been widely applied in consumer electronics and wearable devices, where in ACEL technique can make a significant impact for its development. This review discusses the ACEL technique in detail covering different device architectures, materials and fabrication methods highlighting the use of electrospinning techniques. In the second part, the review will briefly summarize the research works in flexible light emitting field, covering both in optical and mechanical performances
Stretchable alternating-current electroluminescent (ACEL) devices are required due to their potential in wearable, biomedical, e-skin, robotic, lighting, and display applications; however, one of the main hurdles is achieving uniform electroluminesence, demanding an optimal combination of transparency, conductivity, and stretchability in electrodes. We therefore propose a fabrication scheme involving strategically combining two-dimensional graphene layers with a silver nanowires (Ag NWs) embedded PEDOT:PSS film. The developed hybrid electrode overcomes the limitations of commonly known metallic NWs and ionic conductor-based electrodes for ACEL applications. Furthermore, the potential of the hybrid electrode is realized in demonstrating large-area stretchable ACEL devices composed of an 8 × 8 passive array. The prototype ACEL passive array demonstrates efficient and uniform electroluminescence under high levels of mechanical deformation such as bending, rolling, twisting, and stretching.
Electromagnetic (EM) wave emissions from wearable or flexible smart display devices can cause product malfunction and have a detrimental effect on human health. Therefore, EM shielding strategies are becoming increasingly necessary. Consequently, herein, we prepared a transparent acrylic polymer-coated/reduced graphene oxide/silver nanowire (Ag NW) (A/RGO/SAW) EM interference (EMI) shielding film via liquid-to-vapor pressure-assisted wet sintering. The film exhibited enhanced Ag NW network formation and antireflection (AR) effects. The wet-sintered Ag NW shielding film had a threshold radius of curvature (ROC) of 0.31 mm at a film thickness of 100 μm, demonstrating its high flexibility, while the conventional indium tin oxide (ITO) shielding film had a threshold ROC of ~5 mm. The EMI shielding effectiveness (SE) of the A/RGO/SAW multilayer film was approximately twice that of the ITO film at a similar relative transmittance (84%–85%). The optical relative reflectance of the Ag NW layer was reduced due to the AR effect, and the visible light transmittance was considerably improved owing to the different refractive indices in the multilayer shielding film. Because the acrylic coating layer had a high contact angle, the multilayer film exhibited high temperature and humidity durability with little change in the SE over 500 h at 85 °C and 85% relative humidity. The multilayer film comprising wet-sintered Ag NW exhibited high flexibility and humidity durability, high shielding performance (more than 24 dB at a relative transmittance of 85% or more), and high mass productivity, making it highly applicable for use as a transparent shielding material for future flexible devices.
A bio-inspired conductive binary-network of vein–silver nanowires (AgNWs) was embedded in poly(dimethylsiloxane) (PDMS) to prepare a semi-transparent stretchable conductor (vein–AgNWs–PDMS) by a simple dipping process. The special conductive structure was constructed by using veins with a porous structure as an ideal skeleton to load AgNW networks, which allowed the vein–AgNWs–PDMS composite to show a low sheet resistance of 1 Ω sq⁻¹ with 74% transmittance. The figure of merit of vein–AgNWs–PDMS is as high as 2502 and can be adjusted easily by controlling the times of the dipping cycle. Furthermore, the vein–AgNWs–PDMS conductor can retain high conductivity after 150% mechanical elongation and exhibit excellent electromechanical stability in repeated stretch/release tests with 60% strain (500 cycles). As an example of an application, patterned light-emitting diode (LED) arrays using the vein–AgNWs–PDMS conductors have been fabricated, and worked well under deformation. Moreover, the photo-thermal properties of the vein–AgNWs–PDMS composite have been demonstrated by a position heating experiment using near-infrared (NIR) laser irradiation and the generated heat can be effectively dissipated through the vein network to avoid local overheating. Due to the high-performance and facile fabrication process, the vein–AgNWs–PDMS conductors will have multifunctional applications in stretchable electronic devices.
A screen-printed electroluminescent display with different sensing capabilities is presented. The sensing principle is based on the direct relationship between the light intensity of the lamp and the conductivity of the external layers. The proposed device is able to detect the ionic concentration of any conductive species. Using both top and bottom emission architectures, for the first time, a humidity sensor based on electroluminescent display functionalized by graphene oxide nanocomposite is introduced. In this regard, just by coupling the display to a smartphone camera sensor, its potential was expanded for automatically monitoring human respiration in real time. Besides, the research includes a responsive display in which the light is spatially turned on in response to pencil drawing or any other conductive media. The above-mentioned features together with the easiness of manufacturing and cost-effectiveness of this electroluminescent display can open up great opportunities to exploit it in sensing applications and point of care diagnosis.
The present review focuses on the preparations, properties and applications of graphene materials in a few selected functional devices. We have summarized the mechanical exfoliation method, liquid phase stripping, oxidation-reduction method and chemical vapor deposition for the growth of graphene. Several factors such as the substrate, the temperature and reducing agents that influence the properties of graphene are also discussed. In addition, selected applications of graphene, including graphene bulbs, graphene superconductors, graphene chips, rapid heating of graphene, drug carriers, hydrogen storage materials, and graphene battery are surveyed.
The efficiency of CO2 reduction into hydrocarbons is far too low for commercial applications. This is due to the large
limiting potential (UL) required for the protonation of CO*, which is considered the rate limiting step (RLS) that occurs
after the formation of CO on the electrode surface. Statistical analysis of CO adsorption on different adsorption sites,
surfaces, and monolayer (ML) coverages for FCC transition metals (Cu, Ni, Pd, and Pt) displays a fundamental variation
in the surface properties of different metal-CO complexes and within different adsorption sites for the same metal surface.
DFT computations were utilized to predict surface properties and to visualize charge transfer between the CO molecule
and the surface atoms. Investigations of the adsorption mechanisms of CO, from molecular orbital principles, can help in
revealing the reasons behind the different properties exhibited upon adsorption and thus a design principle for an optimized
electro-catalytic surface can be established to reach higher efficiencies and a better product selectivity.
Wearable electronics is expected to be one of the most active research areas in the next decade, therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, light-weight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), sulfur dioxide (SO2), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.
Conductive or semiconducting nanomaterials-based applications such as electronics and sensors often require direct placement of such nanomaterials on insulating surfaces. Most fluidic-based directed assembly techniques on insulating surfaces are diffusion limited and slow. Electrophoretic-based assembly, on the other hand, is fast but can only be utilized for assembly on a conductive surface. Here, we present a new directed assembly technique that enables rapid assembly of nanomaterials on insulating surfaces. The approach leverages and combines fluidic and electrophoretic assembly by applying the electric field through an insulating surface via a conductive film underneath. The new approach (called electro-fluidic) yields an assembly process that is two-orders of magnitude faster compared to fluidic assembly. By understanding the forces on the assembly process, we have demonstrated the controlled assembly of various types of nanomaterials that are conducting, semiconducting and insulating including nanoparticles and single-walled carbon nanotubes (SWCNT) on insulating rigid and flexible substrates. The presented approach showed a great promise for making practical devices in miniaturized sensors and flexible electronics.
Metal nanowires have become the most promising candidates for the next generation of flexible transparent conductive electrodes (FTCEs) with high transmittance and low sheet resistance. In this work, ultra-long silver nanowires (Ag NWs) with ~220 μm (even larger than 400 μm) in length and ~55 nm in diameter (aspect ratio: ~4000) were synthesized via a one-pot polyol process using high molecular weight poly(vinylpyrrolidone) (Mw=1,300,000) and appropriate concentration of FeCl3 (12.5 µM) through hydrothermal reaction. The prepared Ag NWs were purified by a filter cloth (pore size: about 30 x 50 μm2) to remove the Ag nanoparticles (Ag NPs) and short-length Ag NWs. The FTCE based on the ultra-long Ag NWs without any post-treatments exhibits low sheet resistance of 155.0 Ω sq−1 and transmittance of 97.70% at 550 nm. The outstanding performance of FTECs demonstrated that the ultra-long Ag NWs are ideal materials for the applications in flexible transparent optical devices.
Heteroatom doping can open the bandgap and increase the carrier density, thus extending the applications of graphene. Iron chloride (FeCl3) intercalation has proven to be an efficient method for the heavy doping of graphene. In this study, we prepared continuous chemical vapor deposited graphene (CVD-G) consisting of hexagonal adlayer domains to study the FeCl3 intercalation. The structure of the FeCl3-treated CVD-G was easily characterized via atomic force microscopy because of the change in the interlayer distance. FeCl3 crystals several nanometers thick were integrated with the graphene surface, and FeCl3 layer flakes were intercalated between the CVD-G adlayers. The G-band position and two-dimensional band shape in the Raman spectra confirmed the intercalation of the FeCl3 between the graphene layers. The FeCl3 intercalation increased the electrical conductivity of the CVD-G with a well-maintained transmittance, which could be beneficial for a sensitive photodetector. [Figure not available: see fulltext.] © 2017 Tsinghua University Press and Springer-Verlag GmbH Germany
Graphene-based photodetectors have demonstrated mechanical flexibility, large operating bandwidth, and broadband spectral response. However, their linear dynamic range (LDR) is limited by graphene’s intrinsic hot-carrier dynamics, which causes deviation from a linear photoresponse at low incident powers. At the same time, multiplication of hot carriers causes the photoactive region to be smeared over distances of a few micrometers, limiting the use of graphene in high-resolution applications. We present a novel method for engineering photoactive junctions in FeCl3-intercalated graphene using laser irradiation. Photocurrent measured at these planar junctions shows an extraordinary linear response with an LDR value at least 4500 times larger than that of other graphene devices (44 dB) while maintaining high stability against environmental contamination without the need for encapsulation. The observed photoresponse is purely photovoltaic, demonstrating complete quenching of hot-carrier effects. These results pave the way toward the design of ultrathin photodetectors with unprecedented LDR for high-definition imaging and sensing.
Nanomechanical characteristics of standalone silver nanowires (Ag NWs) are a key issue for providing a failure criterion of advanced flexible electrodes that are trending towards smaller radius of curvatures (ROCs). Through in-situ tensile and buckling tests of pentagonal Ag NWs, we demonstrated that the intrinsic fracture strain provides a significant criterion to predict the mechanical and electrical failure of Ag NW electrodes under various strain modes, because the decrease in fracture strain limits figure of merit of flexible devices. The Ag NW electrodes on a polymer substrate exhibited a strain-dependent electrical failure owing to the unique deformation characteristics with a size-dependent brittle-to-ductile transition of the five-fold twinned Ag NWs. All the Ag NWs greater than approximately 40 nm in diameter exhibited brittle fracture with a size-independent stress-strain response under tensile and buckling modes, which leads to the electrical failure of flexible electrodes at the almost same threshold ROC. Meanwhile, the higher ductility of Ag NWs less than 40 nm in diameter resulted in much smaller threshold ROCs of the electrodes due to the highly extended fracture strains, which can afford a high degree of freedom for highly flexible devices.
In this work, the fabrication and performance of flexible alternating current electroluminescent (AC-EL) devices for ammonia (NH3) detection at room temperature are presented for the first time. The AC-EL gas sensor was fabricated by the screen-printing of a ZnS:Cu,Cl phosphor and PEDOT:PSS sensing layers. The effects of parameters including applied voltage, excitation frequency and waveform on light emission and luminance intensity of the AC-EL gas sensor were systematically investigated. From gas-sensing characterization, the AC-EL gas sensor exhibited very high selectivity and a linear response to NH3 in the concentration range of 100–1000 ppm at room temperature. A sensing mechanism of the EL gas sensor was proposed based on the resistance change of the PEDOT:PSS sensing layer via a charge-transfer process.
The efficiency of flexible photovoltaic and organic light emitting devices is heavily dependent on the availability of flexible and transparent conductors with at least a similar workfunction to that of Indium Tin Oxide. Here we present the first study of the work function of large area (up to 9 cm2) FeCl3 intercalated graphene grown by chemical vapour deposition on Nickel, and demonstrate values as large as 5.1 eV. Upon intercalation, a charge density per graphene layer of 5 ⋅ 1013 ± 5 ⋅ 1012 cm−2 is attained, making this material an attractive platform for the study of plasmonic excitations in the infrared wavelength spectrum of interest to the telecommunication industry. Finally, we demonstrate the potential of this material for flexible electronics in a transparent circuit on a polyethylene naphthalate substrate.
The current standard material used for transparent electrodes in displays, touch screens and solar cells is indium tin oxide (ITO) which has low sheet resistance (10 Ω/□), high optical transmission in the visible wavelength (85%) and does not suffer of optical haze. However, ITO is mechanically rigid and incompatible with future demands for flexible applications. Graphene materials share many of the properties desirable for flexible transparent conductors, including high optical transparency, high mechanical flexibility and strength. Whilst pristine graphene is not a good transparent conductor, functionalised graphene is at least 1000 times a better conductor than its pristine counterpart and it outperforms ITO. Here the authors review recent work on a novel graphene-based conductor with sheet resistance as low as 8.8 Ω/□ and 84% optical transmission. This material is obtained by ferric chloride (FeCl3) intercalation into few-layer-graphene (FLG), giving rise to a new system which is the best known flexible and transparent electricity conductor. FeCl3-FLG shows no significant changes in the electrical and structural properties for a long exposure to air, to high levels of humidity and at temperatures of up to 150°C in atmosphere. These properties position FeCl3-FLG as a viable and attractive replacement to ITO.
The growth of graphene using resistive-heating cold-wall chemical vapor deposition (CVD) is demonstrated. This technique is 100 times faster and 99% lower cost than standard CVD. A study of Raman spectroscopy, atomic force microscopy, scanning electron micro-scopy, and electrical magneto-transport measurements shows that cold-wall CVD graphene is of comparable quality to natural graphene. Finally, the first transparent flexible graphene capacitive touch-sensor is demonstrated.
© 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn.
We present the first systematic study of the stability of the structure and electrical properties of FeCl3 intercalated few-layer graphene to high levels of humidity and high temperature. Complementary experimental techniques such as electrical transport, high resolution transmission electron microscopy and Raman spectroscopy conclusively demonstrate the unforseen stability of this transparent conductor to a relative humidity up to 100% at room temperature for 25 days, to a temperature up to 150°C in atmosphere and to a temperature as high as 620°C in vacuum, that is more than twice higher than the temperature at which the intercalation is conducted. The stability of FeCl3 intercalated few-layer graphene together with its unique values of low square resistance and high optical transparency, makes this material an attractive transparent conductor in future flexible electronic applications.
The development of future flexible and transparent electronics relies on
novel materials, which are mechanically flexible, lightweight and
low-cost, in addition to being electrically conductive and optically
transparent. Currently, tin doped indium oxide (ITO) is the most wide
spread transparent conductor in consumer electronics. The mechanical
rigidity of this material limits its use for future flexible electronic
applications. We report novel graphene-based transparent conductors
obtained by intercalating few-layer graphene (FLG) with ferric chloride
(FeCl3). Through a combined study of electrical transport and optical
transmission measurements we demonstrate that FeCl3 enhances the
electrical conductivity of FLG by two orders of magnitude while leaving
these materials highly transparent [1]. We find that the optical
transmittance in the visible range of FeCl3-FLG is typically between 88%
and 84%, whereas the resistivity is as low as 8.8 φ. These
parameters outperform the best values found in ITO (i.e. resistivity of
10 φ at an optical transmittance of 85%), making therefore
FeCl3-FLG the best candidate for flexible and transparent electronics.
[4pt] [1] I. Khrapach, F. Withers, T. H. Bointon, D. K. Pplyushkin, W.
L. Barnes, S. Russo, M. F. Craciun, Adv. Mater. 24, 2844 (2012).
We reveal the effect of UV–ozone treatment on the electrical properties of poly (styrenesulfonate) doped poly (3,4-ethylenedioxythiophene) (PEDOT:PSS) film by clarifying the respective roles of UV light irradiation and exposure to ozone gas. The UV–ozone treatment induced increases in both work function and resistivity. Furthermore, the film thickness was reduced at a rate of 0.13nm/min. The ozone-exposed films also exhibited a marked increase in the work function. However, such variations were not observed in the resistivity and film etching. Angle resolved X-ray photoelectron spectroscopy revealed that the main role of the UV light was to decompose the chemical bonds in the PEDOT:PSS film, resulting in a resistivity increase and film etching. In contrast, the ozone and atomic oxygen were absorbed and oxidized the surface, which was responsible for the increase in the work function. Due to these different functions, UV–ozone treatment is capable of controlling the work function and resistivity of PEDOT:PSS film thus allowing them be adjusted to the device application.
Silver nanowire transparent electrodes have received much attention as a replacement for indium tin oxide, particularly in organic solar cells. In this paper, we show that when silver nanowire electrodes conduct current at levels encountered in organic solar cells, the electrodes can fail in as little as 2 days. Electrode failure is caused by Joule heating which causes the nanowires to breakup and thus create an electrical discontinuity in the nanowire film. More heat is created, and thus failure occurs sooner, in more resistive electrodes and at higher current densities. Suggestions to improve the stability of silver nanowire electrodes are given.
Future wearable electronics, displays and photovoltaic devices rely on highly
conductive, transparent and yet mechanically flexible materials. Nowadays
indium tin oxide (ITO) is the most wide spread transparent conductor in
optoelectronic applications, however the mechanical rigidity of this material
limits its use for future flexible devices. Here we report novel transparent
conductors based on few layer graphene (FLG) intercalated with ferric chloride
(FeCl3) with an outstandingly high electrical conductivity and optical
transparency. We show that upon intercalation a record low sheet resistance of
8.8 Ohm/square is attained together with an optical transmittance higher than
84% in the visible range. These parameters outperform the best values of ITO
and of other carbon-based materials, making these novel transparent conductors
the best candidates for future flexible optoelectronics.
Graphene has attracted great attentions since its first discovery in 2004. Various approaches have been proposed to control its physical and electronic properties. Here, we report that graphene based intercalation compounds is an efficient method to modify the electronic properties of few layer graphene (FLG). FeCl3 intercalated FLG were successfully prepared by two-zone vapor transport method. This is the first report on full intercalation for graphene samples. The features of the Raman G peak of such few-layer graphene intercalation compounds (FLGIC) are in good agreement with their full intercalation structures. The FLGIC presents single Lorentzian 2D peak, similar to that of single layer graphene, indicating the loss of electronic coupling between adjacent graphene layers. First principle calculations further reveal that the band structure of FLGIC is similar to single layer graphene but with strong doping effect due to the charge transfer from graphene to FeCl3. The successful fabrication of FLGIC opens a new way to modify properties of FLG for fundamental studies and future applications. Comment: 19 pages, 6 figures, accepted by Advanced Functional Materials
At present, thick film (powder based) alternating current electroluminescence (AC-EL) is the only technology available for the fabrication of large area, laterally structured and coloured light sources by simple printing techniques. Substrates for printing may be based on flexible polymers or glass, so the final devices can take up a huge variety of shapes. After an introduction of the underlying physics and chemistry, the review highlights the technical progress behind this development, concentrating on luminescent and dielectric materials used. Limitations of the available materials as well as room for further improvement are also discussed.
Alternating current thick film light emitters has been prepared by using ZnS:Cu commercial phosphors and thick film technology. The dependence of electroluminescent emission on excitation frequency and voltage applied to light emission devices was studied. Electro-luminescent spectra were decomposed into four Gaussians corresponding to emission transitions and their respective peak position wave-lengths and amplitudes were analyzed as a function of the applied voltage frequency. The time constants associated to every of those centres have been calculated by determining the extinction times of the related light emission. A straight relationship between electro-luminescence extinction time and frequency response for each emission wavelength has been found.
It is shown that the infra-red emission of zinc sulphide phosphors is dependent upon the copper concentration. Infra-red emission occurs after simultaneous excitation by ultra-violet and infra-red in phosphors containing less than 5 × 10-4 g atoms Cu per mole ZnS. For greater concentrations of copper infra-red emission does not occur but such phosphors are electroluminescent.
Characteristic emissions at 575, 615 and 665 nm have been observed in a three-electrode electrochemical cell under anodic polarization for Sm3+ ions inserted into a semiconducting zinc oxide electrode. The electroluminescence intensity varies with the square-root of the reciprocal of the applied potential according to the Alfrey–Taylor equation. The intensity of the light emitted increases with dopant concentration and reaches a maximum for ca. 0.5 atom% of Sm3+ in ZnO; above this concentration the light intensity decreases. Structural analysis of a polycrystalline sample by scanning electron microscopy indicates that the inserted rare-earth ions induce important dislocations in the polycrystalline structure and do not substitute for zinc in the crystal lattice.
We investigate the optoelectronic properties of novel graphene/FeCl3-intercalated few-layer graphene (FeCl3-FLG, dubbed graphexeter) heterostructures using photovoltage spectroscopy. We observe a prominent photovoltage signal generated at the graphene/FeCl3-FLG and graphene/Au interfaces, whereas the photovoltage at the FeCl3-FLG/Au interface is negligible. The sign of the photovoltage changes upon sweeping the chemical potential of the pristine graphene through the charge neutrality point, and we show that this is due to the photothermoelectric effect. Our results are a first step toward all-graphene-based photodetectors and photovoltaics.
An apparatus for the measurement of electroluminescence in single crystals of zinc sulphide under a range of conditions is described. The results of the measurements are compared with existing theories, which are shown to be unsatisfactory. Modified forms of these theories are developed which are in much better agreement with experiment.
By tensile testing the mechanical properties of thin films of the intrinsically conductive poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) under different relative humidities are investigated. It can be shown that the fracture behaviour strongly depends on humidity and reaches from brittle to plastic. The fracture surfaces are first investigated by scanning electron microscopy (SEM). The surfaces change from smooth at 23% rH to rough with shear lips for samples tested at 55% rH. Atomic force microscopy then reveals the topography of fracture surfaces at the nanometer scale and thus gives insights into the morphology of PEDOT:PSS thin films. By combining the experimental findings of the tensile tests and the AFM scans a micromechanical model for the deformation behavior of PEDOT:PSS can then be derived.
The present study is focused on the spectroscopic properties of ac powder electroluminescent lamps, in which the electroluminescent materials are based on ZnS-Cu, in order to understand the mechanisms of the electroluminescence and improve their performances. To this purpose ad hoc sets of devices have been built and their performances have been evaluated by comparing spectroscopic measurements performed by changing alternatively the applied frequency and the voltage. The emission wavelength of these devices (i.e. the color of the lamps) is found to be strictly related to the applied frequency, while the voltage mainly determines the intensity of the emission. (C) 2002 Elsevier Science B.V. All rights reserved.
A novel wet-chemical precipitation method is optimized for the synthesis of ZnS nanocrystals doped with Cu+ and halogen. The nanoparticles were stabilized by capping with polyvinyl pyrrolidone (PVP). XRD studies show the phase singularity of ZnS particles having zinc-blende (cubic) structure. TEM as well as XRD line broadening indicate that the average crystallite size of undoped samples is ∼2 nm. The effects of change in stoichiometry and doping with Cu+ and halogen on the photoluminescence properties of ZnS nanophosphors have been investigated. Sulfur vacancy (VS) related emission with peak maximum at 434 nm has been dominant in undoped ZnS nanoparticles. Unlike in the case of microcrystalline ZnS phosphor, incorporation of halogens in nanoparticles did not result VZn related self-activated emission. However, emission characteristics of nanophosphors have been changed with Cu+ activation due to energy transfer from vacancy centers to dopant centers. The use of halogen as co-activator helps to increase the solubility of Cu+ ions in ZnS lattice and also enhances the donor–acceptor type emission efficiency. With increase in Cu+ doping, Cu-Blue centers (CuZn−Cui+), which were dominant at low Cu+ concentrations, has been transformed into Cu-Green (CuZn−) centers and the later is found to be situated near the surface regions of nanoparticles. From these studies we have shown that, by controlling the defect chemistry and suitable doping, photoluminescence emission tunability over a wide wavelength range, i.e., from 434 to 514 nm, can be achieved in ZnS nanophosphors.
Polymer and organic solar cells degrade during illumination and in the dark. This is in contrast to photovoltaics based on inorganic semiconductors such as silicon. Long operational lifetimes of solar cell devices are required in real-life application and the understanding and alleviation of the degradation phenomena are a prerequisite for successful application of this new and promising technology. In this review, the current understanding of stability/degradation in organic and polymer solar cell devices is presented and the methods for studying and elucidating degradation are discussed. Methods for enhancing the stability through the choice of better active materials, encapsulation, application of getter materials and UV-filters are also discussed.
Experimental studies of the tensile behavior of metallic nanowires show a wide range of failure modes, ranging from ductile necking to brittle/localized shear failure-often in the same diameter wires. We performed large-scale molecular dynamics simulations of copper nanowires with a range of nanowire lengths and provide unequivocal evidence for a transition in nanowire failure mode with change in nanowire length. Short nanowires fail via a ductile mode with serrated stress-strain curves, while long wires exhibit extreme shear localization and abrupt failure. We developed a simple model for predicting the critical nanowire length for this failure mode transition and showed that it is in excellent agreement with both the simulation results and the extant experimental data. The present results provide a new paradigm for the design of nanoscale mechanical systems that demarcates graceful and catastrophic failure.
Instantaneous electrical breakdown measurements of GaN and Ag nanowires are performed by an in situ transmission electron microscopy method. Our results directly reveal the mechanism that typical thermally heated semiconductor nanowires break at the midpoint, while metallic nanowires breakdown near the two ends due to the stress induced by electromigration. The different breakdown mechanisms for the nanowires are caused by the different thermal and electrical properties of the materials.
For the first time, large-area CVD-grown graphene films transferred onto flexible PET substrates were used as transparent conductive electrodes in alternating current electroluminescence (ACEL) devices. The flexible ACEL device based on a single-layer graphene electrode has a turn-on voltage of 80 V; at 480 V (16 kHz), the luminance and luminous efficiency are 1140 cd/m(2) and 5.0 lm/W, respectively. The turn-on voltage increases and the luminance decreases with increasing stacked layers of graphene, which means the single-layer graphene is the best optimal choice as the transparent conductive electrode. Furthermore, it demonstrates that the graphene-based ACEL device is highly flexible and can work very well even under a very large strain of 5.4%, suggesting great potential applications in flexible optoelectronics.
Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications.
We report a comprehensive study of transparent and conductive silver nanowire (Ag NW) electrodes, including a scalable fabrication process, morphologies, and optical, mechanical adhesion, and flexibility properties, and various routes to improve the performance. We utilized a synthesis specifically designed for long and thin wires for improved performance in terms of sheet resistance and optical transmittance. Twenty Omega/sq and approximately 80% specular transmittance, and 8 ohms/sq and 80% diffusive transmittance in the visible range are achieved, which fall in the same range as the best indium tin oxide (ITO) samples on plastic substrates for flexible electronics and solar cells. The Ag NW electrodes show optical transparencies superior to ITO for near-infrared wavelengths (2-fold higher transmission). Owing to light scattering effects, the Ag NW network has the largest difference between diffusive transmittance and specular transmittance when compared with ITO and carbon nanotube electrodes, a property which could greatly enhance solar cell performance. A mechanical study shows that Ag NW electrodes on flexible substrates show excellent robustness when subjected to bending. We also study the electrical conductance of Ag nanowires and their junctions and report a facile electrochemical method for a Au coating to reduce the wire-to-wire junction resistance for better overall film conductance. Simple mechanical pressing was also found to increase the NW film conductance due to the reduction of junction resistance. The overall properties of transparent Ag NW electrodes meet the requirements of transparent electrodes for many applications and could be an immediate ITO replacement for flexible electronics and solar cells.
From published transmittance and sheet resistance data, we have calculated a figure of merit for transparent, conducting graphene films; the DC to optical conductivity ratio, sigma(DC)/sigma(Op). For most reported results, this conductivity ratio clusters around the values sigma(DC)/sigma(Op) = 0.7, 4.5, and 11. We show that these represent fundamental limiting values for networks of graphene flakes, undoped graphene stacks, and graphite films, respectively. The limiting value for graphene flake networks is much too low for transparent-electrode applications. For graphite, a conductivity ratio of 11 gives R(s) = 377Omega/ for T = 90%, far short of the 10 Omega/ minimum requirement for transparent conductors in current driven applications. However, we suggest that substrate-induced doping can potentially increase the 2-dimensional DC conductivity enough to make graphene a viable transparent conductor. We show that four randomly stacked graphene layers can display T approximately 90% and 10 Omega/ if the product of carrier density and mobility reaches nmu = 1.3 x 10(17) V(-1) s(-1). Given achieved doping values and attainable mobilities, this is just possible, resulting in potential values of sigma(DC)/sigma(Op) of up to 330. This is high enough for any transparent conductor application.
The application of transparent single-walled carbon nanotube (SWCNT) electrodes in rigid and flexible alternating current electroluminescence (ACEL) devices is demonstrated. SWCNT thin-film electrodes (50-160 nm) were made using a spray-coating process suitable for adjusting the transparency and sheet resistance. The dispersing procedure was optimized by comparing the transparency to sheet resistance ratio (T/R) of the electrodes. The emission intensity was as high as that for indium-tin oxide (ITO)-based ACEL devices with transparencies comparable to those of ITO-coated polymer slides.
Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.
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Organic Solar Cells: Fundamentals, Devices and Upscaling
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Failure: Long = Brittle and Short = Ductile
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