rGO Film Research Articles

Solution-processable (Pc′)Eu(Pc′)Eu[TP(OH)PP]/rGO bilayer heterojunction organic transistors with exceptional excellent ambipolar performance

For the purpose of fabricating next generation of microelectronics and photonics, the transistor that simultaneously provides high-efficiency charge transport and air-stable ambipolar performance becomes highly desired. In this paper, the bilayer heterojunction field-effect transistors, named as t-Pc-1/rGO (HFET-1) and t-Pc-2/rGO (HFET-2), are constructed for the first time by using a simple two-step solution-processing approach, in which the high conductive reduced graphene oxide (rGO) film as the sub-layer and the film of ambipolar sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-deckers (Pc′)Eu(Pc′)Eu[TP(OH)PP] {Pc′ = Pc, [Pc(OPh)8]} (t-Pc-1, t-Pc-2) as the top layer, respectively. The resulting bilayer heterojunction devices exhibit significantly improved air-stable ambipolar performance with the carrier mobilities of ca. 107 to 108 fold higher than those of pristine triple-deckers, and the Ion/Ioff of 102 to 103 fold higher than that of the single-component rGO device. In particular, due to the heterojunction effect in an “accumulation mode”, the device HFET-2 shows the ultrahigh and balanced mobilities between hole, 30.9 cm2 V−1 s−1, and electron, 39.6 cm2 V−1 s−1, with the optimized ON/OFF ratio of 103 for both carriers, representing the best result for ambipolar OFET devices reported thus far.

Facile preparation of binder–free electrode for electrochemical capacitors based on reduced graphene oxide composite film

Binder-free electrode based on reduced graphene oxide (rGO) is attracting attention for electrochemical capacitors. Here the binder-free electrodes have been fabricated by activating the composite films of GO and carbonized cornstalk-cores. In the composites, the rGO sheets are found to be tightly adhered to the activated bio‑carbon which is intercalated between the rGO sheets to prevent them from stacking. Moreover, the influences of the mass ratios of GO to bio‑carbon on the electrochemical performance have been systematically investigated. The optimal binder-free electrode (rGO/ACCS1/1) prepared from the composite films with 1:1 mass ratio of GO to bio‑carbon exhibits a specific capacitance as high as 278Fg−1 at scan rate of 1mVs−1 and shows excellent stability in 6M KOH electrolyte. Furthermore, the optimal electrode can retain 47.8% of the initial specific capacitance even at current density of 100Ag−1, indicating a fast charge-discharge capability. This work provides a simple method to prepare binder-free composite electrodes by introducing renewable and inexpensive biomass based carbon into activated rGO films.

Engineering the volumetric effect of Polypyrrole for auto-deformable supercapacitor

Polypyrrole (PPy) is one of the most extensively studied conducting polymers and it has promising application prospects in supercapacitors. However, PPy-based supercapacitors generally suffer from poor cycling stability due to the volumetric effect induced by ion doping/de-doping during the redox reactions. Therefore, the volumetric effect has usually been considered deleterious for supercapacitor applications. Herein, we demonstrate that the volumetric effect of PPy can be collected by synergy of flexible electrodes and solid-sate electrolytes. Furthermore, the accumulative volumetric effect is utilized in auto-deformable supercapacitors for the first time. The as-designed supercapacitor consists of flexible electrodes (PPy film, reduced graphene oxide (rGO) film) and a polyvinyl alcohol (PVA) gel electrolyte. When the redox reaction starts, the volumetric change of the PPy film induced by Na+ ion insertion is captured by the PVA gel electrolyte, resulting in mechanical deformation of the supercapacitor. As the accumulative volumetric effect drives greater deformation of the device, more electrochemically active sites are generated in the PPy film, leading to a higher energy storage capacity of the supercapacitor. Specifically, a certain correlation exists between the deformation degree and the energy storage capacity. As the deformation degree approaches 100% from 0%, the discharge capacity increases to 359 mF/cm3 from 101 mF/cm3. This auto-deformation characteristic endows the supercapacitor with subjective initiative, which establishes an important foundation for a smart energy storage device.

Thermally Conductive Reduced Graphene Oxide Thin Films for Extreme Temperature Sensors

AbstractReduced graphene oxide (RGO) films are promising in applications ranging from electronics to flexible sensors. Though high electrical and thermal conductivities have been reported for RGO films, existing thermal conductivity data for RGO films show large variations from 30 to 2600 W m−1 K−1. Further, there is a lack of data at low temperatures (<300 K), which is critical for the understanding of thermal transport mechanisms. In this work, a temperature‐dependent study of thermal (10–300 K) and electrical (10–3000 K) transport in annealed RGO films indicates the potential application of RGO films for sensing temperatures across an extremely wide range. The room‐temperature thermal conductivity increases significantly from 46.1 to 118.7 W m−1 K−1 with increasing annealing temperature from 1000 to 3000 K with a corresponding increase in the electrical conductivity from 5.2 to 1481.0 S cm−1. In addition, films reduced at 3000 K are promising for sensing extreme temperatures as demonstrated through the measured electrical resistivity from 10 to 3000 K. Sensors based on RGO films are advantageous over conventional temperature sensors due to the wide temperature range and flexibility. Thus, this material is useful in many applications including flexible electronics and thermal management systems.

Surfactant-free carbon black@graphene conductive ink for flexible electronics

The capabilities of conductive ink with both excellent conductivity and flexibility properties are extremely important for the construction of next-generation flexible electronic devices. However, the development of an appropriate ink possessing high conductivity and good dispersity remains a big challenge for ink-jet printing. Here, an original synthesis method of surfactant-free carbon black@graphene (CB@rGO) conductive ink is reported via freeze-drying process and reduction in p-phenylenediamine. The CB@rGO ink unambiguously displays a well-defined and smooth morphology, extremely the CB@rGO conductive particles showing good stability in many solvents. The CB@rGO film exhibited outstanding flexibility which is showed by the durable conductivity after bending 1000 times. Furthermore, it has an excellent conductivity of 714 ± 90 S m−1, and these data increased to 5091 ± 200 S m−1 after the high temperature post-processing increased by 198% compared to the traditional rGO film. Notably, the absence of surfactant in conductive fillers’ dispersing process contributed to the high conductivity of CB@rGO ink compared with the traditional ones.

Enhanced gas barrier property of stacking-controlled reduced graphene oxide films for encapsulation of polymer solar cells

Compact stacking of building blocks is essential in order to utilize the impermeable nature of reduced graphene oxide (rGO) for encapsulating barriers in organic electronics. To obtain the desired accumulation characteristic, rGO films were fabricated via spraying process using phase-controlled graphene oxide (GO) dispersion. The rGO laminate prepared from the isotropic-phase dispersion exhibits a more favorable face-on orientation of rGO building blocks than that from the nematic-phase GO, which implies effective stacking of building blocks. As a result, the resulting gas barrier performance of the low-temperature-annealed rGO film is superior to previously reported low-temperature solution-processed materials. Fabricated gas barriers are adopted to seal the polymer solar cell with 57.2 times longer lifetime than that of the unsealed device. A device covered by an optimized rGO/polyethylene naphthalate gas barrier maintains photovoltaic performance as high as 88% of the initial efficiency after 28 days.

The Effect of Swelling on Charge’s Transmission of Chitosan and Reduced Graphene Oxide Films Electrodes

Chitosan (CS) and reduced graphene oxide (rGO) films are suitable materials for matrix electrochemical devices. However, CS_rGO films show a swelling effect after water permeation yielding into electrochemical disturbs measurement and a challenge for the point-of-care of sensor uses. In order to optimize the transducional measures, further investigations were conducted to analyze the appropriate CS:rGO ratio obtained by CS acetic hydrogel and several contents (0.2%, 0.4%, 0.6%, 0.8% and 1%) of rGO (obtained by Hummer’s method and subsequently reduced thermally at 400º C). After sonication of 3 hrs to ensure a homogenous phase, dispersion was poured into dish plate and dried for 24hrs at 60º C. Subsequently, CS:rGO films were neutralized by 3 different solutions: (A) ethanol solution 80%, (B) ethanol 80%/sodium hydroxide 0,02M (50:50 v/v) and (C) sodium hydroxide 0,02M and left dried on room temperature. Neutralized and non-neutralized films were compared and analyzed at Electrochemical Impedance of Spectroscopy. The electrochemical impedance spectra were recorded using buffer acetate pH 6 and 0.1 M of sodium chloride. Potential used was open circuit potential (OCP), signal amplitude, 10mV, and frequency varying from 10kHz down to 10mHz. The OCP range was -0,1 to -0,18 V. The swelling degree level performed the wettability analysis. Chemical, structural and morphological surface’s alterations were analyzed at FTIR, XRD and FEG-SEM microscopy, respectively. CS_rGO films non-neutralized after wetted with buffer solution at pH 6, shows instability and a great impedance value even in higher rGO contents. The addition of rGO into CS polymer decreased the swelling degree and the neutralized method (B) seems to show the lowest swelling level (Table 1), turning films more stable after water contact, followed by an unchanged surface morphology, and a non- shrinkage aspect. Due to the high rGO hydrophobic portion for the samples contents at rGO 0.8% and at 1%, the nanocomposite agglomeration character related a low portion of coating area being in a real contact with electrolyte solution resulting in a high impedance value, even for low swelling results. The neutralizations methods might provide charge reorganization on films surface, as showed the bands of carboxylate ion, –COO-, important group of hydroxyls linkage,shifted from two strong bands at 1560 cm-1and 1410 cm-1 to 1543 cm-1and 1315 cm-1vibrations, detailed in Figure 1. The crystalline structure of CS_rGO films changed for an amorphous on after the rGO contents but kept unchanged after the neutralization methods, as described by diffratograms in Figure 2. The addition of rGO provides a lamellar disorder and after certain rGO proportion the films presented agglomerations and an increase in the porous sizes. After neutralizations, there was a pronounced of the porous size and was noticed a more sponge aspect of films. The porous and wrinkles formation may be analyzed by FEG-SEM analysis in Figure 3. Conductivity and capacitive measurements were analyzed for each rGO content and after neutralization treatments are described in Figure 4 and the Nyquist plots were obtained and described in Figure 5. The circuits fittings were described in Figure 6.There was a decreasing of resistance behavior as much as rGO increased and inversely, as low as the swelling level. The NaOH treatment neutralized the cationic films surface, controlled the water entrance and minimized the repulsion electrostatic allowing the charges to pass. The NaOH/EtOH treatment seems to result in non-uniform charges distribution on the films surface loading in unstable material for charges percolation. EtOH treatment presented the lowest swelling level due to water extraction of films but the hydroxyls groups linked to the surface may resulted in a hindrance of charges percolation on the surface and in the bulk of films. It was noted that for rGO 0.8% content or more, after all neutralization treatments promoted, resulted ina high resistance value due to the formation of hydrophobic portions agglomerated which may interfered the double layer formation. At high rGO contents, EIS spectra showed at lower frequencies an increasing of Randles circle diameter, indicating higher double layer impedance for sample of rGO 0.8%. The circuit fittings was R(RQ)([RW]Q)for all films except for NaOH/EtOH treatment whose circuits fitting was given by R(RQ)(RQ)([RW]Q).The physical interpretation may relate to a more porous and grooves formation. After the ethanol neutralization, the films aspect was similar to a veil whereas chitosan seems to overlaps the rGO. Thus, the CS_rGO films neutralized with NaOH assures more stability to films until the rGO 0.6%. Figure 1

(Invited) Assembly of Electrochemically Reduced Graphene Oxide, at the Nano and Microscales, for the Preparation of Functional Coatings.

Graphene oxide (GO) presents the advantage of being easily dispersed in water, which facilitates the assembly of nano and microstructures by numerous methods, in order to form uniform and thickness-controlled functional coatings. For example, the electrophoretic deposition (EPD) is one of the most used techniques to produce anticorrosive coatings onto metals, including GO and reduced graphene oxide (rGO) coatings. We have used a variation of the EPD process of GO, which consisted in changing the GO’s charge to positive values allowing the electrophoretic deposition of GO onto the cathode (cEPD). The coating diminished by three times the corrosion rate of carbon steel. The preparation of these coatings also implies the understanding of the mechanism through which the electrochemical reduction of the GO is carried out.1 An electrochemical reduction mechanism of GO involving hydrogenation/hydrogenolysis reactions is suggested as the main reason to achieve an effective anticorrosive-coating by cEPD in comparison to the films produced by an anodic EPD. For this reason, we studied the electrochemical reduction of GO in aqueous and organic media containing H+ donor, to investigate the role of H+ in the reduction mechanism. In aqueous electrolyte, in both acid and basic pH, the H+ enhanced the removal of oxygenated groups by electrochemical reduction and promoted the loss of some sp2 domains due to hydrogenation reactions of the graphitic domains. The electrochemical reduction of GO in organic media, free of H+, resulted in the restoration, to some degree, of the sp2 domains. However, the removal of the oxygenated groups seemed hindered when compared to the same process in presence of H+ donor, in the organic solvent, at the same potential intervals. Considering that through these studies it is possible to choose a route for the preparation of functional films, recently we proceeded to modify electrochemically the rGO through with 5-membered alkyne chains. The resulting rGO film presented lower conductivity, due to the loss of graphitic domains, and an increased hydrophobicity. The modified rGO film was evaluated as an anticorrosive coating for carbon steel, showing a better protection from corrosion in comparison to the protection granted by the regular rGO film. [1] J.A. Quezada-Rentería, L.F. Chazaro-Ruiz, J.R. Rangel-Mendez, Synthesis of reduced graphene oxide (rGO) films onto carbon steel by cathodic electrophoretic deposition: Anticorrosive coating, Carbon 122 (2017) 266-275.

(Invited) Large Low Temperature Thermoelectric Power Factor from Nanostructured Carbon-Based Nanocoatings

In an effort to create a paintable/printable thermoelectric materials, comprised exclusively of organic components, polyaniline (PANi), graphene, and double-walled carbon nanotubes (DWNT) were alternately deposited from aqueous solutions using the layer-by-layer assembly technique. Graphene and DWNT are stabilized with an intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). A 1 µm thick film, composed of 80 PANi/graphene-PEDOT:PSS/PANi/DWNT-PEDOT:PSS quadlayers (QL) exhibits electrical conductivity (σ) of 1.88 X 105 S/m and a Seebeck coefficient (S) of 120 µV/K, producing a thermoelectric power factor (S 2∙σ) of 2710 µW/(m∙K2). This is the highest value ever reported for a completely organic material measured at room temperature. Furthermore, this performance matches or exceeds that of commercial bismuth telluride. Air-stable n-type organic thermoelectric nanocomposites were achieved by depositing layers of double-walled carbon nanotubes (DWNT), stabilized with polyethylenimine (PEI), and graphene oxide (GO) in a layer-by-layer fashion from aqueous solutions. A 30 bilayer film (~ 610 nm thick), comprised of this DWNT-PEI/GO sequence, exhibits electrical conductivity of 27.3 S/cm and Seebeck coefficient of -30 µV/K, producing a power factor of 2.5 µW/(m∙K2). Low temperature thermal reduction (150 °C for 30 min) of this composite thin film significantly improves its thermoelectric performance. An electrical conductivity of 460 S/cm and Seebeck coefficient of -93 µV/K are achieved. A 30 BL DWNT-PEI/reduced graphene oxide (rGO) film (~480 nm thick) exhibits a power factor as large as 400 µW/(m∙K2), which is one of the highest values reported for an organic n-type material. The combination of water-based processing, air stability and high power factor is a major step toward producing efficient thermoelectric devices on flexible substrates (e.g. textiles for clothing). For the first time, there is a real opportunity to harness waste heat from unconventional sources, such as body heat to power devices in an environmentally-benign way. Figure 1

Influence of protons on reduction degree and defect formation in electrochemically reduced graphene oxide

The electrochemical reduction of GO was investigated in aqueous, at both acid and basic pH, and organic media, to identify the possible role of protons (H+) in the reduction mechanism of this material. The obtained rGO films were characterized by FTIR, electrochemical methods, Raman and XPS spectroscopy. Data showed that the reduction was more efficient in acid and basic media due to the presence of protons and the capacity of water that works as a proton donor, resulting in C/O ratios of 3.8 and 7.8, respectively. Mostly hydroxyl, epoxide and carbonyl moieties were removed. In a proton-free organic electrolyte, a C/O ratio of 1.8 was obtained for most of the samples; nevertheless, the graphitic carbon sp2 domains were restored to a large extent in the absence of H+. The characterization of the material showed that the presence of protons, during the electrochemical reduction, caused hydrogenation reactions, which targeted the graphitic domains in rGO and resulted in the loss of sp2 hybridization. The presence of such defects modified the electrochemical properties of the rGO films, where, despite of exhibiting higher C/O ratio, the films reduced in aqueous electrolytes displayed lower electron transfer (e.g. ferrocyanide redox-probe) than those reduced in organic electrolyte.

Electrophoretic deposition of reduced graphene oxide thin films for reduction of cross-sectional heat diffusion in glass windows

Abstract Effective management of heat transfer, such as conduction and radiation, through glass windows is one of the most challenging issues in smart window technology. In this work, reduced Graphene Oxide (rGO) thin films of varying thicknesses are fabricated onto Fluorine-doped Tin Oxide (FTO) glass via electrophoretic deposition technique. The sample thicknesses increase with increasing number of deposition cycles (5, 10, 20 cycles). It is hypothesized that such rGO thin films, which are well-known for their high thermal conductivities, can conduct heat away laterally towards heat sinks and reduce near-infrared (NIR) transmittance through them, thus effectively slowing down the temperature increment indoors. The performance of rGO/FTO in reducing indoor temperatures is investigated with a solar simulator and a UV-Vis-NIR spectrophotometer. The 20-cycles rGO thin films showed 30% more NIR blocked at 1000 nm as compared to clean FTO, as well as the least temperature increment of 0.57 °C following 30 min of solar irradiation. Furthermore, the visible transmittance of the as-fabricated rGO films remain on par with commercial solar films, enabling up to 60% of visible light transmittance for optimal balance of transparency and heat reduction. These results suggest that the rGO thin films have great potential in blocking heat transfer and are highly recommended for smart window applications.

Dual Carbonaceous Materials Synergetic Protection Silicon as a High-Performance Free-Standing Anode for Lithium-Ion Battery.

Silicon is the one of the most promising anode material alternatives for next-generation lithium-ion batteries. However, the low electronic conductivity, unstable formation of solid electrolyte interphase, and the extremely high volume expansion (up to 300%) which results in pulverization of Si and rapid fading of its capacity have been identified as primary reasons for hindering its application. In this work, we put forward to introduce dual carbonaceous materials synergetic protection to overcome the drawbacks of the silicon anode. The silicon nanoparticle was coated by pyrolysed carbon, and meanwhile anchored on the surface of reduced graphene oxide, to form a self-standing film composite (C@Si/rGO). The C@Si/rGO film electrode displays high flexibility and an ordered porous structure, which could not only buffer the Si nanoparticle expansion during lithiation/delithiation processes, but also provides the channels for fast electron transfer and lithium ion transport. Therefore, the self-standing C@Si/rGO film electrode shows a high reversible capacity of 1002 mAh g−1 over 100 cycles and exhibits much better rate capability, validating it as a promising anode for constructing high performance lithium-ion batteries.

Band-like transport in high vacuum thermal reduced graphene oxide films

Measurements of electrical conductivity were carried out at temperatures ranging between 77 K and 450 K on high vacuum thermal reduced graphene oxide (rGO) films. The investigated samples were characterized in composition and structure before being analyzed in terms of electrical conduction. Their electrical conductivity was also measured in air at room temperature. Measurements have demonstrated that at first graphene oxide (GO) was not stable both in air and vacuum. It stabilized after having been subjected to 7 thermal cycles under high vacuum conditions, about 10−7 torr, up to a Tmax of 450 K. At room temperature the initial GO material had a very low conductivity, of the order of 10−10 Ω−1 x cm−1, which increased to about 2.5 Ω−1x cm−1 when it was thermal stabilized in rGO. The stabilization process, induced by the high vacuum heating procedure, seems due to a good reduction of GO, which gives rise to such expansion of the conjugated π-electron system that a band-like transport with small thermal activation energies (Ea = 10–50 meV) occurs. The performed electrical conductivity measurements are presented and discussed.

Dual synergistic immobilization effect on lithium polysulfides for lithium–sulfur batteries

Although lithium sulfur batteries (LSBs) possess extremely high specific capacity and ultrahigh energy density, the low conductivity and severe shuttle effect greatly restrict its practical application. Herein, we report a facile strategy to overcome the problems via a double-layer structure, in which one provides strong chemisorption by functionalized reduced graphene oxide (rGO) while the other confines polysulfides physically through coating a layer of rGO film on the electrode. The strategy not only alleviates the dissolution and diffusion of polysulfides but also inhibits polysulfides from penetrating into anode to some extent and enhances the electrical conductivity of electrode. The LSBs employing double-layer structure electrodes exhibit high initial capacity of 1353mAhg−1 at 0.1C and 78% capacity retention after 100cycles, good cycling stability with only 0.056% capacity decay per cycle at 1C, and remarkable rate capability with 92% reversible capacity retention. The current findings manifest that the double-layer structure can effectively improve the electrochemical performance via the dual synergistic effect of both chemical interaction and physical confinement.

Flexible supercapacitor electrode with high performance prepared from graphene oxide films assembled in the presence of p-phenylenediamine and urea

The flexible reduced graphene oxide (rGO) films are prepared by treating the graphene oxide (GO) films assembled in the presence of urea and p-phenylenediamine (PPD) with hydroiodic acid firstly and then heating at 165 °C. The addition of urea can overcome the aggregation of GO sheets induced by the PPD, and the formed microcrystallines of urea and PPD can act as the templates to regulate the structure of GO films during the drying process. Compared with the rGO films obtained from pure GO films, measurements based on the two-electrode system reveal that the capacitive performance of the films can be dramatically improved when the GO films are assembled in the presence of urea and PPD. The selected flexible film exhibits a specific capacitance of about 430 F g−1 in 1.0 mol L−1 H2SO4 electrolyte, and the cells fabricated by the films exhibit a maximum energy density of 8.96 Wh kg−1 at the power density of 100.42 W kg−1, and maximum power density of 1.70 kW kg−1 at the energy density of 7.92 Wh kg−1 based on the active materials, and can retain about 85% of its initial capacitance after 10,000 cycles. This novel strategy may be developed as a route to prepare flexible N-doped rGO electrode materials with high-performance.

“Click” Chemistry on Gold Electrodes Modified with Reduced Graphene Oxide by Electrophoretic Deposition

The coating of electrical interfaces with reduced graphene oxide (rGO) films and their subsequent chemical modification are essential steps in the fabrication of graphene-based sensing platforms. In this work, electrophoretic deposition (EPD) of graphene oxide at 2.5 V for 300 s followed by vapor treatment were employed to coat gold electrodes uniformly with rGO. These interfaces showed excellent electron transfer characteristics for redox mediators such as ferrocene methanol and potassium ferrocyanide. Functional groups were integrated onto the Au/rGO electrodes by the electro-reduction of an aryldiazonium salt, 4-((triisopropylsilyl)ethylenyl)benzenediazonium tetrafluoroborate (TIPS-Eth-ArN) in our case. Chemical deprotection of the triisopropylsilyl function resulted in propargyl-terminated Au/rGO electrodes to which azidomethylferrocene was chemically linked using the Cu(I) catalyzed “click” chemistry.

NO2 gas sensing performance enhancement based on reduced graphene oxide decorated V2O5 thin films

Here, we demonstrate improved NO2 gas sensing properties based on reduced graphene oxide (rGO) decorated V2O5 thin film. Excluding the DC sputtering grown V2O5 thin film, rGO was spread over V2O5 thin film by the drop cast method. The formation of several p–n heterojunctions was greatly affected by the current–voltage relation of the rGO-decorated V2O5 thin film due to the p-type and n-type nature of rGO and V2O5, respectively. Initially with rGO decoration on V2O5 thin film, current decreased in comparison to the pristine V2O5 thin film, whereas depositing rGO film on a glass substrate drastically increased current. Among all sensors, only the rGO-decorated V2O5 sensor revealed a maximum NO2 gas sensing response for 100 ppm at 150 °C, and it achieved an approximately 61% higher response than the V2O5 sensor. The elaborate mechanism for an extremely high sensing response is attributed to the formation and modulation of p–n heterojunctions at the interface of rGO and V2O5. In addition, the presence of active sites like oxygenous functional groups on the rGO surface enhanced the sensing response. On that account, sensors based on rGO-decorated V2O5 thin film are highly suitable for the purpose of NO2 gas sensing. They enable the timely detection of the gas, further protecting the ecosystem from its harmful effects.

Multidimensional graphene and ZnO-based heterostructure for flexible transparent ultraviolet photodetector

A multidimensional graphene and ZnO-based heterostructure for flexible transparent ultraviolet photodetector (UV-PD) applications is successfully fabricated on an indium tin oxide-coated polyethylene terephthalate substrate (ITO-coated PET). In this prototype, chemically reduced graphene oxide film is used as a charge transfer network and a template layer for the low-temperature growth of high quality vertically aligned zinc oxide nanorods array (ZNRA) on ITO-coated PET substrate. Graphene quantum dots decorated on the ZNRA significantly enhanced the photocurrent of the device. The synergistic effects of the rGO film and GQDs on the performance of the UV-PD are also systematically explored. The fabricated flexible UV-PD shows high detectivity (~1012 cmHz1/2 W−1), high responsivity (~13 AW−1) and good response time (~5 s) at a low bias of 2 V. Importantly, the fabrication process is facile, inexpensive, solution-based, low-temperature (120 °C), and provides a promising platform for flexible transparent UV-PD applications.

Improved DSSC photovoltaic performance using reduced graphene oxide–carbon nanotube/platinum assisted with customised triple-tail surfactant as counter electrode and zinc oxide nanowire/titanium dioxide nanoparticle bilayer nanocomposite as photoanode

In this work, reduced graphene oxide (rGO) was produced from graphene oxide (GO) by a reduction process, which utilised hydrazine hydrate as reducing agent. GO was initially synthesised by electrochemical exfoliation assisted with customised triple-tail sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-silphonate (TC14) surfactant. The produced TC184-rGO solution was subsequently hybridised with multiwalled carbon nanotubes (MWCNTs) from waste palm oil. The produced TC14-rGO and TC14-rGO/MWCNTs hybrid solution was fabricated as thin films by spray coating method. Afterwards, Pt nanoparticle (NP) coating was fabricated. The films were used as counter electrode (CE) for dye-sensitised solar cell (DSSC) application. Three other CEs, namely TC14-rGO, TC14-rGO/MWCNTs hybrid and TC14-rGO/Pt hybrid, were fabricated for comparison. Zinc oxide nanowire (NWR)/titanium dioxide nanoparticle (NP) bilayer was utilised as photoanode and fabricated via sol–gel immersion and squeegee method. Solar simulator measurement showed that the highest DSSC performance was exhibited by TC14-rGO/MWCNTs/Pt hybrid, which presented an energy conversion efficiency, open-circuit voltage, short-circuit-current density and fill factor of 0.0842%, 0.608 V, 0.285 mA/cm2 and 0.397, respectively. The combination of TC14-rGO/MWCNTs/Pt hybrid CE and ZnO NWR/TiO2 NP bilayer photoanode improved the DSSC performance due to the large surface area of TC14-rGO and MWCNTs, the high electrical conductivity of MWCNTs and the high quality and less agglomeration of thin rGO film assisted with triple-tail TC14 surfactant. The ZnO NWR/TiO2 NP bilayer photoanode also demonstrated a large surface area that can optimally adsorb dye molecules and increase the photo-exciton electrons, which further improve the DSSC performance.

Hand-in-Hand Reinforced rGO Film Used as an Auxiliary Functional Layer for High-Performance Li-S Batteries.

For lithium-sulfur (Li-S) batteries, a promising candidate for future high-energy storage devices, several prominent problems still need to be solved urgently, such as limited rate capability and poor cycle life caused by the insulating nature of sulfur and the shuttle of soluble polysulfides produced during battery operation. In this work, a facile vacuum filtration method is employed to graft polyethyleneimine to reduced graphene oxide (rGO) in a "hand-in-hand" way using the amino and catechol groups from polydopamine. The resulting polymer-reinforced rGO (PPG) film is applied as a free-standing auxiliary functional layer for Li-S batteries. It has been confirmed by both theoretical calculations and experimental methods that, benefiting from the rich amine groups and oxygen-containing functional groups, the as-prepared PPG composite film shows great ability to capture polysulfides. Moreover, its high conductivity enables itself to function as a polysulfide reservoir, thus facilitating the successive reutilization of the trapped active materials and improving sulfur utilization. For this reason, the PPG film can also be regarded as a cathode material, serving as a novel "SPPG cathode" together with the pure sulfur cathode. The cell assembled with the pure sulfur cathode and the PPG auxiliary functional layer displays high reversible capacity, excellent Coulombic efficiency, and good cycling stability, suggesting that the rational auxiliary functional layer design ensures a good match with pure sulfur cathodes and shows the potential to achieve energy-dense Li-S batteries.