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Electropulsing-induced phase decompositions and microstructural changes in AZO-5 thin films were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall effect measurement and photoluminescence (PL) measurement techniques. It was found that the electropulsing induced phase decomposition started with spinodal decomposition, which was accompanied by discontinuous precipitation in the AZO-5 thin films. Both circular phase decompositions and the crystal orientation occurred. Inappropriate electropulsing might damage zones, which resulted in tremendous decrease in electrical conductivity. Circular changes in both the peak position and the width of the PL wavelength were observed in the EPT AZO-5 thin films. Formation of zones favored reducing the roughness of the thin film.

Due to its abundance, high theoretical capacity, and environmental compatibility, manganese dioxide (MnO2) is regarded as a potential electrode material for sodium-ion batteries. Nevertheless, severe side reactions including manganese dissolution and the Mn3+ disproportionation reaction are common challenges to manganese-based electrodes that cause a huge capacity fading, further limiting their practical applications. To address these issues, here the environmentally friendly K-birnessite MnO2 (K0.3MnO2) nanosheets are directly inkjet-printed on the stainless steel sheet to serve as the electrode, while a diglyme-based electrolyte is used to fabricate a sodium-ion battery. In contrast to the conventional two-step redox reactions involving Mn4+/Mn3+/Mn2+ couples, the as-printed K0.3MnO2 electrode shows an enhanced redox activity of the Mn4+/Mn3+ couple, along with a suppressed redox activity of the Mn3+/Mn2+ couple that restricts the side reactions. The active particle size, electrode structure and electrolyte conditions could be identified as the key factors that contribute to the performance optimization. The electrode simultaneously and unprecedentedly achieves a working voltage of 2.5 V, maximum energy and power densities of 587 W h kgcathode−1 and 75 kW kgcathode−1, respectively, with 99.5% capacity retention for 500 cycles at 1 A g−1.

Harvesting wave energy based on waving potential, a newly found electrokinetic effect, is attractive but limited mainly to monolayer graphene. Here we demonstrate that moving a transparent flexible ZnO nanofilm across the surface of ionic solutions can generate electricity. The generated electricity increases linearly with the moving velocity with an open-circuit voltage up to tens of millivolt and a short-circuit current at the order of microampere. The harvested electricity can be efficiently scaled up through series and parallel connections. Theoretical simulations show that it is the proper electrical property that endows the ZnO nanofilm with the outstanding capacity in harvesting the wave energy.

Graphene quantum dot–polyaniline (PANI–GQD) composite films were synthesized by a chemical oxidation polymerization process. The optical properties of the PANI–GQD composite were studied by varying the mole concentration of PANI and the size of the GQDs. The Au/PANI–GQDs/ITO sandwich device was fabricated in order to investigate the transport properties of the composite. A stable hysteresis loop was observed in response to the applied voltage. By varying the PANI content and size of the GQDs, the area within the hysteresis loop and electrical conductance behavior of the device can be tuned in a controlled manner. Both the tunable luminescence and electrical hysteresis behavior are attributed to surface states of the GQDs. The PANI–GQD composite films are expected to find application in photonic devices.

Graphene oxide (GO) was synthesized by a hydrothermal method using glucose solution as the sole reagent. The wavelength-dependent photoresponse of GO was investigated by fabricating metal–GO–metal photodetectors. The devices demonstrated a broadband photoresponse from 290 to 1610 nm covering deep ultraviolet (UV) to near-infrared (NIR), which is the broadest spectral range yet demonstrated on GO. The response times of the photodetectors in the UV and visible range are about 100 ms, which are at least one order of magnitude faster than photodetectors based solely on GO reported previously. The responsivity of the photodetector can be as high as 23.6 mA W−1 in the visible range. The wavelength-dependent photoresponse is closely related to the absorption characteristics of GO. Potential for a self-powered GO based photodetector is first demonstrated, and the device shows a prominent photoresponse at zero bias. The GO based photodetectors pave the way for developing low-cost, broadband, self-powered as well as spectrally tuneable photodetectors.

Electropulsing-induced microstructure evolution of thermoelectric (Bi0.25Sb0.75)2Te3 thin films was studied by X-ray diffraction, scanning electron microscopy and Hall effect measurement techniques. Electropulsing-induced circular phase transformations and crystal orientation changes were detected and related to the changes in electrical conductivity of the thin films. After adequate electropulsing, the electrical conductivity of the thin films increased by about 28.5%. The effects of electropulsing on electrical conductivity are discussed in terms of decomposition of metastable semiconductor and dislocation dynamics.

Molybdenum disulphide (MoS2), which is a typical semiconductor from the family of layered transition metal dichalcogenides (TMDs), is an attractive material for optoelectronic and photodetection applications because of its tunable bandgap and high quantum luminescence efficiency. Although a high photoresponsivity of 880–2000 AW−1 and photogain up to 5000 have been demonstrated in MoS2-based photodetectors, the light absorption and gain mechanisms are two fundamental issues preventing these materials from further improvement. In addition, it is still debated whether monolayer or multilayer MoS2 could deliver better performance. Here, we demonstrate a photoresponsivity of approximately 104 AW−1 and a photogain of approximately 107 electrons per photon in an n-n heterostructure photodetector that consists of a multilayer MoS2 thin film covered with a thin layer of graphene quantum dots (GQDs). The enhanced light-matter interaction results from effective charge transfer and the re-absorption of photons, leading to enhanced light absorption and the creation of electron-hole pairs. It is feasible to scale up the device and obtain a fast response, thus making it one step closer to practical applications.

Polyaniline-functionalized graphene quantum dots (PANI-GQD) and pristine graphene quantum dots (GQDs) were utilized for optoelectronic devices. The PANI-GQD based photodetector exhibited higher responsivity which is about an order of magnitude at 405 nm and 7 folds at 532 nm as compared to GQD-based photodetectors. The improved photoresponse is attributed to the enhanced interconnection of GQD by island-like polymer matrices, which facilitate carrier transport within the polymer matrices. The optically tunable current–voltage (I–V) hysteresis of PANI-GQD was also demonstrated. The hysteresis magnifies progressively with light intensity at a scan range of ±1 V. Both GQD and PANI-GQD devices change from positive to negative photocurrent when the bias reaches 4 V. Photogenerated carriers are excited to the trapping states in GQDs with increased bias. The trapped charges interact with charges injected from the electrodes which results in a net decrease of free charge carriers and a negative photocurrent. The photocurrent switching phenomenon in GQD and PANI-GQD devices may open up novel applications in optoelectronics.

Graphene has attracted much attention at various research fields due to its unique optical, electronic and mechanical properties. Up to now, graphene has not been widely used in optoelectronic fields due to the lack of large-area uniform doped graphene (n-doped and p-doped) with smooth surface. Therefore, it is rather desired to develop some effective doping methods to extend graphene to optoelectronics. Here we developed a novel doping method to prepare large-area (> centimeter scale) uniform doped graphene film with a nanoscale roughness(RMS roughness ∼1.4 nm), the method (nano-metal film doping method) is simple but effective. Using this method electron doping (electron-injection) may be easily realized by the simple thermal deposition of Ag nano-film on a transferred CVD graphene. The doping effectiveness has been proved by Raman spectroscopy and spectroscopic ellipsometry. Importantly, our method sheds light on some potential applications of graphene in optoelectronic devices such as photodetectors, LEDs, phototransistors, solar cells, lasers etc.

Nitrogen-doped graphene quantum dots (N-GQDs) were fabricated by microwave-assisted hydrothermal technique. The optical properties of the N-GQDs were studied. The luminescence of the N-GQDs can be tuned by varying the excitation wavelength. Furthermore, two-photon luminescence of the N-GQDs excited by near-infrared laser can be obtained. It is shown that N-doping play a key role on two-photon luminescence. The N-GQDs are expected to find application in biological applications including bioimaging and sensing., {"references":["X. Yan, X. Cui, B. S. Li, L. S. Li, \"Large, Solution-Processable Graphene\nQuantum Dots as Light Absorbers for Photovoltaics\", Nano. Letter, 2010,\n10, 1869-1873.","L. A. Ponomarenko, F.Schedin, M. I. Katsnelson, R.Yang, E. W. Hill, K.\nS. Novoselov, A. K. Geim, \"Chaotic Dirac Billiard in Graphene Quantum\nDots. Science 2008, 320, 356–358.","C. O. Girit, J. C. Meyer, R. Erni, M. D. Rossell, C. Kisielowski, L.Yang,\nC. H. Park,; M. F. Crommie,; M. L. Cohen, S. 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Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7–11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode.

Graphene quantum dots (GQDs) have attracted great attention due to their unique optoelectronic properties. There remains a critical challenge to utilize the water-soluble GQDs for device applications. Here we report a facile method to fabricate a GQD–agar composite. The composite exhibits excellent optical stability and no luminescence quenching is observed. The composite is successfully applied as a colour converting material in blue light-emitting diodes (LEDs) to achieve white light emission. The luminous efficiency and light conversion efficiency of the white LED are 42.2 lm W−1 and 61.1% respectively. The light conversion efficiency of the WLED is stable for over 100 hours of continuous operation.

The authors report the fabrication of heterojunction light emitting diodes (LEDs) based on two-dimensional (2D) hexagonal ordered n-type ZnO nanomesh and p-type GaN. The 2D ZnO nanomesh array was prepared by employing polystyrene spheres as a template. When a forward bias was applied to the LED, a strong ultraviolet (UV) electroluminescence peaked at 385 nm can be observed. The peak deconvolution revealed three emission peaks at 370, 388, and 420 nm. The origin of these emission peaks will be discussed. In addition, the LED was capable of exciting a red phosphor to convert UV light into red light.