We report a facile method of synthesizing graphene quantum dots（GQDs） with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π –π ＊ gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.
The performance of P3HT：PCBM solar cells was improved by anode modification using spin-coated Tb（aca）3phen ultrathin films. The modification of the Tb（aca）3phen ultrathin film between the indium tin oxide （ITO） anode and the PEDOT：PSS layer resulted in a maximum power conversion efficiency （PCE） of 2.99% compared to 2.66% for the reference device, which was due to the increase in the short-circuit current density （Jsc）. The PCE improvement could be attributed to the short-wavelength energy utilization and the optimized morphology of the active layers. Tb（aca）3phen with its strong down-conversion luminescence properties is suitable for the P3HT：PCBM blend active layer, and the absorption region of the ternary blend films is extended into the near ultraviolet region. Furthermore, the crystallization and the surface morphol- ogy of P3HT：PCBM films were improved with the Tb（aca）3phen ultrathin film. The ultraviolent-visible absorption spectra, atomic force microscope （AFM）, and X-ray diffraction （XRD） of the films were investigated. Both anode modification and short-wavelength energy utilization using Tb（aca）3phen in P3HT：PCBM solar cells led to about a 12% PCE increase.
We have researched the performances of organic photovoltaic devices with the bulk heterojunction (BHJ) structure using the organic solution-processable functionalized graphene (SPFGraphene) material as the electron-accepter material and P3OT as the donor material. The structural configuration of the device is ITO/PEDOT:PSS/P3OT:PCBM-SPFGraphene/LiF/Al. Given the P3OT/PCBM (1:1) mixture with 8wt% of SPFGraphene, the open-circuit voltage (Voc) of the device reaches 0.64 V, a short-circuit current density (Jsc) reaches 5.7 mA/cm2, a fill factor (FF) reaches 0.42, and the power conversion efficiency ( ) reaches 1.53% at illumination at 100 mW/cm2 AM1.5. We further studied the reason for the device performances improvement. In the P3OT:PCBM-SPFGraphene composite, the SPFGraphene material acts as exciton dissociation sites and provides the transport pathways of the lowest unoccupied molecular orbital (LUMO)-SPFGraphene-Al. Furthermore, adding SPFGraphene to P3OT results in appropriate energetic distance between the highest occupied molecular orbital (HOMO) and LUMO of the donor/acceptor and provides higher exciton dissociation volume mobility of carrier transport. We have researched the effect of annealing treatment for the devices and found that the devices with annealing treatment at 180°C show better performances compared with devices without annealed treatment. The devices with annealed treatment show the best performance, with an enhancement of the power conversion efficiency from 1.53% to 1.75%.
WANG HaiTeng HE DaWei WANG YongSheng LIU ZhiYong WU HongPeng WANG JiGang ZHAO Yu
In order to investigate the impedance matching properties of microwave absorbers,the ternary nanocomposites of GO/PANI/Fe3O4（GPF） are prepared via a two-step method,GO/PANI composites are synthesized by dilute polymerization in the presence of aniline monomer and GO,and GO/PANI/Fe3O4 is prepared via a co-precipitation method.The obtained nanocomposites are characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,and Fourier transform infrared spectroscopy（FTIR）,respectively.The microwave absorbability reveals enhanced microwave absorption properties compared with GO,PANI,and GO/PANI.The maximum reflection loss of GO/PANI/Fe3O4 is up to-27 dB at 14 GHz with its thickness being 2 mm,and its absorption bandwidths exceeding-10 dB are more than 11.2 GHz with its thickness values being in the range from 1.5 mm-4 mm.It provides that GO/PANI/Fe3O4 can be used as an attractive candidate for microwave absorbers.
A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy(TEM) and Fourier transform infrared spectroscopy(FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/ GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss(RL) of GO/PANI/GAunano with a thickness of 2 mm is up to-24.61 d B at 15.45 GHz, and the bandwidth corresponding to RL at-10 d B can reach 4.08 GHz(from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.
To improve the specific capacitance and rate capability of electrode material for supercapacitors, a three-dimensional graphene/polyaniline （3DGN/PANI） composite is prepared via in situ polymerization on GN hydrogel. PANI grows on the GN surface as a thin film, and its content in the composite is controlled by the concentration of the reaction monomer. The specific capacitance of the 3DGN/PANI composite containing 10 wt% PANI reaches 322.8 F.g-1 at a current density of 1 A.g-1, nearly twice as large as that of the pure 3DGN （162.8 F.g-1）. The capacitance of the composite is 307.9 F.g-1 at 30 A.g-1 （maintaining 95.4%）, and 89% retention after 500 cycles. This study demonstrates the exciting potential of 3DGN/PANI with high capacitance, excellent rate capability and long cycling life for supercapacitors.
We synthesize Au@SiO2 composite particles with a core-shell structure, and utilize the Au@SiO2 nanoparticles to modulate the fluorescence emission of the graphene quantum dot （GQD） through varying the silica shell thickness. The silica shell thickness can be easily controlled by varying the coating time. After silica coating, we investigate the influence of the silica thickness on the fluorescence emission of the GQD and find that the fluorescence property of the GQD can be changed as expected by varying the thickness of the silica shell. We propose an optimized coating time for the silica shell under the interaction of fluorescence quenching and enhancement.
