Junwei Li

Hefei University of Technology, Hefei, Anhui Sheng, China

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Publications (9)15.56 Total impact

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    ABSTRACT: A bulk-heterojunction hybrid solar cell based on CdS quantum dots (QDs) as electron acceptor and P3HT as donor was fabricated for the first time. The CdS QDs synthesized by a one-pot method had good crystallinity and stability. The hybrid thin film of CdS-QDs and conjugated polymer was made by simple spin-coating deposition of CdS-QDs/P3HT composite solution on ITO substrates and then treated by bidentate ligand ethanedithiol. Under AM1.5G illumination, the power-conversion efficiency (PCE) of the thiol-treated monolayer film was more than three times higher than that of the untreated device. The hybrid solar cell based on the assembled trilayer blend film with ethanedithiol by a layer-by-layer approach exhibited a further improved PCE of 0.86%, which was sixfold higher than that of the thiol-treated monolayer device. The results can be explained via ethanedithiol effectively displacing the existing stearate ligands on the surface of QDs in situ and connecting nanoparticles by its end function group, shortening the interdot space and thus improving electron transport between the QDs. The morphology of the thiol-treated blend film was briefly investigated.
    physica status solidi (a) 08/2012; 209(8):1583-1587. · 1.21 Impact Factor
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    ABSTRACT: A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdTe semiconductor Quantum dots (QDs) via the electrochemistry method. The Low growth temperature and slow injection of Te precursors are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during nanocrystal growth. The experimental results showed that a low concentration of Te precursor would definitely influence the growth procedure. The narrow absorption peaks in the UV-visible absorption spectra, as well as transmission electron microscopy images indicated that the as-prepared CdTe QDs had a good monodispersity. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The QDs exhibited high fluorescence QYs about 50% and the best of QY 67% without any postpreparative treatment over a broad spectral range of 516-609 nm, which could be further broadened by long-term refluxing. The current work suggested that electrochemical method was an attractive approach to the synthesis of high-quality II-VI semiconductor QDs at a large scale.
    Journal of Nanoscience and Nanotechnology 05/2012; 12(5):3806-11. · 1.15 Impact Factor
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    ABSTRACT: Sb-doped ZnTe nanoribbons (NRs) with enhanced p-type conductivity were successfully synthesized by a simple thermal co-evaporation method. Nanodevices, including nano-field-effect transistors (FETs) and nano-photodetectors (nanoPDs), were constructed based on the ZnTe:Sb NRs and their structure dependent device performances were systemically investigated. It is found that the transport properties of the ZnTe nanostructures as well as the device structures play a critical role in determining the device performances. In contrast to the nano-metal-oxide-semiconductor FETs (nanoMOSFETs) with back-gate structure, the top-gate nano-metal-insulator-semiconductor FETs (nanoMISFETs) show much enhanced performances in all aspects. On the other hand, owing to the appropriate p-type doping, nano-photodetectors (nanoPDs) based on the ZnTe:Sb NRs exhibit excellent device performances, such as high responsivity and photoconductive gain, fast response speed, large detectivity and so on. Moreover, the response time could be effectively shortened by using nano-heterojunction photodetectors (nanoHPDs). It is expected that knowledge gained from this work could be readily extended to nanodevices based on other nanostructures.
    Journal of Materials Chemistry 03/2012; 22(13):6206-6212. · 5.97 Impact Factor
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    ABSTRACT: Silicon based optoelectronic integration is restricted by its poor optoelectronic properties arising from the indirect band structure. Here, by combining silicon with another promising optoelectronic material, the CdS nanoribbon (NR), devices with heterojunction structure were constructed. The CdS NRs were also doped with gallium to improve their n-type conductivity. A host of nano-optoelectronic devices, including light emitting diodes, photovoltaic devices, and photodetectors, were successfully constructed on the basis of the CdS:Ga NR/Si heterojunctions. They all exhibited excellent device performances as regards high stability, high efficiency, and fast response speed. It is expected that the CdS NR/Si heterojunctions will have great potential for future applications of Si based optoelectronic integration.
    Nanotechnology 09/2011; 22(40):405201. · 3.84 Impact Factor
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    ABSTRACT: To reduce the size and to lower energy consumption are very important for the portable X-ray detector. It is clear that the nanodetector based on nanotechnology will be the future trend. The single-crystalline Zn<sub>0.75</sub>Cd<sub>0.25</sub>Te nanoribbons are synthesised by a two-step process, and the X-ray detectors from individual nanoribbon are fabricated. The X-ray detecting performances are carried out by using three kinds of X-ray source with different energy of 8.857, 9.659 and 11.564 KeV, respectively. The nanodetectors exhibit a high sensitivity, fast response speed, which are attributed to the high-aspect ratio, nearly perfect single-crystalline quality and the reduction of the recombination barrier in the ribbon. The remarkable X-ray responsivity implies that the Zn<sub>0.75</sub>Cd<sub>0.25</sub>Te nanoribbons are a very attractive candidate for application in X-ray nanodetectors at room temperature.
    Micro & Nano Letters 09/2011; · 0.85 Impact Factor
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    ABSTRACT: The atmosphere compensating technique with an individual selenium source is, first, used in the growth of phosphorus-doped p-type ZnSe nanowires. The morphology and structure characterisations reveal that the as-synthesised ZnSe nanowires have a wurtzite structure with a diameter of about 160 nm, a growth direction of [001]. The electrical properties characterisations demonstrate that the selenium atmosphere compensation technique assisted with phosphorus-doping leads to a substantial action in p-type conductivity of ZnSe nanowires with a high mobility of 1.25 cm<sup>2</sup> V<sup>-1</sup> S<sup>-1</sup> and carrier concentration of 1.47×10<sup>18</sup> cm<sup>-3</sup>. The photoluminescence measurements show a dominant emission and two donor-acceptor pair emission.
    Micro & Nano Letters 07/2011; · 0.85 Impact Factor
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    ABSTRACT: Resonant tunneling is firstly found in twin p-type ZnTe nanowire field-effect transistors. The twin ZnTe nanowires are synthesized via the thermal evaporation process. X-ray diffraction and high-resolution transmission electron microscopy characterization indicate that the as-grown twin nanowire has a zinc-blende crystal structure with an integrated growth direction of [11-1]. The twin plane is (11-1) and the angle between the mirror symmetrical planes is 141°. The formation of twins is attributed to the surface tension from the eutectic liquid droplet. Field-effect transistors based on single ZnTe twin nanowire are constructed, the corresponding electrical measurements demonstrate that the twin nanowires have a p-type conductivity with a mobility (μ h ) of 0.11cm2 V−1 S−1, and a carrier concentration (n h ) of 1.1×1017cm−3. Significantly, the negative differential resistance with a peak-to-valley current ratio of about 1.3 is observed in p-type twin ZnTe nanowire field-effect transistors at room temperature. As the periodic barriers produced in the periodic twin interfaces can form multi-barrier and multi-well along one-dimensional direction. The multibarrier can be modulated under external electrical field. When the resonant condition is met, the space charge will be enhanced with the inherent feedback mechanism, and the resonant tunneling will occur.
    Applied Physics A 01/2011; 102(2):469-475. · 1.69 Impact Factor
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    ABSTRACT: Highly luminescent blue-emitting CdS/ZnS core/shell quantum dots (QDs) were synthesized in N-oleoylmorpholine by two facile steps: first, the CdS core QDs were prepared via a simple one-pot method involving a direct reaction of Cd precursor cadmium stearate and S precursor S powder in solvent N-oleoylmorpholine; second, ZnS shells were successively overcoated on CdS core through the decomposition of single molecular precursor zinc diethyldithiocarbamate. The thickness of shell was precisely tuned by controlling drip feed speed and amount of shell precursor. The obtained CdS/ZnS core/shell QDs showed the maximum photoluminescent quantum yield of 54.8% and narrow spectra bandwidth, exhibiting high monodispersity, good color purity and long fluorescent lifetimes. The CdS/ZnS core/shell QDs with tunable emission wavelength of 424–470nm were obtained by controlling the thickness of ZnS shell overgrown on different-sized CdS QDs, which are promising materials for blue light-emitting devices.
    Materials Chemistry and Physics - MATER CHEM PHYS. 01/2011; 130(3):909-914.
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    ABSTRACT: Ternarysemiconductor Zn0.3Cd0.7Te nanoribbons are, firstly, synthesized via a two-step process, and the structure characterizations reveal that the as-synthesized nanoribbons are single-crystalline with a zinc blende structure and a crystal growth direction of [1–10]. Nano-field-effect transistors are fabricated based on single nanoribbon, and the electron transport characteristics demonstrate that the Zn0.3Cd0.7Te ribbons have p-type conductivity with a mobility (μh) of 5.7cm2V−1S−1 and carrier concentration (nh) about 1.1×1017cm−3. The prepared nanoribbons with significant p-type conductivity will be a very attractive candidate for nanoelectronic devices.
    Materials Letters - MATER LETT. 01/2011; 65(12):1753-1755.