Anode material based on SWCNT for infrared quantum dot light-emitting devices

We present an optical model based on Green’s function to investigate the effect of using single-wall carbon nanotube (SWCNT) as anode for infrared quantum dot light-emitting devices (IR QD-LEDs). To the best of our knowledge, there is no report in using SWCNT as anode in IR QD-LEDs. We have studied the emitted power distribution among the different optical modes (external propagating mode (photon outcoupling efficiency), substrate, anode/organics, and surface plasmon modes (SP)), angular intensity distribution, viewing angle effect on the optical characteristics, and the emission spectral characteristics. We have found that the light outcoupling efficiency of IR QD-LEDs based on SWCNT as anode was increased nearly by a factor of 4 relative to that one based on indium-tin oxide (ITO). We also investigated the effect of using different cathode materials on the optical characteristics of IR QD-LEDs.     

Highly efficient white quantum dot light-emitting diode based on ZnO quantum dot

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. Here, we report a simply solution-processed white QD-LED using ZnO QDs as emitters. The device is demonstrated with a maximum luminance of 300 cd/m², exhibiting the Commission Internationale de l’Enclairage coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 120 h. These results indicate that ZnO QDs provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices.     

Numerical model of multilayer organic light-emitting devices

A numerical model of multilayer organic light-emitting devices is presented in this article. This model is based on the drift-diffusion equations which include charge injection, transport, space charge effects, trapping, heterojunction interface and recombination process. The device structure in the simulation is ITO/CuPc (20 nm)/NPD (40 nm)/Alq3 (60 nm)/LiF/Al. There are two heterojunctions which should be dealt with in the simulation. The I--V characteristics, carrier distribution and recombination rate of a device are calculated. The simulation results and measured data are in good agreement.     

石墨烯纳米带量子点中的量子混沌现象

在20 mK的极低温下测量了石墨烯纳米带量子点的电子输运性质,观测到清晰的库仑阻塞菱形块和对应量子点激发态的电导峰.对库仑阻塞近邻电导峰间距和峰值进行了统计分析,发现其统计分布分别满足无规矩阵理论描述的Wigner-Dyson分布和Porter-Thomas分布,说明石墨烯纳米带量子点在低温下出现了量子混沌现象.还讨论了这种长方形量子点中量子混沌的可能成因. 关键词： 石墨烯纳米带 量子点 库仑阻塞 量子混沌     

Bright hybrid white light-emitting quantum dot device with direct charge injection into quantum dot

A bright white quantum dot light-emitting device(white-QLED) with 4-[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-2- [3-(tri-phenylen-2-yl)phen-3-yl]quinazoline deposited on a thin film of mixed green/red-QDs as a bilayer emitter is fabricated. The optimized white-QLED exhibits a turn-on voltage of 3.2 V and a maximum brightness of 3660 cd/m~2@8 V with the Commission Internationale de l'Eclairage(CIE) chromaticity in the region of white light. The ultra-thin layer of QDs is proved to be critical for the white light generation in the devices. Excitation mechanism in the white-QLEDs is investigated by the detailed analyses of electroluminescence(EL) spectral and the fluorescence lifetime of QDs. The results show that charge injection is a dominant mechanism of excitation in the white-QLED.     

Flexible Ag electrode for quantum dot light-emitting diode

In this paper, we have fabricated quantum dot light-emitting diode (QD-LED) based on silver (Ag) electrode. The QD-LED with Ag electrode is demonstrated with decreased leakage current, improved luminous efficiency, low turn-on voltages, and saturated emission exhibiting the Commission Internationale de l’Enclairage coordinates of (0.59, 0.40). Meanwhile, compared to the QD-LED with indium tin oxide-coated polyethylene terephthalate electrode, the electroluminescence intensity was enhanced twice for QD-LED based on Ag electrode, and turn-on voltage was reduced to 4.7 V, which was attributed to the higher conductivity and better transmission of Ag electrode.     

Sputtered gold nanoparticles enhanced quantum dot light-emitting diodes

Surface plasmonic effects of metallic particles have been known to be an effective method to improve the performances of light emitting didoes.In this work,we report the sputtered Au nanoparticles enhanced electroluminescence in inverted quantum dot light emitting diodes(ITO/AuNPs/ZnMgO/QDs/TFB/PEDOT:PSS/Al).By combining the timeresolved photoluminescence,transient electroluminescence,and ultraviolet photoelectron spectrometer measurements,the enhancement of the internal field enhanced exciton coupling to surface plasmons and the electron injection rate increasing with Au nanoparticles’incorporation can be explained.Phenomenological numerical calculations indicate that the electron mobility of the electron transport layer increases from 1.39×10~(-5)cm~2/V·s to 1.91×10~(-5)cm~2/V·s for Au NPs modified device.As a result,the maximum device luminescence is enhanced by 1.41 fold(from 14600 cd/cm~2to 20720 cd/cm~2)and maximum current efficiency is improved by 1.29 fold(from 3.12 cd/A to 4.02 cd/A).     

半导体InAs量子点单光子发射器件

文章概述了量子点单光子源的研究现状,综述了微腔量子点耦合单光子发射器件制备中关键的低密度InAs量子点外延技术,单量子点单光子发射二阶关联函数HBT检测方法,分布布拉格反馈微腔结构的制备以及实现液氮温度下电驱动微腔量子点单光子发射器件等研究结果.     

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.     

Helical states around a mass-inverted quantum dot in graphene

Topologically protected helical states at a mass-inverted quantum dot in graphene are studied by analyzing both tight-binding and kernel polynomial method calculations. The mass-inverted quantum dot is introduced by considering a heterojunction between two different mass domains, which is similar to the domain wall in bilayer graphene. The numerical results show emergent metallic channels across the mass gap when the signs of the mass terms are opposite. The eigenstates of the metallic channels are revealed to be doubly degenerate—each state propagates along opposite directions, maintaining the time-reversal symmetry of graphene. The robustness of the metallic channels is further examined, concluding with the fact that helical states are secured unless atomic vacancies form near the domain wall. Such helical states circulating along the topological defects may pave a novel route to engineering topological states based on graphene.     

White light-emitting quantum dot diodes and tuning of luminescence processes

A novel white light-emitting diode based on a large Stokes shift (~200 nm) and using pure green light-emitting CdSeS quantum dots (QDs) with an Ag/ZnSnO/QDs/spiro-TPD/ITO structure has been fabricated in which ZnSnO and spiro-TPD are served as the electron and hole transport layer, respectively. The large Stokes shift of the CdSeS QDs excludes potentially Förster resonance energy transfer process, which allows spiro-TPD to act as both an emitter and hole transport layer. The devices exhibit a wide EL spectrum consisting of three components: blue emission from spiro-TPD, green emission from QD band–band recombination, and red emission from QD surface-state recombination. We further found that as the intensity ratios among these three components vary with bias the color of the QD light-emitting diodes is tunable. The device displays a good white light-emitting characteristic with CIE coordinates of (0.281, 0.384) at an appropriate bias.     

Tailoring multilayer quantum wells for spin devices

In this article, we have developed new exact analytical solutions of a nonlinear evolution equation that appear in mathematical physics, a \((2+1)\)-dimensional generalised time-fractional Hirota equation, which describes the wave propagation in an erbium-doped nonlinear fibre with higher-order dispersion. By virtue of the tanh-expansion and complete discrimination system by means of fractional complex transform, travelling wave solutions are derived. Wave interaction for the wave propagation strength and angle of field quantity under the long wave limit are analysed: Bell-shape solitons are found and it is found that the complex transform coefficient in the system affects the direction of the wave propagation, patterns of the soliton interaction, distance and direction.     

基于Si-rich SiNx/N-rich SiNy多层膜结构电致发光特性研究

利用等离子体增强化学气相沉积法制备了富硅氮化硅/富氮氮化硅多层膜,并以此氮化硅基多层膜作为有源层构建电致发光器件,在室温下观察到了较强的电致可见发光.在此基础上,研究多层膜结构中作为势垒层的富氮氮化硅层对器件电致发光性质的影响,实验结果表明通过改变势垒层的Si/N组分,调制其势垒高度,器件的电致发光效率可得到显著地提高.     

Design of graphene coupling enhanced quantum dot infrared photodetector

Optical Review - The conventional quantum dot infrared photodetector (QDIP) has a weak ability to capture light, which limits the further improvement of absorptivity. In this paper, the graphene...     

量子点器件的三端电测量研究

利用三端电测量方法，研究了调制掺杂二维电子气结构的量子点器件输运特性.报道了可分别测量二维电子气电阻和量子点隧穿电阻的实验方法.实验结果表明：量子点的横向耦合控制了量子点器件在小偏压下的电输运特性. 关键词： 自组装量子点 二维电子气 量子隧穿 肖特基接触     

拓扑石墨烯电极分子器件输运特性

利用密度泛函理论结合非平衡格林函数方法,研究了不同拓扑能带结构的石墨烯电极分子器件输运特性.结果表明器件导通电压与电极禁带宽度正相关,同时器件在输运过程中表现出负微分电阻特性,峰谷电流比可达2697.分析认为器件导通源自于偏压升高过程中两电极能带匹配.器件负微分电阻特性源自于偏压升高过程中两电极能带交错.散射态分析表明,能带匹配后散射态分布较为离域,有利于电子通过器件.能带交错后散射态局域于电极处,表明电子输运受到抑制.     

A graphene quantum dot realized by an armchair graphene nanoribbon with line defect

The electron transport in a semiconducting armchair graphene nanoribbon with line defect is theoretically investigated, by coupling it to two normal metallic leads. It is found that the line defect induces a new localized quantum state near the Dirac point, and that the coupling between this state and the leads provides a channel for the resonant tunneling. This means that such a finite‐size nanoribbon can be viewed as a quantum dot. When two line defects are present simultaneously, a coupled quantum dot forms, leading to the splitting of the conductance peaks. With these results, we propose such a structure to be a promising candidate of an electron transistor. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced electron injection in organic light-emitting devices using Al/LiF electrodes

The temperature dependence of the current-voltage-luminescence characteristics in organic light-emitting diodes (OLEDs) with varying thickness of LiF layers are studied to understand the mechanism of the enhanced electron injection by inserting a thin insulating LiF layer at the tris(8-hydroxyquinoline) aluminum (Alq₃)–Al interfaces. At room temperature, the LiF/Al cathode enhances the electron injection and the quantum efficiency (QE) of the electroluminescence (EL), implying that the LiF thin layer lowers the electron-injection barrier. However, at low temperatures it is observed that the injection-limited current dominates and the barrier height for the electron injection in the device with LiF/Al appears to be similar with the Al only device. Thus, our results suggest that at low temperatures the insertion of LiF does not cause a significant band bending of Alq₃ or reduction of the Al work function.     

A first-principles study on DNA sequencing using graphene quantum dot

In this paper, we propose a new device based on graphene quantum dot (GQD) to interrogate nucleotide in a DNA molecule. We have conducted non-equilibrium Green’s function together with the density functional theory simulations to show zero transmission curves for a system which includes nucleobases. The simulation results indicates several characteristic peaks in the electron transmission curve for any single base on the quantum dot which can be utilized to distinguish between bases. Number and positions of the peaks, as well as their amplitude, depend on the type of the bases and their relative position to the dot. Thus, this structure shows remarkable distinction characteristic in zero bias transmission curve and can yield minimal ambiguity in the adenine, cytosine, guanine and thymine nucleotide detection. Due to stacking of nucleobases on the graphene and consequent attenuation in directional fluctuations, stable measurement is also expected.     

High efficiency small molecule white organic light-emitting devices with a multilayer structure

In this paper, a new white organic light-emitting device (WOLED) with multilayer structure has been fabricated. The structure of devices is ITO/N, N-bis-(1-naphthyl)-N, N^′-diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) (40 nm)/NPB: QAD (1%): DCJTB (1%) (10 nm) /DPVBi (10 nm) /2, 9-dimethyl, 4, 7-diphenyl, 1, 10-phenanthroline (BCP) (d nm)/tris-(8-hydroxyquinoline) aluminium (Alq₃)(50-d nm)/LiF (1 nm)/Al (200 nm). In our devices, a red dye 4-(dicyanomethylene)-2-t-butyl-6 (1, 1, 7, 7-tetramethyl julolidyl-9-enyl)-4H-pyran (DCJTB) and a green dye quinacridone (QAD) were co-doped into NPB. The device with 8 nm BCP shows maximum luminance of 12 852 cd/m² at 20 V. The current efficiency and power efficiency reach 9.37 cd/A at 9 V and 3.60 lm/W at 8 V, respectively. The thickness of the blocking layer permit the tuning of the device spectrum to achieve a balanced white emission with Commission International de’Eclairage (CIE) chromaticity coordinates of (0.33,0.33). The CIE coordinates of device change from (0.3278, 0.3043) at 5 V to (0.3251, 0.2967) at 20 V that are well in the white region, which is largely insensitive to the applied bias.