Efficient cathode contacts through Ag-doping in multifunctional strong nucleophilic electron transport layer for high performance inverted OLEDs

This paper presents an efficient and stable green inverted organic light emitting diode (IOLED) using multifunctional and strong nucleophilic quality electron transport material (1,3-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene (m-bPPhenB)) with silver (Ag) as an n-dopant. By the energy level alignment study using in-situ ultraviolet photoelectron spectroscopy measurement, negligible electron injection barrier between indium tin oxide (ITO) and Ag-doped m-bPPhenB (Φ_e ≈ 0.03 eV) is observed and the electrons can be easily tunneled from ITO into Ag-doped m-bPPhenB layer. Also, Ag dopant forms coordination bonds with phenanthroline based unit, which improves electron injection from ITO. Fabricated IOLED devices using an Ag-doped m-bPPhenB have an extremely low driving voltage of 3.6 V and external quantum efficiency of 29.0%. Such good performances of IOLED are attributed to negligible electron injection barrier at the interface between ITO and Ag-doped m-bPPhenB. The Ag-doped IOLED device also shows a good air stability owing to the stable Ag n-dopant. The doping of Ag into special electron transport layer in the IOLED structure could be applicable to various displays and lighting applications.     

Structural,electronic, and magnetic properties of zigzag-edged BN nanoribbons with 558-type line defects

The 558-type line defect is introduced into zigzag-edged BN nanoribbons (ZBNNRs), similar to that be found in graphene, and the structural, electronic, and magnetic properties for such defective ZBNNRs are investigated systematically. It shows that they are highly stable. In the nonmagnetic state, the metallic property of ZBNNRs remains unchanged regardless of the defect positions, but different defect positions give rise to different influences on the total DOS and PDOS at the Fermi level. Interestingly, in the magnetic state, the thermal stability of magnetism is enhanced greatly when the line defect appears at most positions, even comparable with room temperature. When the line defect position shifts from the B-edge to the N-edge, the transition from the half-metal to the magnetic semiconductor or spin unpolarized semiconductor is induced. And also, the response of defect ribbons to an in-plane transverse electric field is essentially different from defect-free ribbons, and the half-metallic feature can be enhanced by an electric field for the line defect introduced into certain positions in a ribbon.     

High-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure

We demonstrate high-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure. Excellent performance is realized by using step-graded p- and n-type doping structure in orange homojunction device. The resulting orange homojunction device exhibits a maximum current efficiency of 30.0 cd/A and low efficiency roll-off. The improvements are mainly attributed to the utilization of step-graded doped profile, which facilitates balanced charge carrier injection and transport. Moreover, one optimized white homojunction device based on two complementary colors shows a maximum efficiency of 15.4 cd/A, and superior color-stability in a wide range of luminance.     

Imaging vibrations of electromechanical few layer graphene resonators with a moving vacuum enclosure

Imaging the vibrations of nanomechanical resonators means measuring their flexural mode shapes from the dependence of their frequency response on in-plane position. Applied to two-dimensional resonators, this technique provides a wealth of information on the mechanical properties of atomically-thin membranes. We present a simple and robust system to image the vibrations of few layer graphene (FLG) resonators at room temperature and in vacuum with an in-plane displacement precision of ≈0.20 μm. It consists of a sturdy vacuum enclosure mounted on a three-axis micropositioning stage and designed for free space optical measurements of vibrations. The system is equipped with ultraflexible radio frequency transmission lines to electrically actuate resonators. With it we characterize the lowest frequency mode of FLG resonators by measuring its frequency response as a function of position on the membrane and by extracting its effective mass. We use the background noise of the undriven vibrational spectrum to calibrate in-plane displacement. Finally, we measure the first three vibration modes of a resonator whose membrane is partially folded and find that folds locally suppress vibrations.     

Photovoltaic properties of a single layer poly [3-(4-octylphenyl)-2,2′-bithiophene] (PTOPT)

A Schottky contact is made from a single layer polymer poly [3-(4-octylphenyl)-2,2′-bithiophene] (PTOPT) in its neutral state and a low work function metal (Al). The electrical and optical properties have been investigated by means of I–V measurements in the dark and under illumination. Various parameters such as the reverse saturation current density, barrier height, and diode quality factor were determined from the I–V curves in the dark of Al/PTOPT/ITO sandwich structure using thermionic emission theory. Spectral response of the device was measured at various wavelengths giving a peak at 500 nm. The IPCE% was obtained for illumination through both the Al and ITO sides. By illuminating the diode with a monochromatic light of wavelength 500 nm, the open-circuit voltage, short-circuit current density, power conversion efficiency, and fill-factor (FF) were obtained. The dependence of photocurrent on light intensity was also recorded and analyzed.     

TiI4-doping induced bulk defects passivation in halide perovskites for high efficient photovoltaic devices

Power conversion efficiency (PCE) and stability are two important properties of perovskite solar cells (PSCs). Particularly, defects in the perovskite films could cause the generation of trap states, thereby increasing the nonradiative recombination. To address this issue, suitable dopants can be incorporated to react with non-bonded atoms or surface dangling bonds to passivate the defects. Herein, we introduced TiI₄ into CH₃NH₃PbI₃ (MAPbI₃) film and obtained a dense and uniform morphology with large crystal grains and low defect density. The champion cell based on 0.5% TiI₄-doped MAPbI₃ achieved a PCE as high as 20.55%, which is superior to those based on pristine MAPbI₃ (17.64%). Moreover, the optimal solar cell showed remarkable stability without encapsulation. It retained 88.03% of its initial PCE after 300 h of storage in ambient. This work demonstrates TiI₄ as a new and effective passivator for MAPbI₃ film.     

The resolution of analogue measuring devices and its associated uncertainty: An investigation with practical recommendations

Despite the popularity of the analogue measuring devices, there is no recognized reference provided comprehensive guidelines for determining their resolution and its associated uncertainty. For filling this gap, this article is introduced as an attempt to explore and investigate all the available works related to this issue. The new terminology “evident space”, “evident resolution”, and “conjunction” were proposed to set a common reference. Two different techniques for determining the analogue resolution were presented and discussed. Several numerical examples were also presented to show different analogue indications and their interpretations. Moreover, reasonable recommendations for determining the resolution uncertainty were suggested depending on the case.     

基于电容的手势识别系统

传统手势识别装置一般依赖于复杂计算设备,在简单场合配置手势识别装置成本过高。针对这一问题,提出了基于电容数字转换器的手势识别系统。具体实施过程中,电容数字转换器采集静态手势特征,滑动窗口滤波加工特征数值,再结合K邻近分类算法判别静态手势。该系统具有对硬件要求低、功耗小、对环境光强不敏感等优点。经过50次试验,系统对于常用的数字零到五手势识别正确率为98%,判别时间小于0.6 s。     

High-performance and stability bifacial flexible self-powered perovskite photodetector by surface plasmon resonance and hydrophobic treatments

Flexible semitransparent photodetectors based on perovskites provide merits in terms of light weight and bifacial advantages but suffer from poor stability. To simultaneously enhance the performance and stability of flexible perovskite photodetectors (PPDs), silver (Ag) nanoparticles are incorporated to improve the responsiveness through the surface plasmon resonance (SPR) effect in the bulk of perovskite layer, and block copolymer F68 is employed to increase the surface hydrophobicity of perovskite film to keep long-term stable devices. Ag@polyvinyl pyrrolidone (PVP) core shell structure enables the sufficiently enhanced film light absorption and device quantum efficiency following the SPR response curve, the amphiphilic F68 make the perovskite less vulnerable to humid ambient exposure. Moreover, the sputtered transparent indium tin oxide back electrode enables the double facial operability of our flexible self-powered photodetectors with a bifacial factor of 80% and improved stability as well. Addressing the poor responsiveness and instability issues extends the potential broad applications of our bifacial flexible perovskite photodetectors.     

可变光片照明系统设计

为解决目前光片荧光显微镜光片厚度单一的问题,基于变倍扩束原理进行了可变光片照明系统设计。首先,对光片照明系统各组成部分进行了高斯光学计算,得到光片厚度与扩束比的关系以及扩束比与各组元垂轴放大率、焦距的关系;然后,设计了基于10倍扩束的可变光片照明系统,得到厚度和长度连续可变的光片;最后,对光片参数、均匀性及系统的公差进行分析。设计结果表明,连续可变光片的厚度为3.33～33.3 m,在YOZ平面上60%的光片高度区域内,低（1）、中（6）和高（10）扩束比下的照度均匀性分别达到0.65、0.4和0.61。公差分析表明,光片厚度在1扩束比时的最大改变量小于设计值的15%,在6和10扩束时小于6%。设计实现了光片厚度的连续变化,且在60%的光片高度区域内有利于样本的观察。