Review of blue perovskite light emitting diodes with optimization strategies for perovskite film and device structure

Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red and green PeLEDs,blue PeLEDs have not been extensively investigated,which limits their commercial applications in the fields of luminance and full-color displays.In this review,blue-PeLED-related research is categorized by the composition of perovskite.The main challenges and corresponding optimization strategies for perovskite films are summarized.Next,the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers.Accordingly,future directions for blue PeLEDs are discussed.This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs,thereby enhancing their development and application scope.

Clockwise vs Counter-Clockwise I-V Hysteresis of Point-Contact Metal-Tip/Pr0.7 Ca0.3MnO3/Pt Devices

Metal-tip/Pr0.7Ca0.3MnO3/Pt devices possess two types of I-V hysteresis： clockwise vs counter clockwise depending on the tip materials. The criteria for categorization of these two types of devices can be simply based on whether the Gibbs free energy of oxidation for the metal tip is lower or higher than that of PCMO, respectively. While the clockwise hysteresis can be attributed to electric field induced oxidation/reduction, the counter clockwise hysteresis can be explained by oxygen vacancy migration in an electrical field. Alternating-current conductance spectra also reveal distinct hopping barriers between these two categories of devices at high resistive states.

High-Efficiency Green Phosphorescent Organic Light-Emitting Diode Based on Simplified Device Structures

A high-efficiency green phosphorescent organic light emitting diode with a simplified structure is achieved that is free of a hole transport layer. The design of this kind of device structure not only saves the consumption of organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting green phosphorescent organic light-emitting diodes （PHOLEDs） exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and current efficiency reach 23.7% and 88 cd/A, respectively. Moreover the device demonstrates satisfactory stability, keeping 23.7% and 88cd/A, 22% and 82cd/A, respectively, at a luminance of 100 and 1000cd/m2. The working mechanism for achieving high efficiency based on such a simple device structure is discussed correspondingly. The improved charge carrier injection and transport balance are proved to prominently contribute to achieve the high efficiency and great stability at high luminance in the green PHOLEDs.

Finite Element Analysis on the Pre-load Structures of the Central Solenoid for the HT-7U Device

The central solenoid is an important part of the HT-7U device. In this paper， the computational analysis of the stress and the displacement on the pre-load structures of the central solenoid have been made by the finite element analysis system COSMOS/M2.0 under room and/or operating temperature. According to the analytical results, the clip aprons and compression plates are all satisfied with safety design criteria.

Analysis of Mechanically Tunable Frequency Selective Surfaces

The frequency selective surface (FSS) has been widely applied by means of its spatial frequency-filter characteristic, but it is always designed and used as a device with fixed frequency response. In order to tune the resonant frequency and switch the frequency channel, a scheme of mechanically tunable FSS is theoretically analyzed by using the method of Floquet's vector modes expansion and fields matching. A double-layer tunable FSS with dipole element can perform a dynamic range of resonant frequency covering whole X-band.

Recent development and progress of structural energy devices

In order to fully replace the traditional fossil energy supply system, the efficiency of electrochemical energy conversion and storage of new energy technology needs to be continuously improved to enhance its market competitiveness. The structural design of energy devices can achieve satisfactory energy conversion and storage performance. To achieve lightweight design, improve mechanical support, enhance electrochemical performance, and adapt to the special shape of the device, the structural energy devices develop very quickly. To help researchers analyze the development and get clear on developing trend,this review is prepared. This review summarizes the latest developments in structural energy devices, including special attention to fuel cells, lithium-ion batteries, lithium metal batteries, and supercapacitors.Finally, the existing problems of structural energy devices are discussed, and the current challenges and future opportunities are summarized and prospected. Structural energy devices can undoubtedly overcome the performance bottlenecks of traditional energy devices, break the limitations of existing materials and structures, and provide a guidance for the development of equipment with high performance,light weight and low cost in the future.

Design and Application of a Near Field Microwave Antenna for the Spin Control of Nitrogen-Vacancy Centers

Controlled manipulation of the electron spin by means of a microwave field is investigated. The near magnetic field generated by a copper wire antenna is measured experimentally and simulated theoretically, and the optimum antenna length and position are obtained. By measuring the change in the fluorescence of nitrogen-vacancy （N-V） centers in diamond after excitation with a 532 nm continuous wave laser at room temperature, it is verified that the spin of the N-V center can be effectively controlled by the microwave field.

Periodic structural defects in Bragg gratings and their application in multiwavelength devices

In this paper, we present the finding that periodic structural defects(PSDs) along a Bragg grating can shift the Bragg wavelength. This effect is theoretically analyzed and confirmed by numerical calculation. We find that the Bragg wavelength shift is determined by the defect size and the period of the defects. The Bragg wavelength can be well tuned by properly designing the PSDs, and this may provide an alternative method to fabricate grating-based multiwavelength devices, including optical filter arrays and laser arrays. In regards to wavelength precision, the proposed method has an advantage over the traditional methods, where the Bragg wavelengths are changed directly by changing the grating period. In addition, the proposed method can maintain grating strength when tuning the wavelength since only the period of defects is changed. This will be a benefit for devices such as arrays.

A Novel Ce3＋/Tb3＋ Codoped Phosphate Glass as Down-Shifting Materials for Enhancing Efficiency of Solar Cells

For the purpose of improving conversion efficiency of solar cells by applying the effect of the wavelength conversion of rare earth ions, photo-luminescence and excitation spectrums of Ce3＋-Tb3＋ doped phosphate glass are investigated. Results show that incorporating Ce3＋ ions to Tb3＋-doped phosphate glass can greatly increase the absorption coefficient in the range 300-400 nm and then the energy transfer （ET） from Ce3＋ to Tb3＋ occurs. In addition, increasing Tb3＋ concentration in Ce3＋/Tb3＋ co-doped phosphate glass can greatly enhance the ET efficiency and 545 nm emission intensity. This shows that Ce3＋/Tb3＋ co-doped phosphate glass would be a promising down-shifting material for enhancing the efficiency of solar cells.

Effect of Poly（Ether Urethane） Introduction on the Performance of Polymer Electrolyte for All-Solid-State Dye-Sensitized Solar Cells

The introduction of poly（ether urethane） （PEUR） into polymer electrolyte based on poly（ethylene oxide）, LiI and I2, has significantly increased the ionic conductivity by nearly two orders of magnitudes. An increment of I3- diffusion coefficient is also observed. All-solid-state dye-sensitized solar cells are constructed using the polymer electrolytes. It was found that PEUR incorporation has a beneficial effect on the enhancement of open circuit voltage VOC by shifting the band edge of TiO2 to a negative value. Scanningelectron microscope images indicate the perfect interfacial contact between the TiO2 electrode and the blend electrolyte.

Electromechanical Behavior of Interdigitated SiO2 Cantilever Arrays

Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The pull-in＇＇ effect in dc driving and the hard spring effect＇＇ in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high Q factor. The mass-spring lump model combined with Green＇s function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors.

Polymer solar cells with an inverted device configuration using polyhedral oligomeric silsesquioxane-[60]fullerene dyad as a novel electron acceptor

A polyhedral oligomeric silsesquioxane-[60]fullerene (POSS-C60) dyad was designed and used as a novel electron acceptor for bulk heterojunction (BHJ) polymer solar cells (PSCs) with an inverted device configuration. The studies of time-resolved photoinduced absorption of the pristine thin film of poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis (2-thienyl)-2,1,3-benzothiadiazole)-5,5'-diyl] (SiPCPDTBT) and the composite thin film of SiPCPDTBT:POSS-C60 indicated efficient electron transfer from SiPCPDTBT to POSS-C60 with inhibited back-transfer. BHJ PSCs made by SiPCPDTBT mixed with POSS-C60 yielded the power conversion efficiencies (PCEs) of 1.50%. Under the same operational conditions, PCEs observed from BHJ PSCs made by SiPCPDTBT mixed with [6,6]-phenyl-C61-butyric acid methyl ester were 0.92%. These results demonstrated that POSS-C60 is a potentially good electron acceptor for inverted BHJ PSCs.

Highly efficient green organic light-emitting devices based on terbium complex by employing hole block material as host

In this work,efficient green electroluminescent（EL）devices with simplified device structure were prepared by doping trivalent terbium complex Tb（PMIP）3into hole block material Tm Py PB.The high triplet energy of Tm Py PB helps to confine excitons within light-emitting layer,while the electron transport characteristic of Tm Py PB facilitates the balance of carriers on Tb（PMIP）a3molecules.By optimizing the doping concentration of Tb（PMIP）a3and the thickness of each functional layer,highly efficient green EL device with the structure of ITO/Mo Oa3（3 nm）/TAPC（50 nm）/Tb（PMIP）a3（30 wt%）：Tm Py PB（25 nm）/Tm Py PB（60 nm）/Li F（1 nm）/Al（100 nm）displayed pure Tb^3＋ characteristic emission with maximum current efficiency,power efficiency and brightness up to 47.24 cd/A（external quantum efficiency（EQE）of 14.4%）,43.63 lm/W and 1694 cd/m^2,respectively.At certain brightness of 100 cd/m^2,the device still maintained a current efficiency of 19.96 cd/A（EQE=6.1%）.Such a device design strategy helps to improve the EL performances of Tb（PMIP）a3and to simplify device fabrication processes,thus reduce the fabrication cost.

Research on the temperature characteristic of Love wave device with structure of multi-waveguides used for gas sensor

This paper aimed at extracting optimal structural parameters for Love wave device with structure of multi-waveguides to improve its temperature stability. The theoretical model dealing with the Love wave propagation in multi-waveguides was established first, the dispersion characteristic is depicted by the acoustic propagation theory of stratified media and boundary conditions. Combing with the dispersion characteristics and Tomar＇s method, the optimal structural parameters for the Love wave device with zero temperature coefficient were extracted, and confirmed by the following experimental results. Excellent temperature coefficient of the Love wave device with SU-8/SiO2 on ST-90°X quartz substrate was evaluated experimentally as only 2.16 ppm/℃, which agrees well with the calculated results. The optimized Love wave device is very promising in gas sensing application.

Inverted polymer solar cells with a solution-processed zinc oxide thin film as an electron collection layer

A solution-processed zinc oxide (ZnO) thin film as an electron collection layer for polymer solar cells (PSCs) with an inverted device structure was investigated. Power conversion efficiencies (PCEs) of PSCs made with a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) are 3.50% and 1.21% for PSCs with and without the ZnO thin film, respectively. Light intensity dependence of the photocurrent and the capacitance-voltage measurement demonstrate that the increased PCEs are due to the restriction of the strong bimolecular recombination in the interface when a thin ZnO layer is inserted between the polymer active layer and the ITO electrode. These results demonstrate that the ZnO thin film plays an important role in the performance of PSCs with an inverted device structure.