Anchoring polysulfide with artificial solid electrolyte interphase for dendrite-free and low N/P ratio Li-S batteries

Lithium sulfur batteries are regarded as a promising candidate for high-energy-density energy storage devices.However,the lithium metal anode in lithium-sulfur batteries encounters the problem of lithium dendrites and lithium metal consumption caused by polysulfide corrosion.Herein we design a dualfunction PMMA/PPC/LiNO3composite as an artificial solid electrolyte interphase(PMCN-SEI)to protect Li metal anode.This SEI offers multiple sites of C=O for polysulfide anchoring to constrain corrosion of Li metal anode.The lithiated polymer group and Li3N in PMCN-SEI can homogenize lithium-ion deposition behavior to achieve a dendrite-free anode.As a result,the PMCN-SEI protected Li metal anode enables the Li||Li symmetric batteries to maintain over 300 cycles(1300 h)at a capacity of 5 m Ah cm^(-2),corresponding to a cumulative capacity of 3.25 Ah cm^(-2).Moreover,Li-S batteries assembled with 20μm of Li metal anode(N/P=1.67)still deliver an initial capacity of 1166 m A h g-1at 0.5C.Hence,introducing polycarbonate polymer/inorganic composite SEI on Li provides a new solution for achieving the high energy density of Li-S batteries.

Influence of O2 Flux on Compositions and Properties of ITO Films Deposited at Room Temperature by Direct-Current Pulse Magnetron Sputtering

Indium tin oxide （ITO） films were deposited on glass substrates at room temperature by dc pulse magnetron sputtering. Varying 02 flux, ITO films with different properties are obtained. Both x-ray diffractometer and x-ray photoelectron spectrometer are used to study the change of crystalline structures and bonding structures of ITO films, respectively. Electrical properties are measured by four-point probe measurements. The results indicate that the chemical structures and compositions of ITO films strongly depend on the O2 flux. With increasing O2 flux, ITO films display better crystallization, which could decrease the resistivity of films. On the contrary, ITO films contain less O vacancies with increasing O2 flux, which could worsen the conductive properties of films. Without any heat treatment onto the samples, the resistivity of the ITO film could reach 6.0 × 10^-4 Ω·cm, with the optimal deposition parameter of 0.2 scem O2 flux.

Effect of In_xGa_(1-x)As Interlayer on Surface Morphology and Optical Properties of GaSb/InGaAs Type-Ⅱ Quantum Dots Grown on InP (100) Substrates

The effects of indium composition in InGaAs interlayer and on optical properties of GaSb/InGaAs QD material on morphology of GaSb/InGaAs quantum dots （QDs） system are studied. AFM images show that the change of the indium composition in InGaAs interlayer can alter the GaSb QD morphology. It is found that low indium composition in InGaAs interlayer can promote the formation of QDs, while high indium composition can inhibit the formation of QDs. The photoluminescence （PL） spectra of GaSb/InGaAs QDs at 8 K under low excitation power indicate that the third root of the excitation power is linear with the peak position, which provides a direct evidence for their luminescence belonging to type-Ⅱ material optical transition. The PL spectra at 8 K under an excitation power of 90row show that the optical properties of GaSb/InGaAs QD material system can be affected by the indium composition in the InGaAs interlayer, and the PL peak position is linear with the indium composition. The optical properties of GaSb/InGaAs QDs can be improved by adjusting the indium composition in the InGaAs interlayer.

Alleviating hysteresis and improving device stability of perovskite solar cells via alternate voltage sweeps

The anomalous hysteresis in a perovskite solar cell induced by an asymmetric field is confirmed by a capacitance–voltage measurement. By applying several cycles of alternating reverse and forward scans, this hysteresis phenomenon is obviously alleviated, resulting in a hysteresis-less state in the perovskite solar cell. Meanwhile, the open-circuit voltage and power conversion efficiency of the perovskite solar cell are enhanced by 55.74% and 61.30%, respectively, while the current density and fill factor keep almost invariable. The operation of alleviating hysteresis is essential for further research and is likely to bring in performance gains.

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet（about 350 nm-360 nm） light-emitting diodes（LEDs） each with specifically designed irregular sawtooth electron blocking layer（EBL） by using the APSYS simulation program.The internal quantum efficiencies（IQEs）,light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAlxGa1-xN irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.

Enhanced performance of AlGaN-based ultraviolet light-emitting diodes with linearly graded AlGaN inserting layer in electron blocking layer

The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.

Theoretical analysis of semi/non-polar In GaN/GaN light-emitting diodes grown on silicon substrates

A theoretical study of polar and semi/non-polar InGaN/GaN light-emitting diodes（LEDs） with different internal surface polarization charges, which can be grown on Si substrates, is conducted by using APSYS software. In comparison with polar structure LEDs, the semi-polar structure exhibits a higher concentration of electrons and holes and radiative recombination rate, and its reduced built-in polarization field weakens the extent of band bending which causes the shift of peak emission wavelength. So the efficiency droop of semi-polar InGaN/GaN LEDs declines obviously and the optical power is significantly improved. In comparison with non-polar structure LEDs, although the concentration of holes and electrons as well as the radiative recombination rate of the semi-polar structure are better in the last two quantum wells（QWs） approaching the p-Ga N side, the uniformity of distribution of carriers and radiative recombination rate for the nonpolar structure is better. So the theoretical analysis indicates that the removal of the internal polarization field in the MQWs active regions for non-polar structure LEDs contributes to the uniform distribution of electrons and holes, and decreases the electron leakage. Thus it enhances the radiative recombination rate, and further improves the IQEs and optical powers, and shows the best photoelectric properties among these three structures.

Enhanced cycle stability of aprotic Li-O_(2) batteries based on a self-defensed redox mediator

LiBr as a promising redox mediator(RM)has been applied in Li-O_(2)batteries to improve oxygen evolution reaction kinetics and reduce overpotentials.However,the redox shuttle of Br_(3)^-can induce the unexpected reactions and thus cause the degradation of LiBr and the corrosion of Li anode,resulting in the poor cyclability and the low round-trip efficiency.Herein,MgBr_(2)is firstly employed with dual functions for Li-O_(2)batteries,which can serve as a RM and a SEI film-forming agent.The Br^(–)is beneficial to facilitating the decomposition of Li_(2)O_(2)and thus decreasing the overpotential.Additionally,a uniform SEI film containing Mg and MgO generates on Li anode surface by the in-situ spontaneous reactions of Mg^(2+)and Li anode in an O_(2)environment,which can suppress the redox shuttle of Br_(3)^-and improve the interface stability of Li anode and electrolyte.Benefiting from these advantages,the cycle life of Li-O_(2)battery with MgBr_(2)electrolyte is significantly extended.

Effect of Doped Boron on the Properties of ZnO Thin Films Prepared by Sol-gel Spin Coating

Transparent conductive boron-doped ZnO thin films were prepared by sol-gel spin coating method. The effect of doped boron concentration on the properties of the films was systematically discussed. The films were characterized by X-ray diffraction, atomic force microscopy, spectrophotometry, and Hall effect measurement system. All the doped and undoped ZnO films were of a single hexagonal structure, and showed a preferred orientation of （002）. The particle size and surface roughness of the films decreased with increased doped boron concentration. All the films exhibited an average transmittance of approximate 90% in visible-light region and an energy gap of about 3.3 cV. The maximum carrier concentration, the highest carrier mobility and the lowest resistivity were observed at a doped boron concentration of 0.5%（molar fraction）. Based on these results, we suggested that the saturation concentration of doped boron in ZnO film is 0.5%（molar fraction）.

Enhancement of blue InGaN light-emitting diodes by using AlGaN increased composition-graded barriers

The characteristics ofnitride-based blue light-emitting diodes （LEDs） with A1GaN composition-graded barriers are analyzed numerically. The carrier concentrations in the quantum wells （QWs）, the energy band di- agrams, the electrostatic fields, and the light output power are investigated by APSYS software. The simulation results show that the LED with AlGaN composition-graded barriers has a better performance than its AlGaN/InGaN counterpart owing to the increase of hole injection and the enhancement of electron confinement. The simulation results also suggest that the output power is enhanced significantly and the efficiency droop is markedly improved when the AIGaN barriers are replaced by AlGaN composition-graded barriers.