WU Ma-jiaqi,ZHANG Chi,WANG Wei-gao,YANG Lian-qiao,ZHANG Jian-hua,WEI Bin
Abstract：Due to the simple structure， high light-emitting efficiency， simple manufacturing process and ultra-thin thickness characteristics for organic light-emitting diode （OLED）， flexible OLED devices with bending and folding capabilities can be fabricated by combining flexible substrates. These devices play an important role in flexible display， flexible lighting and other fields. When subjected to external load mainly bending， the inorganic thin films in the flexible OLED devices are prone to failure in the form of cracks， delamination and buckling. These failures reduce the conductivity and destroy the original structure of the devices， thereby affecting their efficiency and reliability. The use of the neutral layer can effectively reduce the strain in the key parts of the devices， thereby reducing or eliminating failure， and the reliability of the devices in the bending state can also be improved. In recent years， a series of studies based on neutral layers of flexible OLED devices have been reported successively. This paper reviews the application of neutral layer technology in flexible OLED devices. Firstly， the concept of neutral layer and the method of determining the single neutral layer’s position are discussed. Then， the application of single neutral layer and multiple neutral layers in practical devices is introduced. Finally， we give an outlook on the future development direction of flexible OLED devices.
Abstract：An all-solid-state quasi-continuous-wave（QCW） Nd：YAG slab laser with a high power was demonstrated. A Nd：YAG slab crystal is adopted for gain medium， a plane-concave cavity is set up， and the laser beam travels along a zigzag path in the slab. An average output power of 3420 W is obtained at a pump power of 9 kW， corresponding to a repetition rate of 1 kHz. The pulse width is 80 μs with a pulse energy of 3.42 J， and the laser beam quality with AO system β is 4.1 times of the diffraction limit.
LIN shu-di,WU haixia,SONG jie,HUANG rui,LYU you-ming
Abstract：The cesium lead bromide perovskite thin films prepared by chemical vapor deposition （CVD） have excellent optoelectronic properties， but the thin films generally have two different phase structures， CsPbBr3 and CsPb2Br5. In our work， CVD method is considered to prepare cesium lead bromide perovskite thin films， and the effects of reaction pressure and N2 flow on CsPb2Br5 in the thin films were studied by X-ray diffraction （XRD）， scanning electron microscopy （SEM）， energy dispersive spectroscopy （EDS） and fluorescence spectrometer. The results show that the change of the reaction pressure has no effect on the CsPb2Br5 phase. However， with the decrease of the N2 flow， part of the CsPb2Br5 phase in the film gradually transforms into the CsPbBr3 phase， and its luminescence also converts from a broadband emission dominated by ~640nm to a narrowband emission dominated by ~525nm. Experimental results reveal that N2 flow is an effective means to control the phase structure and luminescence properties of CsPb2Br5.
Keywords：CVD;cesium lead bromide perovskite film;CsPb2Br5
LI Xuan,ZHENG Hao-cheng,LV Wen-li,XU Su-nan,SUN Lei,PENG Ying-quan
Abstract：Inverted organic light-emitting diodes （IOLEDs） consists of a bottom cathode followed by the formation of an electron injection layer （EIL）， an electron transport layer （ETL）， a light emission layer （EML）， a hole transport layer （HTL） and an anode， which have been widely studied to match the existing n-type thin film transistor technology. In IOLEDs studies， various EIL structures were studied to improve the efficiency of electron injection from the bottom cathode to ETL. In this paper， we report on high efficiency green phosphorescent IOLEDs utilizing ultra-thin Mg as EIL. The ultra-thin Mg films deposited on quartz substrates exhibited excellent light transmittance. IOLEDs based on the 2 nm Mg as EIL demonstrated the optimal device performance， with the maximum current efficiency， the maximum external quantum efficiency and turn-on voltage of 46.5 cd/A， 13.3% and3.06 V， respectively.
Abstract：Channel crosstalk is one important feature of multi-core fiber communication based on space division multiplexing technology， which could affect the signal quality and transmission distance of the broadband fiber amplification system. This paper is focused on the crosstalk problems of a 19-core weak coupling optical fiber， as that can benefit much to develop high-volume communicating fiber based on fiber extrusion technology； Then， the optical coupling theory and finite element method are adopted to complete the numerical simulation of fiber performance， here， key parameters of groove size， core refractive index distribution and their influence on the crosstalk of the fiber are optimized wholly. The simulation results show that the optimized fiber has a low crosstalk of -156dB/100m at 1550nm， which could meet the requirements of future long-distance high-capacity optical fiber communication.
Abstract：Lead-halide perovskite single-crystal （SC） X-ray detectors have received considerable attentions due to their strong stopping power and high carrier transport efficiency. However， the application of lead-halide perovskite for wearable electronics is inhibited by their toxicity. ABX3 hybrid perovskites have versatile structures， which enable the combination of optoelectronic properties and environmentally friendly processing through B-site engineering. In this perspective， we summarize the state of the art in perovskite SC X-ray detectors， providing an overview of B-site engineering from lead-based to lead-free and then metal-free. Later， perspective for future perovskite wearable electronics are proposed. We hope that this perspective will provide a helpful guide for structure design towards highly efficient and eco-friendly perovskite wearable electronics.
Abstract：In order to study the localized states in high-strain InGaAs/GaAs multiple quantum wells （MQWs）， a five-period In0.3Ga0.7As/GaAs MQWs structure was designed and grown by metal-organic chemical vapor deposition （MOCVD） technique in this paper. By means of AFM and temperature-dependent PL， the material disorder in MQWs such as defects and component fluctuation were found， the existence and origin of localized states in MQWs were verified. The influence of the localized states on the spectra at low temperature was different for different measurement positions， exhibiting a bimodal distribution and an "S"-shaped change in peak position， respectively. This further indicated that different disorder within the material lead to different depths of localized states. Based on the fitting of the temperature-bandgap relationship， the potential distribution of the MQWs structure containing localized states was proposed， and the recombination mechanism of the localized state carriers and free carriers was revealed. The optical properties of localized states at different depths under different excitation power densities are studied with the help of excitation power-dependent PL measurement.
Abstract：Perovskite solar cells （PSCs） have undergone unprecedented rapid development in the past decade. A certified power conversion efficiency （PCE） of 25.7% has been achieved， which is comparable to that of commercialized silicon solar cells. However， the inferior stability under heat and moisture has hindered their commercial application. Two-dimensional （2D） or quasi-2D perovskite materials have attracted considerable interest due to their superior structural and environmental stability in comparison with their 3D counterpart. The organic spacers play a very important role in 2D perovskites and they could directly affect the optoelectronic properties of the materials and the PCE of the devices. The organic spacers for 2D PSCs mainly include aliphatic spacers and aromatic spacers. The aromatic spacers have received more and more attention because of their large dielectric constants， superior charge transport properties and tunable self-assembly structures. In this review， we systematically summarize the effects of aromatic spacers on the structural and optoelectronic properties of 2D perovskite materials， and their applications in 2D PSCs.
Keywords：two-dimensional perovskite;solar cell;stability;charge transport
Abstract：Metal halide perovskite solar cells have been able to achieve certified photovoltaic conversion efficiencies of 25.7%， approaching the maximum certified efficiency of 26.7% for crystalline silicon solar cells. It is well known that the component engineering of the crystal structure of ABX3 perovskite materials plays a key role in achieving efficient and stable devices， especially the component engineering of the X-site halide anion， which has received much attention from researchers in recent years. Recently， researchers have carried out several studies on the introduction of pseudo-halide anions as doping components， precursor additives， thin film post-treatment materials， charge transport materials， interfacial passivation， and modifiers for perovskite crystals， and the results demonstrate that pseudo-halide ion modification is an important strategy to improve device efficiency and stability. This review provides a detailed comparison and summary of the various types of pseudo-halide ions currently available for use in perovskite solar cells and provides an in-depth summary of the mechanisms and nature of their effects on perovskite crystal film morphology， photovoltaic properties， carrier migration properties， and device photovoltaic characteristics and stability. At the same time， this paper also provides an outlook and analysis of the currently unexplored pseudo-halide ions， to effectively contribute to the enhancement of the photovoltaic properties of perovskite solar cells in future research.
Keywords：Pseudo-halide ions;Component engineering;perovskite solar cells;Defect passivation
Abstract：Dual-emission fluorescence carbon quantum dots （GP-CQDs） were synthesized by a one-step hydrothermal method using glucose and p-phenylenediamine as carbon sources. The morphology and spectral properties of GP-CQDs were studied. It was found that the GP-CQDs have dual emission fluorescence signals at 348 nm and 452 nm under a single excitation wavelength at 300 nm. When MnO4- was added to the GP-CQDs solution， the fluorescence signal of GP-CQDs at 452 nm was completely quenched； however， the signals at 348 nm keep stable. When S2-was added to the quenching system above， a new fluorescence emission peak was generated at 425 nm. Compared with the original fluorescence peak at 452 nm， the peak was blue-shifted， and the fluorescence intensity at 425 nm was linearly enhanced with the S2- concentration. With the fluorescence peak at 425 nm as the response signal and the 348 nm fluorescence peak as the reference signal， a ratiometric fluorescence sensing probe for S2- determination can be directly constructed. Under the optimal condition， this method shows a good linear relationship in the range of 3.1×10-8 mol/L ~ 8.0×10-6 mol/L and the detection limit was calculated to be 9.41×10-9 mol/L （3σ/K）. The basic mechanism of the proposed method was further discussed. Moreover， this method can be applied to detect S2- in environmental water samples with satisfactory results.
SU Peng,GAO Xin,ZHANG Yue,ZHAO Ren-ze,FU Ding-yang,BO Bao-xue
Abstract：Broad-area stripe semiconductor lasers are widely used in laser pumping， laser processing and other fields. In order to solve the problems of wide output spectrum and small tuning range of Broad-area stripe semiconductor lasers， reflective diffraction gratings with diffraction efficiency of 28% and 55% was used as a feedback element to construct a broad-area 970 nm semiconductor laser with a grating external cavity. The effect of the parameters of semiconductor laser with a grating external cavity in Littrow configuration on its performance （tuning range， power， threshold current， linewidth） was investigated. The experimental results show that the tunable laser output with narrow linewidth can be obtained by optimizing the structure， the tuning range of the outer cavity laser can be increased by increasing the temperature appropriately， and the tuning range of the outer cavity laser can be improved and the threshold current can be reduced by using a grating with higher diffraction efficiency. The maximum wavelength tuning range of semiconductor laser with a grating external cavity based on S-polarization is 27.87nm， the spectral linewidth pressure is narrowed to 0.2nm， and the output power can reach 1.11W.
Keywords：semiconductor laser;diffraction grating;wavelength tuning;threshold current
Abstract：A series of Gd2（1-x-y）ZnTiO6： xBi3+， yEu3+ phosphors with dual emission centers were prepared by high-temperature solidphase method. The structure， luminescence properties and temperature sensing characteristics of the material were systematically studied by X-ray diffraction， scanning electron microscopy， fluorescence spectroscopy， lifetime decay curve and variable temperature emission spectroscopy， respectively. In Gd2ZnTiO6： Bi3+， Eu3+ phosphor， Bi3+ and Eu3+ ions occupy Gd3+ ion position. Under UV excitation， the excitation spectra of Eu3+ and emission spectra of Bi3+ overlap， indicating that there may be energy transfer from Bi3+ to Eu3+ . The fluorescence intensity ratio technique was used to explore the different temperature response characteristics of Bi3+ blue light emission and Eu3+ red light emission. In the temperature range of 293~473 K， the maximum relative temperature sensitivity of Gd2ZnTiO6： Bi3+， Eu3+ phosphors was 1.133% % K-1， and the maximum absolute sensitivity value was 0.73 %K-1 ， respectively. Therefore， Gd2ZnTiO6： Bi3+， Eu3+ phosphor is a potential non-contact optical temperature measurement material.
Keywords：Gd2ZnTiO6;Bi3+， Eu3+;double perovskite;fluorescence energy transfer;optical thermometry;fluorescence intensity ratio
LIU Ping,LI Yu,WEI Chuang-chuang,QIAN Lei,YIN Zhe,DENG Zheng-bo,TANG Ai-wei
Abstract：In recent years， flexible display technologies have attracted widespread attention in the field of folding mobile phones and wearable electronics. Especially， flexible displays are indispensable in these flexible electronics. Among them， quantum dot electroluminescent diodes （QLEDs） have great advantages due to their high color purity， high efficiency and good stability. In this paper， we first give a brief introduction of flexible QLEDs （flex-QLEDs） and summarize the recent development of flex-QLEDs. Then we discussed the device structure and the interface regulation of flex-QLEDs. For flex-QLEDs with multilayer heterostructures， the strategies are categorized into three： anode interface regulation， cathode interface regulation， and light-emitting layer regulation. The regulation focuses on reducing the surface roughness， enhancing the interfacial force， and optimizing the energy level. Finally， the performances of advanced flex-QLEDs are compared and summarized， and the future challenges and opportunities are prospected.
TAN Li,LUO Zhishan,LI Qian,HAN Jiang,ZOU Chao,CHANG Xiaoyong,QUAN Zewei
Abstract：Zero-dimensional （0D） hybrid metal halides with tunable self-trapped exciton （STE） emissions are promising for lighting and displaying applications. In particular， 0D hybrid metal halides with dual-band emissions arising from singlet and triplet STEs have potentials in white-light solid-state lighting. Herein， two 0D hybrid antimony chlorides， （C24H20P）2SbCl5 （I） and （C24H20P）2SbCl5⋅H2O⋅0.5DMF （II） （C24H20P = tetraphenylphosphonium， Ph4P） are reported. The compounds I and II exhibit single broadband red and yellow emissions upon low-energy （LE） photons （e.g. 360 nm） excitation， respectively， arising from their triplet STEs. In addition， upon high-energy （HE） photons （e.g. 310 nm） excitation， the compound II shows a dual-band emission with an additional blue emission band deriving from singlet STEs， exhibiting a warm-white emission. Intriguingly， a reversible phase transformation between I and II is achieved through a dynamic insertion and extraction of DMF and water molecules. This work unravels the effect of small molecules on the crystalline structures and the conversion between single- and dual-band emission properties in 0D antimony halides， which could guide the design of 0D hybrid metal halides for sensor applications.
Abstract：A series of Na3Sc2（1-x）（BO3）3：xTb3+ phosphors were prepared by high-temperature solid-state method， we investigated the crystal structure， surface morphology， elemental composition， and luminescence properties through X-Ray diffraction （XRD）， scanning electron microscope （SEM）， photoluminescence （PL） spectrum， vacuum ultra violet （VUV） fluorescence spectrum， high temperature fluorescence spectrum and fluorescence decay lifetime. The results indicate that the Na3Sc2（1-x）（BO3）3：xTb3+ phosphors can emit bright green light （~553nm） under 242 nm UV excitation. The PL intensity of Na3Sc2（1-x）（BO3）3：xTb3+ reaches the maximum when x = 0.025. Vacuum UV fluorescence spectra show that these phosphors could be also excited by 187 nm deep ultraviolet light. And when the ambient temperature starts to rise from room temperature， the Na3Sc1.95 （BO3）3：0.025Tb3+ exhibit an anti-thermal-quenching phenomenon. When the temperature reaches 473 K， the luminescence intensity of the sample reached the highest， 109.3% of that at room temperature （298 K）， The strong emission and high thermal stability of these new green phosphors indicate the certain potential application in lighting and display fields.
Keywords：phosphor;Tb3+ doped;anti-thermal-quenching;lighting and display
Abstract：In recent years， photodetectors have been an important research subject due to their potential applications in imaging， communication， medical analysis， environmental monitoring， and biological sensing. Employing the ferroelectric materials featured with typical ferroelectric polarization as absorbers will simplify the device structure and lower the cost. In the current work， self-powered ultraviolet photodetectors have been fabricated based on ferroelectric PbZr0.52Ti0.48O3（PZT）thin films. The ferroelectric PZT thin films were prepared using a sol-gel method. Morphological， structural， electrical， and ferroelectric characterizations showed that the as-grown ferroelectric PZT thin films possessed a smooth and dense surface， low density， high remnant polarization（2Pr=35.2 μC/cm2）and coercive electric field（~ 105 V/cm）. On this basis， high-performance self-powered ultraviolet photodetectors with Au/PZT/FTO structure have been fabricated. Interestingly， under the bias voltage of 0 V， the responsivity and detectivity are as high as 0.072 A/W and 4.35×1011 Jones， respectively， which are higher than most of state-of-the-art reported results. The results shown in this paper highlight the superiorities of ferroelectric PZT-based self-powered ultraviolet photodetectors and provide a promising strategy for the development of high-performance self-powered photodetectors with simple device structures in future.
Abstract：At present， promoting the transition of the energy industry to a system that is effective， clean， and flexible has currently emerged as the key to tackling the world's environmental issues. The progress of the Internet of Things and the technology revolution have created a new demand to combine solar equipment and cells into a single component in order to collect energy in a wider range of application situations. Flexible perovskite solar cells （FPSCs） based on flexible polymers such as polyethylene terephthalate （PET） and polyethylene naphthalate （PEN） has emerged as a rising star in the third generation of solar cells in the past decade due to their high energy conversion efficiency， high flexibility， low preparation cost and certain portability. In addition， it has a natural affinity for environmentally friendly and economically beneficial roll-to-roll manufacturing technology which will enable it to play a key role in the development of flexible self-powered electronic products， large-scale building integrated photovoltaic （BIPV） and space aerospace. In this review， we emphatically discuss the critical role and briefly summarize the most recent developments of the flexible transparent conductive substrate， low-temperature processed charge transporting layer， and mechanically resilient perovskite film in single and tandem FPSCs. Finally， combined with the large-scale manufacturing technology of FPSCs， we offer some insight into the reliability and operational stability of the package and discuss potential practical applications in large-area modules and so forth.
Keywords：flexible;perovskite solar cell;flexible perovskite tandem solar cell;photovoltaic module
Abstract：As a new generation of display technology， organic light emitting diodes （OLEDs） have been successfully commercialized， but efforts are still needed to develop efficient and stable blue OLED devices. In recent years， a new mechanism combining thermally activated delayed fluorescence （TADF） sensitizers and narrow spectrum final emitters， namely TADF sensitized fluorescence （TSF） has attracted more and more attention. With the continuous innovation of materials and device structures， performances of blue OLEDs based on this mechanism have been significantly improved. Here， focusing on the development of stable and efficient blue sensitizers， the progress in efficiency and lifetime of blue TSF devices in recent years is reviewed， and the future development goals and challenges are further discussed.
Keywords：organic light emitting diode;thermally activated delayed fluorescence;TADF sensitized fluorescence;efficient and stable blue OLED devices
Abstract：Cu（I）-based metal halides， as a new generation of environment-friendly luminescent materials， have attracted extensive attention. Herein， a novel zero-dimensional Cu（I）-based metal halide （C12H24O6）NaCuBr2 was prepared by solution assisted crystallization method. Under 365 nm excitation， （C12H24O6）NaCuBr2 single crystal exhibits ultra-broadband orange red emission with the full width at half maximum of 346 nm and the photoluminescence quantum yield of 42.6%. Theoretical calculation and experimental studies on the low temperature and excitation-dependent emission spectra show that the ultra-broadband emission peaking at 700 nm is derived from the formation of a degenerate energy level by the interaction between the 3d orbital of the Cu+ ion and the 4p orbital of the Br- ion. At low temperature， the degeneracy of the energy level is reduced due to the lattice distortion， and the emission peak at 700 nm is split into two emission peaks at 629 nm and 735 nm， respectively. In addition， the electron is excited to a higher energy level of S3 for （C12H24O6）NaCuBr2 under high energy excitation， which corresponds to the emission peak at 480 nm observed at 77 K. The white light-emitting diode （LED） device prepared using （C12H24O6）NaCuBr2 possesses a color rendering index as high as 90.6， indicating their potential application in the field of full-spectrum lighting.
Keywords：Zero-dimensional structure;Cu-based metal halides;full-spectrum lighting
Abstract：All-inorganic zero-dimensional （0D） metal halides， owing to their intriguing optical properties and easy solution processibility， are emerging as a new generation of luminescent materials and as an alternative to lead halide perovskites for various applications such as solid-state lighting and photodetectors. Herein， a new yellow phosphor is developed based on Cd2+-doped Cs2ZnCl4， which exhibits intense broadband and long-lived （11.4 ms） photoluminescence （PL） at 565 nm upon 270 nm excitation， with a PL quantum yield up to 46.0%. Temperature-dependent PL spectroscopic analyses reveal that the broadband PL originates from the forbidden 3E → 1A1 transition of Cd2+. Specifically， localized exciton emission is observed at low temperatures below 170 K， in parallel with efficient energy transfer from the localized excitons to Cd2+. Besides， the phosphor displays an excellent anti-thermal quenching property， remaining 90% PL intensity at 150 °C in comparison with that at room temperature. These findings provide not only new insights into the excited-state dynamics of Cd2+ in metal halides， but also a new avenue for the exploration of novel and efficient luminescent materials based on 0D metal halides.