Exciton‐Adjustable Interlayers for High Efficiency,Low Efficiency Roll‐Off,and Lifetime Improved Warm White Organic Light‐Emitting Diodes (WOLEDs) Based on a Delayed Fluorescence Assistant Host

Recently, a new route to achieve 100% internal quantum efficiency white organic light‐emitting diodes (WOLEDs) is proposed by utilizing noble‐metal‐free thermally activated delayed fluorescence (TADF) emitters due to the radiative contributions of triplet excitons by effective reverse intersystem crossing. However, a systematic understanding of their reliability and internal degradation mechanisms is still deficient. Here, it demonstrates high performance and operational stable purely organic fluorescent WOLEDs consisting of a TADF assistant host via a strategic exciton management by multi‐interlayers. By introducing such interlayers, carrier recombination zone could be controlled to suppress the generally unavoidable quenching of long‐range triplet excitons, successfully achieving remarkable external quantum efficiency of 15.1%, maximum power efficiency of 48.9 lm W⁻¹, and extended LT50 lifetime (time to 50% of initial luminance of 1000 cd m⁻²) exceeding 2000 h. To this knowledge, this is the first pioneering work for realizing high efficiency, low efficiency roll‐off, and operational stable WOLEDs based on a TADF assistant host. The current findings also indicate that broadening the carrier recombination region in both interlayers and yellow emitting layer as well as restraining exciplex quenching at carrier blocking interface make significant roles on reduced efficiency roll‐off and enhanced operational lifetime.     

Highly Efficient and Color-Stable Thermally Activated Delayed Fluorescence White Light-Emitting Diodes Featured with Single-Doped Single Emissive Layers

Despite their merits of environmental friendliness, low cost, and large-scale production, thermally activated delayed fluorescence (TADF) based white organic light-emitting diodes (WOLEDs) for daily lighting applications still face the formidable challenges of structural simplification and controllable exciton allocation. Here, the state-of-the-art full-TADF WOLEDs with features of the single-doped single emissive layers (EMLs) and ultrasimple trilayer structure are demonstrated. The EMLs are binary systems as yellow TADF emitter (4CzTPNBu) doped blue TADF matrix (ptBCzPO₂TPTZ) with the large steric hindrance and mismatched frontier molecular orbital energy levels to effectively restrain excessive blue-to-yellow triplet exciton transfer and host-dopant interaction induced triplet quenching. Simultaneously, Förster resonance energy transfer is utilized to optimize exciton allocation for the balance of blue and yellow emissions, giving rise to the photoluminescence quantum yield beyond 90%. Consequently, these single-doped EMLs endow their cool white, pure white, and warm white diodes with the high-quality and ultrastable white light and the 100% exciton utilization efficiencies through the extremely simple structures, making them competent for the diverse daily lighting applications.     

All-Oxide Transparent Photodetector Array for Ultrafast Response through Self-Powered Excitonic Photovoltage Operation

Can photodetectors be transparent and operate in self-powered mode? Is it possible to achieve invisible electronics, independent of the external power supply system, for on-site applications? Here, a ZnO/NiO heterojunction-based high-functional transparent ultraviolet (UV) photodetector operating in the self-powered photovoltaic mode with outstanding responsivity and detectivity values of 6.9 A W⁻¹ and 8.0 × 10¹² Jones, respectively, is reported. The highest I_UV/I_dark value of 8.9 × 10⁴ is attained at a wavelength of 385 nm, together with a very small dark current value of 9.15 × 10⁻¹² A. A large-scale sputtering method is adopted to deposit the heterostructure of n-ZnO and p-NiO sequentially. This deposition instinctively forms an abrupt junction, resulting in a high-quality heterojunction device. Moreover, developing a ZnO/NiO-heterojunction–based 4 × 5 matrix array with an output photovoltage of 4.5 V is preferred for integrating photodetectors into sensing and imaging systems. This transparent UV photodetector exhibits the fastest photo-response time (83 ns) reported for array configurations, which is achieved using an exciton-induced photovoltage based on a neutral donor–bound exciton. Overall, this study provides a simple method for achieving a high-performance large-scale transparent UV photodetector with a self-powered array configuration.     

Limitations and Perspectives on Triplet‐Material‐Based Organic Photovoltaic Devices

Organic photovoltaic cells (OPVs) have attracted broad attention and become a very energetic field after the emergence of nonfullerene acceptors. Long‐lifetime triplet excitons are expected to be good candidates for efficiently harvesting a photocurrent. Parallel with the development of OPVs based on singlet materials (S‐OPVs), the potential of triplet materials as photoactive layers has been explored. However, so far, OPVs employing triplet materials in a bulk heterojunction have not exhibited better performance than S‐OPVs. Here, the recent progress of representative OPVs based on triplet materials (T‐OPVs) is briefly summarized. Based on that, the performance limitations of T‐OPVs are analyzed. The shortage of desired triplet materials with favorable optoelectronic properties for OPVs, the tradeoff between long lifetime and high binding energy of triplet excitons, as well as the low charge mobility in most triplet materials are crucial issues restraining the efficiencies of T‐OPVs. To overcome these limitations, first, novel materials with desired optoelectronic properties are urgently demanded; second, systematic investigation on the contribution and dynamics of triplet excitons in T‐OPVs is necessary; third, close multidisciplinary collaboration is required, as proved by the development of S‐OPVs.     

热压细晶高功率微波铁氧体

利用热压工艺制备出了细晶粒（２μｍ）ＹＩＧ铁氧体材料,测量了其微波性能,结果表明,细晶粒铁氧体的自旋波线宽ΔＨｋ显著提高,其ΔＨｋ与晶粒尺寸有ａ０＾－１．７的相依关系。同时,分析讨论了细晶粒铁氧体铁磁共振线宽ΔＨ的致宽因素。     

一种窄线宽的高重复频率窄脉宽主动调Q光纤激光器

提出并演示了一种基于声光调制器(AOM)主动调Q的环形腔双包层光纤激光器获得窄线宽、窄脉宽和高重复频率激光脉冲的方法。通过在腔内采用以双包层增益光纤作为输入尾纤的泵浦剥离器来缩短腔长,可以降低增益光纤正向放大自发辐射(ASE)的反射,抑制其ASE的增益自饱和效应,使腔内有效增益增大,窄线宽调Q脉冲可在环形腔中快速建立,从而不仅可使调Q脉冲脉宽变窄,还允许其重复频率大幅提升。在7 W泵浦功率下,所提出的调Q光纤激光器获得了线宽和脉宽分别窄至0.16 nm和10.4 ns、重复频率高达150 kHz的调Q激光脉冲。     

Ultrafast Responsive and Low-Energy-Consumption Poly(3-hexylthiophene)/Perovskite Quantum Dots Composite Film-Based Photonic Synapse

Emulation of photonic synapses through photo-recordable devices has aroused tremendous discussion owing to the low energy consumption, high parallel, and fault-tolerance in artificial neuromorphic networks. Nonvolatile flash-type photomemory with short photo-programming time, long-term storage, and linear plasticity becomes the most promising candidate. Nevertheless, the systematic studies of mechanism behind the charge transfer process in photomemory are limited. Herein, the physical properties of APbBr₃ perovskite quantum dots (PQDs) on the photoresponsive characteristics of derived poly(3-hexylthiophene-2,5-diyl) (P3HT)/PQDs-based photomemory t hrough facile A-site substitution approach are explored. Benefitting from the lowest valance band maximum and longest exciton lifetime of FAPbBr₃ quantum dot (FA-QDs), P3HT/FA-QDs-derived photomemory not only exhibits shortest photoresponsive characteristic time compared to FA_0.5Cs_0.5PbBr₃ quantum dots (Mix-QDs) and CsPbBr₃ quantum dots (Cs-QDs) but also displays excellent ON/OFF current ratio of 2.2 upon an extremely short illumination duration of 1 ms. Moreover, the device not only achieves linear plasticity of synapses by optical potentiation and electric depression, but also successfully emulates the features of photon synaptic such as pair-pulse facilitation, long-term plasticity, and multiple spike-dependent plasticity and exhibits extremely low energy consumption of 3 × 10⁻¹⁷ J per synaptic event.     

Efficiency Breakthrough of Fluorescence OLEDs by the Strategic Management of “Hot Excitons” at Highly Lying Excitation Triplet Energy Levels

Aggregation-induced emission (AIE) and hybridized local and charge-transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high-efficiency organic light-emitting diodes (OLEDs) by harnessing “hot excitons” at the high-lying triplet exciton states (T_n, n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of T_n→T_n−1. Herein, experimental results and theoretical calculations demonstrate the “hot exciton” process between the high-lying triplet state T₃ and the lowest excited singlet state S₁ in an AIE material 4⁗-(diphenylamino)-2″,5″-diphenyl-[1,1″:4′,1″:4″,1′″:4′″,1⁗-quinquephenyl]-4-carbonitrile (TPB-PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the “hot exciton” process and inhibit the T₃→T₂ loss by doping a blue fluorescent emitter in TPB-PAPC. Finally, the doped TPB-PAPC blue OLEDs achieve a maximum external quantum efficiency (EQE_max) of 9.0% with a small efficiency roll-off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2-(4-(10-(3-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQE_max of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high-performance “hot exciton” molecules and the fabrication of high-performance blue fluorescence OLEDs.     

千赫兹量级窄线宽半导体激光器研究进展

窄线宽半导体激光器由于其高单色性、低频率噪声、高可调谐性等优点,广泛应用于高速相干光通信、分布式传感、激光雷达等领域.随着高品质因子(Q)光学谐振腔、硅光异构集成芯片等技术的发展,窄线宽半导体激光器近十年经历了革命式发展,线宽压缩至千赫兹(kHz)量级,甚至到亚千赫兹量级.文章阐述了千赫兹量级窄线宽半导体激光器的最新进展,针对不同压缩线宽机制的窄线宽激光器进行了分类介绍,深入讨论了优化耦合系数、减少外腔损耗等对窄线宽激光器性能的影响,并针对未来应用需求展望了千赫兹量级窄线宽激光器在进一步压缩线宽、提升输出光功率方面的发展方向.