Solution‐Processed Lead Iodide for Ultrafast All‐Optical Switching of Terahertz Photonic Devices

Solution‐processed lead iodide (PbI₂) governs the charge transport characteristics in the hybrid metal halide perovskites. Besides being a precursor in enhancing the performance of perovskite solar cells, PbI₂ alone offers remarkable optical and ultrasensitive photoresponsive properties that remain largely unexplored. Here, the photophysics and the ultrafast carrier dynamics of the solution processed PbI₂ thin film is probed experimentally. A PbI₂ integrated metamaterial photonic device with switchable picosecond time response at extremely low photoexcitation fluences is demonstrated. Further, findings show strongly confined terahertz field induced tailoring of sensitivity and switching time of the metamaterial resonances for different thicknesses of PbI₂ thin film. The approach has two far reaching consequences: the first lead‐iodide‐based ultrafast photonic device and resonantly confined electromagnetic field tailored transient nonequilibrium dynamics of PbI₂ which could also be applied to a broad range of semiconductors for designing on‐chip, ultrafast, all‐optical switchable photonic devices.     

A Novel Potassium‐Ion‐Based Dual‐Ion Battery

In this work, combining both advantages of potassium‐ion batteries and dual‐ion batteries, a novel potassium‐ion‐based dual‐ion battery (named as K‐DIB) system is developed based on a potassium‐ion electrolyte, using metal foil (Sn, Pb, K, or Na) as anode and expanded graphite as cathode. When using Sn foil as the anode, the K‐DIB presents a high reversible capacity of 66 mAh g^?1 at a current density of 50 mA g^?1 over the voltage window of 3.0–5.0 V, and exhibits excellent long‐term cycling performance with 93% capacity retention for 300 cycles. Moreover, as the Sn foil simultaneously acts as the anode material and the current collector, dead load and dead volume of the battery can be greatly reduced, thus the energy density of the K‐DIB is further improved. It delivers a high energy density of 155 Wh kg^?1 at a power density of 116 W kg^?1, which is comparable with commercial lithium‐ion batteries. Thus, with the advantages of environmentally friendly, cost effective, and high energy density, this K‐DIB shows attractive potential for future energy storage application.     

Aggregation‐Induced Dual‐Phosphorescence from Organic Molecules for Nondoped Light‐Emitting Diodes

Aggregation‐induced emission (AIE) is a beneficial strategy for generating highly effective solid‐state molecular luminescence without suffering losses in quantum yield. However, the majority of reported AIE‐active molecules exhibit only strong fluorescence, which is not ideal for electrical excitation in organic light‐emitting diodes (OLEDs). By introducing various substituent groups onto the biscarbazole compound, a series of molecular materials with aggregation‐induced phosphorescence (AIP) is designed, which exhibits two distinctly different phosphorescence bands and an absolute solid‐state room‐temperature phosphorescence quantum yield up to 64%. Taking advantage of the AIE feature, the AIP molecules are fabricated into OLEDs as a homogeneous light‐emitting layer, which allows for relatively small efficiency roll‐off and shows an external electroluminescence quantum yield of up to 5.8%, more than the theoretical limit for purely fluorescent OLED devices. The design showcases a promising strategy for the production of cost‐effective and highly efficient OLED technology.     

Ultrafast Magnetization Manipulation Using Single Femtosecond Light and Hot‐Electron Pulses

Current‐induced magnetization manipulation is a key issue for spintronic applications. This manipulation must be fast, deterministic, and nondestructive in order to function in device applications. Therefore, single‐ electronic‐pulse‐driven deterministic switching of the magnetization on the picosecond timescale represents a major step toward future developments of ultrafast spintronic systems. Here, the ultrafast magnetization dynamics in engineered Gd_x [FeCo]_1?x ‐based structures are studied to compare the effect of femtosecond laser and hot‐electron pulses. It is demonstrated that a single femtosecond hot‐electron pulse causes deterministic magnetization reversal in either Gd‐rich and FeCo‐rich alloys similarly to a femtosecond laser pulse. In addition, it is shown that the limiting factor of such manipulation for perpendicular magnetized films arises from the formation of a multidomain state due to dipolar interactions. By performing time‐resolved measurements under various magnetic fields, it is demonstrated that the same magnetization dynamics are observed for both light and hot‐electron excitation, and that the full magnetization reversal takes place within 40 ps. The efficiency of the ultrafast current‐induced magnetization manipulation is enhanced due to the ballistic transport of hot electrons before reaching the GdFeCo magnetic layer.     

All‐Dielectric Active Terahertz Photonics Driven by Bound States in the Continuum

The remarkable emergence of all‐dielectric meta‐photonics governed by the physics of high‐index dielectric materials offers a low‐loss platform for efficient manipulation and subwavelength control of electromagnetic waves from microwaves to visible frequencies. Dielectric metasurfaces can focus electromagnetic waves, generate structured beams and vortices, enhance local fields for advanced sensing, and provide novel functionalities for classical and quantum technologies. Recent advances in meta‐photonics are associated with the exploration of exotic electromagnetic modes called the bound states in the continuum (BICs), which offer a simple interference mechanism to achieve large quality factors (Q) through excitation of supercavity modes in dielectric nanostructures and resonant metasurfaces. Here, a BIC‐driven terahertz metasurface with dynamic control of high‐Q silicon supercavities that are reconfigurable at a nanosecond timescale is experimentally demonstrated. It is revealed that such supercavities enable low‐power, optically induced terahertz switching and modulation of sharp resonances for potential applications in lasing, mode multiplexing, and biosensing.     

A Solution‐Processed Ultrafast Optical Switch Based on a Nanostructured Epsilon‐Near‐Zero Medium

All the optical properties of materials are derived from dielectric function. In spectral region where the dielectric permittivity approaches zero, known as epsilon‐near‐zero (ENZ) region, the propagating light within the material attains a very high phase velocity, and meanwhile the material exhibits strong optical nonlinearity. The interplay between the linear and nonlinear optical response in these materials thus offers unprecedented pathways for all‐optical control and device design. Here the authors demonstrate ultrafast all‐optical modulation based on a typical ENZ material of indium tin oxide (ITO) nanocrystals (NCs), accessed by a wet‐chemistry route. In the ENZ region, the authors find that the optical response in these ITO NCs is associated with a strong nonlinear character, exhibiting sub‐picosecond response time (corresponding to frequencies over 2 THz) and modulation depth up to ≈160%. This large optical nonlinearity benefits from the highly confined geometry in addition to the ENZ enhancement effect of the ITO NCs. Based on these ENZ NCs, the authors successfully demonstrate a fiber optical switch that allows switching of continuous laser wave into femtosecond laser pulses. Combined with facile processibility and tunable optical properties, these solution‐processed ENZ NCs may offer a scalable and printable material solution for dynamic photonic and optoelectronic devices.     

Additive‐Assisted Novel Dual‐Salt Electrolyte Addresses Wide Temperature Operation of Lithium–Metal Batteries

In this study, self‐synthesized lithium trifluoro(perfluoro‐tert‐butyloxyl)borate (LiTFPFB) is combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to formulate a novel 1 m dual‐salt electrolyte, which contains lithium difluorophosphate (LiPO₂F₂) additive and dominant carbonate solvents with low melting point and high boiling point. The addition of LiPO₂F₂ into this novel dual‐salt electrolyte dramatically improves cycleability and rate capability of a LiNi_0.5Mn_0.3Co_0.2O₂/Li (NMC/Li) battery, ranging from ?40 to 90 °C. The NMC/Li batteries adopt a Li–metal anode with low thickness of 100 µm (even 50 µm) and a moderately high cathode mass loading level of 10 mg cm^?2. For the first time, this paper provides valuable perspectives for developing practical lithium–metal batteries over a wide temperature range.     

Potassium‐Based Dual Ion Battery with Dual‐Graphite Electrode

A potassium ion battery has potential applications for large scale electric energy storage systems due to the abundance and low cost of potassium resources. Dual graphite batteries, with graphite as both anode and cathode, eliminate the use of transition metal compounds and greatly lower the overall cost. Herein, combining the merits of the potassium ion battery and dual graphite battery, a potassium‐based dual ion battery with dual‐graphite electrode is developed. It delivers a reversible capacity of 62 mA h g^?1 and medium discharge voltage of ≈3.96 V. The intercalation/deintercalation mechanism of K⁺ and PF₆^? into/from graphite is proposed and discussed in detail, with various characterizations to support.     

A Dual‐Stimuli‐Responsive Sodium‐Bromine Battery with Ultrahigh Energy Density

Stimuli‐responsive energy storage devices have emerged for the fast‐growing popularity of intelligent electronics. However, all previously reported stimuli‐responsive energy storage devices have rather low energy densities (<250 Wh kg^–1) and single stimuli‐response, which seriously limit their application scopes in intelligent electronics. Herein, a dual‐stimuli‐responsive sodium‐bromine (Na//Br₂) battery featuring ultrahigh energy density, electrochromic effect, and fast thermal response is demonstrated. Remarkably, the fabricated Na//Br₂ battery exhibits a large operating voltage of 3.3 V and an energy density up to 760 Wh kg^?1, which outperforms those for the state‐of‐the‐art stimuli‐responsive electrochemical energy storage devices. This work offers a promising approach for designing multi‐stimuli‐responsive and high‐energy rechargeable batteries without sacrificing the electrochemical performance.