Interface Engineering Enhances the Photovoltaic Performance of Wide Bandgap FAPbBr3 Perovskite for Application in Low-Light Environments

Underwater solar cells (UWSCs) provide an ideal alternative to the energy supply for long-endurance autonomous underwater vehicles. However, different from conventional solar cells situated on land or above water, UWSCs give preference to use wide bandgap semiconductors (≥1.8 eV) as light absorber to match underwater solar spectra. Among wide bandgap semiconductors, FAPbBr₃ perovskite is under prime consideration owing to its matching optical bandgap (≈2.3 eV), outstanding photoelectric properties, easier processability, etc. Unfortunately, for FAPbBr₃ solar cells, substantial interface defects greatly limit the charge carrier extraction efficiency, thus limiting the device performance, especially in underwater low-light environments. This study employs a molecular self-assembly strategy to effectively eliminate the interfacial defects. As a result, a great improvement in power conversion efficiency (PCE) from 6.44% to 7.49% is obtained, which is among the best efficiency reported for inverted FAPbBr₃ solar cells up to date. Besides, a champion PCE of 30% is obtained under 520 nm monochromatic light irradiation (4.8 mW cm⁻²). These results demonstrate that FAPbBr₃ solar cells present a tremendously promising application in UWSCs.     

Machine Vision Based on an Ultra-Wide Bandgap 2D Semiconductor AsSbO3

Facing the future development trend of miniaturization and intelligence of electronic devices, solar-blind photodetectors based on ultrawide-bandgap 2D semiconductors have the advantages of low dark current, and high signal-to-noise ratio, as well as the features of micro-nanometer miniaturization and multi-functionalization of 2D material devices, which have potential applications in the photoelectric sensor part of high-performance machine vision systems. This study reports a 2D oxide semiconductor, AsSbO₃, with an ultrawide bandgap (4.997 eV for monolayer and 4.4 eV for multilayer) to be used to fabricate highly selective solar-blind UV photodetectors, of which the dark current as low as 100 fA and rejection ratio of UV-C and UV-A reaches 7.6 × 10³. Under 239 nm incident light, the responsivity is 105 mA W⁻¹ and the detectivity is 7.58 × 10¹² Jones. Owing to the remarkable anisotropic crystal structure, AsSbO₃ also shows significant linear dichroism and nonlinear optical properties. Finally, a simple machine vision system is simulated by combining the real-time imaging function in solar-blind UV with a convolutional neural network. This study enriches the material system of ultrawide-bandgap 2D semiconductors and provides insight into the future development of high-performance solar-blind UV optoelectronic devices.     

Controllable Modulation of Efficient Phosphorescence Through Dynamic Metal-Ligand Coordination for Reversible Anti-Counterfeiting Printing of Thermal Development

Dynamically tunable room-temperature phosphorescence (RTP) organic materials have attracted considerable attention in recent years due to their great potential over a wide variety of advanced applications. However, the precise regulation of the intersystem crossing (ISC) process for efficient RTP materials with dynamically modulated properties in a rigid environment is challenging. Herein, an effective strategy for RTP material preparation with controllably regulated properties is developed via the construction of dynamic metal-ligand coordination in a host-guest doped system. The coordination interaction promotes ISC and phosphorescence emission of the guest, thus allowing the modulation of the photophysical properties of doped materials by changing the doping ratio and Zn²⁺ counterions. By taking advantage of the reversible metal-ligand coordination interaction, the coordination-activated, and dissociation-deactivated RTP is dynamically manipulated. With the unique Zn²⁺-responsible RTP enhancement materials, the anti-counterfeiting applications of thermal development, and color inversion have been constructed for inkjet printing of high-resolution patterns with high reversibility for many write/erase cycles. The results show that dynamic metal-ligand coordination strategy is a promising approach for achieving efficient RTP materials with controllably modulated properties.     

On a development possibility of a tunable microwave passband filter based on dielectric resonator with high TC film

Measurements of temperature dependence of "YBa₂Cu₃O_7-x thin film on SrTiO₃ substrate" structure effective impedance have been performed in 8-mm wave band by means of quasioptical dielectric resonator with whyspering gallery modes. This dependence appeared to be a series of quasiperiodical oscillation peaks of high steepness. Experiments on investigation of external electric field impact on parameters of the resonator loaded by the structure were carried out. It was found that electric field up to 3 kV/cm leads to a shift of the effective impedance temperature dependence to lower temperature and doesn't impact on the form of the dependence. Herewith the field of 2.5 kV/cm causes a shift of the resonator frequency by 108 MHz with negligible reduction of the loaded quality factor Q_L (less than in 1.5 times). Operating frequency was 35 GHz and loaded quality was about 10³. A proposal about possibility of tunable passband filter design and ways of retuning bandwidth enhancment are discussed.     

A new tunable 1 ps laser source applied to time-resolved absorption spectroscopy of dye solutions

An original laser technique producing high power, tunable, 1 ps pulses starting from a single standard nanosecond laser is described. Time resolved absorption spectra of dye solutions are shown as an example of application.     

化学响应性光子晶体

光子晶体是一种具有光子带隙结构的周期性电介质材料,如果将响应性材料组装到光子晶体结构中,所形成的光子晶体的带隙结构则对外界环境的变化具有响应性,而被称为响应性光子晶体。响应性光子晶体作为光子晶体的一个新领域,由于其在传感器,生物医学,临床检测等方面的潜在应用,近几年受到广泛关注。根据外界环境的不同,响应性光子晶体可简单分为化学响应性光子晶体、物理响应性光子晶体和生物响应性光子晶体等。本文将对化学响应性光子晶体的国内外研究动态做一简要介绍,重点介绍以下五种化学响应性光子晶体:金属离子响应光子晶体、pH响应光子晶体、氧化还原响应光子晶体、葡萄糖响应光子晶体和光化学响应光子晶体。     

Subtle Polymer Donor and Molecular Acceptor Design Enable Efficient Polymer Solar Cells with a Very Small Energy Loss

A new wide bandgap polymer donor, PNDT‐ST, based on naphtho[2,3‐b:6,7‐b′]dithiophene (NDT) and 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ ethylhexyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD) is developed for efficient nonfullerene polymer solar cells. To better match the energy levels, a new near infrared small molecule of Y6‐T is also developed. The extended π‐conjugation and less twist of PNDT‐ST provides it with higher crystallinity and stronger aggregation than the PBDT‐ST counterpart. The higher lowest occupied molecular orbital level of Y6‐T than Y6 favors the better energy level match with these polymers, resulting in improved open circuit voltage (V_oc) and power conversion efficiency (PCE). The high crystallinity and strong aggregation of PNDT‐ST also induces large phase separation with poorer morphology, leading to lower fill factor and reduced PCE than PBDT‐ST. To mediate the crystallinity and optimize the morphology, PNDT‐ST and PBDT‐ST are blended together with Y6‐T, forming the ternary blend devices. As expected, the two compatible polymers allow continual optimization of the morphology by varying the blend ratio. The optimized ternary blend devices deliver a champion PCE as high as 16.57% with a very small energy loss (E_loss) of 0.521 eV. Such small E_loss is the best record for polymer solar cells with PCEs over 16% to date.     

Self‐Healable and Recyclable Tactile Force Sensors with Post‐Tunable Sensitivity

It is challenging to post‐tune the sensitivity of a tactile force sensor. Herein, a facile method is reported to tailor the sensing properties of conductive polymer composites by utilizing the liquid‐like property of dynamic polymer matrix at low strain rates. The idea is demonstrated using dynamic polymer composites (CB/dPDMS) made via evaporation‐induced gelation of the suspending toluene solution of carbon black (CB) and acid‐catalyzed dynamic polydimethylsiloxane (dPDMS). The dPDMS matrices allow CB to redistribute to change the sensitivity of materials at the liquid‐like state, but exhibit typical solid‐like behavior and thus can be used as strain sensors at normal strain rates. It is shown that the gauge factor of the polymer composites can be easily post‐tuned from 1.4 to 51.5. In addition, the dynamic polymer matrices also endow the composites with interesting self‐healing ability and recyclability. Therefore, it is envisioned that this method can be useful in the design of various novel tactile sensing materials for many applications.     

A sulfur coordination polymer with wide bandgap semiconductivity formed from zinc(II) and 5‐methylsulfanyl‐1,3,4‐thiadiazole‐2‐thione

The sulfur coordination polymer catena‐poly[zinc(II)‐μ₂‐bis[5‐(methylsulfanyl)‐2‐sulfanylidene‐2,3‐dihydro‐1,3,4‐thiadiazol‐3‐ido‐κ²N³:S]], [Zn(C₃H₃N₂S₃)₂]_n or [Zn₂MTT₄]_n, constructed from Zn²⁺ ions and 5‐methylsulfanyl‐1,3,4‐thiadiazole‐2‐thione (HMTT), was synthesized successfully and structurally characterized. [Zn₂MTT₄]_n crystallizes in the tetragonal space group I (No. 82). Each MTT^? ligand (systematic name: 5‐methylsulfanyl‐2‐sulfanylidene‐2,3‐dihydro‐1,3,4‐thiadiazol‐3‐ide) coordinates to two different Zn^II ions, one via the thione group and the other via a ring N atom, with one Zn^II atom being in a tetrahedral ZnS₄ and the other in a tetrahedral ZnN₄ coordination environment. These tetrahedral ZnS₄ and ZnN₄ units are alternately linked by the organic ligands, forming a one‐dimensional chain structure along the c axis. The one‐dimensional chains are further linked via C—H…N and C—H…S hydrogen bonds to form a three‐dimensional network adopting an ABAB‐style arrangement that lies along both the a and b axes. The three‐dimensional Hirshfeld surface analysis and two‐dimensional (2D) fingerprint plots confirm the major interactions as C—H…S hydrogen bonds with a total of 35.1%, while 7.4% are C—H…N hydrogen‐bond interactions. [Zn₂MTT₄]_n possesses high thermal and chemical stability and a linear temperature dependence of the bandgap from room temperature to 270 °C. Further investigation revealed that the bandgap changes sharply in ammonia, but only fluctuates slightly in other solvents, indicating its promising application as a selective sensor.     

波长(频率)可调谐半导体激光器

波长或频率可调谐的半导体激光器在光通信等实际应用领域中有着重要而广泛的应用。文章立足于实际应用,从谐振腔的结构出发,以调谐机理为研究对象,对可调谐半导体激光器进行了分类研究,并对它们的调谐特性做了总结