Polymer Solar Cells with Efficiency >10% Enabled via a Facile Solution‐Processed Al‐Doped ZnO Electron Transporting Layer

A facile and low‐temperature (125 °C) solution‐processed Al‐doped ZnO (AZO) buffer layer functioning very effectively as electron accepting/hole blocking layer for a wide range of polymer:fullerene bulk heterojunction systems, yielding power conversion efficiency in excess of 10% (8%) on glass (plastic) substrates is described. The ammonia‐treatment of the aqueous AZO nanoparticle solution produces compact, crystalline, and smooth thin films, which retain the aluminum doping, and eliminates/reduces the native defects by nitrogen incorporation, making them good electron transporters and energetically matched with the fullerene acceptor. It is demonstrated that highly efficient solar cells can be achieved without the need for additional surface chemical modifications of the buffer layer, which is a common requirement for many metal oxide buffer layers to yield efficient solar cells. Also highly efficient solar cells are achieved with thick AZO films (>50 nm), highlighting the suitability of this material for roll‐to‐roll coating. Preliminary results on the applicability of AZO as electron injection layer in F8BT‐based polymer light emitting diode are also presented.     

Cataluminescence‐based sensors: principle,instrument and application

The cataluminescence (CTL)‐based sensor is a new promising type of chemical transducer, and has attracted much attention of researchers for its potential versatile applications in public safety, emission control and environmental protection. In this review, we briefly introduce the development history of CTL‐based sensors and summarize existing explanations of the CTL reaction mechanism as well as three research strategies for mechanism the CTL mechanism. In the following, all the function units of a typical CTL‐based sensor system are described and the investigation of the sensor materials. CTL‐based sensor arrays, are discussed in detail. We classify the recent novel hyphenated techniques based on CTL coupled to other analysis techniques into the preconcentration‐CTL hyphenated technique, nebulization‐CTL hyphenated technique, plasma‐assisted CTL technique and tandem CTL technique according to the type of analysis combined with CTL and provide a detailed account of novel hyphenated techniques. Owing to the appearance of these novel techniques, the application range of CTL has been expanded as well as the sensitivity and selectivity of CTL system has been greatly improved. Finally, the applications of CTL‐based sensor and sensor arrays in the last several years are classified and summarized. Copyright © 2014 John Wiley & Sons, Ltd.     

Advanced Electrode Materials Comprising of Structure‐Engineered Quantum Dots for High‐Performance Asymmetric Micro‐Supercapacitors

Micro‐supercapacitors (MSCs) as a new class of energy storage devices have attracted great attention due to their unique merits. However, the narrow operating voltage, slow frequency response, and relatively low energy density of MSCs are still insufficient. Therefore, an effective strategy to improve their electrochemical performance by innovating upon the design from various aspects remains a huge challenge. Here, surface and structural engineering by downsizing to quantum dot scale, doping heteroatoms, creating more structural defects, and introducing rich functional groups to two dimensional (2D) materials is employed to tailor their physicochemical properties. The resulting nitrogen‐doped graphene quantum dots (N‐GQDs) and molybdenum disulfide quantum dots (MoS₂‐QDs) show outstanding electrochemical performance as negative and positive electrode materials, respectively. Importantly, the obtained N‐GQDs//MoS₂‐QDs asymmetric MSCs device exhibits a large operating voltage up to 1.5 V (far exceeding that of most reported MSCs), an ultrafast frequency response (with a short time constant of 0.087 ms), a high energy density of 0.55 mWh cm^?3, and long‐term cycling stability. This work not only provides a novel concept for the design of MSCs with enhanced performance but also may have broad application in other energy storage and conversion devices based on QDs materials.     

Ultrathin Few‐Layer GeP Nanosheets via Lithiation‐Assisted Chemical Exfoliation and Their Application in Sodium Storage

Ultrathin few‐layer materials have attracted intensive research attention because of their distinctive and unique properties. Few‐layer GeP (FL‐GP) is potentially interesting for application in electronics and optoelectronics because of its appropriate band gap and good stability under ambient conditions. Nevertheless, it is a challenge to achieve ultrathin few‐layer or single layer GeP from exfoliation of bulk crystals. Here, a lithiation‐assisted chemical exfoliation technique is employed to achieve FL‐GP, in which the interlayer spacing can be efficiently enlarged after a preliminary lithium ion intercalation, allowing the bulk crystal to be readily exfoliated in a following ultrasonication. As a result, ultrathin FL‐GP is obtained. In a demonstration, the FL‐GP/reduced graphene oxide (rGO) demonstrates remarkable sodium storage performance. The FL‐GP with a two‐dimensional structure shortens the ion transport pathways and alleviates the volume variation during sodiation. Meanwhile, the rGO in the composite improves the conductivity of the whole electrode. The as‐prepared FL‐GP/rGO electrode exhibits a high capacity of 504.2 mAh g^?1 at 100 mA g^?1, remarkable rate performance, and superior cycling stability in the half cells. FL‐GP/rGO//Na₃V₂(PO₄)₃ full cells are also assembled and demonstrated satisfactory electrochemical performance, indicating potential application of the as‐prepared anode materials.     

Facile and Scalable Preparation of Ruthenium Oxide‐Based Flexible Micro‐Supercapacitors

Tremendous efforts have been invested in the development of the internet of things during the past 10 years. Implantable sensors still need embedded miniaturized energy harvesting devices, since commercialized thin films and microbatteries do not provide sufficient power densities and suffer from limited lifetime. Therefore, micro‐supercapacitors are good candidates to store energy and deliver power pulses while providing non‐constant voltage output with time. However, multistep expensive protocols involving mask aligners and sophisticated cleanrooms are used to prepare these devices. Here, a simple and versatile laser‐writing procedure to integrate flexible micro‐supercapacitors and microbatteries on current‐collector‐free polyimide foils is reported, starting from commercial powders. Ruthenium oxide (RuO₂)‐based micro‐supercapacitors are prepared by laser irradiation of a bilayered tetrachloroauric acid (HAuCl₄ · 3H₂O)–cellulose acetate/RuO₂ film deposited by spin‐coating, which leads to adherent Au/RuO₂ electrodes with a unique pillar morphology. The as‐prepared microdevices deliver 27 mF cm^?2/540 F cm^?3 in 1 m H₂SO₄ and retain 80% of the initial capacitance after 10 000 cycles. This simple process is applied to make carbon‐based micro‐supercapacitors, as well as metal oxide based pseudocapacitors and battery electrodes, thus offering a straightforward solution to prepare low‐cost flexible microdevices at a large scale.     

Wide‐Bandgap Perovskite/Gallium Arsenide Tandem Solar Cells

Gallium arsenide (GaAs) photovoltaic (PV) cells have been widely investigated due to their merits such as thin‐film feasibility, flexibility, and high efficiency. To further increase their performance, a wider bandgap PV structure such as indium gallium phosphide (InGaP) has been integrated in two‐terminal (2T) tandem configuration. However, it increases the overall fabrication cost, complicated tunnel‐junction diode connecting subcells are inevitable, and materials are limited by lattice matching. Here, high‐efficiency and stable wide‐bandgap perovskite PVs having comparable bandgap to InGaP (1.8–1.9 eV) are developed, which can be stable low‐cost add‐on layers to further enhance the performance of GaAs PVs as tandem configurations by showing an efficiency improvement from 21.68% to 24.27% (2T configuration) and 25.19% (4T configuration). This approach is also feasible for thin‐film GaAs PV, essential to reduce its fabrication cost for commercialization, with performance increasing from 21.85% to 24.32% and superior flexibility (1000 times bending) in a tandem configuration. Additionally, potential routes to over 30% stable perovskite/GaAs tandems, comparable to InGaP/GaAs with lower cost, are considered. This work can be an initial step to reach the objective of improving the usability of GaAs PV technology with enhanced performance for applications for which lightness and flexibility are crucial, without a significant additional cost increase.     

Photoemission Spectroscopy Characterization of Halide Perovskites

Controlling the surface and interface properties of halide perovskites (HaPs) materials is key to improve performance and stability of HaP‐based optoelectronic devices such as solar cells. Here, an overview is given on the use of different photoemission spectroscopy (PES) techniques as a tool kit to investigate chemical and electronic properties of surfaces and interfaces in research on HaP compounds. The primary focus of the article is X‐ray photoelectron spectroscopy (XPS), hard X‐ray photoemission spectroscopy (HAXPES), ultraviolet photoemission spectroscopy (UPS), and inverse photoemission spectroscopy (IPES), highlighting the importance of good practices during PES measurements. Starting from the working principles of PES, critical measurement conditions are discussed. In particular, the exposure of the HaP surface to vacuum and high energy radiation can cause accelerated ageing, degradation, and also ionic migration in the sample. The impact of these changes on the electronic and chemical properties is discussed, followed by an analysis of the specific challenges encountered when performing PES measurements of HaPs. These include the deviation from pristine surface conditions, determination of “soft” band edges, and assessment of band bending. The review concludes by emphasizing good practices for PES measurements of HaP samples and outlining the scope of operando type measurements to capture the transient behavior of HaPs in the experiment.     

A High‐Energy NASICON‐Type Cathode Material for Na‐Ion Batteries

Over the last decade, Na‐ion batteries have been extensively studied as low‐cost alternatives to Li‐ion batteries for large‐scale grid storage applications; however, the development of high‐energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)‐structured cathodes with formula Na_xM₂(PO₄)₃, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON‐type compound, Na₄MnCr(PO₄)₃, is reported as a promising cathode material for Na‐ion batteries that deliver a high specific capacity of 130 mAh g^?1 during discharge utilizing high‐voltage Mn^2+/3+ (3.5 V), Mn^3+/4+ (4.0 V), and Cr^3+/4+ (4.35 V) transition metal redox. In addition, Na₄MnCr(PO₄)₃ exhibits a high rate capability (97 mAh g^?1 at 5 C) and excellent all‐temperature performance. In situ X‐ray diffraction and synchrotron X‐ray diffraction analyses reveal reversible structural evolution for both charge and discharge.