Spotlights Cite This: J. Phys. Chem. Lett. 2017, 8, 5240-5240
pubs.acs.org/JPCL
Spotlights: Volume 8, Issue 20
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HIGHLY EFFICIENT SOLUTION-PROCESSED DEEP-RED ORGANIC LIGHT-EMITTING DIODES BASED ON AN EXCIPLEX HOST COMPOSED OF A HOLE TRANSPORTER AND A BIPOLAR HOST Organic light-emitting diodes (OLEDs) have gained popularity in a multitude of uses, including in full-color flat-panel displays and solid-state lighting. OLEDs are particularly attractive because of their flexibility, high efficiency, and low power consumption, but the development of deep-red OLEDs lags far behind that of their blue, green, and orange counterparts. Huang et al. (10.1021/acs.jpclett.7b02326) studied the electroluminescent efficiencies of deep-red OLEDs using an exciplex as hosta cost-effective choice because an exciplex can be formed by physical blending. They discovered a unique exciplex consisting of a typical hole transporter and a bipolar material (instead of the common combination of hole transporter and electron transporter), and they used experimental data and careful analysis to confirm that the exciplex is an excellent host for red phosphorescent OLEDs (PhOLEDs). Compared with the polymer-based cohost and a bipolar host, the exciplexforming cohost improved the electroluminescent performances by managing the radiative decays and host−guest energy transfer.
remarkable electrochemical performance, with better stability and improved rate performance. The presence of Al in the lattice enhanced its structural stability, showing a capacity retention of 83% after 100 cycles within a 1.5- to 4.3-V window. The authors also used electrochemical impedance spectroscopy measurements at various states of charge to probe the surface and bulk effects of Al doping. Their method may prove useful in the development of structurally stable, high-voltage cathode material for SIBs for the purposes of large-scale energy storage.
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THERMALLY DRIVEN RESISTIVE SWITCHING IN SOLUTION-PROCESSABLE THIN FILMS OF COORDINATION POLYMERS Metal−organic coordination polymers (CPs) in thin film configurations on organically functionalized surfaces are promising for a variety of technological applications. Worthy of particular mention is the emergence of thin-film electronic and electrochemical devices based on electrically conductive CPs. Metal-tetracyanoquinodimethane (M-TCNQ) solids are an interesting class of air-stable semiconducting CPs with unusual magnetic properties. For example, they exhibit longrange ordering at high temperatures as well as bistable electrical characteristics such as resistive switching. Rana et al. (10.1021/ acs.jpclett.7b02138) describe thermally driven resistive switching in thin films of CPs. Specifically, thin films of Ag-TCNQ and Cu-TCNQ consistently showed reversible high-resistance states (HRS) at 300 K and low-resistance states (LRS) at elevated temperatures. The authors found a remarkable enhancement of electrical resistivity between the HRS and LRS, an improvement over conventional electric field-induced resistive switching in vapor-deposited thin films. They attribute this phenomenon to the alternation of the Schottky barrier at the metal−semiconductor interface by thermal energy kT rather than to the formation of conductive filaments as was commonly believed for metal−TCNQ-based materials. The authors also explored the possibility of forming hybrid or amalgamated thin films of CPs in liquid-phase heteroepitaxy. They present an example of sacrificial growth of thin films involving CPs that enabled the growth of M-TCNQs without the use of M as precursor cum substrate, specifically for AgTCNQ. Their findings could aid in the development of solution-processable nonvolatile memory devices of CPs.
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EFFICIENT METHOD OF DESIGNING STABLE LAYERED CATHODE MATERIAL FOR SODIUM ION BATTERIES USING ALUMINUM DOPING Human activity has contributed to the increase of carbon dioxide in the Earth’s atmosphere over the past 300 years, and now many humans are working to reduce these and other greenhouse gas emissions to reverse the deleterious effects on the world’s climate. Reducing our reliance on fossil fuels is seen as an important step, and electric vehicles (EVs) and their hybrid cousins (HEVs) are rapidly gaining in popularity. The preferred power source for EVs and HEVs is the lithium ion battery (LIB), but LIBs are not without their problems, which include safety issues, performance challenges, low power density, and increased demand for raw lithium. Sodium-ion batteries (SIBs) are an attractive alternative for electrochemical energy storage and conversion because they are inexpensive and safe and because sodium is an abundant resource on the Earth’s crust, but they have their own challenges, e.g., low specific energy, short cycling life, and insufficient specific power. As an important component of SIBs, cathode materials have a significant effect on SIB electrochemical performance. Ramasamy et al. (10.1021/acs.jpclett.7b02012) studied the influence of aluminum doping of manganese sites on the structural and electrochemical properties of a P2− Na0.5Mn0.5‑xAlxCo0.5O2 cathode for SIBs. The authors carried out detailed structural, morphological, and electrochemical investigations using X-ray diffraction, cyclic voltammetry, and galvanostatic charge−discharge measurements. They used Rietveld refinement to confirm that Al doping caused TMO6octahedra shrinkage, resulting in wider interlayer spacing. After the Al concentration was optimized, the cathode exhibited © 2017 American Chemical Society
Published: October 19, 2017 5240
DOI: 10.1021/acs.jpclett.7b02680 J. Phys. Chem. Lett. 2017, 8, 5240−5240
