Aggregation-induced emission type thermally activated delayed fluorescent materials for high efficiency in non-doped organic light-emitting diodes

Aggregation-induced emission (AIE) type thermally activated delayed fluorescent (TADF) emitters were developed by asymmetric substitution of donor moieties to a diphenylsulfone acceptor. The AIE properties of the TADF emitters increased the quantum efficiency of the non-doped TADF devices and asymmetric substitution was more effective than symmetric substitution to enhance the quantum efficiency of the non-doped devices.     

Emulating synaptic plasticity in ionic liquid-gated zinc tin oxide neuromorphic transistor

Journal of Materials Science: Materials in Electronics - Real-time interpretation and modification of information can impart revolutionary advancements in the evolution of the internet of things....     

Enhanced Mechanical Energy Harvesting in Triboelectric Nanogenerator by the Reinforcement of Polypyrrole-Decorated rGO Sheets in PDMS

Energy harvesting triboelectric nanogenerators (TENGs) to scavenge unused mechanical energy have received significant attention in this decade. Herein, the development of reduced graphene oxide (rGO):polypyrrole (PPy) hybrid-modified polydimethylsiloxane (PDMS) as TENG for various device applications is reported. The bulk of PDMS is altered by different fillers such as rGO, PPy, and the binary hybrids of rGO and PPy with varying weight ratios. Among various PDMS composites, 1 wt% of 1:8 rGO:PPy–PDMS composite exhibits higher TENG responses than other PDMS composite. The superior TENG performances of 1 wt% 1:8 rGO:PPy–PDMS composite are attributed to the formation of intensified negative charges inside the PDMS matrix. This charge intensification in the composite is due to various mechanisms, including the charge trapping ability of rGO:PPy filler, microcapacitor formation by introducing hybrid filler in the system with proper conducting networks, and the electron-donating nature of PPy conducting polymer. A 3D stacked device proposed using 1 wt% 1:8 rGO:PPy–PDMS composite delivered a short-circuit current of 16 μA and an open-circuit potential of 60 V by simple palm pressing. Also, the ability of the stacked device for charging/powering portable devices and light-emitting diodes is demonstrated.     

Engineering microstructure of LiFe(MoO4)2 as an advanced anode material for rechargeable lithium-ion battery

Graphite is considered as an ideal anode material for lithium-ion battery (LIB) due to its high stability, good conductivity and wide source of availability. However, the low energy density and theoretical capacity of graphite cannot meet the needs of high performance anode materials. To circumvent this issue, alternative materials have been sought for many years now. Herein, we report the synthesis of highly crystalline lithium iron molybdate LiFe(MoO₄)₂ by combustion method and evaluated its performance as an anode material for lithium-ion batteries. Triclinic LiFe(MoO₄)₂ crystals having particle size 2–5 μm with good crystallinity were obtained. The material shows long cycle life and high rate performance than commercial graphite and exhibits first reversible discharge capacity of 931.6 mAh/g at a current density of 100 mA/g which is three times higher than commercial graphite. The high specific capacity together with the outstanding rate and cycle performance makes LiFe(MoO₄)₂ a promising anode material for LIB. A detailed analysis on the crystal structure and electronic properties of LiFe(MoO₄)₂ is presented based on DFT studies to complement the experimental observations.

     

A New Design Strategy for Efficient Thermally Activated Delayed Fluorescence Organic Emitters: From Twisted to Planar Structures

In the traditional molecular design of thermally activated delayed fluorescence (TADF) emitters composed of electron‐donor and electron‐acceptor moieties, achieving a small singlet–triplet energy gap (ΔE_ST) in strongly twisted structures usually translates into a small fluorescence oscillator strength, which can significantly decrease the emission quantum yield and limit efficiency in organic light‐emitting diode devices. Here, based on the results of quantum‐chemical calculations on TADF emitters composed of carbazole donor and 2,4,6‐triphenyl‐1,3,5‐triazine acceptor moieties, a new strategy is proposed for the molecular design of efficient TADF emitters that combine a small ΔE_ST with a large fluorescence oscillator strength. Since this strategy goes beyond the traditional framework of structurally twisted, charge‐transfer type emitters, importantly, it opens the way for coplanar molecules to be efficient TADF emitters. Here, a new emitter, composed of azatriangulene and diphenyltriazine moieties, is theoretically designed, which is coplanar due to intramolecular H‐bonding interactions. The synthesis of this hexamethylazatriangulene‐triazine (HMAT‐TRZ) emitter and its preliminary photophysical characterizations point to HMAT‐TRZ as a potential efficient TADF emitter.     

Synchronous distributed load balancing on dynamic networks

In this paper, three distributed load-balancing algorithms for dynamic networks are investigated. Dynamic networks are networks in which the topology may change dynamically. The definition of a dynamic network is introduced and its graph model is presented. The main result of this study consists in proving the convergence toward the uniform load distribution of the diffusion algorithm on an arbitrary dynamic network despite communication link failures. We also give two adaptations of this algorithm (the GAE and the relaxed diffusion). Note that the hypotheses of our result are realistic and that for example the network does not have to be maintained connected. To study the behavior of these algorithms, we compare the load evolution by several simulations.     

Screen printed nanosized ZnO thick film

Nanosized ZnO was prepared by polyol synthesis. Fluorescence spectrum of the ZnO colloid at varying pump intensities was studied. The powder was extracted and characterized by XRD and BET. The extracted powder was screen printed on glass substrates using ethyl cellulose as binder and turpinol as solvent. Coherent back scattering studies were performed on the screen printed sample which showed evidence of weak localization. The screen printed pattern showed strong UV emission.     

Rapid microwave synthesis and photoluminescence properties of rare earth-based coordination polymer core-shell particles

Coordination polymer (CP) core-shell particles, with Eu-based CP as the core and La-based CP as the shell, were prepared using a facile microwave heating method. Pyridine-2, 5-dicarboxylic acid (PDA) was selected as the organic building blo, and DMF was used as the solvent. SEM and TEM images show that the resultant cores are nanospheres with diameters of 200–400 nm. Products with different shell thickness were prepared. The luminescence properties of the core-shell structures were studied and the influence of the La-based CP shell on the photoluminescence properties of the core were investigated. The fluorescence intensity and lifetime of the Eu-based CP core were varied with the addition of shell thickness. Both of them increases at first and then decreases with the increase of shell thickness.     

Influence of surface states on the voltage robustness of AlGaN/GaN HFET power devices

In this work we discuss the influence of the donor-like surface state density (SSD) on leakage currents and the breakdown voltages of AlGaN/GaN heterostructure field-effect transistors (HFET) at high temperature reverse bias (HTRB) step stress. A method to extract charges at the surface by high voltage capacitance voltage (HV–CV) profiling of the gate–drain diode of a HFET is presented. Two samples with different surface passivation are compared. The SSD of the first sample is found to be similar to the polarization charge, whereas it is elevated by a factor of three on the second sample. The influence of the SSD on the electric field is investigated with electroluminescence (EL). The elevated SSD of the second sample engenders severe deficiencies in robustness found in the HTRB. The stress data, the simulation model and the images of EL indicate that the catastrophic failure arises in the dielectric underneath the gate field plate (GFP).