Simulated 1200V SiC-MOSFET short-circuit behavior

International audienc

Solution-processed blue phosphorescent OLEDs with carbazole-based polymeric host materials

International audienceA new carbazole-based polymer PEPEK varying from the previously reported PEPK by the length of the spacer between the polymer backbone and the pendent carbazole moiety was investigated as polymeric host for solution-processed devices. Interestingly, if the two polymers are structurally close since the length of the alkyl chain only differs from one carbon atom, the previously reported PEPK gave higher performances than the newly synthesized PEPEK when tested as host for the wide bandgap triplet emitter FIrpic. To optimize electroluminescence performances, two device configurations were examined. On doping the emissive layer of phosphorescent organic light-emitting devices (OLEDs) at 16 wt% with FIrpic, best PEPK-based OLEDs gave an efficacy of 15.14 cd/A whereas PEPEK-based devices furnished an efficiency of 12.17 cd/A in the same conditions. To determine the origin of this unexpected behavior, the new polymer PEPEK was characterized by UV–visible absorption and luminescence spectroscopy as well as cyclic voltammetry. Thermal properties of PEPEK were also examined and compared to those of PEPK

Development and Static Mode Characterization of a New Low-Loss AC Switch Based on Super-Gain BJT

International audienceThis paper deals with an innovative low-loss AC switch, named as TBBS (transistor based bidirectional switch), based on the association of super-gain BJTs developed by the GREMAN laboratory. The main characterization results of the super-gain BJT are reminded to identify the key parameters that are essential to build the TBBS. A complete characterization database in static mode of this new AC switch is discussed. In particular, its forward and reverse-biased features have been measured to see the evolution of the DC current gain as a function of the current density. The TBBS makes sense when using the super-gain BJT (bipolar junction transistor) in reverse mode. It means that the reverse DC current gain has to be sufficient (at least higher than 1 compared with the conventional BJT one). This new AC switch is bidirectional in current and voltage, totally controllable (turn-on and turn-off) and the most attractive solution in terms of on-state power losses. Further, its manufacturing process is as easier as existing device such as triac

Metametha dataset

Comparison of N fluxes (N20, NH3, NO3 …) between 5 fertilization managements : livestock effluents, digestates and mineral nitrogen. This dataset was collected in part of Metametha project, funded by ADEME. During three years (2017,2019 and 2019) measurements were made in soil, water and air, at wheat and rapessed plots fertilized with slurry cattle, manure cattle, raw digestates, solid and liquid treated digestates and mineral nitrogen. (2019-12-12

Poly(2-(N-carbazolyl)ethyl acrylate) as a host for high efficiency polymer light-emitting devices

International audiencePoly(2-(N-carbazolyl)ethyl acrylate), a poly(acrylate) comprised of carbazole-side groups attached via a flexible chain to the polymer backbone (PVAK) has been tested as host for solution-processed polymer light-emitting devices (PLEDs). This non-conjugated polymer proved to be an excellent candidate to host wide-bandgap phosphors. Notably, this polymer exhibited a high thermal stability (Td = 322 °C), a glass transition temperature (Tg) of 91 °C and a wide bandgap corresponding to the pendent carbazole units and the disrupted π-conjugation of the polymer main chain, making this polymeric host a suitable candidate for wide bandgap triplet emitters. When tested as a host for FIrpic and Ir(ppy)3, the resulting blue and green light-emitting devices showed a maximum luminous efficiency of 18.25 and 17.74 cd/A, respectively, which are comparable to recent reports of devices made using other carbazole-based oxygen-rich polymeric hosts. The polymer was also characterized by UV–visible absorption, photoluminescence spectroscopy as well as cyclic voltammetr

Bis(diphenylamino)naphthalene host materials: careful selection of the substitution pattern for the design of fully solution-processed triple-layered electro-luminescent devices

International audienceTwo new triarylamine-based wide bandgap small molecules differing by the position of their substituents were investigated as hosts for solution-processed organic light-emitting diodes (OLEDs). Blue-green, green and red OLEDs were realized with FIrpic, Ir(ppy)2(acac) and Ir(ppy)2(dbm) as triplet emitters respectively and the three layers constituting the device stacking were successively deposited with orthogonal solvents. Interestingly, one of the two bis(diphenylamino)naphthalene-based compounds, (NAP-1,5-DPA), furnished significantly enhanced EL performances compared to its isomeric counterpart. A maximum luminance of 3905 cd m−2 at 21 V was notably achieved with this material for devices comprising FIrpic as dopant. To get a deeper insight into these major differences in devices, the two host materials were characterized by UV-visible absorption and luminescence spectroscopy, and cyclic voltammetry. Thin films of the two materials were also examined by optical and atomic force microscopy. Thermal properties of the two hosts were also investigated as well as their electronic characteristics by theoretical calculations

Low-cost zinc complexes for white organic light-emitting devices

International audienceA series of blue fluorescent Zn (II) tetradentate Schiff base complexes has been designed and synthesized for applications in organic light-emitting diodes. The five complexeswere investigated as dopantmaterials or as single emitters of multilayered p-i OLEDs. White OLEDs were achieved using these compounds as dopants of 4,4′,4″- tris(N-carbazolyl)triphenylamine and best devices exhibited a high qualitywhite-lightemission with remarkable CIE (Commission Internationale de l'Eclairage) coordinates (0.33, 0.34).When used as single emitters, sky-blue and blue electroluminescent devices were prepared, except with one complex that gave yellow OLEDs. Optical properties of these complexes were examined by UV-visible absorption and luminescence spectroscopy. Their electrochemical properties are also reported. These results open the route to the development of cost-effective complexes for white organic light-emitting devices application

Iridium (III) soft salts from dinuclear cationic and mononuclear anionic complexes for OLEDs devices

International audienceTwo iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety

A novel class of photoinitiators with a thermally activated delayed fluorescence (TADF) property

WOS:000434245500081Photoinitiators exhibiting efficient thermally activated delayed fluorescence (TADF) are investigated. Known TADF metal complexes (copper-based structures) and purely organic molecules (carbazole/sulfone based organic structures) are used, for the first time, in the FRP of methacrylates, the CP of diepoxides and the synthesis of acrylate/diepoxide interpenetrated polymer networks, in thick films (1.4 mm), under air, under soft conditions using violet light delivered by a LED emitting at 405 nm. They are incorporated into two-component systems in combination with an iodonium salt and/or into three-component systems with iodonium salt/amine or N-vinylcarbazole or 9H-carbazole-9-ethanol (CARET) systems. A comparison with non-TADF analogues highlights the benefits of the TADF process. Using the copper complexes, the performances are better than those achieved with a conventional reference photoinitiator (bis acylphosphineoxide); the organic structures are noticeab ly less efficient. These systems exhibit a photoredox catalyst behavior. The involved chemical mechanism has been investigated using steady state photolysis, cyclic voltammetry, fluorescence spectroscopy, laser flash photolysis and electron spin resonance spin trapping techniques. The TADF property is found to be very important in increasing the excited state lifetime of the photoredox catalyst for better interactions with additives (i.e. a longer excited state lifetime is important to increase the yields of bimolecular reactions)

Carbazole Derivatives with Thermally Activated Delayed Fluorescence Property as Photoinitiators/Photoredox Catalysts for LED 3D Printing Technology

This paper is devoted to the effect of a thermally activated delayed fluorescence (TADF) property in new photoinitiators/photoredox catalysts. Four carbazole derivatives <b>A1</b>–<b>A4</b> exhibiting a TADF character are synthesized and proposed for the first time as high performance visible light photoinitiators/metal-free photoredox catalysts, in the presence of an amine or/and an iodonium salt, for both the free radical polymerization (FRP) of (meth)­acrylates and the cationic polymerization (CP) of epoxides upon visible light exposure using light-emitting diodes (LEDs) at 405, 455, and 477 nm. Interestingly, the impact of the substituent effect on the excited state lifetimes and therefore on the photoinitiating ability of a series of substituted carbazoles was clearly evidenced and examined. Upon bromination of the carbazole core, clear effects on the excited state lifetimes and light absorption were demonstrated, enabling to tune the initiator performance. Excellent polymerization initiating abilities are found, and high final monomer conversions are obtained. The use of these novel carbazole-based systems in photocurable cationic formulations for LED projector 3D printing is particularly outlined. TADF molecules allow a more efficient reaction from the excited singlet state as a result of their prolonged lifetimes; i.e., this effect is well highlighted through a comparison with previously published none-TADF metal-free photoredox catalysts. A full picture of the involved photochemical mechanisms is also provided. Carbazoles exhibiting a TADF character pave the way toward metal-free photoredox catalysts active in both oxidative and reductive cycles with efficiency on par with those of the traditional metal-based photoredox catalysts/photoinitiators