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Blocking Layer (blocking + layer)
Selected AbstractsDesign of Hole Blocking Layer with Electron Transport Channels for High Performance Polymer Light-Emitting Diodes,ADVANCED MATERIALS, Issue 10 2008Chung-Chin Hsiao A novel dual-functional composite layer composed of a high ionization potential nonconjugated polymer or conjugated molecular material and an inorganic salt of a low work function metal is demonstrated. The composite provides superior hole blocking along with promising electron transport capability and results in good device performance for two model electroluminescent polymers, PFO and MEH-PPV. [source] Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution-Processed Multilayer Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Biwu Ma Abstract Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ-VB)2Ir(C,N), where PPZ-VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the C,N ligands represent a family of four different cyclometallating ligands including 1-phenylpyrazolyl (PPZ) (1), 2-(4,6-difluorophenyl)pyridyl (DFPPY) (2), 2-(p-tolyl)pyridyl (TPY) (3), and 2-phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180,°C for 30,min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high-performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating C,N ligand in order to tune the triplet energy within the range of 3.0,2.2,eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all-solution processed OLEDs with (PPZ-VB)2IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ-VB)2IrDFPPY (2), (PPZ-VB)2IrTPY(3), and (PPZ-VB)2IrPQ(4), used as crosslinkable phosphorescent emitters. [source] Synthesis and characterization of novel poly(p -phenylenevinylene) derivatives containing phenothiazine-5-oxide and phenothiazine-5, 5-dioxide moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2007L. Y. Yang Abstract PPV-based copolymers containing phenothiazine-5-oxide and phenothiazine-5, 5-dioxide moieties have been successfully synthesized by Wittig-Horner reaction and characterized by means of UV-vis, photoluminescence, electroluminescence spectra, and cyclic voltammetry. All of these copolymers can be dissolved in common organic solvents such as chloroform, tetrahydrofuran, and toluene. The PL maxima in the film state are located at 582, 556, and 552 nm for P1, P2, and P3, respectively. The HOMO and LUMO levels of P2 are found to be ,5.21 and ,2.68 eV, respectively; whereas those of P3 are found to be ,5.26 and ,2.71 eV, respectively. The cyclic voltammetry result indicates that the conversion of electron-donating sulfide to electron-withdrawing sulfoxide or sulfone group in polymers plays a dominating role in increasing its oxidation potential. Yellowish-green light ranging from 568 to 540 nm was observed for the single layer device with the configuration of ITO/Polymer/Ca/Al. Double layer devices with Zn (BTZ)2as a hole blocking layer exhibited enhanced EL performance compared to the single layer devices. The maximum brightness of the double layer devices of P1, P2, and P3 is 278, 400, and 796 cd/m2, respectively. The results of EL and electrochemical analyses revealed that they are promising candidate materials for organic, light-emitting diodes with hole-transporting ability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4291,4299, 2007 [source] The origin of the high ideality factor in AlGaN-based quantum well ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010K. B. Lee Abstract The ideality factor of AlGaN-based quantum well ultraviolet light emitting diodes (LEDs) is found to be dependent on both material quality and the presence of electron blocking layer (EBL). The ideality factor of the 340,nm LEDs decreases from 6.9 to 4.9 in the low bias regime (1,,,V,,,2) as the structural dislocation density reduces from 5,×,109 to 9,×,108,cm,2. Moreover, the ideality factor of the 310,nm LEDs decreases with increasing thickness of the AlGaN EBL which is placed between the barrier after the QW and the p-type layer. The slope of the I,V characteristics is temperature independent, indicating that the carrier tunneling is the dominant mechanism. The characteristic tunneling energy extracted from the I,V characteristics decreases from the order of 200 to around 100,meV as the dislocation density in the LED is reduced and with the insertion of a 10,nm EBL. This is attributed to the suppression of deep level states assisted electron tunneling into p-type layer. [source] Confinement factor, near and far field patterns in InGaN MQW laser diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005J. Martín Abstract In this work the influence of the QW number in the active region on spectral characteristics in InGaN multi quamtun well lasers is analyzed. A comparison between the abrupt index step structure (Step) and a graded-index structure (GRIN) is done. The effect of the introduction of a p-AlxGa1,xN electron blocking layer, placed above the last InGaN barrier in the Step structure is also analyzed. Calculations of the confinement factor, near and far field patterns were carried out. We found that with the adequate aluminum content in this layer, the confinement factor, near and far field patterns are improved, and values similar to those obtained with GRIN structure can be reached. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High stability of CdZnSSe active layers in ZnSe-based laser diodes by introducing strain-compensating barrier layersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004Arne Gust Abstract A series of four similar laser structures with an emission wavelength of 520 nm was grown by molecular beam epitaxy. The difference was the alternating implementation of an additional 5 nm thick ZnSSe layer with a high sulfur composition of 25% neighboring the quantum well on the n-, p- or n-& p-side. A high stability of the CdZnSSe active layer was observed by introducing such a kind of strain compensating barrier layers. In lifetime measurements a large improvement was noticed by the p- and n- & p-side barrier layers. With respect to the strain compensating effect of only one barrier layer, the p-side layer is more effective than the n-side one. It is assumed that the p-side barrier layer acts not only as strain-compensating layer, but also as blocking layer against the Cd diffusion into the p-doped layers. A lifetime extension of one order of magnitude could be achieved. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electroluminescent properties of a partially-conjugated hyperbranched poly(p -phenylene vinylene)POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2006Benhu Fan Abstract In this paper, the electroluminescent properties of a new partially-conjugated hyperbranched poly (p -phenylene vinylene) (HPPV) were studied. The single layer light-emitting device with HPPV as the emitting layer emits blue-green light at 496,nm, with a luminance of 160,cd/m2 at 9,V, a turn-on voltage of 4.3,V and an electroluminescent efficiency of 0.028,cd/A. By doping an electron-transport material [2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole, PBD] into the emitting layer and inserting a thin layer of tris(8-hydroxy-quinoline)aluminum (Alq3) as electron transporting/hole blocking layer for the devices, the electroluminescent efficiency of 1.42,cd/A and luminance of 1700,cd/m2 were achieved. The results demonstrate that the devices with the hyperbranched polymers as emitting material can achieve high efficiency through optimization of device structures. Copyright © 2006 John Wiley & Sons, Ltd. [source] Solar cells utilizing small molecular weight organic semiconductorsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2007Barry P. Rand Abstract In this review, we focus on the field of organic photovoltaic cells based on small molecular weight materials. In particular, we discuss the physical processes that lead to photocurrent generation in organic solar cells, as well as the various architectures employed to optimize device performance. These include the donor,acceptor heterojunction for efficient exciton dissociation, the exciton blocking layer, the mixed or bulk heterojunction, and the stacked or tandem cell. We show how the choice of materials with known energy levels and absorption spectra affect device performance, particularly the open-circuit voltage and short-circuit current density. We also discuss the typical materials and growth techniques used to fabricate devices, as well as the issue of device stability, all of which are critical for the commercialization of low-cost and high-performance organic solar cells. Copyright © 2007 John Wiley & Sons, Ltd. [source] Quantum dot-based protein micro- and nanoarrays for detection of prostate cancer biomarkersPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 9 2008Anisha Gokarna Abstract In this article, we demonstrate the fabrication and detection of cancer protein biochips consisting of micro- and nanoarrays whereby pegylated quantum dots (QDs) conjugated to antibodies (Abs) of prostate specific antigens (PSA) were used for the detection of clinical biomarkers such as PSA. BSA which acts as an efficient blocking layer in microarrays, tends to show an interaction with QDs. In view of this fact, we investigated two series of samples which were fabricated in the presence and absence of BSA blocking layer. Variation in the incubation time required for the antigen,antibody interaction to take place, different proteins as controls and the effect of bare QDs on these microarrays, were the three main parameters which were studied in these two series. Samples fabricated in the absence of BSA blocking layer exhibited an extremely high specificity in the detection of cancer proteins and were also marked by negligible nonspecific binding effects of QDs, in stark contrast to the samples fabricated using BSA as a blocking layer. Fabrication of nanoarrays of QD-conjugated PSA Abs having a spot size of nearly 900,nm has also been demonstrated. Thus, we show the potential offered by QDs in in vitro analysis of cancer biomarker imaging. [source] | ||||||||||