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Antagonistic responses between magnetoconductance (MC) and magnetoelectroluminescence (MEL) in the polymer light-emitting diodes with an interfacial layer between Al cathode and active layer are simultaneously measured. As the interfacial layer (tetraoctylammonium bromide) is used, the significant increase in the number of injected negative polarons and the blocking of positive polarons promote the triplets-(free polaron) reaction and provide a good explanation for the reason that electroluminescence (EL) efficiency is maximal in the trap free space charge limited current regime at high bias. By fitting of MC and MEL curves using Lorentzian and non-Lorentzian empirical equations, three magnetic field dependent mechanisms, which are the intersystem crossing between singlet/triplet polaron pairs, the triplets-(free polaron) reaction, and the triplets-(trapped polaron) reaction are elucidated. The distribution of the three components is tunable by varying the applied electric field, which primarily modulates the triplets-(free polaron) reaction rate. The results pave a new route toward understanding the mechanism of organic spintronics for developing of multifunctional devices.

The enhancement of the hole injection ability of indium tin oxide (ITO) by spin-coating ammonium salts onto it is investigated. The work function of the ITO is increased via spin-coating an NH4Br aqueous solution onto it, which is observed using ultra-violet photoelectron spectroscopy. The formation of H-bonds at the interface between the ITO and the NH4Br is corroborated by utilising the surface sensitivity of synchrotron X-ray photoelectron spectroscopy at low photoelectron take-off angles. We illustrate the increase in the work function of the ITO with a possible scheme involving H-bonding between NH4+ and the ITO. Polymer light-emitting diodes (PLEDs) with ITO/NH4Br showed significantly enhanced performances compared to those with ITO only, with higher current density (924 mA cm−2vs. 903 mA cm−2) and brightness (44 224 cd m−2vs. 1987 cd m−2) at a bias voltage of 7.0 V. To confirm the advantages of general ammonium salts for enhancing device performance, PLEDs with ITO coated by NH4Cl, NH4H2PO4, and (NH4)2SO4 were fabricated and their performances were verified.

An efficient electron injection/hole blocking layer, N-[3-(trimethoxysily)propyl]ethylenediamine that was grafted onto zinc oxide (ZnO/PEDA-TMS), was used in inverted polymer light-emitting diodes (PLEDs). PEDA-TMS induced a strong dipole directed towards ZnO, which was enhanced by vacuum energy level shifts of ultra-violet photoelectron spectroscopic observations, reducing the barrier height between ZnO and the emissive layer. The effect of annealing ZnO on the performance of PLEDs was analyzed using an electron-only device and capacitance–voltage ( C – V ) characterization. Following annealing at 300 °C, ZnO provided effective electron injection and blocked holes, which enhanced the recombination of the electrons and holes. The eletroluminescence efficiency of an inverted PLED with a ZnO/PEDA-TMS layer is comparable to that of a conventional device. The electron injection mechanism of the inverted device can be explained by C – V behaviors, which are correlated with the threshold voltage and turn-on voltage.

A novel approach is developed to design linear passive retro-directive antenna arrays by properly making use of 90deg hybrids. For a 90deg hybrid, when its direct port and coupled port are terminated with the same reflection coefficient, the phase difference of the reflected signals at the other two ports are reversed to that of the incident signals. This then becomes to be a phase difference reversal circuit (or a retro-directive circuit) and leads to the design of linear retro-directive antenna arrays using 90deg hybrids. The formulas and a folding method on designing linear retro-directive array circuits with arbitrary element numbers are presented with the measurement results of three-element, four-element, and six-element retro-directive antenna arrays.

The present work reports on the fabrication of polymer light-emitting diodes by blending a small amount of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) with poly(2,3-dibutoxy-1,4-phenylene vinylene) (DB-PPV). The optical spectra of the devices made of various ratios of the DB-PPV/MEH-PPV blends have shown that the inter-chain interactions of MEH-PPV chains were efficiently suppressed in the presence of DB-PPV as the host, resulting in the improvement of thermal stability and electroluminescence (EL) efficiency of the devices. The enhanced performance of the devices is attributed to the efficient Főrster energy transfer and charge trapping on the polymer blends of the DB-PPV/MEH-PPV host–guest system.

An efficient top-emissive polymer light-emitting diode (T-PLED) employing Ag as a semitransparent cathode is achieved by adding Au nanoparticles to a phenyl-substituted poly(para-phenylene vinylene) copolymer (HY-PPV). The efficiency of the T-PLED with Au nanoparticles is 3.4 cd/A, which is much higher than that of the T-PLED without such particles (0.15 cd/A). The superior performance of the device is attributed to the balance between the electron and hole currents induced by the Au nanoparticles, which increases the probability of hole–electron recombination. Furthermore, the device's stability in air can be significantly improved because of the use of stable electrodes.

This investigation reports the luminescent and electric properties of phenyl-substituted poly(para-phenylene vinylene) copolymer (HY-PPV) in which Au nanoparticles were incorporated. Incorporating a few amounts of Au nanoparticles into HY-PPV film enhances the electroluminescence (EL) efficiency of HY-PPV-based polymer light emitting diodes (PLEDs) using Al and Cu as cathodes. Blue-shifts in the emission spectra and a decrease in the capacitance of the emitting layer were observed. These unique behaviors are due to the increase in the density of the effective hole trap centers and affect the electronic configuration of HY-PPV, induced by the Au nanoparticles, which increase the probability of hole–electron recombination and shift the emission spectra toward higher photo energies.

An efficient polymer light-emitting diode (PLED) was fabricated by inserting polyurethane (PU) between a poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) layer and an Al cathode. The electroluminescence (EL) efficiency of the PU-based device can reach 1.27 cd/A, which is much higher than that of a device without PU (0.015 cd/A). The enhanced performance is attributed to both the hole-blocking capacity of the PU layer and the specific interaction between PU and the deposited Al, significantly facilitating the injection of electrons. Furthermore, the electron injection ability of PU-based devices was found to strongly depend on the thicknesses of the PU and Al layers.

This work reports on the fabrication of an efficient polymer light-emitting device by applying iridium (Ir) complex, dibenzo[ f , h ]-quinoxaline iridium (acetylacetonate) [Ir(DBQ) 2 (acac)], as the phosphorescent dopant, poly(9-vinylcarbazole) as the matrix layer, and 2-(4-biphenylyl)-5-(4- tert -butyl-phenyl)-(1,3,4-oxadiazole) as the electron transport material. The trapping of charge carriers at the Ir(DBQ) 2 (acac) dopant sites dominates the electroluminescence (EL) of the devices. The device emits red electrophosphorescence centered at 610 nm, exclusively from the Ir dopant and an EL efficiency of 8.5 cd/A (1287 cd/m 2 ) biased at 14.5 mA/cm 2 .

In this paper, retro- and reflecto-nulling antenna array presented in the last year APMC is extended to the case of odd number of array elements. It can yield two nulls at the incident angle and the reflection angle of the incident wave. With the use of 90° hybrids and the proper phase shifters, in order to design a retro- and reflecto-nulling antenna arrays with odd number of elements, a folding method is developed and results of three- and five-element retro- and reflecto-nulling antenna arrays are presented.

In this paper, a novel approach of linear retro- and reflecto-nulling antenna array using 90deg hybrids and 90deg phase shifters is described. A four-element passive array with experimental results is presented. The measured patterns demonstrate that the nulls of the re-transmitted radiation are at the angles of incident and reflection. This approach can be implemented as an TV-element linear retro- and reflecto-nulling antenna array with Nto be a multiple of 4.

In this paper, a novel folding method to design 90deg hybrids circuits for linear retro-directive arrays with arbitrary number of elements is proposed. Three-element, four-element, and six-element passive retro-directive array with experimental results are presented. The measured patterns demonstrate that the main beam is aligned with the incident angle. This approach can be implemented as an arbitrary odd-number and even-number linear retro-directive antenna array.

In this paper, a novel approach is developed for achieving a reflecto-nulling antenna array which can make the null of re-transmitted radiation pattern at the reflection angle of the incident wave without using digital signal processing techniques. The array is designed by properly utilizing 90deg hybrids. For a 90deg hybrid, if the input port and isolated port are connected to the receiving antenna and transmitting antenna, it can be shown as the direct port and coupled port are terminated with two out-of-phase reflection coefficients Gamma and -Gamma, the re-transmitted radiation pattern will have a null at the specular direction -thetasi when the incident angle is thetasi. The formulas and measurement results of a four-element reflecto-nulling antenna array are presented with the measurement arrangement.

In this paper, a novel approach is developed for achieving a three-element retro-directive antenna array. The array is designed by properly making use of 90/spl deg/ hybrids. For a 90/spl deg/ hybrid, it can be shown as the two signals with relative difference of /spl Delta//spl Phi/ are connected to its input and isolated ports, the phase difference of the output signals from these two ports become -/spl Delta//spl Phi/, if the direct port and coupled port are terminated with the same reflection coefficient /spl Gamma/. In other words, a 90/spl deg/ hybrid becomes a phase conjugation circuit. The formulas and measurement results of the phase conjugation circuit and a three-element retro-directive antenna array are presented with the measurement arrangement.

In this paper, a novel approach of linear retro-directive antenna array using 90deg hybrids is proposed. Three-element and four-element passive retro-directive array with experimental results are presented. The measured patterns demonstrate that the main beam is aligned with the incident angle. This approach can be implemented as an arbitrary odd-number and even-number linear retro-directive antenna array

We investigate solution-processed tetra-n-alkyl ammonium bromides (TAABs) as electron extraction layers (EELs) in bulk heterojunction (BHJ) solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The EELs of TAABs lead to simultaneous increases in open-circuit voltage (VOC), short-circuit current density, and fill factor, enhancing the power conversion efficiency of BHJ solar cells from 2.38% to 4.02–4.19%. It is interesting that the same increase in VOC of about 0.14 V is obtained for devices with Al, Ag, and Au cathodes by using the EEL of TOAB. The self-assembly of TOAB into the lamellar structure stacked upright atop P3HT:PCBM is corroborated by synchrotron X-ray diffraction. The surface morphologies of TAABs atop P3HT:PCBM, explored by atomic force microscopy, show that there are ultrathin layers of TAABs in the regions beside large island clusters. The underlying mechanism is inferred that the TAAB molecules introduce anisotropic dipoles toward P3HT:PCBM which significantly elevate the vacuum level of the metal cathode for the efficient electron extraction. Our results provide a simple method to fabricate high performance BHJ solar cells by solution processing.

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This work presents the fabrication of high-brightness (over 30000cd∕m2) top-emissive polymer light-emitting diodes (PLEDs) using a hybrid semitransparent cathode capable of efficient injection of electrons. The composite cathode is comprised of the organic oxide/Al complex as the injection buffer layer covered by a thin Ag overlayer. The anode is made of Ag:Ag2O coated on the glass substrate. The electroluminescence (EL) efficiency of 8.9cd∕A for phenyl-substituted poly(para-phenylene vinylene) copolymer based top-emissive PLED markedly exceeds that of 4.3cd∕A for the control device with the bottom-emissive configuration. The high performance is attributed to the balanced injection of charge carriers and the effective extraction of EL emission from the top cathode. The optical microcavity effect significantly promotes the EL emission in the direction along the surface normal.