Naphthyl end-capped quarterthiophene: A simple organic semiconductor with high mobility and air stability

An organic semiconductor that can be mass produced is synthesized by end-capping quaterthiophene with naphthyl units (NaT4). An organic thin-film transistor (OTFT, see figure) has been fabricated using this organic semiconductor, and exhibits stability under ambient conditions with a mobility of up to 0.40 cm(2) V-1 s(-1).

Heterojunction ambipolar organic transistors fabricated by a two-step vacuum-deposition process

Ambipolar organic field-effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two-step vacuum-deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 degrees C) acts as the first (p-type component) layer, and hexadecafluorophthalocyaninatocopper (F16CuPc) deposited at room temperature (25 degrees C) acts as the second (n-type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10(-4) cm(2) V-1 s(-1) in air. Conductive channels are at the interface between the F16CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F16CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin-film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum-deposition process.

Application of ceramic carbon materials for solid-phase extraction of organic compounds

Ceramic carbon materials were developed as new sorbents for solid-phase extraction of organic compounds using chlorpromazine as a representative. The macroporosity and heterogeneity of ceramic carbon materials allow extracting a large amount of chlorpromazine over a short time. Thus, the highly sensitive and selective determination of chlorpromazine in urine sample was achieved by differential pulse voltammograms after only 1-min extraction. The total analysis time was less than 3 min. In comparison with other electrochemical and electrochemi-luminescent methods following 1-min extraction, the proposed method improved sensitivity by about 2 and 1 order of magnitude, respectively. The fast extraction, diversity, and conductivity of ceramic carbon materials make them promising sorbents for various solid-phase extractions, such as solid-phase microextraction, thin-film microextraction, and electrochemically controlled solidphase extraction. The preliminary applications of ceramic carbon materials in chromatography were also studied.

Novel < 110 >-oriented organic-inorganic perovskite compound stabilized by N-(3-aminopropyl) imidazole with improved optical properties

In the organic-inorganic perovskites family, the < 100 >-oriented type has been extensively investigated as a result of its unique magnetic, optical, and electrical properties, and only one type of < 110 >-oriented hybrid perovskite stabilized by methylammonium and iodoformamidinium cations or the latter themselves has been known so far. In this paper, another novel < 110 >-oriented organic-inorganic perovskite (C6H13N3)-PbBr4 (compound 1) has been prepared by reacting N-(3-aminopropyl)imidazole (API) with PbBr2 in hydrobromic acid. The crystal structure is determined, which indicates that the perovskite is stabilized by API. The introduction of the optically active organic ligand API into the hybrid perovskite results in a red shift and a great enhancement of photoluminescence in the perovskite with respect to organic ligand API itself. These results have been explained according to calculation based on density-functional theory. Moreover, the excellent film processing ability for the perovskite (C6H13N3)PbBr4 together with the improved optical properties makes it have potential application in optoelectronic devices.

Novel highly stable semiconductors based on phenanthrene for organic field-effect transistors

Two novel phenanthrene-based conjugated oligomers were synthesized and used as p-channel semiconductors in field-effect transistors; they exhibit high mobility and excellent stability during long-time ambient storage and under UV irradiation.

Ambipolar organic field-effect transistors with air stability, high mobility, and balanced transport

Ambipolar organic field-effect transistors (OFETs) based on the organic heterojunction of copper-hexadecafluoro-phthalocyanine (F16CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T) were fabricated. The ambipolar OFETs eliminated the injection barrier for the electrons and holes though symmetrical Au source and drain electrodes were used, and exhibited air stability and balanced ambipolar transport behavior. High field-effect mobilities of 0.04 cm(2)/V s for the holes and 0.036 cm(2)/V s for the electrons were obtained. The capacitance-voltage characteristic of metal-oxide-semiconductor (MOS) diode confirmed that electrons and holes are transported at F16CuPc and BP2T layers, respectively. On this ground, complementary MOS-like inverters comprising two identical ambipolar OFETs were constructed.

Improved n-type organic transistors by introducing organic heterojunction buffer layer under source/drain electrodes

N-type organic thin-film transistors (OTFTs) employing hexadecafluorophthalocyaninatocopper (F16CuPc) as active layer and p-type copper phthalocyanine (CuPc) as buffer layer are demonstrated. The highest field-effect mobility is 7.6x10(-2) cm(2)/V s. The improved performance was attributed to the decrease of contact resistance due to the introduction of highly conductive F16CuPc/CuPc organic heterojunction. Therefore, current method provides an effective path to improve the performance of OTFTs.

Negative differential resistance effect in organic devices based on an anthracene derivative

The authors observed a negative differential resistance (NDR) in organic devices consisting of 9,10-bis-(9,9-diphenyl-9H-fluoren-2-yl)-anthracene (DPFA) sandwiched between Ag and indium tin oxide electrodes. The large NDR shown in current-voltage characteristics is reproducible, resulting in that the organic devices can be electrically switched between a high conductance state (on state) and a low conductance state (off state). It can be found that the currents at both on to off states are space-charge limited and attributed to the electron traps at the Ag/DPFA interface. The large and reproducible NDR makes the devices of tremendous potential in low power memory and logic circuits.

White organic light-emitting devices with a phosphorescent multiple emissive layer

A phosphorescent multiple emissive layer, in which a blue emissive layer is sandwiched between red and green ones, is employed in a white organic light-emitting device (OLED). This OLED has a maximum luminance of 48 000 cd/m(2) at 17 V, a maximum power efficiency of 9.9 lm/W at 4 V, and a color rendering index of 82. In addition, the emission color of this device is fairly stable at high luminances: its Commission Internationale de l(')Eclairage coordinate slightly changes from (0.431, 0.436) to (0.400, 0.430) when the luminance ranges from 2000 to 40 000 cd/m(2).

Fabrication of self-assembled palladium nanosheets using layered organic/inorganic hybrid as the template

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl2) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl4}(2-) network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

Preparation of a carbon supported Pt catalyst using an improved organic sol method and its electrocatalytic activity for methanol oxidation

The organic sol method for preparing ultrafine transition metal colloid particles reported for the first time by Bonnemann et al. [H. Bonnemann, W Brijoux, R. Brinkmann, E. Dinjus, T. Jou beta en, B. Korall, Angew. Chem. Int. Ed. Engl., 30 (1991) 1312] has been improved in this paper. The improved organic sol method uses SnCl2 as the reductant and methanol as the organic solvent. Thus, this method is very simple and inexpensive. It was found that the average size of the Pt particles in the Pt/C catalysts can be controlled by adjusting the evaporating temperature of the solvent. Therefore, the Pt/C catalysts prepared by the same method are suitable for evaluating the size effect of the Pt particles on electrocatalytic performance for methanol oxidation. The results of the X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that when the evaporating temperatures of the solvent are 65, 60, 50, 40, and 30 degrees C, the average sizes of the Pt particles in the Pt/C catalysts prepared are: 2.2, 3.2, 3.8, 4.3, and 4.8 nm, respectively. The X-ray photoelectron spectroscopic (XPS) results demonstrated that the small Pt particles are easily oxidized and the decomposition/adsorption of methanol cannot proceed on the surfaces of Pt oxides.

Performance improvement by charge trapping of doping fluorescent dyes in organic memory devices

We studied the memory effect in the devices consisting of dye-doped N, N'-di(naphthalene-1-yl)-N, N'-diphenyl-benzidine sandwiched between indium-tin oxide and Ag electrodes. It was found that the on/off current ratio was greatly improved by the doped fluorescent dyes compared with nondoping devices. A mechanism of charge trapping was demonstrated to explain the improvement of the memory effect. For the off state, the conduction process is dominated by the trapping current, which is a characteristic of the space-charge limited current, whereas the on state is dominated by the detrapping current, and interpreted by Poole-Frenkel emission.

Organic heterojunction with reverse rectifying characteristics and its application in field-effect transistors

A diode with a reverse rectifying characteristics was fabricated based on the organic heterojunction of copper phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F16CuPc). At the heterojunction interface, HOMO of CuPc is bended upwards and LUMO of F16CuPc is bended downwards, since the charge carriers were accumulated at both side of the interface, electrons in F16CuPc and holes in CuPc. The thickness of holes accumulated at the CuPc layer is about 10 nm. which was determined by fabricating organic field-effect transistors with active layers in series of thickness. By utilizing the heterojunction-effect, the threshold voltage in organic transistors can be modified.

Highly efficient iridium(III) complexes with diphenylquinoline ligands for organic light-emitting diodes: Synthesis and effect of fluorinated substitutes on electrochemistry, photophysics and electroluminescence

A series of novel cyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline ligands with fluorinated substituent were prepared and characterized by elemental analysis, NMR and mass spectroscopy. The cyclic voltammetry, absorption, emission and electroluminescent properties of these complexes were systematically investigated. Electrochemical studies showed that the oxidation of the fluorinated complexes occurred at more positive potentials (in the range 0.57-0.69 V) than the unfluorinated complex 1 (0.42 V). In view of the energy level, the lowering of the LUMO by fluorination is significantly less than that of the HOMO. The weak and low energies absorption bands in the range of 300-600 nm are well resolved, likely associated with MLCT and (3)pi-pi* transitions. These complexes show strong orange red emission both in the solution and solid state. The emission maxima of the fluorinated complexes showed blue shift by 9, 24 and 15 nm for 2, 3 and 4, respectively, with respect to the unfluorinated analogous 1. Multilayered organic light-emitting diodes (OLEDs) were fabricated by using the complexes as dopant materials. Significantly higher performance and lower turn-on voltage were achieved using the fluorinated complexes as the emitter than that using the unfluorinated counterpart 1 under the same doping level.

Effect of dye-doped concentration on the charge carrier recombination in molecularly doped organic light-emitting devices

The effect of the concentration of 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl- 9-enyl)-4H-pyran(DCJTB) as dopant in tris(8-hydroxyquinoline) aluminium (Alq(3)) on the charge carrier recombination was studied by transient electroluminescence (EL). The electron-hole recombination coefficient (gamma) was determined from the long-time component of the temporal decay of the EL intensity after a rectangular voltage pulse was turned off. It was found that the coefficient monotonically decreased with an increase in the DCJTB-doping concentration. The monotonic decrease is attributed to concentration quenching on the excitons and coincided well with the reduction of the EL efficiency.