Papers by Keyword: Organic Semiconductors

Abstract: Tris [4-(diethylamino) phenyl] amine (TDAPA) is an organic molecular semiconductor generally used to enhance the charge transport of the devices for some time now. TDAPA is dissolved in various Polar and Non-polar solvents like DMF, Acetone, Acetonitrile, Ethanol, Methanol, Toluene and Chloroform. Absorption spectrum of solution is recorded using UV-Vis spectroscopy and absorption peak for different solvents were observed in UV and Near-UV region. PL study and Pl Excitation study is also carried out for these solvents. Results for absorption and photoluminescence show some interesting phenomenon of Stokes’ shift. The colour coordinates for respective emission are represented by CIE 1931. The study is successfully carried out for better understanding of effect of these solvents on the optical properties of TDAPA.

Abstract: The properties of organic polymers implanted with low-energy ions are of scientific and practical interest. In this work, we consider the nanostructure produced in the near-surface region of polymethylmethacrylate (PMMA) implanted with silicon (Si⁺) ions at energy of 50 keV and ion fluence of 10¹⁶ ions/cm². By controlled local chemical modification in a depth of 150 – 200 nm, in PMMA was created a nano-thin bi-layer configuration consisting of ion-modified layer and ion-implanted layer with carbonaceous nanostructure. Such complex nanoscale arrangement and organic transconductance configuration was characterized by direct current electrical measurements. The field-effect configuration in Si⁺-implanted PMMA was driven through the formed ion-implanted buried planar layer (as a channel with a thickness of about 100 nm) of nanoclustered amorphous carbon as an organic semiconductor. The values of performance parameters, such as the charge carrier mobility, contact resistance and gate leakage current of this particular type of organic field-effect transistor configuration were determined.

Abstract: Stochastic resonance (SR) phenomenon is emerged in organic field effect transistors (OFETs) using $\pi$-conjugated polymer, where application of external noise to the OFET system enhances signal/information processing performance which is often found in biological systems.The channel conductivity of the OFET is slightly increased by spin-coating using heated semiconductor polymer solution with heated glass substrate.In order to improve frequency responses of OFET, optimal width of the gate electrode is explored. Furthermore, it turns out that scratching and removing semiconductor film outside the source-drain electrodes and the channel enhances the On-Off current ratio of the device. These fabrication processes lead to steeper nonlinearity on the $I_{\rm DS}$ {\it vs.} $V_{\rm GS}$ curve, resulting in emergence of SR, which is fingerprinted in increase of correlation value between input and output signals with increase of intensity of external noise.

Abstract: The effect of substitution pattern of the linear-type π-conjugated oligothiophenes is examined. The material solubility, thermal properties, and charge transport characteristics of two hexyl subsituted quinquethiophenes (DH5T) were determined along with the characteristics of an organic field-effect transistor (OFET). The solubility of 4,7-bis (3’-hexyl-2,2’-bithiophene-5-yl) thiophene (β-DH5T), which featured a lateral substitution, was significantly better than that of α,α’-dihexylquinquethiophene (α-DH5T) by altering the directional position of the alkyl group, which makes it a good candidate for solution-processed OFETs. Despite the well-defined vertical alignment of α-DH5T, the hole mobility of the β-DH5T film (3.02 × 10^–3 cm² V^–1 s^–1) was one order of magnitude higher than the hole mobility of the α-DH5T film (2.47 × 10^–4 cm² V^–1 s^–1) prepared by solution processing.

Abstract: Engineering, stability and orientation of semiconducting molecules are necessary to achieve the high efficiency of multifunctional organic-based devices. Several conjugated molecules facilitate the use of external magnetic fields to tailor both their molecular orientation and electronic properties while being processed for bio or opto-electronic applications. In this work, molecular thin films of vanadyl phthalocynine (VOPc) layers forming conducting channels in organic field-effect transistors were investigated. Three systems based on 100 nm thick VOPc thin film were grown, one in absence of magnetic field, while the other two with parallel and perpendicular to the substrate plane, respectively. Devices were ex-situ investigated by electrical characterization and confocal scanning Raman spectroscopy (SRS). All molecular layers growth on Au electrodes presented enhancement of the Raman signal.

Abstract: Poly [2-methoxy, 5-(2¢-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) is a well known hole-conducting semiconductor utilized in the fabrication of optoelectronic devices because of its interesting electroluminescence. However, both electroluminescence and electrical conduction in this material sharply deteriorate upon exposure to oxygen, necessitating fabrication and hermetic sealing of the MEH-PPV-based devices in oxygen-free environments. Same shortcoming has excluded the material from applications requiring air exposure. We have recently presented a model for the oxidation mechanism of an MEH-PPV layer and have shown that such layers, after oxidation at certain conditions, can support air-stable electrical conduction. Here, we describe the experimental conditions required for the preparation of an oxidized MEHPPV layer, and provide experimental data on the stability of such layers at different conditions. It is shown that the fabricated air-stable oxidized MEH-PPV layers are excellent for a number of chemical sensor applications.

Abstract: The emergence of spintronics (spin-based electronics), which exploits electronic charge as well as the spin degree of freedom to store/process data has already seen some of its fundamental results turned into actual devices during the last decade. Information encoded in spins persists even when the device is switched off; it can be manipulated with and without using magnetic fields and can be written using little energy. Eventually, spintronics aims at spin control of electrical properties (I-V characteristics), contrary to the common process of controlling the magnetization (spins) via application of electrical field. In the meantime, another revolution in electronics appears to be unfolding, with the evolution of Molecular Spintronics which aims at manipulating spins and charges in electronic devices containing one or more molecules, because a long spin lifetime is expected from the very small spin-orbit coupling in organic semiconductors. This futuristic area is fascinating because it promises the integration of memory and logic functions,

Abstract: A series of organic light-emitting diodes (OLEDs) with or without a bathocuproine (BCP) layer inserted in the control device indium-tin-oxide (ITO)\ N,N'-bis-(1-naphthl)-diphenyl-1,1'- biphenyl-4,4'-diamine (NPB)\ tris(8-quinolinolato) aluminum (Alq)\LiF\Al have been fabricated and measured. Different influences of the BCP layer on electroluminescence (EL) of the OLEDs have been investigated. It is found that the highest efficiency of the OLED with a 1-nm BCP layer inserted between NPB and Alq increases to 3.99 cd/A, ~48% higher than that of the control device, while the EL efficiencies of the devices with other structures are similar to the latter. This phenomenon is ascribed to the hole-blocking effect of the BCP layer and the resulting higher density of carriers in the emission zone of the OLED. The EL performances of the OLEDs with different thicknesses of BCP layer are also discussed in details.