Organic Electronics 2005 Volume 6 №04

Elsevier. — 43 p. — ISSN: 1566-1199.«Organic Electronics» is a journal whose primary interdisciplinary focus is on materials and phenomena related to organic devices such as light emitting diodes, thin film transistors, photovoltaic cells, sensors, memories, etc.Papers suitable for publication in this journal cover such topics as photoconductive and electronic properties of organic materials, thin film structures and characterization in the context of organic devices, charge and exciton transport, organic electronic and optoelectronic devices.«Organic Electronics» provides the forum for applied, fundamental and interdisciplinary contributions spanning the wide range of electronic properties and applications of organic materials. A Letters section is included for rapid publication of short articles announcing significant and highly original results.149-160
Soon Moon Jeong, Won Hoe Koo, Sang Hun Choi, Hong Koo Baik. Properties of organic light emitting diodes by aluminum cathodes modification using Ar⁺ ion beam
Abstract:
Organic light-emitting diodes (OLEDs) with aluminum cathodes prepared by the ion beam-assisted deposition (IBAD) have a longer lifetime than thermally evaporated one. The electroluminescent features were examined to compare the rate of degradation in the devices with thermally evaporated Al cathodes and ion beam-assisted Al cathodes. The dense and highly packed Al cathode effectively prevents the permeation of H₂O and O₂ through pinhole defects, which results in retarding dark spot growth. Employing thin Al buffer layer diminished Ar⁺ ion-induced damages in phenyl-substituted poly-p-phenylene-vinylene (Ph-PPVs) and limited permeation against H₂O and O₂. The interface between Al and Ph-PPV may be modified in IBAD case, even though buffered Al layer was deposited to 30 nm by thermal evaporation prior to Ar⁺ ion beam irradiation. It is believed that the buffered Al film cannot screen the Ar⁺ ions or Al atoms wholly due to the existence of pinholes or non-deposited regions among the columnar structures.161-167
M. Schro¨dner, R.-I. Stohn, K. Schultheis, S. Sensfuss, H.-K. Roth. Polymer field effect transistors made by laser patterning
Abstract:
Polymer field effect transistors (PFETs) were made from polymeric semiconductors and insulators on flexible polymeric substrates. The electrodes were patterned from thin films of conducting polymers or metals using an excimer laser. This technique yields highly resolved source and drain electrode patterns with channel lengths below 10 lm which is a preposition for fast transistors and electronic circuits. Together with the available processing rates this technique makes a well-balanced compromise between pattern resolution and processing demands. Moreover, these PFETs show a long-term stability ofmore than two years without any special protection.168-174
M. Gorgoi, D.R.T. Zahn. ‘‘Band bending’’ in copper phthalocyanine on hydrogen-passivated Si(111)
Abstract:
Ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) were employed to study the electronic density of states of copper phthalocyanine (CuPc) layers deposited onto hydrogen passivated Si(111) substrates. The highest occupied and lowest unoccupied molecular orbital (HOMO respectively LUMO) features are found to shift gradually in the same direction with increasing film thickness. At approximately 15 nm, the shifts saturate with a total amount of about 0.4 eV.175-181
M. Andreasson, M. Tengelin-Nilsson, T.G. Andersson, L. Ilver, J. Kanski. Importance of ITO surface conditions for the interaction with thin CuPc layers
Abstract:
The electronic interaction between the transparent anode material indium tin oxide (ITO) and the common organic hole injection material copper phtalocyanine has been investigated by means of angle-resolved UV photoemission. The study was made on two differently treated ITO substrates, both cleaned in common organic solvents and one of them heated in air after the cleaning. The heat treatment efficiently removes surface carbon-containing contamination, and has also an oxidizing effect. As a result, the ITO work function is increased by 0.4–0.6 eV. This surface preparation has significant impact on the electronic properties of adsorbed CuPc. We find that the Pc HOMO level, important for transport properties, is shifting by 0.5 eV depending on surface conditions. This is interpreted as an effect of Fermi level pinning within the gap of the spin-split Cu derived bl_g molecular orbitals.182-187
Joshua N. Haddock, Xiaohong Zhang, Benoit Domercq, Bernard Kippelen. Fullerene based n-type organic thin-film transistors
Abstract:
Significant progress has been made in the area of p-type organic field effect transistors while progress in developing n-type materials and devices has been comparatively lacking, a limiting factor in the pursuit to develop complementary organic electronic circuits. Given the need for n-type organic semiconductors we have carried out studies using two different fullerene molecules, C₆₀ and C₇₀. Here, we report mobilities for C₆₀ ranging from 0.02 cm²/V s up to 0.65 cm²/V s (depending on channel length), and mobilities from 0.003 cm²/V s up to 0.066 cm²/V s for C₇₀. All devices were fabricated with organic films deposited under high vacuum but tested at ambient pressures under nitrogen.188-192
Himadri S. Majumdar, Jayanta K. Baral, Ronald Osterbacka, Olli Ikkala, Henrik Stubb. Fullerene-based bistable devices and associated negative differential resistance effect
Abstract:
We have observed bistability in single layer devices made from fullerenes (C60) mixed with polystyrene (PS) and sandwiched between two Al electrodes. By merely changing the concentration of C60 in PS we found three distinctly different device properties, namely a true insulator, a bistable device switching between an OFF and an ON state having ON–OFF current ratios larger than 104 and a write-once, read-many times (WORM) device. An additional negative differential resistance (NDR) was observed in the ON state of both the bistable and WORM devices leading to multilevel switching capability of the devices. This opens up a wide range of application possibilities of such devices in disposable printable electronics.