Organic Electronics 2002 Volume 3 №01

Elsevier. — 52 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.1-7
L. Gross, C. Seidel, H. Fuchs. Organic monolayers with uniform domain orientation and reduced antiphase boundaries – MBE of perylene on Au(110)
Abstract:
The growth of epitaxial monolayers of perylene on Au(1 1 0) was investigated by means of scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The preparation was done by molecular beam epitaxy (MBE). The experimental setup allowed us to perform LEED or STM measurements during evaporation. The pattern of the adsorbed perylene molecules shows several dosage-induced structural transitions, leading to a final coincident monolayer structure with uniform domain orientation and a low density of antiphase boundaries. The underlying Au(110) interface exhibits several different reconstructions, depending on the perylene coverage.9-13
Paulo N.M. dos Anjos, Hany Aziz, Nan-Xing Hu, Zoran D. Popovic. Temperature dependence of electroluminescence degradation in organic light emitting devices without and with a copper phthalocyanine buffer layer
Abstract
Temperature dependence of electroluminescence degradation was investigated in two types of organic light emitting devices (OLEDs) based on tris(8-hydroxyquinoline) aluminum (AlQ3) emitter molecule, one without and another with copper phthalocyanine (CuPc) buffer layer at the hole-injecting contact interface. Electroluminescence degradation in time was measured for devices operated at 22 and 70 °C. Results unexpectedly showed that devices without the CuPc buffer layer demonstrated negligible change in half-life when operated at 22 or 70 °C, while devices with the CuPc layer showed the expected decrease in half-life when the temperature was increased. The results are explained within the framework of recently proposed OLED degradation mechanism, which identifies AlQ₃ cations as unstable, leading to device degradation.15-21
E.Z. Kurmaev, K. Endo, T. Ida, T. Otsuka, S.Y. Kim, G.S. Chang, A. Moewes, N.Y. Kim, C.N. Whang, D.L. Ederer. The electronic structure of TPD films grown by different methods
Abstract
We present X-ray photoelectron spectra and X-ray emission spectra of N,N'-bis (3-methylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,40-diamine (TPD) films excited with synchrotron radiation. The measurements are compared with densityfunctional theory calculations performed for a TPD monomer and the electronic structure of this material is discussed in detail. The TPD films studied in this work were prepared by ionized and neutral cluster beam deposition (ICBD and NCBD, respectively) as well as by thermal evaporation. X-ray fluorescence measurements show that the ICBD technique provides the most promising way of preparing high quality TPD films with strong electroluminescence. C–N bonds in the TPD structure are destroyed under NCBD as well as under thermal evaporation.23-31
M.I. Alonso, M. Garriga, N. Karl, J.O. Oss o, F. Schreiber. Anisotropic optical properties of single crystalline PTCDA studied by spectroscopic ellipsometry
Abstract:
We report anisotropic spectra of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) in the optical energy range 1.5–3.7 eV, measured at room temperature by spectroscopic ellipsometry. The results were obtained on single crystals of α-PTCDA grown by temperature gradient sublimation. Spectra were measured at highly symmetric positions of the plane of incidence relative to the sample crystallographic axes and are presented as pseudo-values of refractive index n and extinction coefficient hki, which reflect a very large anisotropy of these optical functions. The spectroscopic properties of the excited states in the molecular plane (1 0 2) are analyzed; in particular, we identify clear Davydov splittings proving the formation of coherent excitons in the crystal. Out-of-plane, we observe a relatively narrow absorption peak at 2.9 eV that is ascribed to a charge-transfer transition.33-42
G. Ferrari, D. Natali, M. Sampietro, F.P. Wenzl, U. Scherf, C. Schmitt, R. Guntner, G. Leising. Current noise spectroscopy on mLPPP based organic light emitting diodes
Abstract:
Noise spectroscopy is presented to be a powerful tool to investigate the current flowing in organic light emitting diodes (oLEDs) with high sensitivity. Measurements can be performed over the whole bias range of interest, from reverse bias up to high values of forward bias voltage. From these measurements one can gain insight into the microscopic conduction processes dominating the device current and obtain valuable information for improved device modeling. In particular it is shown that the low frequency power spectrum of the tested oLEDs has a power law dependence around (1/f)^1.3 almost irrespective of device characteristics and of measurement conditions. Additionally, noise spectra are also proposed as a means to sense the initial state and the growth of degradation phenomena in these devices. The onset of degradation is shown to be signaled by current spikes that reflect on a net increase of the white noise component of about three orders of magnitude in the power spectral density, when degradation is just hardly beginning to be visible as dark spots on the emitting surface.43-51
P. Stallinga, H.L. Gomes, M. Murgia, K. Mullen. Interface state mapping in a Schottky barrier of the organic semiconductor terrylene
Abstract:
In this work we quantitatively map interface states in energy in a Schottky barrier between aluminum and the vacuum sublimed organic semiconductor terrylene. The density map of these interface states was extracted from the admittance spectroscopy data. They revealed an interface state density of ~ 2x10¹² cm ² eV ^-1 close to the valence band which decreases slightly towards midgap. Additional dc measurements show that the semiconductor bulk activation energy is 0.33 eV which may correspond to an acceptor level.