André Moliton

Transport phenomena in implanted electroactive polymers

Abstract We present an overview of microscopic properties of electroactive implanted polymers according to various implantation parameters. The induced electrical properties are recorded with a general band scheme where every transport mechanism is described by basic formula. From the study of electrical parameters (direct conductivity, thermopower) with temperature, we show that low energy implanted samples present a behaviour similar to that of lightly chemically doped ones.

Thermo Electric Power Versus Temperature in Implanted Polyparaphenylene (PPP)

Abstract Polyparaphenylene (PPP) samples were implanted with alkali metal ions using different energies. They were characterized and the evolution of thermo electric power versus temperature was followed. The results may be analyzed in terms of a variable range hopping process between localized states induced near the Fermi level through implantation. Furthermore with samples implanted at low energy, a transition toward values characteristic of the expected doping shows up (n type doping with alkali metals).

Optimization of etching parameters of a fluorinated polyimide using the RIBE technique

A parametric study of etching a new type of fluorinated polyimide (6FDA-ODA) has been carried out. This kind of material was especially elaborated for plasma etching (reactive ion etching, RIE); its behaviour was tested with the reactive ion beam etching (RIBE) technique which uses an (O + ) reactive ion beam and allows independent control of the ion energy and current density of the beam. Etch rates were measured as a function of energy (E), current density (J) and incident angle (θ) of the beam with the sample normal. These rates were shown to present a maximum value (1000 A min -1 ) for an energy flux of about 3 W cm -2 ) (E = 6keV and J = 0.5 mA cm -2 ) and decreased when 9 increased. These results were then compared with etching rates obtained with chemically inert ions (Ar + ): in this case, etching rates were five times lower than those measured with O + ions.

On ranges in PPP and conductivity effects

Abstract In this paper, we present a theoretical and experimental study of ion ranges in a PPP (polyparaphenylene) target and the effect on the conductivity of the material, which is an intrinsic insulator.

Spectroscopic studies of ion implanted PPV films

Abstract The main results of the spectroscopic analyses (infrared and ultraviolet - visible - near infrared) carried out on PPV films before and after ion implantation with halogen and alkali ions are presented in this paper. The influence of both ions nature and implantation parameters on optical properties of this polymer have been pointed out and the appearence of a weak band due to doping has been observed by infrared spectroscopy.

Self-development of cellulose nitrate in linear and nonlinear regimes by ion irradiation

Abstract The general shrinkage behaviour of cellulose nitrate is studied as a function of ion fluence in the linear and the nonlinear regimes. During the first one, the self-developed thickness is linearly dependent on the exposure time, and the shrinkage rate follows a linear relationship with the lost energy E 1 and the ion influence rate φ, according to the law v = kE 1 φ ( k is a constant). In the nonlinear regime, the etch rate seems to be decreasing. We show that this fact is not the result of a change of the nature of the polymer, but that the previous law is still true providing that E 1 is the real lost energy in the remaining thickness of cellulose nitrate (CN). No separate effect of the nuclear stopping power S n or the electronic stopping power Se is observed.

Transport mechanisms in 8-tris-hydroxyquinoline aluminium (Alq3) electronic layers: a study by photodipolar absorption

This paper describes the role of traps in the electronic conductivity of tris(8-hydroxyquinoline)aluminium (Alq3) in a conventional sandwich structure with indium tin oxide and aluminium electrodes. New results obtained by photodipolar absorption techniques and impedance spectroscopy are presented. The former method acts as a probe to highlight the role of traps. It is shown that optical pumping of electrons to trap levels gives a clear increase in dielectric absorption due to the reorientation of dipoles associated with trapped charges. The trap depth is estimated to be around E t = 0.19 eV, a value in good agreement with theoretical calculations and thermoluminescence measurements. The latter method permits a representation of the sample in terms of a circuit composed of a parallel capacitor (C p) and resistor (R p) both in series with a resistor R s ≈ 50 Ω located on the anode side. A logarithmic plot of R p as a function of the dc bias voltage gives a linear law that is recognized, for the first time, to be a consequence of a trapped charge limited (TCL) current. The linearity can be improved by the introduction of a field-dependent mobility.

Optical characterization of polychromatic organic light emitting diodes

Luminance and quantum yields of organic light emitting diodes (OLEDs) are generally calculated by using a hypothetic monochromatic emission even though the actual external emission is lower than the internal emission because of internal reflection, and is polychromatic. For organic materials, we present the effects of the total internal reflection on quantum yields. Calculations for the luminance and the efficiency of an ideal pseudomonochromatic source are compared with those for a real polychromatic source. While we demonstrate that the calculation of the yield is practically unchanged whatever hypothesis is used, we do show, however, that by assuming that the source is pseudomonochromatic, the luminances of green and blue OLEDs are overvalued or undervalued by a factor of 4, respectively.

Elaboration of transparent conductive oxide films for flexible organic electroluminescent devices

In this study, we presented high-performance flexible organic light-emitting diodes (FOLEDs); to do so, we prepared indium-tin oxide (ITO) thin layers by ion beam sputtering (IBS) on polyethylene terephtalate (PET) substrates in soft low temperature conditions. The IBS technology seems well adapted to us to adjust the conduction level of the interface films to the one of the various organic materials making up the fabrication processes of the organic optoelectronic components; moreover this technique does not require a high substrate temperature or an annealing after ITO deposition to crystallize the obtained layers. Because of the great number of deposition parameters (oxygen flow, substrate temperature, deposition rate...) playing interdependent roles and strongly influencing the electrical, optical and structural properties of the layers, we optimized the effects of these different parameters separately by using electrical and optical characterizations as well as X-ray diffraction analyses. The performances of FOLEDs on PET substrate with different ITO thicknesses were investigated and compared to the ones of a conventional organic light-emitting diode realized on glass substrate and according to the same device configuration.

Surface modelling of organic solar cells

Modelling of physical phenomena in optoelectronic devices enables to define new strategies to optimize organic components (organic photovoltaic cells (OPVs), organic light emitting diodes (OLEDs), etc ….).