Publications by Libero Zuppiroli

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We have investigated the doping mechanism of pentacene with iodine and its impact on the structure and on the electronic properties of single crystals, powders, and thin films in a large range of iodine concentration up to six iodine per pentacene (PEN) molecule (I/PEN = 6). Three regimes of doping have been identified. In the low doping regime I/PEN < 0.05, the pristine pentacene structure of single crystals is maintained. Electron spin resonance (ESR) evidences a Pauli susceptibility, that is, the charact

We investigate heterojunction photovoltaic devices using the carbocyanine 1,1'-diethyl-3,3,3',3'-tetramethylcarbocyanine perchlorate (Cy5) as donor and buckminsterfullerene (C60) as acceptor. We find that photocurrent generation occurs at the in ...

Recently there has been a growing amount of attention devoted to tuneable photonic crystals (PhCs) where the optical response of PhC structures can be dynamically modified. We will show how infiltrating planar PhCs with a synthetic organic material allows ...

We have used electrically detected magnetic resonance (EDMR) to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline (Alq3). These devices were designed to identify the microscopic origin of different spin-depe ...

Doping of organic light-emitting devices using highly luminescent molecules is a well-established strategy to improve brightness, efficiency and lifetime or to adjust emission color and color purity. Laser dyes from the pyran-containing donor-acceptor family are particularly interesting for emission in the yellow and red spectral domain. In solution, these polar dyes show marked solvatochromic shifts in the absorption and emission. The fluorescence quantum efficiency also depends strongly on solvent polarit

Electrically detected magnetic resonance (EDMR) was used to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline (Alq3). These devices were designed to identify the microscopic origin of different spin dependen ...

The possibility of using surface-adsorbed monolayers on oxidized GaAs single crystals is investigated to explore liquid crystal (LC) wettability and alignment. A technological process is developed to chemically activate the GaAs surface with a view to perform the infiltration of tunable two-dimensional (2-D) photonic crystals with LC materials. We demonstrate a vapor growth method to fabricate self-organized monolayers of carboxylated derivatives on plasma-activated surfaces. Our monolayers strongly increas

We present some typical applications of our device simulation model "MOLED" which has proven to be a very useful tool for obtaining insight into the functioning of multi-layer organic light-emitting devices (OLED's). Our general approach consists of combin ...

Understanding the growth mechanism in molecular organic thin films is fundamental to their applications in organic electronics. We present an extensive study of the growth mechanism of pentacene thin films on silicon dioxide (SiO2) using atomic force microscopy. For a fixed substrate temperature Ts, the deposition rate κ is found to be a key parameter in controlling the nucleation density in the submonolayer regime and hence transport properties in the first layer of the organic

Oriented films of tetracene and pentacene have been obtained by high vacuum sublimation onto oriented poly(tetrafluoroethylene) (PTFE) substrates. Polymorphism, orientation, and morphology of the pentacene and tetracene films are studied as a function of deposition parameters [substrate temperature (Ts), deposition time (t), and deposition rate (τ)] using X-ray and electron diffraction, transmission and scanning electron microscopies and atomic force microscopy (AFM). Oriented films of the tr

By applying various surface treatments to the oxide gate of pentacene transistors, both in vacuum (H2, O2 and Ar plasma treatments) and in aqueous solution, we were able to vary the balance between oxygen-free radicals (Si•), oxygen-centered radicals (Si−O ...

The invention concerns a electroluminescent device with a multilayer structure comprising: i) a first electrode including a layer, consisting of a transparent or translucent conductive material selected among metal oxides and metal nitrides, said layer being deposited on a transparent support, consisting of a glass, silicon, alumina plate, or a polymer sheet; ii) a second electrode; iii) a layer, arranged between the two electrodes, comprising a semiconductor and electroluminescent solid organic substance,

Several organic and inorganic materials have emerged as promising candidates for the active layer of field-effect transistors (FETs) fabricated on flexible substrates. The charge transport models necessary for device optimization in these systems are at di ...

A new series of iridium(III) mixed ligand complexes TBA[Ir(ppy)2(CN)2] (1), TBA[Ir(ppy)2(NCS)2] (2), TBA[Ir(ppy)2(NCO)2] (3), and [Ir(ppy)2(acac) (4) (ppy = 2-phenylpyridine; acac = acetoylacetonate, TBA = tetrabutylammonium cation) have been developed and fully characterized by UV-vis, emission, IR, NMR, and cyclic voltammetric studies. The lowest energy MLCT transitions are tuned from 463 to 494 nm by tuning the energy of the HOM

The internal electric field in multilayer organic light-emitting diodes (OLEDs) is investigated using a combination of experimental measurement and numerical device modeling. This approach results in a detailed understanding of the functioning of a multilayer OLED. The method is applied to a standard device structure that has received broad attention in literature. From the experimental part, we have demonstrated that the average electric field inside the hole transport layer is larger than or equal to the

Monolayer adsorption of benzoic acid derivatives on activated oxide surfaces from solution and from the vapor phase are investigated with the view of modifying the work function of a conductive substrate. Para-substituted benzoic acids with a wide range of electrical dipoles allow adsorption to be followed by measuring the surface potential of the grafted substrates using the Kelvin probe technique. From the linear correlation between adsorbed molecular dipole and work function, it is possible to obtain the

MOLED solves the dynamics of electrons and holes in multilayer organic light emitting diodes (OLED). The carriers are injected on the positive and negative electrodes of the device by tunneling through a potential barrier. Thermal excitation processes across the barrier are also included. In the interior of the device the electron-hole recombination occurs when the two carriers are close enough, according to a model inspired from the one of Langevin. A fraction of these recombined pairs gives photons. The c

We present a theoretical and experimental study of a multilayer organic light emitting device (OLED) with a partially doped emission layer. An extended version of our established "MOLED" device model is used to understand the effects of the partially doped layer on the transport behavior and on the radiative charge recombination distribution as a function of applied bias. A step by step discussion of the possible mechanisms that can be introduced by doping and the resulting changes on the device properties

We present a model of charge transport in organic molecular semiconductors based on the effects of lattice fluctuations on the quantum coherence of the electronic state of the charge carrier. Thermal intermolecular phonons and librations tend to localize p ...

In organic light emitting devices, doping of the electroactive organic layer with highly luminescent molecules has been shown to considerably increase device performance and lifetime. In most cases, the doping molecule does not act as a charge donor or an acceptor as in classical semiconductors, but is used to enhance light emission and to tune the emission color. By using the laser dye derivative 4-(dicyanomethylene)-2-methyl-6-{ 2-[(4-diphenylamino)phenyl]ethyl}-4H-pyran as dopant in a standard organic li

Libero Zuppiroli

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Electronic and structural evidences for charge transfer and localization in iodine-doped pentacene

Interface modification to optimize charge separation in cyanine heterojunction photovoltaic devices

Tuning the optical properties of planar photonic crystals by liquid crystal infiltration

Transport and recombination in organic light-emitting diodes studied by electrically detected magnetic resonance

Space charge and polarization effects upon doping organic light-emitting diodes with pyran-containing donor-acceptor molecules

Spin dependent transport and recombination in organic light-emitting diodes

Benzoic and aliphatic carboxylic acid monomolecular layers on oxidized GaAs surface as a tool for two-dimensional photonic crystal infiltration

Insights into OLED functioning through coordinated experimental measurements and numerical model simulations

Correlated growth in ultrathin pentacene films on silicon oxide: effect of deposition rate

Orienting tetracene and pentacene thin films onto friction-transferred poly(tetrafluoroethylene) substrate

From oxide surface to organic transistor properties: the nature and the role of oxide gate surface defects

Electroluminescent device

Charge transport mechanisms in organic and microcrystalline silicon field-effect transistors

Highly Phosphorescence Iridium Complexes and their Application in Organic Light-Emitting Devices

Internal electric field and charge distribution in multilayer organic light-emitting diodes

Solution versus vapor growth of dipolar layers on activated oxide substrates

MOLED: simulation of multilayer organic light emitting diodes

Conditions of recombination zone splitting in organic light-emitting diodes

Quantum coherence and carriers mobility in organic semiconductors

Splitting of the recombination zone in organic light emitting diodes by dye doping