T. Fasolino

Optical properties of polystyrene-ZnO nanocomposite scattering layer to improve light extraction in organic light-emitting diode

In this work, experimental measurements on polystyrene-ZnO nanocomposite scattering films and on organic light-emitting device with and without the scattering layers are presented. The results are also compared with Henyey-Greenstein radiativetransfer model to narrow down the parameters that can be important in the identification of more suitable scattering layers. As a result, an increase of efficiency of about 30% has been obtained that it can be translated in 60% of outcoupled light in respect to the total generated amount.

Insights into thermal degradation of organic light emitting diodes induced by glass transition through impedance spectroscopy

Highly sensitive alternate current (ac) impedance measurements with variable temperature have been performed to investigate the optical and electrical failure mechanisms during the glass transition phenomena in the archetypal ITO/TPD/Alq3/Al organic light emitting diode (OLED) structure. Since the device degradation is mainly related to the lower glass transition temperature (Tg) of the N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), this study is focused on the frequency response of thin TPD films approaching the glassy region. The related experimental data are discussed in the framework of the universal dielectric response model. By ac measurements, TPD glass transition temperature is located and temperature regions with different OLED behaviors are evidenced. The relation between the behaviors of TPD frequency response and of the OLED electro-optical response, while the temperature approaches the glass transition region, is discussed.

Electrooptical Analysis of Effects Induced by Floating Metallic Interlayers in Organic LEDs

The aim of this paper is to investigate the electrical and optical property modifications that can be related to the presence of a nanometric metallic layer at the interface between two organic emissive materials in a stacked structure. For purposes of comparison, reference devices have also been analyzed to emphasize the increase of electrical switching and hysteresis behaviors in current-voltage plots and spectral variations in electroluminescence. In this paper, we have tried to summarize the electrical effects of the floating nanometric thin metallic layer by extracting a small number of parameters which can represent the current state of the device.

Electrical stress effects on organic thin-film transistor with solution-processed TIPS-pentacene and poly-4-vinylphenol dielectric

Organic thin-film transistors (OTFTs) with bottom-gate top-contacts architecture have been fabricated on glass substrates using solution-processed TIPS-pentacene (triisopropylsilyl pentacene) as semiconductor and cross-linked PVP (poly(4-vinylphenol)) as insulator, with Gold contacts evaporated through shadow masks. Applying constant electrical stress for short time on both gate and drain, an increase of drain current respect just finished devices have been observed in output and transfer characteristics.

Organic LED safe-operating area investigated through high applied field dependences

In this paper, the electrical and optical properties of organic light emitting diodes (OLEDs) are analyzed, deriving the devices limits at high applied electric fields. In particular, for different device thicknesses, it is possible to conclude that the optical breakdown can be attributed to a surface phenomenon, that the temperature of electrical failure is significantly different from the optical one, that the two phenomena of failure are markedly similar at different thicknesses and that there is a maximum field beyond which the thin cathode may be destroyed due to phenomena not agreeable to thermal events.

CATHECTOR: A GAMMA-RAY DETECTOR IN A CATHETER

This work is aimed to study the feasibility of a low energy gamma-ray detector for nuclear medicine to be inserted into a body cavity, duct, or vessel. The small dimension detector concept is based on a CsI:Tl scintillation crystal coupled to a Si Avalanche Photodiode (APD) mounted in a catheter. Due to the availability of Tc in nuclear medicine departments, 140 keV photons have been considered for detector design. At this energy the response concerns a more extended volume nearby the cathector than in the case of beta emitting radiotracers. Monte Carlo simulations have been performed and results have then been compared to experimental ones. The latter have been obtained using a Co radioisotopic source and a laboratory setup including a detector having dimensions not optimized coupled to a low-noise conventional electronics. Count rates and sensitivities have been measured approaching a point source to the detector along some paths and considering different background irradiation levels.

INK‐JET PRINTING OF PF6 FOR OLED APPLICATIONS

In the last years there has been much interest in applying ink‐jet printing (IJP) technology to the deposition of several materials for organic electronics applications, including metals, polymers and nanoparticles dispersions on flexible substrates. The aim of this work is to study the effect of ink‐jet deposition of polymer films in the manufacturing of OLED devices comparing their performances to standard technologies. The ink‐jet printed polymer is introduced in an hybrid structure in which other layers are deposited by vacuum thermal evaporation. The electrical and optical properties of the obtained devices are investigated.OLEDs with the same structure were fabricated by spin‐coating a polymer film by the same solution used as ink. Results have been compared to the above ones to determine how the deposition method affects the device optoelectronic properties.