DC lifetime of encapsulated organic light emitting diodes

Organic light emitting diodes (OLEDs) are ideal sources for chemical and biological optical sensors, due to their simplicity, low cost (disposable applications) and possibility to be integrated on chip and fabricated in the form of large 2D arrays (microarray fluorescence) even on flexible plastic substrates. OLEDs with lifetimes of a few hundreds of hours at initial luminance values in the range (500÷1000) cd/m 2 are suitable for the above applications, but these lifetimes can be achieved only by a proper encapsulation. Fast, simple and inexpensive encapsulation methods are highly desirable to keep the low cost profile and for this reasonwe report two different encapsulation structures and…

Donor/acceptor heterojunction organic solar cells

Organic solar cells (OSCs) have made very good improvements in recent years, reaching power conversion efficiencies above 10% [1]. This have been achieved through chemical synthesis of new organic materials with improved properties and also by new and more or less complex structures such as donor/acceptor (D/A) or bulk heterojunction OSCs. Here we report the results of initial development of OSCs based on the simple D/A heterojunction [2]. Copper phtalocyanine (CuPc) is used as donor organic material, whereas perylenetetracarboxylic dianhydride (PTCDA) and fullerene (C60) as acceptor organic materials. Moreover bathocuproine (BCP) is used as exciton blocking layer. Devices are fabricated by…

Microstrutural, Optical and electro-optical Properties Of Ba0.5Sr0.5TiO3 Thin Film Deposited By Pulsed Laser Deposition For Active Low Loss Waveguide Applications

Barium Strontium Titanate (Ba0.5Sr0.5TiO3 or BST) films were grown by means of a reactive pulsed laser deposition technique on SiO2/Si substrates. Microstructural and surface morphology of BST films were characterized by X-ray diffraction (XRD) scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Enhanced efficiency of organic light emitting diodes by NaOH surface treatment of indium tin oxide anode

Fabrication and Characterization of Dye-Sensitized Solar Cells

Among the next-generation solar cells, a predominant role is played by Dye sensitized solar cells (DSSC) based on ruthenium complexes as sensitizers. They take advantage of a photoelectrochemical system to transform solar radiation into electric energy. In fact, DSSCs represent a cost-effective alternative to traditional silicon-based photovoltaic devices and they do not require expensive and sophisticated apparatus for their fabrication. In this work, we have produced and tested ruthenium DSSCs. In particular, we have measured the main parameters of these cells, such as the electrical and power performances and the efficiency levels, at different irradiance levels and at different incident…

A simple method for measuring OLEDs efficiency

External quantum efficiency (EQE) of organic light emitting diodes (OLEDs) is among the most important parameters for devices assessment and for comparing OLEDs performance. The EQE is the ratio of the total number of photons emitted by the OLED in all directions to the number of electrons injected.

Blue-violet heterojunction LEDs based on hydrothermally synthesized ZnO nanorods

Zinc oxide nanorods have great potential for the realization of high efficiency heterostructure LEDs based on p-doped GaN. Well-aligned vertical nanorods are desirable to enhance the LED outcoupling performances due to a better confinement of the light [1]. However, due to the lack of reproducible p-type ZnO, a p-GaN substrate is still needed. This work reports on the fabrication of n-ZnO/p-GaN heterojunction LEDs based on vertical ZnO nanorods grown by hydrothermal method. The chemical reaction in the hydrothermal growth of ZnO is based on the decomposition of zinc nitrate, (Zn(NO3)2) with resulting Zn2+ ions reacting with the hydroxyl ions obtained by the thermal degradation of hexamethyl…

Electrochemical and chemical synthesis of CIS/Zn(S,O,OH) for thin film solar cells

In this work, we are reporting results on the electrodeposition of the CuInSe2 thin films on molybdenum thin foil substrates. We have used an aqueous non-buffered electrolyte and a careful choice of deposition parameters to ensure a good quality and composition of the deposited films. In addition, CdS was replaced in the buffer layer with a wider bandgap Zn(S,O,OH) film obtained by chemical bath deposition. The deposited films were annealed in inert atmosphere at different temperatures. The influence of annealing temperature on the properties of the films is briefly discussed. Films were also characterized by photoelectrochemical and I-V measurements. Structural characterization was carried…

Fabrication and characterization of Donor/Acceptor heterojunction organic solar cells

Results of initial development of organic solar cells having the Donor/Acceptor heterojunction structure with and without an exciton blocking layer are reported. Characterization is carried out in AM1.0 condition with 100 mW/cm2 incident optical power density. The best device has the exciton blocking layer and exhibits an open circuit voltage VOC = 0.43 V, a short circuit current density JSC = 2.35 mA/cm2 with a fill factor FF ≈ 50%, an external quantum efficiency (electrons/s over incident photons/s) EQE ≈ 5% and a power conversion efficiency of about 0.5%.

Characterization of charge transport in molecular organic films by the Time of Flight method

A simple method for the photometric characterization of organic light-emitting diodes

A simple method for the photometric characterization of organic light-emitting diodes (OLEDs) is reported. It is based on the indirect measurement of the total emitted optical power by using a calibrated photodiode and the optical emission spectrum and space emission diagram of the OLED. From this and by measuring the current–voltage characteristic of the OLED all the relevant radiometric and photometric quantities can be extracted, including the external quantum efficiency. The usual method to collect all photons emitted by a LED source in the half space uses an integrating sphere with the LED source placed at the entrance hole and a photodiode (PD) placed at an exit hole at some point on …

Measuring the efficiency of OLEDs using a Si photodiode

LED organici con emissione nel blu

We report the development of blue organic light emitting diodes (OLEDs) based on molecular materials. Electrical characteristics and quantum efficiency of single layer devices and triple layer devices comprising further a hole blocking layer and an electron injection layer are compared and prospects for applications to passive matrix displays and fluorescence integrated biosensors are also discussed.

Localization in Structured Environments with UWB Devices without Acceleration Measurements, and Velocity Estimation Using a Kalman–Bucy Filter

In this work, a novel scheme for velocity and position estimation in a UWB range-based localization system is proposed. The suggested estimation strategy allows to overcome two main problems typically encountered in the localization systems. The first one is that it can be suitable for use in environments where the GPS signal is not present or where it might fail. The second one is that no accelerometer measurements are needed for the localization task. Moreover, to deal with the velocity estimation problem, a suitable Kalman–Bucy filter is designed and it is compared, experimentally, with a particle filter by showing the features of the two algorithms in order to be used in a localization …

Novel Configuration for a C-Band Axial Vircator With High Output Power

We present a novel configuration for an axial virtual cathode oscillator (Vircator) operating in the C-band and designed for high output power applications. In order to enhance the efficiency, we have employed a geometry with up to seven reflectors along the drift space. While in previous research works this optimization process has been performed only varying the reflectors radii while using a fixed distance between reflectors,in our work we propose an optimization in terms of both reflectors radii and distances. Our optimized structure for the axial Vircator is able to provide an efficiency up to 15.6% and an output power of 1.6 GW in the C-band, with a working voltage of 510 kV and a cat…

A comparative study of encapsulation structures for OLEDs

Encapsulation is the final and most important step in the fabrication of organic light emitting diodes (OLEDs). An OLED operated in air can have a lifetime, defined as the time it takes for the luminance to decrease to half of its initial value, up to a few hours or less [1] due to degradation mechanisms induced by water vapour and oxygen. For emerging niche applications, such as OLED fluorescence biosensors [2] for routine laboratory analysis, the OLED is operated for a short period of time and then it must be disposed of. In this case OLEDs lifetimes of the order of a few hundreds of hours at initial luminance values in the range (500 1000) cd/m2 can be considered acceptable. To keep th…

Misura della mobilità dei portatori di carica in semiconduttori organici

Comparison between SiC and GaN switching devices in fast-recharging systems for electric vehicles

Recently, the improvement of the semiconductor devices to achieve higher efficiency and higher power density has risen to interest. Si carbide and gallium nitride offer faster switching frequency and lower losses; however, the knowledge of the behaviour of these devices is not mature. In this paper, a system for fast charging of batteries for electric vehicles based on an isolated DC-DC converter equipped with both SiC and GaN devices is presented and an interesting experimental comparison among these two technologies will be given in terms of dynamic performances, electromagnetic compatibility, stability, efficiency, and so on.