Search results for "OLEDs"
showing 10 items of 12 documents
A simple method for the photometric characterization of organic light-emitting diodes
2022
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 …
Hybrid organic-inorganic Light Emitting Diodes
2013
Hybrid organic inorganic light emitting diodes are nowadays attracting great attention due to their intrinsic air stability and solution processability, which could result in low-cost, large area, light emitting devices. Despite the fact that high luminance values have been already demonstrated in recent publications, the efficiency of HyLEDs has been limited by its peculiar hole-dominated electronic mechanism. In particular, the electron injection is promoted by the hole accumulation at the metal oxide EIL/organic interface, but at the same time this mechanism leads to limits the device efficiency. It is known from the research in OLEDs that when the recombination zone is close to an inter…
Diarylethenes in Optically Switchable Organic Light-Emitting Diodes: Direct Investigation of the Reversible Charge Carrier Trapping Process
2021
Advanced optical materials 10, (2021). doi:10.1002/adom.202101116
Flexible light-emitting electrochemical cells with single-walled carbon nanotube anodes
2016
Abstract In this work, we demonstrate flexible solution processed light emitting electrochemical cells (LECs) which use single-walled carbon nanotubes (SWCNTs) films as the substrate. The SWCNTs were synthesized by an integrated aerosol method and dry-transferred on the plastic substrates at room temperature. The addition of a screen printed poly (3,4-ethylene dioxythiophene) doped with poly (styrene sulfonate) (PEDOT:PSS) film onto the nanostructured electrode further homogenizes the surface and enlarges the work function, enhancing the hole injection into the active layer. By using an efficient phosphorescent ionic transition metal complex (iTMC) as the active material, efficacies up to 9…
A simple method for measuring OLEDs efficiency
2015
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.
DC lifetime of encapsulated organic light emitting diodes
2016
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…
A comparative study of encapsulation structures for OLEDs
2007
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…
Efficiency enhancement of organic light emitting diodes by NaOH surface treatment of the ITO anode
2009
Abstract Organic light emitting diodes (OLEDs) based on tris-(8-idroxyquinoline)aluminum (Alq 3 ) with enhanced efficiency are reported here. This is obtained by improving the charge carrier balance, through a preliminary NaOH surface treatment of the indium tin oxide (ITO) anode, in order to decrease its work function and, consequently, reduce the hole injection. The obtained devices exhibit a 1.36% external quantum efficiency and a 1.2 lm/W power efficiency at a current density of 60 mA/cm 2 . These values are more than double as compared with those of identical reference devices fabricated without the preliminary NaOH surface treatment.
LED organici con emissione nel blu
2007
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.
Study of voltage decrease in organic light emitting diodes during the initial stage of lifetime
2016
Abstract We report the results of lifetime DC testing at constant current of not-encapsulated organic light emitting diodes (OLEDs) based on Tris (8 idroxyquinoline) aluminum (Alq3) as emitting material. In particular, a voltage decrease during the initial stage of the lifetime test is observed. The cause of this behavior is also discussed, mainly linked to initial Joule self-heating of the device, rising its temperature above room temperature until thermal equilibrium is reached at steady state.