Search results for "organic light emitting diode"
showing 9 items of 9 documents
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…
Impedance of space-charge-limited currents in organic light-emitting diodes with double injection and strong recombination
2006
The impedance model for a one-carrier space-charge-limited (SCL) current has been applied to explain some experimental features of double carrier organic light-emitting diodes. We report the analytical model of impedance of bipolar drift transport in SCL regime in the limit of infinite recombination. In this limit the ac impedance function is identical to that of a single carrier device, with a transit time modified by the sum of mobilities for electrons and holes, μn+μp. The static capacitance C(ω→0) is a factor of ¾ lower than the geometric capacitance, as observed for single carrier devices, but it is shifted to higher frequencies. It follows that impedance measurements in the dual-carri…
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.
Effects of steric encumbrance of iridium( iii ) complex core on performance of solution-processed organic light emitting diodes
2020
Iridium(iii) complexes are the most frequently applied commercialized green and red emitters for organic light emitting diode (OLED) displays. Throughout years a significant research effort has been devoted to modify these compounds, in order to make them suitable for cost-effective solution-processing techniques, such as inkjet printing. To achieve this, the inherent tendency of the complex molecules to form poorly emissive aggregates needs to be suppressed. In many cases this has been achieved by an encapsulation of the iridium(iii) complex core with dendritic structures, composed of either passive or charge-transporting fragments. In order to validate this approach, we acquired three str…
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.
Millisecond radiative recombination in poly(phenylene vinylene)-based light-emitting diodes from transient electroluminescence
2007
The current and electroluminescence transient responses of standard poly phenylene vinylene -based light-emitting devices have been investigated. The electroluminescence time response is longer milliseconds scale than the current switch-off time by more than one order of magnitude, in the case of small area devices 0.1 cm2 . For large area devices 6 cm2 the electroluminescence decay time decreases from 1.45 ms to 100 s with increasing bias voltage. The fast current decay limits the electroluminescence decay at higher voltages. Several approaches are discussed to interpret the observed slow decrease of electroluminescence after turning off the bias. One relies upon the Langevin-type bimolecu…
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.
New Electroactive Polymers with Electronically Isolated 4,7-Diarylfluorene Chromophores as Positive Charge Transporting Layer Materials for OLEDs
2021
The OLED materials were developed in the frame of project funded by the Research Council of Lithuania (grant No. S-LLT-19-2). B.Z. is thankful to the National Natural Science Foundation of China (No. 51773195), and the Research & Development Projects in Key Areas of Guangdong Province, China (No. 2019B010933001). We are also obliged to D. Volyniuk for measurements of the ionization potentials.
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…