Control of Light-Emitting Polymer Devices Using Polymer/Polymer Interfaces

1997 ◽  
Vol 488 ◽  
Author(s):  
A. J. Epstein ◽  
Y. Z. Wang ◽  
D. D. Gebler ◽  
D. K. Fu ◽  
T. M. Swager
Keyword(s):  
Reverse Bias ◽  
Forward Bias ◽  
Single Layer ◽  
Hole Transport ◽  
Cathode Side ◽  
Emeraldine Base ◽  
Polymer Interfaces ◽  
Light Emitting ◽  
Polymer Devices ◽  
Control Light

AbstractWe present the use of polymer/polymer interfaces to control light-emitting polymer devices. Bilayer devices utilizing poly(9-vinyl carbazole) (PVK) as a hole transporting/electron blocking polymer together with a pyridine containing electron transporting layer show dramatically improved efficiency and brightness as compared to single layer devices. This is attributed to charge confinement and exciplex emission at the PVK/emitting polymer interface. The introduction of emeraldine base (EB) form of polyaniline (PAN) on both side of the emitting layer enables the device to work under both forward and reverse bias, as well as in AC modes. Interfaces play an important role in the operation of these devices. Furthermore, when the EB is replaced by sulfonated polyaniline (SPAN) on the cathode side and the emitting layer is properly modified to balance electron and hole transport, the device generates different colors of light, red under forward bias and green under reverse bias.

Highly efficient single-layer blue polymer light-emitting diodes based on hole-transporting group substituted poly(fluorene-co-dibenzothiophene-S,S-dioxide)

2017 ◽  
Vol 5 (37) ◽  
pp. 9680-9686 ◽  
Author(s):  
Feng Peng ◽  
Na Li ◽  
Lei Ying ◽  
Wenkai Zhong ◽  
Ting Guo ◽  
...  
Keyword(s):  
Blue Light ◽  
High Performance ◽  
Light Emitting Diodes ◽  
Single Layer ◽  
Random Copolymer ◽  
Hole Transport ◽  
Light Emitting ◽  
Hole Transporting ◽  
Polymer Light Emitting Diodes ◽  
Copolymer Poly

We developed a series of high-performance blue light-emitting polymers that contain hole-transport moieties comprising carbazole or triphenylamine substituents in the side chains of random copolymer poly(fluorene-co-dibenzothiophene-S,S-dioxide) (PFSO).

ZnO Nanowire/p-GaN Heterojunction LEDs

2007 ◽  
Vol 1018 ◽  
Author(s):  
Heiko O. Jacobs ◽  
Jesse Cole ◽  
Amir M. Dabiran ◽  
Heiko O. Jacobs
Keyword(s):  
Reverse Bias ◽  
Forward Bias ◽  
Zno Nanowires ◽  
Hole Injection ◽  
Zno Nanowire ◽  
Defect States ◽  
Light Emitting ◽  
Current Voltage ◽  
Distinct Color ◽  
Two Peaks

AbstractThis article reports forward and reverse biased emission in vertical ZnO nanowire/p-GaN heterojunction light emitting diodes (LEDs) grown out of solution on Mg-doped p-GaN films. The electroluminescence spectra under forward and reverse bias are distinctly different. Forward bias showed two peaks centered around 390 nm and 585 nm, while reverse bias showed a single peak at 510 nm. Analysis of the current-voltage characteristics and electroluminescence spectra is presented to determine the transport mechanism and location of electron hole recombination. Reverse bias transport and luminescence are attributed to hot-hole injection from the ZnO nanowires into the GaN film through tunneling breakdown. Forward bias transport and luminescence are attributed to hole injection from the GaN into the ZnO and recombination at defect states inside the ZnO yielding distinct color variations between individual wires. Major resistive losses occurred in the GaN lateral thin film connecting to the vertical ZnO nanowires.

Single-layer small molecular organic light emitting diodes without hole transport layer

2009 ◽  
Vol 517 (11) ◽  
pp. 3382-3384 ◽  
Author(s):  
Zhaoxin Wu ◽  
Bo Jiao ◽  
Xuanke Zhao ◽  
Xun Hou ◽  
Liduo Wang ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Single Layer ◽  
Hole Transport ◽  
Organic Light Emitting Diodes ◽  
Transport Layer ◽  
Hole Transport Layer ◽  
Light Emitting ◽  
Organic Light

Visible Electroluminescence from Al-Porous Silicon Reverse Bias Diodes Formed on the Base of Degenerate N-Type Silicon

1994 ◽  
Vol 358 ◽  
Author(s):  
S. Lazarouk ◽  
V. Bondarenko ◽  
P. Pershukevich ◽  
S. La Monica ◽  
G. Maiello ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Reverse Bias ◽  
Light Emission ◽  
Electrochemical Etching ◽  
Forward Bias ◽  
Applied Bias ◽  
Light Emitting ◽  
Type Silicon ◽  
Silicon Devices ◽  
Preparation Conditions

ABSTRACTWe demonstrate current induced visible light emission from Schottky junctions between aluminium electrodes and porous silicon formed by electrochemical etching of degenerate n+ -type silicon. HF concentration and anodizing current were chosen to yield preparation conditions in the transition region between electropolishing and porous silicon formation regimes. The light emitting diodes were formed by magnetron sputtering of aluminum on the porous silicon surface. Visible electroluminescence (EL) was recorded when dc or ac voltages larger than 4 V were applied between the aluminium electrodes. The visible EL appears in the dark, at the edge of the electrodes at a reverse bias of 5-6 V. The intensity of emitted light increases with applied voltage; at applied bias higher than 7 V the light emitted was observable by the naked eye at normal daylight. Compared to forward bias solid state contact porous silicon devices, the structure has an increased stability (after 100 hours of continuous operation under a 7 V reverse bias, no appreciable modification was observed in emission intensity). The main features of this electroluminescence are very similar to the ones observed under avalanche breakdown of silicon p-n junctions.

Influence of Different Atmospheres on the Life Time of Porous Silicon Light-Emitting Devices

2002 ◽  
Vol 737 ◽  
Author(s):  
B.R. Jumayev ◽  
H.L. Tam ◽  
K.W. Cheah ◽  
N.E. Korsunska
Keyword(s):  
Porous Silicon ◽  
Reverse Bias ◽  
Present Report ◽  
Forward Bias ◽  
Life Time ◽  
Visible Range ◽  
Light Emitting ◽  
Light Emitting Devices ◽  
Cu Alloy ◽  
Metal Diffusion

ABSTRACTIn present report, we investigated the degradation processes in porous silicon light-emitting devices (LED) in different atmospheres (O2, N2, air and vacuum) by photoluminescence (PL), electroluminescence (EL), lifetime (LT) and I-V characteristic measurements as well as by Energy Dispersive X-ray Spectroscopy (EDS). The contacts were made by evaporation of Au and Au/Cu alloy. The LEDs emit in visible range at forward and reverse bias. As a rule, full width at half maximum of EL spectrum is wider than that of PL spectrum. The bias direction of applied voltage during degradation change EL, PL, I-V characteristics, and LT of the LEDs. At forward bias, LT degradation is less than that in reverse bias.The degradation of LEDs during forward bias did not produce any change in the spectral shape of EL and PL. At reverse bias, degradation led to red shift in the peak of EL and PL. The results show that the lifetime of LEDs with Au contact is longer than Au-Cu. Operating in different atmospheres, the LT in vacuum is longest and is more than 100 hours in reverse bias at room temperature.Possible mechanisms of degradation of LEDs are discussed. It is proposed that degradation is connected mainly with two processes: oxidation and metal diffusion. It is shown that the oxygen and metal in ionic state can diffuse quickly. Hence, in forward bias, the diffusion of metal would dominate, and in reverse bias, diffusion of oxygen dominates.

scholarly journals Virtual Screening of TADF Emitters for Single-Layer OLEDs

2021 ◽  
Vol 9 ◽  
Author(s):  
Kun-Han Lin ◽  
Gert-Jan A. H. Wetzelaer ◽  
Paul W. M. Blom ◽  
Denis Andrienko
Keyword(s):  
Light Emitting Diode ◽  
Single Layer ◽  
Delayed Fluorescence ◽  
Hole Transport ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Organic Light Emitting Diode ◽  
Thermally Activated ◽  
Organic Light ◽  
Donor And Acceptor

Thermally-activated delayed fluorescence (TADF) is a concept which helps to harvest triplet excitations, boosting the efficiency of an organic light-emitting diode. TADF can be observed in molecules with spatially separated donor and acceptor groups with a reduced triplet-singlet energy level splitting. TADF materials with balanced electron and hole transport are attractive for realizing efficient single-layer organic light emitting diodes, greatly simplifying their manufacturing and improving their stability. Our goal here is to computationally screen such materials and provide a comprehensive database of compounds with a range of emission wavelengths, ionization energies, and electron affinities.

Ni–Cu Nanoparticles-Embedded Ag-Based Reflector for High-Efficiency Light-Emitting Diodes

2020 ◽  
Vol 20 (11) ◽  
pp. 6732-6737
Author(s):  
Eun-Kyung Chu ◽  
Kab Ha ◽  
Beom-Rae Noh ◽  
Young-Ju Kwon ◽  
Semi Oh ◽  
...  
Keyword(s):  
Flip Chip ◽  
High Efficiency ◽  
Light Emitting Diodes ◽  
Forward Bias ◽  
Light Output ◽  
Single Layer ◽  
Cu Nanoparticles ◽  
Light Emitting ◽  
Forward Bias Voltage ◽  
Ag Reflector

We investigated the use of a silver reflector embedded with Ni–Cu nanoparticles to achieve low resistance and high reflectivity in GaN-based flip-chip light-emitting diodes. Compared to a single layer of Ag, the NC-NPs/Ag reflector exhibits a higher light reflectance of ~90% at a wavelength of 450 nm, a lower contact resistance of 4.75 × 10−5 II cm2, and improved thermal stability after annealing at 400°C. The NC-NPs formed after the annealing process prevents agglomeration of the Ag layer, while also reducing the Schottky barrier height between the p-GaN layer and metal reflector. The LED fabricated with a NC-NPs/Ag reflector exhibited a forward-bias voltage of 3.13 V and an improvement in light output power of 36.6% (at 20 mA), when compared with the LED composed of a Ag SL. This result indicates that the NC-NPs/Ag reflector is a promising p-type reflector for high-intensity light-emitting diodes.

Degradation of AlGaN/GaN Light Emitting Diodes caused by Carbon Contamination with Reverse-bias Stress Test in Water Vapor

2016 ◽  
Vol 19 (1) ◽  
pp. 011-013
Author(s):  
Hsiang Chen ◽  
Yun Yang He ◽  
Min Han Lin ◽  
Shang Ren Lin ◽  
Sheng-Hao Hung ◽  
...  
Keyword(s):  
Reverse Bias ◽  
Light Emitting Diodes ◽  
Ion Beam ◽  
Stress Test ◽  
Forward Bias ◽  
X Ray Diffraction ◽  
Carbon Contamination ◽  
Light Emitting ◽  
Bias Stress ◽  
Focus Ion Beam

Resolving failure origins of AlGaN/GaN light emitting diodes (LED) has received intensive study recently. In this study, formation of GaCO3 caused by carbon contamination may result in deformation of the electrode near the surface and degrade the device. The electrochemical reactions may cause device damages. Degradation in electrical properties is observed in I-V characteristics. Forward-bias and reverse-bias EL images are used to trace the damaged areas. Furthermore, focus ion beam (FIB), scanning electron microscope (SEM), energy dispersive X-ray diffraction (EDX) are applied to examine the damaged areas. Results indicate that formation of GaCO3 may deform the electrode, generate the reverse-bias EL and cause the degradation.

Excitation Mechanisms and Light Emitting Device Performances in Er-Doped Crystalline Si

1996 ◽  
Vol 422 ◽  
Author(s):  
F. Priolo ◽  
S. Coffa ◽  
G. Franzo ◽  
A. Polman
Keyword(s):  
Reverse Bias ◽  
Crystalline Silicon ◽  
Forward Bias ◽  
Depletion Region ◽  
Impact Excitation ◽  
Electron Hole ◽  
Light Emitting ◽  
Temperature Operating ◽  
Excitation Mechanisms ◽  
Er Doped

AbstractIn this paper the performances of room temperature operating light emitting diodes (LEDs), fabricated by Er ion implantation of crystalline silicon, are investigated in detail. It is shown that 1.54 μm emission is observed under both forward and reverse bias operation, with a much higher intensity under reverse bias. The excitation mechanisms of Er3+ are demonstrated to be very different in the two cases: under forward bias Er is excited through the electron - hole recombination at an Er - related level, while under reverse bias impact excitation by hot carriers represents the excitation process. This last mechanism is shown to occur with a cross section of 6 × 10−17 cm2 and population inversion of the excitable Er sites within the depletion region is demonstrated. The efficiency and limitations of this approach are also discussed.

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