Search query: green light emitting diodes

Related papers:

abstract: CONJUGATED polymers are organic semiconductors, the semiconducting behaviour being associated with the p molecular orbitals delocalized along the polymer chain. Their main advantage over non polymeric organic semiconductors is the possibility of processing the polymer to form useful and robust structures. The response of the system to electronic excitation is nonlinear the injection of an electron and a hole on the conjugated chain can lead to a self localized excited state which can then decay radiatively, suggesting the possibility of using these materials in electroluminescent devices. We demonstrate here that poly(p phenylene vinylene) prepared by way of a solution processable precursor, can be used as the active element in a large area light emitting diode. The combination of good structural properties of this polymer, its ease of fabrication, and light emission in the green yellow part of the spectrum with reasonably high efficiency, suggest that the polymer can be used for the development of large area light emitting displays.
author_names: Jeremy H Burroughes

Donal D C Bradley

A Robinson Brown

R N Marks

K Mackay

Richard H Friend

P L Burns

Andrew B Holmes
title: Light emitting diodes based on conjugated polymers
venue: Nature
year: 1990

abstract: Solid state light emitting devices based on direct bandgap semiconductors have, over the past two decades, been utilized as energy efficient sources of lighting. However, fabrication of these devices typically relies on expensive high temperature and high vacuum processes, rendering them uneconomical for use in large area displays. Here, we report high brightness light emitting diodes based on solution processed organometal halide perovskites. We demonstrate electroluminescence in the near infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15 nm layer of CH3NH3PbI(3 x)Cl(x) perovskite emitter is sandwiched between larger bandgap titanium dioxide (TiO2) and poly(9,9' dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr( 1) m( 2) at a current density of 363 mA cm( 2) with highest external and internal quantum efficiencies of 0.76% and 3.4% respectively. In our green light emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364 cd m( 2) at a current density of 123 mA cm( 2) giving external and internal quantum efficiencies of 0.1% and 0.4% respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour tunable light emitters for low cost display, lighting and optical communication applications.
author_names: Zhi-Kuang Tan

Reza Saberi Moghaddam

May Ling Lai

Pablo Docampo

Ruben Higler

Felix Deschler

Michael B Price

Aditya Sadhanala

Luis M Pazos

Dan Credgington

Fabian C Hanusch

Thomas Bein

Henry J Snaith

Richard H Friend
title: Bright light emitting diodes based on organometal halide perovskite.
venue: Nature nanotechnology
year: 2014

abstract: Metal halide perovskite materials are an emerging class of solution processable semiconductors with considerable potential for use in optoelectronic devices1 3. For example, light emitting diodes (LEDs) based on these materials could see application in flat panel displays and solid state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4 8. However, the highest reported external quantum efficiencies of green and red light emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively still well behind the performance of organic LEDs10 12 and inorganic quantum dot LEDs13. Here we describe visible light emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3) the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display.A strategy for managing the compositional distribution in metal halide perovskite light emitting diodes enables them to surpass 20% external quantum efficiency a step towards their practical application in lighting and displays.
author_names: Kebin Lin

Jun Xing

Li Na Quan

F Pelayo Garcia Arquer

Xiwen Gong

Jianxun Lu

Liqiang Xie

Weijie Zhao

Di Zhang

Chuanzhong Yan

Wenqiang Li

Xinyi Liu

Yan Lu

Jeffrey Kirman

Edward H Sargent

Qihua Xiong

Zhanhua Wei
title: Perovskite light emitting diodes with external quantum efficiency exceeding 20 per cent
venue: Nature
year: 2018

abstract: Optimization of internal quantum efficiency (IQE) for InGaN quantum wells (QWs) light emitting diodes (LEDs) is investigated. Staggered InGaN QWs with large electron hole wavefunction overlap and improved radiative recombination rate are investigated for nitride LEDs application. The effect of interface abruptness in staggered InGaN QWs on radiative recombination rate is studied. Studies show that the less interface abruptness between the InGaN sub layers will not affect the performance of the staggered InGaN QWs detrimentally. The growths of linearly shaped staggered InGaN QWs by employing graded growth temperature grading are presented. The effect of current injection efficiency on IQE of InGaN QWs LEDs and other approaches to reduce dislocation in InGaN QWs LEDs are also discussed. The optimization of both radiative efficiency and current injection efficiency in InGaN QWs LEDs are required for achieving high IQE devices emitting in the green spectral regime and longer.
author_names: Hongping Zhao

Guangyu Liu

Jing Zhang

Jonathan D Poplawsky

Volkmar Dierolf

Nelson Tansu
title: Approaches for high internal quantum efficiency green InGaN light emitting diodes with large overlap quantum wells.
venue: Optics express
year: 2011

abstract: Considerable effort is being expended on the development of efficient silicon light emitting devices compatible with silicon based integrated circuit technology. Although several approaches are being explored, all presently suffer from low emission efficiencies, with values in the 0.01 0.1% range regarded as high. Here we report a large increase in silicon light emitting diode power conversion efficiency to values above 1% near room temperature close to the values of representative direct bandgap emitters of a little more than a decade ago. Our devices are based on normally weak one and two phonon assisted sub bandgap light emission processes. Their design takes advantage of the reciprocity between light absorption and emission by maximizing absorption at relevant sub bandgap wavelengths while reducing the scope for parasitic non radiative recombination within the diode. Each feature individually is shown to improve the emission efficiency by a factor of ten, which accounts for the improvement by a factor of one hundred on the efficiency of baseline devices.
author_names: Martin A Green

Jianhua Zhao

Aihua Wang

Peter J Reece

Michael Gal
title: Efficient silicon light emitting diodes
venue: Nature
year: 2001

abstract: High brightness InGaN/AlGaN double heterostructure blue green light emitting diodes with a luminous intensity of 2 cd were fabricated by increasing an indium mole fraction of the InGaN active layer up to 0.23. Both Zn and Si were codoped into the InGaN active layer to afford relatively stronger luminescence. The blue green emission intensity of room temperature photoluminescence became maximum when the electron carrier concentration of the InGaN active layer was around 1x1019 cm 3. Donor acceptor pair recombination is a dominant emission mechanism of the InGaN active layer. The external quantum efficiency was as high as 2.4% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half maximum of the electroluminescence were 500 and 80 nm, respectively.
author_names: Shuji Nakamura

Takashi Mukai

Masayuki Senoh
title: High brightness InGaN/AlGaN double heterostructure blue green light emitting diodes
year: 1994

abstract: Perovskite light emitting diodes (LEDs) are attracting great attention due to their efficient and narrow emission. Quasi two dimensional perovskites with Ruddlesden Popper type layered structures can enlarge exciton binding energy and confine charge carriers and are considered good candidate materials for efficient LEDs. However, these materials usually contain a mixture of phases and the phase impurity could cause low emission efficiency. In addition, converting three dimensional into quasi two dimensional perovskite introduces more defects on the surface or at the grain boundaries due to the reduction of crystal sizes. Both factors limit the emission efficiency of LEDs. Here, firstly, through composition and phase engineering, optimal quasi two dimensional perovskites are selected. Secondly, surface passivation is carried out by coating organic small molecule trioctylphosphine oxide on the perovskite thin film surface. Accordingly, green LEDs based on quasi two dimensional perovskite reach a current efficiency of 62.4 cd A 1 and external quantum efficiency of 14.36%.Solution processable halide perovskites have high luminous efficiency and excellent chemical tunability, making them ideal candidates for light emitting diodes. Here Yang et al. achieve high external quantum efficiency of 14% in the devices by fine tuning the phase and passivating the surface defects.
author_names: Xiaolei Yang

Xingwang Zhang

Jinxiang Deng

Zema Chu

Qi Jiang

Junhua Meng

Pengyan Wang

Liu Qi Zhang

Zhigang Yin

Jingbi You
title: Efficient green light emitting diodes based on quasi two dimensional composition and phase engineered perovskite with surface passivation
venue: Nature Communications
year: 2018

abstract: A series of highly emissive three coordinate copper(I) complexes, (dtpb)Cu(I)X [X Cl (1) Br (2) I (3) dtpb =1,2 bis(o ditolylphosphino)benzene] were synthesized and investigated in prototype organic light emitting diodes (OLEDs) 1 3 showed excellent photoluminescent performance in both degassed dichloromethane solutions [quantum yield (Ph) 0.43 0.60; lifetime (t) 4.9 6.5 ms] and amorphous films (Ph 0.57 0.71; t 3.2 6.1 ms) Conventional OLEDs containing 2 in the emitting layer exhibited bright green luminescence with a current efficiency of 65.3 cd/A and a maximum external quantum efficiency of 21.3%
author_names: Masashi Hashimoto

Satoshi Igawa

Masataka Yashima

Isao Kawata

Mikio Hoshino

Masahisa Osawa
title: Highly efficient green organic light emitting diodes containing luminescent three coordinate copper(I) complexes.
venue: Journal of the American Chemical Society
year: 2011

abstract: Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are promising for the realization of highly efficient light emitters. However, such devices have so far suffered from efficiency roll off at high luminance. Here, we report the design and synthesis of two diboron based molecules, CzDBA and tBuCzDBA, which show excellent TADF properties and yield efficient OLEDs with very low efficiency roll off. These donor acceptor donor (D A D) type and rod like compounds concurrently generate TADF with a photoluminescence quantum yield of ~100% and an 84% horizontal dipole ratio in the thin film. A green OLED based on CzDBA exhibits a high external quantum efficiency of 37.8 0.6% a current efficiency of 139.6 2.8 cd A 1 and a power efficiency of 121.6 3.1 lm W 1 with an efficiency roll off of only 0.3% at 1,000 cd m 2. The device has a peak emission wavelength of 528 nm and colour coordinates of the Commission International de l'Eclairage (CIE) of (0.31, 0.61) making it attractive for colour display applications.Organic light emitting diodes featuring the compounds CzDBA and tBuCzBDA are shown to not only offer high external quantum efficiency, but also minimal reduction in performance at high brightness.
author_names: Tien-Lin Wu

Min-Jie Huang

Chih-Chun Lin

Pei-Yun Huang

Tsu-Yu Chou

Ren-Wu Chen-Cheng

Hao-Wu Lin

Rai-Shung Liu

Chien-Hong Cheng
title: Diboron compound based organic light emitting diodes with high efficiency and reduced efficiency roll off
year: 2018

abstract: InGaN GaN multiquantum well (MQW) blue and green light emitting diodes (LEDs) were prepared by organometallic vapor phase epitaxy, and the properties of these LEDs were evaluated by photoluminescence (PL) double crystal X ray diffraction, and electroluminescence (EL) measurements. It was found that there were only small shifts observed in PL and EL peak positions of the blue MQW LEDs when the number of quantum well (QW) increased. However, significant shifts in PL and EL peak positions were observed in green MQW LEDs when the number of QW increased. It was also found that there was a large blue shift in EL peak position under high current injection in blue MQW LEDs. However, the blue shift in green MQW LEDs was negligibly small when the injection current was large. These observations could all be attributed to the rapid relaxation in green MQW LEDs since the In composition ratio in the InGaN well was high for the green MQW LEDs. The forward voltage V/sub f/ of green MQW LEDs was also found to be larger than that of blue MQW LEDs due to the same reason.
author_names: Shoou Jinn Chang

Wei-Chih Lai

Yan Kuin Su

Jiann-Fuh Chen

C H Liu

Uang Heay Liaw
title: InGaN GaN multiquantum well blue and green light emitting diodes
year: 2002