The Experts below are selected from a list of 8811 Experts worldwide ranked by ideXlab platform
Woo Young Kim - One of the best experts on this subject based on the ideXlab platform.
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quantitative analysis of charge distribution in bi Emissive Layer white organic light emitting diodes with two fluorescent dopants
Scientific Reports, 2018Co-Authors: Ji Young Kim, Woo Young Kim, Kok Wai CheahAbstract:This work seeks to establish a quantitative method which can estimate the holes and electrons ratio in the emission zones. We fabricated multiLayered white organic light-emitting diodes (WOLEDs) with the device structure of ITO/NPB(80 nm)/MADN:BUBD-1(7%)(20 nm)/MADN:DCJTB(0.3%)(20 nm)/TPBi(X nm)/LiF(2 nm)/Al as a case study on the charge recombination distribution in the Emissive Layer. The result shows a trend in the charge recombination ratio depending on the electron transport Layer thickness. We obtained an empirical relationship between electron transport Layer thicknesses and emission ratio in EML. In addition, the electroluminescent spectra were analyzed by fitting a Gaussian distribution for the two Emissive Layers to calculate the intensity ratio of the energy transitions. The arrival time of hole and electrons from each electrode was determined using the thickness and mobility of TPBi as electron transport Layer. From these initial results, we derived an empirical mechanism to meet with a linear relationship that can allow us to design custom- made WOLEDs.
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improvement of efficiency roll off in blue phosphorescence oled using double dopants Emissive Layer
Journal of Luminescence, 2015Co-Authors: Seung Il Yoo, Ju-an Yoon, Nam Ho Kim, Woo Young Kim, Jin Wook Kim, Jin Sung Kang, C B MoonAbstract:Abstract Blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated using double dopants FIrpic and FIr6 in Emissive Layer (EML) with structure of ITO/NPB (700 A)/mCP:FIrpic-8%:FIr6- x % (300 A)/TPBi (300 A)/Liq (20 A)/Al (1200 A). We optimized concentration of the second dopant FIr6 in the presence of a fixed FIrpic to observe its effect on electrical performance of PHOLED device. 24.8 cd/A of luminous efficiency was achieved by the device with dopant ratio of 8%FIrpic:4%FIr6 in EML. Efficiency roll-off was also improved 20% compared to the PHOLED device singly dopped with FIrpic or FIr6 only. Second doping proved its effect in stabilizing charge balance in EML and enhancing energy transfer of triplet excitons between two dopants.
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study of triplet exciton s energy transfer in white phosphorescent organic light emitting diodes with multi doped single Emissive Layer
Optical Materials, 2015Co-Authors: Jin Wook Kim, Ju-an Yoon, Nam Ho Kim, Woo Young Kim, Kok Wai Cheah, Seung Il Yoo, Jin Sung Kang, Furong ZhuAbstract:Abstract The performance of three color single Emissive Layer white phosphorescent organic light-emitting diodes (PHOLEDs), with different hole transporting materials of N,N′-diphenyl-N,N′-bis(l-naphthyl-phenyl)-(l,l′-biphenyl)-4,4′-diamine (NPB), 4,4_,4_-tris_N-carbazolyl_tri-Phenylamine (TCTA) and 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), was analyzed. It is found that the luminous efficiency of white PHOLEDs is closely related to the triplet exciton energy level in the hole transporting Layer (HTL). White PHOLEDs with a TAPC as HTL, having the highest triplet exciton energy level amongst the three different hole transporting materials, yielded external quantum efficiency of 25.5% at 4.5 V and a high luminous efficiency of 51 cd/A at 4.5 V with CIE color coordinates of (0.34, 0.39) at 10 V. The results reveal that the effective confinement of triplet excitons in white PHOLEDs with a high triplet exciton energy level HTL (TAPC) allows improving the luminous efficiency, as compared to the devices made with NPB and TCTA. Additionally, we demonstrated possibility for the loss of intensity in EL spectra of the white PHOLED devices with NPB and TCTA as HTL compared to that of the device with TAPC as HTL.
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Study of energy transfer in single and multi-Emissive Layer using Gaussian peak fitting
Journal of Luminescence, 2014Co-Authors: Ju-an Yoon, You-hyun Kim, Nam Ho Kim, Chang-bum Moon, Woo Young KimAbstract:Abstract White organic light-emitting diodes(WOLEDs) were fabricated with the device structure of ITO(1800 A)/NPB(700 A)/Emissive Layer(300 A)/Bphen(300 A)/Liq(20 A)/Al(1200 A) using the two complementary colors method. Then, we investigated their electrical and optical characteristics to determine luminous efficiency, luminance and color coordinates of single, double, triple and quadruple Emissive Layered-WOLED. Thickness of Emissive Layer was fixed at 30 A, and DPASN and BAlq were used for blue Emissive host material and DCJTB was added as red dopant in the Emissive Layer. Then, we investigated the performance of OLEDs via its charge blocking structure and its different Emissive region with Emissive Layers. Luminous efficiency of 5.30 cd/A at 50 mA/cm2 of current density is obtained in WOLED device with double Emissive Layer of DPASN:DCJTB-0.1% (150 A)/BAlq:DCJTB-0.1% (150 A) and these are 80% higher than WOLED device with single Emissive Layer of DPASN:DCJTB-0.1% (300 A).
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High efficient white organic light-emitting diodes with single Emissive Layer using phosphorescent red, green, and blue dopants
Applied Physics Letters, 2013Co-Authors: You-hyun Kim, Kok Wai Cheah, Woo Young KimAbstract:Phosphorescent white organic light-emitting diodes (PHWOLEDs) with single Emissive Layer were fabricated by co-doping phosphorescent blue, green, and red emitters with different concentrations. WOLEDs using Ir(piq)3 and Ir(ppy)3 as red and green dopants along with 8% of Firpic as blue dopant with host materials of 4CzPBP in the Emissive Layer were compared under various doping ratio between Ir(piq)3 and Ir(ppy)3. Triplet-triplet Dexter energy transfer in single Emissive PHWOLEDs including three primary colors was saturated from higher triplet energy levels to lower triplet energy levels directly.
Jiangshan Chen - One of the best experts on this subject based on the ideXlab platform.
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achieving extreme utilization of excitons by an efficient sandwich type Emissive Layer architecture for reduced efficiency roll off and improved operational stability in organic light emitting diodes
ACS Applied Materials & Interfaces, 2016Co-Authors: Zhongbin Wu, Jiangshan Chen, Jiaxiu Wang, Dezhi Yang, Xianfeng Qiao, Saad M Alshehri, Tansir AhamadAbstract:It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the Emissive Layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W–1 and a maximum current efficiency of 93.5 cd A–1. At the high brightness of 5 000 cd m–2, they still remain as high as 23.3%, 71.1 lm W–1, and 88.3 cd A–1, respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m–2, which is significantly higher than that of compared devices with conventi...
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achieving extreme utilization of excitons by an efficient sandwich type Emissive Layer architecture for reduced efficiency roll off and improved operational stability in organic light emitting diodes
ACS Applied Materials & Interfaces, 2016Co-Authors: Ning Sun, Jiangshan Chen, Liping Zhu, Jiaxiu Wang, Dezhi Yang, Xianfeng Qiao, Saad M Alshehri, Hengda Sun, Tansir AhamadAbstract:It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the Emissive Layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W–1 and a maximum current efficiency of 93.5 cd A–1. At the high brightness of 5 000 cd m–2, they still remain as high as 23.3%, 71.1 lm W–1, and 88.3 cd A–1, respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m–2, which is significantly higher than that of compared devices with conventi...
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improving color stability of blue orange complementary white oleds by using single host double Emissive Layer structure comprehensive experimental investigation into the device working mechanism
Organic Electronics, 2012Co-Authors: Yongbiao Zhao, Jiangshan ChenAbstract:In this paper, we successfully improved the spectral stability in blue/orange complementary white organic light-emitting diodes (OLEDs) by utilizing hole-type single host double Emissive Layer structure. The demonstrated double Emissive Layer structure effectively suppresses the direct recombination of electron-hole pairs on the hole-trapping orange phosphor and thus reduces the deteriorated effect of charge trapping on electroluminescence spectrum stability by controlling exciton recombination zone. It is shown that the white light emission is a cascade energy transfer process from host to blue phosphor and then to orange phosphor, which seems to be less affected by the driving conditions. Thus, the change in Commission Internationale de L'Eclairage coordinates (CIE) in the white OLEDs is less than (+/- 0.010, +/- 0.007) as the voltage increases from 4 V to 9 V, which correspond to the luminance increasing from 200 cd m(-2) to about 20,000 cd m(-2). This is superior to that of co-doped single Emissive Layer devices, which show much larger CIEs variation of (+/- 0.05, +/- 0.02) in the same driving voltage range. We gave detailed analysis on the exciton recombination processes and well elucidated the working mechanism of the fabricated double Emissive Layer structure white OLEDs. (C) 2012 Elsevier B.V. All rights reserved.
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Improving color stability of blue/orange complementary white OLEDs by using single-host double-Emissive Layer structure: Comprehensive experimental investigation into the device working mechanism
Organic Electronics, 2012Co-Authors: Yongbiao Zhao, Liping Zhu, Jiangshan ChenAbstract:In this paper, we successfully improved the spectral stability in blue/orange complementary white organic light-emitting diodes (OLEDs) by utilizing hole-type single host double Emissive Layer structure. The demonstrated double Emissive Layer structure effectively suppresses the direct recombination of electron-hole pairs on the hole-trapping orange phosphor and thus reduces the deteriorated effect of charge trapping on electroluminescence spectrum stability by controlling exciton recombination zone. It is shown that the white light emission is a cascade energy transfer process from host to blue phosphor and then to orange phosphor, which seems to be less affected by the driving conditions. Thus, the change in Commission Internationale de L'Eclairage coordinates (CIE) in the white OLEDs is less than (+/- 0.010, +/- 0.007) as the voltage increases from 4 V to 9 V, which correspond to the luminance increasing from 200 cd m(-2) to about 20,000 cd m(-2). This is superior to that of co-doped single Emissive Layer devices, which show much larger CIEs variation of (+/- 0.05, +/- 0.02) in the same driving voltage range. We gave detailed analysis on the exciton recombination processes and well elucidated the working mechanism of the fabricated double Emissive Layer structure white OLEDs. (C) 2012 Elsevier B.V. All rights reserved.
Russell J. Holmes - One of the best experts on this subject based on the ideXlab platform.
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Isolating Degradation Mechanisms in Mixed Emissive Layer Organic Light-Emitting Devices
ACS Applied Materials & Interfaces, 2018Co-Authors: John S. Bangsund, Kyle W. Hershey, Russell J. HolmesAbstract:Degradation in organic light-emitting devices (OLEDs) is generally driven by reactions involving excitons and polarons. Accordingly, a common design strategy to improve OLED lifetime is to reduce the density of these species by engineering an Emissive Layer architecture to achieve a broad exciton recombination zone. Here, the effect of exciton density on device degradation is analyzed in a mixed host Emissive Layer (M-EML) architecture which exhibits a broad recombination zone. To gain further insight into the dominant degradation mechanism, losses in the exciton formation efficiency and photoluminescence (PL) efficiency are decoupled by tracking the Emissive Layer PL during device degradation. By varying the starting luminance and M-EML thickness, the rate of PL degradation is found to depend strongly on recombination zone width and hence exciton density. In contrast, losses in the exciton formation depend only weakly on the recombination zone, and thus may originate outside of the Emissive Layer. These ...
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investigating the role of Emissive Layer architecture on the exciton recombination zone in organic light emitting devices
Advanced Functional Materials, 2013Co-Authors: Nicholas C Erickson, Russell J. HolmesAbstract:An experimental approach to determine the spatial extent and location of the exciton recombination zone in an organic light-emitting device (OLED) is demonstrated. This technique is applicable to a wide variety of OLED structures and is used to examine OLEDs which have a double- (D-EML), mixed- (M-EML), or graded-Emissive Layer (G-EML) architecture. The location of exciton recombination in an OLED is an important design parameter, as the local optical field sensed by the exciton greatly determines the efficiency and angular distribution of far-field light extraction. The spatial extent of exciton recombination is an important parameter that can strongly impact exciton quenching and OLED efficiency, particularly under high excitation. A direct measurement of the exciton density profile is achieved through the inclusion of a thin, exciton sensitizing strip in the OLED Emissive Layer which locally quenches guest excitons and whose position in the Emissive Layer can be translated across the device to probe exciton formation. In the case of the G-EML device architecture, an electronic model is developed to predict the location and extent of the exciton density profile by considering the drift, diffusion, and recombination of charge carriers within the device.
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Investigating the Role of Emissive Layer Architecture on the Exciton Recombination Zone in Organic Light‐Emitting Devices
Advanced Functional Materials, 2013Co-Authors: Nicholas C Erickson, Russell J. HolmesAbstract:An experimental approach to determine the spatial extent and location of the exciton recombination zone in an organic light-emitting device (OLED) is demonstrated. This technique is applicable to a wide variety of OLED structures and is used to examine OLEDs which have a double- (D-EML), mixed- (M-EML), or graded-Emissive Layer (G-EML) architecture. The location of exciton recombination in an OLED is an important design parameter, as the local optical field sensed by the exciton greatly determines the efficiency and angular distribution of far-field light extraction. The spatial extent of exciton recombination is an important parameter that can strongly impact exciton quenching and OLED efficiency, particularly under high excitation. A direct measurement of the exciton density profile is achieved through the inclusion of a thin, exciton sensitizing strip in the OLED Emissive Layer which locally quenches guest excitons and whose position in the Emissive Layer can be translated across the device to probe exciton formation. In the case of the G-EML device architecture, an electronic model is developed to predict the location and extent of the exciton density profile by considering the drift, diffusion, and recombination of charge carriers within the device.
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highly efficient single Layer organic light emitting devices based on a graded composition Emissive Layer
Applied Physics Letters, 2010Co-Authors: Nicholas C Erickson, Russell J. HolmesAbstract:We demonstrate highly efficient electrophosphorescence from devices comprising a single organic Layer. High efficiency is realized by combining both hole- and electron-transporting host materials (HTMs and ETMs, respectively) into a single, graded-composition Emissive Layer with the green phosphorescent emitter fac-tris(2-phenylpyridine) iridium (III). The composition is continuously graded to realize nearly 100% HTM at the anode and nearly 100% ETM at the cathode. Peak external quantum and power efficiencies of ηEQE=(19.3±0.4)% and ηP=(66.5±1.3) lm/W are realized at a luminance level of 600 cd/m2.
M N Kamalasanan - One of the best experts on this subject based on the ideXlab platform.
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study of shifting of recombination zone in multi Emissive Layer organic light emitting devices and its effect on color stability
Journal of Luminescence, 2013Co-Authors: Priyanka Tyagi, Ritu Srivastava, Arunandan Kumar, Suneet Tuli, M N KamalasananAbstract:Abstract Color stability in multi-Emissive Layer organic light emitting devices (Me-OLEDs) has been investigated. Me-OLEDs were based on multiple emitters with a common host CBP doped with three dopants, BCzVBi, Ir(ppy) 3 and Ir(btp) 2 acac for blue, green and red emission. A major variation in CIE coordinates were found from (0.312, 0.294) to (0.236, 0.267) with increase in voltage from 6 to 9 V. This coordinate shift in Me-OLEDs has been attributed to the shifting of recombination zone with increase in voltage. In order to support our experimental observation, the EL spectrum of Me-OLEDs has been expressed as a linear combination of EL intensities of OLEDs with its individual constituting Layers as emitters. In this way, the contribution of each Layer in the EL spectrum of Me-OLEDs has been evaluated at each voltage. It has been observed from these calculations that the contribution of red emitter decreases from 47% to 33.33% and blue emitter increases from 38% to 51.67% with the increase in voltage from 6 to 9 V. This supports our hypothesis of shifting of recombination zone with the change in voltage. This shifting has been attributed to the field dependency of electron mobility in CBP. Me-OLED with CBP Layers between the emitters was fabricated to improve the color stability. Significant improvement in color stability was achieved without changes in current efficiency in Me-OLED with interLayers.
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efficiency enhancement of organic light emitting diode via surface energy transfer between exciton and surface plasmon
Organic Electronics, 2012Co-Authors: Priyanka Tyagi, Ritu Srivastava, Arunandan Kumar, Dalip Singh Mehta, M N KamalasananAbstract:Abstract Organic light emitting diodes (OLEDs) with surface plasmon (SP) enhanced emission have been fabricated. Gold nanoclusters (GNCs) deposited using thermal evaporation technique has been used for localization of surface plasmons. Size of GNCs and distance of GNCs from the Emissive Layer have been optimized using steady state and time resolved photoluminescence (PL) results. 3.2 Times enhancement in PL intensity and 2.8 times enhancement in electroluminescence intensity of OLED have been obtained when GNCs of size 9.3 nm has been introduced at a distance of 5 nm from Emissive Layer. Distance dependence of energy transfer efficiency between exciton and SPs was found to be of 1/ R 4 type, which is typically the dependence for dipole-surface energy transfer.
Tansir Ahamad - One of the best experts on this subject based on the ideXlab platform.
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achieving extreme utilization of excitons by an efficient sandwich type Emissive Layer architecture for reduced efficiency roll off and improved operational stability in organic light emitting diodes
ACS Applied Materials & Interfaces, 2016Co-Authors: Zhongbin Wu, Jiangshan Chen, Jiaxiu Wang, Dezhi Yang, Xianfeng Qiao, Saad M Alshehri, Tansir AhamadAbstract:It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the Emissive Layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W–1 and a maximum current efficiency of 93.5 cd A–1. At the high brightness of 5 000 cd m–2, they still remain as high as 23.3%, 71.1 lm W–1, and 88.3 cd A–1, respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m–2, which is significantly higher than that of compared devices with conventi...
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achieving extreme utilization of excitons by an efficient sandwich type Emissive Layer architecture for reduced efficiency roll off and improved operational stability in organic light emitting diodes
ACS Applied Materials & Interfaces, 2016Co-Authors: Ning Sun, Jiangshan Chen, Liping Zhu, Jiaxiu Wang, Dezhi Yang, Xianfeng Qiao, Saad M Alshehri, Hengda Sun, Tansir AhamadAbstract:It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the Emissive Layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W–1 and a maximum current efficiency of 93.5 cd A–1. At the high brightness of 5 000 cd m–2, they still remain as high as 23.3%, 71.1 lm W–1, and 88.3 cd A–1, respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m–2, which is significantly higher than that of compared devices with conventi...