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1.
A study of hybrid light‐emitting diodes (HyLEDs) fabricated with and without solution‐processible Cs2CO3 and Ba(OH)2 inorganic interlayers is presented. The interlayers are deposited between a zinc oxide electron‐injection layer and a fluorescent emissive polymer poly(9‐dioctyl fluorine–alt‐benzothiadiazole) (F8BT) layer, with a thermally evaporated MoO3/Au layer used as top anode contact. In comparison to Cs2CO3, the Ba(OH)2 interlayer shows improved charge carrier balance in bipolar devices and reduced exciton quenching in photoluminance studies at the ZnO/Ba(OH)2/F8BT interface compared to the Cs2CO3 interlayer. A luminance efficiency of ≈28 cd A?1 (external quantum efficiency (EQE) ≈ 9%) is achieved for ≈1.2 μm thick single F8BT layer based HyLEDs. Enhanced out‐coupling with the aid of a hemispherical lens allows further efficiency improvement by a factor of 1.7, increasing the luminance efficiency to ≈47cd A?1, corresponding to an EQE of 15%. The photovoltaic response of these structures is also studied to gain an insight into the effects of interfacial properties on the photoinduced charge generation and back‐recombination, which reveal that Ba(OH)2 acts as better hole blocking layer than the Cs2CO3 interlayer. 相似文献
2.
Daniele Braga Nicholas C. Erickson Michael J. Renn Russell J. Holmes C. Daniel Frisbie 《Advanced functional materials》2012,22(8):1623-1631
Switching and control of efficient red, green, and blue active matrix organic light‐emitting devices (AMOLEDs) by printed organic thin‐film electrochemical transistors (OETs) are demonstrated. These all‐organic pixels are characterized by high luminance at low operating voltages and by extremely small transistor dimensions with respect to the OLED active area. A maximum brightness of ≈900 cd m?2 is achieved at diode supply voltages near 4 V and pixel selector (gate) voltages below 1 V. The ratio of OLED to OET area is greater than 100:1 and the pixels may be switched at rates up to 100 Hz. Essential to this demonstration are the use of a high capacitance electrolyte as the gate dielectric layer in the OETs, which affords extremely large transistor transconductances, and novel graded emissive layer (G‐EML) OLED architectures that exhibit low turn‐on voltages and high luminescence efficiency. Collectively, these results suggest that printed OETs, combined with efficient, low voltage OLEDs, could be employed in the fabrication of flexible full‐color AMOLED displays. 相似文献
3.
Stephan van Reenen René A. J. Janssen Martijn Kemerink 《Advanced functional materials》2012,22(21):4547-4556
The operational mechanism of polymer light‐emitting electrochemical cells (LECs) in sandwich geometry is studied by admittance spectroscopy in combination with numerical modeling. At bias voltages below the bandgap of the semiconducting polymer, this allows the determination of the dielectric constant of the active layer, the conductivity of mobile ions, and the thickness of the electric double layers. At bias voltages above the bandgap, p–n junction formation gives rise to an increase in capacitance at intermediate frequencies (≈10 kHz). The time and voltage dependence of this junction are successfully studied and modeled. It is shown that impedance measurements cannot be used to determine the junction width. Instead, the capacitance at intermediate biases corresponds to a low‐conductivity region that can be significantly wider than the recombination zone. Finally, the long settling time of sandwich polymer LECs is shown to be due to a slow process of dissociation of salt molecules that continues after the light‐emitting p–n junction has formed. This implies that in order to significantly decrease the response‐time of LECs an electrolyte/salt combination with a minimal ion binding energy must be used. 相似文献
4.
Stephan van Reenen Piotr Matyba Andrzej Dzwilewski René A. J. Janssen Ludvig Edman Martijn Kemerink 《Advanced functional materials》2011,21(10):1795-1802
Incorporation of ions in the active layer of organic semiconductor devices may lead to attractive device properties like enhanced injection and improved carrier transport. In this paper, we investigate the effect of the salt concentration on the operation of light‐emitting electrochemical cells, using experiments and numerical calculations. The current density and light emission are shown to increase linearly with increasing ion concentration over a wide range of concentrations. The increasing current is accompanied by an ion redistribution, leading to a narrowing of the recombination zone. Hence, in absence of detrimental side reactions and doping‐related luminescence quenching, the ion concentration should be as high as possible. 相似文献
5.
Current injection in organic semiconductors remains difficult to predict due in large part to the challenge of characterizing the contact energy barrier and interface density of states directly in organic electronic devices. Here, resonant coupling to surface plasmon polariton modes of a metal contact is demonstrated as a means to carry out internal photoemission (IPE) accurately in disordered organic semiconductor devices and enable direct measurement of the contact injection barrier by isolating true IPE from spurious sub‐gap organic photoconductivity. The substantial increase in sensitivity afforded by resonant coupling enables measurement in the low‐field injection regime where deviation from the standard Fowler prediction is explained quantitatively by the existence of a broad distribution of interface states. This technique is broadly applicable to metals and surface treatments commonly used in organic light emitting diodes, thin film transistors, and photovoltaics, and should therefore provide a quantitative basis to understand and model current injection in these devices over their entire operational lifetime. 相似文献
6.
《Advanced Electronic Materials》2018,4(9)
The highly efficient charge generation and transport is realized by simply stacking several 1,4,5,8,9,11‐hexa‐azatriphenylene hexacarbonitrile (HAT‐CN)/4,4′,4″‐tris(N‐3‐methylphenyl‐N‐phenylamino) triph‐enylamine (m‐MTDATA) organic heterojunctions in series. Mechanism analysis confirms that the highly effective charge transport property benefits from the efficient charge generation and recombination processes at the HAT‐CN/m‐MTDATA interfaces. It is found that the efficient multialternating organic heterojunctions can be used not only as hole and electron transporters to supply large charge injection, but also as excellent charge generation layer (CGL) to fabricate high‐performance tandem organic light‐emitting diodes (OLEDs). The resulting red phosphorescent OLEDs by simultaneously using the multialternating organic heterojunctions as hole and electron transporters realize the power efficiency (PE) of 36.7 lm W−1, current efficiency (CE) of 28.0 cd A−1, and external quantum efficiency (EQE) of 15.4%, whereas the PE, CE, and EQE, respectively, reach 37.1 lm W−1, 56.0 cd A−1, and 31.8% when simultaneously using the multialternating organic heterojunctions as hole and electron transporters and CGL to fabricate tandem red phosphorescent OLEDs, indicating the validity of the multialternating organic heterojunctions as the charge generator and transporters. The results provide us a totally new way of fabricating high‐performance OLEDs. 相似文献
7.
Hannah L. Smith Jordan T. Dull Elena Longhi Stephen Barlow Barry P. Rand Seth R. Marder Antoine Kahn 《Advanced functional materials》2020,30(17)
n‐Doping electron‐transport layers (ETLs) increases their conductivity and improves electron injection into organic light‐emitting diodes (OLEDs). Because of the low electron affinity and large bandgaps of ETLs used in green and blue OLEDs, n‐doping has been notoriously more difficult for these materials. In this work, n‐doping of the polymer poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,7‐diyl)] (F8BT) is demonstrated via solution processing, using the air‐stable n‐dopant (pentamethylcyclopentadienyl)(1,3,5‐trimethylbenzene)ruthenium dimer [RuCp*Mes]2. Undoped and doped F8BT films are characterized using ultraviolet and inverse photoelectron spectroscopy. The ionization energy and electron affinity of the undoped F8BT are found to be 5.8 and 2.8 eV, respectively. Upon doping F8BT with [RuCp*Mes]2, the Fermi level shifts to within 0.25 eV of the F8BT lowest unoccupied molecular orbital, which is indicative of n‐doping. Conductivity measurements reveal a four orders of magnitude increase in the conductivity upon doping and irradiation with ultraviolet light. The [RuCp*Mes]2‐doped F8BT films are incorporated as an ETL into phosphorescent green OLEDs, and the luminance is improved by three orders of magnitude when compared to identical devices with an undoped F8BT ETL. 相似文献
8.
The charge transport and recombination in white‐emitting polymer light‐ emitting diodes (PLEDs) are studied. The PLED investigated has a single emissive layer consisting of a copolymer in which a green and red dye are incorporated in a blue backbone. From single‐carrier devices the effect of the green‐ and red‐emitting dyes on the hole and electron transport is determined. The red dye acts as a deep electron trap thereby strongly reducing the electron transport. By incorporating trap‐assisted recombination for the red emission and bimolecular Langevin recombination for the blue emission, the current and light output of the white PLED can be consistently described. The color shift of single‐layer white‐emitting PLEDs can be explained by the different voltage dependencies of trap‐assisted and bimolecular recombination. 相似文献
9.
Herman T. Nicolai André Hof Jasper L. M. Oosthoek Paul W. M. Blom 《Advanced functional materials》2011,21(8):1505-1510
The charge transport in blue light‐emitting polyspirobifluorene is investigated by both steady‐state current‐voltage measurements and transient electroluminescence. Both measurement techniques yield consistent results and show that the hole transport is space‐charge limited. The electron current is found to be governed by a high intrinsic mobility in combination with electron traps. Numerical simulations on light‐emitting diodes reveal a shift in the recombination zone from the cathode to the anode with increasing bias. 相似文献
10.
Stephan van Reenen René A. J. Janssen Martijn Kemerink 《Advanced functional materials》2015,25(20):3066-3073
The characteristic doping process in polymer light‐emitting electrochemical cells (LECs) causes a tradeoff between luminescence intensity and efficiency. Experiments and numerical modeling on thin film polymer LECs show that, on the one hand, carrier injection and transport benefit from electrochemical doping, leading to increased electron‐hole recombination. On the other hand, the radiative recombination efficiency is reduced by exciton quenching by polarons involved in the doping. Consequently, the quasi‐steady‐state luminescent efficiency decreases with increasing ion concentration. The transient of the luminescent efficiency shows a characteristic roll‐off while the current continuously increases, attributed to ongoing electrochemical doping and the associated exciton quenching. Both effects can be modeled by exciton polaron‐quenching via diffusion‐assisted Förster resonance energy transfer. These results indicate that the tradeoff between efficiency and intensity is fundamental, suggesting that the application realm of future LECs should be sought in high‐brightness, low‐production cost devices, rather than in high‐efficiency devices. 相似文献
11.
Elisa Fresta Verónica Fernández‐Luna Pedro B. Coto Rubén D. Costa 《Advanced functional materials》2018,28(24)
Solid‐state lighting (SSL) is one of the biggest achievements of the 20th century. It has completely changed our modern life with respect to general illumination (light‐emitting diodes), flat devices and displays (organic light‐emitting diodes), and small labeling systems (light‐emitting electrochemical cells). Nowadays, it is however mandatory to make a transition toward green, sustainable, and equally performing lighting systems. In this regard, several groups have realized that the actual SSL technologies can easily and efficiently be improved by getting inspiration from how natural systems that manipulate light have been optimized over millennia. In addition, various natural and biocompatible materials with suitable properties for lighting applications have been used to replace expensive and unsustainable components of current lighting devices. Finally, SSL has also started to revolutionize the biomedical field with the achievement of efficient implantable lighting systems. Herein, the‐state‐of‐art of (i) biological materials for lighting devices, (ii) bioinspired concepts for device designs, and (iii) implantable SSL technologies is summarized, highlighting the perspectives of these emerging fields. 相似文献
12.
Yong Hyun Kim Jonghee Lee Won Mok Kim Cornelius Fuchs Simone Hofmann Hong‐Wei Chang Malte C. Gather Lars Müller‐Meskamp Karl Leo 《Advanced functional materials》2014,24(17):2553-2559
Conventional planar organic light‐emitting diodes (OLEDs) suffer from poor light extraction due to the total internal reflection at the waveguided interfaces. Therefore, the development of efficient light extraction structures is of great necessity and significance to realize practical applications in large area and cost‐effective light sources. In this paper, a high‐performance internal light outcoupling system for white OLEDs with spontaneously formed metal oxide nanostructures is developed. The fabrication process of the outcoupling system is simple and can be scaled to large area manufacturing. The enhancement of external quantum efficiency in white OLEDs comprising the outcoupling system reaches a factor of 1.7, and it is further increased to 2.9 when a hemispherical lens is employed. Together with the improvement of light extraction, excellent color stability over broad viewing angles is achieved. 相似文献
13.
In this contribution, it is shown that the method of laser‐desorption/ionization time‐of‐flight mass spectrometry (LDI‐TOF‐MS) is a powerful technique for analyzing complete organic devices, such as organic light‐emitting diodes (OLEDs) or organic solar cells. LDI‐TOF‐MS has the potential to analyze fully processed organic devices without special pretreatment such as dissolving the device, peeling off the metal cathode, or using additional matrix materials. Thus, devices may be analysed as they are with a minimum of measurement artefacts. It is demonstrated that the method allows an analysis of complex organic multilayer devices, their composition, and incorporated impurities. It even allows possible electrochemical reaction products caused by device degradation to be analyzed. Thus, LDI‐TOF‐MS has major advantages compared to measurements of dissolved samples. As an example, the identification of all of the materials used in a complete OLED is shown. Furthermore, a detailed chemical analysis of long‐term driven OLEDs, including the detection of degradation products, is presented. From these data, several degradation mechanisms can be distinguished. 相似文献
14.
Tengxiao Liu Liping Zhu Cheng Zhong Guohua Xie Shaolong Gong Junfeng Fang Dongge Ma Chuluo Yang 《Advanced functional materials》2017,27(12)
Fluorescent emitters have regained intensive attention in organic light emitting diode (OLED) community owing to the breakthrough of the device efficiency and/or new emitting mechanism. This provides a good chance to develop new near‐infrared (NIR) fluorescent emitter and high‐efficiency device. In this work, a D‐π‐A‐π‐D type compound with naphthothiadiazole as acceptor, namely, 4,4′‐(naphtho[2,3‐c][1,2,5]thiadiazole‐4,9‐diyl)bis(N,N ‐diphenylaniline) (NZ2TPA), is designed and synthesized. The photophysical study and density functional theory analysis reveal that the emission of the compound has obvious hybridized local and charge‐transfer (HLCT) state feature. In addition, the compound shows aggregation‐induced emission (AIE) characteristic. Attributed to its HLCT mechanism and AIE characteristic, NZ2TPA acquires an unprecedentedly high photoluminescent quantum yield of 60% in the neat film, which is the highest among the reported organic small‐molecule NIR emitters and even exceeds most phosphorescent NIR materials. The nondoped devices based on NZ2TPA exhibit excellent performance, achieving a maximum external quantum efficiency (EQE) of 3.9% with the emission peak at 696 nm and a high luminance of 6330 cd m?2, which are among the highest in the reported nondoped NIR fluorescent OLEDs. Moreover, the device remains a high EQE of 2.8% at high brightness of 1000 cd m?2, with very low efficiency roll‐off. 相似文献
15.
Sami Hamwi Jens Meyer Michael Kröger Thomas Winkler Marco Witte Thomas Riedl Antoine Kahn Wolfgang Kowalsky 《Advanced functional materials》2010,20(11):1762-1766
The mechanism of charge generation in transition metal oxide (TMO)‐based charge‐generation layers (CGL) used in stacked organic light‐emitting diodes (OLEDs) is reported upon. An interconnecting unit between two vertically stacked OLEDs, consisting of an abrupt heterointerface between a Cs2CO3‐doped 4,7‐diphenyl‐1,10‐phenanthroline layer and a WO3 film is investigated. Minimum thicknesses are determined for these layers to allow for simultaneous operation of both sub‐OLEDs in the stacked device. Luminance–current density–voltage measurements, angular dependent spectral emission characteristics, and optical device simulations lead to minimum thicknesses of the n‐type doped layer and the TMO layer of 5 and 2.5 nm, respectively. Using data on interface energetic determined by ultraviolet photoelectron and inverse photoemission spectroscopy, it is shown that the actual charge generation occurs between the WO3 layer and its neighboring hole‐transport material, 4,4',4”‐tris(N‐carbazolyl)‐triphenyl amine. The role of the adjacent n‐type doped electron transport layer is only to facilitate electron injection from the TMO into the adjacent sub‐OLED. 相似文献
16.
Ming Liu Xiang‐Long Li Dong Cheng Chen Zhongzhi Xie Xinyi Cai Gaozhan Xie Kunkun Liu Jianxin Tang Shi‐Jian Su Yong Cao 《Advanced functional materials》2015,25(32):5190-5198
Two novel naphtho[1,2‐d]imidazole derivatives are developed as deep‐blue, light‐emitting materials for organic light‐emitting diodes (OLEDs). The 1H‐naphtho[1,2‐d]imidazole based compounds exhibit a significantly superior performance than the 3H‐naphtho[1,2‐d]imidazole analogues in the single‐layer devices. This is because they have a much higher capacity for direct electron‐injection from the cathode compared to their isomeric counterparts resulting in a ground‐breaking EQE (external quantum efficiency) of 4.37% and a low turn‐on voltage of 2.7 V, and this is hitherto the best performance for a non‐doped single‐layer fluorescent OLED. Multi‐layer devices consisting of both hole‐ and electron‐transporting layers, result in identically excellent performances with EQE values of 4.12–6.08% and deep‐blue light emission (Commission Internationale de l'Eclairage (CIE) y values of 0.077–0.115) is obtained for both isomers due to the improved carrier injection and confinement within the emissive layer. In addition, they showed a significantly better blue‐color purity than analogous molecules based on benzimidazole or phenanthro[9,10‐d]imidazole segments. 相似文献
17.
Cheolmin Kim Thang Phan Nguyen Quyet Van Le Jong‐Myeong Jeon Ho Won Jang Soo Young Kim 《Advanced functional materials》2015,25(28):4512-4519
2D transition metal dichalcogenide (TMD) nanosheets, including MoS2, WS2, and TaS2, are used as hole injection layers (HILs) in organic light‐emitting diodes (OLEDs). MoS2, WS2, and TaS2 nanosheets are prepared using an exfoliation by ultrasonication method. The thicknesses and sizes of the TMD nanosheets are measured to be 3.1–4.3 nm and more than 100 nm, respectively. The work functions of the TMD nanosheets increase from 4.4–4.9 to 4.9–5.1 eV following ultraviolet/ozone (UVO) treatment. The turn‐on voltages at 10 cd m?2 for UVO‐treated TMD‐based devices decrease from 7.3–12.8 to 4.3–4.4 V and maximum luminance efficiencies increase from 5.74–9.04 to 12.01–12.66 cd A?1. In addition, this study confirms that the stabilities of the devices in air can be prolonged by using UVO‐treated TMDs as HILs in OLEDs. These results demonstrate the great potential of liquid‐exfoliated TMD nanosheets for use as HILs in OLEDs. 相似文献
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20.
Jiaojiao Song Ouyang Wang Huaibin Shen Qingli Lin Zhaohan Li Lei Wang Xintong Zhang Lin Song Li 《Advanced functional materials》2019,29(33)
In the study of hybrid quantum dot light‐emitting diodes (QLEDs), even for state‐of‐the‐art achievement, there still exists a long‐standing charge balance problem, i.e., sufficient electron injection versus inefficient hole injection due to the large valence band offset of quantum dots (QDs) with respect to the adjacent carrier transport layer. Here the dedicated design and synthesis of high luminescence Zn1?x CdxSe/ZnSe/ZnS QDs is reported by precisely controlled shell growth, which have matched energy level with the adjacent hole transport layer in QLEDs. As emitters, such Zn1?xCdxSe‐ based QLEDs exhibit peak external quantum efficiencies (EQE) of up to 30.9%, maximum brightness of over 334 000 cd m?2, very low efficiency roll‐off at high current density (EQE ≈25% @ current density of 150 mA cm?2), and operational lifetime extended to ≈1 800 000 h at 100 cd m?2. These extraordinary performances make this work the best among all solution‐processed QLEDs reported in literature so far by achieving simultaneously high luminescence and balanced charge injection. These major advances are attributed to the combination of an intermediate ZnSe layer with an ultrathin ZnS outer layer as the shell materials and surface modification with 2‐ethylhexane‐1‐thiol, which can dramatically improve hole injection efficiency and thus lead to more balanced charge injection. 相似文献