Hybrid White Organic Light-emitting Diodes Research Articles

Highly-efficient hybrid white organic light-emitting diodes based on a high radiative exciton ratio deep-blue emitter with improved concentration of phosphorescent dopant

An improved concentration of phosphorescent dopant for highly-efficient hybrid white organic light-emitting diodes based on a high radiative exciton ratio (80%) deep-blue emitter has been developed.

Highly efficient single- and multi-emission-layer fluorescent/phosphorescent hybrid white organic light-emitting diodes with ∼20% external quantum efficiency

A blue fluorophore BBPI was utilized to fabricate fluorescent/phosphorescent hybrid WOLEDs with ∼20% external quantum efficiency.

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

To attain high efficiencies in hybrid white organic light-emitting diodes (WOLEDs), mutual quenching of the fluorophors and phosphors should be minimized. Efforts have been devoted to reducing the triplet quenching of phosphors; however, the quenching of fluorophors by the external heavy-atom effect (EHA) introduced by the phosphors is often ignored. Here, we observed that conventional fluorophors and fluorophors with thermally activated delayed fluorescence (TADF) behave differently in the presence of EHA perturbers. The efficiencies of the conventional fluorophors suffer greatly from the EHA, whereas the TADF fluorophors exhibit negligible changes, which makes TADF materials ideal fluorophors for hybrid devices. WOLEDs using a blue TADF fluorophor and an orange phosphor achieve a maximum forward viewing external quantum efficiency of 19.6% and a maximum forward viewing power efficiency of 50.2 lm W−1, among the best values for hybrid WOLEDs. This report is the first time that the EHA effect has been considered in hybrid WOLEDs and that a general strategy toward highly efficient hybrid WOLEDs with simple structures is proposed. Warm white organic light-emitting diodes with a power efficiency of up to 85.3 lm W–1 are reported by scientists in China. The emitters fabricated by Dongdong Zhang and co-workers from Tsinghua University in Beijing are based on the use of a yellow phosphor (PO-01) and a blue fluorophore (2CzPN), which exhibits thermally activated delayed fluorescence (TADF). The device operates with a total external quantum efficiency of 33.3%. The team says that such high efficiency is made possible by the minimizing the fluorescence quenching processes that can occur between the phosphor and the fluorophore. In particular, their TADF fluorophore is shown to be highly robust against quenching resulting from external heavy atom effects introduced by metal phosphors. The approach could lead to a simpler design of white emitters.

混合型间隔层对荧磷混合式白色有机电致发光器件性能的影响

Novel hybrid white organic light-emitting diodes( HWOLEDs) based on blue-green fluorescent MQAB and red phosphorescent Ir( MDQ)2acac materials were fabricated. 1,3,5-tris( 1-phenyl-1H-benzimidazol-2-yl)-benzene( TPBI),1,3-bis( triphenylsilyl) benzene( UGH3) or a mixture of the two at different ratios was used as a spacer layer. It is found that the mixed spacer of TPBI and UGH3 is able to tune the hole injection / transport effectively. The optimized HWOLEDs with a spacer of m( TPBI) ∶ m( UGH3) = 1∶ 1 exhibits a luminance of 14 700 cd / m2 and a current efficiency of 11. 60 cd / A with an excellent color stability. In comparison with the devices using spacer of pure TPBI or pure UGH3 layer,the current efficiency from the device using mixed spacer enhanced200%- 300%.

A host–guest system comprising high guest concentration to achieve simplified and high-performance hybrid white organic light-emitting diodes

A host–guest system comprising high guest concentration (1.5%) is used to develop high-performance single-EML hybrid WOLEDs and dual-EML WOLEDs.

New platinum complexes exhibiting host dependent photoluminescence as single dopants in double emitting layer, voltage independent hybrid white electroluminescence devices

New platinum complexes (FPtXNDs) bearing 4-hydroxy-1,5-naphthyridines (XNDs) functionalized with phenyl, dimethylamino, morpholino or phenoxazino (X = Ph, dma, mor or pxz) units were used in hybrid white OLEDs.

Efficient hybrid white organic light-emitting diodes with extremely long lifetime: the effect of n-type interlayer.

The effect of n-type interlayer in hybrid white organic light-emitting diodes (WOLEDs) has been systematically investigated by using various n-type materials. A new finding, that the triplet energy rather than electron mobility or hole-blocking ability of interlayer plays a more positive role in the performance of hybrid WOLEDs, is demonstrated. Based on the new finding, a more efficient n-type interlayer bis[2-(2-hydroxyphenyl)-pyridine] beryllium has been employed to realize a high-performance hybrid WOLED. The resulting device (without n-doping technology) exhibits low voltages (i.e., 2.8 V for 1 cd/m2, 3.9 V for 100 cd/m2) and low efficiency roll-off (i.e., 11.5 cd/A at 100 cd/m2 and 11.2 cd/A at 1000 cd/m2). At the display-relevant luminance of 100 cd/m2, a total power efficiency of 16.0 lm/W, a color rendering index of 73 and an extremely long lifetime of 12596265 h are obtained. Such superior results not only comprehensively indicate that the n-type materials are effective interlayers to develop high-performance hybrid WOLEDs but also demonstrate a significant step towards real commercialization in WOLEDs.

도핑 비율에 따른 하이브리드 백색 OLED의 효율 향상에 관한 연구

도핑 비율에 따른 하이브리드 백색 OLED의 효율 향상에 관한 연구

Above 20% external quantum efficiency in novel hybrid white organic light-emitting diodes having green thermally activated delayed fluorescent emitter.

High efficiency hybrid type white organic light-emitting diodes (WOLEDs) combining a green thermally activated delayed fluorescent (TADF) emitting material with red/blue phosphorescent emitting materials were developed by manipulating the device architecture of WOLEDs. Energy transfer between a blue phosphorescent emitting material and a green TADF emitter was efficient and could be managed by controlling the doping concentration of emitters. A high quantum efficiency above 20% was achieved in the hybrid WOLEDs by optimizing the device structure of the hybrid type WOLEDs for the first time and the device performances of the hybrid WOLEDs were comparable to those of all phosphorescent WOLEDs.

Highly efficient and color-stable hybrid warm white organic light-emitting diodes using a blue material with thermally activated delayed fluorescence

Hybrid white organic light-emitting diodes (WOLEDs) often undergo triplet energy loss through the triplet state of the blue fluorophors. Here, blue fluorophors with thermally activated delayed fluorescence (TADF) are introduced to solve this problem. The triplet excitons formed on blue TADF fluorophors can be harvested by either energy transfer to the low-lying triplet states of the phosphor or thermal upconversion to the emissive singlet states, eliminating the energy loss. Moreover, device structures are wisely designed to take full advantages of the charge trapping ability of the TADF dopant, 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene, achieving a color-stable warm white emission. Remarkably, a maximum forward viewing external quantum efficiency (EQE) of 22.5% and a maximum forward viewing power efficiency (PE) of 47.6 lm W−1 are achieved. These values are among the highest reported for hybrid WOLEDs and even comparable to full-phosphorescent ones, demonstrating that the strategy reported here is promising for OLED lighting.

The effect of a charge control layer on the electroluminescent characteristic of blue and white organic light-emitting diodes.

We investigated blue fluorescent organic light-emitting diode (OLED) with a charge control layer (CCL) to produce high efficiency and improve the half-decay lifetime. Three types of devices (device A, B, and C) were fabricated following the number of CCLs within the emitting layer (EML), maintaining the thickness of whole EML. The CCL and host material, 2-methyl-9,10-di(2-naphthyl)anthracene, which has a bipolar property, was able to control the carrier movement with ease inside the EML. Device B demonstrated a maximum luminous efficiency (LE) and external quantum efficiency (EQE) of 9.19 cd/A and 5.78%, respectively. It also showed that the enhancement of the half-decay lifetime, measured at an initial luminance of 1,000 cd/m2, was 1.5 times longer than that of the conventional structure. A hybrid white OLED (WOLED) was also fabricated using a phosphorescent red emitter, bis(2-phenylquinoline)-acetylacetonate iridium III doped in 4,4'-N,N'-dicarbazolyl-biphenyl. The property of the hybrid WOLED with CCL showed a maximum LE and an EQE of 13.46 cd/A and 8.32%, respectively. It also showed white emission with Commission International de L'Éclairage coordinates of (x = 0.41, y = 0.33) at 10 V.

Regulating charges and excitons in simplified hybrid white organic light-emitting diodes: The key role of concentration in single dopant host–guest systems

A series of high-performance hybrid white organic light-emitting diodes (WOLEDs) with simplified structures are developed by systematically investigating the influence of dopant concentrations. An ultrahigh color rendering index of 88 and a peak forward-viewing power efficiency of 44.9lm/W are achieved in the single-emitting-layer WOLED with a low concentration (0.1%) and a moderate concentration (1%), respectively. To investigate the effect of high concentration (4%), a dual-emitting-layer device is realized, achieving an efficiency of 15.8lm/W (1000cd/m2). Besides, the devices show extremely stable color with a Commission Internationale de L’Eclairage (CIEx, y) variation of Δ(x, y)⩽(0.008, 0.008) during a large range of luminance. Furthermore, the origin of the color-stability and working mechanism of the devices are discussed, which can be attributed to the multifunctional dopant which reduces charge mobilities together with a suitable hole transport material which exhibits strong electron- and exciton-blocking ability.

Simplified hybrid white organic light-emitting diodes with efficiency/efficiency roll-off/color rendering index/color-stability trade-off

A high-performance hybrid white organic light-emitting diode (WOLED) based on a simple structure has been developed. The resulting device exhibits a maximum total current efficiency and power efficiency of 35.7 cd/A and 30.6 lm/W, respectively. Even at a high luminance of 1000 cd/m2, a current efficiency of 32.0 cd/A and a power efficiency of 19.4 lm/W are obtained, suggesting that the device exhibits a low efficiency roll-off. Besides, the device shows excellent color-stability during a wide range of luminance and a high color rendering index (CRI) of 83 is obtained. Moreover, the origin of the superior properties is explored comprehensively. Such achieved results demonstrate that high efficiency, low efficiency roll-off, stable color and high CRI can be simultaneously realized in a simplified hybrid WOLEDs. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Investigation and optimization of each organic layer: A simple but effective approach towards achieving high-efficiency hybrid white organic light-emitting diodes

A highly efficient hybrid white organic light-emitting diode based on a simple structure has been successfully fabricated and characterized. By systematically investigating the influence of the emissive layer thickness, electron transporting layer thickness, spacer and hole transporting layer, the forward-viewing current efficiency and power efficiency of the resulting device without any out-coupling schemes or n-doping strategies can be as high as 59.4cd/A and 58.4lm/W, respectively. Besides, a Commission International de l’Eclairage of (0.412, 0.393) and a color rendering index of 60 are obtained at the current density of 11mA/cm2. Through the optimization and investigation, the origin of this unique device is explored comprehensively. Undoubtedly, such presented results will be beneficial to the design of both material and device architecture for ultra high-performance white organic light-emitting diodes.

A hybrid white organic light-emitting diode with above 20% external quantum efficiency and extremely low efficiency roll-off

Based on a delicate device structure design, a novel (phosphorescence/fluorescence) hybrid WOLED with nearly 100% exciton harvesting has been demonstrated.

High‐Performance Hybrid White Organic Light‐Emitting Devices without Interlayer between Fluorescent and Phosphorescent Emissive Regions

By using mixed hosts with bipolar transport properties for blue emissive layers, a novel phosphorescence/fluorescence hybrid white OLED without using an interlayer between the fluorescent and phosphorescent regions is demonstrated. The peak EQE of the device is 19.0% and remains as high as 17.0% at the practical brightness of 1000 cd m(-2) .

Novel Blue Fluorophor with High Triplet Energy Level for High Performance Single-Emitting-Layer Fluorescence and Phosphorescence Hybrid White Organic Light-Emitting Diodes

On the basis of a D-π-A structural strategy incorporating diphenylamine as an electron-donor and 1,3,5-triazine as an electron-acceptor with a short benzene π-conjugated feature, 4-(4,6-diphenoxy-1,3,5-triazin-2-yl)-N,N-diphenylaniline (POTA), a novel blue fluorophor with high triplet energy level has been designed and synthesized to achieve high performance single-emitting-layer (single-EML) fluorescence and phosphorescence hybrid white organic light-emitting diodes (F–P hybrid WOLEDs). POTA exhibits efficient blue electrofluorescence and excellent host features for green and red phosphorescent devices. The single-EML RGB F–P hybrid WOLED based on POTA and green/red complexes shows a maximum total power efficiency of 59.8 ± 1.0 lm W–1 and a maximum total external quantum efficiency of 24.7 ± 0.7%, representing the highest efficiencies among single-EML RGB WOLEDs. Moreover, these performances are comparable with multiple-EML RGB WOLEDs even based on p-i-n structures, providing verification of the high per...

Investigation of triplet harvesting and outcoupling efficiency in highly efficient two-color hybrid white organic light-emitting diodes (Phys. Status Solidi A 8/2013)

Investigation of triplet harvesting and outcoupling efficiency in highly efficient two-color hybrid white organic light-emitting diodes (Phys. Status Solidi A 8/2013)

Color-stable, reduced efficiency roll-off hybrid white organic light emitting diodes with ultra high brightness

High-brightness and color-stable two-wavelength hybrid white organic light emitting diodes (HWOLEDs) with the configuration of indium tin oxide (ITO)/ N, N, N′, N′-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD): tetrafluoro-tetracyanoqino dimethane (F4-TCNQ)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/4,4-N,N-dicarbazolebiphenyl (CBP): iridium (III) diazine complexes (MPPZ)2Ir(acac)/NPB/2-methyl-9,10-di(2-naphthyl)anthracene (MADN): p-bis(p-N,N-di-phenyl-aminostyryl)benzene (DSA-ph)/ bis(10-hydroxybenzo[h] quinolinato)beryllium complex (Bebq2)/LiF/Al have been fabricated and characterized. The optimal brightness of the device is 69932 cd/m2 at a voltage of 13 V, and the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are almost constant during a large voltage change of 6–12 V. Furthermore, a current efficiency of 15.3 cd/A at an illumination-relevant brightness of 1000 cd/m2 is obtained, which rolls off slightly to 13.0 cd/A at an ultra high brightness of 50000 cd/m2 . We attribute this great performance to wisely selecting an appropriate spacer together with effectively utilizing the combinations of exciton-harvested orange-phosphorescence/ blue-fluorescence in the device. Undoubtedly, this is one of the most exciting results in two-wavelength HWOLEDs up to now.

Effects of electron blocking and hole trapping of the red guest emitter materials on hybrid white organic light emitting diodes

Hybrid white organic light emitting diodes (HWOLEDs) with fluorescence and phosphorescence hybrid structures are studied in this work. HWOLEDs were fabricated with blue/red emitting layers: fluorescent host material doped with sky blue material, and bipolar phosphorescent host emitting material doped with red dopant material. An electron blocking layer is applied that provides hole red guest emitter hole trapping effects, increases the charge carrier injection quantity into the emitting layers and controls the recombination zone (RZ) that helps balance the device color. Spacer layers were also inserted to expand the RZ, increase efficiency and reduce energy quenching along with roll-off effects. The resulting high efficiency warm white OLED device has the lower highest occupied molecule orbital level red guest material, current efficiency of 15.9cd/A at current density of 20mA/cm2, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39).