Hybrid White Organic Light-emitting Diodes Research Articles

6-4: High Efficacy, High Color Quality Hybrid White OLEDs Incorporating Red Quantum Dots with Narrow Emission Bands

We propose a hybrid WOLED technology that combines colloidal quantum dot narrow red emitters with organic emitters for high efficacy, high color quality solid state lighting. Spectra analysis indicates this approach will lead to WOLEDs that could achieve high color quality (CRI≥91; R9≥32) at high luminous efficacy of radiation (≥359lm/W).

Extremely high-efficiency and ultrasimplified hybrid white organic light-emitting diodes exploiting double multifunctional blue emitting layers.

Numerous hybrid white organic light-emitting diodes (WOLEDs) have recently been developed. However, their efficiency is not comparable to that of their best all-phosphorescent WOLED counterparts, and the structures are usually complicated, restricting their further development. Herein, a novel concept is used to achieve a hybrid WOLED, whose crucial feature is the exploitation of double multifunctional blue emitting layers. The three-organic-layer WOLED exhibits a total efficiency of 89.3 and 65.1 lm W–1 at 100 and 1000 cd m–2, respectively, making it the most efficient hybrid WOLED reported in the literature so far. Significantly, the efficiencies of hybrid WOLEDs have, for the first time, been demonstrated to be comparable to those of the best all-phosphorescent WOLEDs. In addition, the device exhibits the lowest voltages among hybrid WOLEDs (i.e., 2.4, 2.7 and 3.1 V for 1, 100 and 1000 cd m–2, respectively). Such remarkable performance achieved from such an ultrasimplified structure opens a new path toward low-cost commercialization.

Effect of Triplet Harvesting on the Lifetime Based on Fluorescence and Phosphorescence in Hybrid White Organic Light Emitting Diodes.

We investigated efficient hybrid white organic light emitting diodes (WOLEDs) apply to triplet harvesting (TH) concept based on three complementary colors by mixing containing blue fluorescent emitter with phosphorescent emitters. The TH is to transfer these triplet excitons from a fluorescence to a phosphorescence, where they can decay radiatively. We fabricated several hybrid WOLEDs, having various emitting layer structures with blue fluorescent emitter and red, green phosphorescent emitter. The WOLED exhibited maximum luminous efficiency of 9.02 cd/A, and a maximum external quantum efficiency of 4.17%. The WOLED showed a highly color-stable white emission with the Commission International de L'Éclairage chromaticity of (0.38, 0.36) at 1,000 cd/m2.

High‐Performance Hybrid White Organic Light‐Emitting Diodes with Superior Efficiency/Color Rendering Index/Color Stability and Low Efficiency Roll‐Off Based on a Blue Thermally Activated Delayed Fluorescent Emitter

Thermally activated delayed fluorescence (TADF)‐based white organic light‐emitting diodes (WOLEDs) are highly attractive because the TADF emitters provide a promising alternative route to harvest triplet excitons. One of the major challenges is to achieve superior efficiency/color rendering index/color stability and low efficiency roll‐off simultaneously. In this paper, high‐performance hybrid WOLEDs are demonstrated by employing an efficient blue TADF emitter combined with red and green phosphorescent emitters. The resulting WOLED shows the maximum external quantum efficiency, current efficiency, and power efficiency of 23.0%, 51.0 cd A−1, and 51.7 lm W−1, respectively. Moreover, the device exhibits extremely stable electroluminescence spectra with a high color rendering index of 89 and Commission Internationale de L'Eclairage coordinates of (0.438, 0.438) at the practical brightness of 1000 cd m−2. The achievement of these excellent performances is systematically investigated by versatile experimental and theoretical evidences, from which it is concluded that the utilization of a blue‐green‐red cascade energy transfer structure and the precise manipulation of charges and excitons are the key points. It can be anticipated that this work might be a starting point for further research towards high‐performance hybrid WOLEDs.

The first aggregation-induced emission fluorophore as a solution processed host material in hybrid white organic light-emitting diodes

TheCzPATPEAIE fluorophore for a solution processed host material in hybrid white OLEDs.

Highly Efficient Simplified Single-Emitting-Layer Hybrid WOLEDs with Low Roll-off and Good Color Stability through Enhanced Förster Energy Transfer.

Single-emitting layer hybrid white organic light-emitting diodes (SEL-hybrid-WOLEDs) usually suffer from low efficiency, significant roll-off, and poor color stability, attributed to the incomplete energy transfer from the triplet states of the blue fluorophores to the phosphors. Here, we demonstrate highly efficient SEL-hybrid-WOLEDs with low roll-off and good color-stability utilizing blue thermally activated delayed fluorescence (TADF) materials as the host emitters. The triplet states of the blue TADF host emitter can be up-converted into its singlet states, and then the energy is transferred to the complementary phosphors through the long-range Förster energy transfer, enhancing the energy transfer from the host to the dopant. Simplified SEL-hybrid-WOLEDs achieve the highest forward-viewing external quantum efficiency (EQE) of 20.8% and power efficiency of 51.2 lm/W with CIE coordinates of (0.398, 0.456) at a luminance of 500 cd/m(2). The device EQE only slightly drops to 19.6% at a practical luminance of 1000 cd/m(2) with a power efficiency of 38.7 lm/W. Furthermore, the spectra of the device are rather stable with the raising voltage. The reason can be assigned to the enhanced Förster energy transfer, wide charge recombination zone, as well as the bipolar charge transporting ability of the host emitter. We believe that our work may shed light on the future development of highly efficient SEL-hybrid-WOLEDs with simultaneous low roll-off and good color stability.

Manipulation of Charge and Exciton Distribution Based on Blue Aggregation‐Induced Emission Fluorophors: A Novel Concept to Achieve High‐Performance Hybrid White Organic Light‐Emitting Diodes

The aggregation‐induced emission (AIE) phenomenon is important in organic light‐emitting diodes (OLEDs), for it can potentially solve the aggregation‐caused quenching problem. However, the performance of AIE fluorophor‐based OLEDs (AIE OLEDs) is unsatisfactory, particularly for deep‐blue devices (CIEy < 0.15). Here, by enhancing the device engineering, a deep‐blue AIE OLED exhibits low voltage (i.e., 2.75 V at 1 cd m−2), high luminance (17 721 cd m−2), high efficiency (4.3 lm W−1), and low efficiency roll‐off (3.6 lm W−1 at 1000 cd m−2), which is the best deep‐blue AIE OLED. Then, blue AIE fluorophors, for the first time, have been demonstrated to achieve high‐performance hybrid white OLEDs (WOLEDs). The two‐color WOLEDs exhibit i) stable colors and the highest efficiency among pure‐white hybrid WOLEDs (32.0 lm W−1); ii) stable colors, high efficiency, and very low efficiency roll‐off; or iii) unprecedented efficiencies at high luminances (i.e., 70.2 cd A−1, 43.4 lm W−1 at 10 000 cd m−2). Moreover, a three‐color WOLED exhibits wide correlated color temperatures (10 690–2328 K), which is the first hybrid WOLED showing sunlight‐style emission. These findings will open a novel concept that blue AIE fluorophors are promising candidates to develop high‐performance hybrid WOLEDs, which have a bright prospect for the future displays and lightings.

Efficient fluorescence/phosphorescence white organic light-emitting diodes with ultra high color stability and mild efficiency roll-off

Efficient fluorescence/phosphorescence hybrid white organic light-emitting diodes (OLEDs) with single doped co-host structure have been fabricated. Device using 9-Naphthyl-10 -(4-triphenylamine)anthrancene as the fluorescent dopant and Ir(ppy)3 and Ir(2-phq)3 as the green and orange phosphorescent dopants show the luminous efficiency of 12.4% (17.6 lm/W, 27.5 cd/A) at 1000 cd/m2. Most important to note that the efficiency-brightness roll-off of the device was very mild. With the brightness rising up to 5000 and 10 000 cd/m2, the efficiency could be kept at 11.8% (14.0 lm/W, 26.5 cd/A) and 11.0% (11.8 lm/W, 25.0 cd/A). The Commission Internationale de L'Eclairage (CIE) coordinates and color rending index (CRI) were measured to be (0.45, 0.48) and 65, respectively, and remained the same in a large range of brightness (1000–10 000 cd/m2), which is scarce in the reported white OLEDs. The performance of the device at high luminance (5000 and 10 000 cd/m2) was among the best reported results including fluorescence/phosphorescence hybrid and all-phosphorescent white OLEDs. Moreover, the CRI of the white OLED can be improved to 83 by using a yellow-green emitter (Ir(ppy)2bop) in the device.

Doping-free hybrid white organic light-emitting diodes with fluorescent blue, phosphorescent green and red emission layers

Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m2, respectively.

High-Performance Hybrid White Organic Light-Emitting Diodes Utilizing a Mixed Interlayer as the Universal Carrier Switch**Supported by the National Natural Science Foundation of China under Grant No 61076066, and the Innovation Project of Science and Technology Plan Projects of Shaanxi Province under Grant No 2011KTCQ01-09.

A new interlayer is successfully used to be a universal carrier switch, developing high-performance hybrid white organic light-emitting diodes (WOLEDs). By dint of this interlayer, the two-color hybrid WOLED shows a maximum total current efficiency (CE) and power efficiency (PE) of 48.1 cd/A and 37.6 lm/W, respectively, while the three-color hybrid WOLED shows a maximum total CE and PE of 33.8 cd/A and 25.7 lm/W, respectively. The color rendering index of the three-color hybrid WOLEDs are ≥75, which is already a sufficient level for many commercial lighting applications. In addition, both the two-color and three-color hybrid WOLEDs show low efficiency roll-off and stable color. Furthermore, devices with the new interlayer show much higher performance than devices with the most commonly used 4,4-N,N-dicarbazolebiphenyl and N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine interlayers.

An ideal host-guest system to accomplish high-performance greenish yellow and hybrid white organic light-emitting diodes

Greenish yellow organic light-emitting diodes (GYOLEDs) have steadily attracted researcher's attention since they are important to our life. However, their performance significantly lags behind compared with the three primary colors based OLEDs. Herein, for the first time, an ideal host-guest system has been demonstrated to accomplish high-performance phosphorescent GYOLEDs, where the guest concentration is as low as 2%. The GYOLED exhibits a forward-viewing power efficiency of 57.0 lm/W at 1000 cd/m2, which is the highest among GYOLEDs. Besides, extremely low efficiency roll-off and voltages are achieved. The origin of the high performance is unveiled and it is found that the combined mechanisms of host-guest energy transfer and direct exciton formation on the guest are effective to furnish the greenish yellow emission. Then, by dint of this ideal host-guest system, a simplified but high-performance hybrid white OLED (WOLED) has been developed. The WOLED can exhibit an ultrahigh color rendering index (CRI) of 92, a maximum total efficiency of 27.5 lm/W and a low turn-on voltage of 2.5 V (1 cd/m2), unlocking a novel avenue to simultaneously achieve simplified structure, ultrahigh CRI (>90), high efficiency and low voltage.

High-power-efficiency hybrid white organic light-emitting diodes with a single emitting layer doped with blue delayed fluorescent and yellow phosphorescent emitters

High-efficiency hybrid white organic light-emitting diodes (HWOLEDs) with a blue thermally activated delayed fluorescent (TADF) emitter and a yellow phosphorescent emitter doped in a single emitting layer were developed. Exciton harvesting by the blue TADF and yellow phosphorescent emitters rendered both singlet and triplet excitons to contribute to the white emission, which leads to a high quantum efficiency of 22.4% and a power efficiency of 60.3 lm W−1 in the HWOLEDs. In addition, the electroluminescence spectra of the HWOLEDs were kept stable from 100 cd m−2 to 5, 000 cd m−2.

High Performance Exciplex-Based Fluorescence–Phosphorescence White Organic Light-Emitting Device with Highly Simplified Structure

Exciplex systems have become increasingly important due to their good performance in devices. Considering their bipolar transporting properties, exciplex systems with strong blue fluorescence and high triplet energies could potentially be ideal hosts for fluorescence–phosphorescence hybrid (F–P) white organic light-emitting diodes (WOLEDs). Here we achieved an efficient blue exciplex system formed with a new material (4-dimesitylboryl)phenyltriphenylamine (TPAPB) and 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi), which exhibited a high photoluminescence quantum yield of 44.1%. Using only these two organic materials, a high performance blue-emitting OLED was fabricated with a maximum external quantum efficiency (EQE) of 7.0 ± 0.4%. Such high efficiency is not only among the highest results of blue fluorescent organic light-emitting diodes (OLEDs) but also indicates that high χ (fraction of excitons that can potentially radiatively decay) can be as well achieved via a TTA triplet up-conversion p...

Efficient single-emitting layer hybrid white organic light-emitting diodes with low efficiency roll-off, stable color and extremely high luminance

An efficient single-emitting layer hybrid white organic light-emitting diode (WOLED) was developed, simultaneously fulfilling low efficiency roll-off, stable color and extreme luminance. At the practical luminance of 1000cd/m2, a total current efficiency of 42.8cd/A and power efficiency of 19.2lm/W are achieved, maintaining as high as 40.5cd/A and 15.5lm/W even at 5000cd/m2. Besides, a slight color variation [(0.025, 0.011)] and extreme luminance (∼106cd/m2) are obtained. The working mechanism is unveiled and it is demonstrated that the triplet-exciton-confining ability of electron transport layers plays a more vital role in device performances, particularly for the lifetime.

Novel "hot exciton" blue fluorophores for high performance fluorescent/phosphorescent hybrid white organic light-emitting diodes with superhigh phosphorescent dopant concentration and improved efficiency roll-off.

Two blue fluorophores with excellent hybridized local and charge-transfer (HLCT) and "hot exciton" properties were developed as the blue emitter and the host for orange-red phosphor to achieve highly efficient fluorescent/phosphorescent (F/P) hybrid white organic light-emitting diodes (WOLEDs) in a single-emissive-layer single-dopant (SEML-SD) architecture even at a high concentration of phosphorescent dopant. In the devices, part of the triplet excitons of the blue fluorophores can be utilized to realize reverse intersystem crossing from the triplet excited states to the singlet excited states for blue emission, and the diffusion volume range of the triplet excitons is reduced significantly. When the phosphorescent dopant concentration is up to 1.0 wt %, which is ten times higher than the traditional single-EML-SD F/P hybrid WOLEDs, highly efficient white emission was still achieved with maximum total external quantum efficiency (EQE) of 23.8%, current efficiency (CE) of 56.1 cd A(-1), and power efficiency (PE) of 62.9 lm W(1-). The results will supply a novel method for obtaining high efficiency F/P hybrid WOLEDs in a SEML-SD architecture with easily controllable doping concentration.

Interlayer free hybrid white organic light-emitting diodes with red/blue phosphorescent emitters and a green thermally activated delayed fluorescent emitter

Two different hybrid white organic light-emitting diodes (WOLEDs) with red/blue phosphorescent emitters and a green thermally activated delayed fluorescent (TADF) emitter were designed to develop high efficiency hybrid WOLEDs. One hybrid WOLED (type I) had a device structure with a hybrid emitting layer of green TADF and red phosphorescent emitters stacked on a blue phosphorescent emitting layer and the other hybrid WOLED (type II) had a device architecture with the green TADF emitting layer stacked on a red and blue phosphorescent emitting layer. Efficient energy transfer from the green TADF emitter to the red phosphorescent emitter was observed and balanced white emission could be obtained by optimizing the device structure of the hybrid WOLEDs. A quantum efficiency of 16.2% with a color coordinate of (0.45,0.47) and a quantum efficiency of 18.0% with a color coordinate of (0.37,0.47) were achieved in the type I and type II hybrid WOLEDs, respectively.

Highly Efficient Spiro[fluorene-9,9′-thioxanthene] Core Derived Blue Emitters and Fluorescent/Phosphorescent Hybrid White Organic Light-Emitting Diodes

A series of blue emitters incorporating spiro[fluorene-9,9′-thioxanthene] or spiro[fluorene-9,9′-thioxanthene-S,S-dioxide] as the core and phenylcarbazole or triphenylamine as the arms were designed and synthesized. Their spiro conformation is beneficial for their thermal stability and for reducing the trend of aggregation quenching. By tuning the valence of the sulfur atom, highly efficient local excited (LE) state deep blue emitters and charge-transfer (CT) state blue emitters are obtained. The devices based on the LE emitters TPA-S and CzB-S as the nondoped emissive layer exhibit high external quantum efficiency of 1.76% and 2.03% and Commission Internationale de l’Eclairage (CIE) coordinates of (0.158, 0.039) and (0.160, 0.054), respectively, and their CIEy values are among the smallest ever reported for the deep blue OLEDs and are readily very close to that of the inorganic light-emitting diode [CIE (0.16, 0.02)]. The nondoped device based on the CT emitter TPA-SO2 as the emissive layer also exhibits a high current efficiency of 5.46 cd A–1 and CIE coordinates of (0.154, 0.168). To fully utilize the 25% singlet and 75% triplet excitons, fluorescent/phosphorescent hybrid white organic light-emitting diodes in a single-emissive-layer architecture were also fabricated with TPA-SO2 as the blue emitter as well as the host of orange phosphorescent emitter to give forward-viewing power efficiency of 47.9 lm W–1, which is the highest value ever reported for the devices in a similar architecture without using any out-coupling technology.

Cool and warm hybrid white organic light-emitting diode with blue delayed fluorescent emitter both as blue emitter and triplet host.

A hybrid white organic light-emitting diode (WOLED) with an external quantum efficiency above 20% was developed using a new blue thermally activated delayed fluorescent material, 4,6-di(9H-carbazol-9-yl)isophthalonitrile (DCzIPN), both as a blue emitter and a host for a yellow phosphorescent emitter. DCzIPN showed high quantum efficiency of 16.4% as a blue emitter and 24.9% as a host for a yellow phosphorescent emitter. The hybrid WOLEDs with the DCzIPN host based yellow emitting layer sandwiched between DCzIPN emitter based blue emitting layers exhibited high external quantum efficiency of 22.9% with a warm white color coordinate of (0.39, 0.43) and quantum efficiency of 21.0% with a cool white color coordinate of (0.31, 0.33) by managing the thickness of the yellow emitting layer.

High-performance hybrid white organic light-emitting diodes employing p-type interlayers

A simplified hybrid white organic light-emitting diode (WOLED) employing a p-type interlayer is designed, simultaneously realizing high efficiency, high color rendering index (CRI), low efficiency roll-off, low voltage and stable color. The device exhibits maximum total efficiencies of 29.8cd/A and 20.9lm/W, which slightly decrease to 28.6cd/A and 16.5lm/W even at a high luminance of 5000cd/m2. Besides, a slight color-shift and a CRI of 85 at 100cd/m2 (3.65V) are obtained. Such superior results systematically demonstrate that the use of p-type interlayer is a new way to realize high-performance hybrid WOLEDs.

A high-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor

High-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor.