Phosphorescent OLEDs with extremely low efficiency roll-off enabled via rationally designed benzimidazole-based bipolar hosts

Zhang, Tian; Miao, Jingsheng; Ali, Muhammad Umair; Shi, Ming; He, Yaowu; Fu, Tianchen; Meng, Hong

doi:10.1016/j.dyepig.2020.108477

Cited by 9 publications

(4 citation statements)

References 21 publications

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“…Furthermore, the low turn‐on voltage of OLEDs is affected by several factors including the choice of organic materials, energy level alignment, doping, carrier mobility, contact resistances, injection/ blocking interlayers, electrode materials, structure and configuration of the OLED layers stacking and device engineering. [ 132 , 133 , 134 , 135 , 136 , 137 ] Further, active and inter‐layer materials for OLEDs and OPD consist of either solution‐processed polymers or vacuum‐evaporated small molecules. These materials when solution‐coated or vacuum coated under inert conditions will exhibit high charge carrier mobility due to minimum defect states and traps and improves efficiency.…”

Section: Processing Techniques Materials and Device Performancementioning

confidence: 99%

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring

Dcosta,

Ochoa,

Sanaur

2023

Advanced Science

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Flexible and wearable biosensors are the next‐generation healthcare devices that can efficiently monitor human health conditions in day‐to‐day life. Moreover, the rapid growth and technological advancements in wearable optoelectronics have promoted the development of flexible organic photoplethysmography (PPG) biosensor systems that can be implanted directly onto the human body without any additional interface for efficient bio‐signal monitoring. As an example, the pulse oximeter utilizes PPG signals to monitor the oxygen saturation (SpO2) in the blood volume using two distinct wavelengths with organic light emitting diode (OLED) as light source and an organic photodiode (OPD) as light sensor. Utilizing the flexible and soft properties of organic semiconductors, pulse oximeter can be both flexible and conformal when fabricated on thin polymeric substrates. It can also provide highly efficient human‐machine interface systems that can allow for long‐time biological integration and flawless measurement of signal data. In this work, a clear and systematic overview of the latest progress and updates in flexible and wearable all‐organic pulse oximetry sensors for SpO2 monitoring, including design and geometry, processing techniques and materials, encapsulation of various factors affecting the device performance, and limitations are provided. Finally, some of the research challenges and future opportunities in the field are mentioned.

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Section: Processing Techniques Materials and Device Performancementioning

confidence: 99%

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring

Dcosta,

Ochoa,

Sanaur

2023

Advanced Science

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“…As shown in Figure 1, two cyano-substituted ppy-type cyclometalating ligands and one acetylacetone auxiliary ligand adopt a trans-N,N, cis-C,C, and cis-O,O configuration coordinating to the Ir(III) center, which shows a distorted octahedral geometry similar to that of Ir(ppy) 2 (acac). Specifically, the bond angles of N1−Ir−N2, C1−Ir−O1, and C2−Ir−O2 are 175.95 (10), 173.73 (11), and 174.09° (11) for Ir(3-CN); 172.67 (18), 172.49 (19) Photophysical Properties. To investigate the positional effects of cyano-substitution on the photophysical properties of ppy-based Ir complexes, their UV−vis absorption was measured, and the corresponding data are summarized in Table 1.…”

Section: Synthetic Procedures and Characterization Of Ir(3-cn) Ir(4-c...mentioning

confidence: 99%

“…However, the OLEDs using TADF emitters suffer relatively high efficiency roll-off at high luminance, which can be attributed to bimolecular quenching involving triplet excitons, such as singlet–triplet annihilation (STA) and triplet–triplet annihilation (TTA). – This phenomenon can pose a problem for state-of-the-art active-matrix OLED displays that require high pixel densities and consistently low aperture ratios at high luminance, even approaching 10,000 cd m –2 . Therefore, phosphorescent emitters are still widely applied in commercial OLEDs to achieve high external quantum efficiencies (EQEs) and low efficiency roll-off at high luminance. – Given the high costs associated with transition metal in phosphorescent emitters, it is necessary to develop phosphorescent emitters with extended emitting color ranges using simplified synthetic strategies.…”

Section: Introductionmentioning

confidence: 99%

Positional Isomeric Cyano-Substituted Bis(2-phenylpyridine)(acetylacetonate)iridium Complexes for Efficient Organic Light-Emitting Diodes with Extended Color Range

Xie,

Lee,

Huang

et al. 2023

ACS Appl. Mater. Interfaces

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Bis(2-phenylpyridine)(acetylacetonate)iridium, Ir(ppy) 2 (acac), is a benchmark green emitter for phosphorescent organic light-emitting diodes (PhOLEDs). In this work, we reported three positional isomeric cyano-substituted Ir(ppy) 2 (acac) complexes, i.e., Ir(3-CN), Ir(4-CN), and Ir(10-CN), with the emission in the yellow to red region (544−625 nm). Through theoretical investigation and single-crystal analysis, it was found that the introduction of cyano substitution at various positions of the ppy ligand allows for tuning the electron distribution and coordination bond length of Ir complexes. Therefore, the charge transfer property of Ir complexes is enhanced such that the energy gap of the cyano-substituted Ir(ppy) 2 (acac) complexes was reduced. In addition, Ir(3-CN), Ir(4-CN), and Ir(10-CN) exhibited high PLQYs of 83, 54, and 75%, respectively, with the phosphorescence lifetime in the range of 0.79−2.08 μs. Notably, the device utilizing Ir(3-CN) as the emitter exhibited a maximum external quantum efficiency (EQE) of 25.4%, current efficiency of 56.9 cd A −1 , power efficiency of 68.7 lm W −1 , and brightness of 61,340 cd m −2 at 8 V. The EQE of this device remained 24.3 and 19.9% at luminances of 1,000 and 10,000 cd m −2 , corresponding to the efficiency roll-off of 4.3 and 21.7%, respectively. Comparing to the Ir complexes using the ligand with an extended conjugated structure, our results demonstrated a simple molecular design strategy for phosphorescence emitters with reduced molecular weight for efficient PhOLEDs in the yellow to red color region.

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“…Luckily, the host-guest system was found to be effective to alleviate the concentration caused quenching issue by dispersing the heavy metal emitters homogeneously in a proper host. [6][7][8][9][10][11][12] Thus, the host materials are of equal importance compared to the emitters to achieve high electroluminescent (EL) performance.…”

Section: Introductionmentioning

confidence: 99%

A universal bipolar host based on isonicotinonitrile and carbazole for efficient red, green and blue PhOLEDs

et al. 2022

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Phosphorescent OLEDs with extremely low efficiency roll-off enabled via rationally designed benzimidazole-based bipolar hosts

Cited by 9 publications

References 21 publications

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring

Positional Isomeric Cyano-Substituted Bis(2-phenylpyridine)(acetylacetonate)iridium Complexes for Efficient Organic Light-Emitting Diodes with Extended Color Range

A universal bipolar host based on isonicotinonitrile and carbazole for efficient red, green and blue PhOLEDs

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Phosphorescent OLEDs with extremely low efficiency roll-off enabled via rationally designed benzimidazole-based bipolar hosts

Cited by 9 publications

References 21 publications

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO2Monitoring

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO2Monitoring

Positional Isomeric Cyano-Substituted Bis(2-phenylpyridine)(acetylacetonate)iridium Complexes for Efficient Organic Light-Emitting Diodes with Extended Color Range

A universal bipolar host based on isonicotinonitrile and carbazole for efficient red, green and blue PhOLEDs

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Product

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Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO₂Monitoring