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Title: Spatial exciton allocation strategy with reduced energy loss for high-efficiency fluorescent/phosphorescent hybrid white organic light-emitting diodes

Abstract

Due to the poor operational lifetime of blue phosphorescent dopants and blue thermally activated delayed fluorescent (TADF) materials, hybrid white organic light-emitting diodes (WOLEDs) with conventional blue fluorescent emitters are still preferred for commercial applications in general lighting. However, the improvement in the overall efficiency of hybrid WOLEDs has been limited due to energy losses during the energy transfer process and exciton quenching after the spatial separation of the singlet and triplet excitons. Here we demonstrate the development of a Spatial Exciton Allocation Strategy (SEAS) to achieve close to 100% internal quantum efficiency (IQE) in blue-yellow complementary color hybrid WOLEDs. The employed blue fluorophore not only has a resonant triplet level with the yellow phosphor to reduce energy loss during energy transfer processes and triplet–triplet annihilation (TTA), but also has a resonant singlet level with the electron transport layer to extend singlet exciton distribution and enhance both singlet and triplet exciton utilization. Thus, the resulting hybrid WOLEDs exhibited 104 lm W -1 efficacy at 100 cd m -2 and 74 lm W -1 at 1000 cd m -2 with CIE coordinates of (0.42, 0.44) which is warm white and suitable for indoor lighting.

Authors:
ORCiD logo [1];  [2];  [2];  [3];  [4];  [5];  [3];  [6]
  1. South China Univ. of Technology (SCUT), Guangzhou (China). Inst. of Polymer Optoelectronic Materials and Devices, State Key Lab. of Luminescent Materials and Devices; Univ. of California, Los Angeles, CA (United States). Henry Samueli School of Engineering and Applied Science and Dept. of Materials Science and Engineering
  2. Heilongjiang Univ., Harbin (China). Ministry of Education and State Key Lab. of Functional Inorganic Material Chemistry
  3. Univ. of California, Los Angeles, CA (United States). Henry Samueli School of Engineering and Applied Science and Dept. of Materials Science and Engineering
  4. King Saud Univ., Riyadh (Saudi Arabia). Dept. of Chemistry
  5. King Saud Univ., Riyadh (Saudi Arabia). Dept. of Chemistry; Alfaisal Univ., Riyadh (Saudi Arabia). College of Science and General Studies and Dept. of Chemistry
  6. South China Univ. of Technology (SCUT), Guangzhou (China). Inst. of Polymer Optoelectronic Materials and Devices, State Key Lab. of Luminescent Materials and Devices; King Saud Univ., Riyadh (Saudi Arabia). Dept. of Chemistry
Publication Date:
Research Org.:
Univ. of California, Los Angeles, CA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1429117
Grant/Contract Number:
EE0006674
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Materials Horizons
Additional Journal Information:
Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2051-6347
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Lighting, OLED

Citation Formats

Zhao, Fangchao, Wei, Ying, Xu, Hui, Chen, Dustin, Ahamad, Tansir, Alshehri, Saad, Pei, Qibing, and Ma, Dongge. Spatial exciton allocation strategy with reduced energy loss for high-efficiency fluorescent/phosphorescent hybrid white organic light-emitting diodes. United States: N. p., 2017. Web. doi:10.1039/c7mh00131b.
Zhao, Fangchao, Wei, Ying, Xu, Hui, Chen, Dustin, Ahamad, Tansir, Alshehri, Saad, Pei, Qibing, & Ma, Dongge. Spatial exciton allocation strategy with reduced energy loss for high-efficiency fluorescent/phosphorescent hybrid white organic light-emitting diodes. United States. doi:10.1039/c7mh00131b.
Zhao, Fangchao, Wei, Ying, Xu, Hui, Chen, Dustin, Ahamad, Tansir, Alshehri, Saad, Pei, Qibing, and Ma, Dongge. Wed . "Spatial exciton allocation strategy with reduced energy loss for high-efficiency fluorescent/phosphorescent hybrid white organic light-emitting diodes". United States. doi:10.1039/c7mh00131b. https://www.osti.gov/servlets/purl/1429117.
@article{osti_1429117,
title = {Spatial exciton allocation strategy with reduced energy loss for high-efficiency fluorescent/phosphorescent hybrid white organic light-emitting diodes},
author = {Zhao, Fangchao and Wei, Ying and Xu, Hui and Chen, Dustin and Ahamad, Tansir and Alshehri, Saad and Pei, Qibing and Ma, Dongge},
abstractNote = {Due to the poor operational lifetime of blue phosphorescent dopants and blue thermally activated delayed fluorescent (TADF) materials, hybrid white organic light-emitting diodes (WOLEDs) with conventional blue fluorescent emitters are still preferred for commercial applications in general lighting. However, the improvement in the overall efficiency of hybrid WOLEDs has been limited due to energy losses during the energy transfer process and exciton quenching after the spatial separation of the singlet and triplet excitons. Here we demonstrate the development of a Spatial Exciton Allocation Strategy (SEAS) to achieve close to 100% internal quantum efficiency (IQE) in blue-yellow complementary color hybrid WOLEDs. The employed blue fluorophore not only has a resonant triplet level with the yellow phosphor to reduce energy loss during energy transfer processes and triplet–triplet annihilation (TTA), but also has a resonant singlet level with the electron transport layer to extend singlet exciton distribution and enhance both singlet and triplet exciton utilization. Thus, the resulting hybrid WOLEDs exhibited 104 lm W-1 efficacy at 100 cd m-2 and 74 lm W-1 at 1000 cd m-2 with CIE coordinates of (0.42, 0.44) which is warm white and suitable for indoor lighting.},
doi = {10.1039/c7mh00131b},
journal = {Materials Horizons},
number = 4,
volume = 4,
place = {United States},
year = {Wed May 17 00:00:00 EDT 2017},
month = {Wed May 17 00:00:00 EDT 2017}
}

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  • In this paper, a novel type of white-light organic light emitting diode (OLED) with high color stability was reported, in which the yellow-light emission layer of (4,4{sup ′}-N,N{sup ′}-dicarbazole)biphenyl (CBP) : tris(2-phenylquinoline-C2,N{sup ′})iridium(III) (Ir(2-phq){sub 3}) was sandwiched by double blue-light emission layers of 1,1-bis-[(di-4-tolylamino)pheny1]cyclohexane (TAPC) : bis[4,6-(di-fluorophenyl)-pyridinato-N,C2{sup ′}]picolinate (FIrpic) and tris[3-(3-pyridyl)mesityl]borane (3TPYMB):FIrpic. And, it exhibited the maximum current efficiency of 33.1 cd/A, the turn-on voltage at about 3 V and the maximum luminance in excess of 20000 cd/m{sup 2}. More important, it realized very stable white-light emission, and its CIE(x, y) coordinates only shift from (0.34, 0.37) to (0.33, 0.37)more » as applied voltage increased from 5 V to 12 V. It is believed that the new scheme in emission layer of white-light OLED can fine tune the contribution of primary emission with applied voltage changed, resulting in high quality white-light OLED.« less
  • We have demonstrated high-efficiency greenish-blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a dimesitylboryl-functionalized C^N chelate Pt(II) phosphor, Pt(m-Bptrz)(t-Bu-pytrz-Me). Using a high triplet energy platform and optimized double emissive zone device architecture results in greenish-blue PHOLEDs that exhibit an external quantum efficiency of 24.0% and a power efficiency of 55.8 lm/W. This record high performance is comparable with that of the state-of-the-art Ir-based sky-blue organic light-emitting diodes.
  • We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){submore » 3} as phosphorescent red dopant in electron transport layer.« less
  • We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency,more » and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.« less