| 1. |
- Shi, Furong, et al.
(author)
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A Nitroxide Radical Conjugated Polymer as an Additive to Reduce Nonradiative Energy Loss in Organic Solar Cells
- 2023
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:23
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Journal article (peer-reviewed)abstract
- Nonfullerene-acceptor-based organic solar cells (NFA-OSCs) are now set off to the 20% power conversion efficiency milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Nonradiative recombination, to a great extent, is known to be an inherent material property due to vibrationally induced decay of charge-transfer (CT) states or their back electron transfer to the triplet excitons. Herein, it is shown that the use of a new conjugated nitroxide radical polymer with 2,2,6,6-tetramethyl piperidine-1-oxyl side groups (GDTA) as an additive results in an improvement of the photovoltaic performance of NFA-OSCs based on different active layer materials. Upon the addition of GDTA, the open-circuit voltage (VOC), fill factor (FF), and short-circuit current density (JSC) improve simultaneously. This approach is applied to several material systems including state-of-the-art donor/acceptor pairs showing improvement from 15.8% to 17.6% (in the case of PM6:Y6) and from 17.5% to 18.3% (for PM6:BTP-eC9). Then, the possible reasons behind the observed improvements are discussed. The results point toward the suppression of the CT state to triplet excitons loss channel. This work presents a facile, promising, and generic approach to further improve the performance of NFA-OSCs.
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| 2. |
- Shi, Changsheng, et al.
(author)
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High performance hybrid tandem white organic light-emitting diodes by using a novel intermediate connector
- 2018
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 6:4, s. 767-772
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Journal article (peer-reviewed)abstract
- We propose a novel intermediate connector for fluorescence/phosphorescence hybrid tandem white organic light emitting diodes (WOLEDs). The core of our concept is to insert a thin layer of calcium (Ca) between lithium 8-hydroxyquinolinolate (Liq) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) to construct the intermediate connector. The resultant hybrid tandem WOLEDs exhibit very high device performance. For the color-complementary devices, the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) reach 106.3 cd A−1, 51.4 lm W−1 and 39.6%, respectively, without any out-coupling techniques. At the luminance intensity of 1000 cd m−2, the efficiencies can still be maintained at 102.8 cd A−1, 46.9 lm W−1 and 38.8%. We also obtain a color rendering index (CRI) as high as 93 in a three-primary-color device. Moreover, both the complementary and three-primary-color devices possess excellent stability for the luminance increased from 1000 cd m−2 to 10 000 cd m−2.
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| 3. |
- Shi, Changsheng, et al.
(author)
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Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer
- 2018
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 112:2
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Journal article (peer-reviewed)abstract
- High performance hybrid white organic light-emitting diodes (WOLEDs) were fabricated by inserting a planar heterojunction interlayer between the fluorescent and phosphorescent emitting layers (EMLs). The maximum external quantum efficiency (EQE) of 19.3%, current efficiency of 57.1 cdA(-1), and power efficiency (PE) of 66.2 mu m W-1 were achieved in the optimized device without any light extraction enhancement. At the luminance of 1000 cdm(-2), the EQE and PE remained as high as 18.9% and 60 mu m W-1, respectively, showing the reduced efficiency-roll. In order to disclose the reason for such high performance, the distribution of excitons was analyzed by using ultra-thin fluorescent and phosphorescent layers as sensors. It was found that the heterojunction interlayer can efficiently separate the singlet and triplet excitons, preventing the triplet excitons from being quenched by the fluorescent emitter. The introduction of the heterojunction interlayer between the fluorescent and phosphorescent EMLs should offer a simple and efficient route to fabricate the high performance hybrid WOLEDs. Published by AIP Publishing.
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| 4. |
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| 5. |
- Wang, Lin, et al.
(author)
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Highly Enhanced Luminescence from Single-Crystalline C60·1m-xylene Nanorods
- 2006
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:17, s. 4190-4194
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Journal article (peer-reviewed)abstract
- Single-crystalline C60â1m-xylene nanorods with a hexagonal structure were successfully synthesizedby evaporating a C60 solution in m-xylene at room temperature. The ratio of the length to the diameterof the nanorods can be controlled in the range of 10 to over 1000 for different applications. Thephotoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that forpristine C60 crystals in air. Both UV and Raman results indicate that there is no charge transfer betweenC60 and m-xylene. It was found that the interaction between C60 and m-xylene molecules is of the vander Waals type. This interaction reduces the icosahedral symmetry of C60 molecule and induces strongPL from the solvate nanorods.
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| 6. |
- Wu, Zhongbin, et al.
(author)
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Achieving Extreme Utilization of Excitons by an Efficient Sandwich-Type Emissive Layer Architecture for Reduced Efficiency Roll-Off and Improved Operational Stability in Organic Light-Emitting Diodes
- 2016
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 8:5, s. 3150-3159
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Journal article (peer-reviewed)abstract
- It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the emissive layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W-1 and a maximum current efficiency of 93.5 cd A(-1). At the high brightness of 5 000 cd m(-2), they still remain as high as 23.3%, 71.1 lm W-1, and 88.3 cd A(-1), respectively. And, the device'lifetime is up to 2000 h at initial luminance of 1000 cd m(-2), which is significantly higher than that of compared devices with conventional EML structures. The improvement mechanism is systematically studied by the dependence of the exciton distribution in EML and the exciton quenching processes. It can be seen that the utilization of the efficient sandwich-type EML broadens the recombination zone width, thus greatly reducing the exciton quenching and increasing the probability of the exciton recombination. It is believed that the design concept, provides a new avenue for us to achieve high-performance OLEDs.
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| 7. |
- Wu, Zhongbin, et al.
(author)
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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
- 2016
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In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 26:19, s. 3306-3313
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Zhang, Tianmu, et al.
(author)
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High efficiency phosphorescent white organic light-emitting diodes with low efficiency roll-off achieved by strategic exciton management based on simple ultrathin emitting layer structures
- 2017
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 5:48, s. 12833-12838
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Journal article (peer-reviewed)abstract
- White organic light-emitting diodes (WOLEDs) with ultrathin emitting layer (UEML) structures have vast potential in applications due to highly simplified processing. However, the efficiency and efficiency roll-off at high luminance require further improvement. In this paper, we successfully fabricated high efficiency and low roll-off phosphorescent WOLEDs by strategically controlling the location of red, green and blue UEMLs. The probability of exciton recombination was significantly enhanced, along with greatly suppressed exciton annihilation. The resulting WOLEDs exhibited a maximum external quantum efficiency (EQE) of 20.3%, a current efficiency (CE) of 44.2 cd A(-1), and a power efficiency (PE) of 39.0 lm W-1, and remained as high as 18.8%, 41.9 cd A(-1), and 28.6 lm W-1 at a luminance of 5000 cd m(-2), respectively. Additionally, the devices showed superior warm white emission with a small variation in the Commission Internationale de l'Eclairage (CIE), from (0.47, 0.43) to (0.43, 0.44) in the luminance range of 1000 cd m(-2) to 30000 cd m(-2), and the color rendering index (CRI) was as high as 80. This should be among the best results reported so far for WOLEDs based on UEML structures, indicating the great potential of high-performance WOLEDs fabricated using a very simple technology.
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