Research

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14 pages, 3625 KiB

Open AccessArticle

Color-Tunable Organic Light Emitting Diodes for Deep Blue Emission by Regulating the Optical Micro-Cavity

by Jixin Jiang, Weiye Zheng, Junfei Chen, Zheng Xu, Dandan Song, Bo Qiao and Suling Zhao

Molecules 2020, 25(12), 2867; https://doi.org/10.3390/molecules25122867 - 22 Jun 2020

Cited by 8 | Viewed by 2828

Nowadays, most blue organic light emitting diodes (OLEDs) are fabricated by using sky-blue emitters which are more easily synthesized when compared with other deep blue emitters. Herein, we put forward a new idea of using an optical micro-cavity based on metal electrodes to [...] Read more.

Nowadays, most blue organic light emitting diodes (OLEDs) are fabricated by using sky-blue emitters which are more easily synthesized when compared with other deep blue emitters. Herein, we put forward a new idea of using an optical micro-cavity based on metal electrodes to regulate electroluminance (EL) spectra of sky-blue organic light emitting diodes to obtain a saturated deep blue emission with a narrowed full-width at half-maximum (FWHM). First, we simulate micro-cavity OLEDs and find that the transmission of the anode plays an important role in the forward emission. Meanwhile, the optical path of micro-cavity OLEDs as well as the phase shifting from electrodes influence the EL spectra and induce the extra intensity enhancement. The results show that when the resonant cavity optical path is regulated by changing the thickness of emitting layer (EML) from 25 nm to 75 nm in the micro-cavity, the EL peak of blue OLEDs has a redshift from 479 nm to 493 nm with FWHM shifting from 69.8 nm to 83.2 nm, when compared to the device without the micro-cavity, whose approximate EL peak and FWHM are 487 nm and 87 nm, respectively. However, the efficiency of electroluminescence decreases in micro-cavity OLEDs. We speculate that this is on account of the ohmic contact between ITO and Ag, the surface plasma effect and the rough morphology induced by Ag electrodes. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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12 pages, 2339 KiB

Open AccessArticle

Optical Capacitance/Conductance-Voltage Characteristics of Stored Charges in Organic Light-Emitting Diodes

by Chengwen Zhang, Zheng Xu, Peng Wang, Zilun Qin, S. Wageh, Ahmed Al-Ghamdi and Suling Zhao

Molecules 2020, 25(12), 2818; https://doi.org/10.3390/molecules25122818 - 18 Jun 2020

Cited by 3 | Viewed by 2957

Abstract

In this paper, capacitance/conductance-voltage characteristics (C/G-V) under illumination was achieved to investigate the dynamic mechanism of stored charges in OLEDs with a structure of ITO/ PEDOT:PSS/PMMA/Alq₃/Al. For all devices, at least two peaks presented in the optical capacitance-voltage curve. Compared to [...] Read more.

In this paper, capacitance/conductance-voltage characteristics (C/G-V) under illumination was achieved to investigate the dynamic mechanism of stored charges in OLEDs with a structure of ITO/ PEDOT:PSS/PMMA/Alq₃/Al. For all devices, at least two peaks presented in the optical capacitance-voltage curve. Compared to curves of devices under dark, the first peak increased remarkably with a deviation to V_bi, which can be explained in the form of stored charges combined with the optical conductance characteristics. It was also found that a great decrease in capacitance is followed by the collapse of the first peak with PMMA thickness increased. It can account for the presence of interfacial charges, which is proved further by the conductance curves. To the device with 10 nm PMMA, a third peak took place in optical capacitance and it was due to the storage of electrons by PMMA. Also, the first capacitance peak enhanced approximate linearly as the illumination power increased, which can verify the contribution of the stored charges. Additionally, it shows the potential for the stored charges in optical detections. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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13 pages, 2326 KiB

Open AccessArticle

Theoretical Studies of Photophysical Properties of D−π−A−π−D-Type Diketopyrrolopyrrole-Based Molecules for Organic Light-Emitting Diodes and Organic Solar Cells

by Ruifa Jin, Xiaofei Zhang and Wenmin Xiao

Molecules 2020, 25(3), 667; https://doi.org/10.3390/molecules25030667 - 04 Feb 2020

Cited by 29 | Viewed by 3508

Abstract

A series of D–π–A diketopyrrolopyrrole(DPP)-based small molecules were designed for organic light-emitting diode(OLEDs) and organic solar cell(OSCs) applications. Applying the PBE0/6-31G(d,p) method, the ground state geometry and relevant electronic properties were investigated. The first excited singlet state geometry and the absorption and fluorescent [...] Read more.

A series of D–π–A diketopyrrolopyrrole(DPP)-based small molecules were designed for organic light-emitting diode(OLEDs) and organic solar cell(OSCs) applications. Applying the PBE0/6-31G(d,p) method, the ground state geometry and relevant electronic properties were investigated. The first excited singlet state geometry and the absorption and fluorescent spectra were simulated at the TD-PBE0/6-31G(d,p) level. The calculated results revealed that the photophysical properties were affected through the introduction of different end groups. Furthermore, the electronic transitions corresponding to absorption and emission exhibited an intramolecular charge transfer feature. Our results suggest that the designed molecules acted not only as luminescent for OLEDs, but also as donor materials in OSCs. Moreover, they can also be used as potential electron transfer materials for OLEDs and OSCs. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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10 pages, 3971 KiB

Open AccessArticle

White Light-Emitting Devices Based on Inorganic Perovskite and Organic Materials

by Shuming Chen, Chen Chen, Cong Bao, Muhammad Mujahid, Ye Li, Ping Chen and Yu Duan

Molecules 2019, 24(4), 800; https://doi.org/10.3390/molecules24040800 - 22 Feb 2019

Cited by 22 | Viewed by 5008

Abstract

Perovskite-based materials have attracted considerable attention in photoelectric devices. In this paper, we report the one-step fabrication of spin-coated CsPbBr_2.5I_0.5 perovskite films doped with PAN (polyacrylonitrile) polymer. A red perovskite LED (PeLED) composite film was fabricated which featured a maximum [...] Read more.

Perovskite-based materials have attracted considerable attention in photoelectric devices. In this paper, we report the one-step fabrication of spin-coated CsPbBr_2.5I_0.5 perovskite films doped with PAN (polyacrylonitrile) polymer. A red perovskite LED (PeLED) composite film was fabricated which featured a maximum luminance value of 657 cd/m² at 8 V. We fabricated white PeLEDs by combining hole transporting layer material emission, perovskite–polymer composite material PAN:CsPbBr_2.5I_0.5, and pure inorganic perovskite CsPbBr₃ as a luminescent layer. The maximum luminance of the device was 360 cd/m² at 7 V, and the color coordinate was (0.31, 0.36). We obtained an ideal white light-emitting device that paves the way for further development of white PeLEDs. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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9 pages, 3220 KiB

Open AccessArticle

Effect of Host Moieties on the Phosphorescent Spectrum of Green Platinum Complex

by Yukiko Iwasaki, Hirohiko Fukagawa and Takahisa Shimizu

Molecules 2019, 24(3), 454; https://doi.org/10.3390/molecules24030454 - 28 Jan 2019

Cited by 7 | Viewed by 4261

Abstract

Highly efficient, operationally stable, and pure-color organic light-emitting diodes (OLEDs) are of considerable significance for developing practical wide-color-gamut displays. Further, we have demonstrated the feasibility of an efficient pure green phosphorescent OLED (PHOLED) by employing a narrow-band platinum complex and a top-emitting structure. [...] Read more.

Highly efficient, operationally stable, and pure-color organic light-emitting diodes (OLEDs) are of considerable significance for developing practical wide-color-gamut displays. Further, we have demonstrated the feasibility of an efficient pure green phosphorescent OLED (PHOLED) by employing a narrow-band platinum complex and a top-emitting structure. The utilization of the thermally activated delayed fluorescence (TADF) material as the phosphorescent host is expected to serve as a promising solution for obtaining operationally stable PHOLEDs with high color purity. However, the emission spectrum of the platinum complex in the TADF host exhibits a considerably broad emission spectrum. This study investigates the cause of the spectral change by evaluating the photoluminescence spectra of the platinum complex in various hosts exhibiting different molecular structures. The triazine unit in the host material was observed to result in exciplex formation between the lowest unoccupied molecular orbital (LUMO) of the host and the highest occupied molecular orbital (HOMO) of the platinum complex. Therefore, the TADF material that sterically hinders the triazine unit is considered to be suitable to prevent both exciplex formation and spectral broadening. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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9 pages, 2197 KiB

Open AccessArticle

Deep-Blue and Hybrid-White Organic Light Emitting Diodes Based on a Twisting Carbazole-Benzofuro[2,3-b]Pyrazine Fluorescent Emitter

by Chen-Chao Huang, Miao-Miao Xue, Fu-Peng Wu, Yi Yuan, Liang-Sheng Liao and Man-Keung Fung

Molecules 2019, 24(2), 353; https://doi.org/10.3390/molecules24020353 - 19 Jan 2019

Cited by 19 | Viewed by 4485

Abstract

A novel deep-blue fluorescent emitter was designed and synthesized. The external quantum efficiency (η_EQE) of the blue-emitting, doped, organic light-emitting diode (OLED) was as high as 4.34%. The device also exhibited an excellent color purity with Commission Internationale de l’Eclairage (CIE) [...] Read more.

A novel deep-blue fluorescent emitter was designed and synthesized. The external quantum efficiency (η_EQE) of the blue-emitting, doped, organic light-emitting diode (OLED) was as high as 4.34%. The device also exhibited an excellent color purity with Commission Internationale de l’Eclairage (CIE) coordinates of x = 0.15 and y = 0.05. In addition, the triplet energy had a value of 2.7 eV, which is rare for an emitter with deep-blue emission, which makes it a preferred choice for high-performance white OLEDs. By optimizing the device architectures, the color of hybrid-white OLEDs could be tunable from warm white to cool white using the aforementioned material as a bifunctional material. That is, the η_EQE of the hybrid warm-white OLED is 20.1% with a CIE x and y of 0.46 and 0.48 and the η_EQE of the hybrid cool-white OLED is 9% with a CIE x and y of 0.34 and 0.33. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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8 pages, 2279 KiB

Open AccessArticle

Reduced Efficiency Roll-Off in White Phosphorescent Organic Light-Emitting Diodes Based on Double Emission Layers

by Ren Sheng, Ying Gao, Asu Li, Yu Duan, Yi Zhao, Jie Zheng and Ping Chen

Molecules 2019, 24(1), 211; https://doi.org/10.3390/molecules24010211 - 08 Jan 2019

Viewed by 4269

Abstract

We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device [...] Read more.

We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device with the optimized doping concentration shows a maximum efficiency of 31.0 cd/A with extremely low efficiency roll-off of 30.7 cd/A at 1000 cd/m², 27.2 cd/A at 5000 cd/m², and 25.5 cd/A at 10,000 cd/m², respectively, without any outcoupling structures. This is enabled by the balanced charge carrier transport in EMLs, leading to broader exciton recombination zone. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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8 pages, 1613 KiB

Open AccessArticle

Organic Fluorescent Compounds that Display Efficient Aggregation-Induced Emission Enhancement and Intramolecular Charge Transfer

by Ruibin Hou, Baohua Zhao, Yan Xia and Dongfeng Li

Molecules 2018, 23(6), 1446; https://doi.org/10.3390/molecules23061446 - 14 Jun 2018

Cited by 10 | Viewed by 3730

Abstract

A series of symmetric sulfone-linked organic fluorescent compounds (1a–c) was synthesized and characterized. V-shaped 1a–c were designed as aggregate of intramolecular charge transfer (ICT) and aggregation-induced emission enhancement (AIEE) processes. The 1a–c emitted intense blue [...] Read more.

A series of symmetric sulfone-linked organic fluorescent compounds (1a–c) was synthesized and characterized. V-shaped 1a–c were designed as aggregate of intramolecular charge transfer (ICT) and aggregation-induced emission enhancement (AIEE) processes. The 1a–c emitted intense blue violet lights in normal solvents. A large red shift of the emission wavelength and dramatic decrease of emission efficiency occurred with increasing solvent polarity. The 1a–c will function well as electron transport and blue light-emitting materials through theoretical calculations. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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Review

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39 pages, 2302 KiB

Open AccessReview

Recent Advances on Metal-Based Near-Infrared and Infrared Emitting OLEDs

by Malika Ibrahim-Ouali and Frédéric Dumur

Molecules 2019, 24(7), 1412; https://doi.org/10.3390/molecules24071412 - 10 Apr 2019

Cited by 83 | Viewed by 6874

Abstract

During the past decades, the development of emissive materials for organic light-emitting diodes (OLEDs) in infrared region has focused the interest of numerous research groups as these devices can find interest in applications ranging from optical communication to defense. To date, metal complexes [...] Read more.

During the past decades, the development of emissive materials for organic light-emitting diodes (OLEDs) in infrared region has focused the interest of numerous research groups as these devices can find interest in applications ranging from optical communication to defense. To date, metal complexes have been most widely studied to elaborate near-infrared (NIR) emitters due to their low energy emissive triplet states and their facile access. In this review, an overview of the different metal complexes used in OLEDs and enabling to get an infrared emission is provided. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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28 pages, 2959 KiB

Open AccessReview

Recent Developments in Tandem White Organic Light-Emitting Diodes

by Peng Xiao, Junhua Huang, Yicong Yu and Baiquan Liu

Molecules 2019, 24(1), 151; https://doi.org/10.3390/molecules24010151 - 02 Jan 2019

Cited by 22 | Viewed by 6275

Abstract

Tandem white organic light-emitting diodes (WOLEDs) are promising for the lighting and displays field since their current efficiency, external quantum efficiency and lifetime can be strikingly enhanced compared with single-unit devices. In this invited review, we have firstly described fundamental concepts of tandem [...] Read more.

Tandem white organic light-emitting diodes (WOLEDs) are promising for the lighting and displays field since their current efficiency, external quantum efficiency and lifetime can be strikingly enhanced compared with single-unit devices. In this invited review, we have firstly described fundamental concepts of tandem device architectures and their use in WOLEDs. Then, we have summarized the state-of-the-art strategies to achieve high-performance tandem WOLEDs in recent years. Specifically, we have highlighted the developments in the four types of tandem WOLEDs (i.e., tandem fluorescent WOLEDs, tandem phosphorescent WOLEDs, tandem thermally activated delayed fluorescent WOLEDs, and tandem hybrid WOLEDs). Furthermore, we have introduced doping-free tandem WOLEDs. In the end, we have given an outlook for the future development of tandem WOLEDs. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes II)

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