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Park C, Shin J, Kim S, Lee S, Park J, Park J, Park S, Yoo S, Jang MS. Fast and rigorous optical simulation of periodically corrugated light-emitting diodes based on a diffraction matrix method. OPTICS EXPRESS 2023; 31:20410-20423. [PMID: 37381436 DOI: 10.1364/oe.489758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 05/10/2023] [Indexed: 06/30/2023]
Abstract
Increasing the light extraction efficiency has been widely studied for highly efficient organic light-emitting diodes (OLEDs). Among many light-extraction approaches proposed so far, adding a corrugation layer has been considered a promising solution for its simplicity and high effectiveness. While the working principle of periodically corrugated OLEDs can be qualitatively explained by the diffraction theory, dipolar emission inside the OLED structure makes its quantitative analysis challenging, making one rely on finite-element electromagnetic simulations that could require huge computing resources. Here, we demonstrate a new simulation method, named the diffraction matrix method (DMM), that can accurately predict the optical characteristics of periodically corrugated OLEDs while achieving calculation speed that is a few orders of magnitude faster. Our method decomposes the light emitted by a dipolar emitter into plane waves with different wavevectors and tracks the diffraction behavior of waves using diffraction matrices. Calculated optical parameters show a quantitative agreement with those predicted by finite-difference time-domain (FDTD) method. Furthermore, the developed method possesses a unique advantage over the conventional approaches that it naturally evaluates the wavevector-dependent power dissipation of a dipole and is thus capable of identifying the loss channels inside OLEDs in a quantitative manner.
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Qiao D, Chen G, Gong Y, Li K, Fan Y, Zhang B, Jia F, Abubakar Y, Jones A, Otung I, Copner N. Design and optical characterization of an efficient polarized organic light emitting diode based on refractive index modulation in the emitting layer. OPTICS EXPRESS 2020; 28:40131-40144. [PMID: 33379545 DOI: 10.1364/oe.412292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 12/10/2020] [Indexed: 06/12/2023]
Abstract
Luminescent liquid Crystal (LC) material is regarded as the most promising material for polarized organic light emission due to their intrinsic characteristics including orderly alignment and luminescence. Nevertheless, the optical extraction efficiency of LC based organic light emitting diodes (OLEDs) devices still requires significant effort and innovation towards real-world applications. In this paper, we propose the design of a highly linearly polarized light-emission from OLEDs with integrated refractive index nanograting in the emissive layer (EML) based on photo aligned luminescent liquid crystal material. The simulation results indicate that the geometrically optimized polarized device yields an external quantum efficiency (EQE) up to 47% with a polarized ratio up to 28 dB at a 550 nm emission wavelength. This conceptual design offers a new opportunity to achieve efficient polarized organic luminescence, and it is (to the best of our knowledge) the first approach that enhances the light extraction of OLEDs based on luminescent liquid crystal via index grating in the EML.
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Ke X, Gu H, Chen L, Zhao X, Tian J, Shi Y, Chen X, Zhang C, Jiang H, Liu S. Multi-objective collaborative optimization strategy for efficiency and chromaticity of stratified OLEDs based on an optical simulation method and sensitivity analysis. OPTICS EXPRESS 2020; 28:27532-27546. [PMID: 32988045 DOI: 10.1364/oe.398998] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 08/26/2020] [Indexed: 06/11/2023]
Abstract
The low efficiency and dissatisfactory chromaticity remain as important challenges on the road to the OLED commercialization. In this paper, we propose a multi-objective collaborative optimization strategy to simultaneously improve the efficiency and ameliorate the chromaticity of the stratified OLED devices. Based on the formulations derived for the current efficiency and the chromaticity Commission International de L'Eclairage (CIE) of OLEDs, an optical sensitivity model is presented to quantitatively analyze the influence of the layer thickness on the current efficiency and the CIE. Subsequently, an evaluation function is defined to effectively balance the current efficiency as well as the CIE, and a collaborative optimization strategy is further proposed to simultaneously improve both of them. Simulations are comprehensively performed on a typical top-emitting blue OLED to demonstrate the necessity and the effectivity of the proposed strategy. The influences of the layer thickness incorporated in the blue OLED are ranked based on the sensitivity analysis method, and by optimizing the relative sensitive layer thicknesses in the optical views, a 16% improvement can be achieved for the current efficiency of the OLED with desired CIE meantime. Hence, the proposed multi-objective collaborative optimization strategy can be well applied to design high-performance OLED devices by improving the efficiency without chromaticity quality degradation.
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Ma C, Liu YF, Gao XM, Bi YG, Zhang XL, Yin D, Feng J, Sun HB. Enhanced efficiency of organic light-emitting devices by using a directly imprinted nanopillared ultrathin metallic electrode. OPTICS LETTERS 2020; 45:4879-4882. [PMID: 32870881 DOI: 10.1364/ol.402754] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 08/01/2020] [Indexed: 06/11/2023]
Abstract
An ultrathin metal film with high transmittance and conductivity has been demonstrated to be a promising transparent electrode for organic light-emitting devices (OLEDs). However, mediocre surface morphology and continuity of evaporated metal films and the surface plasmon-polaritons (SPPs) energy loss between the metal electrode and organic layer still limit the external quantum efficiency (EQE) of OLEDs. Here, nanoimprint lithography has been directly applied on the ultrathin Au film with underlying uncured photopolymer to fabricate the nanopillared anode. Both the conductivity and transmittance of the nanopillared ultrathin Au film have been improved due to the improvement of continuity and surface smoothness. As we expected, the SPPs mode has been coupled into photons and further extracted from OLEDs by using the nanopillared Au film anode. Finally, 19.2% and 70.1% enhancement of current efficiency were achieved compared to the planar device with ultrathin Au anode and ITO anode, respectively.
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Kwon S, Hwang YH, Nam M, Chae H, Lee HS, Jeon Y, Lee S, Kim CY, Choi S, Jeong EG, Choi KC. Recent Progress of Fiber Shaped Lighting Devices for Smart Display Applications-A Fibertronic Perspective. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1903488. [PMID: 31483540 DOI: 10.1002/adma.201903488] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Revised: 06/27/2019] [Indexed: 06/10/2023]
Abstract
Advances in material science and nanotechnology have fostered the miniaturization of devices. Over the past two decades, the form-factor of these devices has evolved from 3D rigid, volumetric devices through 2D film-based flexible electronics, finally to 1D fiber electronics (fibertronics). In this regard, fibertronic strategies toward wearable applications (e.g., electronic textiles (e-textiles)) have attracted considerable attention thanks to their capability to impart various functions into textiles with retaining textiles' intrinsic properties as well as imperceptible irritation by foreign matters. In recent years, extensive research has been carried out to develop various functional devices in the fiber form. Among various features, lighting and display features are the highly desirable functions in wearable electronics. This article discusses the recent progress of materials, architectural designs, and new fabrication technologies of fiber-shaped lighting devices and the current challenges corresponding to each device's operating mechanism. Moreover, opportunities and applications that the revolutionary convergence between the state-of-the-art fibertronic technology and age-long textile industry will bring in the future are also discussed.
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Affiliation(s)
- Seonil Kwon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Yong Ha Hwang
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Minwoo Nam
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Hyeonwook Chae
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Ho Seung Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Yongmin Jeon
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Somin Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Chan Young Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Seungyeop Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Eun Gyo Jeong
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
| | - Kyung Cheol Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea
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Zhang XA, Chen IT, Chang CH. Recent progress in near-field nanolithography using light interactions with colloidal particles: from nanospheres to three-dimensional nanostructures. NANOTECHNOLOGY 2019; 30:352002. [PMID: 31100738 DOI: 10.1088/1361-6528/ab2282] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The advance of nanotechnology is firmly rooted in the development of cost-effective, versatile, and easily accessible nanofabrication techniques. The ability to pattern complex two-dimensional and three-dimensional nanostructured materials are particularly desirable, since they can have novel physical properties that are not found in bulk materials. This review article will report recent progress in utilizing self-assembly of colloidal particles for nanolithography. In these techniques, the near-field interactions of light and colloids are the sole mechanisms employed to generate the intensity distributions for patterning. Based on both 'bottom-up' self-assembly and 'top-down' lithography approaches, these processes are highly versatile and can take advantage of a number of optical effects, allowing the complex 3D nanostructures to be patterned using single exposures. There are several key advantages including low equipment cost, facile structure design, and patterning scalability, which will be discussed in detail. We will outline the underlying optical effects, review the geometries that can be fabricated, discuss key limitations, and highlight potential applications in nanophotonics, optoelectronic devices, and nanoarchitectured materials.
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Affiliation(s)
- Xu A Zhang
- Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, United States of America
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Liang H, Hsu HC, Wu J, He X, Wei MK, Chiu TL, Lin CF, Lee JH, Wang J. Corrugated organic light-emitting diodes to effectively extract internal modes. OPTICS EXPRESS 2019; 27:A372-A384. [PMID: 31052889 DOI: 10.1364/oe.27.00a372] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 03/04/2019] [Indexed: 06/09/2023]
Abstract
We report a corrugated structure to effectively extract the surface plasmon polaritons (SPP) and waveguiding modes in organic light-emitting diodes (OLEDs). This structure is formed by nano-imprint of blazed gratings. To study the optimum extraction condition in terms of grating pitches, we compare the light extraction efficiency of corrugated OLEDs with three kinds of pitches, showing a 42.00% external quantum efficiency (EQE) enhancement ratio with this internal structure. Due to the transfer of SPP and waveguiding modes into substrate mode, the EQE enhancement ratio can be further pushed to 103.02% by attaching a macrolens. The simulation verifies the experimental results and shows the extraction mechanism of the corrugated structure towards transverse electric (TE) and transverse magnetic (TM) waves. We foresee that this method is able to enhance the optical efficiency of devices for both mass-production OLED lighting and display in a cost-effective way.
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Lee JS, Shim YS, Park CH, Hwang H, Park CH, Joo CW, Park YW, Lee J, Ju BK. Enhanced light extraction from organic light-emitting diodes using a quasi-periodic nano-structure. NANOTECHNOLOGY 2019; 30:085302. [PMID: 30524094 DOI: 10.1088/1361-6528/aaf541] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Organic light-emitting diodes with a quasi-periodic nano-structure (QPS) were fabricated via a combination of laser interference lithography (LIL) and reactive ion etching (RIE). The LIL process was used to generate a periodic pattern, whereas the RIE process was used as a supplement to add randomness to the periodic pattern. The period of the fabricated periodic pattern was determined by finite difference time domain solutions. The height and density of the QPS were controlled by the RIE etching time and were optimized. The resulting quasi-periodic nanostructure comprised silicon dioxide (SiO2) with a low refractive index (n = 1.4-1.5), and an external quantum efficiency enhancement of 18% was achieved using the QPS device, without any viewing angle problems or spectral distortion, which are serious drawbacks of periodic patterns.
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Affiliation(s)
- Ju Sung Lee
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Anam-dong, Seoul 139-713, Republic of Korea
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Hwang H, Shim YS, Choi J, Lee DJ, Kim JG, Lee JS, Park YW, Ju BK. Nano-arrayed OLEDs: enhanced outcoupling efficiency and suppressed efficiency roll-off. NANOSCALE 2018; 10:19330-19337. [PMID: 30203819 DOI: 10.1039/c8nr03198c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Organic light-emitting diodes (OLEDs) with an enhanced outcoupling efficiency and a suppressed efficiency roll-off were fabricated by inserting a nanosize pixel-defining layer (nPDL) that defines the OLED emission region as an array of nanoholes. The outcoupling efficiency of the nano-arrayed OLEDs was increased through the reduced surface plasmon polariton loss caused by the wavy diffraction grating at the metal-organic interface, and their efficiency roll-off was suppressed through the diffusive exciton outside the exciton-formation zone. As a result, the nano-arrayed OLEDs exhibited enhancements of 148.7% in the power efficiency and 137.0% in the external quantum efficiency at 1000 cd m-2 compared with a reference device. Furthermore, the critical current density (J0) where the external quantum efficiency decreased to half of its initial value was improved by a factor of 2.5.
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Affiliation(s)
- Ha Hwang
- Display and Nanosystem Laboratory, College of Engineering, Korea University, 145 Anam-ro Seongbuk-gu, Seoul 02841, Republic of Korea.
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Lee J, Han TH, Park MH, Jung DY, Seo J, Seo HK, Cho H, Kim E, Chung J, Choi SY, Kim TS, Lee TW, Yoo S. Synergetic electrode architecture for efficient graphene-based flexible organic light-emitting diodes. Nat Commun 2016; 7:11791. [PMID: 27250743 PMCID: PMC4895731 DOI: 10.1038/ncomms11791] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 04/27/2016] [Indexed: 12/21/2022] Open
Abstract
Graphene-based organic light-emitting diodes (OLEDs) have recently emerged as a key element essential in next-generation displays and lighting, mainly due to their promise for highly flexible light sources. However, their efficiency has been, at best, similar to that of conventional, indium tin oxide-based counterparts. We here propose an ideal electrode structure based on a synergetic interplay of high-index TiO2 layers and low-index hole-injection layers sandwiching graphene electrodes, which results in an ideal situation where enhancement by cavity resonance is maximized yet loss to surface plasmon polariton is mitigated. The proposed approach leads to OLEDs exhibiting ultrahigh external quantum efficiency of 40.8 and 62.1% (64.7 and 103% with a half-ball lens) for single- and multi-junction devices, respectively. The OLEDs made on plastics with those electrodes are repeatedly bendable at a radius of 2.3 mm, partly due to the TiO2 layers withstanding flexural strain up to 4% via crack-deflection toughening. Replacing indium tin oxide with graphene in organic light-emitting diodes is a promising approach to enhance the flexibility of displays and light sources. Here, the authors combine graphene, TiO2 and low-index hole-injection layers to achieve high external quantum efficiency and good bendability.
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Affiliation(s)
- Jaeho Lee
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Tae-Hee Han
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 790-784, Republic of Korea
| | - Min-Ho Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 790-784, Republic of Korea
| | - Dae Yool Jung
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Jeongmin Seo
- Department of Mechanical Engineering, KAIST, Daejeon 305-701, Republic of Korea
| | - Hong-Kyu Seo
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 790-784, Republic of Korea
| | - Hyunsu Cho
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Eunhye Kim
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Jin Chung
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Sung-Yool Choi
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
| | - Taek-Soo Kim
- Department of Mechanical Engineering, KAIST, Daejeon 305-701, Republic of Korea
| | - Tae-Woo Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 790-784, Republic of Korea
| | - Seunghyup Yoo
- School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.,Graphene Research Center, KI for Nanocentury, KAIST, Daejeon 305-701, Republic of Korea
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11
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Matsuzaki J, Yamae K. Development of Highly Efficient Light Extraction Technology with Nano-structure for OLED Devices. J PHOTOPOLYM SCI TEC 2015. [DOI: 10.2494/photopolymer.28.329] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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12
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Choy WCH, Chan WK, Yuan Y. Recent advances in transition metal complexes and light-management engineering in organic optoelectronic devices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:5368-5398. [PMID: 25042158 DOI: 10.1002/adma.201306133] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 05/21/2014] [Indexed: 06/03/2023]
Abstract
Two of the recent major research topics in optoelectronic devices are discussed: the development of new organic materials (both molecular and polymeric) for the active layer of organic optoelectronic devices (particularly organic light-emitting diodes (OLEDs)), and light management, including light extraction for OLEDs and light trapping for organic solar cells (OSCs). In the first section, recent developments of phosphorescent transition metal complexes for OLEDs in the past 3-4 years are reviewed. The discussion is focused on the development of metal complexes based on iridium, platinum, and a few other transition metals. In the second part, different light-management strategies in the design of OLEDs with improved light extraction, and of OSCs with improved light trapping is discussed.
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Affiliation(s)
- Wallace C H Choy
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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13
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Leung SF, Zhang Q, Xiu F, Yu D, Ho JC, Li D, Fan Z. Light Management with Nanostructures for Optoelectronic Devices. J Phys Chem Lett 2014; 5:1479-1495. [PMID: 26269997 DOI: 10.1021/jz500306f] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Light management is of paramount importance to improve the performance of optoelectronic devices including photodetectors, solar cells, and light-emitting diodes. Extensive studies have shown that the efficiency of these optoelectronic devices largely depends on the device structural design. In the case of solar cells, three-dimensional (3-D) nanostructures can remarkably improve device energy conversion efficiency via various light-trapping mechanisms, and a number of nanostructures were fabricated and exhibited tremendous potential for highly efficient photovoltaics. Meanwhile, these optical absorption enhancement schemes can benefit photodetectors by achieving higher quantum efficiency and photon extraction efficiency. On the other hand, low extraction efficiency of a photon from the emissive layer to outside often puts a constraint on the external quantum efficiency (EQE) of LEDs. In this regard, different designs of device configuration based on nanostructured materials such as nanoparticles and nanotextures were developed to improve the out-coupling efficiency of photons in LEDs under various frameworks such as waveguides, plasmonic theory, and so forth. In this Perspective, we aim to provide a comprehensive review of the recent progress of research on various light management nanostructures and their potency to improve performance of optoelectronic devices including photodetectors, solar cells, and LEDs.
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Affiliation(s)
- Siu-Fung Leung
- †Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
| | - Qianpeng Zhang
- †Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
| | - Fei Xiu
- ‡Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
| | - Dongliang Yu
- §Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Zhangjiang Hi-Tech Park, Pudong, Shanghai 201210, China
| | - Johnny C Ho
- ‡Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
| | - Dongdong Li
- §Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Zhangjiang Hi-Tech Park, Pudong, Shanghai 201210, China
| | - Zhiyong Fan
- †Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
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Schwab T, Fuchs C, Scholz R, Zakhidov A, Leo K, Gather MC. Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates. OPTICS EXPRESS 2014; 22:7524-7537. [PMID: 24718126 DOI: 10.1364/oe.22.007524] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Bragg scattering at one-dimensional corrugated substrates allows to improve the light outcoupling from top-emitting organic light-emitting diodes (OLEDs). The OLEDs rely on a highly efficient phosphorescent pin stack and contain metal electrodes that introduce pronounced microcavity effects. A corrugated photoresist layer underneath the bottom electrode introduces light scattering. Compared to optically optimized reference OLEDs without the corrugated substrate, the corrugation increases light outcoupling efficiency but does not adversely affect the electrical properties of the devices. The external quantum efficiency (EQE) is increased from 15 % for an optimized planar layer structure to 17.5 % for a corrugated OLED with a grating period of 1.0 μm and a modulation depth of about 70 nm. Detailed analysis and optical modeling of the angular resolved emission spectra of the OLEDs provide evidence for Bragg scattering of waveguided and surface plasmon modes that are normally confined within the OLED stack into the air-cone. We observe constructive and destructive interference between these scattered modes and the radiative cavity mode. This interference is quantitatively described by a complex summation of Lorentz-like resonances.
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15
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Kaihovirta N, Larsen C, Edman L. Improving the performance of light-emitting electrochemical cells by optical design. ACS APPLIED MATERIALS & INTERFACES 2014; 6:2940-2947. [PMID: 24467323 DOI: 10.1021/am405530d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The organic light-emitting electrochemical cell (LEC) has emerged as an enabling technology for a wide range of novel and low-cost emissive applications, but its efficiency is still relatively modest. The focus in the field has so far almost exclusively been directed toward limiting internal loss mechanisms, whereas external losses resulting from poor light-outcoupling have been overlooked. Here, we report a straightforward procedure for improving the efficiency and emission quality of LECs. We find that our high-performance glass-encapsulated LECs exhibit a near-ideal Lambertian emission profile but that total internal reflection at the glass/air interface and a concomitant edge emission and self-absorption represent a significant loss factor. We demonstrate a 60% improvement in the outcoupled luminance in the forward direction by laminating a light-outcoupling film, featuring a hexagonal array of hemispherical microlenses as the surface structure, onto the front side of the device and a large-area metallic reflector onto the back side. With this scalable approach, yellow-emitting LEC devices with a power conversion efficiency of more than 15 lm W(-1) at a luminance of 100 cd m(-2) were realized. Importantly, we find that the same procedure also can mitigate problems with spatial variation in the light-emission intensity, which is a common and undesired feature of large-area LECs.
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Affiliation(s)
- Nikolai Kaihovirta
- The Organic Photonics and Electronics Group, Department of Physics, Umeå University , SE-901 87 Umeå, Sweden
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16
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Kim SH, Lee CM, Ahn KJ, Yee KJ. Coupling of air/metal and substrate/metal surface plasmon polaritons in Au slit arrays fabricated on quartz substrate. OPTICS EXPRESS 2013; 21:21871-21878. [PMID: 24104079 DOI: 10.1364/oe.21.021871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report on the coupling of the air/metal mode and the substrate/metal mode surface plasmon polaritons in one-dimensional metallic slit arrays fabricated on a dielectric substrate. Anti-crossing is exhibited at an incident angle where the two independent modes can be resonantly excited at a specific wavelength. The size of the anti-crossing gap was measured while changing the metal thickness.
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Fuchs C, Schwab T, Roch T, Eckardt S, Lasagni A, Hofmann S, Lüssem B, Müller-Meskamp L, Leo K, Gather MC, Scholz R. Quantitative allocation of Bragg scattering effects in highly efficient OLEDs fabricated on periodically corrugated substrates. OPTICS EXPRESS 2013; 21:16319-16330. [PMID: 23938484 DOI: 10.1364/oe.21.016319] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Bragg scattering effects in bottom-emitting organic light-emitting diodes (OLEDs) grown on corrugated aluminum-doped zinc oxide electrodes are analyzed. Periodic corrugation is introduced by structuring the oxide electrode via UV laser ablation, a process that enables flexible adjustment of the period and height of corrugation. We demonstrate that fabrication of stable and electrically efficient OLEDs on these rough substrates is feasible. Sharp spectral features are superimposed onto the broad emission spectra of the OLEDs, providing clear evidence for Bragg scattering of light from guided modes into the air cone. Theoretical analysis based on an emissive dipole model and conservation of momentum considerations allows a quantitative description of scattering and the associated dispersion relations.
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Affiliation(s)
- C Fuchs
- Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Straße 1, 01069 Dresden,
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Huang KC, Seo MK, Huo Y, Sarmiento T, Harris JS, Brongersma ML. Antenna electrodes for controlling electroluminescence. Nat Commun 2012; 3:1005. [DOI: 10.1038/ncomms1985] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 07/02/2012] [Indexed: 11/09/2022] Open
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Kluge C, Rädler M, Pradana A, Bremer M, Jakobs PJ, Barié N, Guttmann M, Gerken M. Extraction of guided modes from organic emission layers by compound binary gratings. OPTICS LETTERS 2012; 37:2646-2648. [PMID: 22743482 DOI: 10.1364/ol.37.002646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The extraction of guided modes from a 100 nm organic emission layer by compound binary gratings with multiple superimposed periods at different ratios is investigated. We measure angle-dependent photoluminescence from samples with double-period (350 and 450 nm), triple-period (350, 400, and 450 nm), and multiperiod (350, 400, 450, and 500 nm) gratings and show that each period component produces two outcoupling features due to first-order Bragg scattering of the TE(0) guided mode. The averaged angular color change is reduced by up to a factor of 11 compared to a single-period grating structuring.
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Affiliation(s)
- Christian Kluge
- Institute of Electrical and Information Engineering, Christian-Albrechts-Universität zu Kiel, Kaiserstr. 2 24143 Kiel, Germany. ‑kiel.de
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Müller-Meskamp L, Kim YH, Roch T, Hofmann S, Scholz R, Eckardt S, Leo K, Lasagni AF. Efficiency enhancement of organic solar cells by fabricating periodic surface textures using direct laser interference patterning. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:906-10. [PMID: 22403830 DOI: 10.1002/adma.201104331] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Direct laser interference patterning (DLIP) is used to fabricate large area, two-dimensional periodic surface patterns on polyethylene terephthalate (PET) substrates to enhance the performance of ZnPc:C60 solar cells by light concentration in the absorber layer. Comparing the power conversion efficiencies to the reference cell on flat PET, a relative increase of 21% is observed for the hexagonal pattern with 0.7 μm period, depicted in the figure.
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Affiliation(s)
- Lars Müller-Meskamp
- Dresdner Innovationszentrum Energieeffizienz and Institut für Angewandte Photophysik Technische, Universität Dresden, George-Bähr Straße 1, Dresden, Germany.
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