Analysis of thermal degradation of organic light-emitting diodes with infrared imaging and impedance spectroscopy

Kwak, Kiyeol; Cho, Kyoungah; Kim, Sangsig

doi:10.1364/oe.21.029558

Cited by 39 publications

(29 citation statements)

References 28 publications

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“…One factor that may cause this is elevated device temperature, with an increase in heat within the device possibly due to inefficient electron injection, particularly at an organo-metal interface. 38 To resolve this, an electron-transport layer of tris(8-hydroxyquinolinato)aluminium (Alq 3 ) was thermally deposited on top of the emissive material. 39 Compounds 1-4 were investigated alongside Alq 3 at two different thicknesses: 20 and 50 nm ( Table 4).…”

Section: Oled Fabrication and Characterisationmentioning

confidence: 99%

Effect of end group functionalisation of small molecules featuring the fluorene–thiophene–benzothiadiazole motif as emitters in solution-processed red and orange organic light-emitting diodes

et al. 2019

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A series of red fluorescent materials (compounds 1-4), which each contain the symmetric fluorene-thiophene-BT-thiophene-fluorene core, is presented along with their performance in solution-processed OLED devices.Extending the molecular conjugation through end-capping with additional fluorene units (compound 2), or through incorporation of donor functionalities (compounds 3 and 4) improves OLED performance relative to the parent compound 1. Notably, incorporating triphenylamine donor groups in compound 3 led to solutionprocessed OLED devices operating with a peak luminance of 2888 cd m À2 and a low turn-on voltage (3.6 V). † Electronic supplementary information (ESI) available: The graphs for the oxidation and reduction CV cycles of compounds 1-4 are shown in the ESI in Fig. S1-S4, as well as the optical microscope images in Fig. S5, AFM images of unannealed films and films annealed at 80 1C in Fig. S6 and S7 respectively, OLED data at various annealing temperatures of compound 1-4 in Table S1 and 1 H and 13 C NMR spectra for compounds 1-4 in Fig. S8-S15. Supporting data are accessible from http://dx.doi. a Recorded as an average over 8 devices. b Recorded as an average over 4 devices. c Recorded as an average over 6 devices. d Recorded as an average over 3 devices. The best turn on voltages of each compound was recorded without using Alq 3 .

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Section: Oled Fabrication and Characterisationmentioning

confidence: 99%

Effect of end group functionalisation of small molecules featuring the fluorene–thiophene–benzothiadiazole motif as emitters in solution-processed red and orange organic light-emitting diodes

et al. 2019

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“…Atomic force microscopy, scanning tunneling microscopy, infrared imaging, and impedance spectroscopy have all been used to study the change in film structure on heating. Reflectometry techniques can also be utilized to nondestructively probe the internal layered structure of a multilayer film under thermal stress.…”

Section: Introductionmentioning

confidence: 99%

Diffusion at Interfaces in OLEDs Containing a Doped Phosphorescent Emissive Layer

McEwan

Clulow

Shaw

et al. 2016

Adv Materials Inter

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layers. This stacked structure and the order in which the materials are layered are critical in ensuring optimal device performance. A common arrangement of the organic layers within a device is to have a central emissive layer with adjacent charge transport layers. The charge transport layers serve to transport holes or electrons from the electrodes within the device, ideally trapping them in the emissive layer for exciton formation and radiative decay. As such, it is important that the nature and ordering of these layers do not undergo any significant change during device operation as this will lead to a change in performance and in particular the efficiency of the device. It has been observed that exposure to temperatures above ambient (thermal stress) can lead to a significant drop in device performance. [3] It has been suggested that the drop in device performance caused by thermal stress is due to one or more of the organic layers within a device undergoing a glass transition and subsequent accelerated diffusion. [4,5] It is therefore important that the origin of this change in performance is understood, with a specific focus on temperatures that an OLED might be exposed to in a commercial device, either externally, or by joule heating during operation. [6,7] Atomic force microscopy, [8,9] scanning tunneling microscopy, [10] infrared imaging, and impedance spectroscopy [11] have all been used to study the change in film structure on heating. Reflectometry techniques can also be utilized to nondestructively probe the internal layered structure of a multilayer film under thermal stress. For example, studies using X-ray reflectometry showed that a multilayer device containing a copper phthalocyanine (CuPc) hole injection layer, an N,N′-bis(naphthalen-1-yl)-N,N′-diphenylbenzidine (NPB) hole transport layer, a tris(8-hydroxyquinoline)aluminium (Alq 3 ) emissive layer, and a lithium fluoride (LiF) electron injection layer deposited onto ITO on glass maintained discrete layers up to 100 °C, while annealing at 120 °C caused intermixing of the NPB and Alq 3 and the Alq 3 and LiF layers. [12,13] While the electron density differences of the compounds in that particular layered film were sufficient to provide adequate scattering length density (SLD) contrast for the use of X-ray reflectometry, this is generally not the case, particularly for films that primarily comprise A common feature of organic light-emitting diodes is their stacked multilayer structure, which is critical for efficient charge injection and transport, and light emission. In this study, it is found that a blended layer of the holetransport material tris(4-carbazol-9-ylphenyl)amine with 6 wt% fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy) 3 ] readily undergoes interdiffusion with adjacent layers of typical charge transport materials: bathocuproine; 1,3,5-tris(Nphenylbenzimidazol-2-yl)benzene; N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine; and N,N′-bis(naphthalen-1-yl)-N,N′-diphenylbenzidine. This process is followed using combined neutron reflectom...

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“…In the OLED aging literature, the thermal and electrical characteristics of different physical composition OLEDs have been studied to evaluate its thermal degradation [15]. Nevertheless, no modeling is done.…”

Section: Existing Methods For Aging Modelingmentioning

confidence: 99%

Modeling the Luminance Degradation of OLEDs Using Design of Experiments

Salameh

Haddad

Picot

et al. 2019

IEEE Trans. on Ind. Applicat.

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Modeling the lifespan of OLED (Organic Light-Emitting Diode) is a complex task as it depends on differentpotentially interacting factors. As the literature on this subject is still scant, new parametric models for calculating the lifespan of OLED are proposed in this work. The Design of Experiment (DoE) methodology is used for cost and accuracy reasons. Different lifespan models based on thermal and electrical experimental aging tests are proposed. As stress factors, current density, temperature and their interactions, which are rarely taken into account in aging studies are simultaneously involved. The analysis of the model parameters highlights the prevalence of temperature compared to current density on the luminance performance of OLEDs. Non-linear models appear as the most accurate.

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Analysis of thermal degradation of organic light-emitting diodes with infrared imaging and impedance spectroscopy

Cited by 39 publications

References 28 publications

Effect of end group functionalisation of small molecules featuring the fluorene–thiophene–benzothiadiazole motif as emitters in solution-processed red and orange organic light-emitting diodes

Effect of end group functionalisation of small molecules featuring the fluorene–thiophene–benzothiadiazole motif as emitters in solution-processed red and orange organic light-emitting diodes

Diffusion at Interfaces in OLEDs Containing a Doped Phosphorescent Emissive Layer

Modeling the Luminance Degradation of OLEDs Using Design of Experiments

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