Degradation processes at the cathode/organic interface in organic light emitting devices with Mg:Ag cathodes

Aziz, Hany; Popović, Zoran D.; Tripp, Carl P.; Hu, Nan-Xing; Hor, Ah‐Mee; Xu, Gu

doi:10.1063/1.121442

Cited by 185 publications

(114 citation statements)

References 10 publications

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“…This was successfully done by peeling off the cathode material from the device. [10] However, most of the chemical-analysis work done so far, in particular regarding degradation processes, has been done by dissolving the organic devices and analysing the solutions by different techniques like high-performance liquid chromatography (HPLC), [11] nuclear magnetic resonance (NMR) spectroscopy, [11] or matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). [12] In particular MALDI-TOF-MS has become established for the detailed analysis of polymeric chains and proteins.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Complete Organic Semiconductor Devices by Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry

Scholz

Walzer

Leo

2008

Adv Funct Materials

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In this contribution, it is shown that the method of laser‐desorption/ionization time‐of‐flight mass spectrometry (LDI‐TOF‐MS) is a powerful technique for analyzing complete organic devices, such as organic light‐emitting diodes (OLEDs) or organic solar cells. LDI‐TOF‐MS has the potential to analyze fully processed organic devices without special pretreatment such as dissolving the device, peeling off the metal cathode, or using additional matrix materials. Thus, devices may be analysed as they are with a minimum of measurement artefacts. It is demonstrated that the method allows an analysis of complex organic multilayer devices, their composition, and incorporated impurities. It even allows possible electrochemical reaction products caused by device degradation to be analyzed. Thus, LDI‐TOF‐MS has major advantages compared to measurements of dissolved samples. As an example, the identification of all of the materials used in a complete OLED is shown. Furthermore, a detailed chemical analysis of long‐term driven OLEDs, including the detection of degradation products, is presented. From these data, several degradation mechanisms can be distinguished.

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Section: Introductionmentioning

confidence: 99%

Analysis of Complete Organic Semiconductor Devices by Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry

Scholz

Walzer

Leo

2008

Adv Funct Materials

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“…Gas evolution produced by electrochemical processes going on at the cathode/organic interface in the presence of moisture/oxygen results in bubble formation at the interface, which ultimately causes cathode delamination from the organic layers underneath [111,[725][726][727][728][729]. This causes disruptions in the electron injection at the cathode-organic interface; consequently, dark spots are seen at such sites.…”

Section: Recent Os Device Developmentsmentioning

confidence: 99%

“…Delamination occurs due to the crystalline Alq3 clusters, being thicker than the surrounding amorphous regions, lifting the cathode, leading to loss of contact between Alq3 and the cathode. The areas with no contact appear as nonemissive dark spots [728].…”

Section: Recent Os Device Developmentsmentioning

confidence: 99%

“…Organic coordination compound tris(8-hydroxyquinolinato) aluminum, commonly abbreviated as Alq3, is employed in fabricating OLEDs and its exposure to humidity through pinholes induces the formation of Alq3 crystallites in the originally amorphous films [728], resulting in protruding structures that are several times thicker than the original film with water content higher than that in the amorphous Alq3 regions [728]. The moisture diffusion through the microscopic defects in the cathode causes crystallization of Alq3 in the OLED structure itself, forming Alq3 crystals, which ultimately cause surface irregularities affecting the adhesion between the organic and metal layers.…”

Section: Recent Os Device Developmentsmentioning

confidence: 99%

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Organic semiconductors for device applications: current trends and future prospects

Ahmad

2014

Journal of Polymer Engineering

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Abstract:With the rich experience of developing silicon devices over a period of the last six decades, it is easy to assess the suitability of a new material for device applications by examining charge carrier injection, transport, and extraction across a practically realizable architecture; surface passivation; and packaging and reliability issues besides the feasibility of preparing mechanically robust wafer/substrate of single-crystal or polycrystalline/ amorphous thin films. For material preparation, parameters such as purification of constituent materials, crystal growth, and thin-film deposition with minimum defects/ disorders are equally important. Further, it is relevant to know whether conventional semiconductor processes, already known, would be useable directly or would require completely new technologies. Having found a likely candidate after such a screening, it would be necessary to identify a specific area of application against an existing list of materials available with special reference to cost reduction considerations in large-scale production. Various families of organic semiconductors are reviewed here, especially with the objective of using them in niche areas of large-area electronic displays, flexible organic electronics, and organic photovoltaic solar cells. While doing so, it appears feasible to improve mobility and stability by adjusting π-conjugation and modifying the energy bandgap. Higher conductivity nanocomposites, formed by blending with chemically conjugated C-allotropes and metal nanoparticles, open exciting methods of designing flexible contact/interconnects for organic and flexible electronics as can be seen from the discussion included here.

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“…"Bubble"-formation/gas evolution: Gas evolution produced by electrochemical processes at the cathode/organic interface in the presence of ambient moisture/oxygen leads to the formation of bubble like structures at the cathode/organic interface. These dome-like or bubble-like structures lead to cathode delamination from the organic layers underneath [32][33][34][35][36][37]. This negatively affects electron injection at the cathode-organic interface and dark spots are observed at the site of contact loss.…”

Section: Dark Spot Causative Phenomenamentioning

confidence: 99%

Dependence of dark spot growth on cathode/organic interfacial adhesion in organic light emitting devices

Phatak¹,

Tsui²,

Aziz³

2012

Journal of Applied Physics

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The growth of dark spots in organic light emitting devices (OLEDs) with cathodes deposited at 65°C instead of the conventional room temperature deposition, or which contain a metal-organic-mixed layer at the cathode contact, is investigated. The results reveal a strong correlation between the growth rate of dark spots and adhesion at the cathode-organic interface, where stronger adhesion results in a slower growth of dark spots. The findings shed light on the beneficial effect of increasing interfacial adhesion on improving the ambient stability of OLEDs. Measures for increasing cathode-organic adhesion can be expected to be particularly beneficial for flexible OLEDs where device protection from the ambient is more challenging.

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Degradation processes at the cathode/organic interface in organic light emitting devices with Mg:Ag cathodes

Cited by 185 publications

References 10 publications

Analysis of Complete Organic Semiconductor Devices by Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry

Analysis of Complete Organic Semiconductor Devices by Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry

Organic semiconductors for device applications: current trends and future prospects

Dependence of dark spot growth on cathode/organic interfacial adhesion in organic light emitting devices

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