Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Son, Donghyun; Shimoi, Yukihiro; Marumoto, Kazuhiro

doi:10.1080/15421406.2014.935978

Cited by 10 publications

(10 citation statements)

References 14 publications

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“…Here, the g factor was evaluated from the resonance magnetic field where the ESR spectrum with a first derivative form has a value of zero, and the Δ H pp value was evaluated as the difference between the two magnetic fields at a peak and a valley in the ESR spectrum. The g factor obtained by the fitting analysis is consistent with that of the Alq 3 radial anions ( g = 2.0028) obtained from the previous ESR study for Li‐doped Alq 3 films and that obtained from the DFT calculation . From this consistency, the origin of the signal A is ascribed to the Alq 3 radical anions formed by electron doping due to the reaction at the interfaces of Alq 3 /LiF/Al layer: 3LiF + Al + 3Alq 3 → AlF 3 + 3Li + Alq 3 − …”

Section: Resultssupporting

confidence: 87%

“…For investigating organic devices such as the OLEDs and the constitution materials at a molecular level, electron spin resonance (ESR) spectroscopy is one of most suitable techniques because the ESR method is a highly sensitive and nondestructive technique for directly observing radicals and charges with spins in organic semiconductors and their devices at a molecular level . The ESR studies have demonstrated a clear correlation between the performance deterioration and the charge (and spin) accumulation (or deep trappings) in photovoltaic devices, and have clarified the degradation mechanism due to the charge (and spin) formation during device fabrication .…”

Section: Introductionmentioning

confidence: 99%

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Direct Observation of Radical States and the Correlation with Performance Degradation in Organic Light‐Emitting Diodes During Device Operation

Sato

Son

Ito

et al. 2018

Physica Status Solidi (a)

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Microscopic characterization of radical states in organic light‐emitting diodes (OLEDs) during device operation is useful for elucidating the degradation mechanism because the radical formation has been considered as non‐radiative recombination centers. Electron spin resonance (ESR) spectroscopy is suitable for such characterization because it can directly observe radicals in OLEDs. In this work, the detailed ESR investigation into the radical states in OLEDs during device operation is firstly reported using a typical light‐emitting Alq3‐based OLEDs. The simultaneous measurements of the ESR signal and the luminance of the same OLED are performed to study the direct correlation between the radical states and the performance degradation. These characteristics show that the luminance monotonically decreases and an ESR signal concomitantly increases as the duration of the device operation increases after operating the OLED. Using the analysis of density functional theory (DFT) calculation, the origin of the newly emerged ESR signal is ascribed to the cationic species due to decomposed Alq3 molecules. The elucidation of the radical species formed in OLEDs during device operation has been demonstrated at a molecular level for the first time. This ESR analysis would provide useful knowledge for understanding the degradation mechanism in the OLEDs at the molecular level.

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Direct Observation of Radical States and the Correlation with Performance Degradation in Organic Light‐Emitting Diodes During Device Operation

Sato

Son

Ito

et al. 2018

Physica Status Solidi (a)

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“…47 In addition, the g value increases owing to the large spin−orbit interactions because of bromine heavy atoms. 48 To examine the effects of residual bromines at PTB7 chain ends, we performed DFT calculation using Gaussian 09. 49 As a model molecule of PTB7, we utilized oligomers shown in Figure 2a,b.…”

Section: Resultsmentioning

confidence: 99%

Operando Direct Observation of Charge Accumulation and the Correlation with Performance Deterioration in PTB7 Polymer Solar Cells

Kubodera

Yabusaki

Rachmat

et al. 2018

ACS Appl. Mater. Interfaces

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Polymer solar cells are one of the promising energy sources because of the easy solution-processable production with large area at a low cost without toxicity. Among the polymer materials, a donor-acceptor conjugated copolymer PTB7 has been extensively studied because of the typical high-performance polymer solar cells. Here, we show operando direct observation of charge accumulation in PTB7:PCBM blend solar cells from a microscopic viewpoint using electron spin resonance spectroscopy. The accumulation of ambipolar charges in the PTB7-based cells is directly observed for the first time, which shows a clear correlation with the performance deterioration during device operation. The sites of the ambipolar charge accumulation are elucidated at the molecular level, whose information would be useful for improving the cell durability in addition to the performance improvement.

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“…For Alq 3 , the calculated value ( g ave = 2.00285) is considerably smaller than the experimental value ( g = 2.0036 ± 0.0001). The reason for the larger experimental value may be due to an effect of spin–orbital interaction in a positive EMIM ion in the ion-gel and the Alq 3 anion 42 . That is, an electron on Alq 3 spreads over the positively charged EMIM, which may increase the g -factor by the enhanced spin–orbital interaction.…”

Section: Resultsmentioning

confidence: 98%

Operando direct observation of spin-states and charge-trappings of blue light-emitting-diode materials in thin-film devices

Osawa

Marumoto

2020

Sci Rep

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Spin-states and charge-trappings in blue organic light-emitting diodes (OLEDs) are important issues for developing high-device-performance application such as full-color displays and white illumination. However, they have not yet been completely clarified because of the lack of a study from a microscopic viewpoint. Here, we report operando electron spin resonance (ESR) spectroscopy to investigate the spin-states and charge-trappings in organic semiconductor materials used for blue OLEDs such as a blue light-emitting material 1-bis(2-naphthyl)anthracene (ADN) using metal–insulator–semiconductor (MIS) diodes, hole or electron only devices, and blue OLEDs from the microscopic viewpoint. We have clarified spin-states of electrically accumulated holes and electrons and their charge-trappings in the MIS diodes at the molecular level by directly observing their electrically-induced ESR signals; the spin-states are well reproduced by density functional theory. In contrast to a green light-emitting material, the ADN radical anions largely accumulate in the film, which will cause the large degradation of the molecule and devices. The result will give deeper understanding of blue OLEDs and be useful for developing high-performance and durable devices.

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Study on n-type Doped Electron-Transporting Layers in OLEDs by Electron Spin Resonance

Cited by 10 publications

References 14 publications

Direct Observation of Radical States and the Correlation with Performance Degradation in Organic Light‐Emitting Diodes During Device Operation

Direct Observation of Radical States and the Correlation with Performance Degradation in Organic Light‐Emitting Diodes During Device Operation

Operando Direct Observation of Charge Accumulation and the Correlation with Performance Deterioration in PTB7 Polymer Solar Cells

Operando direct observation of spin-states and charge-trappings of blue light-emitting-diode materials in thin-film devices

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