Electrically Controllable Spin States of Holes and Electrons in Organic Semiconductor Materials

Iguchi, Shohei; Sakurai, Y.; Fujita, Naohiro; Osawa, Fumiya; Marumoto, Kazuhiro

doi:10.1021/acsaelm.9b00551

Cited by 7 publications

(5 citation statements)

References 52 publications

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“…The difference of g-factors for the hole and electron in P3HT has been recently reported with the density functional theory (DFT) calculation. 43 The DFT calculations for P3HT indicate that the electron density on the sulfur atoms of the thiophene groups of the LUMO is greater than that on the sulfur atoms of the thiophenes of the HOMO. 43−45 The nonvanishing electron density on the sulfur atoms associated with the LUMO results in the electron g-factor being larger than the hole g-factor.…”

Section: Resultsmentioning

confidence: 99%

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Wakikawa

Ikoma

2020

J. Phys. Chem. C

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Using electrically and capacitively detected magnetic resonance (EDMR and CDMR) techniques, we clarified recombination in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) films, which is an important elementary process for photoconduction. The modulation frequency dependences of the EDMR and CDMR reveal the coexistence of two types of electron− hole (e−h) pairs with different lifetimes in the device fabricated with a Schottky contact between P3HT and an Al electrode. The short-lived e−h pair is a precursor of the recombination of free carriers in the bulk P3HT. The long-lived e−h pair is involved in the recombination of space charges in the Schottky junction region, which leads to an enhancement of the photocurrent.

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Section: Resultsmentioning

confidence: 99%

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Wakikawa

Ikoma

2020

J. Phys. Chem. C

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“…One reason may be the recombination between holes (positive polarons) in the PEDOT:PSS layer and leakage electrons injected from the cathode passed through the light-emitting layer by V bias ; we will discuss this first reason in more detail later. Another reason may be the formation of bipolarons by increasing the polaron density in the PEDOT:PSS layer 44 – 48 , where a bipolaron is the combination of two polarons and has no spin 44 – 48 . However, the latter reason will be ruled out later by the following results for OLEDs with MoO 3 .…”

Section: Resultsmentioning

confidence: 99%

Operando ESR observation in thermally activated delayed fluorescent organic light-emitting diodes

Yumoto

Katsumata

Osawa

et al. 2023

Sci Rep

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Organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) materials have advantages over OLEDs using conventional fluorescent materials or high-cost phosphorescent materials, including higher efficiency and lower cost. To attain further high device performance, clarifying internal charge states in OLEDs at a microscopic viewpoint is crucial; however, only a few such studies have been performed. Here, we report a microscopic investigation into internal charge states in OLEDs with a TADF material by electron spin resonance (ESR) at a molecular level. We observed operando ESR signals of the OLEDs and identified their origins due to a hole-transport material PEDOT:PSS, gap states at an electron-injection layer, and a host material CBP in the light-emitting layer by performing density functional theory calculation and studying thin films used in the OLEDs. The ESR intensity varied with increasing applied bias before and after the light emission. We find leakage electrons in the OLED at a molecular level, which is suppressed by a further electron-blocking layer MoO3 between the PEDOT:PSS and light-emitting layer, resulting in the enhancement of luminance with a low-voltage drive. Such microscopic information and applying our method to other OLEDs will further improve the OLED performance from the microscopic viewpoint.

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“…The fabricated device was sealed into an ESR sample tube after wiring with Ag paste in a nitrogen-filled glove box (O 2 ≤ 0.5 ppm, H 2 O ≤ 0.5 ppm). The parts of the above-mentioned fabrication method have been described in the previous works 31 , 35 , 46 – 49 .…”

Section: Methodsmentioning

confidence: 99%

“…Its correctness was also confirmed with 2,2-diphenyl-1-picrylhydrazyl (DPPH) as another standard sample. The parts of the above-mentioned characterization method have been described in the previous works 30 – 35 , 46 – 49 .…”

Section: Methodsmentioning

confidence: 99%

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

Osawa

Marumoto

2020

Sci Rep

Self Cite

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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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Electrically Controllable Spin States of Holes and Electrons in Organic Semiconductor Materials

Cited by 7 publications

References 52 publications

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Operando ESR observation in thermally activated delayed fluorescent organic light-emitting diodes

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

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