Theory of carrier accumulation in organic heterojunctions

Takahashi, Jun-ichi

doi:10.1016/j.orgel.2018.10.044

Cited by 13 publications

(15 citation statements)

References 44 publications

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“…In this letter, we prepared two-layered OLED model samples with p-type and n-type organic layers for PS-EH to interpret the built-in potential profile compared with previous reports. [21][22][23][24][25] We show the potential of EH for clarifying the light emitting mechanism in OLED devices.…”

mentioning

confidence: 86%

“…Takahashi suggested that the activation of localized carrier source (ALCS) supplied holes from this level by thermal excitation and that this behavior occurs even at room temperature. [21][22][23] Therefore, the sample heating due to electron beam irradiation cannot be neglected even though the sample temperature increases at most 10 °C under the PS-EH condition. Carriers trapped in the impurity levels could also affect the formation of electric fields.…”

mentioning

confidence: 99%

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Direct visualization of electric potential distribution in organic light emitting diode by phase-shifting electron holography

Sasaki¹,

Yamamoto²,

Anada³

et al. 2021

Appl. Phys. Express

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We utilized phase-shifting electron holography on organic light emitting diodes consisting of N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD) and tris-(8-hydroxyquinoline)aluminum (Alq 3 ) layers to visualize their built-in potential distribution. The bilayer showed three different electric fields, namely, the fields in the α-NPD layer, near the α-NPD/Alq 3 interface, and in the Alq 3 layer measured as −1.8 ± 0.4 MV m −1 , −10.0 ± 2 MV m −1 , 3.1 ± 0.6 MV m −1 , respectively. We show that they are related to hole accumulation in the α-NPD layer, the charge carrier accumulation junction around the α-NPD/Alq 3 interface, and the giant surface potential spontaneously polarized in the Alq 3 layer.

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confidence: 86%

mentioning

confidence: 99%

Direct visualization of electric potential distribution in organic light emitting diode by phase-shifting electron holography

Sasaki¹,

Yamamoto²,

Anada³

et al. 2021

Appl. Phys. Express

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“…Such devices may show a better injection of positive charge carriers and efficient exciton generation in the emissive zone [44,45]. However, increasing the voltage increases the current density and luminance decreases due to charge imbalance and the influence of exciton quenching [46].…”

Section: Electroluminescent Propertiesmentioning

confidence: 99%

Highly Efficient Candlelight Organic Light-Emitting Diode with a Very Low Color Temperature

et al. 2021

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Low color temperature candlelight organic light-emitting diodes (LEDs) are human and environmentally friendly because of the absence of blue emission that might suppress at night the secretion of melatonin and damage retina upon long exposure. Herein, we demonstrated a lighting device incorporating a phenoxazine-based host material, 3,3-bis(phenoxazin-10-ylmethyl)oxetane (BPMO), with the use of orange-red and yellow phosphorescent dyes to mimic candlelight. The resultant BPMO-based simple structured candlelight organic LED device permitted a maximum exposure limit of 57,700 s, much longer than did a candle (2750 s) or an incandescent bulb (1100 s) at 100 lx. The resulting device showed a color temperature of 1690 K, which is significantly much lower than that of oil lamps (1800 K), candles (1900 K), or incandescent bulbs (2500 K). The device showed a melatonin suppression sensitivity of 1.33%, upon exposure for 1.5 h at night, which is 66% and 88% less than the candle and incandescent bulb, respectively. Its maximum power efficacy is 23.1 lm/W, current efficacy 22.4 cd/A, and external quantum efficiency 10.2%, all much higher than the CBP-based devices. These results encourage a scalable synthesis of novel host materials to design and manufacture high-efficiency candlelight organic LEDs.

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“…Among these processes, the carrier motion plays the leading role and is imperative to investigate. It is particularly worth noting the excess charges stored in bulk, which may originate from the charges’ accumulation near the interface [ 16 ] or the traps in localized states [ 17 ]. Moreover, they are ubiquitous and may even cause great damage to the device’s performance.…”

Section: Introductionmentioning

confidence: 99%

A New Benchmark of Charges Storage in Single-Layer Organic Light-Emitting Diodes Based on Electrical and Optical Characteristics

Zhang

Wang

et al. 2021

Molecules

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The storage of charges in organic light-emitting diodes (OLEDs) has drawn much attention for its damage to device performance as well as the loss to carriers. Thus, it is essential to address the issue and do further investigation. The traditional approach to storage analysis is mainly based on transient measurement since it is sensitive to transient instead of steady signal. In this paper, we proposed a new benchmark to investigate the single-layer OLEDs capable of stored charges with poly (methyl methacrylate) (PMMA), which is just based on electrical and optical characteristics. Since the stored charges contribute both to luminance and current of the devices with PMMA, the area between them can be taken as a benchmark and evaluated the storage of charges. In our experiment, the areas of 4 nm, 6 nm, 8 nm, and 10 nm PMMA devices are 0.348, 0.554, 0.808, and 0.894, respectively, indicating a higher capability of storage in thicker PMMA. It is exactly in line with the results taken from transient electroluminescence (EL) measurement. Thus, this new benchmark is practical and provides a more accessible approach to investigate the storage of charges in OLEDs.

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Theory of carrier accumulation in organic heterojunctions

Cited by 13 publications

References 44 publications

Direct visualization of electric potential distribution in organic light emitting diode by phase-shifting electron holography

Direct visualization of electric potential distribution in organic light emitting diode by phase-shifting electron holography

Highly Efficient Candlelight Organic Light-Emitting Diode with a Very Low Color Temperature

A New Benchmark of Charges Storage in Single-Layer Organic Light-Emitting Diodes Based on Electrical and Optical Characteristics

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