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Yoshiaki Oku

Bio: Yoshiaki Oku is an academic researcher from Rohm. The author has contributed to research in topics: Layer (electronics) & Organic semiconductor. The author has an hindex of 9, co-authored 23 publications receiving 269 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors used 1wt-rubrene doped tetraphenylpyrene (TPPy) as an active layer in a lateral organic light-emitting diode structure that allowed field-effect transistor operation.
Abstract: We succeeded in observing bright electroluminescence (EL) from 1wt%-rubrene doped tetraphenylpyrene (TPPy) as an active layer in a lateral organic light-emitting diode structure that allowed field-effect transistor operation. This device configuration provides an organic light-emitting diode structure where the anode (source) and cathode (drain) electrodes are laterally arranged, providing us a chance to control the EL intensity by changing the gate bias. We demonstrated that TPPy provides compatible transistor and EL characteristics. Further, not only rubrene doping into the TPPy host but also adjusting the source-drain channel length significantly improved the EL characteristics. We observed a maximum EL quantum efficiency (ηext) of ∼0.5% with a Cr∕Au source (S)-drain (D) electrode and a slightly higher ηext of ∼0.8% with S-D electrodes of MgAu∕Au, Al∕Au, Cr∕YAu∕Au, and MgAl∕Au multilayers, aiming for simultaneous hole and electron injection.

119 citations

Journal ArticleDOI
TL;DR: Suganuma et al. as discussed by the authors used lift-off patterning of organic semiconductor thin-films to fabricate light-emitting transistors with PN-heteroboundary carrier recombination sites.

26 citations

Journal ArticleDOI
TL;DR: In this article, an ultrathin rubrene doped 1,3,6,8-tetraphenylpyrene (TPPy) layer (d=10nm) was inserted as a sensing layer in a TPPy layer (80nm) and measured the luminance-drain current drain voltage characteristics and the EL spectra depending on the position of the sensing layer.
Abstract: To elucidate the electroluminescence (EL) mechanism of organic light-emitting field-effect transistors (OLEFETs), we determined the carrier recombination and EL emission regions using the local doping method. We demonstrated that the local doping method is a useful technique for estimating the width of these regions in OLEFETs. We inserted an ultrathin rubrene doped 1,3,6,8-tetraphenylpyrene (TPPy) layer (d=10nm) as a sensing layer in a TPPy layer (80nm) and measured the luminance-drain current-drain voltage characteristics and the EL spectra depending on the position of the sensing layer. We confirmed that the EL emission region expanded almost to the height (h≃40nm) of the source-drain electrodes and was independent of the gate bias voltage (Vg). Further, we observed that the EL external quantum efficiency (ηext) significantly decreased as Vg increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of Vg.

23 citations

Journal ArticleDOI
TL;DR: In this article, an alignment-free process for asymmetric contacts of Au and Al and applied it to light-emitting organic field-effect transistors was developed, where electrons were injected efficiently from Al contacts, the emission intensity and onset voltages for light were significantly better than those in a device with conventional Au∕Cr contacts.
Abstract: We developed an alignment-free process for asymmetric contacts of Au and Al and applied it to light-emitting organic field-effect transistors. Because electrons were injected efficiently from Al contacts, the emission intensity and onset voltages for light were significantly better than those in a device with conventional Au∕Cr contacts. Moreover, a device with 1μm channel length asymmetric contacts of Au and Al showed about 50 times higher current than that of the device with conventional Au∕Cr contacts. This significant improvement can be ascribed to both dual space-charge formation of holes and electrons and low carrier injection barriers.

18 citations

Journal ArticleDOI
TL;DR: In this article, a light-emitting transistor (OLET) with a PN-heteroboundary combined with hole and electron transport materials (in other words, p-type and n-type organic semiconductors) along carrier channels is presented.
Abstract: The authors have devised a novel organic light-emitting transistor (OLET) with a PN-heteroboundary combined with hole and electron transport materials (in other words, p-type and n-type organic semiconductors) along carrier channels. In this device, a clear modulation of the current and luminance with the gate voltage was observed. A luminance of 100 cd/m2 or more has been observed at the source–source voltage of 15 V with the turn-on voltage of 10 V or less, which is lower than that of OLETs based on a single organic material. The horizontal PN-heteroboundary structure has been implemented for the first time by using the photolithographic patterning of organic semiconductor thin films. This patterning technique can be applied to the fabrication of not only the OLETs reported in this work, but also to organic integrated circuits or organic displays.

13 citations


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Journal ArticleDOI
TL;DR: Recent advances and future prospects of light-emitting field-effect transistors are explored, with particular emphasis on organic semiconductors and the role played by the material properties, device features and the active layer structure in determining the device performances.
Abstract: Field-effect transistors are emerging as useful device structures for efficient light generation from a variety of materials, including inorganic semiconductors, carbon nanotubes and organic thin films. In particular, organic light-emitting field-effect transistors are a new class of electro-optical devices that could provide a novel architecture to address open questions concerning charge-carrier recombination and light emission in organic materials. These devices have potential applications in optical communication systems, advanced display technology, solid-state lighting and electrically pumped organic lasers. Here, recent advances and future prospects of light-emitting field-effect transistors are explored, with particular emphasis on organic semiconductors and the role played by the material properties, device features and the active layer structure in determining the device performances.

858 citations

Journal ArticleDOI
TL;DR: In this article, a new class of propeller-like luminogenic molecules with aggregation-induced emission (AIE) characteristics has drawn increasing research interest, and tetraphenylethene (TPE) is an archetypal luminogen with a simple molecule structure.
Abstract: Luminescent materials with efficient solid-state emissions are important for the advancement of optoelectronics. Recently, a new class of propeller-like luminogenic molecules with aggregation-induced emission (AIE) characteristics has drawn increasing research interest. Among them, tetraphenylethene (TPE) is an archetypal luminogen with a simple molecule structure but shows a splendid AIE effect. Utilizing TPE as a building block, an effective strategy to create efficient solid-state emitters is developed. In this feature article, we review mainly our recent work on the construction of luminogenic materials from TPE and present their applications in organic light-emitting diodes. The applicability of the synthetic strategy and the utility of the resulting materials are demonstrated.

707 citations

Journal ArticleDOI
TL;DR: The concept of using a p-channel/emitter/n-channel trilayer semiconducting heterostructure in OLETs is introduced, providing a new approach to markedly improve OLET performance and address general fundamental optoelectronic and photonic issues.
Abstract: The potential of organic semiconductor-based devices for light generation is demonstrated by the commercialization of display technologies based on organic light-emitting diodes (OLEDs). Nonetheless, exciton quenching and photon loss processes still limit OLED efficiency and brightness. Organic light-emitting transistors (OLETs) are alternative light sources combining, in the same architecture, the switching mechanism of a thin-film transistor and an electroluminescent device. Thus, OLETs could open a new era in organic optoelectronics and serve as testbeds to address general fundamental optoelectronic and photonic issues. Here, we introduce the concept of using a p-channel/emitter/n-channel trilayer semiconducting heterostructure in OLETs, providing a new approach to markedly improve OLET performance and address these open questions. In this architecture, exciton-charge annihilation and electrode photon losses are prevented. Our devices are >100 times more efficient than the equivalent OLED, >2x more efficient than the optimized OLED with the same emitting layer and >10 times more efficient than any other reported OLETs.

538 citations