A refined imaging method is proposed that can detect the surface vibration velocity of a sample placed on a vibrating piezoelectric transducer surface in air. The piezoelectric ultrasonic transducer is excited using a Barker-coded voltage signal under a constant-voltage drive to obtain a vibration velocity with the same waveform as a coded ultrasonic signal in the time domain. The coded vibration velocity is detected using a laser Doppler vibrometer and is used to image the object placed on the transducer via cross-correlation. A silicone rubber sheet containing the characters “U” and “S” are imaged under low S/N conditions to confirm the performance of the method. Ultrasonic velocity in sample can also be measured with this system.

View full abstract

3D imaging screens are now in common use. In general, 3D imaging techniques require high computing power, specific software, and heavy large-scale hardware. In contrast, we have developed a calculation-free 2D-to-3D automatic conversion imaging screen that uses the nature of specific nanomaterials. Certain nanomaterials, such as nano-scale titanium dioxide, transmit light with relatively low light diffusion. Therefore, a screen made of nanomaterial-coated translucent sheets placed in parallel can display transmission images throughout these sheets, and then 2D picture images projected on the screen can be automatically transformed into 3D images with a stereoscopic background. The screen has several advantages when compared with other 3D imaging techniques in terms of its extremely simple design and low-cost hardware. In addition, because there is no need to perform a 2D-to-3D data transformation, the screen could have a wide range of potential applications.

View full abstract

Recently the pixel number of display and digital camera image sensor increases rapidly and the image quality including depth and texture feeling expression is paid attention to. In this study, focusing on the point of their pixel number/resolution, subjective estimation of image quality dependence on the pixel number is carried out. Two types images for 4K display (3840×2160pixels) are prepared and resized to 1/4, 1/16 and 1/64. They are displayed at 4K display and subjective estimation is carried out by 25 peoples. It is obtained that the image quality increases as the pixel number increases within the range that pixel is distinguished by vision.

View full abstract

Organic transistors are MOS-type field-effect transistors in which an organic semiconductor is used as the active layer. Some organic semiconducting compounds are highly soluble in certain solvents, so that it becomes possible to form a semiconductor thin film by solution coating. Thus, there are considerable expectations for innovative industrial applications, in which low-cost, large-area devices can be produced on plastic films using printing technology. In this report, I introduce the physics of carrier transport in an intermolecularly delocalized electronic state, which is a key factor for realizing high-performance organic transistors. I also describe prospects for the industrial application of printable single-crystal organic semiconductors with mobilities exceeding 10cm²/Vs.

View full abstract

Organic light-emitting diodes are well-recognized advantages in power consumption, viewing angle, response time, and contrast ratio over liquid crystal displays. The primary technical challenge preventing wider commercial implementation remains the drive transistor in the active matrix backplane. In order to commercialize such devices, it is necessary to develop new materials, propose new device processing, and design new device structures. Organic light-emitting transistors (OLETs) function as electroluminescence devices as well as driving transistors. They are very attractive not only for future flexible display applications but also from the standpoint of scientific interest such as emission mechanisms, organic laser operation, etc. In this paper, we describe recent progress of OLETs using organic semiconductor films and the fabrication and characterization of vertical type devices and the potential for the development of flexible organic electronic devices.

View full abstract

Triplet exciton harvesting is a key issue for high-efficiency organic light-emitting diodes (OLEDs). Recently, we demonstrated an alternative pathway for efficient fluorescence-based OLEDs by applying thermally activated delayed fluorescence (TADF) as a singlet energy generation mechanism using materials with a small energy gap between singlet and triplet excited states. The resulting fluorescence-based OLEDs with TADF materials as dopants showed very high internal electroluminescence quantum efficiencies approaching nearly 100% for blue, green, yellow, and red emission. We also found that the OLEDs employing this triplet energy harvesting process have significantly enhanced device operational stability. In this article, we will review the unique features of this triplet harvesting process, i.e., TADF-assisted fluorescence.

View full abstract

We propose an air-stable organic light-emitting diode (OLED) using an inverted OLED. We have developed a practical OLED using the “iOLED” structure consisting of a two-layered electron injection layer (EIL) with a WVTR of 10^-4g/m²/day. The initial EL characteristics of a conventional OLED and the iOLED are almost the same under the condition of practical use. No dark spot formation or shrinkage was observed after 250 days in the iOLED. And the operational stability of the iOLED is greatly superior to that of a conventional OLED using the red phosphorescent material Ir (piq)₃. Finally, we successfully fabricated the flexible AMOLED display using the iOLEDs.

View full abstract

In this review paper, we summarize the series of semiconducting polymers based on the thiazolothiazole heteroaromatic ring in terms of the molecular design, thin film structures and photovoltaic properties. The polymers formed crystalline structures that facilitate charge transport in thin films. Interestingly, the polymers having branched alkyl groups as the side chain, were found to change their backbone orientation, namely “edge-on” and “face-on”, by the molecular weight, side chain composition, and addition of the fullerene derivative. The change in the orientation greatly affected their photovoltaic properties of the solar cells. These results will provide new insight into the design of high-performance semiconducting polymers.

View full abstract

Solar cells are photoelectric conversion devices that constitute an attractive source of clean energy. Organic thin-film solar cells are expected to be the next-generation solar cells. Plasmonic nanoparticles such as gold and silver nanoparticles absorb light, thus generating a localized strong electric field in their vicinity. Such electromagnetic fields can excite photoactive molecules and substrates. For photoelectric conversion, plasmonic nanoparticles are used as the concentrators of light energy in the fabrication of an efficient photoenergy conversion system. Indeed, the photocurrents obtained from various molecule-based photoelectric conversion devices were enhanced by the use of plasmonic nanoparticles. Enhanced performances of organic thin-film solar cells with plasmonic nanoparticles have recently been investigated intensively. This paper gives an overview of as well as reviews some recent developments in this field;it also discusses some important issues regarding plasmonic organic solar cells.

View full abstract

We have succeeded in developing the world's lightest (3g/m²) and thinnest (2μm) mechanically flexible organic photoelectric conversion devices [ultrathin organic solar cells and ultrathin organic light-emitting diodes (LEDs) ] and electronic switches (ultrathin organic transistor integrated circuits) utilizing the intrinsic flexibility and processability at low temperatures of thin organic materials. Successful integration of a transistor and a p-n diode (LED or optical sensor), which are basic components of electronics, on a polymer film with a thickness of only 1μm is expected to lead to the fundamental technology enabling the realization of ultrathin imperceptible wearable electronics that can change their shape according to the shape of the surface on which they are placed in the near future. In this review, the progress in the development and technical issues of ultrathin (∼1μm) flexible electronics as well as their future prospects including their applications in fields ranging from next-generation biomedicine to welfare are introduced.

View full abstract