Hiroshi Ohata

Organic light-emitting diodes with photonic crystals on glass substrate fabricated by nanoimprint lithography

The authors have fabricated organic light-emitting diodes (OLEDs) having two-dimensional photonic crystals (PC) as light extraction elements by employing nanoimprint lithography technique. PCs were imprinted on the glass substrate and OLED layers were formed on the imprinted side of the glass substrate. The device having PC showed the improvement of luminance by a factor of 1.5 compared to normal devices. The authors conclude that the nanoimprint lithography is very useful for the fabrication of the OLEDs with PC.

Optical and electrical characteristics of organic light-emitting diodes with two-dimensional photonic crystals in organic/electrode layers

Efficient light extraction is a critical issue for improving the overall efficiency of organic light-emitting diodes (OLEDs). Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) layers, which are expected to enable versatile control of photons. We fabricate two-dimensional PC structures in organic and electrode layers, in which most light is confined, to extract the light in the waveguide mode. Improvements in OLED efficiency of 20 and 130% are observed in spectrally integrated intensity and the peak intensity of forward-propagating light, respectively, in comparison with samples without PCs. As the thickness of the organic layer is partially reduced, lower operating voltages are found not to degrade light-extraction efficiency. We can expect further improvement in the overall OLED efficiency by optimizing PC structure.

Reduction of operating voltage in organic light-emitting diode by corrugated photonic crystal structure

A reduction of the operating voltage is achieved for an organic light-emitting diode containing a corrugated photonic crystal structure fabricated by the etching of an indium-tin-oxide anode layer. This is due to a partial reduction in the thickness of the organic layer. The light extraction efficiency can be also improved due to the diffraction of confined light by the photonic crystal effect. The voltage reduction is demonstrated in combination with an improvement in the luminance efficiency at constant current for the fabricated device.

Several Blue-Emitting Thin-Film Electroluminescent Devices

Blue-emitting thin-film electroluminescent (EL) devices were studied. As the blue-emitting phosphor, thin-films in which the Tm3+ ion was doped into several hosts (ZnS, Y2O2S, CdF2, ZnF2 and YF3) and CaF2:Eu were investigated. Blue EL emission of Tm3+ ions arising from the 1D2→3H4 or 1G4→3H6 transition was observed in each Tm-doped device. The most dominant lines in these emissions varied with the kind of host materials. The CaF2:Eu thin-film also showed blue electroluminescence due to a parity-allowed 4f6(7F)5d→4f7(8S) transition of the Eu2+ ion.

Dot‐matrix display using organic light‐emitting diodes

— A dot-matrix display with 256 × 64 pixels with a pixel size of 0.34 × 0.30 mm in size, a luminance of 100 cd/m2, and a contrast ratio of 100:1 or better has been developed using organic LED devices. The display provides high luminance, high visibility, and wide viewing angle.

Demonstration of organic light-emitting diodes with photonic crystal on glass substrate fabricated by nanoimprint lithography

In this work, a report on the direct formation of a photonic crystal (PC) structure on a glass substrate using the nanoimprint lithography (NIL) technique and the characteristics of the organic light-emitting diodes (OLED) formed on this substrate is presented

Introduction of photonic crystal structure into organic light-emitting diode

An Organic light-emitting diode (OLED) is very promising device for a flat panel display and an illumination applications due to the possibility of very thin and flexible structures, large area emission, high brightness and low power consumption. To realize a high efficiency is one of the most important issues for these applications. Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) structures, which are expected to realize the versatile control of light. We fabricate two-dimensional PC structures in the organic and indium-tin-oxide anode layers in which most of the light is confined. This results in light extraction from the waveguide mode. Improvements of 20 and 130% are observed in the spectrally-integrated intensity and the peak intensity, respectively, in comparison with samples without PCs. As the thickness of the organic layer is reduced, lower operating voltages are found to maintain the light-extraction efficiency. We can expect further improvement in the overall efficiency by optimizing this structure.