A switchable diffraction device capable of driving with segment electrodes has been proposed and its operating characteristics were analyzed. The switchable diffraction device is based on a variable cavity structure using reversible electrodeposition technology and two kinds of diffraction gratings are designed to be selectively switched according to the driving electrode. The fabricated device was able to switch the diffraction patterns without any interference between the electrodes, which means that the interference between the electrodes will not be a problem in further device integration with driving circuits. However, when the electrode isolation is not perfect due to parasitic resistance between the electrodes, a weak interference between the electrodes is observed in the diffraction pattern. Therefore, it is expected that ensuring complete insulation between the electrodes will be a very important in the integration of the device. The proposed device can be used as a light control device, an image switchable hologram, etc. Furthermore, it is expected to be applied to reconfigurable metasurfaces through integration with active matrix circuits in the future.
In this work, we demonstrate fully uniform blue fluorescence graphene anode OLEDs, which have an emission area of
10×7 mm2. Catalytically grown multilayered graphene films have been used as the anode material. In order to
compensate the current drop, which is due to the graphene’s electrical resistance, we have furnished metal bus lines on
the support. Processing and optical issues involved in graphene anode OLED fabrications are presented. The fabricated
OLEDs with graphene anode showed comparable performances to that of ITO anode OLEDs. Our works shows that
metal bus furnished graphene anode can be extended into large area OLED lighting applications in which flexibility and
transparency is required.
We have fabricated transparent white organic light emitting diode (WOLED) for lighting application based on a hybrid
white OLED and a phosphorescence white OLED. For the hybrid WOLED, a blue fluorescence emitting layer (FLEML)
and green and red phosphorescence emitting layers (PH-EMLs) have been used in the device structure of
ITO/hole transporting layer
(HTL)/PH-EMLs/interlayer/FL-EML/ETL/LiF/Al. The balanced emissions from the FLEML
and the PH-EMLs have been obtained by using appropriate carrier (hole) trapping effects in the PH-EMLs, which
resulted in external and power efficiencies of 15 % and 27 lm/W, respectively, at a luminance of 1000 cd/m2 without any
out-coupling enhancement. The Commission Internationale de L'Eclairage (CIE) coordinates of this hybrid WOLED is
(0.43,0.44) with color rendering index (CRI) of 80 and correlated color temperature (CCT) of 3200 K, respectively, in
the bottom emission structure. Based on this hybrid WOLED, we established highly efficient transparent WOLED by
introduction of a transparent cathode, and obtained over 19 lm/W of power efficiency at a total luminance of 1000 cd/m2
as well as over 60 % of transmittance at 550 nm with the conventional glass encapsulation. Moreover, when the
phosphorescent white OLED was combined with a transparent cathode, the power efficiency was reached up to 24 lm/W
of power efficiency at a total luminance of 1000 cd/m2.
Selective energy transfer from triplet states of the fluorescent blue emission layer to a red phosphorescent dye in a
neighbored triplet harvesting layer has been achieved, which has provided improved efficiency with emissions from
fluorescent and phosphorescent dyes. First of all, it is crucial to find a wide band gap host for a fluorescent blue emission
layer which has larger triplet state band gap than green or red phosphorescent dye. It was found that TcTa is a good wide
band gap host for fluorescent blue dopant(BD) and a efficient blue device was obtained. A phosphorescent red dopant
(RD) was introduced into a neighboring electron transporting layer to harvest triplet states in the fluorescent blue
emission layer and by optimizing the distance between the blue emission layer and the red triplet harvesting layer, we
have succeeded in obtaining the balanced emission of the blue and the red emissions with high efficiency from the
device structure of NPB/TcTa:BD/BAlq/BAlq:RD/BAlq/LiF/Al. The device showed maximum external quantum
efficiency of 16 % at 0.1 mA/cm2 and 13 % of external quantum efficiency, (0.29, 0.23) of CIE coordinates and 920
cd/m2 at 10 mA/cm2. To realize RGB WOLED, a fluorescent green dopant was introduced into the blue emission layer.
The RGB WOLED was successfully obtained through optimization of doping concentration for green dopant and it
showed 10 % of external quantum efficiency, (0.36, 0.36) of CIE coordinates and 1400 cd/m2 at 10 mA/cm2.
Organic light-emitting diode (OLED) has a good candidate for next generation flat panel display (FPD). However, it is very difficult to fabricate high performance OLEDs on plastic substrate because its mechanical and thermal properties are very poor. Before the ITO deposition, we used a new plasma treatment for good contact with ITO and PES. PES substrate is stayed in vacuum above 12 hours to reduce humidity and unknown chemical gas.
We successfully fabricate OLED on PES substrate using PLD-ITO anodes. We can observe more uniform and bright emission image from the OLED and fix the optimum conditions for fabrication process for OLED. Maximum electro luminescence (EL) and current density at a 100 cd/m2 are 2500 cd/m2, 2mA/cm2, respectively and external quantum efficiency of OLED is about a 2.0%.
Organic thin-film transistors (TFTs) using the pentacene as an active electronic material have shown the mobility of 0.8 cm2Vs and the grains larger than 1 micrometers . Deep level transient spectroscopy (DLTS) measurements have been carried out on metal/insulator/organic-semiconductor (MIS) structure devices that have a depletion region at the insulator/organic-semiconductor interface. The very long capacitance transients were measured by the trapping of electronic charge carriers distributed in energy. Based on the DLTS characteristics, the energy levels of hole and electron traps in the obtained pentacene films were approximately Ev+0.24eV, Ev+0.31eV, and Ec- 0.69eV.
The emission color stability of poly(fluorene) derivatives upon thermal annealing or passage of current in an electroluminescent device is affected by the polymer molecular wight, the structure of the main chain polymer unit and particularly by the polymer chain end substituents. Proper attention to these features leads to colorfast blue emission in both photo and electroluminescence. Furthermore, the spectral emission characteristics can be tuned by the incorporation of various comonomers. Preliminary single layer device studies validate the potential utility of poly(fluorene) homo and copolymers for OLED applications.
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