Conductive polymer heightens light emission

Feb. 1, 2001
KAWASAKI?Researchers at Fujitsu Laboratories Ltd. have developed a novel conductive polymer for use in polymer light-emitting diodes (LEDs).
LIGHT-EMITTING DIODES

Incorporating news from O plus E magazine, Tokyo

KAWASAKI—Researchers at Fujitsu Laboratories Ltd. have developed a novel conductive polymer for use in polymer light-emitting diodes (LEDs). The emission intensity of an LED using this polymer material is several times that of conventional polymer LEDs based on the semiconducting polymer MEH PPV.

The new conductive polymer [co(p-PB/m-PB), where PB is polybutadiene] is created by polymerizing p-PB and m-PB together. A tiophen-type conductive polymer, PEDOT:PSS, serves as the hole-insertion layer. This material decreases the semiconductor operation voltage while increasing the diode current. The newly developed material is layered on top using a spin coating method. The cathode electrode is composed of a magnesium and indium alloy, a stable material that easily allows the insertion of electrons. The anode electrode is indium tin oxide on a glass substrate.

The results reveal that the copolymerization ratio between p-PB and m-PB highly influences the emission properties. When the ratio is 1:1, only a small degree of emission is observed. However, at 2:1, strong light is emitted.

For some time, hopes have been high for the development of an emission-type display that utilizes organic materials. Moving-image displays of this kind would exhibit high luminance and wide visible angle. The new polymer has triple bonds, so there is a high degree of copolymerization. Thus, it is suited for large area substrates. By combining this material with thin-film transistors using low-temperature polysilicon technology, development of a large moving-image display also should be possible.

Courtesy O plus E magazine, Tokyo

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