Novel Organic Light-Emitting Transistors with PN-Hetero-Boundary Carrier Recombination Sites Fabricated by Lift-off Patt
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0965-S03-14
Novel Organic Light-Emitting Transistors with PN-Hetero-Boundary Carrier Recombination Sites Fabricated by Lift-off Patterning of Organic Semiconductor Thin Films Naotoshi Suganuma1, Noriyuki Shimoji2, Yoshiaki Oku2, and Kazumi Matsushige3 1
International Innovation Center, Kyoto University, Kyoto, 606-8501, Japan
2
Rohm Co., Ltd., Kyoto, 615-8585, Japan
3
Dept. of Electronic Sci. & Tec., Kyoto University, Kyoto, 615-8510, Japan
ABSTRACT We have devised a novel organic light-emitting transistor (OLET) with PN-hetero-boundary combined with hole and electron transport materials along carrier channels. In this device, a clear modulation of the current and luminance with the gate voltage is observed. The 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. We have implemented the horizontal PN-hetero-boundary structure for the first time by using the photolithographic patterning of the organic semiconductor thin-films. This patterning technique can be applied to fabrication of not only organic light-emitting transistors we report in this paper but also organic integrated circuits or organic displays. INTRODUCTION Organic light-emitting transistors (OLETs) are functioning as an electroluminescence (EL) device as well as a driving transistor. They are very attractive for future flexible display applications and from the standpoint of scientific interest such as the EL mechanism. An OLET itself features an active switching function. As the light-emitting device can control its own luminescence intensity, the display circuit can be much simplified, thereby enabling a high aperture rate of light-emitting area and a high process-ability. Several OLET structures have already been reported, all of which have carrier channels composed of a single material system between source and drain. The performance enhancement of those devices has been achieved with local current concentration by a rough edge electrode [1, 2], using suitable metals for electron and hole injections [3, 4] and narrowing the inter-electrode distance to sub-µm [5]. In these single material systems, however, most of majority carriers do not contribute to EL due to ill-balanced transport capacity, degrading the EL efficiency. It is necessary to control the carrier balance in the light-emitting area in order not only to enhance the luminescence efficiency but also lower the driving voltage. We have successfully fabricated a novel OLET with a horizontal PN-hetero-boundary combined with hole and electron transport materials along the carrier channel. In this device structure, the carrier recombination and thus photon generation happen at the interface between two organic semiconductor materials with different polarity or at a thin light-emitting layer
inserted between two organic semiconductor materials. It is by the intentional insertion of PN-boundary that the carrier balance and the EL efficiency can
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