Novel organic light-emitting transistors with PN-heteroboundary carrier recombination sites fabricated by lift-off patte
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Noriyuki Shimoji and Yoshiaki Oku Rohm Co., Ltd., Kyoto 615-8585, Japan
Kazumi Matsushige Department of Electronic Science & Technology, Kyoto University, Kyoto 615-8510, Japan (Received 27 June 2007; accepted 7 August 2007)
The authors have devised a novel organic light-emitting transistor (OLET) with a PN-heteroboundary combined with hole and electron transport materials (in other words, p-type and n-type organic semiconductors) along carrier channels. In this device, a clear modulation of the current and luminance with the gate voltage was observed. A 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. The horizontal PN-heteroboundary structure has been implemented for the first time by using the photolithographic patterning of organic semiconductor thin films. This patterning technique can be applied to the fabrication of not only the OLETs reported in this work, but also to organic integrated circuits or organic displays.
I. INTRODUCTION
Organic light-emitting transistors (OLETs) function as electroluminescence (EL) devices as well as driving transistors. They are very attractive for future flexibledisplay 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 for the light-emitting area and high process ability. Several OLET structures have already been reported, all of which have carrier channels composed of a single material system between the source and the drain. The performance enhancement of those devices has been achieved with local current concentration by a roughedged electrode,1,2 using suitable metals for electron and hole injections3,4 and narrowing the interelectrode distance to submicron level.5 Moreover, there have been reports of the observation of EL from transistor structures attained by employing a gate insulator with few a)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as the Outstanding Meeting Paper for the 2006 MRS Fall Meeting Symposium S Proceedings, Vol. 965E. DOI: 10.1557/JMR.2007.0393 2982 J. Mater. Res., Vol. 22, No. 11, Nov 2007 http://journals.cambridge.org Downloaded: 13 Mar 2015
career traps on the surface and metal electrodes with suitable work function for the injection of minority carrier.6,7 In these single-material systems, however, the majority of carriers do not efficiently 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 to not only enhance the luminescence efficiency, but also lower the driving voltage. The authors have successfully fabricated a novel OLET with a horizontal PN-heteroboundary combined with hole and elect
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