1 Full-Color Light-Emitting Devices Based on π- and σ-Conjugated Polymer Materials Reiji Hattori, Takeshi Sugano*, Tsuyoshi Fujiki**, Yi He, Jerzy Kanicki Department of Electrical Engineering and Computer Science, Center for Display Technology and Manufacturing, University of Michigan, Ann Arbor, MI * Department of Electrical Engineering, Faculty of Engineering, Osaka University, Osaka, Japan ** Advanced Technology Center, Osaka Gas Co., Ltd., Kyoto, Japan Abstract Two kinds of full-color light-emitting devices have been fabricated using π- and σ-conjugated polymers. One device is based on poly(bithiazole)’s, which have emission peaks ranging throughout visible region. The other device has a novel architecture in which ultraviolet-light emitted by electroluminescent diode, based on an evaporated poly(dimethylsilane) layer, is converted by phosphors into visible light emission. The luminance of 0.2 cd/m 2 is obtained for a green light emitting device (injected current density of 0.8 mA/cm 2 and external quantum efficiency is calculated to be 0.0054%). Introduction Organic light-emitting diode (OLED) is one of the most promising candidates for the next generation of flat panel display (FPD). Recently, a small and monochrome display using OLED has been demonstrated and manufactured in a small quantity [1]. However, to replace the liquid crystal display (LCD) we must resolve the problems associated with full- color, large-area and high-resolution. Therefore, new materials and new schemes for full-color OLED display are needed. Recently, we have reported that poly(bithiazole)’s, which have emission peaks ranging throughout the visible spectrum [2], can be a good candidate for OLED emitter. These materials are a new class of π- conjugated polymer that has thermal decomposition temperature above 300 o C, and they are very stable in the air at room temperature. On the other hand, polysilane is also an attractive material for OLED because of the high hole-mobility and high quantum efficiency [3]. The σ-bonding of Si- backbone is delocalized, so that the polysilane is called “σ-conjugated” polymer in contrast to “π-conjugated” polymer mentioned above. Recently, several papers about electroluminescent (EL) diode using polysilane as an active layer have been reported [4,5,6]. These EL diodes are characterized by an ultraviolet (UV) light- emission originating from the σ-σ * transition in silicon backbone. However, at room temperature, this peak disappears, because of the Si-Si bond-breaking or the phase-transition. We have succeeded in preparing an room temperature organic EL diode emitting UV-light (350 nm) using the poly(dimethylsilane) (PDMS) evaporated film [7]. In this case the room temperature light emission is possible, because PDMS molecules have a rigid conformation and a high crystallinity. In this paper, we focus on two kinds of polymer materials, poly(bithiazole) and poly(dimetylsilane) that can be used in fabrication of OLED. They are π- and σ- conjugated polymers, respectively. Poly(bithiazole)’s Figure 1 shows the EL spectra of poly(bithiazole)’s at room temperature under ambient conditions. The emission peak can be located from blue to red region of the spectrum. These polymers have a high thermal decomposition temperature and are very stable in the air at the room temperature. However, the lifetime of these OLEDs is not very long at present time, because of the electrode instabilities in the air. 400 600 800 1000 WAVELENGTH (nm) INTENSITY (arb. unit) PBBNBT PDPBT PENBT Fig. 1 EL spectra of poly(bithiazole)’s. ISSN0098-0966X/98/2901-1014-$1.00 + .00 (c) 1998 SID ISSN0098-0966X/98/2901-$1.00 + .00 (c) 1998 SID