Adamantane Derivative as Host Material for Efficient Deep-Blue Phosphorescent Organic Light Emitting Diodes
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1212-S01-10
Adamantane Derivative as Host Material for Efficient Deep-Blue Phosphorescent Organic Light Emitting Diodes Hirohiko Fukagawa1, Norimasa Yokoyama2, Shiro Irisa2, and Shizuo Tokito1 1 Japan Broadcasting Corporation (NHK), Science and Technology Research Laboratories, 1-1011 Kinuta, Setagaya-ku, Tokyo 157-8510, Japan 2 Hodogaya Chemical Co. Ltd., 45 Miyukigaoka, Tsukuba City, Ibaraki Pref., 305-0841, Japan ABSTRACT We report on a high efficiency deep-blue phosphorescent organic light-emitting diode (POLED) based on new electron-transporting host material. The new electron-transporting host material is an adamantane derivative with high triplet energy and high electron mobility. The deep blue POLED that we have developed utilizes a deep-blue phosphorescent guest material, iridium(III)bis(4’,6’,-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, and exhibits a power efficiency of about 10.2 lm/W at luminance of 100 cd/m2 and maximum external quantum efficiency (EQE) of about 13 %. The power efficiency of our POLED is much higher than that of POLED using p–bis(triphenylsilyly)benzene (UGH2). The maximum EQE of our POLED was also slightly more than that of POLED using UGH2. The obtained difference in power efficiency originates from the new host material having higher electron mobility than that of UGH2. INTRODUCTION There have been many reports on phosphorescent organic-light emitting diodes (POLEDs) because their emission efficiencies are higher than that of conventional fluorescent OLEDs [1-3]. Red, green, and blue emissions in OLEDs are important for application to fullcolor flat-panel displays and lighting applications. The power efficiency is one of the crucial parameters in discussing the device performance of the OLEDs, which are expected to be applied to displays and lighting applications. The red and green POLEDs with higher power efficiencies have already been reported [4-6]. In contrast, it is difficult to improve the performance of blue POLEDs because blue light is generated from wide-gap excited states. The first reported blue POLED was iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2’]-picolinate (FIrpic) [7]. Currently, the highly-efficient FIrpic-based POLED has been developed [8]. However, the degree of the blueness is not sufficient for full-color flat-panel displays and/or lighting applications since the Commission Internationale de L’Eclairage (CIE) coordinates of FIrpic are approximately (x=0.17, y=0.34). In 2003, two years after was FIrpic reported, the deep blue phosphorescent guest material, iridium(III)bis(4’, 6’-difluorophenylpyridinato)tetrakis(1pyrazolyl)borate (FIr6), was reported [9]. The blue light emission using FIr6 exhibited CIE coordinates of (x=0.16, y=0.26), which are significantly better than those of FIrpic. The host material with high ET is necessary to confine the triplets in the FIr6 guest since FIr6 has a high ET of 2.72 eV. Thus, the requirements for host material applicable for deep blue POLEDs are (i) high triplet energy and (ii) carrier transportability.
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