Silicon Based Inorganic/Organic Hybrid Materials for Deep Blue PHOLEDs
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1197-D03-05
Silicon Based Inorganic/Organic Hybrid Materials for Deep Blue PHOLEDs Soonnam Kwon, Kyung R. Wee, and Sang O. Kang Department of Materials Chemistry, Korea University, Sejong Campus, Chochiwon, Chungnam, 339-700, South Korea ABSTRACT Deep blue PHOLED was achieved in the simple device structure of ITO/SiTPA/SiCBP : FIr6 5 wt%/SiTAZ/Liq/Al, where active layers were silicon based inorganic/organic hybrid materials of the types, SiTPA, SiCBP, and SiTAZ for HTL, EML host, and ETL respectively. Silicon incorporation into organic framework not only provided necessary morphological stability, but also engaged enhanced charge transporting capability essential to achieve highly efficient deep blue PHOLEDs. As a result, high performance silicon based HTL, EML host, and ETL materials were developed, exhibiting high charge mobility in the range of 10-4 ~ 10-3 cm2V-1s-1 and high triplet energy of 2.88 eV, 3.05 eV and 2.84 eV, respectively. Even with the simple four layer device structure of PHOLEDs comprising silicon based active layers, maximum external quantum efficiency (EQE) of 17 % and CIE coordinates of (0.15, 0.22) were achieved. Moreover, an EQE of 15% was recorded at a luminance of 1000 cd m-1, which was the result of reduced efficiency roll-off due to the efficient confinement of FIr6 triplet energy by surrounding silicon based inorganic/organic hybrid materials developed in this work. Structures of inorganic/organic hybrid materials and their photo-physical properties as well as device physics for high performance deep blue PHOLEDs will be presented. INTRODUCTION Phosphorescent organic light emitting devices (PHOLEDs) have received tremendous attention, and have achieved revolutionary advance in efficiency and stability. As a result, red and green PHOLEDs are expected to be applied to commercial products such as AMOLED in near future. However, in the case of blue PHOLED, color, efficiency at high luminance, and stability should be developed further for full fledged applications. The luminance efficiency, in particular, has been the main target of much research of deep blue PHOLEDs for recent several years. The luminance efficiency is limited mainly by the nonradiative decays which are caused not only by host materials of EML layer but also by adjacent HTL and ETL materials, because of the large diffusion length of triplet exciton. So, to avoid the non-radiative decays, the triplet energy of all of the materials including HTL, EML, and ETL should be larger than that of emitting dopant material. The triplet energies of deep blue emitters are larger than 2.8 eV. However, it is not easy to synthesize organic materials which satisfy simultaneously wide bad gap, considerable molecular weight, and high charge mobility. In this work, we report our recent successful development of materials satisfying the above requirements based on new synthesis methods. And we report highly efficient device with only three active layers consisting of HTL, EML, and ETL, in which all the materials are developed by this work.
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