New Ambipolar Hosts Based on Carbazole and 4,5-Diazafluorene Units for Highly Efficient Blue Phosphorescent OLEDs with Low Efficiency Roll-Off

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• 作者：Cai-Jun Zheng ; Jun Ye ; Ming-Fai Lo ; Man-Keung Fung ; Xue-Mei Ou ; Xiao-Hong Zhang ; Chun-Sing Lee
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：February 28, 2012
• 年：2012
• 卷：24
• 期：4
• 页码：643-650
• 全文大小：412K
• 年卷期：v.24,no.4(February 28, 2012)
• ISSN：1520-5002

文摘

Two ambipolar host materials, 9,9-bis(9-methylcarbazol-3-yl)-4,5-diazafluorene (MCAF) and 9,9-bis(9-phenylcarbazaol-3-yl)-4,5-diazafluorene (PCAF), comprising two electron-donating carbazole units and an electron-accepting 4,5-diazafluorene group, have been designed, synthesized, and characterized. Given the nonplanar structure of the sp³-hybridized C9 atom of the 4,5-diazafluorene unit, MCAF and PCAF exhibit high triplet energy levels of 2.82 and 2.83 eV, as well as high glass-transition temperatures of 187 and 188 掳C, respectively. Equipped with ambipolar transport properties as well as suitable highest occupied and lowest unoccupied molecular orbital energy levels, the two compounds excellently perform in blue phosphorescent organic light-emitting devices (PHOLEDs). The MCAF-based blue PHOLED has a very low turn-on voltage of 2.6 V, a high current efficiency of 32.2 cd A^鈥?, a high external quantum efficiency of 17.9%, a high power efficiency of 31.3 lm W^鈥?, and a low efficiency roll-off with a high efficiency of 27.6 cd A^鈥? even at 10鈥?00 cd m^鈥?. These values are among the highest ever reported for devices doped with iridium(III) bis[2-(4鈥?6鈥?difluorophenyl)pyridinato-N,C(2鈥?]-picolinate.

Keywords:

ambipolar host; blue PHOLEDs; 4,5-diazafluorene; carbazole