Achieving high-efficiency non-doped blue organic light-emitting diodes: charge-balance control of bipolar blue fluorescent materials with reduced hole-mobility
Achieving high-efficiency non-doped blue organic light-emitting diodes: charge-balance control of bipolar blue fluorescent materials with reduced hole-mobility
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DOI：
10.1039/b902910a
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发表时间：
2009-01-01
影响因子：
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通讯作者：
Chen, Chao-Tsen
中科院分区：
文献类型：
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作者：
Chi, Chih-Chin;Chiang, Chih-Long;Chen, Chao-Tsen
我们发现了一种提高蓝色有机电致发光器件（OLED）电致发光效率的独特方法。合成了两种缺电子的含4，5-二氮杂芴或二（2，2 '-吡啶基）的蓝色荧光团PhSPN 2DPV（4，5-二氮杂-2'-二苯基氨基-7 '-（2，2”-二苯基乙烯基）-9，9'-螺二芴）和PhFpy 2DPV（N-[7-（2，2-二苯基乙烯基）-9，9 '-二（2，2”-吡啶基）-2-芴基]-N，N-二苯基胺），并表征了其用于非掺杂蓝色OLED。PhFpy 2DPV OLED性能一般，而PhSPN 2DPV OLED性能优于先前已知的PhSPDPV（2-二苯基氨基-7-二苯基乙烯基-9，9 '-螺二芴）OLED显著：最大外量子效率接近5%（在20 mA cm（-2）时为4.6%）和60510 cd m（-2）的峰值电致发光（1810 cd m（-2），20 mA cm（-2））与3.4%（2.9%，20 mA cm（-2））和33020 cd m（-2）（910 cd m（-2），20 mA cm（-2））的PhSPDPV OLED。我们将PhSPN 2DPV OLED的上级性能归因于良好的电荷平衡，这又归因于PhSPN 2DPV的非常低的空穴迁移率。实验结果表明，缺电子部分，4，5-二氮杂芘或二（2，2 '-联吡啶），增加电子亲和力，但降低空穴迁移率。通过飞行时间（TOF）方法测定，PhSPN 2DPV和PhFpy 2DPV的电子迁移率分别为5 x 10（-5）和5 x 10（-4）cm（2）V-1 s（-1）（电场为4.9 x 10（5）V cm（-1））。令人惊讶的是，它们不高于8 × 10（-4）cm（2）V-1 s（-1）的非极性PhSPDPV。另一方面，PhSPN 2DPV和PhFpy 2DPV的空穴迁移率分别为2 × 10（-6）和2 × 10（-4）cm（2）V-1 s（-1），并且它们都显著低于PhSPDPV的6 × 10（-3）cm（2）V-1 s（-1）。对于PhSPN 2DPV和PhFpy 2DPV双极蓝色荧光团，我们已经证明，电子传输和发光功能涉及不同的分子半。此类分子半体的设计极大地促进了高性能OLED荧光团的光学和电子优化。
We found an unusual way in improving electroluminescence efficiency of blue organic light-emitting diodes (OLEDs). Two electron deficient 4,5-diazafluorene- or di(2,2'-pyridyl)-containing blue fluorophores, PhSPN2DPV (4,5-diaza-2'-diphenylamino-7'-(2,2"-diphenylvinyl)-9,9'-spirobifluorene) and PhFpy2DPV (N-[7-(2,2- diphenylvinyl)- 9,9'-di(2,2"-pyridyl)-2-fluorenyl]-N,N-diphenylamine), were synthesized and characterized for non-doped blue OLEDs. Whereas PhFpy2DPV OLED performs ordinarily, PhSPN2DPV OLED outperforms previously known PhSPDPV (2-diphenylamino-7-diphenylvinyl-9,9'-spirobifluorene) OLED significantly: maximum external quantum efficiency of similar to 5% (4.6% at 20 mA cm(-2)) and the peak electroluminance of 60510 cd m(-2) (1810 cd m(-2) at 20 mA cm(-2)) versus 3.4% (2.9% at 20 mA cm(-2)) and 33020 cd m(-2) (910 cd m(-2) at 20 mA cm(-2)) of PhSPDPV OLED. We attribute the superior performance of PhSPN2DPV OLED to the good charge balancing, which is in turn due to the very low hole mobility of PhSPN2DPV. The experimental results reveal that the electron-deficient moiety, 4,5-diazafluorene or di(2,2'-dipyridyl), increases electron affinity but reduces the hole mobility. Electron mobility, determined by time-of-flight (TOF) method, is 5 x 10(-5) and 5 x 10(-4) cm(2) V-1 s(-1) (at an electric field of 4.9 x 10(5) V cm(-1)) for PhSPN2DPV and PhFpy2DPV, respectively. Surprisingly, they are not higher than 8 x 10(-4) cm(2) V-1 s(-1) of nonpolar PhSPDPV. On the other hand, hole mobility is 2 x 10(-6) and 2 x 10(-4) cm(2) V-1 s(-1) for PhSPN2DPV and PhFpy2DPV, respectively, and they are both significantly lower than 6 x 10(-3) cm(2) V-1 s(-1) of PhSPDPV. For PhSPN2DPV and PhFpy2DPV bipolar blue fluorophores, we have demonstrated that electron-transporting and light-emitting functions involve different molecular halves. The design of such molecular halves greatly facilitates the optical and electronic optimizations of fluorophores for high-performance OLEDs.