利用混合式主發光體結構提升載子注入對白色磷光有機發光二極體光電特性之影響

本論文利用有機發光二極體技術來製作全彩平面顯示器方面的應用，以符合未來平面顯示器所需輕薄、省電、美觀及多元化的特性。研究中利用加入具電洞傳輸特性(hole transport-type)主發光材料TCTA於電洞傳輸層(TAPC)與發光層(FIrpic:26DCzPPy)之間作為有機發光二極體元件之緩衝層，由於TCTA的載子移動率(μh~1.6×10-4 cm2/Vs)比電洞傳輸層(μh~1.0×10-2 cm2/Vs)來的慢，因此研究中可藉由改變TCTA的膜厚來調整傳輸到發光層的電洞電流，以達到電子-電洞數量平衡並提高元件發光效率。另外，研究中易透過使用具雙極性之主發光體材料(26DCzPPy)與有較大LUMO能階的電子傳輸層材料(3TPYMB)，改善電子注入的效率並藉以降低驅動電壓，加上3TPYMB具較大的三重態及HOMO能階，可有效侷限三重態激子及電洞於發光層內，進而使元件功率效率有大幅的提升。研究結果顯示，在以TCTA作為緩衝層之研究中，其藍光元件在亮度1000 cd/m2 時，發光效率為23 cd/A及功率效率可達13.5 lm/W，驅動電壓可降至5.1 V。接著並利用將橘紅光摻雜物共摻雜於藍色發光層中，並控制其摻雜區域於載子再結合區域，以製作高效率白光OLED元件，其中橘紅色磷光摻雜物為(Os(bpftz)2(PPh2Me)2)。結果顯示，白光OLED元件在發光亮度為1000 cd/m2時，有最佳發光效率27 cd/A及15.5 lm/W，且元件最大發光效率可達27.8 cd/A及17.7 lm/W，另元件CIEx,y色座標值為(0.33, 0.32)，是一理想白光光源且不會有色偏現象產生。隨後，再利用將電洞TCTA及電子PPT傳輸特性較佳的主發光體材料，分別共摻雜(Co-host)於一雙極性主發光體材料26DCzPPy中作為混合式主發光層結構，以提升電荷載子注入至主發光層，使元件驅動電壓降低，因而提升藍光OLED元件發光效率。其元件發光亮度為1000 cd/m2，電流效率達41.5 cd/A，且功率效率為31 lm/W。另藉由加入橘紅光材料(Os(bpftz)2(PPh2Me)2)且調整其摻雜位置，以製作高效率白光元件，其元件發光亮度為1000 cd/m2，電流效率34.5 cd/A，功率效率可達24 lm/W。若再搭配(Brightness Enhancement Film,BEF)，元件電流效率可再提升至42.5 cd/A，功率效率達到30 lm/W。

關鍵字

混合式主發光體；載子平衡；高效率；白色磷光有機發光二極體。

並列摘要

The device characteristics of blue phosphorescent organic light-emitting diodes (PHOLEDs) with hole-buffer structure were investigated by inserting the hole transport-type host (TCTA) between hole transport layer (HTL) and emitting layer (EML). The hole transport-type host has lower hole mobility (μh~1.6×10-4 cm2/Vs) than HTL material, which could be effectively controlled the hole injection current from HTL to EML. Moreover, the highest occupied molecular orbital (HOMO) level of buffer layer material was between HTL and EML, lead to the reduced of hole injection barrier. The distributed recombination zone and balanced charge carrier injection within emissive layer were achieved through the thickness of buffer layer optimization, therefore the device performances were greatly enhanced. In addition, an bipolar transport-type host material (26DCzPPy) and a high triplet energy electron transport material (3TPYMB) with low-lying lowest unoccupied molecular orbital (LUMO) were used to reduce the driving voltage and effective confined the triplet excitons within emissive layer, which resulted in power efficiency effectively improved. At luminance 1000 cd/m2, the driving voltage decreased to 5.1 V , the yield of 23 cd/A and the power efficiency of 13.5 lm/W was achieved. Next, the highly efficiency white PHOLEDs were investigated by doping the orange-red dopant (Os(bpftz)2(PPh2Me)2) into the right-side of blue-EML(exciton generation zone),As the result, the white PHOLED exhibits a yield of 27 cd/A. and power efficiency of 15.5 lm/W at a luminance of 1000 cd/m2.The white device with a maximum yield of 27.8 cd/A, a power efficiency of 17.7 lm/W. and CIE coordinate of (0.33, 0.32) without color-shift can be achieved. Next, the device characteristics of blue PHOLEDs with composite host structure were investigated by co-doping the hole and electron transport-type host materials with an bipolar host (26DCzPPy).From the results, the performances of OLEDs were improved greatly due to the improved charge carrier injection and confined exciton into recombination zone of composite host structure. Moreover, a high efficiency white OLED was also fabricated by doping Os into bule emitting layer. The white OLED shows the efficiencies of 34.5 cd/A and 24 lm/W at a luminance of 1000 cd/m2. Furthermore, the efficiencies can be increased to 42.5 cd/A and 30 lm/W by attaching an outcoupling brightness enhancement film(BEF) onto substrate.

並列關鍵字

mixed-host structure ； charge carrier balance ； high efficiency ； phosphorescent white organic light-emitting diode

參考文獻

[1] C. Hosokawa, H. Higashi, T. Kusumoto, Appl. Phys. Lett., vol. 62, pp. 3238-3240, 1993.

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[2] M. A. Baldo, V. G. Kozlov, P. E. Burrows, S. R. Forrest, V. S. Ban, B. Koene, and M. E. Thompson, Appl. Phys. Lett., vol. 71, pp. 3033-3035, 1997.