以溶液製程製備小分子電子傳輸層達成多層結構之有機高分子發光元件與樹枝狀磷光發光材料之研究

Abstract

摘要 利用一般的小分子電子傳輸材料透過溶液製程的方式成膜，應用在以Ir(mppy)3 (tris[2-(p-tolyl)pyridine]iridium(III))摻雜PVK (poly(vinylcarbazole)為主的發光層之有機高分子發光二極體上。三種不同的電子傳輸材料，包括TPBi (2,2,2-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole))，TAZ (3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole)還有Bphen (4,7-diphenyl-1,10-phenanthroline)溶於甲醇中，並配合刮刀技術形成一層電子傳輸層，再搭配LiF/Al為陰極結構，這些溶液製程的電子傳輸層不只有良好的電子傳輸能力還有阻擋電洞的效果。其中TPBi元件在亮度為1000 cd/m2時的效率達32 cd/A，此外元件沒有電子傳輸層以LiF/Al和以CsF/Al為陰極結構的元件當亮度達1000 cd/m2，效率個別為3.5 cd/A與17 cd/A。此外TPBi層在不同的退火溫度下會有不同程度的分子聚集現象出現並對元件造成影響，最後找出最適合的退火條件，並將其製程最佳化，其最佳化後的效率達53 cd/A。 最後一樣以PVK為主發光體，樹枝狀磷光發光材料(Dendrimer)為客發光體來做同樣的測試，並調變主客發光體之間的比例，最後發現此材料與一般小分子磷光發光材料較為不同之處，就是可承受較高的客發光體摻雜濃度，即使在高摻雜比例時皆有高於20 cd/A的效率。

Abstract Solution-processed electron transport layers (ETL) have been fabricated by solution process and applied in multilayer polymer light-emitting diodes with tris[2-(p-tolyl) pyridine]iridium(III) blended in poly(vinylcarbazole) as the emissive layer. Three kinds of small molecular electron transport materials, including 2,2',2"-(1,3,5-benzinet riyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), 3-(4-biphenyl)-4-phenyl-5-(4-tert-but ylphenyl)-1,2,4-triazole (TAZ), and 4,7-diphenyl-1,10-phenanthroline (BPhen), are tested and dissolved in methanol to form electron transport layers by blade coating. Such electron transport layer provides efficient electron injection and electron transport ability in the devices. The efficiency of the devices with the combination of ETL and LiF/Al cathode reaches 32 cd/A at 1,000 cd/m2. The efficiency of the device devices without ETL are 3.5 cd/A for LiF/Al cathode and 17 cd/A for CsF/Al cathode at 1,000 cd/m2. The crystallization of the solution-processed ETL can be controlled by annealing temperature to further optimize the device performance to maximal efficiency of 53 cd/A. Finally, we fabricated all solution-processed multilayer devices based on phosphorescent dendrimers and tuned the doping ratio between PVK and the emitting materials. We found that the dendrimer materials can be doped at high ratio. Even at high ratio (host:guest=1:1), the maximal efficiency is still higher than 20 cd/A. This is one of the differences between the phosphorescent dendrimer materials and common phosphorescent light-emitting materials.