高性能電洞注入/傳遞之新型三苯胺聚合物和聚胺酯的合成與性質研究及其在有機電致發光元件的應用

Abstract

在本論文中，應用不同的合成方法來製備出二系列之新型三苯胺聚合物和聚胺酯，分別利用電化學的方法和一般傳統旋轉塗佈法來製作成元件，應用於有機發光二極體。 首先，我們採用不同的結構而分成二個系統來加以探討 (1) 分別以hyperbranched poly(p-methylenetriphenylamine) (PMTPA) 及linear poly(4-vinyltriphenylamine) (PVTPA) 為電聚前驅物。(2) 以OPV(oligo (para-phenylene-(E)-vinylene)) 為主體之聚胺酯。藉由第一個系統的電化學性質對此類三苯胺聚合物應用於電洞傳導層，有了更深入的了解，其優異表現遠超過一般市售之PEDOT:PSS；另外，在第二個系統中我們發現以 IPDI (isophorone diisocyanate) 來當胺酯連接基團，反應所生成之 OPV-IPDI 亦具有良好的電洞傳導性質，並可應用於可撓式高分子發光二極體。 同時，我們也發現在第一個系統中若使用表面改質方法，則可以獲得平整、均一的電聚膜。如此，該電聚膜具有良好的電洞傳導特性並可製作出高性能的發光二極體元件。

The synthesis and characterization of hyperbranched poly(p-methylenetriphenylamine) (PMTPA) are described. We discovered that N-[4-(tosyloxybutyloxymethyl)phenyl]-N,N-diphenylamine showed unexpected chemical reactivity and polymerized to form hyperbranched PMTPA under neat conditions. The hyperbranched PMTPA was electrochemically active and was deposited on electrode surface when oxidized. The SEM study revealed that electropolymerization of PMTPA would form uniform coating onto ITO surface. Polymeric light-emitting diodes (PLEDs) employing electroactive polymers of either hyperbranched PMTPA or linear Poly(4-vinyltriphenylamine) (PVTPA) as hole-transport layer in the EL device of ITO/electrochemically polymerized HTL/EML(PVK-PBD-Ir(ppy)3)/Mg/Ag demonstrated the brightness over 20,000 cd/m2 and low turn-on voltage. In particular, the device performance was very steady regardless of the thickness of the PMTPA layer, ranging from 4 to 10 nm. In addition, PLEDs using a series of linear poly(4-vinyltriphenylamines) (PVTPAs) as hole-transport layer were fabricated. The relationships between their molecular weight, thermal stabilities, surface morphology and electronic properties were investigated. The SEM study revealed that electropolymerization of lowest molecular weight (~2700 g/mol) of PVTPA with 3 CV cycles would form uniform coating on ITO surface and show the highest brightness (~34,400 cd/m2) among others. However, surface modification tactic has to be adopted for the other higher molecular weight of PVTPAs because numerous cracks were observed on the electrode surface. We discovered applying some homogeneous thin film primed the ITO anode prior to the electrodeposition of PVTPA would reduce dramatically the uneven distribution of the electroactive layer and eventually have a smooth, crack-free film surface. By the way, our experiments also showed that the PU polymer could also be applied for flexible PLED with similar performance enhancement. Based on the promising results, we concluded that OPV-IPDI was a good hole-transport material for light-emitting diode application.