High-Performance Hole-Injection/Transport Poly(p-methylenetriphenylamine), Poly(4-vinyltriphenylamine) and Polyurethane for Light-Emitting Diodes (LEDs) Applications
Date Issued
2008
Date
2008
Author(s)
Lin, Kun-Rung
Abstract
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. n 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.y 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.
Subjects
Triphenylamine (TPA)
Poly(p-methylenetriphenylamine) (PMTPA)
Poly(4-vinyltriphenylamine) (PVTPA)
Polymeric light-emitting diodes (PLEDs)
Electropolymerization
Electroluminescence (EL)
Hole-transport layer (HTL)
Polyurethanes (PUs)
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-97-D93549011-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):6b804c402fdbff7af2a2d1057b58c032