Abstract:We developed an organic light emitting diode (LED) that emits orange light at the forward bias (ITO anode and Al cathode) and green light at the reverse bias (ITO cathode and Al anode). The organic LED has a triple layer structure where an emission layer with different doped guest dye on each side is interposed between two hole transport layers. Its brightness, maximum 20 cd/m2 was not strong because electrons are blocked by the hole transport layer near the cathode. However, the EL efficiency (lm/W) for the r… Show more
“…In particular, color tunable devices are very attractive because of their potential for producing higher resolution and less complex display units. To date, tuning of the emission color in OLEDs has been achieved by varying either the voltage polarity [6][7][8] or the current density [9][10][11][12]. Two-color emission can be achieved by fabricating a device structure with double emissive layers of either small molecules [6,7] or polymers [8].…”
“…In particular, color tunable devices are very attractive because of their potential for producing higher resolution and less complex display units. To date, tuning of the emission color in OLEDs has been achieved by varying either the voltage polarity [6][7][8] or the current density [9][10][11][12]. Two-color emission can be achieved by fabricating a device structure with double emissive layers of either small molecules [6,7] or polymers [8].…”
“…Poly( N -vinylcarbazole) (PVK) materials have been extensively studied . They exhibit interesting electrical and optical properties as light emitting diode materials, , solar cells, and applications in various electrochromic devices. , Specifically, PVK shows good hole-transport properties which have important applications for improving the performance of organic electroluminescent devices . Others have reported applications in amperometric chemical sensors .…”
In this work, we describe the synthesis and electropolymerization of conjugated substituted
polyacetylenes, poly(N-alkoxy-(p-ethynylphenyl)carbazole) or PPA-Cz-Cn with electropolymerizable carbazole
side groups to form conjugated polymer network (CPN) films. The phenylacetylene monomer was functionalized
with a carbazole group separated by an alkylene spacer. Polymerization of the monomer in solution is accomplished
using a Rh catalyst to form a “precursor polymer”. The electrochemical behavior and cross-linking of the carbazole
side group was then investigated by cyclic voltammetry (CV) and spectroelectrochemistry. A trend in the redox
electrochemical behavior was observed with varying alkyl spacer length between the poly(phenylacetylene)
backbone and carbazole side-group. The resulting film combines the electrooptical properties of the conjugated
poly(phenylacetylene) polymer with polycarbazole units in a cross-linked electropolymerized film as evidenced
by the CV and spectroelectrochemical behavior. This study emphasizes the preparation of polymer materials
with mixed π-conjugated species arising from the electrochemical cross-linking of a designed precursor polymer.
“…Figure shows the structures of two widely studied triarylamines. Their hole transport properties have been investigated, − and they have been used in organic LEDs. ,− Triarylamine-based HTLs are most commonly prepared by vapor deposition of the molecular material. ,− Polymeric host−guest systems 1,15 and covalent incorporation of triarylamine into polymers 16-20 have also been reported. 1 Structures of commonly used organic hole transport materials.…”
A series of poly(norbornenes) with pendant triarylamine (TPA)
groups has been synthesized
by ring-opening metathesis polymerization and investigated as hole
transport materials in
organic two-layer light-emitting diodes (LEDs). Efficient device
fabrication through spin
casting of the hole transport layer (HTL) was possible, since the
polymers exhibited excellent
film formation properties. LEDs of the form
ITO/poly(norbornene)-TPA/Alq3/Mg (ITO =
indium tin oxide, Alq3 =
tris(8-quinolinato)aluminum) showed bright green emission
with
external quantum efficiencies of up to 0.77% (1.30 lm/W) for 20 nm
thick HTL films. The
length and polarity of the linker between the triarylamine
functionality and the polymer
backbone were varied systematically. The device performance was
found to depend strongly
on these structural differences. Substitution of ester groups by
less polar ether functionalities
greatly enhances external quantum efficiencies, lowers the operating
voltage, and improves
the stability of the device. Further improvement of the device
characteristics is achieved
by reducing the length of the alkyl linker. The HTL can be
conveniently cross-linked by
UV irradiation. Cross-linking was found to decrease device
performance. A maximum
external quantum efficiency of 0.37% was achieved for an
Alq3-LED with cross-linked HTL.
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