Polymeric anodes for improved polymer light-emitting diode performance (original) (raw)
Related papers
2007
We demonstrate that a novel soluble self-doped conducting polyaniline graft copolymer can be used for a hole injection layer (HIL) in polymer light-emitting diodes (PLEDs). The work function of the material (5.18 eV) was similar to that (5.20 eV) of a conventional conducting polymer dispersion, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS). When we fabricated PLEDs by using this material, the currentevoltageeluminescence characteristics were very similar to those of the device using the PEDOT/PSS. When the material was blended with PSS, the luminous efficiency was further improved up to 11.9 cd/A. Since this kind of soluble type HIL has advantages over the conventional PEDOT/PSS dispersion in terms of the solution processibility and film quality, this soluble graft-type conducting polymer can be one of the promising candidates for a HIL in PLEDs.
Increased brightness and lifetime of polymer light-emitting diodes with polyaniline anodes
Synthetic Metals, 1996
The properties of light-emitting diodes based on poly(2-methoxy,.5-( 2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) with indium-tin oxide (ITO) anodes are compared with those in which a layer of polyaniline (PAni) is coated between the IT0 and the emissive polymer. It is found that the PAni injection layer yields higher current, brighter emission and a lower rate of degradation than ITO. The electrical behavior is discussed in terms of bulk and contact current limitation. The improvement in degradation is attributed to reduced oxidation as the PAni layer provides a barrier for the passage of oxygen out of the oxide. In addition, improvement in microscopic short formation indicates planarization of the anode interface by the PAni film.
Polymer, 2007
We demonstrate that a novel soluble self-doped conducting polyaniline graft copolymer can be used for a hole injection layer (HIL) in polymer light-emitting diodes (PLEDs). The work function of the material (5.18 eV) was similar to that (5.20 eV) of a conventional conducting polymer dispersion, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS). When we fabricated PLEDs by using this material, the currentevoltageeluminescence characteristics were very similar to those of the device using the PEDOT/PSS. When the material was blended with PSS, the luminous efficiency was further improved up to 11.9 cd/A. Since this kind of soluble type HIL has advantages over the conventional PEDOT/PSS dispersion in terms of the solution processibility and film quality, this soluble graft-type conducting polymer can be one of the promising candidates for a HIL in PLEDs.
Study and comparison of conducting polymer hole injection layers in light emitting devices
Organic Electronics, 2005
A set of polyaniline-and poly(3,4-ethylene dioxythiophene)-based materials were studied as hole injection layers in polymer light emitting devices. The choice of polymeric counterion/dopant poly(styrenesulfonic acid), and poly(acrylamido-2-methyl-1-propanesulfonic acid), and poly(acrylamide) blended with polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) was found to influence both work function and film morphology, which in turn affects device performance. The work functions of the polymer films spanned the range of over 1 eV and the surface region of the films were found to be low in conducting polymer content compared to the bulk. This was particularly the case of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) blended with poly(acrylamide) which showed device efficiency equal to that of the poly(3,4-ethylene dioxythiophene)-poly(styrenesulfonic acid) reference. The turn on voltage, however, was significantly larger, likely due to the insulating poly(acrylamide)-rich surface region of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid)/poly(acrylamide) film. The polymer blend of polyaniline/ poly(styrenesulfonic acid) yielded the highest work function (5.5 ± 0.1 eV).
2012
Bilayer nanostructured poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) conducting polymer composites have been successfully prepared by oxidative polymerization of the parent monomers, aniline (An) and 3,4-ethylenedioxythiophene (EDOT), in aqueous solutions of p-toluenesulfonic acid (p-TSA). As the first step, PANI nanofibers were obtained in the p-TSA solution using ammonium persulfate (APS) as the oxidant. Subsequently, PEDOT was coated onto the PANI nanofibers by the oxidative polymerization of EDOT to form PEDOT/PANI bilayer nanofibers. The resulting nanostructured material was characterized by SEM and a range of spectroscopic methods, which confirmed that the surface layer of the synthesized materials had features typical of chemically synthesized PEDOT. The presence of the PEDOT layer increased the room temperature electrical conductivity of the PEDOT/PANI nanocomposites by 2 orders of magnitude in comparison with the parent PANI nanofibers. Moreover, PEDOT/PANI nanocomposites on a glassy carbon electrode showed stronger electrocatalytic activity for the oxidation of ascorbic acid than PANI nanofibers.
Chemical Physics Letters, 2006
A monolayer of quarterthiophene-2-phosphonate (4TP) was chemically bound to the surface of indium tin oxide (ITO) and was then p-doped with the strong acceptor, tetrafluorotetracyanoquinodimethane (F 4-TCNQ). This interface modification strongly reduced the barrier for hole injection compared to unmodified ITO. This doped monolayer surface treatment was also superior to the commonly used anode coating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PPS) at driving voltages above 5.2 V.
Journal of Applied Physics, 1995
The addition of zinc oxide ͑ZnO͒ nanoparticles into electroluminescent poly͑vinylcarbazole͒ ͑PVK͒ polymer layers results in increased current densities, brightness, and luminance efficiencies in polymer light emitting devices. For low turn-on voltages, an increase in current density and good stability are achieved. At 9 V, we achieved a brightness of 743 cd/m 2 with a luminance efficiency of 0.35 cd/A for PVK-ZnO nanocomposite devices. Electroluminescence ͑EL͒ spectra reveal that the EL yield of PVK-ZnO nanoparticle devices increased greatly as compared with pure PVK devices. The current-voltage characteristics indicate that the addition of ZnO nanoparticles can facilitate better electrical injection and charge transport.
Polymer light-emitting diodes with doped hole-transport layers
physica status solidi (a), 2011
We demonstrate a solution processed bi-layer PLED based on poly(p-phenylene vinylene) derivatives using orthogonal solvents. To lower the voltage drop the hole transport layer (HTL) based on poly[2,5-bis(2 0-ethylhexyloxy)-co-2,5-bis(butoxy)-1,4-phenylenevinylene] (BEH/BB-PPV (1:3)) is doped with tetracyano-tetrafluoro-quinodimethane (F4TCNQ). The conductivity of BEH/BB-PPV (1:3) was observed to increase by two orders of magnitude upon doping with F4TCNQ. The doped HTL was observed to lower the operating voltage of a double layer PLED, but suffers from additional quenching by the dopant at higher voltages due to the lack of an electron blocking functionality.
Materials and modeling for organic light-emitting diodes
Light-Emitting Diodes: Research, Manufacturing, and Applications, 1997
Polymer light-emitting diodes, based for example on MEH-PPV, are known to be susceptible to oxidative degradation. This leads to loss of conjugation, i.e. lower carrier mobility and higher operating voltage, and to the formation of carbonyl species, i.e. to luminescence quenching. In-situ FTIR has revealed that ITO can act as the source of oxygen. In order to explore further the mechanism of oxidation and to provide guidance for its elimination, we have studied the behavior of MEH-PPV LEDs prepared with a variety of conducting polymer anodes including polyaniline and polythiophene derivatives cast from various solvents and with various molecular and polymeric dopants. In all cases examined, it is found that polymer anodes lead to significant improvement in lifetime over devices with ITO as the anode contact. Moreover, in contrast to the variability observed for ITO anodes, conducting polymers with polymeric dopants yield consistently good devices with power efficiencies of about 0.5% at 5 volts and brightness in excess of 1000 cd/m2. Anodes prepared with small molecule dopants are more variable and exhibit short term behavior which suggests interfacial electrochemistry. We describe the device characteristics in the context of a model of hole-dominated bipolar charge injection with Langevin recombination.