EP1656707A1 - Light-emitting diode - Google Patents

Light-emitting diode

Info

Publication number
EP1656707A1
EP1656707A1 EP04744677A EP04744677A EP1656707A1 EP 1656707 A1 EP1656707 A1 EP 1656707A1 EP 04744677 A EP04744677 A EP 04744677A EP 04744677 A EP04744677 A EP 04744677A EP 1656707 A1 EP1656707 A1 EP 1656707A1
Authority
EP
European Patent Office
Prior art keywords
light
led
emitting
poly
pedot
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04744677A
Other languages
German (de)
English (en)
French (fr)
Inventor
Margaretha M. De Kok-Van Breemen
Michael Buechel
Suzanna H. P. M. De Winter
Simone I. E. Vulto
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP04744677A priority Critical patent/EP1656707A1/en
Publication of EP1656707A1 publication Critical patent/EP1656707A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
    • H10K85/1135—Polyethylene dioxythiophene [PEDOT]; Derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/17—Carrier injection layers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/114—Poly-phenylenevinylene; Derivatives thereof

Definitions

  • the invention pertains to a light-emitting diode (LED) comprising layers of an anode, an acidic hole conducting-injecting material, a light-entitting polymer, and a cathode.
  • LED light-emitting diode
  • Most poly-LEDs consist of two polymer layers sandwiched between two electrode materials: one hole conducting-injecting material and the light-emitting polymer.
  • the light-emitting polymer can be of the PAN type [poly(p-arylene vinylene)].
  • PEDT poly(3,4-emylenedioxythiophene, PEDT), available as an aqueous dispersion thereof with polystyrene sulfonic acid (PSS) can be used.
  • PEDOT This dispersion is called PEDOT and is commercially available from HC Starck as BAYTRO ⁇ ® P VP CH 8000 (high ohmic) or Baytron® P VP Al 4083 (low ohmic). Because of the acidic nature of PSS the pH for a PEDOT solution of a solid content of 2.5 % is below 2.
  • the function of PSS is to keep PEDT soluble and stable in solution. In fact, the PEDT is polymerized in the presence of PSS. The PEDT is doped (oxidized) instantaneously during the polymerization. This results in a charged polymer, which is able to conduct holes.
  • the negatively charged sulfonate groups act as counter ion balance for the doped, positively charged PEDT units (in general one on three to four units in PEDT are positively doped).
  • Such LEDs are well known in the art, for instance see US 2003/0011306, which is incorporated by reference. There is a continuous need for improving the efficacy of such LEDs, in particular for improving the brightness of the displays containing these LEDs.
  • US 6,284,435 it was proposed to improve the quantum efficiency by adding highly polarizable organic anion surfactant additives, such as lithium salts of various ether sulfate anionic surfactants.
  • LEDs comprising PEDOT as the hole conducting-injection material and PAN-type polymers as Ught-emirting polymers can considerably be improved by a simple and cheap method without the need of using expensive surfactants or other organic materials.
  • increased brightness levels can be obtained at higher voltages (at least 10 V, preferably at least 15 V) in pulsed driving modes when at least partially neutralized PEDOT is used in combination with a PAV.
  • the invention also relates to a LED comprising pulsed mode driving means adapted for providing a voltage of at least IO N, preferable at least 15 N.
  • Neutralization can be effected by removal of protons from PEDOT and replacement by metal ions, for instance by addition of a base, such as a metal hydroxide, or by another material that is able to remove protons from PEDOT.
  • a base such as a metal hydroxide
  • the neutralization with sodium hydroxide as an example, and the structures of the polymers are given in Scheme 1.
  • the hole conducting-injecting material comprises a poly(3,4-ethylenedioxythio ⁇ hene poly(styrenesulfonate) (PEDOT), which is obtainable by at least partially neutralizing the PEDOT with an anion that is comprised or formed from a sodium or potassium compound, and the Ught-emitting material comprises a light-emitting p-arylene-vinylene polymer (PAN) thereof.
  • the sodium or potassium compound is preferably sodium or potassium hydroxide, nitrate, carbonate, or hydrogen carbonate, and more preferably sodium hydroxide. The best results are obtained when PEDOT is neutralized to a pH of at least 3.
  • the pH is 3-7, more preferably 5.5-6.5.
  • the neutralization of PEDOT can be obtained by a common base-acid reaction, for instance with sodium hydroxide, or in situ by capturing protons from PEDOT under the conditions used for removing the aqueous solvent, as is for instance the case with sodium nitrate that under these conditions forms a nitrate anion which captures a proton from PEDOT, that leaves the solution as gaseous nitric acid.
  • the invention further relates to a method for increasing the efficiency of a light-emitting diode (LED) comprising layers of an anode, an acidic hole conducting- injecting material, a light-ermtting polymer, and a cathode, wherein the hole conducting- injecting material comprises poly(3,4-emylenedioxvthiophene poly(styrenesulfonate) (PEDOT) and the light-en ⁇ tting material comprises light-emitting poly(p-arylene vinylene) (PAN), characterized in that the acidic hole conducting-injecting material is at least partially neutralized with an anion that is comprised or formed from a sodium or potassium compound.
  • the hole conducting- injecting material comprises poly(3,4-emylenedioxvthiophene poly(styrenesulfonate) (PEDOT)
  • PAN poly(p-arylene vinylene)
  • Fig. 1 shows schematically, in a cross-sectional view an embodiment of an LED in accordance with the invention.
  • FIG. 1 A schematic view of a LED is given in Fig. 1.
  • a LED with a substrate 1, which is usually glass, an anode 2, which may be ITO, a layer 3 comprising PEDOT, a layer 4 comprising PPV, and a cathode 5.
  • a substrate 1 which is usually glass
  • an anode 2 which may be ITO
  • a layer 3 comprising PEDOT
  • a layer 4 comprising PPV
  • cathode 5 a cathode 5.
  • the material for use in the conductive transparent polymer (CTP) layer is the mixture of poly-3,4-emylenechoxythiophene and polystyrene sulfonic acid (PEDOT).
  • the active layer is situated between two electrode layers of electroconductive materials.
  • At least one of said electrode layers must be transparent or translucent to the emitted light in the active layer.
  • One of the electrode layers serves as the (positive) electrode for injecting holes into the active layer.
  • the material of this electrode layer has a high work function and is generally formed by a layer of indium oxide or indium-tin oxide (ITO). ha addition, such layers are transparent to the emitted light in the active layer. Particularly ITO is suitable because of its satisfactory electrical conductivity and high transparency.
  • the other electrode layer serves as the (negative) electrode for injecting electrons into the active layer.
  • the material for this layer has a lower work function and is generally formed from a layer of, for example, indium, calcium, barium, or magnesium.
  • the electrode layer of ITO is provided by vacuum evaporation, sputtering, or a CVD process.
  • This electrode layer and often also the negative electrode layer, for example, of calcium, are structured in accordance with a pattern by means of a customary photolithographic process or by partly covering it with a mask during the vacuum deposition process, which corresponds to the desired pattern for a display.
  • the electrodes of the first and second electrode layers have line structures, which intersect each other at right angles and hence form a matrix of separately drivable rectangular LEDs.
  • the rectangular LEDs constitute the pixels or picture elements of the display. If the electrodes of the first and second electrode layers are connected to an electrical source, light-emitting pixels are formed at the intersection of the electrodes.
  • the pixel structure is not limited to a particular shape. Basically all pixel shapes are possible leading to a segmented display, e.g. for showing icons or simple figures. It should be noted that according to the present invention, apart from passive matrix structures also active matrix structures could be used.
  • the light-emitting polymers may be any electroluminescent material of the poly (p-arylene vinylene) (PAN) type such as poly(p-phenylene vinylene), the phenylene group of which may be substituted, as disclosed in WO 98/27136.
  • PAN poly(p-phenylene vinylene)
  • a poly(p-phenylene vinylene) (PPV), more particular a phenyl-substituted PPN is a preferred type of polymer to be used.
  • PAN- type polymers contain at least two, the same or different, arylene-vinylene moieties.
  • the copolymers and the like according to this invention may further comprise other Ught-emitting moieties, such as fluorene or spirofluorene moieties.
  • soluble conjugated polymers are used because they can be easily applied, for example in a spin-coating process or by ink jetting.
  • solubility is improved by substituting a conjugated PPN derivative with alkyl and/or alkoxy or phenyl groups.
  • the light emitting material may also be a doped low molecular material, such as 8- hydroxyquinolin-aluminum doped with a dye, such as quinacridone, deposited in a vacuum process.
  • said polymer may comprise 5 to 10 % non-conjugated units. It has been found that such non-conjugated units increase the electroluminescence efficiency, which is defined by the number of photons per injected electron in the active layer.
  • the above-mentioned conjugated PAV derivatives can be dissolved in the customary organic solvents, for example halogenated hydrocarbons such as chloroform, and optionally substituted aromatic hydrocarbons such as toluene, xylenes, anisole, chlorobenzene, and mesitylene. Methylbenzoate and tetrahydrofurane can also be used as solvents.
  • the degree of polymerization of the conjugated polymer ranges between 10 and 100,000.
  • the layer thickness of the light en ⁇ tting layer of the conjugated polymer often ranges between 10 and 250 nm, in particular between 50 and 130 nm.
  • the LED structure can be provided on a substrate, which is made, for example, from glass, quartz glass, ceramic, or synthetic resin material. Transistors or other electronic means may be present between the substrate and the transparent electrode forming a so-called active matrix substrate.
  • a translucent or transparent substrate Preferably, use is made of a translucent or transparent substrate.
  • a flexible elecfroluminescent device is desired, use is made of a transparent foil of a synthetic resin. Suitable transparent and flexible synthetic resins are, for example, polyamide, polyethylene terephthalate, polycarbonate, polyethene, and polyvinyl chloride. The invention is illustrated by the following example.
  • Cs Cs (comparison example) or Na. It was found that CsOH had no beneficial effect on the efficacy of the LED. Brightness above 100.000 cd/m2 could not be obtained in the pH range 1-7. NaOH, on the contrary had a beneficial effect on the efficacy. The higher the pH, the higher the efficacy was found.
  • the use of NaOH as base further made it possible to obtain LEDs with brightness above 100.000 cdm2. At pH 4 and higher even brightness above 200.000 cd/m2 was possible.
  • the device used to obtain the date in the table had a standard device configuration of ITO, 200 nm PEDOT, 80 nm SY-LEP, and Ba/Al cathode.
  • SY-LEP was commercially obtained from Covion, Germany, which is a copolymer of at least the building blocks with the following structures:
  • Noltages at which the indicated brightness levels are obtained are indicated between brackets.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Organic Chemistry (AREA)
  • Electroluminescent Light Sources (AREA)
EP04744677A 2003-08-06 2004-07-29 Light-emitting diode Withdrawn EP1656707A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP04744677A EP1656707A1 (en) 2003-08-06 2004-07-29 Light-emitting diode

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP03102446 2003-08-06
EP04744677A EP1656707A1 (en) 2003-08-06 2004-07-29 Light-emitting diode
PCT/IB2004/051324 WO2005015654A1 (en) 2003-08-06 2004-07-29 Light-emitting diode

Publications (1)

Publication Number Publication Date
EP1656707A1 true EP1656707A1 (en) 2006-05-17

Family

ID=34130281

Family Applications (1)

Application Number Title Priority Date Filing Date
EP04744677A Withdrawn EP1656707A1 (en) 2003-08-06 2004-07-29 Light-emitting diode

Country Status (6)

Country Link
EP (1) EP1656707A1 (ko)
JP (1) JP2007501514A (ko)
KR (1) KR20060061810A (ko)
CN (1) CN1833323A (ko)
TW (1) TW200510511A (ko)
WO (1) WO2005015654A1 (ko)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4381080B2 (ja) * 2003-09-29 2009-12-09 大日本印刷株式会社 有機エレクトロルミネッセンス素子およびその製造方法
US20070077451A1 (en) * 2005-09-30 2007-04-05 Pierre-Marc Allemand Neutralized anode buffer layers to improve processing and performances of organic electronic devices
JP4301260B2 (ja) 2006-07-06 2009-07-22 セイコーエプソン株式会社 有機ｅｌ装置の製造方法及び電子機器
JP5037104B2 (ja) * 2006-12-11 2012-09-26 信越ポリマー株式会社 導電性積層体及びその製造方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19652261A1 (de) * 1996-12-16 1998-06-18 Hoechst Ag Arylsubstituierte Poly(p-arylenvinylene), Verfahren zur Herstellung und deren Verwendung in Elektroluminszenzbauelementen
EP1382075A1 (en) * 2001-04-17 2004-01-21 Koninklijke Philips Electronics N.V. Led comprising a conductive transparent polymer layer with low sulfate and high metal ion content
DE10123115B4 (de) * 2001-05-07 2006-05-24 Samsung SDI Co., Ltd., Suwon Löcherinjektionsschicht einer organischen Leuchtdiode und Verfahren zu deren Herstellung

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2005015654A1 *

Also Published As

Publication number Publication date
CN1833323A (zh) 2006-09-13
KR20060061810A (ko) 2006-06-08
WO2005015654A1 (en) 2005-02-17
TW200510511A (en) 2005-03-16
JP2007501514A (ja) 2007-01-25

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