WO2014209148A1 - Organic light-emitting diode for injection of the charge carriers - Google Patents

Organic light-emitting diode for injection of the charge carriers Download PDF

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Publication number
WO2014209148A1
WO2014209148A1 PCT/RU2013/000537 RU2013000537W WO2014209148A1 WO 2014209148 A1 WO2014209148 A1 WO 2014209148A1 RU 2013000537 W RU2013000537 W RU 2013000537W WO 2014209148 A1 WO2014209148 A1 WO 2014209148A1
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Prior art keywords
oled
quantum dots
band
transport layer
semiconductor
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PCT/RU2013/000537
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French (fr)
Inventor
Alexey Grigorjevich VITUKHNOVSKII
Andrey Alexandrovich VASCHENKO
Denis Nikolaevich BYCHKOVSKII
Alexey Ruslanovich KOVSH
Vladislav Evgenjevich BUGROV
Maxim Anatoljevich ODNOBLYUDOV
Oleg Andreevich STRELETSKII
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Optogan-Organic Lightning Solutions, Llc (Optogan-Osr, Llc)
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Priority to PCT/RU2013/000537 priority Critical patent/WO2014209148A1/en
Publication of WO2014209148A1 publication Critical patent/WO2014209148A1/en

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    • 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]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/80—Constructional details
    • H10K59/805—Electrodes
    • H10K59/8052—Cathodes
    • H10K59/80523—Multilayers, e.g. opaque multilayers

Definitions

  • the present invention relates to the field of optics and electroluminescent nanostructures .
  • the invention relates to light-emitting diodes and applications thereof.
  • OLED-technology i.e. technology based on Organic Light Emitting Diodes
  • OLED-technology opens up new possibilities in fabrication of efficient organic light-emitting devices with a great measure of consumer appeal.
  • OLED- technology also faces many challenges and problems.
  • the nearest prior art to the present invention is an OLED based on quantum dots disclosed in [A.A. Vaschenko, V.S.Lebedev, A. G. Vituhnovsky, B.Vasilev, I.G.Samatov, "Electroluminescence quantum dots CdSe / CdS and energy transfer of excitonic excitation in organic light-emitting diode ", JETP Letters, 96 (2012) 118, Jeonghun Kwak, Wan Ki Bae, Donggu Lee et al, " Bright and Efficient Full-Color Colloidal Quantum Dot Light- Emitting Diodes Using an Inverted Device Structure, Optical Materials Express 2 (2012) 59] .
  • the main structural component of the device is a monolayer of semiconductor quantum dots located within a hole or electron transport layers. More specifically, the active layer of OLEDs described therein is an organic matrix with embedded quantum dots (core/shell semiconductor nanocrystals , or nanoobjects) .
  • ITO Indium tin oxide
  • anode As described e.g. in Jianming Zhou, Indium Tin Oxide (ITO) Deposition, Pattering and Schottky Contact Fabrication, Ph.D Thesis, Rochester Institute of Technology, 2005) , but there is a great challenge in finding or creating an appropriate cathode as the materials used at the moment still do not provide uniform electron and hole injection and have large workfunctions of several electron volts. Non-uniform electron and hole charge injection leads to low measures of efficiency of the device.
  • the present invention aims to overcome the aforementioned problems of the prior art and can be used to fabricate low-cost and efficient devices, e.g. displays for alphanumeric and graphical information, as well as new sources of light for illumination.
  • an organic light-emitting diode comprises a transparent anode, a hole transport layer located on the anode, an active region located within the hole transport layer comprising semiconductor quantum dots, an electron transport layer located at a distance from the active region, and a cathode located on the electron transport layer. It is characterized in that the cathode comprises a layer of 2D-ordered linear-chained carbon and a layer of one of the following materials: a low workfunction metal and a low work function metal alloy.
  • 2D-ordered linear-chained carbon is meant a hexagonal close-packed lattice of linear chains formed by carbon.
  • Such design of a cathode significantly increases the amount of injected electrons which eventually results in achievement of the optimal electron-hole balance and a high quantum efficiency of the electroluminescence.
  • semiconductor quantum dots nanoparticles
  • the layer of 2D-ordered linear-chained carbon (2) comprises ordered domains having a domain width up to 104 nanometers and a domain thickness ranging from 1 to 100 nanometers.
  • the low work function metal alloy comprises at least one of the following alloys: CaAl and MgAg.
  • the OLED further comprises a transparent substrate, wherein the anode is located on said substrate.
  • the substrate is an essential element of most OLED structures made by conventional fabrication methods.
  • the substrate can be made of Polyethylene Terephthalate (PET) or glass.
  • the low work function metal or metal alloy has a work function optimized in accordance with the Fermi level of linear-chained carbon.
  • the semiconductor quantum dots substantially form a monolayer within the hole transport layer.
  • the semiconductor quantum dots substantially form a monolayer within the hole transport layer.
  • the semiconductor quantum dots are two- component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large-band-gap semiconductor.
  • Such two-component core/shell quantum dot structure provides high quantum efficiency of electroluminescence at low applied voltages. It also provides a possibility to control the emission spectra by regulating the size of the nanocrystal and/or thickness of the shell and radius of the core.
  • the low-band-gap semiconductor is one of the following: CdSe and CdTe.
  • the large- band-gap semiconductor can be one of the following: CdS and ZnS.
  • the thickness of each of the hole transport layer and the electron transport layer does not exceed 100 nanometers.
  • OLED according to any of abovementioned embodiments can be used as a pixel of a display.
  • the display can be, for example, an alphanumeric display of a device.
  • a display device comprising ... is provided, characterized in that at least a part of said pixels comprise an OLED as defined in any of the abovementioned embodiments.
  • the present invention provides stable organic light-emitting diodes operating at low voltages with high quantum efficiency of luminescence and the emission spectrum pre-defined in the visible range by using two-layer cathode.
  • Fig. 1 shows the structure of an OLED according to an embodiment of the present invention.
  • Fig. 2 is a schematic illustration of a 2D- ordered linear-chained carbon film.
  • OLED organic light-emitting diode
  • a transparent substrate e.g. made of glass or polymer film, such as PET- Polyethylene Terephthalate .
  • This sequence may comprise several steps. An example of such sequence is described below in detail to provide a clear understanding of the structure, its elements and connections between them.
  • a transparent anode (6) made of any convenient material or composite with a workfunction of 4.5-5 eV is deposited in a vacuum chamber by thermal evaporation. It is then covered with a hole transport layer (4), e.g. PEDOT:PSS - Poly (3,4- ethylenedioxythiophene ) poly (styrenesulfonate) , to increase the charge injection from the anode into an organic layer inside said hole transport layer (4) and located close to CdSe/CdS core/shell nanocrystal (quantum dot) monolayer (5) . Then, an electron transport layer (3), e.g.
  • a hole transport layer (4) e.g. PEDOT:PSS - Poly (3,4- ethylenedioxythiophene ) poly (styrenesulfonate)
  • Alq3 (Tris ( 8-hydroxy- quinolinato) aluminum)
  • a cathode made of two sequential layers of 2D-ordered linear-chained carbon (2) and a low work function metal layer (1) (e.g., CaAl or AgMg) is deposited.
  • the linear-chained carbon has a thickness varying from a few nanometers up to 100 nm with carbon sheet (domain) sized up to 8 ⁇ ⁇ ⁇ ⁇ 3 nm.
  • the linear-chained carbon layer is covered with low workfunction metal, thereby optimizing the cathode layer workfunction .
  • the hole transport layer (4) (e.g., TPD - N, N ' -bis (3-methylphenyl) -N, N 1 -bis (phenyl) -benzidine) doped with the quantum dots can be deposited e.g. using spin-coating method. During the deposition the quantum dots are self-assembled into a monolayer.
  • the quantum dots themselves (the two-component semiconductor nanocrystals ) can be synthesized by means of colloidal chemistry.
  • the nanocrystal of this embodiment consists of low-band-gap semiconductor core (e.g. CdSe, CdTe) and large-band-gap semiconductor shell (e.g., CdS, ZnS) .
  • Nanocrystals can be additionally covered with surface-active agent (e.g., tri-n-octylphospine oxide - TOPO) to prevent aggregation.
  • Core diameter of the nanoparticles can range, for example, from 2.0 nm to 6.0 nm, and the shell thickness - from 1.0 nm to 3.0 nm.
  • a pre-set amount of the material providing a hole transport is deposited on the monolayer of quantum dots using spin-coating technique. Typical thickness for both the hole and electron transport layers does not exceed 100 nm.
  • the wavelength of the light (8) emitted by the device is determined by the size of nanoparticles.
  • a method for two-layer cathode (Fig. 1, (1), (2)) deposition is described hereafter.
  • the layer of linear-chained carbon is deposited by vacuum condensation of carbon flow, wherein the substrate and the growing film are bombarded by inert gas ions.
  • the carbon flux produced by thermal evaporation or by ion sputtering, simultaneously with an Ar+ ion flow, is directed to the substrate.
  • the ion source is located in a special chamber connected to the evaporation chamber by a small aperture.
  • the ion average energy is the key parameter for this method. Since the deposition of linear-chained carbon takes place at relatively low temperatures (20-200°C), it gives the possibility to utilize a great variety of organic materials (e.g., polyethylene, polyurethane, or organometallic complex Alq3) .
  • Linear-chained carbon film shown on Fig. 2, is a hexagonal close-packed lattice of linear chains formed by carbon.
  • the film is stabilized by interleaved arbitrarily oriented curvatures forming the layers at the distance of 2 to 8 self-assembled carbon atoms.
  • This technology makes it possible to obtain continuous films free of undesired islands and covering the substrate completely. Starting from 5A in thickness, the film replicates the original topography of the substrate surface. As demonstrated by Atomic Force Microscopy (AFM) research, these films have an atomically smooth surface.
  • AFM Atomic Force Microscopy
  • a voltage (of about 5V) is applied to the device, it establishes charge injection from cathode and anode into an organic matrix. It is followed by the excitation of the organic molecules in the hole transport layer and further resonant excitation transfer from the molecules to the quantum dots via Forster energy transfer mechanism [Th. Forster, Ann. Phys . 437, 55 (1948)]. Being excited, the quantum dots recombine radiatively in the spectrum range 400-650 nm. The Forster energy transfer takes place between two different sides: donor molecules, and acceptors which in this case are quantum dots. The energy transfer behaves non-radiatively over tens of nanometers and it is an outcome of the dipole-dipole interaction .
  • a Schottky electron emission (or cold emission) from linear-chained carbon (2) occurs due to the thermal excitation of electrons from the Fermi level located above the potential barrier.
  • the mechanism of the field emission from the spl-carbon films differs from the quantum tunneling through the potential barrier also known as Fowler-Nordheim tunneling. Therefore, this distinctive type of field emission has an important advantage as it occurs at low applied fields. It is essential for development of highly efficient light emitting diodes.
  • thermoelectron emission occurs at the room temperature and behaves in accordance to Schottky law .
  • the organic light emitting diode based on semiconductor quantum dots according to the present invention can be used as a pixel of alphanumeric display.
  • the display can be e.g. a computer display, and in this case the OLED has to be fabricated to meet the requirements expressed for standard computer monitors (rated voltage is 5-10 V, and brightness is around 100 cd/m 2 ) .

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Nanotechnology (AREA)
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  • Optics & Photonics (AREA)
  • Electroluminescent Light Sources (AREA)

Abstract

The present invention relates to the field of optics and electroluminescent nanostructures. In particular, the invention relates to light-emitting diodes and applications thereof. An organic light-emitting diode (OLED) comprises a transparent anode (6), a hole transport layer (4) located on the anode (6), an active region located within the hole transport layer comprising semiconductor quantum dots (5), an electron transport layer (3) located at a distance from the active region and a cathode located on the electron transport layer (3), wherein the cathode comprises a layer of 2D-ordered linear-chained carbon (2) and a layer of one of the following materials: a low work function metal and a low work function metal alloy (1).

Description

ORGANIC LIGHT-EMITTING DIODE FOR INJECTION OF THE
CHARGE CARRIERS
FIELD OF THE INVENTION
The present invention relates to the field of optics and electroluminescent nanostructures . In particular, the invention relates to light-emitting diodes and applications thereof.
PRIOR ART
High relevance of a new generation of alphanumeric displays is mostly caused by the growing amount of visual information due to progress in computer technology. Development of highly efficient light sources is necessary for energy saving and for use in housing and utilities infrastructure.
There are several technologies that can be attributed to the new generation of displays. One of the most promising is OLED-technology (i.e. technology based on Organic Light Emitting Diodes) , which opens up new possibilities in fabrication of efficient organic light-emitting devices with a great measure of consumer appeal. However, the development of OLED- technology also faces many challenges and problems.
For example, there is an ever-growing demand to control the emission spectra of the diodes to be able to emit a full RGB color range when used in displays, and to irradiate a convenient white light when used in regular light sources. Currently multilayer structures with three active layers emitting red, green and blue component of light, respectively, are used for this purpose. This design, however, has the disadvantage of high cost and complexity in fabrication, requiring several expensive luminescent materials, which renders it unprofitable. The solution to this is fabrication of OLEDs based on a single luminescent material which is capable to emit light with a desired spectrum. However, in this solution it is quite challenging to make the injected electrons and holes to recombine radiatively. Also, in conventional OLEDs the emission takes place in thick layers of polymer (emission layers) , wherein the luminescence efficiency is quite low.
The nearest prior art to the present invention is an OLED based on quantum dots disclosed in [A.A. Vaschenko, V.S.Lebedev, A. G. Vituhnovsky, B.Vasilev, I.G.Samatov, "Electroluminescence quantum dots CdSe / CdS and energy transfer of excitonic excitation in organic light-emitting diode ", JETP Letters, 96 (2012) 118, Jeonghun Kwak, Wan Ki Bae, Donggu Lee et al, " Bright and Efficient Full-Color Colloidal Quantum Dot Light- Emitting Diodes Using an Inverted Device Structure, Optical Materials Express 2 (2012) 59] . The main structural component of the device is a monolayer of semiconductor quantum dots located within a hole or electron transport layers. More specifically, the active layer of OLEDs described therein is an organic matrix with embedded quantum dots (core/shell semiconductor nanocrystals , or nanoobjects) .
At the same time, a problem that is not clearly addressed in prior art is the limitations to the location of Fermi levels in cathode and anode materials which are imposed by the need to achieve efficient radiant recombination of injected electrons and holes.
It is known that both the cathode and the anode materials are equally important as the luminescent dyes used in OLED technology. Indium tin oxide (ITO) is known to be a suitable material for use as an anode (as described e.g. in Jianming Zhou, Indium Tin Oxide (ITO) Deposition, Pattering and Schottky Contact Fabrication, Ph.D Thesis, Rochester Institute of Technology, 2005) , but there is a great challenge in finding or creating an appropriate cathode as the materials used at the moment still do not provide uniform electron and hole injection and have large workfunctions of several electron volts. Non-uniform electron and hole charge injection leads to low measures of efficiency of the device.
SUMMARY OF THE INVENTION
The present invention aims to overcome the aforementioned problems of the prior art and can be used to fabricate low-cost and efficient devices, e.g. displays for alphanumeric and graphical information, as well as new sources of light for illumination.
According to a first embodiment of the present invention, an organic light-emitting diode (OLED) is provided. The OLED comprises a transparent anode, a hole transport layer located on the anode, an active region located within the hole transport layer comprising semiconductor quantum dots, an electron transport layer located at a distance from the active region, and a cathode located on the electron transport layer. It is characterized in that the cathode comprises a layer of 2D-ordered linear-chained carbon and a layer of one of the following materials: a low workfunction metal and a low work function metal alloy.
By 2D-ordered linear-chained carbon is meant a hexagonal close-packed lattice of linear chains formed by carbon.
Such design of a cathode significantly increases the amount of injected electrons which eventually results in achievement of the optimal electron-hole balance and a high quantum efficiency of the electroluminescence.
The use of semiconductor quantum dots (nanoparticles) as the light emitters provides stability of the device because they are not highly susceptible to the influence of the environment.
According to an embodiment of the present invention, the layer of 2D-ordered linear-chained carbon (2) comprises ordered domains having a domain width up to 104 nanometers and a domain thickness ranging from 1 to 100 nanometers.
According to an embodiment of the invention, the low work function metal alloy comprises at least one of the following alloys: CaAl and MgAg.
According to an embodiment of the present invention, the OLED further comprises a transparent substrate, wherein the anode is located on said substrate.
The substrate is an essential element of most OLED structures made by conventional fabrication methods. According to an embodiment of the invention, the substrate can be made of Polyethylene Terephthalate (PET) or glass.
According to an embodiment of the invention, the low work function metal or metal alloy has a work function optimized in accordance with the Fermi level of linear-chained carbon.
According to an embodiment of the present invention, the semiconductor quantum dots substantially form a monolayer within the hole transport layer.
According to an embodiment of the invention, the semiconductor quantum dots substantially form a monolayer within the hole transport layer.
According to an embodiment of the present invention, the semiconductor quantum dots are two- component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large-band-gap semiconductor.
Such two-component core/shell quantum dot structure provides high quantum efficiency of electroluminescence at low applied voltages. It also provides a possibility to control the emission spectra by regulating the size of the nanocrystal and/or thickness of the shell and radius of the core.
According to an embodiment of the invention, the low-band-gap semiconductor is one of the following: CdSe and CdTe. At the same time, the large- band-gap semiconductor can be one of the following: CdS and ZnS.
According to an embodiment of the present invention, the thickness of each of the hole transport layer and the electron transport layer does not exceed 100 nanometers.
According to an embodiment of the invention, OLED according to any of abovementioned embodiments can be used as a pixel of a display.
The display can be, for example, an alphanumeric display of a device.
According to an embodiment of the invention, a display device comprising ... is provided, characterized in that at least a part of said pixels comprise an OLED as defined in any of the abovementioned embodiments.
The present invention provides stable organic light-emitting diodes operating at low voltages with high quantum efficiency of luminescence and the emission spectrum pre-defined in the visible range by using two-layer cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows the structure of an OLED according to an embodiment of the present invention. Fig. 2 is a schematic illustration of a 2D- ordered linear-chained carbon film.
DETAILED DESCRIPTION OF THE EMBODIMENTS
A more detailed description of the present invention is provided below, with reference to the accompanying drawings.
The structure of an organic light-emitting diode (OLED) according to an embodiment of the present invention is shown on Fig. 1. The OLED can be sequentially deposited on a transparent substrate (7) e.g. made of glass or polymer film, such as PET- Polyethylene Terephthalate . This sequence may comprise several steps. An example of such sequence is described below in detail to provide a clear understanding of the structure, its elements and connections between them.
First, a transparent anode (6) made of any convenient material or composite with a workfunction of 4.5-5 eV is deposited in a vacuum chamber by thermal evaporation. It is then covered with a hole transport layer (4), e.g. PEDOT:PSS - Poly (3,4- ethylenedioxythiophene ) poly (styrenesulfonate) , to increase the charge injection from the anode into an organic layer inside said hole transport layer (4) and located close to CdSe/CdS core/shell nanocrystal (quantum dot) monolayer (5) . Then, an electron transport layer (3), e.g. Alq3 (Tris ( 8-hydroxy- quinolinato) aluminum) , is deposited at a pre-defined distance from the nanocrystal monolayer. Finally, a cathode made of two sequential layers of 2D-ordered linear-chained carbon (2) and a low work function metal layer (1) (e.g., CaAl or AgMg) is deposited.
According to one embodiment of the invention, the linear-chained carbon has a thickness varying from a few nanometers up to 100 nm with carbon sheet (domain) sized up to 8 ÷ ΙΟχΙΟ3 nm. The linear-chained carbon layer is covered with low workfunction metal, thereby optimizing the cathode layer workfunction .
The hole transport layer (4) (e.g., TPD - N, N ' -bis (3-methylphenyl) -N, N 1 -bis (phenyl) -benzidine) doped with the quantum dots can be deposited e.g. using spin-coating method. During the deposition the quantum dots are self-assembled into a monolayer. The quantum dots themselves (the two-component semiconductor nanocrystals ) can be synthesized by means of colloidal chemistry.
The nanocrystal of this embodiment consists of low-band-gap semiconductor core (e.g. CdSe, CdTe) and large-band-gap semiconductor shell (e.g., CdS, ZnS) . Nanocrystals can be additionally covered with surface-active agent (e.g., tri-n-octylphospine oxide - TOPO) to prevent aggregation. Core diameter of the nanoparticles can range, for example, from 2.0 nm to 6.0 nm, and the shell thickness - from 1.0 nm to 3.0 nm.
After a monolayer of quantum dots has been deposited, a pre-set amount of the material providing a hole transport is deposited on the monolayer of quantum dots using spin-coating technique. Typical thickness for both the hole and electron transport layers does not exceed 100 nm. The wavelength of the light (8) emitted by the device is determined by the size of nanoparticles.
An example of a method for two-layer cathode (Fig. 1, (1), (2)) deposition is described hereafter. The layer of linear-chained carbon is deposited by vacuum condensation of carbon flow, wherein the substrate and the growing film are bombarded by inert gas ions. The carbon flux produced by thermal evaporation or by ion sputtering, simultaneously with an Ar+ ion flow, is directed to the substrate. The ion source is located in a special chamber connected to the evaporation chamber by a small aperture. The ion average energy is the key parameter for this method. Since the deposition of linear-chained carbon takes place at relatively low temperatures (20-200°C), it gives the possibility to utilize a great variety of organic materials (e.g., polyethylene, polyurethane, or organometallic complex Alq3) .
Linear-chained carbon film, shown on Fig. 2, is a hexagonal close-packed lattice of linear chains formed by carbon. The film is stabilized by interleaved arbitrarily oriented curvatures forming the layers at the distance of 2 to 8 self-assembled carbon atoms. This technology makes it possible to obtain continuous films free of undesired islands and covering the substrate completely. Starting from 5A in thickness, the film replicates the original topography of the substrate surface. As demonstrated by Atomic Force Microscopy (AFM) research, these films have an atomically smooth surface.
The general operation principle of an OLED according to an embodiment of the present invention is described below.
When a voltage (of about 5V) is applied to the device, it establishes charge injection from cathode and anode into an organic matrix. It is followed by the excitation of the organic molecules in the hole transport layer and further resonant excitation transfer from the molecules to the quantum dots via Forster energy transfer mechanism [Th. Forster, Ann. Phys . 437, 55 (1948)]. Being excited, the quantum dots recombine radiatively in the spectrum range 400-650 nm. The Forster energy transfer takes place between two different sides: donor molecules, and acceptors which in this case are quantum dots. The energy transfer behaves non-radiatively over tens of nanometers and it is an outcome of the dipole-dipole interaction . Returning to the charge injection step, a Schottky electron emission (or cold emission) from linear-chained carbon (2) occurs due to the thermal excitation of electrons from the Fermi level located above the potential barrier. This makes the spl-carbon films good electron emitters even at low applied electric fields (such as 104 - 105 V/cm) . It is worth mentioning that the mechanism of the field emission from the spl-carbon films differs from the quantum tunneling through the potential barrier also known as Fowler-Nordheim tunneling. Therefore, this distinctive type of field emission has an important advantage as it occurs at low applied fields. It is essential for development of highly efficient light emitting diodes.
As the zigzag chains of carbon atoms formed by spl-bonds have a built-in electric field due to the quantum dimensional effect, the electron work functions of these chains are decreased in the directions transverse to the chain and becomes as much as 0.4 eV. The thermoelectron emission occurs at the room temperature and behaves in accordance to Schottky law .
The organic light emitting diode based on semiconductor quantum dots according to the present invention can be used as a pixel of alphanumeric display. The display can be e.g. a computer display, and in this case the OLED has to be fabricated to meet the requirements expressed for standard computer monitors (rated voltage is 5-10 V, and brightness is around 100 cd/m2) .
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

1. An organic light-emitting diode (OLED) , comprising :
- a transparent anode (6),
- a hole transport layer (4) located on the anode
(6) ,
an active region located within the hole transport layer comprising semiconductor quantum dots (5) ,
- an electron transport layer (3) located at a distance from the active region,
a cathode located on the electron transport layer (3),
characterized in that the cathode comprises a layer of 2D-ordered linear-chained carbon (2) and a layer of one of the following materials: a low work function metal and a low work function metal alloy (1) .
2. An OLED of claim 1, wherein the layer of
2D-ordered linear-chained carbon (2) comprises ordered domains having a domain width in the layer dimension up to 104 nanometers and a domain thickness ranging from 1 to 100 nanometers.
3. An OLED of claim 1, wherein the low work function metal alloy (1) comprises at least one of the following alloys: CaAl and MgAg.
4. An OLED of claim 2, wherein the low work function metal alloy (1) comprises at least one of the following alloys: CaAl and MgAg.
5. An OLED of any of claims 1-4, further comprising a transparent substrate (7), wherein the anode (6) is located on said substrate (7).
6. An OLED of any of claims 1-4, wherein the substrate (7) is made of one of the following materials: Polyethylene Terephthalate (PET) and glass.
7. An OLED of any of claims 1-4, wherein the semiconductor quantum dots (5) substantially form a monolayer within the hole transport layer (4).
8. An OLED of claim 5, wherein the semiconductor quantum dots (5) substantially form a monolayer within the hole transport layer (4).
9. An OLED of claim 6, wherein the semiconductor quantum dots (5) substantially form a monolayer within the hole transport layer (4).
10. An OLED of any of claims 1-4,8,9, wherein the semiconductor quantum dots (5) are two-component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large- band-gap semiconductor.
11. An OLED of claim 5, wherein the semiconductor quantum dots (5) are two-component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large- band-gap semiconductor.
12. An OLED of claim 6, wherein the semiconductor quantum dots (5) are two-component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large- band-gap semiconductor.
13. An OLED of claim 7, wherein the semiconductor quantum dots (5) are two-component semiconductor quantum dots comprising a core made of low-band-gap semiconductor and a shell made of large- band-gap semiconductor.
14. An OLED of claim 10, wherein the low- band-gap semiconductor is one of the following: CdSe and CdTe; and wherein the large-band-gap semiconductor is one of the following: CdS and ZnS.
15. An OLED of any of claims 11-13, wherein the low-band-gap semiconductor is one of the following: CdSe and CdTe; and wherein the large-band- gap semiconductor is one of the following: CdS and ZnS.
16. And OLED of claim 1, wherein the thickness of each of the hole transport layer (4) and the electron transport layer (3) does not exceed 100 nanometers.
17. Use of an OLED according to any of claims 1-4 as a pixel of a display.
PCT/RU2013/000537 2013-06-24 2013-06-24 Organic light-emitting diode for injection of the charge carriers WO2014209148A1 (en)

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