Patent Application
20080074047
For the tandem organic electroluminescent element 2, the anode 201 comprises material(s) with a relatively high work function, and the cathode 203 comprises material(s) with a relatively low work function. One of the cathode 203 and the anode 201 is a transparent electrode, while the other is either a transparent electrode or an opaque electrode. For example, the transparent electrode of ITO (Indium Tin Oxide) may be used as the anode 201, and materials, such as magnesium, magnesium-silver alloy, calcium, lithium-aluminum alloy, etc., may be used as the material of the cathode 203.
Carrier mobility of the first high charge injection layer 205 and the second high charge injection layer 207 of the present invention should be at least 1×10−4 cm2/Vs for providing enough charge injection ability. That is, the first high charge injection layer 205 has a hole mobility equal to or more than 1×10−4 cm2/Vs, and the second high charge injection layer 207 has an electron mobility equal to or more than 1×10−4 cm2/Vs. Preferably, the carrier mobility of the high charge injection layers should be higher than that of any ETL of the tandem organic electroluminescent element.
The first high charge injection layer 205 comprises the first material and a first substrate, and the second high charge injection layer 207 comprises the second material and a second substrate. The first substrate and the second substrate can be the same or different organic substances, and the first material and the second material can be the same or different and independently selected from the group consisting of organic substances and inorganic substances.
Generally speaking, the first substrate and the second substrate usually adopt different materials for hole and electron transportation ability, respectively. However, some organic materials have characteristics for promoting both hole and electron transportation, and are suitable materials for both the first substrate and the second substrate. For example, the materials suitable for both the first substrate and the second substrate may comprise but are not limited to: copper phthalocyanine (CuPc), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), carbazole derivatives like 4,4-bis(9-dicarbazolyl)-biphenyl (CBP), distyrylarylene derivatives like 4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl (DPVBi), anthracene derivatives, and fluorene derivatives. Other suitable materials comprise all kinds of metal phthalocyanines, including but not limited to, ZnPc, MgPc, and PbPc.
As mentioned above, the first high charge injection layer 205 is adjacent to the anode 201 so the more preferable material thereof is organic compounds with high electron withdrawing ability. Preferably, the material of the first substrate is aromatic tertiary amine, which comprises at least one trivalent nitrogen that is bonded to a carbon atom, and has at least one aromatic ring. The aromatic tertiary amine can be an arylamine, such as a monoaryl amine, a diarylamine, a triarylamine, or a polymeric arylamine. Other suitable triarylamines substituted with one or more vinyl radicals and/or comprising at least one active hydrogen-containing group can also been used. More preferred aromatic tertiary amines are those which include at least two aromatic tertiary amine portions, for example, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), N,N,N′,N′-tetranaphthyl-benzidine (TNB), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1-1′-biphenyl-4-4′-diamine (TPD), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′-biphenyl-4,4″-diamine (α-NPD), 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (TDATA), 4,4′,4″-tris(3-methyl-phenyl-phenylamino)-triphenylamine (MTDATA), poly(vinyltriphenylamine (PVT), and poly(n-vinylcarbazole) (PVK).
As mentioned above, the second high charge injection layer 207 is adjacent to the cathode 203 so the more preferable material thereof is organic compounds with high electron transportation ability. Preferred materials of the second substrate are metal chelated oxinoid compounds (also referred as 8-quinolinol or 8-hydroxyquinoline), such as tris(8-hydroxyquinoline) aluminum. The materials of the second substrate can also be butadiene derivatives, triazines derivatives, hydroxyquinoline derivatives, benzazole derivatives, silole derivatives like 2,5-bis(2′,2″-bipridin-6-yl)-1,1-dimethyl-3,4-diphenyl silacyclopentadien, 2,5-bis(1-naphthyl)-1,3,4-oxadiazole (BND), 2-(4-biphenylyl)-5-(4-tert-butyl phenyl)-1,3,4-oxadiazole (PBD), 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7), 1,2,4-triazole derivative (TAZ), 4,7-diphenyl-1,10-phenanthroline (BPhen), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene (TPBI), Tris(8-hydroxyquinoline)aluminum (Alq), bis(10-hydroxybenzo[h]quinolinato)beryllium (BeBq), bis(2-methyl-8-quinolinolato)(para-phenyl-phenolato)aluminum (III) (BAlq), and bis[2-(2-hydroxyphenyl)benzoxazolate]zinc.
The inorganic substances suitable for the first material include a p type dopant, and preferably are a first metal or its compound having a work function of more than 4.2 eV The hole transport rate of the first high charge injection layer 205 can be increased by doping the p type dopant thereinto. Most metals can be the p type dopant except for rare earth metals and the alloys thereof. Preferably, the p type dopant is a metal selected from the group consisting of gold, silver, copper, zinc, cobalt, nickel, compounds thereof, and compounds thereof. The metal compound can be an organometallic complex, an organic salt, an inorganic salt, an oxide, or a halide.
As mentioned above, an organic substance can be used as the first material. For example the first material can be provided by, but is not limited to, 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (F4-TCNQ) and/or 7,7,8,8-tetracyanoquinodimethane (TCNQ).
The inorganic substances suitable for the second material comprise an n type dopant, and a second metal or its compound having a work function of less than 4.2 eV is preferable. The electron transport rate of the second high charge injection layer 207 can be increased by doping the n type dopant thereinto. The second metal can be an alkali metal, such as lithium, sodium, potassium, rubidium, or cesium, an alkaline earth metal, such as magnesium, calcium, strontium, or barium, a rare earth metal, such as lanthanum, samarium, europium, thorium, dysprosium, erbium, or ytterbium, or an alloy of the aforementioned metals, such as an aluminum alloy or an indium alloy. The metal compound can be an organometallic complex, an organic salt, an inorganic salt, an oxide, or a halide.
The first organic electroluminescent unit 209 and the second organic electroluminescent unit 211 can be the same or different in their elements, structures, photochromes, materials, and manufacturing processes, as long as they can provide the desired electron transport rate and hole transport rate, respectively. The first organic electroluminescent unit 209 and the second organic electroluminescent unit 211 can be any known organic electroluminescent unit and comprises a light emitting layer and an optional multilayer structure comprising one or more of the following layers: an EIL, an ETL, a HTL, a HIL, an electron blocking layer (EBL) and a hole blocking layer (HBL). For example, the multilayer structure can be, but not limited to, HTL/EL/ETL, HIL/HTL/EL/ETL, HIL/HTL/EL/ETL/EIL, HIL/HTL/EBL or HBL/EL/ETL/EIL, HIL/HTL/EL/HBL/ETL/EIL, etc. Optionally, a high charge injection layer can be disposed between two electroluminescent units. For instance, if both the structures of the first organic electroluminescent unit 209 and the second organic electroluminescent unit 211 are HTL/EL/ETL, a high charge injection layer can be added between the ETL of the first unit 209 and the HTL of the second unit 211. Moreover, a charge generation layer (CGL) can be inserted into the first unit 209 and the second unit 211 for transferring electrical energy into light energy. With the photoelectric effect, electrons can be generated to improve the luminous efficiency of the element and provide multi-photon emission embodiments.
The efficacy of the present invention is further illustrated in
Referring to
As shown in
With the aforementioned results, the tandem organic electroluminescent element 2 of the present invention can improve luminous efficiency effectively without an overlarge operation voltage. In addition, there are high charge injection layers in the tandem organic electroluminescent element 2 of the present invention, and the charges flow steadily and the connection interface between the units is therefore stable.
The embodiments illustrated for the present invention show a tandem organic electroluminescent element comprising an anode, a cathode, a first high charge injection layer, a second high charge injection layer, a first organic electroluminescent unit, and a second organic electroluminescent unit. Those skilled in this field would appreciate the workability of a second embodiment of the present invention according to the aforementioned embodiment, wherein a tandem organic electroluminescent element 4 comprises an anode 41, a cathode 43, a first high charge injection layer 45, a second high charge injection layer 47, and a plurality of organic electroluminescent units 49 as shown in
A third embodiment of the present invention is an organic electroluminescent display. The organic electroluminescent display comprises a plurality of tandem organic electroluminescent elements as recited above and a substrate. The substrate comprises a plurality of thin film transistors, wherein the plurality of thin film transistors is electrically connected to a plurality of electrodes of the tandem organic electroluminescent elements. With this tandem organic electroluminescent element, the present invention prevents low luminous efficiency, high power consumption, and increased cost resulting from excessively high operation voltage and instability of the connection interface of the units. Moreover, the tandem organic electroluminescent element further has the characteristic of a high carrier transport rate.
The above disclosure is related to the detailed technical contents and inventive features thereof. Those skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.
| Number | Date | Country | Kind |
|---|---|---|---|
| 095135191 | Sep 2006 | TW | national |
