Patent Application
20080007168
For a tandem organic electroluminescent element 1, the anode 13 comprises material(s) with relatively high work function, and the cathode 11 comprises material(s) with relatively low work function. The limitations of the electrodes are that one of the cathode 11 and the anode 13 is a transparent electrode, and the other is either a transparent electrode or an opaque electrode. For example, ITO may be used as the material of the transparent electrode as the anode 13, and materials, such as magnesium, magnesium-silver alloy, calcium, lithium-aluminum alloy, etc., may be used as the material of cathode 11.
The first organic electroluminescent unit 15 and the second organic electroluminescent unit 17 can be any known organic electroluminescent unit. The first and the second organic electroluminescent units, 15, 17 comprise a light emitting layer, and optionally has a multilayer structure that further comprises any one or more of the following layers: an EIL, an ETL, a HTL, a HIL, an electron blocking layer (EBL), or a hole blocking layer (HBL). For example, the multilayer structure is, 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. For a tandem organic electroluminescent element, the structure or the material of each tandem organic electroluminescent unit can be identical or different only if the unit has the required electron and hole transport ability.
The connecting layer 19 comprises a bipolar organic compound and a conductive dopant. Any bipolar organic compound with at least 1×10−7 mm2/V·sec carrier mobility is suitable for the present invention. For example, the bipolar organic compound is made of, but not limited to, anthracene derivatives, fluorene derivatives, spirofluorene derivatives, pyrene derivatives, oligomer or a mixture thereof. More specifically, the connecting layer 19 may use an anthracene derivative, such as 9,10-di-(2-naphthyl) anthracene (ADN), 2-(t-Butyl)-9,10-di(2-naphthyl)anthracene (TBADN), or 2-methyl-9,10-di(2-naphthyl) anthracene (MADN) as the bipolar organic compound.
The conductive dopant of the connecting layer 19 can be any proper conductive metal or metal oxide only if the transparency and the conductivity of the materials are suitable. For example, the materials can be, but not limited to, metals such as aluminum, calcium, silver, nickel, titanium, magnesium, or an alloy thereof, metal compounds such as ITO, ZnO:Al, ZnO, InN, SnO2, or a combination of the recited metals and metal compounds. Because of the poor transparency, the concentration of the metal should not be too high. Furthermore, lateral electricity leakage would occur as the concentration of the conductive dopant is too high, resulting in decreased efficiency of the organic electroluminescent element. Based on the aforementioned considerations, the concentrations of the conductive dopants in the connecting layer 19 is generally present in an amount ranging from 5% to 65%, preferably from 10% to 60%, and more preferably from 20% to 50%.
When mixing the conductive dopants and the bipolar organic compound, the considerations of the whole conductivity of the connecting layer 19 comprise the following: conductivity of the conductive substances, thickness of the connecting layer 19, and concentration of the conductive substances. The conductivity of the connecting layer would be optimized by well formulating these three considerations.
The efficacy of the tandem organic electroluminescent element 2 is shown in
Referring to
As shown in
Moreover, because the connecting layer of the tandem organic electroluminescent element of the present invention comprises both a metal conductive substance and another component, there is relatively high resistance, low lateral currents and nonoccurrence of crosstalk. Given the above, the tandem organic electroluminescent element of the invention improves the luminous efficiency effectively without affecting the transparency. It also avoids weakened carrier injection ability, crosstalk, and/or lateral electricity leakage.
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 plurality of substrates. The substrate comprises a plurality of thin film transistors, wherein the plurality of thin film transistors are electrically connected to a plurality of electrodes of the tandem organic electroluminescent elements. With this tandem organic electroluminescent element, crosstalk, weakened carrier injection ability, bad reproducibility resulting from overly thin metal, bad transparency, and/or lateral electricity leakage would be improved. The present invention has high transparency and a high carrier transport rate which further improves the interior luminous efficiency of the display.
Though the embodiments illustrated for the present invention show a tandem organic electroluminescent element comprising an anode, a cathode, a first organic electroluminescent unit, a second organic electroluminescent unit, and a connecting layer, the people skilled in this field would appreciate the workability of a fourth embodiment of the present invention, wherein a tandem organic electroluminescent element 4 comprises an anode 41 a cathode 43, N organic electroluminescent elements 45, and (N−1) connecting layers 47, as shown in
The above disclosure is related to the detailed technical contents and inventive features thereof. People 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 |
|---|---|---|---|
| 095124970 | Jul 2006 | TW | national |
