Tandem OLED with intermediate alloy layer

Abstract

A tandem OLED device is provided that includes an anode, a cathode, at least two electroluminescent cells disposed between the anode and the cathode, and an alloy thin film disposed between the two electroluminescent cells. The alloy film may be disposed between a p-type film and an n-type film.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 413,557, filed on October 5, 2022, entitled "Tandem OLEDs with Intermediate Alloy Layers", which is currently pending. BACKGROUND OF THE INVENTION

[0003] The present invention relates to tandem OLED devices. More particularly, the present invention relates to an OLED device having an intermediate layer.

[0004] An organic light-emitting diode device (OLED) typically includes an anode, a cathode, and an organic electroluminescent layer sandwiched between the anode and the cathode. The organic electroluminescent layer typically includes a hole transport layer, a light-emitting layer, and an electron transport layer. OLEDs are attractive because of their low driving voltage, high brightness, wide viewing angle, and ability to display full-color and other applications. Tang et al. describe multi-layer OLEDs in their U.S. Patents Nos. 4,769,292 and 4,885,211.

[0005] OLEDs can emit different colors, such as red, green, blue, or white, depending on the luminescent properties of their light-emitting layers.

[0006] Tandem OLED structures (sometimes referred to as stacked OLEDs or cascaded OLEDs) have been disclosed by, for example, Jones et al. in U.S. Patent No. 6,337,492, Tanaka et al. in U.S. Patent No. 6,107,734, Kido et al. in Japanese Patent Publication Nos. 2003 / 045676A and 2003 / 0189401A1, and Liao et al. in U.S. Patent No. 6,717,358 and U.S. Patent Application Publication Nos. 2003 / 0170491A1.

[0007] A tandem OLED is fabricated by vertically stacking a plurality of individual OLED units and driving the stack with a single power supply. The advantages are increased current efficiency, lifetime, or both. However, problems include:

[0008] 1. The tandem structure with multiple OLED units increases the driving voltage (approximately proportional to the number of OLED units), which is not favorable for power consumption.

[0009] 2. As the required voltage increases, a larger capacitor size is needed. The high voltage required to drive the OLEDs makes it challenging to fabricate the backplane for very small pixel displays, such as microdisplays.

[0010] Therefore, for widespread applications in OLED displays, it is necessary to reduce the driving voltage and improve the power efficiency of tandem OLED devices.

[0011] U.S. Patent No. 7,955,719 (Hatwar et al.) has a general background and teaches a tandem OLED device with an intermediate connector.

[0012] Despite these developments, there is still a need to improve the efficiency and driving voltage of tandem OLED devices while maintaining good broadband emission.

[0013] All references mentioned herein are incorporated herein by reference. Summary of the Invention

[0014] The present invention relates to a tandem OLED device comprising an anode, a cathode, at least two electroluminescent units disposed between the anode and the cathode, and an alloy thin film disposed between the two electroluminescent units.

[0015] The OLED units may each include a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), an emission layer (EML), a hole blocking layer (HBL), an electron transport layer (ETL), and / or an electron injection layer (EIL). The alloy film may be disposed between a p-type film and an n-type film. The alloy film may comprise a first metal and a second metal or a first metal, a second metal, and a third metal. The alloy film may be bilayer, comprising a first layer including two different metals and a second layer including a third metal. The first metal may be, for example, a noble metal. The second metal may be, for example, an alkaline earth metal or a rare earth metal. The third metal may be, for example, an alkali metal halide or an organic compound containing an alkali metal. Each of the first metal, the second metal, and the third metal may be co-deposited by thermal evaporation to fabricate the alloy film. The thickness of the alloy film may be, for example, from 1 nm to 8 nm. Brief Description of the Drawings

[0016] Figure 1 is a simplified isometric view of a tandem OLED architecture with an alloy film connecting OLED units according to an exemplary embodiment of the present invention. Two or more OLED units may be stacked in the tandem OLED.

[0017] Figure 2 is a graph of current density versus voltage (J-V) of a tandem OLED using three different metals as an intermediate layer according to the present invention. Detailed Description

[0018] Reference is now made to the drawings, in which like reference numerals refer to like elements throughout the several views, in Figure 1Shown in is a tandem OLED 10 according to an exemplary embodiment of the present invention, which has an alloy thin film 12 as an intermediate layer between OLED units 14, 16. The tandem OLED 10 includes two or more typical OLED units, each unit including a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), an emission layer (EML), a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL).

[0019] The alloy thin film 12 is disposed between a p-type film 18 and an n-type film 20. The alloy film 12 can be a single layer and can be composed of two materials (e.g., metal 1 and metal 2) or three materials (e.g., metal 1, metal 2, and material 3). The alloy film can be a bilayer, including metal 1 and metal 2 as one layer and material 3 as another layer. Metal 1 can be, for example, a noble metal (e.g., Ag, Au, Pt) with a weight ratio of 1% to 99% in the alloy. Metal 2 can be, for example, an alkaline earth metal (e.g., Mg or Ca) or a rare earth metal (e.g., Yb) with a weight ratio of 1% to 99% in the alloy. Material 3 can be, for example, an alkali metal halide (e.g., LiF, CsF) or an organic compound containing an alkali metal (e.g., LiQ). Metal 1, metal 2, and / or material 3 can be co-deposited by thermal evaporation to fabricate the alloy film. The thickness of the alloy film can be, for example, from 1 nm to 8 nm.

[0020] Example:

[0021] Three green tandem (2-unit) OLED devices were fabricated using calcium, Mg:Ag alloy, and Mg:Ag:LiF alloy as the intermediate metal films, respectively. The current density-voltage (J-V) curves of the tandem OLED devices are as Figure 2 shown. The tandem OLED with the alloy film shows a lower driving voltage than the tandem OLED with a Ca layer. At the same current density of 50 mA / cm 2 , the driving voltages of Ca, Mg:Ag, and Mg:Ag:LiF are 13.8 V, 12.6 V, and 12.3 V, respectively.

[0022] Examples of benefits

[0023] Applying the proposed alloy layer to the tandem OLED device. This device will allow for the following:

[0024] (1) High efficiency;

[0025] (2) Long lifespan;

[0026] (3) Low power consumption and reduced driving voltage; and

[0027] (4) Suitable for high-resolution microdisplays with lower backplane voltage requirements.

[0028] The present invention is applicable to both white OLEDs with color filters and directly patterned OLEDs.

[0029] It should be understood that the present disclosure only teaches an example of an illustrative embodiment and those skilled in the art can easily conceive of many variations of the present invention after reading the present disclosure and the scope of the present invention is determined by the appended claims.

Claims

1. A tandem OLED device, comprising: (a) an anode; (b) a cathode; (c) at least two electroluminescent units disposed between the anode and the cathode; and (d) an alloy film disposed between the two electroluminescent units.

2. The tandem OLED device according to claim 1, wherein each of the electroluminescent units comprises a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), an emission layer (EML), a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL).

3. The tandem OLED device according to claim 1, wherein the alloy film is disposed between a p-type film and an n-type film.

4. The tandem OLED device according to claim 1, wherein the alloy film comprises a first metal and a second metal.

5. The tandem OLED device according to claim 1, wherein the alloy film comprises a first metal, a second metal, and a third metal.

6. The tandem OLED device according to claim 1, wherein the alloy film is bilayer, comprising a first layer containing two different metals and a second layer containing a third metal.

7. The tandem OLED device according to claim 4, wherein the first metal is a noble metal.

8. The tandem OLED device according to claim 4, wherein the second metal is an alkaline earth metal or a rare earth metal.

9. The tandem OLED device according to claim 5, wherein the third metal is an alkali metal halide or an organic compound containing an alkali metal.

10. The tandem OLED device according to claim 5, wherein each of the first metal, the second metal, and the third metal is co-deposited by thermal evaporation to form the alloy film.

11. The tandem OLED device according to claim 1, wherein the thickness of the alloy film ranges from 1 nm to 8 nm.

Images