CN108735904B - QLED capable of improving light-emitting efficiency and preparation method thereof - Google Patents

Abstract

The invention discloses a QLED capable of improving light extraction efficiency and a preparation method thereof. The QLED sequentially comprises a substrate, a bottom electrode, a quantum dot light-emitting layer, a nanoparticle layer in which nanoparticles are agglomerated with each other, and a top electrode, wherein the nanoparticle layer is non-planar structure. In the present invention, a nanoparticle layer in which the nanoparticles are agglomerated with each other is introduced on top of the QLED, and the nanoparticle layer has a non-planar structure, and the optical extraction rate of the QLED can be improved by using the nanoparticle layer, thereby effectively improving the luminous efficiency of the QLED. At the same time, the structure of the present invention does not affect the electrical performance of the QLED device and meets the requirements of industrialization.

Description

A QLED capable of improving light extraction efficiency and preparation method thereof

technical field

The invention relates to the field of display, in particular to a QLED capable of improving light extraction efficiency and a preparation method thereof.

Background technique

Compared with organic fluorescent emitters, quantum dot-based QLEDs have the advantages of high color purity, long lifetime, and easy dispersion, and can be fabricated by printing processes, and are generally considered to be strong competitors for next-generation display technologies.

In the prior art, QLED is a planar thin film structure, and due to the different refractive indices of each thin film, optical reflection will be generated at the interface of the thin film. So the light emitted from the quantum dots is confined to the QLED. Theoretical calculations suggest that only about 20% of the light will be emitted from the QLED, and the remaining 80% of the light will be confined to different parts of the QLED, which leads to the low light extraction efficiency of the existing QLED.

Therefore, the existing technology still needs to be improved and developed.

SUMMARY OF THE INVENTION

In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a QLED capable of improving light extraction efficiency and a preparation method thereof, aiming at solving the problem of low light extraction efficiency of the existing QLED.

The technical scheme of the present invention is as follows:

A QLED capable of improving light extraction efficiency, wherein, it sequentially includes a substrate, a bottom electrode, a quantum dot light-emitting layer, a nanoparticle layer where nanoparticles are agglomerated with each other, and a top electrode, and the nanoparticle layer has a non-planar structure.

In the QLED capable of improving light extraction efficiency, the agglomeration degree of the nanoparticle layer is less than 1 μm in the plane and less than 100 nm in the longitudinal direction.

In the QLED capable of improving light extraction efficiency, the nanoparticle layer is an amorphous non-planar structure.

In the QLED capable of improving light extraction efficiency, the thickness of the nanoparticle layer is 10-100 nm.

In the QLED capable of improving light extraction efficiency, the material of the nanoparticle layer is TiO _x or ZnO.

In the QLED capable of improving light extraction efficiency, the size of the nanoparticles in the nanoparticle layer is less than 30 nm.

In the QLED capable of improving light extraction efficiency, an electron transport layer is further arranged between the quantum dot light-emitting layer and the nanoparticle layer of the QLED.

In the QLED capable of improving light extraction efficiency, a hole transport layer and a hole injection layer are further arranged between the bottom electrode of the QLED and the quantum dot light-emitting layer.

A preparation method of the above-mentioned QLED capable of improving light extraction efficiency, wherein, comprising the steps of:

A. Make the bottom electrode on the substrate;

B, depositing a quantum dot light-emitting layer on the bottom electrode;

C, on the quantum dot light-emitting layer, a nanoparticle layer in which the nanoparticles are agglomerated with each other is made by a solution method, and the nanoparticle layer is a non-planar structure;

D. The top electrode is fabricated on the surface of the nanoparticle layer.

In the preparation method, wherein, in the step C, a spin coating method is used to prepare the nanoparticle layer.

Beneficial effects: the present invention introduces a nanoparticle layer in which the nanoparticles are agglomerated with each other at the top of the QLED, and the nanoparticle layer has a non-planar structure, and the optical extraction rate of the QLED can be improved by using the nanoparticle layer, thereby effectively improving the QLED's luminescence efficiency. At the same time, the structure of the present invention does not affect the electrical performance of the QLED device and meets the requirements of industrialization.

Description of drawings

FIG. 1 is a schematic structural diagram of a preferred embodiment of a QLED capable of improving light extraction efficiency according to the present invention.

FIG. 2 is a schematic structural diagram of a specific embodiment of a QLED capable of improving light extraction efficiency according to the present invention.

FIG. 3 is a flow chart of a preferred embodiment of a method for preparing a QLED capable of improving light extraction efficiency of the present invention.

FIG. 4 is a schematic diagram illustrating the change of the rotational speed with time during spin coating in Example 1 of the present invention.

5 is a SEM cross-sectional view of agglomeration of nanoparticles in the QLED prepared in Example 1 of the present invention.

FIG. 6 is a schematic diagram of the luminous intensity of the QLED prepared in Example 1 of the present invention as a function of wavelength.

FIG. 7 is a schematic diagram of the change of the rotational speed with time during spin coating in the second embodiment of the present invention.

FIG. 8 is a schematic diagram of the change of the rotational speed with time during spin coating in Example 3 of the present invention.

Detailed ways

The present invention provides a QLED capable of improving light extraction efficiency and a preparation method thereof. In order to make the purpose, technical solution and effect of the present invention clearer and clearer, the present invention is further described below in detail. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Please refer to FIG. 1 . FIG. 1 is a schematic structural diagram of a preferred embodiment of a QLED capable of improving light extraction efficiency of the present invention. As shown in the figure, it sequentially includes a substrate 11 , a bottom electrode 12 , a quantum dot light-emitting layer 13 , and a space between nanoparticles The nanoparticle layer 14 and the top electrode 15 agglomerated with each other, the nanoparticle layer 14 is a non-planar structure.

The invention can improve the optical extraction rate of the QLED by adding a non-planar structure to the top electrode interface of the QLED, thereby effectively improving the luminous efficiency of the QLED. The non-planar structure formed by the above-mentioned nanoparticle layer 14 can not only ensure a simple manufacturing process, which is beneficial to large-scale application, and at the same time, the added non-planar structure will not affect the original device electrical performance of the QLED.

The nanoparticle layer 14 introduced in the present invention requires the nanoparticles to be able to agglomerate with each other. Preferably, the agglomeration degree of the nanoparticle layer 14 is less than 1 μm in the plane and less than 100 nm in the longitudinal direction. That is to say, in the nanoparticle layer 14 , the size of the agglomerates formed by each nanoparticle agglomeration is less than 1 μm in the plane, and the thickness in the longitudinal direction is less than 100 nm. Under the above conditions, the light extraction efficiency can be further improved, and the original electrical performance of the QLED can be guaranteed. For the agglomeration of nanoparticles, it can be controlled by solution processing, such as controlling the rotation speed and time. The agglomerated nanoparticles can be uniformly distributed on the quantum dot light-emitting layer 13 .

Preferably, the nanoparticle layer 14 is an amorphous non-planar structure. That is, the nanoparticles in the nanoparticle layer 14 are randomly agglomerated with each other, and adjacent nanoparticles can be arbitrarily agglomerated, which can also improve the uniformity of the distribution of nanoparticles, thereby improving the light extraction efficiency.

The nanoparticle layer 14 can be not only one layer, but also a multi-layer structure. If the multi-layer structure is adopted, it will be beneficial to improve the optical extraction rate, thereby improving the light extraction efficiency. The thickness of the nanoparticle layer 14 is preferably 10-100 nm, for example, 50 nm.

Further, the material of the nanoparticle layer 14 is TiO _x or ZnO, and can also be a material of its derivatives, or a material with electron transport function, that is, an ETL material. In addition, the material of the nanoparticle layer can also be a doped material, for example, Mg-doped ZnO (that is, ZnO is doped with Mg, the same below), Al-doped ZnO, La-doped ZnO, Y-doped ZnO, Mg-doped TiO, Al-doped TiO, La-doped TiO, or Y-doped TiO. The doping concentration is preferably less than 10% in mass percent.

Further, the size of nanoparticles in the nanoparticle layer 14 is less than 30 nm. For example, if the nanoparticle is spherical, its diameter is less than 30 nm, and if it is irregular, its maximum length is less than 30 nm.

An electron transport layer is also arranged between the quantum dot light-emitting layer 13 and the nanoparticle layer 14 of the QLED. A hole transport layer and a hole injection layer are further arranged between the bottom electrode 12 of the QLED and the quantum dot light-emitting layer 13 . For example, as shown in FIG. 2 , which is a schematic structural diagram of a specific embodiment of a QLED that can improve light extraction efficiency, it includes, from bottom to top, a substrate 21 , a bottom electrode 22 , a hole injection layer 23 , and a hole transport layer 24 , a quantum dot light-emitting layer 25 , an electron transport layer 26 , a nanoparticle layer 27 , and a top electrode 28 .

The thickness of the quantum dot light-emitting layer is preferably 10-100 nm. The bottom electrode may be patterned ITO or TCO or the like. The top electrode is an aluminum electrode or a silver electrode, and the thickness of the top electrode is preferably 30-800 nm. The material of the hole injection layer is at least one of PEDOT:PSS, MoO ₃ , VO ₂ or WO ₃ . The thickness of the hole injection layer is preferably 10-150 nm. The material of the hole transport layer is at least one of TFB, poly-TPD, PVK, NiO, MoO ₃ , NPB, and CBP. The thickness of the hole transport layer is preferably 10-150 nm. The material of the electron transport layer is preferably at least one of LiF, CsF, Cs ₂ CO ₃ , ZnO, and Alq ₃ .

The present invention also provides a preparation method of the above-mentioned QLED capable of improving light extraction efficiency, as shown in FIG. 3 , which includes the steps:

S1, making a bottom electrode on the substrate;

S2, depositing a quantum dot light-emitting layer on the bottom electrode;

S3, on the quantum dot light-emitting layer, a nanoparticle layer in which the nanoparticles are agglomerated with each other is made by a solution method, and the nanoparticle layer has a non-planar structure;

S4, making a top electrode on the surface of the nanoparticle layer.

Further, in the step S3, a spin coating method is used to fabricate the nanoparticle layer. By spin coating, the nanoparticles are spread evenly. And during the rotation process, the nanoparticles form agglomerates of a certain distribution and size, thereby destroying the flatness of the surface and increasing the light extraction efficiency.

Example 1

In this embodiment, the material of the nanoparticle layer is ETL-1, and the ETL-1 is specifically ZnO, and the corresponding relationship between the rotational speed and time during spin coating is shown in FIG. 4 . After preparing the substrate, bottom electrode, hole injection layer, hole transport layer, and quantum dot light-emitting layer in sequence, the solution of ETL-1 is added to the low-speed rotation at point A to spread it evenly on the substrate. As the time increases and the rotation speed increases, the solution begins to volatilize. At the 40th second, a solvent (alcohols, such as methanol, ethanol, propanol, etc.) is added. Due to the action of the solvent and the high-speed rotation, the solvent drives the quantum The point particle arrangement changes, so that the nanoparticles form agglomeration of a certain distribution and size, thereby destroying the flatness of the surface and increasing the light extraction efficiency. The surface of the ETL-1 material was agglomerated, and the surface after metal deposition was shown in Figure 5. Bumps of different sizes are distributed on the surface, which destroys the flatness of the metal electrode. As shown in Figure 6, the QLED treated QLED has a 10% higher luminous intensity than the untreated one.

Embodiment 2

After spin-coating the material of ETL-1, spin-coat another layer of nanoparticle material ETL-2. The ETL-2 material is specifically Y-doped ZnO, and the doping ratio is 2.5% (that is, in the ETL-2 material, the mass of Y ratio of 2.5%). The corresponding relationship between the rotational speed and time during spin coating of ETL-2 is shown in Figure 7. Spinning at low speed at point A is to add the solution of ETL-2 to spread it evenly on the substrate. As the time increases and the rotation speed increases, the solution begins to volatilize. At the 20th second, the solvent of ETL-1 (alcohols, such as methanol, ethanol, propanol, etc.) is added. Partial penetration of the ETL-1 and ETL-2 two-layer materials leads to an increase in the roughness of the film, thereby destroying the flatness of the surface and increasing the light extraction efficiency.

Embodiment 3

ETL-3 is a mixture of two nanomaterials N and M (the mass ratio of N and M can range from 1:99 to 99:1). The solubility of solvent L for N is much greater than that for M, where M is ZnO, N is TiO _x , and L is benzene (such as toluene) or alcohol (such as methanol, ethanol, propanol, etc.). The corresponding relationship between the rotational speed and time during spin coating of ETL-3 is shown in Figure 8. Spinning at low speed at point A is to add the ETL-3 solution to spread it evenly on the substrate. With the increase of time and the increase of rotation speed, the solution began to volatilize. At the 80th second, L solvent was added, and 100 microliters was added at a time, and the interval was 10 seconds. Due to the action of the solvent, the N material on the surface of the film is partially dissolved during high-speed rotation, resulting in an increase in the roughness of the film, thereby destroying the flatness of the surface and increasing the light extraction efficiency.

In the above embodiment, by improving the structure of the QLED, it is verified by experiments that the light extraction efficiency of the QLED can be improved by 5% to 30%.

To sum up, the present invention introduces a nanoparticle layer in which the nanoparticles are agglomerated with each other at the top of the QLED, and the nanoparticle layer has a non-planar structure. The use of the nanoparticle layer can improve the optical extraction rate of the QLED, thereby effectively improving the QLED. luminous efficiency. At the same time, the structure of the present invention does not affect the electrical performance of the QLED device and meets the requirements of industrialization.

It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above descriptions, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention.

Claims (9)

1. A QLED capable of improving light-emitting efficiency is characterized by sequentially comprising a substrate, a bottom electrode, a quantum dot light-emitting layer, a nanoparticle layer and a top electrode, wherein nanoparticles are agglomerated with each other, and the nanoparticle layer is of a non-planar structure;

the agglomeration degree of the nanoparticle layer is as follows: less than 1 μm in plan and less than 100nm in the longitudinal direction.

2. A QLED capable of improving light extraction efficiency as recited in claim 1, wherein the nanoparticle layer has an amorphous non-planar structure.

3. The QLED of claim 1, wherein the thickness of the nanoparticle layer is 10-100 nm.

4. The QLED of claim 1, wherein the material of the nanoparticle layer is TiO_xOr ZnO.

5. The QLED of claim 1, wherein the nanoparticle layer has a nanoparticle size of less than 30 nm.

6. The QLED of claim 1, wherein an electron transport layer is disposed between the quantum dot light emitting layer and the nanoparticle layer.

7. The QLED of claim 6, wherein a hole transport layer and a hole injection layer are disposed between the bottom electrode and the quantum dot light emitting layer.

8. The method according to claim 1, wherein the method for manufacturing a QLED with improved light extraction efficiency comprises the steps of:

A. manufacturing a bottom electrode on a substrate;

B. depositing a quantum dot light-emitting layer on the bottom electrode;

C. preparing a nanoparticle layer with nanoparticles agglomerated with each other on the quantum dot light-emitting layer by a solution method, wherein the nanoparticle layer is of a non-planar structure;

D. and manufacturing a top electrode on the surface of the nano particle layer.

9. The production method according to claim 8, wherein in the step C, the nanoparticle layer is produced by a spin coating method.

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