[0028] The present invention provides a QLED device with high luminous efficiency and a preparation method thereof. In order to make the objectives, technical solutions and effects of the present invention clearer and clearer, the present invention will be described in further detail below. 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.
[0029] See figure 1 , figure 1 It is a flowchart of a preferred embodiment of a method for manufacturing a QLED device with high luminous efficiency according to the present invention. As shown in the figure, it includes the steps:
[0030] S100. Depositing a composite hole injection layer on the ITO substrate; wherein the composite hole injection layer is made by dispersing metal nanoparticles in the hole injection layer and stirring uniformly;
[0031] S200, depositing a hole transport layer on the composite hole injection layer;
[0032] S300, depositing a quantum dot light-emitting layer on the hole transport layer;
[0033] S400, sequentially depositing an electron transport layer and an electron injection layer on the quantum dot light-emitting layer, and finally evaporating a cathode on the electron injection layer to produce a QLED device.
[0034] The core improvement of the present invention: the surface plasma enhancement effect of metal nanoparticles is applied to QLED devices, and a small amount of metal nanoparticles are added to the hole injection layer to prepare a composite hole injection layer. Then, the prepared composite hole injection layer is used to replace the existing hole injection layer in a QLED device, thereby realizing an effective improvement in the luminous efficiency of the QLED device.
[0035] Among them, the principle of enhancing the luminous efficiency of QLED devices by surface plasma of metal nanoparticles is as follows:
[0036] figure 2 It is a schematic diagram of the QLED device of the present invention and its "near field effect" and "far field effect". Among them, the QLED device of the present invention from top to bottom is: cathode 1, electron injection layer 2, electron transport layer 3, quantum dot light emitting layer 4, hole transport layer 5, composite hole injection layer 6 (in the hole injection layer) Disperse with metal nanoparticles 7) and anode 8. Specifically, there are a large number of freely moving electrons on the surface of metal nanoparticles. When there is no external effect, the free electrons on the surface of metal nanoparticles are in equilibrium, but when the quantum dot light-emitting layer of the QLED device is illuminated by photons generated by the radiation transition On the surface of metal nanoparticles, the interaction of free electrons and photons on the surface of the metal nanoparticles will produce an electron density wave that propagates along the surface of the metal nanoparticle. This electron density wave is called surface plasmon. It produces an electric field with varying intensity in its propagation direction, figure 2 The middle arrow refers to the law of electric field intensity change. When the distance to the metal nanoparticles is very close (usually 5~10nm), the intensity of the local electric field generated by the metal nanoparticles will first increase and then decrease. This effect is called "Near-Field Effect". Such as figure 2 The "9" refers to the near-field effect; when the distance from the metal nanoparticles continues to increase, the intensity of the electric field will change from large to small again. This is called the "Far-Field Effect (Far-FieldEffect )",Such as figure 2 The "10" refers to the far-field effect. Theoretically, the local electric field intensity generated by the "near field effect" is higher than the "far field effect".
[0037] In principle, whether it is the "near field effect" or the "far field effect", the local electric field generated by them can increase the effective electric field in the QLED device, promote carrier transmission and composite luminous efficiency. However, in QLED devices, if the excitons formed by the carriers (electrons and holes) injected by the electrodes at both ends are in direct contact with the metal material, the excitons will be quenched, that is, the excitons will be lost in a non-radiative recombination manner. Therefore, it is not a very ideal method to directly use the "near field effect" to improve the luminous efficiency of QLED devices.
[0038] The present invention mainly utilizes the "far field effect" of metal nanoparticles to realize the improvement of the luminous efficiency of QLED devices. This is because the "far-field effect" of plasma can generate a strong local electric field, which can effectively promote carrier transport and radiation recombination in QLED devices, thereby greatly improving the luminous efficiency of QLED devices. The specific method is to mix 0.1%-10% metal nanoparticles in the hole injection layer material as the composite hole injection layer, in order to avoid the metal nanoparticles in the hole injection layer and quantum dots (QDs) light-emitting layer Direct contact leads to quenching of luminescence, and a hole transport layer is prepared on the composite hole injection layer. The hole transport layer can separate the quantum dot light emitting layer from the metal nanoparticles. This hole transport layer can be used at the same time. To increase the efficiency of hole transport.
[0039] Specifically, the metal nanoparticles may be common metal nanoparticles such as gold (Au) nanoparticles, silver (Ag) nanoparticles, or copper (Cu) nanoparticles, and other metal nanoparticles with similar functions. The particle size of the metal nanoparticles is between 0 and 100 nm. Taking Au nanoparticles as an example, the present invention provides a method for preparing Au nanoparticles. The Au nanoparticles of the present invention adopt sodium citrate (Na 3 C 6 H 5 O 7 ) Reduced chloroauric acid (HAuCl 4 ) Method, the specific preparation method of Au nanoparticles is as image 3 Shown:
[0040] S1: Na 3 C 6 H 5 O 7 And HAuCl 4 Formulated to a concentration of 0.01g/mLNa 3 C 6 H 5 O 7 Aqueous solution and concentration of 0.01g/mL HAuCl 4 Aqueous solution;
[0041] S2: Then use a pipette to add 1 mL of HAuCl 4 Add the aqueous solution to a 100mL volumetric flask, add deionized water to the volumetric flask to dilute to the mark, and dilute the diluted HAuCl 4 Stir the solution evenly;
[0042] S3: After mixing HAuCl 4 The solution is heated, and after boiling, add 1 mL of Na in the volumetric flask drop by drop 3 C 6 H 5 O 7 The aqueous solution reacts and continues to be heated. After 15 minutes of reaction, the solution in the volumetric flask is allowed to cool naturally;
[0043] S4: Wash and centrifuge the cooled solution for later use.
[0044] Among them, the size of Au nanoparticles can be adjusted by adding Na 3 C 6 H 5 O 7 The amount to control. Preferably, the size of the Au nanoparticles in the present invention is 30-40 nm.
[0045] Before preparing the QLED device, the ITO substrate is cleaned. The specific cleaning process includes: placing the patterned ITO substrate in acetone, washing solution, deionized water, and isopropanol in order for ultrasonic cleaning, each of which lasts for about 15 minutes. After the ultrasound is completed, the ITO substrate is placed in a clean oven and dried for later use. Through the above ultrasonic cleaning process, dust and chemical dirt on the surface of the ITO substrate can be effectively removed.
[0046] Further, before the step S100, it includes: treating the surface of the ITO substrate with oxygen plasma or ultraviolet-ozone. The specific pretreatment steps are: take out the dried ITO substrate, and then treat the surface of the ITO substrate with oxygen plasma for 5 to 10 minutes (for example, treat the surface of the ITO substrate for 5 minutes) to further remove the organic matter attached to the surface of the ITO substrate, or UV- Ozone treats the surface of the ITO substrate for 5-10 minutes (for example, treats the surface of the ITO substrate for 5 minutes) to further remove the organic matter attached to the surface of the ITO substrate, thereby improving the work function of the ITO substrate.
[0047] In the step S100, a composite hole injection layer dispersed with metal nanoparticles is deposited on the ITO substrate. After depositing a composite hole injection layer on the ITO substrate, place the ITO substrate deposited with the composite hole injection layer on a heating stage at 150~180℃ (for example, the temperature of the heating stage is 150℃) and heat for 10~15min (Such as 10min) to remove water. The heating process is completed in air. Preferably, the material of the hole injection layer used to prepare the composite hole injection layer can be PEDOT:PSS, or other materials with good hole injection performance. Preferably, the thickness of the composite hole injection layer is 0-100 nm. More preferably, the thickness of the composite hole injection layer is 40-50 nm.
[0048] In the step S200, the dried ITO substrate with the composite hole injection layer deposited is placed in a nitrogen atmosphere, and a hole transport layer is deposited on the composite hole injection layer. Preferably, the material of the hole transport layer can be one or two of Poly-TPD and PVK, or other high-performance hole transport layer materials. One or two of Poly-TPD and PVK are used as the material of the hole transport layer because Poly-TPD has good film-forming properties and hole transport properties, and Poly-TPD can improve the balance between electrons and holes , Increase the recombination probability of holes and electrons. PVK can effectively reduce the hole injection barrier from the ITO substrate to the quantum dot light-emitting layer and the electron transport layer, thereby improving the performance of the QLED device.
[0049] Furthermore, in order to effectively separate the metal nanoparticles in the composite hole layer from the quantum dot light-emitting layer and avoid direct contact between the metal nanoparticles in the hole injection layer and the quantum dot light-emitting layer, the present invention will The thickness of the hole transport layer is controlled to be greater than or equal to 10 nm. After the hole transport layer is deposited, the resulting substrate is placed on a heating stage for heat treatment to remove the solvent, and then the substrate is naturally cooled.
[0050] In the step S300, after the substrate prepared in the step S200 is cooled, a quantum dot light-emitting layer is deposited on the hole transport layer, and the thickness of the quantum dot light-emitting layer is preferably 10-100 nm. After the deposition is completed, the prepared substrate is placed on a heating table at 80-100°C (such as 80°C) and heated for 10 minutes to remove residual solvent.
[0051] In the step S400, an electron transport layer and an electron injection layer are sequentially deposited on the quantum dot light-emitting layer, and finally a cathode is vapor-deposited on the electron injection layer to produce a QLED device. Wherein, the material of the electron transport layer is n-type zinc oxide, which is because the n-type zinc oxide has high electron transport performance. The thickness of the electron transport layer is preferably 30-60 nm. The electron injection layer can be low work function Ca, Ba and other metals, or CsF, LiF, CsCO 3 Such compounds can also be other electrolyte-type electron injection layer materials. Finally, the ITO substrate on which each functional layer has been deposited is placed in an evaporation chamber and a cathode is evaporated on the electron injection layer through a mask plate to produce a QLED device. Preferably, the cathode is metallic Ag or metallic Al. This is because metallic Ag or metallic Al with low work function is used as a cathode to facilitate electron injection. Wherein, the thickness of the cathode layer is 80-100 nm (such as 100 nm).
[0052] The present invention also provides a QLED device, wherein the QLED device is prepared by using any of the above-mentioned methods for preparing a QLED device with high luminous efficiency. The present invention incorporates metal nanoparticles into the hole injection layer material, and uses the surface plasma enhancement effect of the metal nanoparticles to prepare a QLED device. In the QLED device, the "far-field effect" of the plasma can produce strong localization. Domain electric field, which can effectively promote carrier transport and radiation recombination in QLED devices, thereby greatly improving the luminous efficiency of QLED devices.
[0053] In summary, the present invention provides a QLED device with high luminous efficiency and a preparation method thereof. The present invention applies the surface plasmon enhancement effect of metal nanoparticles to the QLED device, by doping the hole injection layer A small amount of metal nanoparticles is used to prepare a composite hole injection layer. Then the prepared composite hole injection layer is used to replace the existing hole injection layer in QLED devices, thereby effectively promoting carrier transport and radiation recombination in QLED devices, and realizing the effective luminous efficiency of QLED devices improve.
[0054] It should be understood that the application of the present invention is not limited to the above examples, and those of ordinary skill in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention.
