CN113594382A

CN113594382A - Positive QLED device based on double-layer hole injection layers and preparation method thereof

Info

Publication number: CN113594382A
Application number: CN202110219357.9A
Authority: CN
Inventors: 杜祖亮; 杜佳佳; 蒋晓红; 王啊强; 王帅冰
Original assignee: Henan University
Current assignee: Henan University
Priority date: 2021-02-26
Filing date: 2021-02-26
Publication date: 2021-11-02

Abstract

The invention provides a positive QLED device based on a double-layer hole injection layer and a preparation method thereof, and relates to the technical field of light emitting diodes. The invention provides a positive type QLED device, comprising: the structure comprises a glass substrate with an ITO transparent electrode, and a first hole injection layer, a second hole injection layer, a hole transport layer, a quantum dot light emitting layer, an electron transport layer and a top electrode layer which are sequentially arranged on the surface of the ITO transparent electrode from bottom to top; the first hole injection layer and the second hole injection layer are respectively a NiO layer and a PEDOT PSS layer. The positive QLED device provided by the invention adopts NiO/PEDOT and PSS double-layer hole injection layers, so that the problem of corrosion to an ITO electrode can be solved, a hole injection barrier can be effectively reduced, the hole injection efficiency is improved, carriers are balanced, the efficiency of the positive QLED device is improved, and the service life of the positive QLED device is prolonged.

Description

Positive QLED device based on double-layer hole injection layers and preparation method thereof

Technical Field

The invention relates to the technical field of light emitting diodes, in particular to a positive QLED device based on a double-layer hole injection layer and a preparation method thereof.

Background

Quantum dot light emitting diodes (QLEDs for short) have the advantages of adjustable emission wavelength in the visible light range, narrow half-peak width, high brightness, and can be prepared by a solution method.

Currently, the most commonly used hole injection material in the construction of QLED devices is PEDOT: PSS (i.e., poly (3, 4-ethylenedioxythiophene): polystyrene sulfonate). However, the PEDOT PSS is unstable and is easily oxidized by air, and the ITO electrode is corroded by the PEDOT PSS due to the hygroscopicity and acidity of a PSS chain, so that the performance and the service life of the device are influenced. NiO is used as a p-type semiconductor, is a substitute material of PEDOT (Poly ethylene glycol ether ketone) PSS (Poly ethylene glycol ether ketone) due to good environmental stability, and solves the problem of corrosion of an ITO (indium tin oxide) electrode. PSS is replaced by PEDOT, so that hole injection efficiency of the QLED device is low, the problem of unbalanced carrier injection is caused, and the use of the QLED device is also influenced.

Disclosure of Invention

In view of the above, the present invention aims to provide a positive QLED device based on a double hole injection layer and a method for manufacturing the same. The positive QLED device provided by the invention adopts NiO/PEDOT PSS double-layer hole injection layers, so that the problem of corrosion to an ITO electrode can be solved, a hole injection barrier can be effectively reduced, the hole injection efficiency is improved, and carriers are balanced.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a positive QLED device based on a double-layer hole injection layer, which comprises:

the structure comprises a glass substrate with an ITO transparent electrode, and a first hole injection layer, a second hole injection layer, a hole transport layer, a quantum dot light emitting layer, an electron transport layer and a top electrode layer which are sequentially arranged on the surface of the ITO transparent electrode from bottom to top;

the first hole injection layer is a NiO layer, and the thickness of the first hole injection layer is 10-20 nm;

the second hole injection layer is a PEDOT PSS layer, and the thickness of the second hole injection layer is 20-40 nm.

Preferably, the material of the hole transport layer is one or more of PVK, TFB, poly-TPD, TCTA and CBP-V; the thickness of the hole transport layer is 20-35 nm.

Preferably, the quantum dot light emitting layer is one or more of a ZnCdSeS/ZnS green light quantum dot light emitting layer, a CdZnSe/ZnSe/ZnS red light quantum dot light emitting layer and a CdSe/ZnS blue light quantum dot light emitting layer; the thickness of the quantum dot light-emitting layer is 20-30 nm.

Preferably, the electron transmission layer is a ZnO layer, and the thickness of the electron transmission layer is 25-35 nm.

Preferably, the top electrode layer is an Al, Ag, Cu or Au electrode layer; the thickness of the top electrode layer is 80-100 nm.

The invention provides a preparation method of a positive type QLED device based on a double-layer hole injection layer, which comprises the following steps:

carrying out ultraviolet ozone pretreatment on the glass substrate with the ITO transparent electrode to obtain a pretreated glass substrate;

mixing nickel acetate tetrahydrate, monoethanolamine and ethanol, and carrying out sol-gelation to obtain a NiO precursor solution; spin-coating the NiO precursor solution and PEDOT on the surface of the pretreated glass substrate in sequence, performing first annealing after PSS, and forming a first hole injection layer and a second hole injection layer on the surface of the glass substrate; the temperature of the first annealing is 90-170 ℃;

carrying out second annealing after spin-coating the solution of the hole transport layer on the surface of the second hole injection layer to form a hole transport layer;

spin-coating the solution of the quantum dot light-emitting layer on the surface of the hole transport layer, and then carrying out third annealing to form the quantum dot light-emitting layer;

carrying out fourth annealing after the solution of the electron transport layer is coated on the surface of the quantum dot light-emitting layer in a spin mode, and forming the electron transport layer;

and (3) evaporating a top electrode on the surface of the electron transport layer, and then packaging the formed device to obtain the positive QLED device based on the double-layer hole injection layer.

Preferably, the dosage ratio of the nickel acetate tetrahydrate, the monoethanolamine and the ethanol is 1mmol: 50-70 muL: 8-15 mL; the sol-gelation temperature is 50-70 ℃, and the time is 2-3 h; and the rotation speed of the spin coating of the NiO precursor solution is 3000-5000 rpm.

Preferably, the rotation speed of the spin coating of the PEDOT: PSS is 2000-4000 rpm.

Preferably, the time of the ultraviolet ozone pretreatment is 10-25 min.

Preferably, the solution of the hole transport layer is formed by dissolving one or more of PVK, TFB, poly-TPD, TCTA and CBP-V in chlorobenzene or toluene; the concentration of the solution of the hole transport layer is 8-10 mg/mL; the rotating speed of the solution for spin coating the hole transport layer is 2000-4000 rpm;

the solution of the quantum dot light-emitting layer is formed by dissolving one or more of ZnCdSeS/ZnS green light quantum dots, CdZnSe/ZnSe/ZnS red light quantum dots and CdSe/ZnS blue light quantum dots in n-octane; the concentration of the solution of the quantum dot light-emitting layer is 10-18 mg/mL; the rotating speed of the solution for spin coating the quantum dot light-emitting layer is 2000-4000 rpm;

the solution of the electron transport layer is formed by dissolving ZnO in ethanol; the concentration of the solution of the electron transport layer is 25-35 mg/mL; the rotating speed of the solution for spin coating the electron transport layer is 2000-4000 rpm.

The invention provides a positive QLED device based on a double-layer hole injection layer, which comprises: the structure comprises a glass substrate with an ITO transparent electrode, and a first hole injection layer, a second hole injection layer, a hole transport layer, a quantum dot light emitting layer, an electron transport layer and a top electrode layer which are sequentially arranged on the surface of the ITO transparent electrode from bottom to top; the first hole injection layer is a NiO layer, and the thickness of the first hole injection layer is 10-20 nm; the second hole injection layer is a PEDOT PSS layer, and the thickness of the second hole injection layer is 20-40 nm. According to the invention, the NiO layer is used as a first hole injection layer on the surface of the glass substrate, and the PEDOT PSS layer is used as a second hole injection layer, so that on one hand, the NiO layer has good stability, can be used as a barrier layer between the ITO transparent electrode and the PEDOT PSS layer, can prevent the ITO electrode from being corroded by the hygroscopicity and acidity of the PEDOT PSS, and has better film forming property when NiO forms a film on the surface of the ITO substrate compared with the PEDOT PSS; and the PEDOT/PSS layer has low barrier and high hole injection efficiency, and can solve the problem of low hole injection efficiency of the NiO layer. The positive QLED device provided by the invention adopts NiO/PEDOT PSS double-layer hole injection layers, not only can solve the problem of corrosion to an ITO electrode, but also can effectively reduce a hole injection barrier, improve the hole injection efficiency and balance carriers, further improve the efficiency and prolong the service life of the positive QLED device, is applied to the electronic display fields of light-emitting diodes, solar cells, electronic textiles and the like, and has wide application prospect. The embodiment result shows that the maximum current efficiency of the positive QLED device based on the double-layer hole injection layer is 78.67cd/A, the External Quantum Efficiency (EQE) is 18.12 percent, and the power efficiency is 77.23 lm/W.

The preparation method of the positive type QLED device based on the double-layer hole injection layer is simple in process, easy to operate and convenient for large-scale production.

Drawings

Fig. 1 is a schematic view of the structure of a positive type QLED device constructed in example 1;

FIG. 2 is a graph showing the effect of the contact angle test of the NiO precursor solution and the conventional PEDOT, PSS, on the ITO substrate in example 1, and FIG. 2 (a) is a graph showing the effect of the contact angle test of the NiO precursor solution on the ITO substrate, and (b) is a graph showing the effect of the contact angle test of the conventional PEDOT, PSS, on the ITO substrate;

fig. 3 is an SEM test chart of the NiO thin film layer formed in example 1;

FIG. 4 is an AFM image of the NiO thin film formed in example 1 and an ITO substrate, and in FIG. 4, (a) is an AFM image of the ITO substrate, and (b) is an AFM image of the NiO thin film;

FIG. 5 is an XRD pattern of NiO films formed at different annealing temperatures;

FIG. 6 is a graph of the transmittance of NiO films formed at different annealing temperatures;

FIG. 7 is a graph showing the photoelectric performance of the green QLED devices constructed in examples 1-3 at different annealing temperatures, wherein (a) in FIG. 7 is a J-V-L characteristic graph, and (b) is η_A-L-η_PA graph;

FIG. 8 is a graph showing the photoelectric properties of the red QLED device constructed in example 4, in which (a) of FIG. 8 is a J-V-L characteristic graph, and (b) is η_A-L-η_PA graph;

FIG. 9 is a graph showing the photoelectric performance of the blue QLED device constructed in example 5, in which (a) of FIG. 9 is a J-V-L characteristic graph, and (b) is η_A-L-η_PGraph is shown.

Detailed Description

The invention relates to a positive type QLED device based on a double-layer hole injection layer, which comprises a glass substrate with an ITO (indium tin oxide) transparent electrode. The invention has no special requirements on the ITO transparent electrode, and the ITO transparent electrode well known by the technicians in the field can be adopted; the ITO transparent electrode is an n-type semiconductor material with high conductivity and high visible light transmittance, and serves as an anode of the QLED device in the invention.

The invention provides a positive QLED device based on double-layer hole injection layers, which comprises a first hole injection layer arranged on the surface of an ITO transparent electrode. In the invention, the first hole injection layer is a NiO layer, and the thickness of the first hole injection layer is 10-20 nm. The NiO layer is used as the first hole injection layer, the NiO layer is good in stability, and can be used as a barrier layer between the ITO transparent electrode and the PEDOT PSS layer, so that the moisture absorption and acidity of the PEDOT PSS can be prevented from corroding the ITO electrode.

The positive QLED device based on the double-layer hole injection layer comprises a second hole injection layer arranged on the surface of the first hole injection layer. In the invention, the second hole injection layer is a PEDOT PSS layer with the thickness of 20-40 nm, preferably 22-28 nm. According to the invention, the PEDOT PSS layer is used as the second hole injection layer, the PEDOT PSS layer has low barrier and high hole injection efficiency, and the problem of low hole injection efficiency of the NiO layer can be solved.

The positive QLED device based on the double-layer hole injection layer comprises a hole transport layer arranged on the surface of the second hole injection layer. In the present invention, the material of the hole transport layer is preferably one or more of PVK (polyvinylcarbazole), TFB (poly [9, 9-dioctylfluorene-co-N- (4-butylphenyl) -diphenylamine ]), poly-TPD (poly [ [ (4-butylphenyl) imino ] [1,1 '-biphenyl ] ]), TCTA (4,4',4 ″ -tris (carbazol-9-yl) triphenylamine), and CBP-V (4,4'-N, N' -dicarbazolylbiphenyl), and in the present embodiment, the hole transport layer is preferably TFB. In the present invention, the thickness of the hole transport layer is preferably 20 to 35nm, and more preferably 20 to 30 nm. One or more of PVK, TFB, poly-TPD, TCTA and CBP-V are used as hole transport layers, so that different light emitting layers can be matched.

The invention provides a positive QLED device based on a double-layer hole injection layer, which comprises a quantum dot light-emitting layer arranged on the surface of a hole transport layer. In the invention, the quantum dot light emitting layer is preferably one or more of a ZnCdSeS/ZnS green light quantum dot light emitting layer, a CdZnSe/ZnSe/ZnS red light quantum dot light emitting layer and a CdSe/ZnS blue light quantum dot light emitting layer; in the embodiment of the invention, a ZnCdSeS/ZnS green light quantum dot light-emitting layer, a CdZnSe/ZnSe/ZnS red light quantum dot light-emitting layer and a CdSe/ZnS blue light quantum dot light-emitting layer are respectively used as quantum dot light-emitting layers. In the invention, the thickness of the quantum dot light-emitting layer is preferably 20-30 nm, and more preferably 20-25 nm. One or more of a ZnCdSeS/ZnS green light quantum dot light-emitting layer, a CdZnSe/ZnSe/ZnS red light quantum dot light-emitting layer and a CdSe/ZnS blue light quantum dot light-emitting layer are used as quantum dot light-emitting layers to obtain a red-green-blue three-primary-color light-emitting device.

The invention provides a positive QLED device based on a double-layer hole injection layer, which comprises an electron transport layer arranged on the surface of a quantum dot light-emitting layer. In the present invention, the electron transport layer is preferably a ZnO layer; the thickness of the electron transport layer is preferably 25-35 nm, and more preferably 25-30 nm. The ZnO layer is used as the electron transport layer, and is beneficial to electron injection.

The positive QLED device based on the double-layer hole injection layer comprises a top electrode layer arranged on the surface of an electron transport layer. In the invention, the top electrode layer is an Al, Ag, Cu or Au electrode layer; in the embodiment of the present invention, the top electrode layer is preferably an Al electrode layer. In the invention, the thickness of the top electrode layer is preferably 80-100 nm, and more preferably 90-100 nm; the top electrode serves as the cathode of the QLED device.

The positive QLED device provided by the invention adopts NiO/PEDOT PSS double-layer hole injection layers, not only can solve the problem of corrosion to an ITO electrode, but also can effectively reduce a hole injection barrier, improve the hole injection efficiency and balance carriers, further improve the efficiency and prolong the service life of the positive QLED device, is applied to the electronic display fields of light-emitting diodes, solar cells, electronic textiles and the like, and has wide application prospect.

The invention carries out ultraviolet ozone pretreatment on the glass substrate with the ITO transparent electrode to obtain the pretreated glass substrate. The source of the glass substrate with the ITO transparent electrode is not particularly required by the invention, and the commercially available products well known to the person skilled in the art can be adopted; in the examples of the present invention, the glass substrate with an ITO transparent electrode was purchased from Tinwell Technology Ltd. The glass substrate with the ITO transparent electrode is preferably cleaned before ultraviolet ozone pretreatment, and the cleaning method is not particularly required by the invention, and the glass substrate with the ITO transparent electrode is cleaned by a cleaning method well known to a person skilled in the art. In the invention, the time of the ultraviolet ozone pretreatment is preferably 10-25 min, and specifically may be 10min, 15min, 20min or 25 min. In the embodiment of the present invention, the cleaned glass substrate with the ITO transparent electrode is preferably placed in an ultraviolet ozone treatment apparatus, which is available from shanghai four-color trade company, ltd, for ultraviolet ozone pretreatment. According to the invention, the glass substrate with the ITO transparent electrode is subjected to ultraviolet ozone pretreatment, so that the ITO work function can be increased, the hydrophilicity of the surface of the substrate is enhanced, and the wettability between the NiO first hole injection thin film layer and the substrate is enhanced.

The method mixes nickel acetate tetrahydrate, monoethanolamine and ethanol for sol-gelation to obtain NiO precursor solution. In the invention, the dosage ratio of the nickel acetate tetrahydrate, the monoethanolamine and the ethanol is preferably 1mmol: 50-70 muL: 8-15 mL, and more preferably 1mmol:60 muL: 10 mL. The sources of the nickel acetate tetrahydrate, monoethanolamine and ethanol are not particularly required in the present invention, and commercially available products well known to those skilled in the art may be used. In the invention, the sol-gelation temperature is preferably 50-70 ℃, more preferably 60 ℃, and the time is preferably 2-3 h, more preferably 2 h; the specific operation of sol-gelation is preferably: sequentially adding nickel acetate tetrahydrate, monoethanolamine and ethanol into a sample bottle, and stirring the obtained mixed solution at the temperature of 50-70 ℃ to perform sol-gelation. In the invention, the nickel acetate tetrahydrate is used as a precursor of nickel, and hydrolysis and polycondensation reactions are carried out in organic media monoethanolamine and ethanol to realize sol-gelation, so as to obtain the NiO precursor solution. After the NiO precursor solution is obtained, the NiO precursor solution is preferably filtered by using a filter head with the diameter of 0.45 mu m, and then the subsequent spin coating is carried out. The method adopts a sol-gel method to prepare the NiO first hole injection layer, and has the advantages of easily obtained raw materials, simple preparation method and low cost.

After the NiO precursor solution is obtained, the NiO precursor solution and PEDOT are sequentially spin-coated on the surface of the pretreated glass substrate, first annealing is carried out after PSS, and a first hole injection layer and a second hole injection layer are formed on the surface of the glass substrate. In the invention, the rotation speed of the spin coating of the NiO precursor solution is preferably 3000-5000 rpm, and specifically can be 3000rpm, 4000rpm or 5000 rpm; the time for spin coating the NiO precursor solution is preferably 50-70 s; the amount of NiO precursor solution in each spin coating is subject to the thickness requirement of finally reaching the first hole injection layer. The invention has no special requirements on the operation method of the spin coating, and the spin coating method known by the technical personnel in the field is adopted to ensure the uniformity of the spin coating. PSS is not particularly required to be sourced, and commercial products well known to those skilled in the art can be adopted; in the examples of the invention, the PEDOT: PSS model is CLEVOS PVPAI 4083 (aqueous solution consisting of PEDOT and PSS) available from Heraeus. According to the invention, preferably, 0.45-micrometer filter head needle tubes are used for filtering the PEDOT: PSS, and then spin coating is carried out. PSS is preferably spun at the rotating speed of 2000-4000 rpm, more preferably 2500-3000 rpm; PSS is preferably coated for 40-50 s, more preferably 45 s; PSS amount is subject to meeting the thickness requirement of the second hole injection layer during each spin coating. In the invention, the temperature of the first annealing is 90-170 ℃, preferably 110-150 ℃, and more preferably 130 ℃; the first annealing time is preferably 10-30 min, and more preferably 15-20 min. In the first annealing process, the NiO precursor solution is converted into NiO, so that a first hole injection layer is formed on the surface of the glass substrate with the ITO transparent electrode; and volatilizing a solvent of PEDOT and PSS to form a second hole injection layer on the surface of the first hole injection layer.

After the second hole injection layer is formed, the method carries out second annealing after the solution of the hole transport layer is coated on the surface of the second hole injection layer in a spin mode, and the hole transport layer is formed on the surface of the second hole injection layer. In the present invention, the solution of the hole transport layer is preferably formed by dissolving one or more of PVK, TFB, poly-TPD, TCTA, and CBP-V, each of which is preferably in a powder form, in chlorobenzene or toluene; the concentration of the solution of the hole transport layer is preferably 8-10 mg/mL. Further, when the hole transport layer is preferably PVK, the solution of the hole transport layer is preferably formed by dissolving PVK in toluene, and the concentration of the solution of the hole transport layer is preferably 8 mg/mL; when the hole transport layer is preferably TFB, the solution of the hole transport layer is preferably formed by dissolving TFB in chlorobenzene, and the concentration of the solution of the hole transport layer is preferably 8 mg/mL; when the hole transport layer is preferably poly-TPD, TCTA or CBP-V, the solution of the hole transport layer is preferably formed by dissolving poly-TPD, TCTA or CBP-V in chlorobenzene, and the concentration of the solution of the hole transport layer is preferably 10 mg/mL. The present invention does not require any particular source for the PVK, TFB, poly-TPD, TCTA and CBP-V, and commercially available products well known to those skilled in the art may be used. The solution of the hole transport layer is preferably filtered by using a 0.20 μm filter head and then spin-coated. In the invention, the rotating speed of the solution for spin coating the hole transport layer is preferably 2000-4000 rpm, more preferably 2500 rpm; the time for spin coating the solution of the hole transport layer is preferably 40-50 s; the amount of the solution for spin-coating the hole transport layer at each time is based on meeting the thickness requirement of the hole transport layer. In the invention, the temperature of the second annealing treatment is preferably 100-200 ℃, more preferably 150-160 ℃, and the time is preferably 10-30 min, more preferably 25-30 min. The spin-coated solution of the hole transport layer is annealed to enable the PVK, TFB, poly-TPD, TCTA or CBP-V to generate a cross-linking reaction, so that the hole transport layer is formed on the surface of the second hole injection layer.

After the hole transport layer is formed, the solution of the quantum dot light-emitting layer is coated on the surface of the hole transport layer in a spin mode, then third annealing is carried out, and the quantum dot light-emitting layer is formed on the surface of the hole transport layer. In the invention, the solution of the quantum dot light-emitting layer is preferably formed by dissolving one or more of ZnCdSeS/ZnS green quantum dots, CdZnSe/ZnSe/ZnS red quantum dots and CdSe/ZnS blue quantum dots in n-octane; the concentration of the solution of the quantum dot light-emitting layer is preferably 10-18 mg/mL, and more preferably 15-18 mg/mL. The invention has no special requirements on the sources of the ZnCdSeS/ZnS green quantum dots, the CdZnSe/ZnSe/ZnS red quantum dots and the CdSe/ZnS blue quantum dots, and the blue-light quantum dots are prepared by commercial products or preparation methods which are well known by the technicians in the field; in the embodiment of the invention, the ZnCdSeS/ZnS green quantum dots and the CdZnSe/ZnSe/ZnS red quantum dots are the references' Effect of shell cracking on the optical properties in CdSe/CdS/Zn_0.5Cd_0.5S/ZnS and CdSe/CdS/Zn_xCd_1-xS/ZnS core/multishell nanocrystals "(Xu S, Shen H, Zhou C, et al. journal of physical Chemistry C,2011,115(43): 20876-. In the invention, the solution of the quantum dot light-emitting layer is preferably filtered by using a filter tip with the diameter of 0.20 mu m and then is subjected to spin coating. In the invention, the rotating speed of the solution for spin coating the quantum dot light-emitting layer is preferably 2000-4000 rpm, more preferably 2500-3000 rpm; the time for spin coating the solution of the quantum dot light-emitting layer is preferably 40-60 s; the solution amount of the quantum dot light-emitting layer is subject to meeting the thickness requirement of the quantum dot light-emitting layer. In the invention, the temperature of the third annealing is preferably 50-70 ℃, more preferably 60 ℃, and the time is preferably 10-30 min, more preferably 20-30 min; hair brushAnd annealing the solution of the quantum dot light-emitting layer after spin coating to volatilize the solvent in the solution of the quantum dot light-emitting layer, so that the quantum dot light-emitting layer is formed on the surface of the hole transport layer.

After the quantum dot light emitting layer is formed, the solution of the electron transmission layer is coated on the surface of the quantum dot light emitting layer in a spin mode, and then fourth annealing is carried out, so that the electron transmission layer is formed. In the present invention, the solution of the electron transport layer is preferably formed by dissolving ZnO in ethanol; the concentration of the solution of the electron transport layer is preferably 25-35 mg/mL, and more preferably 30-35 mg/mL. The invention preferably uses a 0.20 μm filter head to filter the solution of the electron transport layer and then spin-coat. In the invention, the rotating speed of the solution for spin coating the electron transport layer is preferably 2000-4000 rpm, more preferably 3000-4000 rpm; the time for spin-coating the solution of the electron transport layer is preferably 40-60 s; the amount of the solution for spin-coating the electron transport layer at a time is such that the thickness requirement of the electron transport layer is satisfied. After the solution of the electron transport layer is spin-coated, the edge of the glass substrate is preferably wiped by toluene, and after the ITO transparent electrode is exposed, the solution of the spin-coated electron transport layer is annealed; the fourth annealing temperature is preferably 50-100 ℃, preferably 60-80 ℃, and the time is preferably 10-30 min. The solution of the electron transport layer after spin coating is annealed, so that the solvent in the solution of the electron transport layer is volatilized, and the electron transport layer is formed on the surface of the quantum dot light-emitting layer.

After the electron transport layer is formed, the formed device is packaged after the top electrode is evaporated on the surface of the electron transport layer, and the positive QLED device based on the double-layer hole injection layer is obtained. In the embodiment of the invention, the evaporation is preferably carried out in a thermal evaporation coating machine; the degree of vacuum of the evaporation is preferably less than 5 x 10^-7mbar, the evaporation rate being preferably

The present invention does not require any particular method for operating the vapor deposition, and a vapor deposition method known to those skilled in the art may be used. In the invention, the packaging is excellentSelecting ultraviolet curing resin, specifically: and packaging the device formed after the top electrode is evaporated by using ultraviolet curing resin, covering a cover glass, and curing under the irradiation of an ultraviolet lamp to finish packaging. The ultraviolet curing resin is not particularly required by the invention, and the ultraviolet curing resin well known to those skilled in the art can be adopted, and in the embodiment of the invention, the adopted ultraviolet curing resin is ultraviolet glue with the model number of NOA 61. In the invention, the power of the ultraviolet lamp irradiation is preferably 6W, and the wavelength is preferably 365 nm; the curing time is preferably 2-5 min.

The preparation method of the positive QLED device based on the double-layer hole injection layer is simple in process, easy to operate and convenient for large-scale production.

The following provides a detailed description of the dual-layer hole injection layer-based positive QLED device and the method for manufacturing the same, with reference to the following examples, which should not be construed as limiting the scope of the invention.

Example 1

A positive QLED device (green quantum dot light emitting diode device) based on NiO/PEDOT PSS double-layer hole injection layer is constructed as ITO/NiO/PEDOT PSS/TFB/QDs/ZnO/Al, as shown in FIG. 1: and ITO is used as an anode of the QLED device, NiO/PEDOT, namely PSS, TFB, ZnCdSeS/ZnSQDs and ZnO are respectively used as a hole injection layer, a hole transport layer, a quantum dot light-emitting layer and an electron transport layer of the QLED device, and Al is used as a cathode, namely a top electrode, of the QLED device.

The construction process of the QLED device is as follows:

(1) and (3) quickly putting the cleaned glass substrate with the ITO transparent electrode into an ultraviolet ozone treatment instrument, and carrying out ultraviolet ozone pretreatment for 15min to obtain the pretreated glass substrate.

(2) Preparing NiO by adopting a sol-gel method: putting 1mmol of precursor material nickel acetate tetrahydrate into a 25mL sample bottle, adding 60 mu L of monoethanolamine solution into the sample bottle by using a liquid transfer gun, finally adding 10mL of ethanol solution, placing the sample bottle on a stirring table, stirring for 2h at 60 ℃, uniformly dissolving to obtain NiO precursor solution, filtering the NiO precursor solution by using a filter head with the diameter of 0.45 mu m, sucking 60 mu L of filtered NiO precursor solution by using the liquid transfer gun, dripping the filtered NiO precursor solution into the center of an ITO substrate, and keeping the substrate to spin-coat for 60s at 5000 rpm.

(3) Sucking PEDOT (PSS) (model number: CLEVOS P VP AI 4083) by using a filter tip needle tube with 0.45 mu m, dripping the filtered PEDOT (PSS) solution on an ITO substrate spin-coated with NiO precursor solution, and keeping the substrate spin-coated for 45s at 2500 rpm; and taking down the substrate, wiping the edge of the substrate with ultrapure water to expose an electrode, annealing at 130 ℃ for 15min on a heating table, taking down the substrate after annealing is finished, and sequentially forming a NiO thin film layer (the thickness is 15nm) and a PEDOT (the thickness is about 25nm) PSS thin film layer (the thickness is about 25nm) on the ITO substrate, wherein the NiO thin film layer and the PEDOT (the thickness is about 25nm) are marked as ITO/NiO/PEDOT and the PSS substrate.

(4) Filtering TFB solution (8mg/mL) dissolved in chlorobenzene by using a 0.20-micron filter head, sucking 60-microliter of the filtered TFB solution by using a pipette gun, dripping the filtered TFB solution on the ITO/NiO/PEDOT: PSS substrate, and spin-coating the substrate for 45s at 2500 rpm; and taking down the substrate, placing the substrate on a heating table, carrying out annealing treatment at 150 ℃ for 30min, taking down the substrate after the annealing is finished, and forming a TFB layer on the ITO/NiO/PEDOT/PSS substrate, wherein the thickness of the TFB layer is about 20nm and the TFB layer is marked as the ITO/NiO/PEDOT/PSS/TFB substrate.

(5) Filtering ZnCdSeS/ZnS QDs solution (18mg/mL) dissolved in n-octane by using a filter head with the diameter of 0.20 μm, sucking 60 μ L of filtered QDs solution by using a pipette gun, dripping the filtered QDs solution on the ITO/NiO/PEDOT: PSS/TFB substrate, and keeping the substrate to spin-coat for 45s at the condition of 2500 rpm; taking down the substrate, placing the substrate on a heating table, carrying out annealing treatment at 60 ℃ for 30min, taking down the substrate after the annealing is finished, and forming a QDs layer (quantum dot layer) on the ITO/NiO/PEDOT (PSS/TFB) substrate, wherein the thickness of the QDs layer is about 25nm and the QDs layer is marked as the ITO/NiO/PEDOT (PSS/TFB/QDs) substrate.

(6) Filtering ZnO solution (30mg/mL) dissolved in ethanol with 0.20 μm filter head, sucking 60 μ L of filtered ZnO solution with pipette, dropping on the ITO/NiO/PEDOT: PSS/TFB/QDs substrate, and spin-coating at 3500rpm for 45 s; and then wiping the edge of the substrate by using a toluene solution to expose an electrode, placing the substrate on a heating table, and carrying out annealing treatment at 60 ℃ for 30min to form a ZnO thin film layer with the thickness of about 25nm on the ITO/NiO/PEDOT/PSS/TFB/QDs substrate, wherein the thickness is marked as ITO/NiO/PEDOT/PSS/TFB/QDs/ZnO substrate.

(7) Placing the ITO/NiO/PEDOT, PSS/TFB/QDs/ZnO substrate in a thermal evaporation coating machine, and when the vacuum degree of the coating machine is lower than 5.00 multiplied by 10^-7Aluminium granules (density 2.702 g/cm) were carried out at mbar³Boiling point of 2467 deg.C, melting point of 660.4 deg.C, purity of 99.99%), and maintaining evaporation rate

And breaking vacuum after the evaporation is finished, taking out the substrate, forming an aluminum electrode on the ITO/NiO/PEDOT, PSS/TFB/QDs/ZnO substrate, wherein the thickness of the electrode is 100nm, and the formed device is marked as an ITO/NiO/PEDOT, PSS/TFB/QDs/ZnO/Al device.

(8) Packaging of the device: and packaging the constructed ITO/NiO/PEDOT/PSS/TFB/QDs/ZnO/Al devices with ultraviolet curing resin and cover glass, and curing under the irradiation of an ultraviolet lamp to obtain the positive QLED device based on the NiO/PEDOT/PSS double-layer hole injection layer.

And (3) testing the contact angle of the NiO precursor solution in the step (2) on the ITO substrate, comparing the contact angle with the contact angle of traditional PEDOT (PSS) on the ITO substrate to evaluate the film forming property of the NiO precursor solution, wherein the test result is shown in FIG. 2, wherein (a) in FIG. 2 is the contact angle test result of the NiO precursor solution on the ITO substrate, and (b) is the contact angle test result of traditional PEDOT (PSS) on the ITO substrate. As can be seen from FIG. 2, the contact angle of the NiO precursor solution on the ITO substrate is 7.43 degrees, while the contact angle of the conventional PEDOT: PSS on the ITO substrate is 14.9 degrees, and therefore, the wettability of the NiO precursor solution on the ITO substrate is better.

The NiO thin film layer formed in step (3) was subjected to SEM test, and the test results are shown in fig. 3. As can be seen from FIG. 3, the NiO surface has good film-forming property, and the thin film is dense and flat.

And (3) performing an AFM test on the NiO thin film formed in the step (3) and the ITO substrate, wherein the test results are shown in FIG. 4, and in FIG. 4, (a) is an AFM image of the ITO substrate, and (b) is an AFM image of the NiO thin film. As can be seen from FIG. 4, the surface roughness of the ITO substrate is close to 3.0nm, the surface roughness of the NiO film in the range of 2.0 μm × 2.0 μm is less than 2.0nm, and when the QLED device is constructed by the NiO film with lower roughness, the method is beneficial to reducing the hole injection barrier and improving the hole injection efficiency.

The elemental composition and the crystal structure of the NiO film formed in step (3) at the annealing temperature of 130 ℃ are characterized, and the results are shown in fig. 5(XRD chart), and in order to illustrate the influence of the annealing temperature on the formation of the crystal structure of the NiO film, XRD charts at the annealing temperature of 200 ℃ and the annealing temperature of 500 ℃ are also shown in fig. 5, respectively. As can be seen from fig. 5, the intensity of the NiO diffraction peak gradually increased with the increase of the annealing temperature, which indicates that the crystallinity of the NiO film increased as the temperature increased to favor the growth crystallization of NiO; from an XRD (X-ray diffraction) pattern of the NiO film after annealing at 130 ℃, the NiO is amorphous, the amorphous NiO has good film forming property and smoother film forming, and the method is more favorable for reducing a hole injection barrier and improving the hole injection efficiency.

The transmittance test of the NiO film formed in step (3) at the annealing temperature of 130 ℃ was performed, and the test results are shown in fig. 6, and in order to illustrate the influence of the annealing temperature on the transmittance of the NiO film, a transmittance curve at the annealing temperature of 180 ℃ is also shown in fig. 6. As can be seen from fig. 6, as the annealing temperature increased, the NiO film transmittance gradually decreased; the NiO film has transmittance of more than 80% in the whole visible light wavelength range (400 nm-760 nm) and transmittance of more than 90% in the green light wavelength range (500 nm-577 nm).

The green QLED device (NiO film annealing temperature of 130 ℃) constructed in example 1 was subjected to photoelectric property test, and the test results are shown in FIG. 7, wherein (a) in FIG. 7 is a J-V-L diagram, and (b) is eta_A-L-η_PFIG. 7 shows a standard device, referred to as ITO// PEDOT device, having the structure PSS/TFB/QDs/ZnO/Al; the corresponding device performance parameters are listed in table 1.

Example 2

The annealing temperature in the step (3) was changed to 110 ℃ and the rest was the same as in example 1.

The NiO film formed in example 2 at the annealing temperature of 110 ℃ was subjected to a transmittance test, and the test results are shown in fig. 6. As can be seen from FIG. 6, the NiO film has a transmittance of 80% or more over the entire visible light wavelength range (400nm to 760nm) and a transmittance of 90% or more over the green light wavelength range (500nm to 577 nm).

The green QLED device (NiO film annealing temperature of 110 ℃) constructed in the example 2 is subjected to photoelectric property test, and the test result is shown in figure 7; the corresponding device performance parameters are listed in table 1.

Example 3

The annealing temperature in the step (3) was changed to 150 ℃ and the rest was the same as in example 1.

The NiO film formed in example 3 at the annealing temperature of 150 c was subjected to a transmittance test, and the test results are shown in fig. 6. As can be seen from FIG. 6, the NiO film has a transmittance of 80% or more over the entire visible light wavelength range (400nm to 760nm) and a transmittance of 90% or more over the green light wavelength range (500nm to 577 nm).

The green QLED device (NiO film annealing temperature of 150 ℃) constructed in the embodiment 3 is subjected to photoelectric property test, and the test result is shown in figure 7; the corresponding device performance parameters are listed in table 1.

TABLE 1 Performance of Green QLED devices at different annealing temperatures for examples 1-3

As can be seen from fig. 7 and table 1, the performance of the green QLED devices constructed by NiO in examples 1 to 3 is significantly improved compared with that of the standard devices, and the device performance is optimal when the annealing temperature of NiO is 130 ℃, the maximum current efficiency is 78.67cd/a, the EQE (external quantum efficiency) is 18.12%, and the power efficiency is 77.23 lm/W.

Example 4

A positive QLED device (red quantum dot light emitting diode device) based on NiO/PEDOT PSS double-layer hole injection layer is formed by ITO/NiO/PEDOT PSS/TFB/QDs/ZnO/Al: and ITO is used as an anode of the QLED device, NiO/PEDOT, namely PSS, TFB, CdZnSe/ZnSe/ZnS QDs and ZnO are respectively used as a hole injection layer, a hole transport layer, a quantum dot light emitting layer and an electron transport layer of the QLED device, and Al is used as a cathode, namely a top electrode, of the QLED device.

The construction process of the QLED device is as follows:

(5) Filtering CdZnSe/ZnSe/ZnS QDs solution (18mg/mL) dissolved in n-octane by using a filter head with the diameter of 0.20 μm, sucking 60 μ L of the filtered QDs solution by using a pipette gun, dropping the filtered QDs solution on the ITO/NiO/PEDOT: PSS/TFB substrate, and keeping the substrate to spin-coat for 45s at 3000 rpm; taking down the substrate, placing the substrate on a heating table, carrying out annealing treatment at 60 ℃ for 30min, taking down the substrate after the annealing is finished, and forming a QDs layer (quantum dot layer) on the ITO/NiO/PEDOT (PSS/TFB) substrate, wherein the thickness of the QDs layer is about 25nm and the QDs layer is marked as the ITO/NiO/PEDOT (PSS/TFB/QDs) substrate.

The red QLED device constructed in example 4 was subjected to photoelectric property test, and the test results are shown in FIG. 8, FIG. 8 (a)Is a J-V-L characteristic curve diagram, and (b) is eta_A-L-η_PA graph; the corresponding device performance parameters are listed in table 2.

Table 2 performance of red QLED devices constructed in example 4

As can be seen from FIG. 8 and Table 2, the performance of the red QLED device constructed by NiO is improved compared with the standard device, the maximum current efficiency and the power efficiency are respectively 19.64cd/A and 28.05lm/W, and the EQE is 14.10%.

Example 5

A positive QLED device (blue quantum dot light emitting diode device) based on NiO/PEDOT PSS double-layer hole injection layers is formed by an ITO/NiO/PEDOT PSS/CBP-V/QDs/ZnO/Al: the ITO is used as an anode of the QLED device, NiO/PEDOT, namely PSS, CBP-V, CdSe/ZnS QDs and ZnO are respectively used as a hole injection layer, a hole transport layer, a quantum dot light-emitting layer and an electron transport layer of the QLED device, and Al is used as a cathode, namely a top electrode, of the QLED device.

The construction process of the QLED device is as follows:

(4) Filtering CBP-V solution (10mg/mL) dissolved in chlorobenzene by using a 0.20 mu m filter head, sucking 60 mu L of filtered CBP-V solution by using a pipette and dripping the filtered CBP-V solution on the ITO/NiO/PEDOT: PSS substrate, and spin-coating the substrate for 45s at 2500 rpm; and taking down the substrate, placing the substrate on a heating table, carrying out annealing treatment at 150 ℃ for 30min, taking down the substrate after the annealing is finished, and forming a CBP-V layer with the thickness of about 20nm on the ITO/NiO/PEDOT/PSS substrate, wherein the thickness is marked as ITO/NiO/PEDOT/PSS/CBP-V substrate.

(5) Filtering CdSe/ZnS QDs solution (10mg/mL) dissolved in n-octane with a 0.20 μm filter head, sucking 60 μ L of the filtered QDs solution with a pipette, dropping the filtered QDs solution on the ITO/NiO/PEDOT: PSS/CBP-V substrate, keeping the substrate at 3000rpm, spin-coating for 45s, taking down the substrate, placing the substrate on a heating table, annealing at 60 ℃ for 30min, taking down the substrate after the annealing is finished, and forming a QDs layer (namely a quantum dot layer) on the ITO/NiO/PEDOT: PSS/TFB substrate, wherein the thickness of the QDs layer is about 20nm and the QDs layer is marked as ITO/NiO/PEDOT: PSS/CBP-V/QDs substrate.

(6) Filtering ZnO solution (30mg/mL) dissolved in ethanol with a 0.20 μm filter head, sucking 60 μ L of the filtered ZnO solution with a pipette, dropping the filtered ZnO solution on the ITO/NiO/PEDOT, PSS/CBP-V/QDs substrate, and spin-coating the substrate at 3500rpm for 45 s; and then wiping the edge of the substrate by using a toluene solution to expose an electrode, placing the substrate on a heating table to carry out annealing treatment for 30min at 60 ℃, and forming a ZnO thin film layer with the thickness of 25nm on the ITO/NiO/PEDOT, PSS/CBP-V/QDs substrate, wherein the thickness is marked as ITO/NiO/PEDOT, PSS/CBP-V/QDs/ZnO substrate.

(7) Placing the ITO/NiO/PEDOT, PSS/CBP-V/QDs/ZnO substrate in a thermal evaporation wayIn the film coating machine, when the vacuum degree of the film coating machine is lower than 5.00 multiplied by 10^-7Aluminium granules (density 2.702 g/cm) were carried out at mbar³Boiling point of 2467 deg.C, melting point of 660.4 deg.C, purity of 99.99%), and maintaining evaporation rate

Breaking vacuum after the evaporation is finished, taking out the substrate, forming an aluminum electrode on the ITO/NiO/PEDOT, PSS/CBP-V/QDs/ZnO substrate, wherein the thickness of the electrode is 100nm, and the formed device is marked as an ITO/NiO/PEDOT, PSS/CBP-V/QDs/ZnO/Al device.

(8) Packaging of the device: and packaging the constructed ITO/NiO/PEDOT/PSS/CBP-V/QDs/ZnO/Al devices with ultraviolet curing resin and cover glass, and curing under the irradiation of an ultraviolet lamp to obtain the positive QLED device based on the NiO/PEDOT/PSS double-layer hole injection layer.

The photoelectric performance of the blue-light QLED device constructed in example 5 was tested, and the test results are shown in FIG. 9, (a) is a J-V-L characteristic curve, and (b) is η_A-L-η_PA graph; the corresponding device performance parameters are listed in table 3.

Table 3 performance of blue QLED devices constructed in example 5

As can be seen from FIG. 9 and Table 3, the performance of the blue QLED device constructed by NiO is improved compared with the standard device, the maximum current efficiency and the power efficiency are respectively 7.42cd/A and 4.66lm/W, and the EQE is 11.09%.

The positive QLED device provided by the invention adopts NiO/PEDOT/PSS double-layer hole injection layers, so that the problem of corrosion to an ITO electrode can be solved, a hole injection barrier can be effectively reduced, the hole injection efficiency can be improved, carriers can be balanced, the efficiency of the positive QLED device can be improved, and the service life of the positive QLED device can be prolonged.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A positive QLED device based on a dual hole injection layer, comprising:

2. The positive QLED device as claimed in claim 1, wherein the hole transport layer is made of one or more of PVK, TFB, poly-TPD, TCTA and CBP-V; the thickness of the hole transport layer is 20-35 nm.

3. The positive QLED device according to claim 1, wherein the quantum dot light emitting layer is one or more of a ZnCdSeS/ZnS green quantum dot light emitting layer, a CdZnSe/ZnSe/ZnS red quantum dot light emitting layer, and a CdSe/ZnS blue quantum dot light emitting layer; the thickness of the quantum dot light-emitting layer is 20-30 nm.

4. The positive QLED device according to claim 1, wherein the electron transport layer is a ZnO layer, and the thickness of the electron transport layer is 25 to 35 nm.

5. The positive QLED device of claim 1, wherein the top electrode layer is an Al, Ag, Cu or Au electrode layer; the thickness of the top electrode layer is 80-100 nm.

6. The method for preparing a positive type QLED device based on a double-layer hole injection layer as claimed in any one of claims 1 to 5, comprising the steps of:

7. The preparation method according to claim 6, wherein the dosage ratio of the nickel acetate tetrahydrate, the monoethanolamine and the ethanol is 1mmol: 50-70 μ L: 8-15 mL; the sol-gelation temperature is 50-70 ℃, and the time is 2-3 h; and the rotation speed of the spin coating of the NiO precursor solution is 3000-5000 rpm.

8. The preparation method according to claim 6, wherein the spin coating speed of the PEDOT/PSS is 2000-4000 rpm.

9. The method according to claim 6, wherein the ultraviolet ozone pretreatment is performed for 10 to 25 min.

10. The production method according to claim 6, wherein the solution of the hole transport layer is formed by dissolving one or more of PVK, TFB, poly-TPD, TCTA, and CBP-V in chlorobenzene or toluene; the concentration of the solution of the hole transport layer is 8-10 mg/mL; the rotating speed of the solution for spin coating the hole transport layer is 2000-4000 rpm;