CN114300630B - ZnO-based composite material, preparation method thereof and QLED device - Google Patents
ZnO-based composite material, preparation method thereof and QLED device Download PDFInfo
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Abstract
The invention provides a ZnO-based composite material, a preparation method thereof and a QLED device, and belongs to the technical field of photoelectric materials. The ZnO-based composite layer material provided by the invention has the advantages that the resistance is higher than that of ZnO, the electron mobility of an electron transport layer is reduced, the electron injection and transport efficiency is reduced, and the electron injection capacity of the ZnO layer is effectively regulated and controlled; wherein the amino group is modified by SiO 2 NH of coating layer 2 The end capping can form a dipole layer at the interface of the light-emitting layer/the electron transmission layer to form a reverse electric field between the interfaces, change the electron injection mode, further regulate and control the electron transmission of the interfaces, enable the charge injection of the QLED to approach to complete balance, and reduce non-radiative recombination caused by unbalanced carrier injection; siO (SiO) 2 The shell layer isolates the direct contact between ZnO and the quantum dot, effectively weakens the fluorescence quenching of the defect state on the ZnO surface to the quantum dot, and finally improves the external quantum efficiency and the service life of the QLED device.
Description
Technical Field
The invention relates to the technical field of photoelectric materials, in particular to a ZnO-based composite material, a preparation method thereof and a QLED device.
Background
Colloidal Quantum Dots (QDs) are of great interest because of their broad absorption peak, narrow emission peak, continuously tunable emission wavelength over the entire visible region, and excellent photoluminescence quantum yield (PLQY). This also determines that the quantum dot Light Emitting Diode (Quantum Dot Light Emitting Diodes, QLED) using the quantum dot as the Light Emitting material has advantages of high color purity, high Light Emitting efficiency, and the like, so that it is the most promising next-generation illumination display technology after the conventional Light Emitting Diode (Light Emitting Diodes, LED) and the Organic Light-Emitting Diode (OLED).
It is currently believed that the main factors affecting QLED performance are the fluorescence quantum yield of the quantum dots themselves and the charge injection of the QLED. The ZnO nano-crystal is far higher than Liq by virtue of the ZnO nano-crystal 3 And the electron transmission capability of organic materials is the first choice of materials of an electron transmission layer of the QLED device. However, a ZnO electron transport layer is also presentIn some cases: on one hand, the transmission potential barrier between ZnO and quantum dots is small, and the electron transmission rate is higher than the hole transmission rate, so that the carrier injection is unbalanced, the quantum dots are negatively charged, and non-radiative Auger recombination is caused; on the other hand, the excessive defect state on the surface of ZnO nanocrystals is easy to cause fluorescence quenching of quantum dots. Both of these effects severely affect the external quantum efficiency and lifetime of the device. There are generally two solutions to the above problem: 1) In-situ ion doping changes the energy level position of the material, weakens the electron transmission capacity of the material, reduces the surface defect state concentration of the material, and inhibits the fluorescence quenching effect; 2) An inert layer is introduced at the interface between the quantum dot and ZnO to block the electron transmission to a certain extent, so that the contact between the QDs and the ZnO surface is isolated, and fluorescence quenching is weakened. However, a large number of documents demonstrate that both of the above methods have their limitations: 1) The ZnO nanocrystals doped with ions can cause more obvious efficiency roll-off of the QLED as an electron transport layer, and influence the brightness of the device; 2) The introduction of inert intercalation increases the complexity of the interface, making device construction and performance regulation more difficult.
Accordingly, there is a need to provide a ZnO based composite material that can increase the external quantum efficiency of a QLED device and increase the operating life of the QLED device.
Disclosure of Invention
The invention aims to provide a ZnO-based composite material, a preparation method thereof and a QLED device.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a ZnO-based composite material, which comprises ZnO nano particles and SiO coated on the surfaces of the ZnO nano particles in sequence 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is (1-7): 1.
preferably, the ZnO nanoparticles are mixed with SiO 2 The mass ratio of the coating layer is 100: (0.1-20).
Preferably, the SiO 2 Coating and amine group modificationSiO of (2) 2 The total average thickness of the coating layer is 0.1-3 nm.
Preferably, the average particle size of the ZnO-based composite is 3-6 nm.
The invention also provides a preparation method of the ZnO-based composite material, which comprises the following steps:
(1) ZnO nano particles are mixed with a silicon source and a solvent for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles;
(2) The SiO obtained in the step (1) is treated 2 And mixing the mixed solution coated with the ZnO nano particles with an amino silicon source, and then carrying out hydrolysis reaction to obtain the ZnO-based composite material.
Preferably, the temperature of the hydrolysis reaction in the step (1) and the step (2) is independently 0 to 90 ℃, and the time of the hydrolysis reaction is independently 10min to 10h.
Preferably, the silicon source in the step (1) is one of ethyl orthosilicate, methyl orthosilicate and propyl orthosilicate.
Preferably, the solvent in the step (1) is a mixed solution of absolute ethyl alcohol and dimethyl sulfoxide.
Preferably, the aminosilane source in step (2) comprises one or more of 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane and 3- (methacryloyl) propyl trimethoxysilane.
The invention also provides a QLED device, which sequentially comprises the following components from the upper layer to the lower layer: an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode; the electron transport layer is made of the ZnO-based composite material or the ZnO-based composite material prepared by the preparation method according to the technical scheme.
The invention provides a ZnO-based composite layer material, which comprises ZnO nano particles and SiO coated on the surfaces of the ZnO nano particles in sequence 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is (1-7): 1. the book is provided withThe ZnO-based composite material provided by the invention has the advantages that the resistance is higher than that of ZnO, the electron mobility of an electron transport layer is reduced, the electron injection and transport efficiency is reduced, and the electron injection capacity of the ZnO layer is effectively regulated and controlled; wherein the amino group is modified by SiO 2 NH of coating layer 2 The end capping can form a dipole layer at the interface of the light-emitting layer/electron transport layer (namely QDs/ETL), a reverse electric field between the interfaces is formed, the electron injection mode is changed, the electron transport of the QDs/ETL is further regulated, the charge injection of the QLED approaches to complete balance, and the non-radiative recombination caused by unbalanced carrier injection is reduced; siO (SiO) 2 The shell layer isolates the direct contact between ZnO and the quantum dot, effectively weakens the fluorescence quenching of the defect state on the ZnO surface to the quantum dot, and finally improves the external quantum efficiency and the service life of the QLED device.
The results of the examples show that the ZnO-based composite material provided by the invention is characterized by UV-vis, UPS, C-AFM and the photoelectric test result of a single-type carrier device shows that ZnO/SiO with a core-shell structure 2 -NH 2 The conduction band position moves upwards, so that the injection barrier of electrons is increased, and the injection rate of electrons is effectively weakened; as can be seen from XPS characterization, znO/SiO with core-shell structure 2 -NH 2 The surface defect is obviously passivated, so that the fluorescence quenching effect of ZnO on QDs is inhibited; the external quantum efficiency of the QLED device prepared by the ZnO-based composite material provided by the invention is improved from 15.82% of a control device to 23.99%, and the improvement amplitude is 51.64%; znO and ZnO/SiO 2 -NH 2 QLED devices with 50/10 of the electron transport layer are converted into an initial brightness of 1000cd/m 2 T of (2) 95 About 85.91h and 353.20 h, respectively; t (T) 90 About 159.10h and 591.14h, respectively, and T 50 About 3153.70h and 11189.97h respectively, the service life is greatly prolonged.
Drawings
FIG. 1 is an XRD pattern of nanomaterial samples provided in comparative example 1 and examples 1-4 of the present invention;
FIG. 2 is an FT-IR chart of nanomaterial samples provided in comparative example 1 and examples 1-4 of the present invention;
FIG. 3 is a UV-vis graph of nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention;
FIG. 4 is a PL spectrum of nanomaterial sample provided in comparative example 1 and examples 1-4 of the present invention;
FIG. 5 is a TEM image of a nanomaterial sample provided in comparative example 1 of the present invention;
FIG. 6 is a TEM image of a nanomaterial sample provided in example 1 of the present invention;
FIG. 7 is a TEM image of a nanomaterial sample provided in example 2 of the present invention;
FIG. 8 is a TEM image of a nanomaterial sample provided in example 3 of the present invention;
FIG. 9 is a Si2pXPS spectrum of a nanomaterial sample provided in comparative example 1 and examples 1-3 of the present invention;
FIG. 10 is an N1sXPS spectrum of nanomaterial samples provided in examples 1-3 of the present invention;
FIG. 11 is an O1sXPS spectrum of a nanomaterial sample provided in example 1 of the present invention;
FIG. 12 is an O1sXPS spectrum of a nanomaterial sample provided in example 2 of the present invention;
FIG. 13 is an O1sXPS spectrum of a nanomaterial sample provided in example 3 of the present invention;
FIG. 14 is an O1sXPS spectrum of a nanomaterial sample provided in example 4 of the present invention;
FIG. 15 is a UPS spectrum at 6.0-3.5 eV for nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention;
FIG. 16 is a UPS spectrum at 18-16 eV for nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention;
FIG. 17 is a UPS spectrum at 3.3-3.7 eV for nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention;
FIG. 18 is a J-V characteristic of a single type carrier device of nanomaterial samples provided in comparative example 1 and examples 1-4 of the present invention;
FIG. 19 is a C-AFM image of nanomaterial samples provided in comparative example 1 and example 3 of the present invention; wherein, fig. 19 (a) is comparative example 1, fig. 19 (b) is C-AFM (AFM current image) of comparative example 1, fig. 19 (C) is AFM image of example 3, and fig. 19 (d) is C-AFM (AFM current image) of example 3;
FIG. 20 is a fluorescence spectrum obtained by testing the quantum dot fluorescence quenching effect of five composite board samples provided in test examples 1-5 of the present invention;
FIG. 21 is a graph of transient fluorescence spectrum obtained by testing the quenching effect of quantum dot fluorescence of five composite plate samples provided in test examples 1-5 of the present invention;
fig. 22 is a schematic view showing the device structure of QLEDs of application examples 1 to 4 of the present invention and comparative application example 1;
FIG. 23 is a J-V-L characteristic curve of the devices of the QLEDs of application examples 1 to 4 of the present invention and comparative example application example 1;
FIG. 24 is a CE-L-EQE characteristic curve of the devices of the QLEDs of application examples 1 to 4 of the present invention and comparative example application example 1;
FIG. 25 is a J-V-L characteristic curve of the QLED devices provided in comparative application examples 1 to 2 and application example 1 of the present invention;
FIG. 26 is a CE-L-EQE characteristic curve of the QLED devices provided in comparative application examples 1-2 and application example 1 of the present invention;
FIG. 27 is a graph of EQE-L for the QLED devices provided in comparative application examples 1-2 and application example 1 of the present invention;
FIG. 28 is a graph showing the L/L ratio of QLED devices provided in comparative application example 1 and application example 1 of the present invention 0 Attenuation curve versus graph.
Detailed Description
The invention provides a ZnO-based composite material, which comprises ZnO nano particles and SiO coated on the surfaces of the ZnO nano particles in sequence 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is (1-7): 1.
the ZnO-based composite material provided by the invention comprises ZnO nano particles. The ZnO-based composite material provided by the invention takes ZnO nano-particles as the core of the composite material, and the electron transmission capability of the ZnO nano-particles can be obviously improved by coating the surfaces of the ZnO nano-particles with the shell layers of other materials.
In the present invention, the average particle diameter of the ZnO nanoparticles is preferably 1 to 10nm, more preferably 2 to 6nm. The invention is more beneficial to the complete coating of the ZnO nano particles by the coating layer by controlling the average particle size of the ZnO nano particles within the range, thereby regulating and improving the surface defects of the ZnO nano particles and further improving the electron transmission capability of the composite material.
The source of the ZnO nano-particles is not particularly limited, and the ZnO nano-particles can be prepared by a preparation method of ZnO nano-particles which is well known to a person skilled in the art. In the present invention, the preparation method of the ZnO nanoparticle preferably includes:
And mixing the soluble zinc salt solution with an alkali solution to carry out hydrolysis reaction, so as to obtain ZnO nano particles.
In the present invention, the solute of the soluble zinc salt solution is preferably one or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc acetylacetonate and zinc gluconate.
In the present invention, the solvent of the soluble zinc salt solution is preferably one or more of water, ethanol, methanol, propanol, isopropanol, acetone, dimethyl sulfoxide, tetrahydrofuran, dimethylformamide, methyl acetate, ethyl acetate, propyl acetate, chlorobenzene and acetonitrile.
In the present invention, the concentration of the soluble zinc salt solution is preferably 0.01 to 0.5mol/L, more preferably 0.05 to 0.2mol/L.
In the present invention, the alkali solution is preferably one or more of potassium hydroxide solution, sodium hydroxide solution, aqueous ammonia and tetramethylammonium hydroxide solution.
In the present invention, the solvent of the alkali solution is preferably one or more of water, ethanol, methanol, propanol, isopropanol, acetone, dimethyl sulfoxide, tetrahydrofuran, dimethylformamide, methyl acetate, ethyl acetate, propyl acetate, chlorobenzene, and acetonitrile.
In the present invention, the concentration of the alkali solution is preferably 0.1 to 2mol/L, more preferably 0.3 to 0.8 mol/L.
The mixing operation is not particularly limited in the present invention, and the mixing operation well known to those skilled in the art can be used to ensure uniform mixing of the solutions. In the present invention, the mixing is preferably performed by stirring.
In the present invention, zn in the soluble zinc salt 2+ OH with alkaline solution - The ratio of the amounts of the substances is preferably 1:4 to 2:1, more preferably 1:2 to 1:1. The invention can improve the hydrolysis degree of the soluble zinc salt by controlling the concentration of hydroxide ions in the alkali solution and zinc ions in the soluble zinc salt within the range, thereby leading the hydrolysis to be more sufficient.
In the present invention, the temperature of the hydrolysis reaction is preferably 0 to 50 ℃, more preferably 10 to 30 ℃; the hydrolysis reaction time is preferably 10min to 4 hours, more preferably 30min to 1.5 hours. The invention can make the crystallinity of the obtained nano particles better and the crystal grains finer by controlling the temperature and time of the hydrolysis reaction within the above range.
The ZnO-based composite material provided by the invention further comprises SiO which is coated on the surface of the ZnO nano-particle in sequence 2 Coating layer and amino-modified SiO 2 And a coating layer.
In the present invention, the ZnO nanoparticle is mixed with SiO 2 The mass ratio of the coating layer is preferably 100: (0.1 to 20), more preferably 100: (1-18), most preferably 100: (5-15). The invention controls ZnO nano particles and SiO 2 The quality ratio of the coating layer is in the range, so that the direct contact between ZnO and the quantum dots is isolated, the fluorescence quenching of the defect state on the surface of ZnO to the quantum dots is weakened, and the external quantum efficiency and the service life of the QLED device are effectively improved.
In the present invention, the SiO 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is (1-7): 1, preferably (2 to 6): 1, more preferably (3 to 5): 1, most preferably 4:1. The invention is realized by controlling SiO 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layers is in the range, and the average thickness of each coating layer can be controlled respectively, so that the defect of the surface of the ZnO nano-particle is improved, and the electron transmission capacity of the ZnO nano-particle is improved.
In the present invention, the SiO 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layers is preferably0.1 to 3nm, more preferably 0.5 to 2.5nm, and most preferably 1 to 2nm. The invention is realized by controlling SiO 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer is in the range, which is more beneficial to improving the defect of the ZnO nano particle surface and improving the electron transmission capability.
The invention relates to the SiO 2 Average thickness of coating layer and amino group modified SiO 2 The average thickness of the coating layers is not particularly limited, and the mass ratio of the coating layers to the ZnO nanoparticles is satisfied. In the present invention, the SiO 2 The average thickness of the coating layer is extremely thin, the specific average thickness is difficult to observe through an electron microscope, and the coating layer is modified with amino group SiO 2 The interface of the coating layer is not obvious, so that the invention can be realized by SiO 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layers regulates the average thickness of each coating layer.
In the present invention, the average particle diameter of the ZnO-based composite material is preferably 2 to 6nm, more preferably 3 to 5nm. The invention can make ZnO-based composite material have larger specific surface area under the condition of nanometer-level tiny average particle diameter by controlling the average particle diameter of ZnO-based composite material in the range, and the contact between particles is more sufficient, and the film layer is more compact when the ZnO-based composite material is used as an electron transport layer material.
The ZnO-based composite material provided by the invention passes through SiO 2 Coating layer and amino-modified SiO 2 The combined action of the coating layers can effectively improve the defect of the ZnO surface, weaken fluorescence quenching of the quantum dots, change the electron injection mode, further regulate and control the electron transmission of the QDs/ETL, and further improve the external quantum efficiency and the service life of the QLED device.
The invention also provides a preparation method of the ZnO-based composite material, which comprises the following steps:
(1) ZnO nano particles are mixed with a silicon source and a solvent for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles;
(2) The SiO obtained in the step (1) is treated 2 Mixing the mixed solution coated with ZnO nano particles with an amino silicon source, and then carrying out hydrolysis reaction to obtainTo ZnO based composites.
The method mixes ZnO nano particles with a silicon source and a solvent for hydrolysis reaction to obtain SiO 2 And (3) coating the mixed solution of ZnO nano-particles.
In the present invention, the silicon source is preferably one of ethyl orthosilicate, methyl orthosilicate, or propyl orthosilicate.
In the present invention, the solvent is preferably a mixed solution of anhydrous ethanol and dimethyl sulfoxide. In the present invention, the mass ratio of the anhydrous ethanol to the dimethyl sulfoxide is preferably 2:1 to 1:9, and more preferably 1:1 to 1:5.
In the invention, the ZnO nano-particles are preferably dispersed in a solvent to obtain ZnO nano-particle dispersion liquid, and then a silicon source is added. In the present invention, the concentration of the ZnO nanoparticle dispersion is preferably 1 to 20g/L, more preferably 3 to 10g/L.
In the present invention, the temperature of the hydrolysis reaction is preferably 0 to 90 ℃, more preferably 20 to 50 ℃; the hydrolysis reaction time is preferably 10min to 10h, more preferably 20min to 2h, and most preferably 1h to 1.5h. The invention is more favorable for fully carrying out the hydrolysis reaction by controlling the temperature and the time of the hydrolysis reaction within the range, thereby obtaining the fully coated SiO 2 And coating ZnO nano particles.
SiO is obtained 2 After coating the mixed solution of ZnO nano particles, the invention leads the SiO to be 2 And mixing the mixed solution coated with the ZnO nano particles with an amino silicon source, and then carrying out hydrolysis reaction to obtain the ZnO-based composite material.
In the present invention, the aminosilane source includes one or more of 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, and 3- (methacryloyl) propyl trimethoxysilane.
In the present invention, the temperature of the hydrolysis reaction is preferably 0 to 90 ℃, more preferably 20 to 50 ℃; the hydrolysis reaction time is preferably 10min to 10h, more preferably 20min to 2h, and most preferably 1 to 1.5h. The method is more favorable for fully carrying out the hydrolysis reaction by controlling the temperature and time of the hydrolysis reaction within the range, so as to obtain the ZnO-based composite material with complete coating.
After the hydrolysis reaction is completed, the invention preferably carries out precipitation separation on the products of the hydrolysis reaction to obtain the ZnO-based composite material.
In the present invention, the solvent for precipitation separation is preferably a mixed solution of absolute ethanol and n-heptane; the mass ratio of the absolute ethyl alcohol to the n-heptane is preferably 5:95-50:50, more preferably 10:90-25:70. The invention is more favorable for fully separating out the ZnO-based composite material in the mixed solution by controlling the mass ratio of the absolute ethyl alcohol to the n-heptane within the range, thereby obtaining the ZnO-based composite material with good crystallinity.
The preparation method of the ZnO-based composite material can ensure that the prepared ZnO-based composite material has more complete structure, finer crystal grains, simple preparation process, easily controlled parameters and low cost.
The technical scheme of the invention also provides a QLED device, which sequentially comprises the following steps from an upper layer to a lower layer: an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode; the electron transport layer is made of the ZnO-based composite material or the ZnO-based composite material prepared by the preparation method according to the technical scheme.
The materials and average thicknesses of the anode, the hole injection layer, the hole transport layer, the light emitting layer and the cathode are not particularly limited, and materials and average thicknesses of layers constituting the QLED device, which are well known to those skilled in the art, may be used.
The preparation method of the QLED device has no special requirement, and the method for preparing the QLED device is well known to the person skilled in the art. In the present invention, the preparation method of the QLED device preferably includes the steps of:
(1) Sequentially spin-coating the raw materials of the hole injection layer, the hole transport layer, the light-emitting layer and the electron transport layer on the surface of the anode to obtain a composite substrate;
(2) And (3) depositing a cathode on the surface of the electron transport layer of the composite substrate obtained in the step (1) to obtain the QLED device.
The spin coating operation of the raw materials of the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, and the operation of depositing the cathode are not particularly limited, and the operation of manufacturing the QLED device, which is well known to those skilled in the art, may be adopted.
The QLED device provided by the invention can effectively inhibit the fluorescence quenching effect of the luminescent layer by using the ZnO-based composite material provided by the invention as an electron transmission layer, thereby having high external quantum efficiency and longer service life.
The technical solutions of the present invention will be clearly and completely described in the following in connection with the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
A ZnO-based composite material is prepared from ZnO nanoparticles and SiO sequentially coated on the surfaces of the ZnO nanoparticles 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is 1:1.
wherein ZnO nano particles and SiO 2 The mass ratio of the coating layer is 100:1.5; siO (SiO) 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer is 0.9nm; the average particle size of the ZnO-based composite was 4.4nm.
The ZnO nanoparticles used in this example were prepared by the following preparation method: zinc acetate is dissolved in dimethyl sulfoxide to obtain zinc acetate solution with the concentration of 0.1M, tetramethyl ammonium hydroxide is dissolved in absolute ethyl alcohol to obtain tetramethyl ammonium hydroxide solution with the concentration of 0.45M, and the two solutions are mixed under the stirring condition for hydrolysis reaction (the temperature is 22 ℃ for 1 h) to obtain ZnO nano particles; wherein, the mol ratio of zinc acetate to tetramethylammonium hydroxide is 2:3.
The preparation method of the ZnO-based composite material comprises the following steps:
(1) ZnO nanoparticles (240 mg) were mixed with a solvent (40 mL) (a mixed solution of anhydrous ethanol and dimethyl sulfoxide in a mass ratio of 1:5) and a silicon source (ethyl orthosilicate, 3.6 mg) for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles; wherein, znO nano particles and a solvent are mixed to obtain a dispersion liquid with the concentration of 6mg/mL, and then ethyl orthosilicate is added, the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1.5h.
(2) The SiO obtained in the step (1) is treated 2 Mixing the mixed solution coated with ZnO nano particles with an amino silicon source (3-aminopropyl triethoxysilane, 3.6 mg) and then carrying out hydrolysis reaction to obtain a ZnO-based composite material, which is named ZnO/SiO 2 -NH 2 -10/10; wherein the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1h.
Application example 1
The ZnO-based composite material provided in the embodiment 1 is adopted to prepare a QLED device, and the QLED device comprises the following components in sequence from an upper layer to a lower layer: an anode (ITO substrate, average thickness-200 nm), a hole injection layer (PEDOT: PSS, average thickness-10 nm), a hole transport layer (TFB, average thickness-40 nm), a light emitting layer (ZnCdSeS/ZnS quantum dot, average thickness-30 nm), an electron transport layer (ZnO-based material, average thickness-80 nm) and a cathode (Al, average thickness-300 nm); wherein the electron transport layer is the ZnO based composite provided in example 1.
The preparation method comprises the following steps:
(1) Anode pretreatment: taking an ITO substrate as an anode, firstly, ultrasonically cleaning the ITO substrate rubbed by a detergent for 15 minutes by sequentially using a detergent solution, ultrapure water, acetone and isopropanol, and then performing ultraviolet ozone treatment for 10 minutes to obtain a clean ITO substrate;
(2) Coating a hole injection layer: spin-coating the mixture of poly 3, 4-ethylenedioxythiophene/polystyrene sulfonic acid on the clean ITO substrate obtained in the step (1) at a rotation speed of 5000rpm, wiping the edge of the ITO substrate by a cotton swab dipped with ultrapure water until the electrode is exposed, heating and annealing for 15 minutes at 140 ℃, naturally standing and cooling to room temperature to obtain a composite substrate I;
(3) Coating a hole transport layer: transferring the composite substrate I obtained in the step (2) into a glove box filled with nitrogen, taking 40 mu L of TFB chlorobenzene solution with the concentration of 8mg/mL, spin-coating the TFB chlorobenzene solution on the surface of a hole injection layer of the composite substrate I at 3000rpm, annealing for 30 minutes at the temperature of 150 ℃, naturally placing and cooling to the room temperature to obtain a composite substrate II;
(4) Coating a light-emitting layer: spin-coating a green quantum dot (with a structure of ZnCdSeS/ZnS) n-octane solution of 18mg/mL on the surface of a hole transport layer of a composite substrate II at 4000rpm to form a film, and naturally standing until the film is dried to obtain a composite substrate III;
(5) Coating an electron transport layer: dispersing the ZnO-based composite material provided in the embodiment 1 into ethanol solution (the concentration is 30 mg/mL), spin-coating the ZnO-based composite material on the surface of a luminescent layer of a composite substrate III at 4000rpm to form a film, then wiping the edge of the substrate by using a cotton swab dipped with a small amount of toluene, exposing an electrode at the edge, annealing at the temperature of 60 ℃ for 30 minutes, naturally standing and cooling to room temperature to obtain a composite substrate IV;
(6) And (3) depositing a cathode: transferring the composite substrate IV obtained in the step (5) to a vacuum degree of less than or equal to 5 multiplied by 10 -6 And (3) depositing an aluminum electrode serving as a cathode in the Mbar high vacuum deposition chamber by a conventional evaporation method, dripping 2-3 drops of ultraviolet curing glue in the center of the surface of the cathode, covering a cover glass, removing bubbles, and irradiating the ultraviolet curing glue for 3 min by an ultraviolet lamp to cure the ultraviolet curing glue to obtain the QLED device.
Example 2
A ZnO-based composite material is prepared from ZnO nanoparticles and SiO sequentially coated on the surfaces of the ZnO nanoparticles 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is 3:1.
wherein ZnO nano particles and SiO 2 The mass ratio of the coating layer is 100:4.5; siO (SiO) 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer was 1.4nm; the average particle size of the ZnO-based composite was 4.9nm.
The ZnO nanoparticles used in this example were the same as in example 1.
The preparation method of the ZnO-based composite material comprises the following steps:
(1) ZnO nanoparticles (240 mg) were mixed with a solvent (40 mL) (a mixed solution of anhydrous ethanol and dimethyl sulfoxide in a mass ratio of 1:5) and a silicon source (ethyl orthosilicate, 10.8 mg) for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles; wherein, znO nano particles and a solvent are mixed to obtain a dispersion liquid with the concentration of 6mg/mL, and then ethyl orthosilicate is added, the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1.5h.
(2) The SiO obtained in the step (1) is treated 2 Mixing the mixed solution coated with ZnO nano particles with an amino silicon source (3-aminopropyl triethoxysilane, 3.6 mg) and then carrying out hydrolysis reaction to obtain a ZnO-based composite material, which is named ZnO/SiO 2 -NH 2 -30/10; wherein the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1h.
Example 3
A ZnO-based composite material is prepared from ZnO nanoparticles and SiO sequentially coated on the surfaces of the ZnO nanoparticles 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is 5:1.
wherein ZnO nano particles and SiO 2 The mass ratio of the coating layer is 100:7.5; siO (SiO) 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer was 1.9nm; the average particle size of the ZnO-based composite was 5.5nm.
The ZnO nanoparticles used in this example were the same as in example 1.
The preparation method of the ZnO-based composite material comprises the following steps:
(1) ZnO nanoparticles (240 mg) were mixed with a solvent (40 mL) (a mixed solution of anhydrous ethanol and dimethyl sulfoxide in a mass ratio of 1:5) and a silicon source (ethyl orthosilicate, 18 mg) for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles; wherein, znO nano particles and a solvent are mixed to obtain a dispersion liquid with the concentration of 6mg/mL, and then ethyl orthosilicate is added, the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1.5h.
(2) The SiO obtained in the step (1) is treated 2 Mixing the mixed solution coated with ZnO nano particles with an amino silicon source (3-aminopropyl triethoxysilane, 3.6 mg) and then carrying out hydrolysis reaction to obtain a ZnO-based composite material, which is named ZnO/SiO 2 -NH 2 -50/10; wherein the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1h.
Example 4
A ZnO-based composite material is prepared from ZnO nanoparticles and SiO sequentially coated on the surfaces of the ZnO nanoparticles 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is 7:1.
wherein ZnO nano particles and SiO 2 The mass ratio of the coating layer is 100:10.5; siO (SiO) 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer was 2.6nm; the average particle size of the ZnO-based composite was 6.2nm.
The ZnO nanoparticles used in this example were the same as in example 1.
The preparation method of the ZnO-based composite material comprises the following steps:
(1) ZnO nanoparticles (240 mg) were mixed with a solvent (40 mL) (a mixed solution of anhydrous ethanol and dimethyl sulfoxide in a mass ratio of 1:5) and a silicon source (ethyl orthosilicate, 25.2 mg) for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles; wherein, znO nano particles and a solvent are mixed to obtain a dispersion liquid with the concentration of 6mg/mL, and then ethyl orthosilicate is added, the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1.5h.
(2) The SiO obtained in the step (1) is treated 2 Mixing the mixed solution coated with ZnO nano particles with an amino silicon source (3-aminopropyl triethoxysilane, 3.6 mg) and then carrying out hydrolysis reaction to obtain a ZnO-based composite material, which is named ZnO/SiO 2 -NH 2 -70/10; wherein the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1h.
Application examples 2 to 4
The ZnO-based composite materials provided in examples 2 to 4 are adopted to prepare QLED devices respectively, and the QLED devices are sequentially from the upper layer to the lower layer: an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode; wherein the electron transport layers are the ZnO-based composite materials provided in examples 2 to 4, respectively. The specific preparation method is the same as that of application example 1.
Comparative example 1
The ZnO nanoparticle used in example 1 was used as comparative example 1 and was designated ZnO.
Comparative application example 1
The electron transport layer in the OLED device of application example 1 was replaced with ZnO nanoparticles of comparative example 1.
Comparative example 2
A ZnO-based composite material is prepared from ZnO nanoparticles and SiO coated on the surfaces of the ZnO nanoparticles 2 A coating layer; wherein ZnO nano particles and SiO 2 The mass ratio of the coating layer is 100: 30; siO (SiO) 2 The average thickness of the coating layer is 1.8nm; the average particle size of the ZnO-based composite was 5.3nm.
The ZnO nanoparticles used in this example were the same as in example 1.
The preparation method of the ZnO-based composite material comprises the following steps:
ZnO nanoparticles (240 mg) were mixed with a solvent (40 mL) (a mixed solution of anhydrous ethanol and dimethyl sulfoxide in a mass ratio of 1:5) and a silicon source (ethyl orthosilicate, 72 mg) for hydrolysis reaction to obtain SiO 2 The mixed solution of the coated ZnO nano particles is marked as ZnO/SiO 2 The method comprises the steps of carrying out a first treatment on the surface of the Wherein, znO nano particles and a solvent are mixed to obtain a dispersion liquid with the concentration of 6mg/mL, and then ethyl orthosilicate is added, the temperature of the hydrolysis reaction is 40 ℃, and the time of the hydrolysis reaction is 1.5h.
Comparative application example 2
The electron transport layer in the OLED device of application example 1 was replaced with ZnO/SiO of comparative example 2 2 And (3) nanoparticles.
To investigate ZnO/SiO 2 /SiO 2 -NH 2 The following examples were prepared to facilitate transient-steady state fluorescence spectroscopy testing of the present invention.
Test example 1
The same anode and light-emitting layer materials as in application example 1 were used, and a light-emitting layer was spin-coated on the anode surface, denoted ito+qds (anode+light-emitting layer), by the same spin-coating operation as in application example 1.
Test example 2
The same anode, znO, and light-emitting layer materials as comparative application example 1 were used, and a light-emitting layer was spin-coated on the anode surface using the same spin-coating operation as comparative application example 1, denoted ito+qds+zno (anode+light-emitting layer+zno of comparative example 1).
Test example 3
The same anode, light-emitting layer material and ZnO/SiO as in application example 1 were used 2 -NH 2 10/10, the same spin-on light-emitting layer and ZnO/SiO as in application example 1 were used 2 -NH 2 Operation of-10/10 will give off light layers and ZnO/SiO 2 -NH 2 Spin-coating was performed at-10/10, respectively, and was designated ITO+QDs+ZnO/SiO 2 -NH 2 10/10 (anode + luminescent layer + sample of example 1).
Test example 4
The same anode, light-emitting layer material and ZnO/SiO as in application example 2 were used 2 -NH 2 30/10, the same spin-on light-emitting layer and ZnO/SiO as in application example 2 were used 2 -NH 2 Operation of-30/10 will give off light layer and ZnO/SiO 2 -NH 2 Spin-coating was performed at 30/10, respectively, and was designated ITO+QDs+ZnO/SiO 2 -NH 2 30/10 (anode + luminescent layer + sample of example 2).
Test example 5
The same anode, light-emitting layer material and ZnO/SiO as in application example 3 were used 2 -NH 2 50/10, the same spin-on light-emitting layer and ZnO/SiO as in application example 3 were used 2 -NH 2 Operation of-50/10 will give off light layer and ZnO/SiO 2 /SiO 2 Spin-coating, namely ITO+QDs+ZnO/SiO 2 -NH 2 50/10 (anode + luminescent layer + sample of example 3).
Performance testing
ZnO, znO/SiO provided in comparative example 1 and examples 1 to 4 2 -NH 2 -10/10、 ZnO/SiO 2 -NH 2 -30/10、ZnO/SiO 2 -NH 2 -50/10 and ZnO/SiO 2 -NH 2 -70/10, XRD, FT-IR, UV-vis and PL spectra were measured. As shown in fig. 1.
XRD detection was performed on the ZnO nanoparticles of comparative example 1 and the ZnO-based composites of examples 1 to 4, and XRD patterns were obtained as shown in FIG. 1. As can be seen from FIG. 1, all samples showed ZnO characteristic peaks of hexagonal wurtzite crystal form, and the positions of the characteristic peaks were not changed basically, but after the samples of examples 1 to 4 were coated with shell layers and modified, diffraction peaks were widened, which indicates that crystallinity of ZnO nanoparticles was reduced, and the reason for formation may be SiO 2 The shell layer prevents further growth of the ZnO nanoparticles.
Comparative example 1 the nanomaterial samples provided in examples 1, 2, 3, and 4 were subjected to FT-IR detection to obtain FT-IR spectra as shown in fig. 2. The FT-IR spectrum of FIG. 2 shows that ZnO nanoparticles are all 3000-3500 cm -1 Has a wider absorption peak in the range due to the stretching vibration mode of the-OH groups on the ZnO surface, 454cm -1 Another distinct absorption peak was observed at this point, due to the stretching vibrational mode of the Zn-O bond. Examples 1 to 4 provide ZnO/SiO 2 -NH 2 2929cm in nanoparticles -1 And 2850cm -1 The two peaks at this point originate from the asymmetric and symmetric telescopic vibrational modes of the C-H group in the ethyl chain in the silicate. In addition, at 943cm -1 The peak at 882cm is due to the vibrational mode of Si-O-Si groups formed by self-condensation of organosilanes -1 The peak at which corresponds to the Si-O-Zn bond. Si-O-Zn bond showed that ZnO and SiO were formed on the surface of the nanoparticle due to successful coating of ZnO nanoparticle with silane 2 Covalent bonds between them. In addition, examples 1 to 4 provide ZnO/SiO 2 -NH 2 Nanoparticles at 1263cm -1 There is a relatively weak peak due to the stretching vibration of the C-N bonds, which can infer the presence of bonded C-N bonds in the nanocrystals, thus determining the nanocrystals as ZnO/SiO 2 -NH 2 The structure is formed.
Comparative example 1 UV-vis detection of nanomaterial samples provided in example 1, example 2, and example 3The UV-vis spectra obtained are shown in FIG. 3. As can be seen from FIG. 3, examples 1 to 4 provide ZnO/SiO as compared with ZnO of comparative example 1 2 -NH 2 The absorption edge of the nanoparticle appears obviously red-shifted, and the absorption edge gradually blue-shifts along with the increase of the coating agent ethyl orthosilicate. It can be deduced from this that ZnO/SiO is comparable to that of comparative example 1 2 /SiO 2 -NH 2 The forbidden band width of the ZnO cores in the nanocrystals decreases and increases as the ratio of capping agent increases.
Comparative example 1 the nanomaterial samples provided in examples 1, 2, 3, and 4 were subjected to PL spectrum testing to obtain PL spectra as shown in fig. 4. As can be seen from FIG. 4, znO has two fluorescence emission peaks, namely, an intrinsic emission peak of ZnO in the 375nm ultraviolet region and a defect fluorescence peak of ZnO in the 500-600 nm visible region. The spectrum curve is normalized by taking the intrinsic peak as the reference, and the ZnO/SiO is found 2 -NH 2 The intrinsic peak position of the nanoparticles is not shifted substantially, but the defect peak gradually shifts blue and increases and decreases compared to the ZnO defect peak intensity, indicating an increase in ZnO surface defect states, which may be due to the increase in oxygen vacancies of the ZnO nanoparticles.
The nanomaterial samples provided in comparative example 1 and examples 1 to 3 were tested using a transmission electron microscope, and TEM images obtained are shown in fig. 5 to 8. Wherein FIG. 5 is a TEM image of ZnO of comparative example 1, and FIGS. 6, 7 and 8 are ZnO/SiO of examples 1 to 3, respectively 2 -NH 2 TEM image of nanoparticles. ZnO of comparative example 1 and ZnO/SiO provided in examples 1 to 3 were first observed 2 -NH 2 The nanoparticles were uniformly dispersed in absolute ethanol.
As can be seen from FIGS. 5 to 8, each nanoparticle was sufficiently dispersed in absolute ethanol, the dispersibility was substantially unchanged, and the average diameters of the nanoparticles of comparative example 1 and examples 1 to 3 were about 3.51,4.41, 4.93 and 5.48nm, respectively.
XPS test was performed on the nanomaterial samples provided in comparative example 1 and examples 1 to 3, and XPS spectra obtained are shown in fig. 9 to 14. Wherein, FIG. 9 is XPS Si2p pattern of nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention; FIG. 10 shows the present inventionXPS N1 s spectra of examples 1-3; FIG. 11 is an XPS spectrum of O1s according to example 1 of the present invention; FIG. 12 is an O1sXPS spectrum of example 2 of the present invention; FIG. 13 is an XPS spectrum of O1s according to example 3 of the present invention; FIG. 14 is an XPS spectrum of O1s according to example 4 of the present invention. The Si2p spectrum results in FIG. 9 show that ZnO/SiO 2 -NH 2 There is a bonded Si element whose peak is located at 101.1.+ -. 0.2eV. Furthermore, the N1 s XPS spectrum results in FIG. 10 show that ZnO/SiO 2 -NH 2 In the presence of free-NH 2 And hydrogen bonded-NH 2 Radicals having peaks at 399.8 and 402.7eV, respectively, and free-NH at 399.8eV 2 The radical is much higher than the hydrogen-bonded-NH at 402.9eV 2 Peak to peak. Thus, based on the combined results of XRD, FT-IR, TEM and XPS tests, znO/SiO can be substantially determined 2 -NH 2 Is formed by the steps of (a). As shown in FIGS. 11-14, the O1s core energy spectrum of ZnO nanoparticles can be peak-fitted to three peaks centered on 529.9 + -0.1 eV, 531.1 + -0.1 eV and 532.6 + -0.1 eV, respectively, O-Zn bonding (O M ) Oxygen vacancy (O) V ) And hydroxy oxygen (O) H ) A peak. With the increase of the proportion of the coating agent, siO 2 An increase in the average coating thickness was 532.6.+ -. 0.1eV of oxyhydrogen (O) H ) The peak gradually decreased to complete disappearance, leaving only 529.9.+ -. 0.1eV (O M ) And 531.1 + -0.1 eV (O) V ) Two peaks, which should be attributed to SiO 2 The reaction of hydroxyl groups on the ZnO surface with the coating agent in the coating process can be presumed that ZnO nanoparticles are gradually coated with SiO 2 The coating tends to be complete. SiO is modified by amino group 2 Increasing the proportion of coating agent and modifying SiO with amino group 2 The oxygen vacancies of the coated nanoparticles gradually increased so that the defect state of ZnO increased, which is consistent with the steady state fluorescence spectrum data. Therefore, it is presumed that the surface defect state of ZnO is protected from passivation due to environmental effects after it is coated and modified. With modification of SiO by amine groups 2 The adding proportion of the coating agent is increased, more Si-O-Zn bonds are formed, and ZnO/SiO with core-shell structure is formed 2 /SiO 2 -NH 2 The overall surface defects of the nanoparticles are reduced.
The electronic structures of the nanomaterial samples provided in comparative example 1 and examples 1-3 were subjected to UPS spectral characterization using UPS, and the characterization results are shown in fig. 15-17. Wherein, FIG. 15 is a UPS spectrum of the nanomaterial sample provided in comparative example 1 and examples 1-3 of the present invention under 6.0-3.5 eV; FIG. 16 is a UPS spectrum at 18-16 eV for nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention; FIG. 17 is a UPS spectrum at 3.3-3.7 eV for nanomaterial samples provided in comparative example 1 and examples 1-3 of the present invention.
The UPS spectra of FIGS. 15-17 show ZnO, znO/SiO provided in comparative example 1 and examples 1-3, respectively 2 -NH 2 -10/10、ZnO/SiO 2 -NH 2 -30/10、ZnO/SiO 2 -NH 2 50/10 of the Fermi edge (E Onset ) And secondary electron cut-off edge (E) Cutoff ) And the absorption edge are shown in figures 15, 16 and 17, respectively.
The J-V characteristic test was performed on the single type carrier devices of the nanomaterial samples provided in comparative example 1 and examples 1 to 4, and the J-V characteristic curves obtained by the test are shown in fig. 18. At the same applied voltage, the charge mobility is proportional to the current density of the single type carrier device, thus for testing ZnO/SiO 2 -NH 2 Single type carrier devices were fabricated and tested. The structure of the pass sub-device is as follows: ITO/ZnO (or ZnO/SiO) 2 -NH 2 ) QDs/ZnO (or ZnO/SiO) 2 -NH 2 ) The structure of the pure hole device is ITO/PEDOT, PSS/TFB/QDs/Au. As can be seen from FIG. 18, comparing the current densities at the same voltage, it can be found that ZnO/SiO-based 2 -NH 2 Has a lower current density than a ZnO based pure electric device. And along with the increase of the adding proportion of the coating agent, the coating agent is closer to the pure hole device, and when the adding proportion of the coating agent TEOS and APTES reaches 50/10 uL, the difference between the coating agent TEOS and the APTES is the smallest, that is to say, the carrier injection of the device basically reaches balance; when the addition ratio reaches 70/10uL, the current density of the pure electronic device is smaller than that of the pure hole device. It has further been demonstrated that ZnO/SiO is used 2 -NH 2 As the electron transport layer, the electron transport efficiency is effectively suppressed, and the problem of imbalance in the injection of the QLED is greatly improved.
For the inventionThe nanomaterial samples provided in comparative example 1 and example 3 were subjected to C-AFM testing, and the C-AFM images obtained by the testing are shown in fig. 19; fig. 19 (a) is comparative example 1, fig. 19 (b) is a C-AFM (AFM current image) of comparative example 1, fig. 19 (C) is an AFM image of example 3, and fig. 19 (d) is a C-AFM (AFM current image) of example 3. FIG. 19 ZnO and ZnO/SiO 2 -NH 2 C-AFM contrast of 50/10 strongly demonstrates SiO coating 2 After the shell layer is subjected to amido end sealing, the resistance of the ZnO nanocrystalline film is increased, and the electron mobility is reduced. Therefore, based on single carrier device photoelectric test data and C-AFM image evidence, siO is coated 2 And the amido modification can reduce the electron transmission efficiency from the Al cathode to the quantum dot layer, and effectively balance the carrier injection of the device.
The quantum dot fluorescence quenching effect of the five composite board samples provided in the test examples 1 to 5 is tested, and fluorescence spectrum diagrams obtained by the test are shown in figures 20 to 21; wherein, fig. 20 is a steady state fluorescence spectrum, and fig. 21 is a transient state fluorescence spectrum.
As can be seen from fig. 20 to 21, the exciton lifetime after PL decay curve fitting of the quantum dot film on the ITO substrate was approximately 6.26ns, and there was a significant drop in direct contact with ZnO. This is because ZnO surfaces have a large number of surface defects (mainly oxygen vacancies) that cause fluorescence quenching of the quantum dots, and thus, when the quantum dots are in direct contact with ZnO, quenching of excitons of the quantum dots is caused. Experiments prove that ZnO/SiO can be prepared by adjusting the adding proportion of the coating agent 2 -NH 2 The exciton lifetime of the surface QDs is increased to 5.81ns, which effectively inhibits fluorescence quenching caused by surface defects of ZnO. FIG. 18 results of a single type carrier device photoelectric performance test and the C-AFM image of FIG. 19 also show ZnO/SiO 2 -NH 2 Compared with the increase of ZnO resistance, the electron mobility is reduced, and in theory, the negative charge accumulation of the quantum dots can be obviously reduced, so that the radiation recombination probability of the quantum dot layer is improved. The steady-state-transient fluorescence characterization results of FIGS. 20-21 prove that exciton quenching at the QDs/ZnO interface is effectively inhibited, so that the radiation recombination probability of effective luminescence in the quantum dot luminescent layer is increased, and the external quantum efficiency of the QLED device is further improved.
Fig. 22 is a schematic view of the device structure of QLEDs of application examples 1 to 4 and comparative example application example 1. The structure of the QLED device shown in FIG. 22 can be abbreviated as ITO/PEDOT: PSS/TFB/QDs/ETL/Al.
The J-V-L test was performed on the devices of QLEDs of application examples 1 to 4 and comparative example application example 1, and the J-V-L characteristic curves obtained are shown in FIG. 23.
As shown in FIG. 23, the QLED has an on-voltage of about 2.2V, in the ohmic region (0-2V), znO/SiO 2 -NH 2 The leakage current of the QLED devices of examples 1 to 4 as electron transport layers was slightly smaller than that of the device of comparative application example 1 and had a gradually decreasing trend, which was attributed to SiO 2 The shell layer influences ZnO/SiO 2 -NH 2 Electron transport capability of nanocrystals.
J-V-L test was performed on the devices of QLEDs of application examples 1 to 4 and comparative example application example 1, and the CE-L-EQE characteristic curves obtained after processing the data are shown in FIG. 24. Fig. 24 shows the CE-L-EQE characteristic of the QLED, from which it can be seen that the device performance of the QLED is gradually improved and the problem of the efficiency roll-off is significantly improved until the amount of the capping agent TEOS reaches 50 uL.
According to the above pair ZnO/SiO 2 -NH 2 Can be inferred from the analysis of the properties and the analysis of the energy level structure:
1)ZnO/SiO 2 -NH 2 the resistance of the ZnO layer is higher than that of ZnO, the electron mobility of the electron transport layer is reduced, the electron injection and transport efficiency is reduced, the electron injection capability of the ZnO layer is effectively regulated and controlled, and the NH 2 The end capping can form a dipole layer at the QDs/ETL interface to form a reverse electric field between the interfaces, and change the electron injection mode, so that the carrier injection of the QLED device is further balanced;
2) The ZnO coating layer isolates the direct contact between ZnO and the quantum dot, and effectively weakens the fluorescence quenching of the defect state on the ZnO surface to the quantum dot.
The QLED devices provided in comparative examples 1-2 and application example 1 were subjected to J-V-L test, the J-V-L characteristic curve obtained by the test is shown in FIG. 25, the CE-L-PE characteristic curve obtained by processing the data is shown in FIG. 26, and the EQE-L characteristic curve is shown in FIG. 27.
As can be seen from FIGS. 25 to 27, application example 1 was conducted with ZnO/SiO as compared with comparative application example 2 2 -NH 2 The current efficiency CE and the external quantum efficiency EQE of the QLED serving as the electron transport layer are greatly improved. Through extensive literature investigation, the effect of introducing a series of amine groups into the photoelectric device can be basically determined, the amine groups are blocked at the QDs/ETL interface to form a dipole layer, a built-in reverse electric field is formed, the electron transmission of the QDs/ETL is further regulated, the charge injection of the QLED is close to complete balance, and the non-radiative recombination caused by unbalanced carrier injection is reduced.
Stability of QLED devices of application example 1 and comparative application example 1 was tested to obtain L/L 0 The attenuation curve versus graph is shown in fig. 28.
At an initial brightness of 25000cd/m 2 Under continuous DC driving conditions, by the formula L 0 n ×T 0.5 =k (where K is a constant, 1<n<2) Calculating the working life of the QLED, and assuming that the acceleration coefficient n=1.5, and the standard ZnO and ZnO/SiO 2 -NH 2 QLED devices with 50/10 of the electron transport layer are converted into an initial brightness of 1000cd/m 2 T of (2) 95 About 85.91h and 353.20h, respectively; t (T) 90 About 159.10h and 591.14h, respectively, and T 50 About 3153.70h and 11189.97h, respectively. As can be demonstrated by FIG. 28, znO/SiO was used 2 -NH 2 The working life of the QLED device can be greatly prolonged by using the electron transport layer.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. A QLED device comprises, in order from an upper layer to a lower layer: an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode; the electron transport layer is made of ZnO-based composite material;
The ZnO-based composite material comprises ZnO nanoparticlesParticles and SiO coated on the surfaces of the ZnO nano particles in turn 2 Coating layer and amino-modified SiO 2 A coating layer; the SiO is 2 Coating layer and amino-modified SiO 2 The mass ratio of the coating layer is (1-7): 1.
2. the QLED device of claim 1, wherein the ZnO nanoparticles are mixed with SiO 2 The mass ratio of the coating layer is 100: (0.1-20).
3. The QLED device of claim 1, wherein the SiO 2 Coating layer and amino-modified SiO 2 The total average thickness of the coating layer is 0.1-3 nm.
4. A QLED device according to any one of claims 1 to 3, wherein the ZnO based composite has an average particle diameter of 3 to 6nm.
5. The QLED device according to any one of claims 1 to 4, wherein the method for preparing the ZnO based composite material comprises the steps of:
(1) ZnO nano particles are mixed with a silicon source and a solvent for hydrolysis reaction to obtain SiO 2 A mixed solution of coated ZnO nano-particles;
(2) The SiO obtained in the step (1) is treated 2 And mixing the mixed solution coated with the ZnO nano particles with an amino silicon source, and then carrying out hydrolysis reaction to obtain the ZnO-based composite material.
6. The QLED device according to claim 5, wherein the temperature of the hydrolysis reaction in step (1) and step (2) is independently 0 to 90 ℃, and the time of the hydrolysis reaction is independently 10min to 10h.
7. The QLED device of claim 5, wherein the silicon source in step (1) is one of ethyl orthosilicate, methyl orthosilicate, and propyl orthosilicate.
8. The QLED device of claim 5, wherein the solvent in step (1) is a mixed solution of anhydrous ethanol and dimethyl sulfoxide.
9. The QLED device of claim 5, wherein the aminosilane source in step (2) comprises one or more of 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, and 3- (methacryloyl) propyl trimethoxysilane.
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