CN115960601A - Quantum dot light-emitting layer, preparation method thereof and quantum dot light-emitting diode device - Google Patents
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- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
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Abstract
The application discloses a quantum dot light-emitting layer, a preparation method thereof and a quantum dot light-emitting diode device. The quantum dot light-emitting layer comprises quantum dot materials and a main body material, the quantum dot materials comprise first quantum dots, and the main body material is filled in gaps among the first quantum dots; the first quantum dot is a core-shell quantum dot and comprises a core layer and a shell layer; the band gap width of the main body material is larger than or equal to the band gap width of the outermost shell material of the first quantum dot. The quantum dot light-emitting layer eliminates quantum dot gaps, so that uninterrupted transmission of carriers in a continuous phase can be guaranteed, and the problems that the carriers are difficult to transport and the carriers are captured by defects at an interface due to the quantum dot gaps in the light-emitting layer of the QLED device are solved; and the current efficiency and stability of the QLED device can be improved, so that the requirements of commercial application on high efficiency and reliability of the QLED device are met.
Description
Technical Field
The application relates to the technical field of display, in particular to a quantum dot light-emitting layer, a preparation method thereof and a quantum dot light-emitting diode device.
Background
Quantum dot light emitting diode devices (QLEDs) are an ideal solution for the next generation of display technologies, and because quantum dots have excellent light emitting characteristics such as nearly 100% light emitting efficiency, high color purity (light emitting peak width less than 25 nm), adjustable wavelength (from ultraviolet to infrared), and chemical/photochemical stability possessed by inorganic crystals, solution processing and manufacturing methods with large area and high yield can be used to realize flexible display with high color gamut, high contrast, fast response, high cost performance, and low energy consumption, they have been paid attention to by many workers at home and abroad.
In recent years, with the intensive research on the performance of QLED devices, current Efficiency (CE) and lifetime (T) 95 @1000 nit), the External Quantum Efficiency (EQE) of the QLED device based on the cadmium-containing system is as high as 20.5%, the operating life is as long as 30000 hours, and the performance of the Organic Light Emitting Diode (OLED) can be compared with that of the commercially applied QLED device.
In the QLED device, the device consists of an Anode (Anode), a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), a light-emitting layer (EML), an Electron Transport Layer (ETL) and a Cathode (Cathode), wherein the light-emitting layer is prepared from quantum dot nano-particles by a solution method, and the quantum dot nano-particles are arranged in a layer-by-layer stacking manner; when the device normally works, electrons and holes are injected into the quantum dot light-emitting layer through the anode and the cathode via the transport layer to carry out composite light emission. Common quantum dot nanoparticles are generally in a regular spherical or cubic structure, and in the process of forming a light emitting layer by stacking through a solution method, gaps can be formed among quantum dots, so that electrons and holes cannot be effectively transferred due to the discontinuity of a transport medium, charge accumulation is generated, and the internal resistance of a device is increased. For example, the particle size distribution of the quantum dots of three primary colors of red, green and blue obtained by the existing process is between 6 nm and 15nm, the quantum dot thin film is obtained by the solution process including the printing processes of spin coating, spray coating, transfer printing and the like, and the quantum dots have obvious gaps, as shown in fig. 1. Meanwhile, the existence of gaps in the luminescent layer leads to more defect states at the interface, and carriers are easily captured to generate non-radiative recombination, thus leading to poor photoelectric performance of the device.
Therefore, how to solve the problems of carrier transport difficulty and carrier capture by defects at an interface caused by quantum dot gaps in a light emitting layer of a QLED device so as to meet the requirements of commercial application on high efficiency and reliability of the QLED device is one of the main problems to be overcome at present.
Therefore, it is desirable to provide a quantum dot light emitting layer and a quantum dot light emitting diode device capable of solving the quantum dot gap in the light emitting layer of the QLED device to avoid the problems of carrier transport difficulty and carrier capture by defects at the interface.
Disclosure of Invention
The utility model aims to overcome prior art's not enough, provide a quantum dot luminescent layer, can solve the problem that the quantum dot clearance leads to the carrier to transport the difficulty and interface department defect catches the carrier in the QLED device luminescent layer, can solve the QLED device current inefficiency that produces from this and the relatively poor problem of stability to satisfy the demand of commercial application to QLED device high efficiency and reliability.
The application provides a quantum dot light-emitting layer, which comprises a quantum dot material and a main body material, wherein the quantum dot material comprises first quantum dots, and the main body material is filled in gaps among the first quantum dots;
the first quantum dot is a core-shell quantum dot and comprises a core layer and a shell layer; the band gap width (Eg) of the host material is greater than or equal to the band gap width (Eg) of the outermost shell material of the first quantum dot.
Optionally, in some embodiments of the present application, a difference between a band gap width of the host material and a band gap width of an outermost shell material of the first quantum dot is less than or equal to 0.8eV.
Optionally, in some embodiments of the present application, a lattice mismatch between the host material and the shell material of the first quantum dot is less than or equal to 5%.
Optionally, in some embodiments of the present application, a mass ratio of the first quantum dot to the host material is 100:5 to 20.
Optionally, in some embodiments of the present application, the quantum dot material further comprises a second quantum dot; the band gap width (Eg) of the second quantum dot is larger than or equal to the band gap width (Eg) of the outermost shell material of the first quantum dot, namely (Eg (second quantum dot) -Eg (first quantum dot-shell) ≥ 0).
Optionally, in some embodiments of the present application, the material of the second quantum dot is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP, and InGaP.
Optionally, in some embodiments of the present application, a lattice mismatch between the host material and the second quantum dot is less than or equal to 5%.
Optionally, in some embodiments of the present application, the energy level of the second quantum dot is the same as the host material.
Optionally, in some embodiments of the present application, the mass percentage of the second quantum dots in the quantum dot material is less than or equal to 20%.
Optionally, in some embodiments of the present application, a mass ratio of the first quantum dot to the second quantum dot is 100:1 to 15; and a mass ratio of the total mass of the second quantum dots and the host material to the first quantum dots is 5% to 20%.
Optionally, in some embodiments of the present application, the first quantum dot is a Type I core-shell quantum dot.
Optionally, in some embodiments of the present application, the core layer material of the first quantum dot includes: binary, multi-element and multi-element gradient alloy consisting of elements of II-VI groups, III-V groups and IV-VI groups and quantum dots containing core-shell components. The core layer material of the first quantum dot comprises one of CdSe, cdS, cdTe, cdSeTe, cdZnS, pbSe, znTe, cdSeS, pbS, pbTe, hgS, hgSe, hgTe, gaP, gaAs, inP, inAs, inZnP and InGaP.
Optionally, in some embodiments of the present application, the shell material of the first quantum dot is selected from a composition that can form a Type I core-shell structure with the core. The shell material of the first quantum dot comprises one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP.
Optionally, in some embodiments of the present application, the host material comprises a chalcogenide material. For example, the host material may be cadmium sulfide, zinc sulfide, indium sulfide, lead sulfide, or gallium sulfide. The preparation of the main body material is obtained by a continuous ion layer adsorption reaction method.
Optionally, in some embodiments of the present application, the second quantum dot is a nanoparticle having a particle size of 2 to 5nm.
Correspondingly, the application also provides a preparation method of the quantum dot light-emitting layer, which comprises the following steps:
step one, preparing a quantum dot luminescent layer film by adopting a quantum dot material;
and step two, filling the main body material into the gap between the quantum dots in the quantum dot light-emitting layer film by adopting a continuous ion-layer adsorption reaction method (SILAR) to obtain the quantum dot light-emitting layer.
Optionally, in some embodiments of the present application, the step of preparing the quantum dot light emitting layer by using a sequential ionic layer adsorption reaction method (SILAR) comprises: continuously soaking the annealed quantum dot light-emitting layer film in an alcohol phase solution of a metal cation precursor and an alcohol phase solution of a sulfur precursor; and circularly performing the soaking step. In the present application, using the SILAR method, filling of the host material can be achieved in a manner similar to the growth of quantum dot shells.
Optionally, in some embodiments of the present application, the step of preparing the quantum dot light emitting layer by using a sequential ionic layer adsorption reaction method (SILAR) comprises: the quantum dot light emitting layer film is placed in an alcohol phase solution of a metal cation precursor to be soaked for 30 s-1 min, then the film is washed by an alcohol reagent for 30 s-1 min, then the film is soaked in the alcohol phase solution of a sulfur precursor for 30 s-1 min, and the film is continuously cleaned in the alcohol reagent;
repeating the steps for 2-10 times to ensure that the gap of the quantum dot light emitting layer is filled with the main material, and then annealing at 100-150 ℃ for 1-15 min to remove the residual alcohol solvent.
Optionally, in some embodiments of the present application, the metal cation precursor includes a metal cation (labeled M) of at least one of cadmium (Cd), zinc (Zn), indium (In), lead (Pb), and gallium (Ga).
Optionally, in some embodiments herein, the sulfur precursor is a sulfur-containing salt compound comprising a metal sulfide and/or an organic sulfide; for example, sodium sulfide, potassium sulfide, ammonium sulfide.
In this application, use alcohol phase solution can not destroy quantum dot luminescent layer film structure, simultaneously, after the by-product impurity that the bulk material reaction produced was got rid of to alcohol phase solvent washing film, can get rid of low boiling alcohol phase solvent through low temperature annealing, can not remain on quantum dot luminescent layer film. The precursor of the multi-metal cation can be formed by mixing metal cation salts according to a certain proportion.
In addition, this application still provides a quantum dot light emitting diode device, including positive pole, negative pole and setting up the positive pole with quantum dot luminescent layer between the negative pole, quantum dot luminescent layer is foretell quantum dot luminescent layer.
The beneficial effect of this application lies in:
the quantum dot light-emitting layer fills the gap of the quantum dot light-emitting layer through the main body material, so that the continuity of a carrier in the transportation process of a device and the probability of passivating the surface defects of quantum dots to reduce the carrier capture are obtained, and the photoelectric performance and the stability of the device are further improved.
The quantum dot light-emitting layer fills gaps between quantum dots and quantum dots with the main body material through a continuous ionic layer adsorption reaction method (SILAR), so that gaps between the quantum dots are effectively eliminated, and the obtained quantum dot light-emitting layer can ensure that carriers are uninterruptedly transmitted in a continuous phase. Meanwhile, the filled main body material passivates the surface of the quantum dot, the possibility of capturing carriers by interface defects is reduced, and non-radiative recombination is reduced, so that the carrier transport process in the device is improved, the internal defects of a light emitting layer are reduced, and the photoelectric performance and the stability of the device are further improved.
The QLED device obtained by the application has excellent current efficiency and stability, and meets the requirements of commercial application on high efficiency and reliability of the QLED device.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of a quantum dot stack of a light emitting layer of a comparative example device provided herein;
fig. 2 is a first schematic view illustrating quantum dot stacking in a quantum dot light-emitting layer of a device provided by an embodiment of the present application;
fig. 3 is a second schematic view illustrating quantum dot stacking in a quantum dot light-emitting layer of a device provided in an embodiment of the present application;
fig. 4 is a schematic diagram of an energy level structure of a quantum dot light emitting diode device provided by an embodiment of the present application;
fig. 5 is a graph of an electroluminescence spectrum of a quantum dot light emitting diode device provided in example 3 of the present application;
fig. 6 is a graph of an electroluminescence spectrum of the quantum dot light emitting diode device provided in example 4 of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The embodiment of the application provides a quantum dot light-emitting layer, a preparation method thereof and a quantum dot light-emitting diode device. The following are detailed descriptions. It should be noted that the following description of the embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". The terms first, second, third and the like are used merely as labels, and do not impose numerical requirements or an established order. Various embodiments of the invention may exist in a range of forms; it is to be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention; accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, it is contemplated that the description of a range from 1 to 6 has specifically disclosed sub-ranges such as, for example, from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within a range such as, for example, 1, 2, 3, 4, 5, and 6, as applicable regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any number (fractional or integer) recited within the indicated range.
The inventor finds that, in the work of researching quantum dot materials and quantum dot light-emitting diode devices, the quantum dot materials used in the light-emitting layer in the QLED device structure generally consist of core-shell structures, the particle size is 8-15nm, and obvious gaps exist between the quantum dots and the quantum dots in the stacked light-emitting layer thin film. When the QLED device works, electrons and holes are injected into a wide band gap shell layer in a quantum dot light-emitting layer structure through a transmission layer by a cathode and an anode, and then injected into a quantum dot core in an energy transfer mode to carry out radiation composite luminescence; the gaps among the quantum dots generate discontinuous carrier transmission channels, so that charge injection potential barriers are raised, and meanwhile, the existence of the gaps exposes the surfaces of the quantum dots, so that defects are easily generated to capture carriers, and the photoelectric conversion efficiency is reduced. In previous research work, the carrier transport performance is enhanced by filling gaps of quantum dots in a manner of doping an organic polymer material in a light emitting layer, but the quantum dots of the inorganic nano material and the organic polymer belong to different phases, and the contact surface of the quantum dots and the organic polymer is easy to generate more defect states; meanwhile, a Type I heterojunction needs to be formed between the organic high polymer material and the quantum dot light-emitting layer so as to obtain electrons and holes which can be effectively injected into the quantum dots, and the types of the selectable organic high polymers are less. In addition, the quantum dots with uniform size are orderly arranged, so that overlarge gaps caused by uneven size are reduced, and meanwhile, the influence of a defect state on photoelectric performance is reduced by utilizing an effective mode, such as a thick shell layer, a short-chain ligand and the like to passivate the surface defects of the quantum dots. But still can not effectively eliminate the adverse effect of the quantum dot light-emitting layer because of the existence of the gap.
The present embodiment provides a quantum dot light-emitting layer, as shown in fig. 2 and 3. The quantum dot light-emitting layer comprises quantum dot materials and a main body material, wherein the quantum dot materials comprise first quantum dots, and the main body material is filled in gaps among the first quantum dots. And the first quantum dots are core-shell quantum dots, and the band gap width of the main body material is greater than or equal to that of the shell layer material of the first quantum dots. In particular, the host material is used to fill gaps between the quantum dot materials. After the gaps in the quantum dot light emitting layer are filled with the main body material, the gaps among the quantum dots are reduced, and the elimination of the gaps can ensure the uninterrupted transmission of current carriers in a continuous phase; meanwhile, the filled main body material can passivate the surface of the quantum dot, reduce the possibility of capturing a carrier by an interface defect, reduce non-radiative recombination, further improve the carrier transport process in a device and reduce the internal defect of a light-emitting layer, and provide a foundation for improving the photoelectric property and the stability of the device.
The particle size distribution of the red, green and blue quantum dots obtained by the prior art is between 6 and 15nm, the quantum dot film is obtained by the solution process, including spin coating, spray coating, transfer printing and other printing processes, and an obvious gap exists between the quantum dots, as shown in figure 1. After filling with the host material, the gap of the quantum dot light emitting layer is reduced, as shown in fig. 2.
Further, the host material includes a chalcogenide material. For example, the host material may be cadmium sulfide, zinc sulfide, indium sulfide, lead sulfide, or gallium sulfide. The preparation of the host material can be obtained by a continuous ion-shell adsorption reaction method.
In the present invention, the quantum dot material includes a first quantum dot and/or a second quantum dot.
In an embodiment, the quantum dot material is comprised of first quantum dots, as shown in fig. 2. In this case, the mass ratio of the first quantum dot to the host material is related to the interstitial volume generated by the different particle diameters of the quantum dots. For example, the mass ratio of the first quantum dot to the host material may be 100: 5. 100, and (2) a step of: 6. 100, and (2) a step of: 7. 100, and (2) a step of: 8. 100: 9. 100: 10. 100: 11. 100: 12. 100, and (2) a step of: 13. 100, and (2) a step of: 14. 100, and (2) a step of: 15. 100, and (2) a step of: 16. 100, and (2) a step of: 17. 100, and (2) a step of: 18. 100, and (2) a step of: 19 or 100:20. further, the first quantum dot is a Type I core-shell quantum dot, and comprises a core layer and a shell layer. Further, the core layer material of the first quantum dot includes: binary, multi-element and multi-element gradual change alloy consisting of elements of II-VI groups, III-V groups and IV-VI groups and quantum dots consisting of core-shell components. Accordingly, the shell material of the first quantum dot is selected to form a Type I core-shell structure with the core.
Further, the core layer material of the first quantum dot is selected from one of, but not limited to, cdSe, cdS, cdTe, cdSeTe, cdZnS, pbSe, znTe, cdSeS, pbS, pbTe, hgS, hgSe, hgTe, gaP, gaAs, inP, inAs, inZnP, and InGaP. The shell material of the first quantum dot is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP. Therefore, the first quantum dot is a single-component core-shell quantum dot, namely, the core layer and the shell layer are respectively made of single-component quantum dot materials.
Further, the band gap width (Eg) of the host material is greater than or equal to the band gap width (Eg) of the outermost shell material of the first quantum dot, namely Eg (host material) -Eg (first quantum dot-shell) is greater than or equal to 0. At the moment, the first quantum dots in the light-emitting layer are used as cores to form a Type I heterogeneous energy level structure with the host material, so that carriers are effectively confined in the quantum dots; meanwhile, the continuity of the carrier transmission channel is ensured without a gap. In addition, E g (host Material) -E g The (first quantum dot-shell layer) is less than or equal to 0.8eV, so that the difficulty of carrier injection caused by the overlarge band gap width of the main material can be avoided, and factors which are not beneficial to device stability, such as increase of internal impedance of the device, increase of working voltage, generation of Joule heat and the like can be avoided.
In some embodiments, the host material has a lattice mismatch with a shell material of the first quantum dot of less than or equal to 5%. If the lattice mismatch is greater than 5%, crystal defects are generated near the growth interface due to lattice stress, causing quenching of carriers at non-radiative recombination centers to reduce radiative recombination efficiency.
In another embodiment, the quantum dot material is comprised of the first quantum dot and the second quantum dot, as shown in fig. 3. Further, the mass percentage of the second quantum dots in the quantum dot material is less than or equal to 20%. The mass ratio of the first quantum dot to the second quantum dot to the host material is related to the interstitial volume generated by the different particle sizes of the quantum dots. For example, the mass ratio of the first quantum dot to the second quantum dot may be 100: 1. 100, and (2) a step of: 2. 100, and (2) a step of: 3. 100: 4. 100: 5. 100, and (2) a step of: 6. 100: 7. 100, and (2) a step of: 8. 100, and (2) a step of: 9. 100, and (2) a step of: 10. 100, and (2) a step of: 11. 100, and (2) a step of: 12. 100: 13. 100, and (2) a step of: 14 or 100:15; further, the mass ratio of the total mass of the second quantum dots and the host material to the first quantum dots is 5: 100. 6: 100. 7: 100. 8: 100. 9: 100. 10: 100. 11: 100. 12: 100. 13: 100. 14: 100. 15: 100. 16: 100. 17: 100. 18: 100. 19:100 or 20:100.
further, the second quantum dot is selected from one of, but not limited to, cdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znss, pbS, pbSeS, inZnP, and InGaP. Furthermore, the second quantum dots are nanoparticles with the particle size of 2-5 nm. It can be seen that the second quantum dot is a single-component quantum dot, i.e., is composed of a single-component quantum dot material.
Further, the band gap width (Eg) of the second quantum dot is larger than or equal to the band gap width (Eg) of the outermost shell material of the first quantum dot, namely Eg (second quantum dot) -Eg (first quantum dot-shell) is larger than or equal to 0.
Further, the lattice mismatch between the host material and the second quantum dots is less than or equal to 5%.
Further, the energy level of the second quantum dot is consistent with the host material. Further, the lattice parameter and the band gap width of the second quantum dot material are consistent with those of the host material. For example, the second quantum dot material may be selected in accordance with the composition of the host material composition, in which case the host material may be understood as an additional shell structure of the quantum dot.
In the quantum dot light emitting layer, the quantum dots are generally stacked in a close-coupled arrangement, as shown in fig. 1; at this time, the quantum dot light emitting layer includes the following two possible cases: (1) when the quantum dot core center spacing s is more than 10 nm; (2) when the distance s between the quantum dot cores is less than or equal to 10 nm.
For example, when the distance s between the luminescent centers of the adjacent first quantum dots is less than or equal to 10nm, a relatively significant energy resonance transfer effect (FRET) occurs, resulting in energy loss. In order to reduce the energy resonance transfer loss among the quantum dots, when the nuclear center distance s of the quantum dots is less than or equal to 10nm, the nuclear center distance of the first quantum dots is increased by doping the second quantum dots, as shown in fig. 3; the principle is as follows: the second quantum dot material is used as the spacer for the first quantum dots, S between the first quantum dots is increased to the extent that the energy resonance transfer loss is reduced, and then the gap is filled with the main body material to obtain the effect of the invention. Furthermore, the doping of the second quantum dots is controlled within the range of less than or equal to 20% in mass percentage, so that the problem of aging of a device function layer material under high current density due to the fact that the working voltage of a device is increased due to the introduction of too many wide-band-gap second quantum dot components is avoided. Therefore, the second quantum dots have the functions of increasing the distance between the luminescent cores of the first quantum dots, reducing the energy resonance transfer (FRET) effect, avoiding the formation of unevenly distributed energy level barriers in the luminescent layer film in order to obtain the energy level morphology with flat carrier transmission, and selecting materials with evenly distributed components and consistent with the energy level of the filling main body.
For example, when the core center-to-center spacing s of adjacent first quantum dots is greater than 10nm, where the energy resonance transfer problem is small, only the first quantum dots can be used as the quantum dot material, and the second quantum dots are not needed to increase the spacing of the first quantum dots. At this time, the quantum dot light emitting layer is prepared from the first quantum dot and the host material, as shown in fig. 2. At this time, the quantum dots in the light emitting layer form a Type I hetero-level structure with the host material as a core, contributing to confinement of carriers inside the quantum dots.
The embodiment of the application also provides a preparation method of the quantum dot light-emitting layer, which comprises the following steps:
preparing a quantum dot light-emitting layer film by adopting a quantum dot material;
and step two, filling the main body material into the gap between the quantum dots in the film of the quantum dot light-emitting layer by adopting a continuous ionic layer adsorption reaction method (SILAR) to obtain the quantum dot light-emitting layer.
Further, the quantum dot material comprises a first quantum dot and/or a second quantum dot. In detail, the band gap width of the second quantum dot is greater than or equal to the band gap width of the outermost shell material of the first quantum dot. The first quantum dots are Type I Type core-shell quantum dots. The core layer material of the first quantum dot is selected from any one of CdSe, cdS, cdTe, cdSeTe, cdSN, pbSe, znTe, cdSeS, pbS, pbTe, hgS, hgSe, hgTe, gaP, gaAs, inP, inAs, inZnP and InGaP; the shell material of the first quantum dot is selected from any one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP. The particle size of the second quantum dots is 2-5 nm. The material of the second quantum dot is selected from any one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP.
Further, the host material is a chalcogenide material, and the band gap width of the host material is greater than or equal to that of the shell material of the first quantum dot. The difference between the band gap width of the main body material and the band gap width of the outermost shell material of the first quantum dot is less than or equal to 0.8eV. The lattice mismatch degree of the main body material and the shell material of the first quantum dots is less than or equal to 5%.
Further, the step of preparing the quantum dot light emitting layer by using a sequential ionic layer adsorption reaction method (SILAR) comprises:
s1, placing the annealed quantum dot light-emitting layer film in an alcohol phase solution of a metal cation precursor for soaking for 30S-1 min, and then washing the film for 30S-1 min by using an alcohol reagent;
s2, placing the quantum dot light-emitting layer film obtained in the step S1 in an alcohol phase solution of a sulfur precursor, soaking for 30S-1 min, and continuously cleaning in an alcohol reagent;
and S3, repeating the steps S1 and S2 for 2 to 10 times to ensure that the gap of the quantum dot light-emitting layer is filled with the main material, and then annealing at 100 to 150 ℃ for 1 to 15min to remove residual alcohol solvent.
Specifically, the metal cation precursor includes a metal cation of at least one of cadmium (Cd), zinc (Zn), indium (In), lead (Pb), and gallium (Ga). The sulfur precursor is a sulfur-containing salicylic compound containing a metal sulfide and/or an organic sulfide. For example, sodium sulfide, potassium sulfide, ammonium sulfide. After being continuously immersed in the alcohol phase solution of the metal cation precursor and the alcohol phase solution of the sulfur precursor, the metal cation precursor and the sulfur precursor can react to generate metal sulfide, such as cadmium sulfide, zinc sulfide, indium sulfide, lead sulfide or gallium sulfide, that is, the host material in the quantum dot light emitting layer.
In addition, in the preparation method of the quantum dot light-emitting layer, the quantum dot light-emitting layer is prepared by adopting a continuous ionic layer adsorption reaction method (SILAR) (repeating the step of continuously soaking in an alcohol phase solution of a metal cation precursor and an alcohol phase solution of a sulfur precursor), and the main body material can be filled in a manner similar to the growth of a quantum dot shell layer.
When the distance s between the centers of the luminescent cores of the adjacent quantum dots is less than or equal to 10nm, at the moment, when the luminescent layer of the quantum dots is prepared, the second quantum dots are mixed with the first quantum dots according to a certain proportion, the distance between the first quantum dots is increased in a form of approximately regular distribution by the second quantum dots, and the energy loss caused by resonance transfer is reduced. When the quantum dot core center spacing s is more than 10nm, the quantum dot light-emitting layer can be prepared by only adopting the first quantum dot as a quantum dot material.
The embodiment of the application also provides a quantum dot light emitting diode device (QLED device), which comprises an anode, a cathode and a quantum dot light emitting layer arranged between the anode and the cathode, wherein the quantum dot light emitting layer is the quantum dot light emitting layer.
The embodiment of the application also provides a printing quantum dot display screen, which comprises the quantum dot light-emitting diode.
Further, the quantum dot light emitting diode includes an anode 1, a hole injection layer 2, a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, and a cathode 6, as shown in fig. 4.
Further, the anode is selected from one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene and carbon nanotubes; the material of the hole injection layer is PEDOT: one or more of PSS, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide and copper oxide; the hole transport layer is made of one or more of PVK, poly-TPD, CBP, TCTA and TFB; the quantum dot light-emitting layer comprises a red, green and blue multi-component mixed quantum dot light-emitting layer; the electron transport layer is made of n-type ZnO or TiO 2 、SnO、Ta 2 O 3 、AlZnO、ZnSnO、InSnO、Alq 3 、Ca、Ba、CsF、LiF、CsCO 3 One or more of; the cathode is selected from one or more of Al, ca, ba and Ag.
In the application, a 128-channel life test system customized by Guangzhou New View company is adopted for the life test of the device. The system is constructed by driving a QLED by a constant voltage and constant current source and testing the change of voltage or current; a photodiode detector and test system for testing the variation of brightness (photocurrent) of the QLED; the luminance meter tests the luminance (photocurrent) of the calibration QLED.
The present application has been repeated several times, and the present invention will now be described in further detail with reference to some test results, which will be described in detail below with reference to specific examples.
Example 1
The present embodiment provides a quantum dot light emitting layer, which includes a quantum dot material and a host material, where the host material fills a gap between a quantum dot and a quantum dot in the quantum dot material.
The quantum dot material in the quantum dot light-emitting layer adopts red quantum dot CdSe/CdS with the grain diameter of about 14nm, after spin coating to form a film, the film is continuously soaked in a cadmium acetate ethanol solution and a sodium sulfide ethanol solution through SILAR, reaction byproducts are removed by cleaning with ethanol, the cycle is carried out for 3 times, and finally, the residual ethanol solvent is removed by annealing on a hot plate at 120 ℃ for 10min, so that the red quantum dot light-emitting layer film of cadmium sulfide formed by filling quantum dots in gaps is obtained. The main body material of cadmium sulfide is consistent with the CdS component of the quantum dot shell, so that interface defects cannot be generated due to the problem of interface lattice matching degree, and meanwhile, because the surface defects of the quantum dots of the luminous layer after filling are passivated, the quenching effect on current carriers is reduced, and the cadmium sulfide is also an important factor for obtaining high performance of a device.
Example 2
The present embodiment provides a quantum dot light emitting layer, which includes a quantum dot material and a host material, where the host material fills a gap between a quantum dot and a quantum dot in the quantum dot material.
In the quantum dot light-emitting layer of the embodiment, blue quantum dots ZnCdSe/ZnS are selected as the quantum dot material, and the particle size is about 8nm. If only blue quantum dots ZnCdSe/ZnS are used as quantum dot materials, the distance between the central cores of the quantum dots is less than 10nm after the quantum dots are stacked to form a film, an obvious FERT effect can be generated, and in addition, when the particle size of the quantum dots is small, the generated specific surface area is larger, and the possibility of existence of defect states is higher. Thus, in this example, zinc sulfide nanoparticles with a particle size of about 4nm were added to the ZnCdSe/ZnS quantum dot solution in an amount of 10 mass%.
After a quantum dot solution containing 18mg of ZnCdSe/ZnS and 2mg of ZnS in each milliliter is used for spin coating to form a film, the film is continuously soaked in a zinc acetate methanol solution and a sodium sulfide methanol solution by SILAR, reaction byproducts are removed by cleaning with methanol, the cycle is carried out for 5 times, and finally, the residual methanol solvent is removed by annealing on a hot plate at 100 ℃ for 15min, so that the blue quantum dot light-emitting layer film of zinc sulfide formed by filling quantum dots in gaps is obtained.
Example 3
The present embodiment provides a quantum dot light emitting diode device (QLED device), and a method for manufacturing the same includes the steps of:
spin-coated hole injection layer on anode ITO PEDOT: PSS material, annealing at 100 ℃ for 15min; then forming a hole transport layer TFB on the hole injection layer, and annealing for 15min at 100 ℃; forming a luminescent layer of CdSe/CdS red quantum dots (please refer to the luminescent layer of quantum dots in example 1) on the hole transport layer as the bearing part, and annealing at 80 ℃ for 10min to remove the residual solvent of the luminescent layer film; soaking the annealed quantum dot light-emitting layer film in a cadmium acetate ethanol solution for 45s, then washing the film for 1min by using ethanol after soaking in a sodium sulfide ethanol solution for 45s, so as to remove excessive ions which are adhered to the surface of the film and do not participate in the reaction, and circulating for 3 times to obtain a red light-emitting layer film filled with a zinc sulfide main body material; spin-coating an ethanol solution containing ZnO on the luminescent layer to obtain an electron transport layer; and finally, forming the electroluminescent device by evaporating an Ag cathode and packaging.
The electroluminescent spectrum analysis of the quantum dot light emitting diode device of the present embodiment is shown in fig. 5.
Example 4
The present embodiment provides a quantum dot light emitting diode device (QLED device), and a method for manufacturing the quantum dot light emitting diode device (QLED device) includes the steps of:
spin-coated hole injection layer on anode ITO PEDOT: PSS material, annealing at 100 ℃ for 15min; then forming a hole transport layer PVK on the hole injection layer, and annealing for 15min at 100 ℃; forming a light-emitting layer (refer to the quantum dot light-emitting layer in example 2) of ZnCdSe/ZnS blue quantum dots containing 10% by mass of ZnS on the hole transport layer as a carrier, and annealing at 80 ℃ for 10min to remove the residual solvent of the light-emitting layer thin film; soaking the annealed quantum dot light-emitting layer film in a zinc acetate methanol solution for 30s, then washing the film for 1min by using methanol, then soaking the film in a sodium sulfide methanol solution for 30s, then washing the film for 1min by using methanol to remove excessive ions which are adhered to the surface of the film and do not participate in the reaction, and circulating for 5 times to obtain a blue light-emitting layer film filled with a zinc sulfide main body material; spin-coating an ethanol solution containing ZnMgO on the luminescent layer to obtain an electron transport layer; and finally, forming the electroluminescent device by evaporating an Al cathode and packaging.
The electroluminescence spectrum of the quantum dot light emitting diode device of this embodiment is analyzed, as shown in fig. 6.
Comparative example 1
The quantum dot light emitting diode device of comparative example 1 is substantially the same as example 1 except that: the luminescent layer is CdSe/CdS quantum dots. The structure of the quantum dot light emitting layer in the quantum dot light emitting diode device can be referred to fig. 1.
Comparative example 2
The quantum dot light emitting diode device of comparative example 2 is substantially the same as example 2 except that: the luminescent layer is ZnCdSe/ZnS quantum dots. The structure of the quantum dot light emitting layer in the quantum dot light emitting diode device can be referred to fig. 1.
Test example 1
The photoelectric properties and the lifetimes of the quantum dot light emitting diode devices obtained in example 3, example 4, comparative example 1, and comparative example 2 were measured, and the results are shown in table 1, in which the devices were recorded.
Table 1 test data of light emitting diode devices prepared in examples and comparative examples
From the data in table 1 it can be derived:
the quantum dot light-emitting diode device prepared in example 3 had an electroluminescence peak position of 625nm, a half-peak width of 25nm, an External Quantum Efficiency (EQE) of 19.5%, and a lifetime (T) 95 @1000 nit) is 2300h. At the same time, the turn-on voltage (V) of the device T ) A 0.2V reduction relative to the device of comparative example 1.
The quantum dot light-emitting diode device prepared in example 4 had an electroluminescence peak position of 472nm, a half-peak width of 22nm, an External Quantum Efficiency (EQE) of 17%, and a lifetime (T) 95 @1000 nit) was 150h. The blue quantum dot light-emitting diode device has high turn-on voltage due to the large forbidden bandwidth of the blue quantum dot, and the turn-on voltage (V) is obtained after the light-emitting layer is processed by adopting the scheme of the invention T ) Reduced by 0.4V relative to the comparative example, i.e.The quantum dot light-emitting diode device has smaller resistance and better conductivity.
In the quantum dot light emitting diode device in the comparative example, the transport ability of carriers inside the light emitting layer was reduced due to the existence of gaps between the quantum dots, resulting in the obtained External Quantum Efficiency (EQE) and lifetime (T) 95 @1000 nit) is lower than the device performance of the light-emitting layer filled with the host material. Therefore, by adopting the quantum dot light-emitting diode device of the comparative example, the surface of the quantum dot of the light-emitting layer has more non-passivated defects and gaps between the quantum dot and the quantum dot which are not filled, so that the transmission capability of charges among the quantum dots is poor, and meanwhile, FRET (fluorescence resonance energy) generated between adjacent quantum dots causes partial energy loss, so that the photoelectric performance of the comparative example device is poor.
In conclusion, the quantum dot light-emitting layer eliminates quantum dot gaps, so that uninterrupted transmission of carriers in a continuous phase can be guaranteed, and the problems that carrier transportation is difficult and the carriers are captured by defects at an interface due to the quantum dot gaps in the light-emitting layer of the QLED device are solved; and further, the current efficiency and stability of the QLED device can be improved, so that the requirements of commercial application on the high efficiency and reliability of the QLED device are met.
According to the quantum dot light emitting layer, the gap between the quantum dot light emitting layers is filled by using a wide-band-gap inorganic semiconductor as a main body material through an SILAR (continuous ion layer adsorption reaction) method, and continuous transmission of carriers in the quantum dot light emitting layers is guaranteed. Meanwhile, the lattice mismatch degree of the selected main material and the quantum dot shell layer is less than or equal to 5%, the defect state density at the interface is effectively passivated after filling, the possibility of capturing carriers by the interface defects is reduced, non-radiative recombination is reduced, the carrier transport process in the device is improved, the internal defects of the light emitting layer are reduced, and the photoelectric performance and the stability of the device are improved.
A luminescent layer in the QLED device is prepared from a first quantum dot with a Type I core-shell structure, and a shell layer has the functions of passivating the surface defect state of a quantum dot core and improving the fluorescence yield of the quantum dot on one hand, and binding electron and hole wave functions in the core on the other hand, so that the situation that excitons are delocalized to the non-radiative recombination center of the shell layer surface state are quenched is avoided.
The quantum dot light emitting layer, the preparation method thereof and the quantum dot light emitting diode device provided in the embodiments of the present application are described in detail above, and specific examples are applied herein to illustrate the principles and embodiments of the present application, and the description of the above embodiments is only used to help understanding the method and the core concept of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.
Claims (16)
1. The quantum dot light-emitting layer is characterized by comprising a quantum dot material and a main body material, wherein the quantum dot material comprises first quantum dots, and the main body material is filled in gaps among the first quantum dots;
the first quantum dot is a core-shell quantum dot and comprises a core layer and a shell layer; the band gap width of the main body material is larger than or equal to the band gap width of the shell material of the first quantum dot.
2. The quantum dot light emitting layer of claim 1, wherein the difference between the band gap width of the host material and the band gap width of the outermost shell material of the first quantum dot is less than or equal to 0.8eV; and/or
The lattice mismatch degree of the host material and the shell material of the first quantum dot is less than or equal to 5%.
3. The quantum dot light-emitting layer according to claim 1 or 2, wherein the mass ratio of the first quantum dot to the host material is 100:5 to 20.
4. The quantum dot light emitting layer of claim 1, wherein the quantum dot material further comprises a second quantum dot having a band gap width greater than or equal to a band gap width of an outermost shell material of the first quantum dot.
5. The quantum dot light emitting layer of claim 4, wherein the host material has a lattice mismatch with the second quantum dot of less than or equal to 5%; and/or
The energy level of the second quantum dot is the same as the host material; and/or
The second quantum dot is less than or equal to 20% by mass of the quantum dot material.
6. The quantum dot light-emitting layer of claim 4 or 5, wherein the mass ratio of the first quantum dot to the second quantum dot is 100:1 to 15; and a mass ratio of a total mass of the second quantum dots and the host material to the first quantum dots is 5% to 20%.
7. The quantum dot light emitting layer of claim 1, wherein the first quantum dot is a Type I core-shell quantum dot;
the core-layer material of the first quantum dot is selected from one of CdSe, cdS, cdTe, cdSeTe, cdSnS, pbSe, znTe, cdSeS, pbS, pbTe, hgS, hgSe, hgTe, gaP, gaAs, inP, inAs, inZnP and InGaP;
the shell material of the first quantum dot is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP.
8. The quantum dot light emitting layer of claim 1, wherein the host material is a chalcogenide material; the main body material is selected from one of cadmium sulfide, zinc sulfide, indium sulfide, lead sulfide and gallium sulfide.
9. The quantum dot light-emitting layer according to claim 4 or 5, wherein the particle size of the second quantum dot is 2 to 5nm;
the material of the second quantum dots is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP.
10. A preparation method of a quantum dot light-emitting layer is characterized by comprising the following steps:
step one, preparing a quantum dot luminescent layer film by adopting a quantum dot material;
and step two, filling the main body material into gaps among quantum dots in the quantum dot light-emitting layer film by adopting a continuous ionic layer adsorption reaction method to obtain the quantum dot light-emitting layer.
11. The method of claim 10, wherein the quantum dot material comprises a first quantum dot and/or a second quantum dot; the band gap width of the second quantum dot is larger than or equal to the band gap width of the outermost shell material of the first quantum dot;
the first quantum dots are Type I Type core-shell quantum dots; the core layer material of the first quantum dot is selected from one of CdSe, cdS, cdTe, cdSeTe, cdSnS, pbSe, znTe, cdSeS, pbS, pbTe, hgS, hgSe, hgTe, gaP, gaAs, inP, inAs, inZnP and InGaP; the shell material of the first quantum dot is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP;
the particle size of the second quantum dots is 2-5 nm; the material of the second quantum dots is selected from one of CdS, cdTe, cdSeTe, cdZnSe, cdZnS, cdSeS, znSe, znSeS, znS, pbS, pbSeS, inZnP and InGaP.
12. The method of claim 11, wherein the host material is a chalcogenide material, and the band gap width of the host material is greater than or equal to the band gap width of the shell material of the first quantum dot;
the difference between the band gap width of the main body material and the band gap width of the outermost shell material of the first quantum dot is less than or equal to 0.8eV;
the lattice mismatch degree of the main body material and the shell material of the first quantum dots is less than or equal to 5%.
13. The method of any one of claims 10 to 12, wherein the step of preparing the quantum dot light emitting layer by using a continuous ionic layer adsorption reaction method comprises: continuously soaking the annealed quantum dot light-emitting layer film in an alcohol phase solution of a metal cation precursor and an alcohol phase solution of a sulfur precursor; and circularly performing the soaking step.
14. The method of claim 13, wherein the step of preparing the quantum dot light-emitting layer by using a continuous ionic layer adsorption reaction comprises:
placing the quantum dot light-emitting layer film in an alcohol phase solution of a metal cation precursor, soaking for 30 s-1 min, and washing with an alcohol reagent; then soaking the sulfur precursor in an alcohol phase solution of the sulfur precursor for 30 s-1 min, and cleaning the sulfur precursor by using an alcohol reagent;
repeating the steps for 2-10 times to realize that the gap of the quantum dot light-emitting layer is filled by the main material, and then annealing at 100-150 ℃ for 1-15 min to remove the residual alcohol solvent.
15. The method of claim 13 or 14, wherein the metal cation precursor comprises a metal cation of at least one of Cd, zn, in, pb, and Ga;
the sulfur precursor is a sulfur-containing salicylic compound containing a metal sulfide and/or an organic sulfide.
16. A quantum dot light emitting diode device comprising an anode, a cathode and a quantum dot light emitting layer disposed between the anode and the cathode, wherein the quantum dot light emitting layer is the quantum dot light emitting layer of any one of claims 1 to 9.
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| PCT/CN2022/118788 WO2023056829A1 (en) | 2021-10-08 | 2022-09-14 | Quantum dot light-emitting layer, preparation method for quantum dot light-emitting layer, and quantum dot light-emitting diode device |
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