QWLED of three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots and preparation method of QWLED

Abstract

The invention relates to a QWLED of a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots and a preparation method of the QWLED, and belongs to the field of LED preparation. The QWLED sequentially comprises an electrode layer, an inorganic electron transport layer, a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer, an organic hole transport layer and an ITO glass substrate from top to bottom, and the CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer is of a three-dimensional heterojunction quantum well structure formed by compounding wide bandgap cadmium selenide quantum dots and narrow bandgap lead sulfide quantum dots. The CdSe / PbS quantum well composite material prepared by the invention has a three-dimensional depletion region and a three-dimensional heterojunction structure, high quantum efficiency, good optical characteristics and structural stability, and the prepared LED device with the three-dimensional depletion region and the three-dimensional heterojunction quantum well structure has excellent electroluminescent efficiency and external quantum efficiency, and can be used as a light emitting diode device of the three-dimensional depletion region and the three-dimensional heterojunction quantum well structure. And the method has huge application potential in the fields of high-brightness, long-service-life and high-resolution display technology and the like.

Description

Technical Field

[0001] The present invention belongs to the field of LED preparation, and particularly relates to a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots and a preparation method thereof. Background Art

[0002] Quantum dots, as quasi-zero-dimensional materials with all three-dimensional scales in the range of 1-100 nm, can control the size, shape, and emission wavelength of quantum dots by adjusting parameters such as quantum dot growth time, reaction temperature, and ligands. Lead sulfide quantum dots, as a type of P-type semiconductor nanomaterial, have an adjustable bandgap (0.7-2.1 eV) and are an excellent choice for wavelength-tunable quantum dot devices due to their low cost, solution processability, and adjustable bandgap. Lead sulfide quantum dots are considered an excellent choice for applications such as near-infrared light-emitting LEDs and solar cells due to their relatively large size. However, there is still room for expansion in the research on lead sulfide quantum dots within the visible light excitation wavelength range.

[0003] In order to solve the surface defects of lead sulfide quantum dot materials, researchers have been seeking how to passivate defects and further improve their photoelectric performance. Studies have shown that on the one hand, the lattice mismatch can be greatly reduced by forming a core-shell structure and strictly controlling the temperature and precursor concentration during the synthesis of the quantum dot core-shell structure. On the other hand, other materials are added to the lead sulfide quantum dots to form a composite material to adjust the band structure, thereby improving its photoelectric performance. (CN114447237A) provides a quantum dot light-emitting diode based on lead-based quantum dots and a block polymer coated on the surface of the lead-based quantum dots and a preparation method thereof: wherein the lead-based quantum dots are quantum dots of lead sulfide, lead selenide and lead telluride; the block polymer is one or more of polystyrene-poly (4-vinyl pyrimidine), poly 4-methylstyrene-poly (4-vinyl pyrimidine) and poly 3-methylstyrene-poly (4-vinyl pyrimidine), and these block polymers are mainly used to repair the surface defects of the lead-based quantum dots, so as to improve the photoelectric performance of the quantum dots. (CN114933898A) reports a method for preparing transition metal doped lead sulfide quantum dots: first synthesize an organic lead precursor doped with transition metal ions, use a hot injection method to obtain a lead sulfide colloidal quantum dot solution doped with transition metals, centrifuge and purify to obtain lead sulfide colloidal quantum dots doped with transition metals, which can effectively reduce the surface defect rate of quantum dots and improve the photoelectric performance of quantum dots. (CN103525416A) provides a blue light-excited green semiconductor nanocrystal for LED and a preparation method thereof: ZnS / PbS / ZnS quantum wells are synthesized by an aqueous phase synthesis method, which can emit green light under 450-460nm wavelength light excitation, and the emission spectrum range is 505-550nm, which effectively improves the photoluminescence performance of lead sulfide quantum dots, but due to the poor lattice matching of ZnS and PbS in this quantum well material, and the difficulty in forming ZnS nuclei, the obtained quantum well material has poor consistency. (CN118579830A) discloses a PbS quantum dot-SnS2 heterostructure material and its preparation method and application: This heterojunction is a composite of flower-shaped SnS2 nanosheets and PbS quantum dots, which is mainly used in the field of gas sensing, and its photoelectric properties are limited. In addition, the luminous performance of quantum dot light-emitting diodes depends on the charge distribution of the quantum dot light-emitting layer and its performance, and is directly related to the carrier concentration in the light-emitting layer. Generally speaking, the higher the carrier concentration, the shorter the life of photogenerated carriers or electrogenerated carriers in the semiconductor, the higher the probability of Auger recombination, and the more unfavorable the semiconductor luminous performance. Therefore, the effective photoelectric effect of the diode usually occurs in the depletion region. This three-dimensional composite light-emitting layer with a three-dimensional depletion region formed by means of a heterojunction has a simple preparation process, and can effectively play the synergistic effect of the energy bands of each component in the composite material and the conductive properties of the material, thereby realizing the overall photoelectric performance improvement of the heterojunction.

[0004] In summary, the lead sulfide quantum dot materials and devices mentioned in most literatures or patents cannot effectively passivate surface defects or form an effective composite light-emitting layer theoretically, thus affecting the application of lead sulfide quantum dot materials in electroluminescence. SUMMARY OF THE INVENTION

[0005] The purpose of the present invention is to provide a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots and a preparation method thereof. The prepared QWLED is a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots. The present invention respectively prepares PbS quantum dots and CdSe quantum dots by a thermal injection method, and further mixes the two quantum dot solutions to form a CdSe / PbS quantum dot material composite with a three-dimensional depletion region and a three-dimensional heterojunction quantum well structure, and demonstrates a preparation method of a three-dimensional heterojunction quantum well LED. The three-dimensional heterojunction quantum well structure is novel, the device structure is stable and efficient. The prepared CdSe / PbS three-dimensional heterojunction quantum well material has a three-dimensional heterojunction quantum well structure, high quantum efficiency, good optical properties and structural stability. The prepared three-dimensional heterojunction quantum well LED device has excellent electroluminescence efficiency and external quantum efficiency, and has great application potential in the fields of high brightness, long life and high resolution display technology, etc.

[0006] To achieve the above purpose, the technical solution of the present invention is: a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots, which sequentially includes an electrode layer, an inorganic electron transport layer, a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate from top to bottom. The CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer is a three-dimensional heterojunction quantum well structure formed by the composite of wide-bandgap cadmium selenide quantum dots and narrow-bandgap lead sulfide quantum dots.

[0007] Further, the CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer includes a plurality of PbS quantum dots with a depletion region, and a plurality of CdSe quantum dots with a depletion region surrounding each PbS quantum dot with a depletion region, and each CdSe quantum dot with a depletion region isolates the direct contact between the PbS quantum dot with a depletion region and the inorganic electron transport layer and the organic hole transport layer.

[0008] Further, the PbS quantum dot with a depletion region includes a PbS quantum dot material neutral region from the inside to the outside, and a PbS quantum dot contact depletion region in direct contact with the CdSe quantum dot with a depletion region; the CdSe quantum dot with a depletion region includes a CdSe quantum dot material neutral region from the inside to the outside, and a CdSe quantum dot contact depletion region in direct contact with the PbS quantum dot with a depletion region.

[0009] Further, the inorganic electron transport layer is a ZnMgO electron transport layer.

[0010] Further, the organic hole transport layer includes a TFB hole transport layer and a PEDOT:PSS hole transport layer.

[0011] The present invention also provides a preparation method of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots as described in any one of the above, comprising the following steps:

[0012] (1) Clean the ITO conductive glass with deionized water, acetone, and isopropanol for 15 - 25 min respectively, and dry it with nitrogen at a predetermined temperature.

[0013] (2) Spin-coat the PEDOT:PSS solution on the ITO conductive glass obtained in step (1) in a glove box with a spin coater, and then put the conductive glass sheet on a heating table for annealing.

[0014] (3) Dissolve TFB in a toluene solution, then spin-coat the solution on the conductive glass sheet obtained in step (2) in a glove box with a spin coater, and then put the conductive glass sheet on a heating table for annealing.

[0015] (4) Spin-coat the CdSe / PbS mixed quantum dot solution on the conductive glass sheet obtained in step (3) in a glove box with a spin coater, and then put the conductive glass sheet on a heating table for annealing.

[0016] (5) In a glove box, spin-coat the Zn 0.85 Mg 0.15 O solution on the conductive glass sheet obtained in step (4) with a spin coater, and then put the conductive glass sheet on a heating table for annealing.

[0017] (6) Evaporate electrodes on the conductive glass sheet obtained in step (5) using a thermal evaporation machine, and thus obtain a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots.

[0018] Further, in step (2), the PEDOT:PSS solution is first filtered through a 0.22 - 0.45 μm filter head, the annealing temperature is 100 - 120 °C, the environmental conditions are in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 20 - 30 min; in step (3), the concentration of the TFB solution is 8 - 10 mg / ml, the annealing temperature is 160 - 200 °C, the environmental conditions are in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 15 - 30 min; in step (5), Zn 0.85 Mg 0.15The concentration of the O solution is 15 - 25 mg / ml, the annealing temperature is 100 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where the oxygen and water are both less than 1 ppm, and the annealing time is 10 - 20 min; in step (6), the electrode layer is a silver electrode with a thickness of 100 nm.

[0019] Furthermore, in step (4), the specific method for preparing the CdSe quantum dot solution is as follows:

[0020] Step S61: Dissolve a predetermined amount of selenium powder and TOP solution at a set temperature to prepare a selenium precursor solution; stir a predetermined amount of cadmium oxide and oleic acid at a set temperature for a set time, then inject ODE solution and raise the solution temperature; take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the solution temperature reaches the set value and maintain for a set time, and at the same time use an ultraviolet lamp for excitation; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n - hexane, obtain the quantum dot solution, and store it under low - temperature conditions;

[0021] Step S62: Take out the supernatant of a part of the quantum dot solution after standing, dissolve oleic acid with methanol, then add n - hexane solution and take out the upper layer solution, add an appropriate amount of absolute ethanol for centrifugation, and finally dissolve the precipitate with n - hexane to obtain a purified CdSe quantum dot solution, and finally prepare a CdSe quantum dot solution with a concentration of 10 - 30 mg / ml.

[0022] Furthermore, in step (4), the specific method for preparing the PbS quantum dot solution is as follows:

[0023] Step S71: Dissolve a predetermined amount of lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolve a predetermined amount of sulfur powder in tri - n - octylphosphine and inject it into a three - necked flask at a predetermined speed, and finally quickly cool the quantum dot solution by means of a water bath, dilute it with n - hexane, obtain the quantum dot solution, and store it under low - temperature conditions;

[0024] Step S72: Take out the supernatant of a part of the quantum dot solution after standing, dissolve it with ethanol, then add n - hexane solution and take out the upper layer solution, add absolute ethanol for centrifugation, and finally dissolve the precipitate with n - hexane to obtain a purified PbS quantum dot solution, and finally prepare a PbS quantum dot solution with a concentration of 10 - 30 mg / ml.

[0025] Further, in the selenium precursor solution, the mass of selenium powder is 0.084 g - 0.128 g, and the stirring temperature is 120 - 150 °C; the mass of cadmium oxide is 0.0182 g - 0.0257 g, the stirring temperature is 120 - 150 °C, the ODE solution is injected when the stirring time reaches 30 min, and at the same time, the temperature is raised to 270 - 300 °C, the selenium precursor solution is quickly injected, and the holding time is 8 - 10 min. It is excited by an ultraviolet lamp at 2 min. During the quantum dot cleaning, the ratio of the quantum dot supernatant to ethanol is 2:1 - 1:1. The precipitate is dissolved in n - hexane, the upper layer solution is extracted, an excessive amount of absolute ethanol is added, and it is centrifuged at 6000 - 8000 rpm for 5 - 10 min. Then the quantum dots are dissolved in n - hexane, and the above cleaning process is repeated twice.

[0026] Further, in the lead precursor solution, the amount of substance of lead oxide is 0.4 - 0.6 mmol, 1.0 - 1.2 ml of oleic acid, 8 - 10 ml of octadecene, the stirring temperature is 120 - 150 °C, the stirring time is 5 - 10 min, and after dissolution, it is raised to 270 - 300 °C; the amount of substance of sulfur powder is 0.50 - 0.75 mmol, 1.40 - 1.70 ml of tri - n - octylphosphine, the stirring temperature is 120 - 150 °C, and after dissolution, it is injected into the lead precursor three - necked flask at a rate of 1.0 - 2.0 ml / h, and the holding time is 8 - 10 min. During the quantum dot cleaning, the ratio of the quantum dot supernatant to ethanol is 2:1 - 1:1. The precipitate is dissolved in n - hexane, the upper layer solution is extracted, an excessive amount of absolute ethanol is added, and it is centrifuged at 6000 - 8000 rpm for 5 - 10 min. Then the quantum dots are dissolved in n - hexane, and the above cleaning process is repeated twice.

[0027] Further, in step (4), in the CdSe / PbS mixed solution, the volume ratio of the CdSe quantum dot solution to the PbS quantum dot solution is 1:2 - 2:1, the annealing temperature is 60 - 90 °C, the environmental condition is in a glove box with a nitrogen atmosphere where the oxygen and water are both less than 1 ppm, and the annealing time is 10 - 30 min.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses CdSe quantum dots and PbS quantum dots to form a composite light-emitting layer with a three-dimensional quantum well heterojunction structure, and further prepares an LED device including an electrode, an inorganic electron transport layer, a three-dimensional heterojunction quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate. Compared with the prior art, the present invention adopts a thermal injection method and a liquid-phase mixing method, which not only realizes the stable control of the three-dimensional heterojunction quantum well structure but also can adjust the balance of electron and hole currents in the composite material. Through the effective encapsulation and isolation of PbS quantum dots by CdSe quantum dots, a stable three-dimensional heterojunction quantum well structure is formed. The band bending at the heterojunction interface and the existence of the depletion region significantly promote the effective recombination of electrons and holes, thereby achieving a higher overlap of electron and hole wave functions in terms of material properties. The coating of CdSe quantum dots on the surface of PbS quantum dots effectively reduces the generation of surface defects of quantum dots and the exciton quenching phenomenon, and further improves the structural stability, quantum efficiency, and photoluminescence intensity of the three-dimensional quantum well heterojunction. The materials and device preparation processes of the present invention are simple and reliable, and the components of the light-emitting layer are easy to adjust. The composite light-emitting layer, as an efficient recombination center for electron and hole currents, provides an effective method for the preparation of high-performance light-emitting three-dimensional heterojunction quantum well materials and devices.

[0029] The present invention can make full use of the excellent band regulation ability of three-dimensional heterojunction materials in three-dimensional quantum well luminescence, prepare three-dimensional heterojunction quantum well materials with PbS quantum dots as the well region, and further design and optimize the device structure to optimize the electro-optical performance of the device; obtain a preparation method of a QWLED with a CdSe / PbS quantum dot three-dimensional heterojunction quantum well composite material as the light-emitting layer, which has high external quantum efficiency and high light-emitting intensity. Brief Description of the Drawings

[0030] Figure 1 is a structural diagram of a single CdSe quantum dot, a PbS quantum dot, its CdSe / PbS heterojunction quantum well, and its three-dimensional heterojunction quantum well composite light-emitting layer;

[0031] Figure 2 is a structural diagram of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots;

[0032] In the figure: 1 is a single PbS quantum dot including the depletion region, 2 is a single CdSe quantum dot including the depletion region, 3 is a three-dimensional heterojunction quantum well composite light-emitting layer, 4 is the neutral region of the CdSe quantum dot material, 5 is the neutral region of the PbS quantum dot material, 6 is the CdSe quantum dot contact depletion region, 7 is the PbS quantum dot contact depletion region, 8 is a silver electrode, 9 is Zn 0.85 Mg 0.15The O is the electron transport layer, 10 is the CdSe / PbS quantum dot three-dimensional heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate. Detailed implementation manners

[0033] The technical solution of the present invention will be specifically described below in conjunction with the accompanying drawings.

[0034] The present invention provides a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots, which sequentially includes an electrode layer, an inorganic electron transport layer, a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate from top to bottom. The CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer is a three-dimensional heterojunction quantum well structure formed by the composite of wide-bandgap cadmium selenide quantum dots and narrow-bandgap lead sulfide quantum dots. The CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer includes a plurality of PbS quantum dots with depletion regions, and a plurality of CdSe quantum dots with depletion regions surrounding each PbS quantum dot with a depletion region. Moreover, each CdSe quantum dot with a depletion region isolates the direct contact between the PbS quantum dot with a depletion region and the inorganic electron transport layer and the organic hole transport layer. The PbS quantum dot with a depletion region includes a PbS quantum dot material neutral region from the inside to the outside, and a PbS quantum dot contact depletion region in direct contact with the CdSe quantum dot with a depletion region; the CdSe quantum dot with a depletion region includes a CdSe quantum dot material neutral region from the inside to the outside, and a CdSe quantum dot contact depletion region in direct contact with the PbS quantum dot with a depletion region.

[0035] The present invention also provides a preparation method of a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots as described in any one of the above, including the following steps:

[0036] (1) Wash the ITO conductive glass with deionized water, acetone, and isopropanol for 15 - 25 min respectively, and dry it with nitrogen at a predetermined temperature;

[0037] (2) Spin-coat the PEDOT:PSS solution on the ITO conductive glass in step (1) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing;

[0038] (3) Dissolve TFB in a toluene solution, and then spin-coat the solution on the conductive glass sheet in step (2) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing;

[0039] (4) Spin-coat the CdSe / PbS mixed quantum dot solution on the conductive glass sheet in step (3) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing;

[0040] (5) In the glove box, Zn 0.85 Mg 0.15 The MgO solution was spin-coated on the conductive glass sheet in step (4) using a spin coater, and then the conductive glass sheet was placed on a heating table for annealing;

[0041] (6) The conductive glass sheet obtained in step (5) was evaporated with electrodes using a thermal evaporation machine, and then the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots was obtained.

[0042] The following are specific implementation examples of the present invention.

[0043] Example 1

[0044] 1) Put the ITO glass into a beaker, pour in acetone solution, isopropyl alcohol solution and deionized water solution in sequence, and ultrasonically clean each for 25 min. Take it out, dry it with nitrogen at 60 °C, and put it into a clean and dry petri dish.

[0045] 2) After filtering the PEDOT:PSS solution with a 0.45 μm filter head, spin-coat it on the ITO glass at a low speed of 500 rpm / s for 5 s and a high speed of 3000 rpm / s for 40 s using a spin coater, and then put the glass sheet on a heating table for annealing at 120 °C for 30 min.

[0046] 3) Take 10 mg of TFB and 1 ml of toluene solution. After dissolving TFB in toluene to prepare a solution with a concentration of 10 mg / mL, spin-coat it on the glass sheet at a low speed of 500 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s using a spin coater, and then put the glass sheet on a heating table for annealing at 200 °C for 30 min.

[0047] 4) Preparation of CdSe quantum dots: Add 0.128 g of selenium powder and 2 ml of TOP solution into a three-necked flask, stir and dissolve at 150 °C to prepare a selenium precursor solution; Add 0.0257 g of cadmium oxide and 5 ml of oleic acid, stir at 150 °C for 30 min, then inject 15 ml of ODE solution, and raise the solution temperature to 300 °C; Take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 300 °C and keep it for 10 min. At the same time, use an ultraviolet lamp to excite at 2 min; Finally, quickly cool the quantum dot solution by water bath, dilute it with n-hexane to obtain a quantum dot solution; Then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 2:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add excessive absolute ethanol and centrifuge at 8000 rpm for 10 min, then dissolve the quantum dots with n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 30 mg / ml quantum dot solution, and store it under low temperature conditions.

[0048] 5) Preparation of PbS quantum dots: Add 0.6 mmol of lead oxide, 1.2 ml of oleic acid and 10 ml of octadecene into a three-necked flask, stir at 150 °C for 10 min, and raise the temperature to 300 °C after dissolution to prepare a lead precursor solution; Take 0.75 mmol of sulfur powder and 1.70 ml of trioctylphosphine, stir at 150 °C until completely dissolved, then inject it into the three-necked flask of the lead precursor at a speed of 2.0 ml / h, and keep it for 10 min after injection; Finally, quickly cool the quantum dot solution by water bath, dilute it with n-hexane to obtain a quantum dot solution; Then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 2:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add excessive absolute ethanol and centrifuge at 8000 rpm for 10 min, then dissolve the quantum dots with n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 30 mg / ml quantum dot solution, and store it under low temperature conditions.

[0049] 6) Take the above CdSe quantum dot solution and PbS quantum dot solution respectively, form a CdSe / PbS quantum dot mixed solution according to the volume ratio of CdSe quantum dot solution: PbS quantum dot solution of 2:1, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s, then place the above glass sample on a heating table and anneal at 90 °C for 30 min. Figure 1It is a structural diagram of a composite light-emitting layer of a single CdSe quantum dot, a PbS quantum dot, a CdSe / PbS heterojunction quantum well, and a three-dimensional heterojunction quantum well; where 1 is a single PbS quantum dot in the depletion region, 2 is a single CdSe quantum dot in the depletion region, 3 is a three-dimensional heterojunction quantum well composite light-emitting layer, 4 is the neutral region of the CdSe quantum dot material, 5 is the neutral region of the PbS quantum dot material, 6 is the contact depletion region of the CdSe quantum dot, and 7 is the contact depletion region of the PbS quantum dot.

[0050] 7) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 25 mg / ml, spin-coat it at a low speed of 500 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s with a spin coater, and then place the glass slide on a heating table and anneal it at 120 °C for 20 min.

[0051] 8) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots. Figure 2 It is a structural diagram of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots; where 8 is the silver electrode, 9 is the Zn 0.85 Mg 0.15 O electron transport layer, 10 is the CdSe / PbS quantum dot three-dimensional heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0052] Example 2

[0053] 1) Place the ITO glass in a beaker, pour acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, and ultrasonically clean each for 20 min. Take it out, dry it with nitrogen at 60 °C, and place it in a clean and dry petri dish.

[0054] 2) After filtering the PEDOT:PSS solution with a 0.45-μm filter head, spin-coat it at a low speed of 500 rpm / s for 5 s and a high speed of 3000 rpm / s for 40 s with a spin coater, spin-coat the PEDOT:PSS solution on the ITO glass, and then place the glass slide on a heating table and anneal it at 110 °C for 25 min.

[0055] 3) Take 9 mg of TFB and 1 ml of toluene solution, dissolve TFB in toluene to prepare a solution with a concentration of 9 mg / mL, then spin-coat it at a low speed of 500 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s with a spin coater, and then place the glass slide on a heating table and anneal it at 180 °C for 25 min.

[0056] 4) Preparation of CdSe quantum dots: Add 0.106 g of selenium powder and 2 ml of TOP solution into a three-necked flask, stir and dissolve at 150 °C to prepare a selenium precursor solution; add 0.0220 g of cadmium oxide and 5 ml of oleic acid, stir at 135 °C for 30 min, then inject 15 ml of ODE solution and raise the solution temperature to 285 °C; take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 285 °C and keep it for 9 min. At the same time, use an ultraviolet lamp to excite at 2 min; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 1.5:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of absolute ethanol and centrifuge at 7000 rpm for 7 min, then dissolve the quantum dots with n-hexane, repeat the above washing process twice, dissolve the quantum dots in n-hexane to form a 20 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0057] 5) Preparation of PbS quantum dots: Add 0.5 mmol of lead oxide, 1.1 ml of oleic acid and 9 ml of octadecene into a three-necked flask, stir at 125 °C for 7.5 min, and raise the temperature to 290 °C after dissolution to prepare a lead precursor solution; take 0.625 mmol of sulfur powder and 1.55 ml of trioctylphosphine, stir at 135 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a speed of 2.0 ml / h, and keep it for 9 min after injection; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 1.5:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of absolute ethanol and centrifuge at 7000 rpm for 7.5 min, then dissolve the quantum dots with n-hexane, repeat the above washing process twice, dissolve the quantum dots in n-hexane to form a 20 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0058] 6) Take the above CdSe quantum dot solution and PbS quantum dot solution respectively, form a CdSe / PbS quantum dot mixed solution according to the volume ratio of the CdSe quantum dot solution:PbS quantum dot solution of 1:1, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s, and then place the above glass slide on a heating table and anneal at 75 °C for 20 min. Figure 1It is a structural diagram of a composite light-emitting layer of a single CdSe quantum dot, a PbS quantum dot, a CdSe / PbS heterojunction quantum well, and a three-dimensional heterojunction quantum well; where 1 is a single PbS quantum dot in the depletion region, 2 is a single CdSe quantum dot in the depletion region, 3 is a three-dimensional heterojunction quantum well composite light-emitting layer, 4 is the neutral region of the CdSe quantum dot material, 5 is the neutral region of the PbS quantum dot material, 6 is the contact depletion region of the CdSe quantum dot, and 7 is the contact depletion region of the PbS quantum dot.

[0059] 7) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 20 mg / ml, spin-coat it at a low speed of 500 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s with a spin coater, and then put the glass slide on a heating table and anneal it at 110 °C for 15 min.

[0060] 8) Thermally evaporate a 100-nm silver electrode, and a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots can be obtained. Figure 2 It is a structural diagram of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots; where 8 is the silver electrode, 9 is the Zn 0.85 Mg 0.15 O electron transport layer, 10 is the CdSe / PbS quantum dot three-dimensional heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0061] Example 3

[0062] 1) Put the ITO glass into a beaker, pour acetone solution, isopropyl alcohol solution, and deionized water solution in sequence, and ultrasonically clean each for 15 min. Take it out, dry it with nitrogen at 60 °C, and put it into a clean and dry petri dish.

[0063] 2) After filtering the PEDOT:PSS solution with a 0.22-μm filter head, spin-coat it at a low speed of 500 rpm / s for 5 s and a high speed of 3000 rpm / s for 40 s with a spin coater, spin-coat the PEDOT:PSS solution on the ITO glass, and then put the glass slide on a heating table and anneal it at 100 °C for 20 min.

[0064] 3) Take 8 mg of TFB and 1 ml of toluene solution, dissolve the TFB in toluene to prepare a solution with a concentration of 8 mg / mL, then spin-coat it at a speed of 500 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s with a spin coater, and then put the glass slide on a heating table and anneal it at 160 °C for 15 min.

[0065] 4) Preparation of CdSe quantum dots: Add 0.084 g of selenium powder and 2 ml of TOP solution into a three-necked flask, stir and dissolve at 120 °C to prepare a selenium precursor solution; add 0.0182 g of cadmium oxide and 5 ml of oleic acid, stir at 120 °C for 30 min, then inject 15 ml of ODE solution, and raise the solution temperature to 270 °C; take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the temperature of the cadmium precursor solution reaches 300 °C and keep it for 8 min. At the same time, use an ultraviolet lamp to excite at 2 min; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 1:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add excessive absolute ethanol and centrifuge at 8000 rpm for 5 min, then dissolve the quantum dots with n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 10 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0066] 5) Preparation of PbS quantum dots: Add 0.4 mmol of lead oxide, 1.0 ml of oleic acid and 8 ml of octadecene into a three-necked flask, stir at 120 °C for 5 min, and raise the temperature to 270 °C after dissolution to prepare a lead precursor solution; take 0.50 mmol of sulfur powder and 1.40 ml of trioctylphosphine, stir at 120 °C until completely dissolved, and then inject it into the three-necked flask of the lead precursor at a speed of 1.0 ml / h, and keep it for 8 min after injection; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution; then take the quantum dot solution, the ratio of the quantum dot supernatant to ethanol is 1:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add excessive absolute ethanol and centrifuge at 6000 rpm for 5 min, then dissolve the quantum dots with n-hexane, repeat the above cleaning process twice, dissolve the quantum dots in n-hexane to form a 10 mg / ml quantum dot solution, and store it under low-temperature conditions.

[0067] 6) Take the above CdSe quantum dot solution and PbS quantum dot solution respectively, form a CdSe / PbS quantum dot mixed solution according to the volume ratio of CdSe quantum dot solution:PbS quantum dot solution of 1:2, and spin-coat it with a spin coater at a low speed of 300 rpm / s for 5 s and a high speed of 2000 rpm / s for 40 s, then place the above glass slide on a heating table and anneal it at 60 °C for 10 min. Figure 1It is a structural diagram of a single CdSe quantum dot, a PbS quantum dot, a CdSe / PbS heterojunction quantum well, and a three-dimensional heterojunction quantum well composite light-emitting layer; where 1 is a single PbS quantum dot in the depletion region, 2 is a single CdSe quantum dot in the depletion region, 3 is a three-dimensional heterojunction quantum well composite light-emitting layer, 4 is the neutral region of the CdSe quantum dot material, 5 is the neutral region of the PbS quantum dot material, 6 is the contact depletion region of the CdSe quantum dot, and 7 is the contact depletion region of the PbS quantum dot.

[0068] 7) Take a Zn 0.85 Mg 0.15 O solution with a concentration of 15 mg / ml, spin-coat it with a spin coater at a low speed of 500 rpm / s for 5 s and a high speed of 1000 rpm / s for 40 s, and then place the glass slide on a heating table and anneal it at 100 °C for 10 min.

[0069] 8) Thermally evaporate a 100-nm silver electrode to obtain a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots. Figure 2 Structural diagram of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots; where 8 is the silver electrode, 9 is Zn 0.85 Mg 0.15 O electron transport layer, 10 is the CdSe / PbS quantum dot three-dimensional heterojunction quantum well composite light-emitting layer, 11 is the TFB hole transport layer, 12 is the PEDOT:PSS hole transport layer, and 13 is the ITO glass substrate.

[0070] The above are the preferred embodiments of the present invention. All changes made according to the technical solution of the present invention, when the functional effects produced do not exceed the scope of the technical solution of the present invention, fall within the protection scope of the present invention.

Claims

1. A QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots, characterized in that, From top to bottom, it sequentially includes an electrode layer, an inorganic electron transport layer, a CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer, an organic hole transport layer, and an ITO glass substrate. The CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer is a three-dimensional heterojunction quantum well structure formed by the composite of wide-bandgap cadmium selenide quantum dots and narrow-bandgap lead sulfide quantum dots.

2. The QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 1, wherein The CdSe / PbS three-dimensional heterojunction quantum well composite light-emitting layer includes a plurality of PbS quantum dots with depletion regions, and a plurality of CdSe quantum dots surrounding each PbS quantum dot with a depletion region. Each CdSe quantum dot with a depletion region isolates the direct contact between the PbS quantum dot with a depletion region and the inorganic electron transport layer and the organic hole transport layer.

3. The QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 2, characterized in that, The PbS quantum dot with a depletion region includes a neutral region of PbS quantum dot material from the inside to the outside, and a PbS quantum dot contact depletion region in direct contact with the CdSe quantum dot with a depletion region; the CdSe quantum dot with a depletion region includes a neutral region of CdSe quantum dot material from the inside to the outside, and a CdSe quantum dot contact depletion region in direct contact with the PbS quantum dot with a depletion region.

4. A preparation method of a QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots as described in any one of claims 1-3, characterized in that, It includes the following steps: (1) Wash the ITO conductive glass with deionized water, acetone, and isopropanol for 15 - 25 min respectively, and dry it with nitrogen at a predetermined temperature. (2) Spin-coat the PEDOT:PSS solution on the ITO conductive glass in step (1) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing. (3) Dissolve TFB in toluene solution, and then spin-coat the solution on the conductive glass sheet in step (2) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing. (4) Spin-coat the CdSe / PbS mixed quantum dot solution on the conductive glass sheet in step (3) with a spin coater in a glove box, and then put the conductive glass sheet on a heating table for annealing. (5) In the glove box, Zn 0.85 Mg 0.15 The solution is spin-coated on the conductive glass sheet of step (4) using a spin coater, and then the conductive glass sheet is placed on a heating stage for annealing; (6) Evaporate electrodes on the conductive glass sheet obtained in step (5) using a thermal evaporation machine, and then a QWLED based on a three-dimensional heterojunction quantum well composite light-emitting layer of cadmium selenide and lead sulfide quantum dots is obtained.

5. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 4, characterized in that, In step (2), the PEDOT:PSS solution is first filtered through a 0.22 - 0.45 μm filter head, the annealing temperature is 100 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 20 - 30 min; in step (3), the concentration of the TFB solution is 8 - 10 mg / ml, the annealing temperature is 160 - 200 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 15 - 30 min; in step (5), the concentration of the Zn 0.85 Mg 0.15 O solution is 15 - 25 mg / ml, the annealing temperature is 100 - 120 °C, the environmental condition is in a glove box with a nitrogen atmosphere where both oxygen and water are less than 1 ppm, and the annealing time is 10 - 20 min; in step (6), the electrode layer is a silver electrode with a thickness of 100 nm.

6. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 4, characterized in that, In step (4), the specific method for preparing the CdSe quantum dot solution is as follows: Step S61: Stir and dissolve a predetermined amount of selenium powder and TOP solution at a set temperature to prepare a selenium precursor solution; stir a predetermined amount of cadmium oxide and oleic acid at a set temperature for a set time, then inject ODE solution, and raise the solution temperature. Take the selenium precursor solution, quickly inject it into the cadmium precursor solution when the solution temperature reaches the set value and keep it for a set time, and at the same time use an ultraviolet lamp for excitation; finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane, obtain the quantum dot solution, and store it under low-temperature conditions. Step S62: Take out the supernatant of a part of the quantum dot solution after standing still, dissolve oleic acid with methanol, then add n-hexane solution and take out the upper layer solution, add an appropriate amount of absolute ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified CdSe quantum dot solution, and finally prepare the concentration of the CdSe quantum dot solution to be 10 - 30 mg / ml.

7. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 4, characterized in that In step (4), the specific method for preparing the PbS quantum dot solution is as follows: Step S71: Dissolve a predetermined amount of lead oxide, oleic acid, and octadecene at a set temperature to prepare a lead precursor solution; dissolve a predetermined amount of sulfur powder in trioctylphosphine and inject it into a three-necked flask at a predetermined rate. Finally, quickly cool the quantum dot solution by means of a water bath, dilute it with n-hexane to obtain a quantum dot solution, and store it under low-temperature conditions. Step S72: Take out a part of the supernatant of the quantum dot solution after standing, dissolve it with ethanol, then add a n-hexane solution and take out the upper layer solution, add anhydrous ethanol for centrifugation, and finally dissolve the precipitate with n-hexane to obtain a purified PbS quantum dot solution, and finally prepare a PbS quantum dot solution with a concentration of 10 - 30 mg / ml.

8. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 6, characterized in that, In the selenium precursor solution, the mass of selenium powder is 0.084 g - 0.128 g, and the stirring temperature is 120 - 150 °C; the mass of cadmium oxide is 0.0182 g - 0.0257 g, the stirring temperature is 120 - 150 °C, when the stirring time reaches 30 min, inject the ODE solution, and at the same time raise the temperature to 270 - 300 °C, quickly inject the selenium precursor solution, keep the time for 8 - 10 min, and excite with an ultraviolet lamp at 2 min; in the quantum dot cleaning, the ratio of the quantum dot supernatant to ethanol is 2:1 - 1:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of anhydrous ethanol and centrifuge at 6000 - 8000 rpm for 5 - 10 min, and then dissolve the quantum dot with n-hexane, and repeat the above cleaning process twice.

9. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 7, characterized in that, In the lead precursor solution, the amount of substance of lead oxide is 0.4 - 0.6 mmol, oleic acid is 1.0 - 1.2 ml, octadecene is 8 - 10 ml, the stirring temperature is 120 - 150 °C, the stirring time is 5 - 10 min, and after dissolution, raise the temperature to 270 - 300 °C; the amount of substance of sulfur powder is 0.50 - 0.75 mmol, trioctylphosphine is 1.40 - 1.70 ml, the stirring temperature is 120 - 150 °C, and after dissolution, inject it into the lead precursor three-necked flask at a rate of 1.0 - 2.0 ml / h, keep the time for 8 - 10 min; in the quantum dot cleaning, the ratio of the quantum dot supernatant to ethanol is 2:1 - 1:1, dissolve the precipitate in n-hexane, extract the upper layer solution, add an excessive amount of anhydrous ethanol and centrifuge at 6000 - 8000 rpm for 5 - 10 min, and then dissolve the quantum dot with n-hexane, and repeat the above cleaning process twice.

10. The preparation method of the QWLED with a three-dimensional heterojunction quantum well composite light-emitting layer based on cadmium selenide and lead sulfide quantum dots according to claim 4, characterized in that, In step (4), the volume ratio of the CdSe quantum dot solution to the PbS quantum dot solution in the CdSe / PbS mixed solution is 1:2 - 2:1, the annealing temperature is 60 - 90 °C, the environmental condition is in a glove box with a nitrogen atmosphere where the oxygen and water are both less than 1 ppm, and the annealing time is 10 - 30 min.

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