CN115108575A - Zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green light LED and preparation method thereof - Google Patents
Zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green light LED and preparation method thereof Download PDFInfo
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Abstract
The invention provides zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green light LED and preparation method thereof, and zero-dimensional Cs 2 CuCl 4 Preparing the nanocrystal by adopting a high-temperature thermal injection method, mixing cesium carbonate, oleic acid and octadecene, heating to 100 ℃, and maintaining for 2 hours under nitrogen to obtain cesium oleate precursor liquid; mixing copper chloride, octadecene, oleic acid and oleylamine, heating to 100 ℃, maintaining for 2 hours under nitrogen, and removing water in the mixture; then, at 100 ℃, the cesium oleate precursor solution is rapidly injected into the mixture, and after 5 minutes of reaction, an ice water bath is usedRapidly cooling the solution, and centrifugally purifying the cooled solution; mixing Cs 2 CuCl 4 And (3) taking the nanocrystalline as a light emitting layer to prepare a green light LED. Cs prepared by the present invention 2 CuCl 4 The nano-crystal has uniform size, the fluorescence quantum yield is up to 90%, the green light LED continuously and stably works in the atmospheric environment, and the working life of the green light LED reaches 9.7 hours under the driving voltage of 8V.
Description
Technical Field
The invention relates to the technical field of semiconductor light-emitting devices, in particular to zero-dimensional Cs 2 CuCl 4 Nanocrystals, green light LEDs and methods of making the same.
Background
The metal halide perovskite nanocrystal is considered as a new generation luminescent material with wide application prospect due to the advantages of high fluorescence quantum yield, high defect tolerance, wide spectrum tunable range, simple preparation process and the like. In recent years, researchers have promoted the external quantum efficiency of perovskite nanocrystal LEDs to more than 20% through material optimization and device structure improvement, showing great application prospects (x.liu, w.xu, s.bai, y.jin, j.wang, r.h.friend, and f.gao, Metal Halide precursors for Light-Emitting Diodes, nat. material.20, 10 (2021)). However, the light-emitting layers of these perovskite devices contain heavy metal lead which is seriously harmful to human health, and the wide application of the perovskite devices in the field of light-emitting display is greatly limited. In addition, the lead halide perovskite nanocrystals have poor stability and are very sensitive to environmental factors such as water, oxygen, light and heat, resulting in short operating life of the device, which seriously hinders the commercialization process of LED devices. (Q.Fan, G.V.biesold-McGee, J.Ma, Q.xu, S.Pan, J.Peng, and Z.Lin, Lead-Free Halide Perovskite Nanocrystals: Crystal Structures, Synthesis, Stabilites, and Optical Properties, Angel.Chem., Int.Ed.59,1030 (2020)). Therefore, from the application point of view, the development of a novel lead-free perovskite LED which is nontoxic and environmentally stable is undoubtedly of great scientific significance and practical value.
Aiming at the problem that the lead element is generally contained in the current high-efficiency perovskite LED, researchers have widely developed the preparation of lead-free perovskite nanocrystals by using non-toxic or low-toxicity metal elements to replace lead, such as CsSnX 3 (X＝Cl,Br,I)、Cs 3 Sb 2 X 9 、Cs 2 AgInCl 6 、Cs 3 Cu 2 X 5 Nanocrystals, and the like. These novel Lead-Free perovskite nanocrystals exhibit good stability and optoelectronic properties (X.Li, X.Gao, X.Zhang, X.Shen, M.Lu, J.Wu, Z.Shi, C.Vicki, J.Hu, X.Bai, W.W.Yu, and Y.Zhang, Lead-Free Halide precursors for Light Emission: Recent Advances and precursors, adv.Sci.8,2003334 (2021)). Among them, recently reported Cu-based halide nanocrystals are particularly interesting because of their advantages of direct band gap, high fluorescence quantum efficiency, non-toxicity, low preparation cost, etc., and have been successfully used as light emitting layers to prepare yellow and blue LEDs.
Literature (Edward P.Booker, James T.Griffiths, etc., Synthesis, Characterization, and Morphological Control of Cs 2 CuCl 4 Nanocrystals, J.Phys.chem.C123, 169511-1956 (2019)) discloses a compound of formula (I) 2 CuCl 4 Method for preparing nanocrystal, Cs prepared by the method 2 CuCl 4 The fluorescence quantum efficiency (PLQY) of the nanocrystal is shown in a table 2 on page 1695954, the PLQY is only 14% at most, while the PLQY of the nanocrystal with different raw material proportions is n/a, and the n/a indicates that the efficiency cannot be tested when the ratio is too small, so that the problems that the nanocrystal is difficult to uniformly nucleate and grow, the surface and in-vivo defects of the nanocrystal are large, the PLQY is low and the like exist.
At present, no lead-free metal halide LED in a green spectral region is reported. The contribution of a green light band, which is one of three primary colors, to the fields of multicolor LED display, high-end lighting, visible light communication, and the like is an indispensable part. Therefore, the lead-free nanocrystalline which has green light emission, is nontoxic and stable and is low in preparation cost is used for preparing a green light LED device, and the lead-free nanocrystalline has very important research value.
Considering the novel lead-free copper-based chloride Cs 2 CuCl 4 The nanocrystalline has the advantages of no toxicity and stable environment, and the intrinsic luminescence of the nanocrystalline is located in a green light wave band. If Cs can be used 2 CuCl 4 The nanocrystalline is used as a luminous layer, and the green light LED which can work stably is prepared through the structural design of the device, so that the blank that a lead-free metal halide LED system is lost in a green light wave band can be filled.
Disclosure of Invention
The invention proposesZero-dimensional Cs 2 CuCl 4 The nanocrystal, the green light LED and the preparation method thereof prepare the nontoxic, stable and green luminous Cs 2 CuCl 4 Nanocrystalline with uniform nanocrystalline size, high fluorescence quantum yield, and Cs 2 CuCl 4 The nanocrystalline is used as a luminous layer, and the green LED based on the lead-free metal halide system is prepared for the first time, so that the application requirements in the fields of colorful display, high-end illumination, visible light communication and the like are met.
The technical scheme of the invention is realized as follows: zero-dimensional Cs 2 CuCl 4 The preparation method of the nanocrystalline comprises the following steps:
(1) mixing 2.5 mmol of cesium carbonate, 2.5 ml of oleic acid and 10 ml of octadecene, heating to 100 ℃, and maintaining for 2 hours under nitrogen to obtain a cesium oleate precursor solution;
(2) 0.27 mmol of copper chloride, 5 ml of octadecene, 0.5 ml of oleic acid and 0.5 ml of oleylamine were mixed and heated to 100 ℃ for 2 hours under nitrogen, and the water content of the mixture was removed;
(3) and (3) quickly injecting 0.5 ml of cesium oleate precursor solution into the mixture obtained in the step (2) at 100 ℃, quickly cooling the cesium oleate precursor solution by using an ice water bath after reacting for 5 minutes, and centrifugally purifying the cooled solution to obtain zero-dimensional Cs 2 CuCl 4 And (4) nanocrystals.
Zero-dimensional Cs prepared by adopting preparation method 2 CuCl 4 And (4) nanocrystals.
Based on zero-dimensional Cs 2 CuCl 4 The green LED comprises a transparent conductive substrate, wherein a hole injection layer, a hole transport layer and Cs are sequentially arranged on the transparent conductive substrate 2 CuCl 4 A nanocrystalline light emitting layer, an electron transport layer, and a contact electrode.
Further, Cs 2 CuCl 4 The thickness of the nanocrystalline light-emitting layer is 40-80 nanometers, wherein the size of a single nanocrystalline is 14-20 nanometers.
Further, the substrate is ITO conductive glass, the thickness of the ITO conductive glass is 120-150 nanometers, and the resistivity of the ITO conductive glass is 1.0 multiplied by 10 –4 ～5.0×10 –3 Ohm cm.
Furthermore, the hole injection layer is polyethylene dioxythiophene-sodium polystyrene sulfonate with a thickness of 25-35 nm, wherein polyethylene dioxythiophene is also called PEDOT, and sodium polystyrene sulfonate is also called PSS.
Furthermore, the hole transport layer is Poly [ bis (4-phenyl) (4-butylphenyl) amine ] (Poly-TPD for short) or Poly (9-vinylcarbazole) (PVK for short) or a composite layer of the two, and the thickness is 10 to 60 nm.
Furthermore, the electron transport layer is 1, 3, 5-tri (1-phenyl-1H-benzimidazole-2-yl) benzene (TPBi for short), and the thickness of the electron transport layer is 30-50 nanometers.
Furthermore, the contact electrode is a composite material of lithium fluoride and metal aluminum, and the thickness of the contact electrode is 100-150 nanometers.
Based on zero-dimensional Cs 2 CuCl 4 The preparation method of the green LED of the nanocrystalline comprises the following steps:
(1) cleaning the transparent conductive substrate;
(2) preparing a hole injection layer on the substrate by adopting a low-temperature solution method;
(3) preparing a hole transport layer on the hole injection layer by adopting a low-temperature solution method;
(4) mixing Cs 2 CuCl 4 Preparing Cs on the hole transport layer by adopting a solution spin coating method for the nanocrystalline solution 2 CuCl 4 A nanocrystalline light-emitting layer;
(5) by thermal vacuum deposition on Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystalline light-emitting layer;
(6) and preparing an electrode on the electron transport layer by adopting a thermal vacuum evaporation method.
Further, in the step (4), the zero-dimensional Cs is added 2 CuCl 4 Dispersing the nano-crystal in n-hexane to obtain Cs 2 CuCl 4 Nano crystal solution, under the protection of inert gas, adding Cs 2 CuCl 4 And uniformly spin-coating the nanocrystal solution on the hole transport layer under the following spin-coating conditions: 2000 rpm/30 seconds, finally annealing the spin-coated sample at 80 ℃ for 10 minutes to obtain green light-emitting Cs 2 CuCl 4 Nanocrystalline light emitting layer。
Further, in the step (2), the hole injection layer is prepared by a one-step solution method; in the step (3), the hole transport layer 3 is prepared according to a one-step solution method.
Further, in the step (5), the electron transport layer 5 is prepared according to a thermal vacuum evaporation method, and the specific steps are as follows:
placing TPBi powder in a crucible, transferring the TPBi powder to a thermal vacuum evaporation chamber, and carrying Cs 2 CuCl 4 The sample of the nanocrystalline luminescent layer was placed upside down at a distance of 30 cm above the crucible, and the evaporation conditions were: the evaporation power is 30 watts, and the evaporation pressure is 1 multiplied by 10 –4 Pascal, the evaporation rate is 3-10 angstroms per second, and the evaporation thickness is 40 nanometers.
The invention has the beneficial effects that:
the invention adopts the Cs with stable environmental protection and low cost 2 CuCl 4 The nano-crystal has uniform size, the fluorescence quantum yield (PLQY) is up to 90 percent, and Cs is converted into the fluorescent quantum yield (PLQY) 2 CuCl 4 The nanocrystalline is used as a luminous layer, and the preparation of the novel lead-free green light LED which is environment-friendly and stable in work is realized. On one hand, the green light LED based on the lead-free metal halide system is realized for the first time, the defect of lead toxicity in the traditional lead halide perovskite LED is overcome, and the harm to the environment and the human body is reduced; on the other hand, by Cs 2 CuCl 4 The prepared green light LED can continuously and stably work in the atmospheric environment, the service life of the prepared green light LED reaches 9.7 hours under the driving voltage of 8V, and the prepared green light LED is obviously superior to the traditional lead-based nanocrystalline LED. Therefore, the LED provided by the invention can overcome the defects of the traditional lead halide perovskite LED in lead toxicity and stability, and provides a feasible scheme for the preparation and research of green light LEDs with environmental protection, stability and low cost.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 shows zero-dimensional Cs-based devices according to the present invention 2 CuCl 4 A green light LED structure schematic diagram of the nanocrystal;
FIG. 2 shows Cs prepared according to the present invention 2 CuCl 4 Transmission electron microscope photograph of the nanocrystal;
FIG. 3 shows Cs prepared according to the present invention 2 CuCl 4 The luminous intensity change curve of the nanocrystalline luminous layer under the continuous heating at 100 ℃;
FIG. 4 is a current density-voltage characteristic curve of green LEDs prepared in examples 1, 2 and 3;
FIG. 5 is a luminance-voltage characteristic curve of green LEDs prepared in examples 1, 2 and 3;
FIG. 6 is an electroluminescence spectrum of green LEDs prepared in examples 1, 2 and 3 at the same driving voltage;
FIG. 7 is an external quantum efficiency of green LEDs prepared in examples 1, 2 and 3;
FIG. 8 is a graph showing the variation of luminous intensity of the green LED prepared in example 3 continuously operated at a driving voltage of 8V;
FIG. 9 shows Cs prepared according to the present invention 2 CuCl 4 The nanocrystalline solution showed a very bright green light under illumination.
Wherein: 1. substrate, 2. hole injection layer, 3. hole transport layer, 4.Cs 2 CuCl 4 A nanocrystalline light emitting layer, 5, an electron transport layer, 6, a contact electrode.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Zero dimension Cs 2 CuCl 4 The preparation method of the nanocrystalline comprises the following steps:
(1) mixing 2.5 mmol of cesium carbonate (aladin brand) powder, 2.5 ml of oleic acid (aladin brand) and 10 ml of octadecene (aladin brand) and heating to 100 ℃, and maintaining under nitrogen for 2 hours to obtain cesium oleate precursor liquid;
(2) 0.27 mmol of copper chloride (aladin brand) powder, 5 ml of octadecene (aladin brand), 0.5 ml of oleic acid (aladin brand) and 0.5 ml of oleylamine (aladin brand) were mixed and heated to 100 ℃ for 2 hours under nitrogen, and the water in the mixture was removed;
(3) and (3) quickly injecting 0.5 ml of cesium oleate precursor into the mixture obtained in the step (2) at 100 ℃, quickly cooling the cesium oleate precursor by using an ice-water bath after reacting for 5 minutes, and centrifugally purifying the cooled solution to obtain zero-dimensional Cs 2 CuCl 4 And (4) nanocrystals.
FIG. 2 shows Cs prepared by high temperature thermal injection 2 CuCl 4 Transmission electron micrograph of nanocrystal from which Cs can be seen 2 CuCl 4 The nano-crystal is spherical, has good crystallization characteristic and obvious self-assembly characteristic, and the average size of the nano-crystal is 18 nanometers.
FIG. 3 shows Cs 2 CuCl 4 The change curve of the luminescence intensity of the nanocrystalline in the continuous heating process at 100 ℃ can be seen from the graph, the luminescence intensity is only attenuated by 5 percent after the nanocrystalline is continuously heated for 100 hours, and the Cs is shown 2 CuCl 4 The nanocrystals have excellent thermal stability.
Cs prepared by the present invention 2 CuCl 4 The nano crystal has uniform size and can realize 90 percent of fluorescence quantum efficiency (PLQY), Cs 2 CuCl 4 A very bright green light was observed for the nanocrystalline solution, as shown in fig. 9.
Based on the zero-dimensional Cs as shown in FIG. 1 2 CuCl 4 The green LED comprises an insulated transparent conductive substrate 1, and a hole injection layer 2, a hole transport layer 3 and Cs are sequentially arranged on the substrate 1 2 CuCl 4 A nanocrystalline light-emitting layer 4, an electron transport layer 5, and a contact electrode 6.
Preferably, the transparent conductive substrate 1 is ITO conductive glass, the thickness of an ITO thin layer is 100-130 nanometers, and the resistivity is 5.0 x 10 < -4 > to 1.0 x 10 < -3 > ohm.
The hole injection layer 2 is polyethylene dioxythiophene-sodium polystyrene sulfonate, and the thickness of the hole injection layer is 25-35 nanometers. Among them, polyethylenedioxythiophene is also called PEDOT, and sodium polystyrene sulfonate is also called PSS.
The hole transport layer 3 is Poly [ bis (4-phenyl) (4-butylphenyl) amine ] (i.e., Poly-TPD), or Poly (9-vinylcarbazole) (i.e., PVK), or a composite layer of the two, and has a thickness of 10 to 60 nm.
The thickness of the Cs2CuCl4 nanocrystalline light-emitting layer is 40-80 nanometers, and the size of a single nanocrystalline is 14-20 nanometers.
The electron transport layer 5 is 1, 3, 5-tri (1-phenyl-1H-benzimidazole-2-yl) benzene (namely TPBi), and the thickness of the electron transport layer is 30-50 nanometers.
The contact electrode 6 is made of a composite material of lithium fluoride and metal aluminum, and the thickness of the contact electrode is 100-150 nanometers.
The preparation method of the green LED based on the zero-dimensional lead-free Cs2CuCl4 nanocrystal is carried out according to the following steps:
(1) cleaning the transparent conductive substrate 1;
(2) preparing a hole injection layer 2 on a substrate 1 by adopting a low-temperature solution method;
(3) preparing a hole transport layer 3 on the hole injection layer 2 by adopting a low-temperature solution method;
(4) preparation of green emitting Cs by high temperature thermal injection 2 CuCl 4 Preparing Cs on the hole transport layer by adopting a nano-crystalline solution and a solution spin-coating method 2 CuCl 4 A nanocrystalline light-emitting layer;
(5) by thermal vacuum deposition on Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystalline light-emitting layer;
(6) and preparing a contact electrode on the electron transport layer by adopting a thermal vacuum evaporation method.
Preferably, the hole injection layer 2 in the step (2) is prepared by a one-step solution method: PSS solution is filtered by a nylon filter head with a water system of 0.45 micron, and the filtered solution is uniformly spin-coated on a transparent conductive substrate in an air environment, wherein the spin-coating conditions are as follows: 3000 r.m./60 s, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes.
Preferably, the hole transport layer 3 in step (3) is prepared according to a one-step solution method: dissolving Poly-TPD or PVK in chlorobenzene solution with the concentration of 6 milligrams per milliliter, stirring for 2 hours at 25 ℃ by using a constant-temperature magnetic stirrer to obtain a precursor solution, and uniformly spin-coating the precursor solution on the hole injection layer in a spin-coating mode under the protection of inert gas. Poly-TPD spin coating conditions were: 3000 r/min/60 s, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes; the PVK spin coating conditions were: 6000 rpm/60 seconds, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes.
Preferably, zero-dimensional Cs is used in step (4) 2 CuCl 4 Dispersing the nano-crystal in n-hexane to obtain Cs 2 CuCl 4 Nano crystal solution, under the protection of inert gas, adding Cs 2 CuCl 4 And uniformly spin-coating the nanocrystal solution on the hole transport layer under the following spin-coating conditions: 2000 rpm/30 seconds, finally annealing the spin-coated sample at 80 ℃ for 10 minutes to obtain green light-emitting Cs 2 CuCl 4 A nanocrystalline light emitting layer.
Preferably, the electron transport layer 5 in step (5) is prepared according to a thermal vacuum evaporation method:
TPBi powder is placed in a crucible and transferred to a thermal vacuum evaporation chamber to carry Cs 2 CuCl 4 The sample of the nanocrystalline luminescent layer was placed upside down at a distance of 30 cm above the crucible, and the evaporation conditions were: the evaporation power is 30 watts, and the evaporation pressure is 1 multiplied by 10 –4 Pascal, the evaporation rate is 3-10 angstroms per second, the evaporation thickness is 40 nanometers, and the evaporation time is 100 minutes.
The preparation method and properties of the present invention will be described below with reference to specific embodiments.
Example 1
The preparation method of the green LED based on the zero-dimensional lead-free Cs2CuCl4 nanocrystal comprises the following steps:
(1) and cleaning the transparent conductive substrate 1, wherein the adopted substrate 1 is ITO conductive glass.
ITO conductive glass is adopted as a substrate 1, and the substrate is chemically cleaned, wherein the cleaning steps are as follows: firstly, putting a substrate into a cleaning agent (Libai brand liquid detergent) to be soaked for 10 minutes, and then washing the substrate with tap water; then, sequentially using acetone and ethanol solution to perform ultrasonic cleaning for 15 minutes respectively, and then circulating once again; then washing the mixture by deionized water, and drying the mixture by high-purity nitrogen for later use.
(2) The hole injection layer 2 is prepared by a low-temperature solution method.
Placing the cleaned transparent conductive substrate 1 in an ultraviolet ozone cleaning machine for treatment for 30 minutes, and then spin-coating a hole injection layer on the treated transparent conductive substrate 1; PSS solution of PEDOT is filtered by a water system 0.45 micron nylon filter head, and the filtered solution is uniformly spin-coated on a transparent conductive substrate 1 in an air environment, wherein the spin-coating conditions are as follows: 3000 rpm/60 s, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes. The thickness of the hole injection layer obtained was 30 nm.
(3) The hole transport layer 3 is prepared by a low-temperature solution method.
12 mg of Poly-TPD (Aladdin brand) powder was dissolved in 2 ml of chlorobenzene solution; then stirring for 2 hours at 25 ℃ by using a constant-temperature magnetic stirrer to obtain a Poly-TPD precursor solution; and then transferring the spin-coated hole injection layer sample and the precursor solution into a glove box protected by inert gas, and uniformly spin-coating the precursor solution on the hole injection layer 2 in a spin-coating manner, wherein the spin-coating conditions are as follows: 3000 rpm/60 s, and finally annealing the spin-coated sample in a glove box at 120 ℃ for 20 minutes. The thickness of the obtained hole transport layer was 30 nm.
(4) Preparation of green emitting Cs by high temperature thermal injection 2 CuCl 4 Preparing Cs on the hole transport layer by using a nanocrystalline solution and a solution spin-coating method 2 CuCl 4 A nanocrystalline light emitting layer 4.
And (2) mixing.5 mmol of cesium carbonate (aladin brand) powder, 2.5 ml of oleic acid (aladin brand) and 10 ml of octadecene (aladin brand) were mixed and heated to 100 ℃ for 2 hours under nitrogen to obtain cesium oleate precursor solution; 0.27 mmole of copper chloride (aladin brand) powder, 5 ml of octadecene (aladin brand), 0.5 ml of oleic acid (aladin brand), and 0.5 ml of oleylamine (aladin brand) were mixed and heated to 100 ℃ for 2 hours under nitrogen, and the water was removed from the mixture; then, 0.5 ml of cesium oleate precursor solution is quickly injected at the temperature of 100 ℃, the cesium oleate precursor solution is quickly cooled by using an ice water bath after 5 minutes of reaction, the cooled solution is centrifugally purified, and finally the centrifuged precipitate is dispersed in n-hexane; under the protection of inert gas, adding Cs 2 CuCl 4 The nanocrystalline solution is uniformly spin-coated on the hole transport layer 3, and the spin-coating conditions are as follows: 2000 rpm/30 seconds; finally, annealing the sample after spin coating at 80 ℃ for 10 minutes to obtain green light-emitting Cs 2 CuCl 4 A nanocrystalline light emitting layer. Prepared Cs 2 CuCl 4 The thickness of the nanocrystalline light emitting layer was 50 nm.
(5) The spin-coated Cs 2 CuCl 4 And a sample of the nanocrystalline light-emitting layer 4 is placed in a vacuum evaporation chamber, and the preparation of the electron transport layer 5 is completed by adopting a thermal vacuum evaporation method.
The method comprises the following specific steps: firstly, 3 g of TPBi (Aladdin brand) powder is placed in a crucible; then will carry Cs 2 CuCl 4 Placing the sample of the nanocrystalline light-emitting layer upside down at a distance of 30 cm above the crucible, starting the mechanical pump, vacuumizing the evaporation chamber, starting the molecular pump to continue vacuumizing when the vacuum degree of the chamber is lower than 5 pascals until the vacuum degree of the chamber is lower than 1.0 multiplied by 10 –4 Starting evaporation at Pascal, setting the evaporation power to be 30 watts, the evaporation rate to be 3-10 angstroms per second, and the thickness of the prepared electron transport layer to be 40 nanometers.
(6) Lithium fluoride (Aladdin brand) and an aluminum electrode are deposited on the surface of the electron transport layer 5 by adopting a thermal vacuum evaporation method and combining a mask plate. Evaporating lithium fluoride and then evaporating aluminum, wherein the thicknesses of the lithium fluoride and the aluminum electrode are respectively 1 nanometer and 100 nanometers.
Example 2
(1) ITO conductive glass is used as the substrate 1. The method of cleaning the transparent conductive substrate 1 in this embodiment is the same as that in embodiment 1.
(2) The hole injection layer 2 is prepared by a low-temperature solution method. The process and preparation parameters in this section are the same as in example 1.
(3) The hole transport layer 3 is prepared by a low-temperature solution method. First, 12 mg of PVK (Aladdin brand) powder was dissolved in 2 ml of chlorobenzene solution; then stirring for 2 hours at 25 ℃ by using a constant-temperature magnetic stirrer to obtain PVK precursor solution; then transferring the prepared hole injection layer sample and the precursor solution into a glove box protected by inert gas, and uniformly spin-coating the precursor solution on the hole injection layer 2 in a spin-coating manner, wherein the spin-coating conditions are as follows: 6000 rpm/60 s, and finally annealing the spin-coated sample in a glove box at 120 ℃ for 20 minutes. The thickness of the obtained hole transport layer was 10 nm.
(4) Preparation of Cs by high-temperature thermal injection method 2 CuCl 4 Nanocrystalline, and further preparing Cs by using solution spin coating technology 2 CuCl 4 A nanocrystalline light emitting layer 4. The process and preparation parameters in this section are the same as in example 1.
(5) The electron transport layer 5 was prepared by thermal vacuum evaporation. The process and preparation parameters in this section are the same as in example 1.
(6) Finally, the contact electrode 6 is prepared by a thermal vacuum evaporation method. The process and preparation parameters in this section are the same as in example 1.
Example 3
(1) ITO conductive glass is used as the substrate 1. The method of cleaning the transparent conductive substrate 1 in this embodiment is the same as that in embodiment 1.
(2) The hole injection layer 2 is prepared by a low-temperature solution method. The process and preparation parameters in this section are the same as in example 1.
(3) The hole transport layer 3 is prepared by a low-temperature solution method. First, 6 mg per ml of Poly-TPD precursor solution was uniformly spin-coated on the hole injection layer 2 under the following conditions: the sample after spin coating was annealed at 3000 rpm/60 sec in a glove box at 120 ℃ for 20 min. After the sample was cooled, the PVK precursor solution at a concentration of 6 mg per ml was then spin coated uniformly onto the Poly-TPD layer under the following conditions: 6000 rpm/60 s, an annealing temperature of 120 ℃ and a time of 20 minutes. The thickness of the obtained composite hole transport layer was 40 nm.
(4) Preparation of Cs by high-temperature thermal injection method 2 CuCl 4 Nanocrystalline, and further preparing Cs by using solution spin coating technology 2 CuCl 4 A nanocrystalline light emitting layer 4. The process and preparation parameters in this section are the same as in example 1.
(5) The electron transport layer 5 was prepared by thermal vacuum evaporation. The process and preparation parameters in this section are the same as in example 1.
(6) Finally, the contact electrode 6 is prepared by a thermal vacuum evaporation method. The process and preparation parameters in this section are the same as in example 1.
The difference between this embodiment and embodiment 1 is that a Poly-TPD/PVK composite hole transport layer is used in the LED device structure. Poly-TPD (1X 10) -4 cm 2 V -1 s -1 ) PVK (1X 10) -6 cm 2 V -1 s -1 ) Has higher hole mobility and is beneficial to injecting hole carriers into Cs 2 CuCl 4 In the nanocrystalline light-emitting layer. And PVK (-5.8eV) has a deeper highest occupied molecular orbital than Poly-TPD (-5.2eV), which is favorable for offsetting a hole injection barrier. Therefore, the use of the Poly-TPD and PVK composite hole transport layer can realize the efficient smooth injection of hole carriers into the light-emitting layer, and is beneficial to improving the performance of the device.
Fig. 4 is a graph of current density versus voltage characteristics of the devices prepared in examples 1, 2, and 3, all of which exhibit significant rectifying characteristics. Device tests show that the Cs-based chip can be realized by all three embodiments 2 CuCl 4 A green LED of a nanocrystalline light emitting layer, which is an LED that realizes green emission for the first time in a lead-free metal halide system. In addition, it was observed that the current density of the LED prepared in example 3 was significantly higher than that of examples 1 and 2, because the use of the composite hole injection layer was advantageousIn hole carrier injection.
Fig. 5 is a luminance-voltage characteristic curve of the devices fabricated in examples 1, 2, and 3. As can be seen, the luminance of all three devices gradually increased with increasing voltage. In contrast, the device in example 3 reached 256cd/m at 10 volts 2 The maximum luminance of (c).
Fig. 6 is an electroluminescence spectrum of the devices prepared in examples 1, 2 and 3 at the same driving voltage (8 v), and it can be seen that all three devices exhibited a distinct green emission with a peak at 510 nm. However, due to the difference of the characteristics of the hole injection layers in the three device structures, the light emitting intensities of the devices under the same driving voltage are obviously different.
FIG. 7 is a comparison of external quantum efficiencies of devices prepared in examples 1, 2, and 3. As can be seen from the graph, the external quantum efficiency of the LED prepared in example 1 was 0.20%, the device in example 2 had the lowest external quantum efficiency of 0.09%, and the device in example 3 had the highest external quantum efficiency of 0.56%. Example 3 shows the highest external quantum efficiency, which is mainly because the Poly-TPD/PVK composite hole transport layer can effectively reduce the hole injection barrier and improve the injection efficiency of hole carriers, thereby greatly increasing the radiative recombination efficiency of the injected carriers in the light emitting layer.
Fig. 8 is a graph showing the change of light intensity of the green LED prepared in example 3 with time at a driving voltage of 8 v, and it can be seen from the graph that the device can continuously operate for 9.7 hours at the driving voltage of 8 v, the light intensity is attenuated by only 50%, and the device shows excellent operation stability.
In one aspect of the invention, non-toxic stable Cs is used 2 CuCl 4 The nanocrystalline is used as a luminous layer, so that the green light LED of a lead-free metal halide system is realized for the first time, and the blank of green light band deletion in the system is filled. On the other hand, the prepared LED overcomes the defect of lead toxicity in the traditional lead-based perovskite device, and reduces the harm to human bodies and the environment; the device has excellent working stability, and the working life of the device reaches 9.7 hours under the driving voltage of 8 volts.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. Zero-dimensional Cs 2 CuCl 4 The preparation method of the nanocrystalline is characterized by comprising the following steps:
(1) mixing 2.5 mmol of cesium carbonate, 2.5 ml of oleic acid and 10 ml of octadecene, heating to 100 ℃, and maintaining for 2 hours under nitrogen to obtain a cesium oleate precursor solution;
(2) 0.27 mmol of copper chloride, 5 ml of octadecene, 0.5 ml of oleic acid and 0.5 ml of oleylamine were mixed and heated to 100 ℃ for 2 hours under nitrogen, and the water content of the mixture was removed;
(3) and (3) quickly injecting 0.5 ml of cesium oleate precursor solution into the mixture obtained in the step (2) at 100 ℃, quickly cooling the cesium oleate precursor solution by using an ice water bath after reacting for 5 minutes, and centrifugally purifying the cooled solution to obtain zero-dimensional Cs 2 CuCl 4 And (4) nanocrystals.
2. Zero-dimensional Cs produced by the method of claim 1 2 CuCl 4 And (4) nanocrystals.
3. The zero-dimensional Cs of claim 2 2 CuCl 4 The green LED comprises a transparent conductive substrate, and a hole injection layer, a hole transport layer, and Cs are sequentially arranged on the transparent conductive substrate 2 CuCl 4 A nanocrystalline light emitting layer, an electron transport layer, and a contact electrode.
4. The green LED of claim 3, wherein Cs is 2 CuCl 4 The thickness of the nanocrystalline light-emitting layer is 40-80 nanometers, and the size of a single nanocrystalline is 14-20 nanometers.
5. The green LED of claim 3, wherein the substrate is ITO conductiveGlass with a thickness of 120-150 nm and a resistivity of 1.0 × 10 –4 ～5.0×10 –3 Ohm cm.
6. The green LED of claim 3, wherein the hole injection layer is poly (ethylenedioxythiophene) -sodium polystyrene sulfonate (pdps) and has a thickness of 25-35 nm.
7. The green LED of claim 3, wherein the hole transport layer is poly [ bis (4-phenyl) (4-butylphenyl) amine ] or poly (9-vinylcarbazole) or a composite layer of both, and has a thickness of 10-60 nm.
8. The green LED of claim 3, wherein the electron transport layer is 1, 3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene and has a thickness of 30-50 nm.
9. The green LED of claim 3, wherein the contact electrode is a composite of lithium fluoride and aluminum metal and has a thickness of 100-150 nm.
10. Based on zero-dimensional Cs 2 CuCl 4 The preparation method of the green LED of the nanocrystalline comprises the following steps:
(1) cleaning the transparent conductive substrate;
(2) preparing a hole injection layer on the substrate by adopting a low-temperature solution method;
(3) preparing a hole transport layer on the hole injection layer by adopting a low-temperature solution method;
(4) mixing Cs 2 CuCl 4 Preparing Cs on the hole transport layer by adopting a solution spin coating method for the nanocrystalline solution 2 CuCl 4 A nanocrystalline light-emitting layer;
(5) by thermal vacuum deposition on Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystal light-emitting layer;
(6) and preparing an electrode on the electron transport layer by adopting a thermal vacuum evaporation method.
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