CN115108575B - 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 a zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green light LED and preparation method thereof, zero-dimensional Cs 2 CuCl 4 The nanocrystalline is prepared by adopting a high-temperature injection method, cesium carbonate, oleic acid and octadecene are mixed and heated to 100 ℃, and maintained for 2 hours under nitrogen to obtain cesium oleate precursor liquid; copper chloride, octadecene, oleic acid and oleylamine were mixed and heated to 100 ℃ and maintained under nitrogen for 2 hours to remove moisture from the mixture; then, at 100 ℃, cesium oleate precursor liquid is rapidly injected into the mixture, after the reaction is carried out for 5 minutes, the cesium oleate precursor liquid is rapidly cooled by using an ice water bath, and the cooled solution is centrifugally purified; cs is processed by 2 CuCl 4 The nanocrystals were used as light emitting layers to prepare green LEDs. Cs prepared by the invention 2 CuCl 4 The nano-crystal has uniform size, the fluorescence quantum yield is up to 90%, the green LED continuously and stably works in the atmospheric environment, and the service life of the green LED reaches 9.7 hours under the 8-volt driving voltage.
Description
Technical Field
The invention relates to the technical field of semiconductor light-emitting devices, in particular to a zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green LED and method of making.
Background
The metal halide perovskite nanocrystalline 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 improved the external quantum efficiency of perovskite nanocrystalline LEDs to over 20% through material optimization and device structure improvement, and have shown great application prospects (X.Liu, W.Xu, S.Bai, Y.Jin, J.Wang, R.H.Friend, and F.Gao, metal Halide Perovskites for Light-emission Diodes, nat. Mater.20,10 (2021)). However, the light-emitting layers of these perovskite devices all contain heavy metal lead which is a serious hazard to human health, greatly limiting their wide application in the field of light-emitting display. In addition, lead halide perovskite nanocrystals are relatively poor in stability and very sensitive to environmental factors such as water, oxygen, light and heat, resulting in a short device operating life, thus severely impeding the commercialization 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, stabilities, and Optical Properties, angew.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 stable in environment clearly has important scientific significance and practical value.
Aiming at the problem that the lead element is commonly contained in the current high-efficiency perovskite LED, researchers have widely developed to use non-toxic or low-toxicity metal elements to replace lead to prepare lead-free perovskite nanocrystals, such as CsSnX 3 (X＝Cl,Br,I)、Cs 3 Sb 2 X 9 、Cs 2 AgInCl 6 、Cs 3 Cu 2 X 5 Nanocrystalline, 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 Perovskites for Light Emission: recent Advances and Perspectives, adv. Sci.8,2003334 (2021)). Among them, recently reported Cu-based halide nanocrystals are particularly interesting because of their direct band gap, high fluorescence quantum efficiency, non-toxicity, and low manufacturing cost, and have been successfully used as light emitting layers for manufacturing 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.C123,16951-16956 (2019)) discloses a Cs 2 CuCl 4 Method for preparing nanocrystalline, cs prepared in this document 2 CuCl 4 The fluorescence quantum efficiency (PLQY) of the nanocrystals is shown in Table 2 of page 16954, the PLQY is only 14% at most, but the PLQY of the nanocrystals with different raw material ratios is n/a, n/a is the efficiency which cannot be tested out when the test is too small, and the problems that the nanocrystals are difficult to uniformly nucleate and grow, the defects on the surfaces and in the bodies of the nanocrystals are many, the PLQY is very low and the like exist.
No lead-free metal halide LEDs in the green spectral region have been reported. The green light band, which is one of the three primary colors, is an indispensable contribution to the fields of multicolor LED display, high-end illumination, visible light communication, and the like. Therefore, the use of lead-free nanocrystals with green emission, non-toxicity, stability, and low manufacturing cost for the manufacture of green LED devices has a very important research value.
Considering 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 positioned in a green light wave band. If Cs can be used 2 CuCl 4 The nanocrystalline is used as a light-emitting layer, and the green light LED which can work stably is prepared through the structural design of the device, so that the blank that the lead-free metal halide LED system is absent in the green light wave band can be filled.
Disclosure of Invention
The invention provides a zero-dimensional Cs 2 CuCl 4 Nanocrystalline, green light LED and preparation method thereof, and prepared non-toxic stable green luminous Cs 2 CuCl 4 Nanocrystalline, nanocrystalline size is even, fluorescence quantum yield is high, cs 2 CuCl 4 The nanocrystalline is used as a light-emitting layer to prepare the green light LED based on the lead-free metal halide system for the first time, thereby meeting the application requirements in the fields of multicolor display, high-end illumination, visible light communication and the like.
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 stepsThe steps are as follows:
(1) 2.5 mmol of cesium carbonate, 2.5 ml of oleic acid and 10 ml of octadecene are mixed and heated to 100 ℃ and maintained under nitrogen for 2 hours to obtain cesium oleate precursor liquid;
(2) 0.27 mmole 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℃and maintained under nitrogen for 2 hours, and the moisture in the mixture was removed;
(3) Then at 100 ℃, 0.5 milliliter of cesium oleate precursor liquid is quickly injected into the mixture in the step (2), after the reaction is carried out for 5 minutes, the cesium oleate precursor liquid is quickly cooled by using an ice water bath, and the cooled solution is centrifugally purified to obtain zero-dimensional Cs 2 CuCl 4 And (3) nanocrystalline.
Zero-dimensional Cs prepared by adopting the preparation method 2 CuCl 4 And (3) nanocrystalline.
Based on zero-dimensional Cs 2 CuCl 4 The nanocrystalline green light 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.
Further, cs 2 CuCl 4 The thickness of the nanocrystalline luminescent layer is 40-80 nanometers, wherein the size of the 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 is 1.0x10 –4 ～5.0×10 –3 Ohm-cm.
Further, the hole injection layer is polyethylene dioxythiophene-sodium polystyrene sulfonate, and the thickness of the hole injection layer is 25-35 nanometers, wherein the polyethylene dioxythiophene is also called PEDOT, and the sodium polystyrene sulfonate is also called PSS.
Further, the hole transport layer is Poly [ bis (4-phenyl) (4-butylphenyl) amine ] (abbreviated as Poly-TPD) or Poly (9-vinylcarbazole) (abbreviated as PVK) or a composite layer of the Poly [ bis (4-phenyl) (4-butylphenyl) amine ] (abbreviated as Poly-TPD) or Poly (9-vinylcarbazole) (abbreviated as PVK) and the thickness is 10-60 nanometers.
Further, the electron transport layer is 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (abbreviated as TPBi) with a thickness of 30-50 nm.
Further, the contact electrode is a composite material of lithium fluoride and metallic 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 nanocrystalline green LED comprises the following steps:
(1) Cleaning the transparent conductive substrate;
(2) Preparing a hole injection layer on a 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) Cs is processed by 2 CuCl 4 Preparation of Cs on hole transport layer by solution spin coating of nanocrystalline solution 2 CuCl 4 A nanocrystalline light emitting layer;
(5) Adopting a thermal vacuum evaporation method to deposit Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystalline luminescent layer;
(6) An electrode is prepared on the electron transport layer by thermal vacuum evaporation.
Further, in step (4), zero-dimensional Cs is obtained 2 CuCl 4 Dispersing the nanocrystalline in n-hexane to obtain Cs 2 CuCl 4 Under the protection of inert gas, the nanocrystalline solution is prepared into Cs 2 CuCl 4 The nanocrystalline solution is uniformly spin-coated on the hole transport layer, and spin-coating conditions are as follows: 2000 rpm/30 s, and finally annealing the spin-coated sample at 80deg.C for 10 min to obtain green light-emitting Cs 2 CuCl 4 A nanocrystalline light emitting layer.
Further, in the step (2), the hole injection layer is prepared by a one-step solution method; in 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:
the TPBi powder is placed in a crucible and transferred to a thermal vacuum evaporation chamber with Cs 2 CuCl 4 The sample of the nanocrystalline luminescent layer is placed at a position 30 cm above the crucible in an inverted mode, and the evaporation conditions are as follows: the evaporation power is 30W, the evaporation pressure is1×10 –4 The rate of evaporation was 3 to 10 angstroms per second, and the thickness of evaporation was 40 nanometers.
The invention has the beneficial effects that:
the invention adopts the Cs with environmental protection, stability and low cost 2 CuCl 4 The nanocrystalline has uniform size, the fluorescence quantum yield (PLQY) is up to 90 percent, and Cs is extracted from the nanocrystalline 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 the 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 human body is reduced; on the other hand by means of Cs 2 CuCl 4 The material has excellent stability advantage, and the prepared green LED can continuously and stably work in the atmospheric environment, and the service life of the green LED reaches 9.7 hours under 8V driving voltage, which is obviously superior to the traditional lead-based nanocrystalline LED. Therefore, the LED of the invention can overcome the defects of the traditional lead halide perovskite LED in lead toxicity and stability, and provides a feasible scheme for green LED preparation research with environmental protection, stability and low cost.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 shows a zero-dimensional Cs-based system according to the invention 2 CuCl 4 A green LED structure schematic diagram of the nanocrystalline;
FIG. 2 shows Cs prepared according to the present invention 2 CuCl 4 Transmission electron microscope pictures of the nanocrystals;
FIG. 3 shows Cs prepared according to the present invention 2 CuCl 4 A luminescence intensity change curve of the nanocrystalline luminescent layer under continuous heating at 100 ℃;
fig. 4 is a current density-voltage characteristic curve of the green LEDs prepared in examples 1, 2 and 3;
fig. 5 is a luminance-voltage characteristic curve of the green LEDs prepared in examples 1, 2 and 3;
fig. 6 is an electroluminescence spectrum of the green LEDs prepared in examples 1, 2 and 3 at the same driving voltage;
fig. 7 is the external quantum efficiency of the green LEDs prepared in examples 1, 2 and 3;
fig. 8 is a graph showing a change in luminous intensity of the green LED prepared in example 3 continuously operated at a driving voltage of 8 v;
FIG. 9 shows Cs prepared according to the present invention 2 CuCl 4 The nanocrystalline solution exhibits very bright green light under illumination.
Wherein: 1. substrate, 2. Hole injection layer, 3. Hole transport layer, 4.Cs 2 CuCl 4 And 5, an electron transport layer and 6, a contact electrode.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.
Zero-dimensional Cs 2 CuCl 4 The preparation method of the nanocrystalline comprises the following steps:
(1) 2.5 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℃and maintained 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℃and maintained under nitrogen for 2 hours to remove the moisture in the mixture;
(3) Then, at 100 ℃, the mixture of the step (2) is quickly addedInjecting 0.5 ml cesium oleate precursor liquid rapidly, cooling rapidly after reacting for 5 min by using ice water bath, centrifuging and purifying the cooled solution to obtain zero-dimensional Cs 2 CuCl 4 And (3) nanocrystalline.
FIG. 2 shows Cs prepared by high temperature hot injection 2 CuCl 4 The transmission electron microscope photograph of the nanocrystalline can see Cs from the figure 2 CuCl 4 The nanocrystalline is spherical, has good crystallization characteristics and obvious self-assembly characteristics, and the average size of the nanocrystalline is 18 nanometers.
FIG. 3 is Cs 2 CuCl 4 The change curve of the luminous intensity of the nanocrystalline in the continuous heating process at 100 ℃ shows that the luminous intensity is only attenuated by 5% after the continuous heating for 100 hours, which indicates Cs 2 CuCl 4 The nanocrystals have excellent thermal stability.
Cs prepared by the invention 2 CuCl 4 The nanocrystalline has uniform size, can realize 90 percent of fluorescence quantum efficiency (PLQY), and Cs 2 CuCl 4 The nanocrystalline solution can observe very bright green light as shown in fig. 9.
As shown in FIG. 1, based on the zero-dimensional Cs 2 CuCl 4 The nanocrystalline green light LED comprises an insulated transparent conductive substrate 1, wherein 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 the ITO thin layer is 100-130 nanometers, and the resistivity is 5.0X10-4-1.0X10-3 ohm cm.
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, polyethylene dioxythiophene 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 ] (namely Poly-TPD), poly (9-vinylcarbazole) (namely PVK) or a composite layer of the Poly [ bis (4-phenyl) (4-butylphenyl) amine ] (namely Poly-TPD), and the thickness is 10-60 nanometers.
The thickness of the Cs2CuCl4 nanocrystalline luminescent layer is 40-80 nanometers, wherein the size of single nanocrystalline is 14-20 nanometers.
The electron transport layer 5 is 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (i.e., TPBi) having a thickness of 30 to 50 nanometers.
The contact electrode 6 is a composite material of lithium fluoride and metallic aluminum, and the thickness of the contact electrode is 100-150 nanometers.
The preparation method of the green LED based on the zero-dimensional leadless Cs2CuCl4 nanocrystalline 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) A hole transport layer 3 is prepared on the hole injection layer 2 by adopting a low-temperature solution method;
(4) Preparation of green light emitted Cs by high temperature heat injection 2 CuCl 4 Nanocrystalline solution and preparation of Cs on hole transport layer using solution spin coating 2 CuCl 4 A nanocrystalline light emitting layer;
(5) Adopting a thermal vacuum evaporation method to deposit Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystalline luminescent layer;
(6) And preparing a contact electrode on the electron transport layer by adopting a thermal vacuum evaporation method.
Preferably, the cavity injection layer 2 in the step (2) is prepared by a one-step solution method: the PEDOT/PSS solution is filtered by a nylon filter head with a water system of 0.45 micrometers, 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 rpm/60 s, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes.
Preferably, the hollow transfer layer 3 in step (3) is prepared according to a one-step solution method: poly-TPD or PVK is dissolved in chlorobenzene solution with the concentration of 6 milligrams per milliliter, and stirred for 2 hours at the temperature of 25 ℃ by a constant-temperature magnetic stirrer to obtain a precursor solution, and the precursor solution is uniformly spin-coated on the hole injection layer in a spin-coating mode under the protection of inert gas. The Poly-TPD spin coating conditions were: 3000 rpm/60 s, and finally annealing the spin-coated sample at 120 ℃ for 20 minutes; the PVK spin coating conditions were: 6000 rpm/60 s, and finally annealing the spin-coated sample at 120 deg.c for 20 min.
Preferably, zero-dimensional Cs is added in step (4) 2 CuCl 4 Dispersing the nanocrystalline in n-hexane to obtain Cs 2 CuCl 4 Under the protection of inert gas, the nanocrystalline solution is prepared into Cs 2 CuCl 4 The nanocrystalline solution is uniformly spin-coated on the hole transport layer, and spin-coating conditions are as follows: 2000 rpm/30 s, and finally annealing the spin-coated sample at 80deg.C for 10 min 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:
the TPBi powder is placed in a crucible and transferred to a thermal vacuum evaporation chamber, carrying Cs 2 CuCl 4 The sample of the nanocrystalline luminescent layer is placed at a position 30 cm above the crucible in an inverted mode, and the evaporation conditions are as follows: the evaporation power is 30W, and the evaporation pressure is 1 multiplied by 10 –4 The rate of evaporation was 3 to 10 angstroms per second, the thickness of evaporation was 40 nanometers, and the evaporation time was 100 minutes.
The preparation method and properties of the present invention are described below with reference to specific embodiments.
Example 1
The preparation method of the green light LED based on the zero-dimensional leadless Cs2CuCl4 nanocrystalline comprises the following steps:
(1) The transparent conductive substrate 1 is cleaned, and the substrate 1 is ITO conductive glass.
The ITO conductive glass is used as a substrate 1, and is subjected to chemical cleaning, wherein the cleaning steps are as follows: firstly, putting a substrate into a cleaning agent (Libai brand liquid detergent) for soaking for 10 minutes, and then washing the substrate cleanly by tap water; then sequentially ultrasonically cleaning the raw materials for 15 minutes by using acetone and ethanol solution respectively, and recycling the raw materials once; and then washing with deionized water, and drying with 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 cleaner for 30 minutes, and then spin-coating a hole injection layer on the treated transparent conductive substrate 1; the PEDOT/PSS solution is filtered by a nylon filter head with a water system of 0.45 micrometers, 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 (Aladin brand) powder was dissolved in 2 ml of chlorobenzene solution; stirring for 2 hours at 25 ℃ by using a constant-temperature magnetic stirrer to obtain a Poly-TPD precursor solution; 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 mode, 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 hole transport layer obtained was 30 nm.
(4) Preparation of green light emitted Cs by high temperature heat injection 2 CuCl 4 Nanocrystalline solution and preparation of Cs on hole transport layer using solution spin coating 2 CuCl 4 A nanocrystalline light-emitting layer 4.
2.5 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℃and maintained under nitrogen for 2 hours to obtain cesium oleate precursor liquid; 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℃and maintained under nitrogen for 2 hours to remove the moisture in the mixture; then 0.5 ml cesium oleate precursor solution is rapidly injected at 100 ℃, the cesium oleate precursor solution is rapidly cooled by using an ice water bath after the reaction is carried out for 5 minutes, and the cooled solution is centrifugally purifiedFinally, dispersing the precipitate after centrifugation in n-hexane; under the protection of inert gas, cs 2 CuCl 4 The nanocrystalline solution is uniformly spin-coated on the hole transport layer 3, and spin-coating conditions are as follows: 2000 revolutions per minute/30 seconds; finally, annealing the spin-coated sample at 80 ℃ for 10 minutes to obtain Cs emitting green light 2 CuCl 4 A nanocrystalline light emitting layer. Cs produced 2 CuCl 4 The thickness of the nanocrystalline light-emitting layer was 50 nm.
(5) Spin-coating Cs 2 CuCl 4 The sample of the nanocrystalline luminescent 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, placing 3 g of TPBi (Aladin) powder into a crucible; then will carry Cs 2 CuCl 4 The sample of the nanocrystalline luminescent layer is placed at a position 30 cm above the crucible in an inverted mode, a mechanical pump is started to vacuumize an evaporation cavity, and after the cavity vacuum degree is lower than 5 Pa, a molecular pump is started to continuously vacuumize until the cavity vacuum degree is lower than 1.0x10 –4 The vapor deposition was started at pascal, the evaporation power was set at 30 watts, the evaporation rate was 3 to 10 angstroms per second, and the thickness of the prepared electron transport layer was 40 nm.
(6) Lithium fluoride (Aladin 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. The lithium fluoride is evaporated first and then the aluminum is evaporated, and the thicknesses of the lithium fluoride and the aluminum electrode are respectively 1 nanometer and 100 nanometers.
Example 2
(1) An 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 of embodiment 1.
(2) The hole injection layer 2 is prepared by a low temperature solution method. The procedure and preparation parameters of this section were 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 (Aladin brand) powder was dissolved in 2 ml of chlorobenzene solution; 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 mode, wherein the spin-coating conditions are as follows: 6000 rpm/60 seconds, and finally annealing the spin-coated sample in a glove box at 120 ℃ for 20 minutes. The thickness of the hole transport layer obtained was 10 nm.
(4) Preparation of Cs by high temperature hot injection 2 CuCl 4 Nanocrystalline and further utilizing solution spin-coating technique to prepare Cs 2 CuCl 4 A nanocrystalline light-emitting layer 4. The procedure and preparation parameters of this section were the same as in example 1.
(5) The electron transport layer 5 is prepared by thermal vacuum evaporation. The procedure and preparation parameters of this section were the same as in example 1.
(6) Finally, the contact electrode 6 is prepared by a thermal vacuum evaporation method. The procedure and preparation parameters of this section were the same as in example 1.
Example 3
(1) An 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 of embodiment 1.
(2) The hole injection layer 2 is prepared by a low temperature solution method. The procedure and preparation parameters of this section were the same as in example 1.
(3) The hole transport layer 3 is prepared by a low temperature solution method. First, 6 mg/ml of a Poly-TPD precursor solution was uniformly spin-coated on the hole injection layer 2 under the following spin-coating conditions: and (3) carrying out annealing treatment on the spin-coated sample in a glove box at a temperature of 3000 rpm/60 seconds, wherein the annealing temperature is 120 ℃ and the annealing time is 20 minutes. After the sample was cooled, a PVK precursor solution at a concentration of 6 mg/ml was spin-coated uniformly onto the Poly-TPD layer under the following conditions: 6000 revolutions per minute/60 seconds, the annealing temperature is 120℃and the time is 20 minutes. The thickness of the obtained composite hole transport layer was 40 nm.
(4) Preparation of Cs by high temperature hot injection 2 CuCl 4 Nanocrystalline and further utilizing solution spin-coating technique to prepare Cs 2 CuCl 4 A nanocrystalline light-emitting layer 4. Process and apparatus for this partThe preparation parameters were the same as in example 1.
(5) The electron transport layer 5 is prepared by thermal vacuum evaporation. The procedure and preparation parameters of this section were the same as in example 1.
(6) Finally, the contact electrode 6 is prepared by a thermal vacuum evaporation method. The procedure and preparation parameters of this section were the same as in example 1.
This example differs from example 1 in that a Poly-TPD/PVK composite hole transport layer was used in the LED device structure. Poly-TPD (1X 10) -4 cm 2 V -1 s -1 ) Ratio PVK (1X 10) -6 cm 2 V -1 s -1 ) Has higher hole mobility and facilitates hole carrier injection into Cs 2 CuCl 4 The nanocrystalline light-emitting layer. Whereas PVK (-5.8 eV) has a deeper highest occupied molecular orbital than Poly-TPD (-5.2 eV), which is beneficial to counteract the hole injection barrier. Therefore, the efficient smooth injection of hole carriers into the light-emitting layer can be realized by using the Poly-TPD and PVK composite hole transport layer, and the device performance is improved.
Fig. 4 is a graph showing current density-voltage characteristics of the devices prepared in examples 1, 2, and 3, each of which shows a remarkable rectifying characteristic. Device testing has shown that all three embodiments can achieve Cs-based 2 CuCl 4 The green LED of the nanocrystalline light emitting layer, which is the LED that first achieved green emission in a lead-free metal halide system. In addition, the current density of the LED prepared in example 3 was observed to be significantly higher than that of examples 1 and 2, because hole carrier injection is favored by using a composite hole injection layer.
Fig. 5 is a graph showing luminance vs. voltage characteristics of the devices prepared in examples 1, 2, and 3. As can be seen from the figure, the brightness of the three devices all gradually increases with increasing voltage. In contrast, the device in example 3 reached 256cd/m at 10 volts 2 Is a maximum luminance of (a).
Fig. 6 shows the electroluminescent spectra of the devices prepared in examples 1, 2, and 3 at the same driving voltage (8 v), and it can be seen from the figure that all three devices show significant green emission with emission peaks at 510 nm. However, due to the difference in the characteristics of the cavity injection layers in the three device structures, the light-emitting intensity of the devices under the same driving voltage is obviously different.
Fig. 7 is a comparison of external quantum efficiencies of the 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 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 injected carriers in the light-emitting layer.
Fig. 8 is a graph showing the change of the emission intensity with time of the green LED prepared in example 3 at 8 v driving voltage, and it can be seen from the graph that the device can be operated continuously for 9.7 hours at 8 v, the emission intensity is only attenuated by 50%, and excellent operation stability is exhibited.
On the one hand, the invention adopts non-toxic stable Cs 2 CuCl 4 The nanocrystalline is used as a light-emitting layer, so that the green light LED of the lead-free metal halide system is realized for the first time, and the blank of the deficiency of green light wave bands 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; and the device has excellent working stability, and the working life of the device under 8V driving voltage reaches 9.7 hours.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (9)
1. Zero-dimensional Cs 2 CuCl 4 The preparation method of the nanocrystalline is characterized by comprising the following steps:
(1) 2.5 mmol of cesium carbonate, 2.5 ml of oleic acid and 10 ml of octadecene are mixed and heated to 100 ℃ and maintained under nitrogen for 2 hours to obtain cesium oleate precursor liquid;
(2) 0.27 mmole 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℃and maintained under nitrogen for 2 hours, and the moisture in the mixture was removed;
(3) Then at 100 ℃, 0.5 milliliter of cesium oleate precursor liquid is quickly injected into the mixture in the step (2), after the reaction is carried out for 5 minutes, the cesium oleate precursor liquid is quickly cooled by using an ice water bath, and the cooled solution is centrifugally purified to obtain zero-dimensional Cs 2 CuCl 4 And (3) nanocrystalline.
2. Based on zero-dimensional Cs 2 CuCl 4 The nanocrystalline green light LED is characterized by comprising 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 Nanocrystalline light-emitting layer, electron transport layer, contact electrode, zero-dimensional Cs 2 CuCl 4 The nanocrystalline is prepared by the preparation method of claim 1.
3. The green LED of claim 2, wherein Cs 2 CuCl 4 The thickness of the nanocrystalline luminescent layer is 40-80 nanometers, wherein the size of the single nanocrystalline is 14-20 nanometers.
4. The green LED of claim 2, wherein the substrate is ITO conductive glass having a thickness of 120-150 nm and a resistivity of 1.0 x 10 –4 ~5.0×10 –3 Ohm ∙ cm.
5. The green LED of claim 2, wherein the hole injection layer is polyethylene dioxythiophene-sodium polystyrene sulfonate, and has a thickness of 25-35 nm.
6. The green LED of claim 2, 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.
7. The green LED of claim 2, wherein the electron transport layer is 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene having a thickness of 30-50 nm.
8. The green LED of claim 2, wherein the contact electrode is a composite of lithium fluoride and metallic aluminum having a thickness of 100-150 nm.
9. Zero-dimensional Cs-based system as claimed in any one of claims 2-8 2 CuCl 4 The preparation method of the nanocrystalline green LED comprises the following steps:
(1) Cleaning the transparent conductive substrate;
(2) Preparing a hole injection layer on a 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) Cs is processed by 2 CuCl 4 Preparation of Cs on hole transport layer by solution spin coating of nanocrystalline solution 2 CuCl 4 A nanocrystalline light emitting layer;
(5) Adopting a thermal vacuum evaporation method to deposit Cs 2 CuCl 4 Preparing an electron transport layer on the nanocrystalline luminescent layer;
(6) An electrode is prepared on the electron transport layer by thermal vacuum evaporation.
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