CN111785846A - A green perovskite light-emitting diode based on surface post-treatment process and its preparation - Google Patents

Abstract

A green light perovskite light-emitting diode based on a surface post-treatment process and preparation thereof belong to the field of semiconductor solid light-emitting devices, in particular to the use of butylamine bromide as a surface passivation layer of a perovskite light-emitting layer, which is used for perovskite led. Its structure includes a transparent conductive substrate, a hole transport layer, a perovskite layer, an electron transport layer, an electrode modification layer, and a metal aluminum electrode. The butylamine bromide is mainly modified on the perovskite light-emitting layer by spin coating. The surface passivation layer improves the compactness of the perovskite layer by inducing the recrystallization process of the perovskite, passivates its surface defects, and effectively reduces the proportion of non-radiative recombination in the film. The start-up voltage of the all-inorganic green perovskite light-emitting diode integrated through this process is significantly reduced, the luminous brightness and luminous efficiency are greatly improved, and the stability is significantly improved.

Description

A green perovskite light-emitting diode based on surface post-treatment process and its preparation

technical field

The invention belongs to the field of perovskite light emitting diodes, and particularly relates to a green light perovskite light emitting diode as the main body, spin-coating butylamine bromide on the surface of the perovskite light emitting layer as a surface passivation layer and its application in semiconductor light emitting devices.

technical background

Light-emitting diodes (LEDs) have been widely used in indication, display, backlight, general lighting and other fields due to their advantages of energy saving, environmental friendliness, small size, fast response, and long life, especially in the issue of energy saving and power saving. LEDs are currently the best option to replace incandescent light bulbs. Commonly used semiconductor light-emitting materials in LED devices include inorganic light-emitting materials, organic light-emitting materials and quantum dot light-emitting materials. Traditional inorganic light-emitting materials have disadvantages such as low color purity and high energy-consuming vacuum deposition preparation process. Although solution-processable organic light-emitting diodes (OLEDs) and quantum dot light-emitting diodes (QLEDs) have good luminescent properties, they are currently undergoing or have just begun commercialization, including the short lifespan of blue OLEDs, the high toxicity of chromium in QLEDs, The disadvantages of low yield and high cost need to be overcome. As a direct bandgap semiconductor material that can be prepared by low temperature solution process, metal halide perovskite material has the characteristics of continuously tunable emission wavelength and high emission color purity, and is considered as a strong competitor for next-generation LED devices.

The structure of the perovskite material used to make the LED is ABX ₃ , wherein A=CH ₃ NH ₃ ⁺ (MA), CH ₃ (NH ₂ ) ₂ ⁺ (FA), Cs ⁺ ; B=Pb ²⁺ , Sn ^{2 +} ; X=Cl ^- , Br ^- , I ^- . The current power conversion efficiency of light-emitting diodes (PeLEDs) based on perovskite materials has exceeded 20%. Despite the rapid development, there are still many basic problems in PeLED devices. The problems between the interfaces introduced when it is combined in the device, or the problems existing when the device works, are urgently needed by researchers to solve. Among them, the morphology quality of the perovskite light-emitting layer directly determines the efficiency and stability of the PeLED device, but the perovskite films prepared by the solution method usually have a high density of defect states. Therefore, developing a surface post-treatment process that can not only improve the morphology quality of the perovskite layer, but also effectively passivate the defect states of the perovskite layer and balance the injection of electrons and holes is of great significance for the fabrication of efficient and stable perovskite light-emitting diodes. .

SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, one of the objects of the present invention is to provide a surface post-treatment process.

Another object of the present invention is to provide a green perovskite light-emitting diode, and the LED device integration process includes the above-mentioned surface post-treatment process.

The inventor's research found that butylamine bromide as a surface passivation layer compounded on the perovskite light-emitting layer of the green perovskite light-emitting diode can induce the perovskite recrystallization process, reduce the number of pinholes on the surface of the film, and improve the Density, passivation of perovskite grain boundaries and defect states on the surface, increasing the proportion of effective radiative recombination, and balancing the rate of electron and hole injection into the perovskite layer. The produced LED has the advantages of low starting voltage, high luminous brightness and luminous efficiency, and good stability. The invention has the advantages of simple manufacturing process, low cost and good repeatability, and is suitable for manufacturing large-area light emitting diodes.

The present invention is achieved by the following technical means:

A green light perovskite light-emitting diode based on surface post-treatment process, characterized in that the device structure comprises an ITO transparent conductive substrate/hole transport layer/(perovskite layer+surface passivation layer)/electron transport layer stacked in sequence / electrode modification layer / aluminum electrode.

The conductive substrate is ITO conductive glass;

The material of the hole transport layer is any semiconductor material in TFB, PEDOT:PSS, CBP, PVK;

The material of the electron transport layer is any semiconductor material among TPBi, F8, BCP, and PCBM.

The general chemical formula of the perovskite light-emitting layer is APbBr ₃ , wherein A is one or more mixed cations in different proportions among cesium, methylamine, and formamidine cations.

The perovskite layer+surface passivation layer refers to that the perovskite layer is compounded with a surface passivation layer.

The electrode modification layer is lithium fluoride (LiF).

The above-mentioned method for a green perovskite light-emitting diode based on a surface post-treatment process is characterized in that, comprising the following steps:

1) Preparation of hole transport layer:

The preparation method of the hole transport layer: spin-coating the diluted hole transport layer dispersion or solution on a clean ITO conductive substrate, and after annealing, a dense hole transport layer film is formed;

Spin coating condition is 3000～5000rpm, time 1min; annealing condition is 150℃, time 10～30min;

2) Preparation of perovskite layer + surface passivation layer:

According to the element molar ratio in the chemical formula APbBr ₃ , the corresponding amount of ABr and PbB ₂ are weighed and dissolved in dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF). One or two mixed solvents are used to obtain the precursor solution; the first step is to spin-coat the precursor solution on the film in step 1) and anneal it; the spin coating conditions are 1500-3000 rpm, and the time is 2 min; the annealing conditions are 80～120℃, time 10～20min; in the second step, butylamine bromide solution is spin-coated on the surface, and after annealing, a surface-passivated perovskite film is obtained; spin coating conditions are 2000～4000rpm, time 30～60s; annealing conditions It is 80～100℃, and the time is 5～10min.

More preferably, the concentration of the precursor solution is 0.2 to 0.4 M, and the concentration of the butylamine bromide solution is 1 to 9 mg/mL.

3) Preparation of electron transport layer:

之间，厚度为30～50nm。The preparation method of the electron transport layer: the electron transport layer is deposited on the thin film in step 2) by vacuum evaporation, and the evaporation rate is kept at

In between, the thickness is 30 to 50 nm.

4) Preparation of electrode modification layer/aluminum electrode:

和

厚度分别为1nm和60～100nm。The preparation method of the electrode modification layer/aluminum electrode: the electrode modification layer and the aluminum electrode are sequentially deposited on the film in step 3) by vacuum evaporation, and the evaporation rates are respectively

and

The thicknesses are 1 nm and 60-100 nm, respectively.

During the evaporation process of steps 3 and 4), the pressure in the evaporation chamber must be less than 3.7×10 ^-6 Torr before evaporation can be started, and the evaporation rate must be kept stable.

The first step solution spin coating method in step 2) is an anti-solvent one-step film-forming method, and the anti-solvent dropping method is that the anti-solvent is added dropwise at a constant speed at the positive 30-35 s after the spin coating, and the dropping time is 1-3 s; The anti-solvent is one or more mixed solvents of chlorobenzene, toluene, ethyl acetate and ether, and the dropwise addition amount is 150-200 μl per 4 cm ² area.

A method for a green light perovskite light emitting diode based on a surface post-treatment process can efficiently and stably emit bright green light at an operating voltage of 3.5-6.5V. It can be used in display and lighting fields such as traffic lights, mobile phone displays, holiday lighting accessories, etc. At the same time, it can also emit bright green light when excited by ultraviolet light.

Compared with the prior art, the present invention has the following advantages:

1) The green light perovskite light-emitting diode based on the surface post-treatment process of the present invention has a simple preparation process, low cost and good repeatability.

2) The present invention is based on the green light perovskite light-emitting diode of the surface post-treatment process. This method of modifying the perovskite light-emitting layer with butylamine bromide as the surface passivation layer has not been reported in the literature. Through experimental tests, It has a lower starting voltage, obtains higher luminous brightness and luminous efficiency, and achieves good stability.

Description of drawings

Fig. 1. Scanning electron microscope photos of the perovskite layer before and after the surface passivation of the BABr prepared in Example 1.

Figure 2. Photoluminescence photos of the perovskite layer before and after the surface passivation of the BABr prepared in Example 1.

Figure 3. Luminance-V curves of the green perovskite light-emitting diode before and after surface passivation of the BABr prepared in Example 1. Figure 4. The EQE-V curves of the green perovskite light-emitting diode before and after the surface passivation of the BABr prepared in Example 1, the inset is the luminescence photo of the device under dark conditions.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and examples, but the present invention is not limited to the following examples.

Example 1

1) Preparation of hole transport layer:

Dilute the purchased Al4083 PEDOT:PSS solution with deionized water at a dilution ratio of 2:1 (volume ratio of PEDOT:PSS and deionized water), and coat it on clean ITO conductive glass by spin coating at 150°C A dense PEDOT:PSS film was formed after annealing for 15 min.

2) Preparation of perovskite layer:

Cesium bromide and lead bromide were added into DMSO at a molar ratio of 1:1 to prepare a perovskite precursor solution with a concentration of 0.2 M. Stir at room temperature for 12 h to obtain a clear and transparent colorless perovskite precursor solution. In a nitrogen glove box, 70uL of the precursor solution was taken by one-step spin coating method, the speed was 2000rpm, the time was 2min, and 150μL of anti-solvent was added dropwise for a positive number of 30s. to room temperature. Then spin-coat 7mg/mL butylamine bromide solution (solvent is isopropanol) on the surface, rotate speed is 3000rpm, time is 40s, and after annealing at 90℃ for 10min, the surface passivation perovskite film is obtained.

3) Preparation of electron transport layer:

厚度为40nm。The electron transport layer was deposited on the film in step 2) by vacuum evaporation, and the evaporation rate was kept at

The thickness is 40nm.

4) Preparation of electrode modification layer/aluminum electrode:

和

厚度分别为1nm和80nm。The electrode modification layer lithium fluoride and aluminum electrode are deposited on the film in step 3) by vacuum evaporation, and the evaporation rates are respectively

and

The thicknesses are 1 nm and 80 nm, respectively.

The fabricated perovskite light-emitting diode achieves stable and high-efficiency electroluminescence within the working voltage of 3.5-6.5V, and is currently at a better level among green light-emitting perovskite light-emitting diodes modified without additives.

It can be seen from Figure 1 that the growth of the perovskite film after BABr surface passivation, the number of surface pinholes is significantly reduced, and the coverage is significantly improved.

It can be seen from Figure 2 that under the condition of ultraviolet light excitation, the perovskite film emits bright green light after the surface passivation of BABr, indicating that the density of defect states in the perovskite layer is significantly reduced, which increases the proportion of effective radiation recombination. Scale (the block on the right below has a much higher green brightness than the block on the left below).

It can be seen from Figure 3 that the luminescence performance of the green perovskite light-emitting diode device with passivation on the surface of BABr has been significantly improved, and the device startup voltage has been reduced from 4.3V to 3.0V, indicating that the increase in the density of the perovskite film makes the device leak during operation. Current decreased; maximum brightness increased from 23cd/m ² to 3296cd/m ² .

It can be seen from Figure 4 that the luminous efficiency of the green perovskite light-emitting diode device with BABr surface passivation has been significantly improved, and the EQE has been increased from 0.08% to 3.90%.

At the same time, it is measured that the half-life of the device is about 60s at room temperature of 25°C and humidity of 35-40%.

Claims (10)

1. The butyl ammonium bromide is applied as a surface passivation layer to be compounded on a perovskite luminous layer of a green perovskite luminous diode.

2. The use of butylammonium bromide according to claim 1 to induce a recrystallization process of perovskite, to improve the morphological quality of perovskite thin films, to passivate surface defects, to increase the fraction of effective radiative recombination, and to balance the rate of injection of electrons and holes into perovskite layers.

3. A green perovskite light emitting diode based on a surface post-treatment process is characterized in that a device structure comprises an ITO transparent conductive substrate/a hole transport layer/(a perovskite layer + a surface passivation layer)/an electron transport layer/an electrode modification layer/an aluminum electrode which are sequentially stacked.

4. The green perovskite light emitting diode based on the surface post-treatment process as claimed in claim 3, wherein the conductive substrate is ITO conductive glass; the hole transport layer is made of any one semiconductor material of TFB, PEDOT, PSS, CBP and PVK; the material of the electron transport layer is any one semiconductor material of TPBi, F8, BCP and PCBM.

5. The green perovskite light emitting diode based on the surface post-treatment process as claimed in claim 3, wherein the perovskite light emitting layer has a chemical formula of APbBr₃Wherein A is one or more mixed cations in different proportions in cesium, methylamine and formamidine cations.

6. A green perovskite light emitting diode based on a surface post-treatment process as claimed in claim 3 wherein the electrode modification layer is lithium fluoride (LiF).

7. The method for preparing the green perovskite light emitting diode based on the surface post-treatment process as claimed in any one of claims 3 to 6, which is characterized by comprising the following steps:

1) preparation of hole transport layer:

the preparation method of the hole transport layer comprises the following steps: spin-coating the diluted hole transport layer dispersion liquid or solution on a clean ITO conductive substrate, and annealing to form a compact hole transport layer film;

the spin coating condition is 3000-5000 rpm, and the time is 1 min; the annealing condition is 150 ℃, and the time is 10-30 min;

2) preparation of perovskite layer + surface passivation layer:

according to the general chemical formula APbBr₃The molar ratio of the elements in the raw materials is mixed, and corresponding amounts of ABr and PbB are weighed₂Dissolving the precursor solution in one or two mixed solvents of dimethyl sulfoxide (DMSO) or N, N-Dimethylformamide (DMF) to obtain a precursor solution; firstly, spin-coating a precursor solution on the film obtained in the step 1) and annealing; the annealing condition is 80-120 ℃, and the time is 10-20 min; secondly, spin-coating a butyl ammonium bromide solution on the surface, and annealing to obtain a perovskite thin film with a passivated surface; the annealing condition is 80-100 ℃, and the time is 5-10 min;

3) preparation of an electron transport layer:

the preparation method of the electron transport layer comprises the following steps: depositing an electron transport layer on the film in step 2) by vacuum evaporation, the evaporation rate being maintained at

The thickness is 30-50 nm;

4) preparing an electrode modification layer/aluminum electrode:

the preparation method of the electrode modification layer/aluminum electrode comprises the following steps: sequentially depositing the electrode modification layer and the aluminum electrode on the film in the step 3) by vacuum evaporation at the evaporation rates of

And

the thicknesses are respectively 1nm and 60-100 nm.

8. The method as claimed in claim 7, wherein the concentration of the precursor solution in step 2) is 0.2-0.4M, the concentration of the butyl ammonium bromide solution is 1-9 mg/mL, the first spin-coating condition in step 2) is 1500-3000 rpm for 2min, the second spin-coating condition is 2000-4000 rpm for 30-60 s, and the pressure in the evaporation chamber during the evaporation process in steps 3 and 4) is less than 3.7 × 10^-6Torr, vapor deposition can be startedThe evaporation rate is kept constant.

9. The method according to claim 7, wherein the first step of the solution spin coating in the step 2) is an anti-solvent one-step film forming method, and the anti-solvent dropping method is that the anti-solvent is dropped at a constant speed from the positive number of 30-35 s after the spin coating, wherein the dropping time is 1-3 s; the antisolvent is one or more of chlorobenzene, toluene, ethyl acetate and diethyl ether, and the dripping amount is 4cm per time²The area is dripped with 150-200 mu l.

10. The application of the green perovskite light emitting diode based on the surface post-treatment process as claimed in any one of claims 3 to 6 is characterized in that the application is in the fields of display and illumination of traffic signal lamps, mobile phone display screens, holiday lamp ornaments and the like. And simultaneously, the ultraviolet light is adopted for excitation, and bright green light can be emitted.

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