A light-emitting layer of a perovskite white light-emitting diode and its preparation method and application

Abstract

The present invention provides a light-emitting layer of a perovskite white light-emitting diode, which is composed of sky blue light-emitting perovskite nanocrystals and PCDTBT8 in a mass ratio of 150 to 400:1. The present invention also provides a method for preparing the light-emitting layer of a perovskite white light-emitting diode, which adopts a mixed solvent strategy to uniformly mix the perovskite nanocrystals and PCDTBT8 in the same solvent, with sky blue light-emitting nanocrystals as the main body and red light-emitting PCDTBT8 as a dopant, and obtains the effect of two-color light emission of a single light-emitting layer through efficient energy transfer from nanocrystals to PCDTBT8. The present invention also provides a perovskite white light-emitting diode having the above-mentioned light-emitting layer. Due to the single light-emitting layer structure, the overall preparation process is simpler, and the light-emitting spectrum and color temperature can be regulated by adjusting the ratio of nanocrystals to PCDTBT8 to meet the application requirements of different scenarios, and has broad promotion and application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of display and lighting, and in particular relates to a light-emitting layer of a perovskite white light-emitting diode and a preparation method thereof, and also relates to a perovskite white light-emitting diode with a single light-emitting layer. Background Art

[0002] With the development of science and technology and society, people have higher and higher demands on the quality of light sources for display and lighting applications. Although light-emitting diodes (LEDs) have been successfully commercialized and applied in display and lighting as the fourth-generation light source, they still face problems such as low color purity due to wide emission bandwidth and low luminous brightness due to poor carrier transport capacity. Perovskite materials are expected to become the ideal materials for the next generation of high-efficiency and low-cost LEDs (light-emitting diodes) due to their excellent optoelectronic properties such as high photoluminescence quantum yield, narrow emission half-width (<20nm), adjustable bandgap (390-1050nm), high carrier mobility, low-temperature solution processability, and low material cost.

[0003] At present, the external quantum efficiency of green PeLEDs and red PeLEDs has exceeded 20%, reaching the level of commercial LEDs. In contrast, the development of Pe-WLEDs (perovskite white light-emitting diodes) has been relatively slow. The current mainstream Pe-WLEDs mainly achieve the co-emission of complementary light by stacking different light-emitting layers together. However, this not only requires complex device manufacturing processes such as solvent orthogonalization, but also requires special intermediate layer design to balance the carrier transport between layers, which greatly increases the difficulty of device preparation. Recent work has shown that white light can be obtained by utilizing lattice distortion to make self-trapped excitons produce broadband emission, but perovskites that can produce self-trapped exciton effects often have poor carrier transport capabilities, which leads to low efficiency of most devices. White light is the most commonly used light source in display and lighting applications, so finding a simple and efficient method to prepare Pe-WLED is very necessary for its development and application. Summary of the invention

[0004] One of the objectives of the present invention is to provide a light-emitting layer of a perovskite white light-emitting diode.

[0005] A second object of the present invention is to provide a method for preparing a light-emitting layer of a perovskite white light-emitting diode.

[0006] A third object of the present invention is to provide a single-light-emitting-layer perovskite white light-emitting diode.

[0007] The technical solution adopted by the present invention to achieve one of the purposes is: to provide a light-emitting layer of a perovskite white light-emitting diode, wherein the light-emitting layer is composed of a molecular formula of FA 0.08 Cs0.92 The perovskite nanocrystals of Pb(Br,Cl)3 and PCDTBT8 are composed in a mass ratio of 150 to 400:1.

[0008] In the light-emitting layer provided by the present invention, the molecular formula is FA 0.08 Cs 0.92 The main body is Pb(Br,Cl)3 perovskite nanocrystals with a central wavelength of 490nm, emitting sky blue light; then the red luminescent polymer PCDTBT8 (central wavelength of 660nm) is doped according to a certain mass ratio. While maintaining the excellent luminescent properties of the perovskite nanocrystals, the energy transfer process from the sky blue light perovskite nanocrystals to the red PCDTBT8 is carried out, so that the obtained luminescent layer can simultaneously realize dual-color light emission, and then the relative intensity of sky blue light and red light can be adjusted by adjusting the doping amount of PCDTBT8 to obtain white luminescence.

[0009] In the present invention, the mass ratio of perovskite nanocrystals to PCDTBT8 is limited to 150-400:1, which achieves the limitation of the intensity of sky blue light and red light. When the amount of perovskite nanocrystals used is higher than the above range, the blue light part is too strong, and its luminescence gradually shifts from the white light area to the sky blue area; and when the amount of perovskite nanocrystals used is lower than the above range, the red light part will be very strong, thereby causing the luminescence to shift to the red light area. In both cases, it is impossible to obtain a more standard white light luminescence.

[0010] In the present invention, FA 0.08 Cs 0.92 The preparation method of Pb(Br,Cl)3 nanocrystals can be hot injection method, ligand-assisted precipitation method or room temperature synthesis method.

[0011] In some preferred embodiments, the method for preparing the perovskite nanocrystals includes the following steps: first, adding a cesium precursor solution and a formamidine precursor solution to a lead precursor solution and reacting for 1 to 3 minutes; second, adding a ligand solution to the reaction solution and reacting for 2 to 4 minutes; third, adding a toluene solution of ZnBr2 and tetraoctylammonium bromide to the reaction solution and continuing to react for 3 to 5 minutes to obtain a crude nanocrystal solution; finally, purifying the crude nanocrystal solution, centrifuging to obtain a precipitate, dispersing the precipitate in cyclohexane, and centrifuging to obtain a supernatant to obtain a perovskite nanocrystal solution.

[0012] In the above preparation method, the addition of ligand solution can stabilize the nanocrystals and adjust the emission spectrum of the nanocrystals. Further, the ligand of the ligand solution includes one or more combinations of didodecyl dimethyl ammonium bromide (DDAB), oleic acid (OA), oleylamine (OAm), hexadecyl trimethyl ammonium bromide (CTAB), and tetrabutyl ammonium p-toluenesulfonate (TBSA). Preferably, the ligand is didodecyl dimethyl ammonium bromide.

[0013] In some preferred embodiments, the cesium precursor solution is an octanoic acid solution of cesium carbonate (cesium carbonate is dissolved in octanoic acid), the formamidine precursor solution is an octanoic acid solution of formamidine acetate, and the lead precursor solution is a toluene solution of lead bromide, lead chloride and tetraoctylammonium bromide.

[0014] Preferably, in the above raw materials, the molar ratio of cesium carbonate to formamidine acetate is 5:1 to 9:1; and in the lead precursor solution, the molar ratio of lead bromide, lead chloride and tetraoctylammonium bromide is 11:9:40. + +FA + With Pb 2+ The molar ratio of ZnBr2 to tetraoctylammonium bromide is 1:1. Further, in the toluene solution of ZnBr2 and tetraoctylammonium bromide, the molar ratio of ZnBr2 to tetraoctylammonium bromide is 1:2, and Zn 2+ With Pb 2+ The amount of substance ratio is 3:10.

[0015] Furthermore, the purification includes primary purification and secondary purification. The primary purification includes: adding ethyl acetate to the crude nanocrystal solution, collecting the precipitate after centrifugation, and dissolving the precipitate in toluene; the secondary purification includes: adding a mixed solution of ethyl acetate and trimethoxyphenylethylamine (MPEA) (volume ratio 500:1) to the toluene dispersion obtained after the primary purification, and centrifuging again to obtain the precipitate.

[0016] In the present invention, a secondary purification method is adopted to treat NCs with a mixed solution of ethyl acetate and trimethoxyphenylethylamine (MPEA), which can passivate the performance defects of NCs, improve the luminescence brightness of NCs and improve their spectral stability.

[0017] Furthermore, the PCDTBT8 used in the present invention is a derivative of PCDTBT (poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]), and the structural formula of the PCDTBT8 is as follows:

[0018]

[0019] After extensive research, it was found that among many red-emitting materials, PCDTBT8 and the sky-blue-emitting perovskite nanocrystals prepared by the present invention have a stronger energy transfer process, thereby achieving stronger red light emission at extremely low doping levels. At the same time, PCDTBT8 also has the advantages of being stable itself and having good solubility in the same solvent as perovskite nanocrystals.

[0020] The technical solution adopted by the present invention to achieve the second purpose is to provide a method for preparing a light-emitting layer of a perovskite white light-emitting diode, comprising the following steps: according to the mass ratio of perovskite nanocrystal to PCDTBT8 being 150 to 400:1, a cyclohexane solution of perovskite nanocrystal and a toluene solution of PCDTBT8 are uniformly mixed to obtain a light-emitting layer solution; the light-emitting layer solution is spin-coated on a transmission layer, and annealed on a hot stage to obtain a light-emitting layer of a perovskite white light-emitting diode; the molecular formula of the perovskite nanocrystal is FA 0.08 Cs 0.92 Pb(Br,Cl)3.

[0021] In the above preparation method, the solubility of perovskite nanocrystals and PCDTBT8 in their respective solvents is fully considered. A mixed solvent system of cyclohexane + toluene is adopted. Through the mixed solvent strategy, the sky blue luminescent perovskite nanocrystals (NCs) (central wavelength 490nm) and the red polymer PCDTBT8 (central wavelength 660nm) are uniformly mixed in the same solvent, and it is ensured that both the perovskite nanocrystals and PCDTBT8 can obtain good dissolution effects.

[0022] Furthermore, in the cyclohexane solution of the perovskite nanocrystal, the content of the perovskite nanocrystal is 20-25 mg / ml, preferably 22 mg / ml. In the toluene solution of PCDTBT8, the content of PCDTBT8 is 0.5-1.5 mg / mL, preferably 1 mg / ml.

[0023] Furthermore, in order to avoid the shedding of surface ligands of perovskite nanocrystals due to high heating temperature during the mixing process, the mixing of the present invention is carried out at room temperature, and stirring is used to promote sufficient mixing of the raw materials. Preferably, the mixing temperature is 20 to 30° C., and the mixing time is 0.5 to 2 hours.

[0024] In some preferred embodiments, the preparation method further comprises: adding toluene to a mixed solution of a cyclohexane solution of perovskite nanocrystals and a toluene solution of PCDTBT8. Studies have shown that excessive toluene content will have an adverse effect on the stability of nanocrystal NCs, thereby affecting the film-forming properties of the final light-emitting layer. Therefore, on the premise of ensuring that PCDTBT8 is fully dissolved, the amount of toluene can be appropriately reduced. Preferably, when the volume ratio of cyclohexane to toluene is 7:3, the optimal balance between the solubility of PCDTBT8 and the stability of perovskite nanocrystals can be achieved.

[0025] Furthermore, the thickness of the light-emitting layer is 30-40 nm.

[0026] The technical solution adopted by the present invention to achieve the third purpose is: to provide a single-light-emitting-layer perovskite white light-emitting diode, which includes, from bottom to top, a substrate and a transparent conductive anode ITO, a hole injection layer HIL, a hole transport layer HTL, a light-emitting layer, an electron transport layer, an electrode modification layer and a metal cathode; wherein the light-emitting layer adopts the light-emitting layer described in one of the purposes of the present invention, or a light-emitting layer prepared by the preparation method described in the second purpose of the present invention.

[0027] In the above-mentioned single-light-emitting layer perovskite white light-emitting diode structure, since the light-emitting layer adopts a single-layer structure to achieve excellent white light emitting performance, the device preparation process is simplified and the production efficiency is improved. Furthermore, by adjusting the doping amount of PCDTBT8 in the light-emitting layer relative to the perovskite nanocrystal, not only can high-efficiency standard white light with CIE coordinates of (0.33, 0.33) be obtained, but also by adjusting the doping amount of PCDTBT8 to control the energy transfer intensity and adjust the luminous color temperature of the device, so as to be applicable to more scenarios and meet different application requirements.

[0028] Preferably, the material of the hole injection layer HIL is PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid)) solution, which is spin-coated on the conductive anode ITO and annealed on a hot plate at 140° C. for 10 min.

[0029] Preferably, the material of the hole transport layer HTL is a chlorobenzene solution of Poly-TPD (poly[bis(4-phenyl)(4-butylphenyl)amine]) with a concentration of 10 mg mL -1 , spin-coated on the hole injection layer and annealed on a hot plate at 140°C for 15 min.

[0030] Preferably, the electron transport layer is TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene), which is deposited on the light-emitting layer by vacuum thermal evaporation with a thickness of 40 nm.

[0031] Preferably, the electrode modification layer and the metal cathode are Ca and Ag respectively, which are deposited on the electron transport layer TPBi by vacuum thermal evaporation, wherein the thickness of Ca is 5 nm and the thickness of Ag is 100 nm.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The light-emitting layer of the perovskite white light-emitting diode provided by the present invention and the preparation method thereof are based on sky blue light-emitting perovskite nanocrystals and red light-emitting PCDTBT8 as a dopant, and the perovskite nanocrystals and PCDTBT8 are uniformly mixed in the same solvent through a mixed solvent strategy. This doping method maintains the excellent performance of the perovskite nanocrystals while achieving the effect of dual-color light emission from a single light-emitting layer through efficient energy transfer from the perovskite nanocrystals to the PCDTBT8.

[0034] (2) The present invention provides a perovskite white light-emitting diode having a single light-emitting layer structure, a simpler preparation process, and the light-emitting spectrum can be regulated by adjusting the ratio of perovskite nanocrystals to PCDTBT8. In particular, by finely controlling the ratio of perovskite nanocrystals to PCDTBT8, Pe-WLEDs devices with different color temperatures can be obtained to suit different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The current density-voltage-luminance curve (JVL curve) of the Pe-WLEDs prepared in Application Examples 1-3 of the present invention;

[0036] Figure 2 The electroluminescence spectrum (EL spectrum) of the Pe-WLED prepared in Application Examples 1-3 of the present invention;

[0037] Figure 3 The CIE coordinate diagram of the electroluminescence spectrum of the Pe-WLEDs prepared in Application Examples 1-3 of the present invention;

[0038] Figure 4 Schematic diagram of the structure of Pe-WLEDs prepared in Application Examples 1-3 of the present invention;

[0039] Figure 5 Energy level and luminescence mechanism diagram of Pe-WLEDs prepared in Application Examples 1-3 of the present invention;

[0040] Among them, 1-substrate and transparent conductive anode ITO; 2-hole injection layer; 3-hole transport layer; 4-light-emitting layer; 5-electron transport layer; 6-electrode modification layer and metal cathode. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0043] The present invention will be further described below in conjunction with specific embodiments, but they are not intended to be limiting of the present invention.

[0044] Example 1

[0045] Step 1: 425 μL of cesium precursor (0.1 M Cs2CO3 dissolved in octanoic acid (OTAc)) and 75 μL of FA precursor (0.2 M formamidine acetate (FA(Ac)) dissolved in OTAc) were quickly added to 4.5 mL of Pb 2+ The precursor solution (0.055 M PbBr2, 0.045 M PbCl2 and 0.2 M tetraoctylammonium bromide (TOAB) in toluene (Tol)) was prepared under open-air magnetic stirring at room temperature for 2 min.

[0046] Then, 1.5 mL of didodecyl dimethyl ammonium bromide (DDAB) (10 mg mL -1 Then, 2.7 mL of ZnBr2 solution (0.05 M ZnBr2 and 0.1 M TOAB dissolved in Tol) was added to the NCs crude solution and stirred for 5 min to passivate the NCs.

[0047] Afterwards, 18 mL of ethyl acetate was added to the crude solution for purification. The crude solution was centrifuged at 10,000 rpm for 5 min, and the precipitate was collected separately after centrifugation and dispersed in 2 mL of Tol. Then, a mixed solution of 4 mL of ethyl acetate and trimethoxyphenylethylamine (MPEA) (volume ratio 500:1) was added to the Tol dispersion, and centrifuged at 10,000 rpm for 5 min again for further purification. The precipitate was dispersed in 1 mL of cyclohexane again, centrifuged at 10,000 rpm for 5 min, and the supernatant was taken in a glass bottle for standby use.

[0048] Step 2: Mix the NCs solution obtained in step 1 and PCDTBT8 solution (1 mg mL -1 Dissolved in Tol) was added into a glass bottle at a mass ratio of NCs to PCDTBT8 of 400:1, and then an appropriate amount of Tol was added to ensure that the volume ratio of cyclohexane and toluene in the final mixed solution was 7:3.

[0049] Step 3: The NCs: PCDTBT8 mixed solution is magnetically stirred at room temperature for 1 hour to obtain the light-emitting layer solution of the perovskite white light-emitting diode.

[0050] Example 2

[0051] Step 1: 425 μL of cesium precursor (0.1 M Cs2CO3 dissolved in octanoic acid (OTAc)) and 75 μL of FA precursor (0.2 M formamidine acetate (FA(Ac)) dissolved in OTAc) were quickly added to 4.5 mL of Pb 2+ The precursor solution (0.055 M PbBr2, 0.045 M PbCl2 and 0.2 M tetraoctylammonium bromide (TOAB) in toluene (Tol)) was prepared under open-air magnetic stirring at room temperature for 2 min.

[0052] Then, 1.5 mL of didodecyl dimethyl ammonium bromide (DDAB) (10 mg mL -1 Then, 2.7 mL of ZnBr2 solution (0.05 M ZnBr2 and 0.1 M TOAB dissolved in Tol) was added to the NCs crude solution and stirred for 5 min to passivate the NCs.

[0053] Afterwards, 18 mL of ethyl acetate was added to the crude solution for purification. The crude solution was centrifuged at 10,000 rpm for 5 min, and the precipitate was collected separately after centrifugation and dispersed in 2 mL of Tol. Then, a mixed solution of 4 mL of ethyl acetate and trimethoxyphenylethylamine (MPEA) (volume ratio 500:1) was added to the Tol dispersion, and centrifuged at 10,000 rpm for 5 min again for further purification. The precipitate was dispersed in 1 mL of cyclohexane again, centrifuged at 10,000 rpm for 5 min, and the supernatant was taken in a glass bottle for standby use.

[0054] Step 2: Mix the NCs solution obtained in step 1 and PCDTBT8 solution (1 mg mL -1 Dissolved in Tol) was added into a glass bottle at a mass ratio of NCs to PCDTBT8 of 250:1, and then an appropriate amount of Tol was added to ensure that the volume ratio of cyclohexane and toluene in the final mixed solution was 7:3.

[0055] Step 3: The NCs: PCDTBT8 mixed solution is magnetically stirred at room temperature for 1 hour to obtain the light-emitting layer solution of the perovskite white light-emitting diode.

[0056] Example 3

[0057] Step 1: 425 μL of cesium precursor (0.1 M Cs2CO3 dissolved in octanoic acid (OTAc)) and 75 μL of FA precursor (0.2 M formamidine acetate (FA(Ac)) dissolved in OTAc) were quickly added to 4.5 mL of Pb 2+ The precursor solution (0.055 M PbBr2, 0.045 M PbCl2 and 0.2 M tetraoctylammonium bromide (TOAB) in toluene (Tol)) was prepared under open-air magnetic stirring at room temperature for 2 min.

[0058] Then, 1.5 mL of didodecyl dimethyl ammonium bromide (DDAB) (10 mg mL -1 Then, 2.7 mL of ZnBr2 solution (0.05 M ZnBr2 and 0.1 M TOAB dissolved in Tol) was added to the NCs crude solution and stirred for 5 min to passivate the NCs.

[0059] Afterwards, 18 mL of ethyl acetate was added to the crude solution for purification. The crude solution was centrifuged at 10,000 rpm for 5 min, and the precipitate was collected separately after centrifugation and dispersed in 2 mL of Tol. Then, a mixed solution of 4 mL of ethyl acetate and trimethoxyphenylethylamine (MPEA) (volume ratio 500:1) was added to the Tol dispersion, and centrifuged at 10,000 rpm for 5 min again for further purification. The precipitate was dispersed in 1 mL of cyclohexane again, centrifuged at 10,000 rpm for 5 min, and the supernatant was taken in a glass bottle for standby use.

[0060] Step 2: Mix the NCs solution obtained in step 1 and PCDTBT8 solution (1 mg mL -1 Dissolved in Tol) was added into a glass bottle at a mass ratio of NCs to PCDTBT8 of 150:1, and then an appropriate amount of Tol was added to ensure that the volume ratio of cyclohexane and toluene in the final mixed solution was 7:3.

[0061] Step 3: The NCs: PCDTBT8 mixed solution is magnetically stirred at room temperature for 1 hour to obtain the light-emitting layer solution of the perovskite white light-emitting diode.

[0062] Application Examples

[0063] according to Figure 4The Pe-WLEDs (perovskite white light-emitting diode) structure shown is first prepared in sequence as a substrate and a transparent conductive anode ITO, a hole injection layer HIL, and a hole transport layer HTL. Then, the light-emitting layer solutions of the perovskite white light-emitting diodes prepared in Examples 1-3 are spin-coated on the corresponding hole transport layer HTL, respectively, with a spin coating thickness of 30 to 40 nm, and annealed on a hot plate at 60° C. for 10 min. Finally, an electron transport layer, an electrode modification layer, and a metal cathode are prepared in sequence to prepare the Pe-WLEDs of Application Examples 1-3, respectively.

[0064] The Pe-WLEDs corresponding to use cases 1-3 were tested for external quantum efficiency, brightness, and CIE coordinates, and the relevant results are shown in Table 1 below.

[0065] Table 1

[0066]

[0067] As can be seen from the above table,

[0068] The external quantum efficiency of the Pe-WLEDs prepared in Example 1-3 is 1.53-1.85%, and the brightness is 489-759 cd / m 2 , the CIE coordinates are in the white light region. In particular, when the mass ratio of nanocrystals NCs to PCDTBT8 is 250:1, the CIE coordinates are (0.33, 0.33) belonging to standard white light. When the ratio of NCs to PCDTBT8 is in the range of 250-400:1, cold white light is obtained; when the ratio of NCs to PCDTBT8 is in the range of 150-250:1, warm white light is obtained.

[0069] In summary, the present invention provides a light-emitting layer of a perovskite white light-emitting diode and a preparation method thereof, wherein NCs and PCDTBT8 are uniformly mixed in the same solvent through a mixed solvent strategy, and the light-emitting layer of the perovskite white light-emitting diode is prepared with the solution. NCs are used as the main body and PCDTBT8 is used as a dopant. This doping method obtains dual-color light emission of a single light-emitting layer through efficient energy transfer from NCs to PCDTBT8 while maintaining the excellent performance of NCs. In addition, the preparation method of the single light-emitting layer makes the preparation process of the perovskite white light-emitting diode simpler, and the light-emitting spectrum can be regulated by adjusting the ratio of NCs and PCDTBT8. In particular, by finely controlling the ratio of NCs and PCDTBT8, Pe-WLEDs devices with different color temperatures can be obtained to suit different scenarios.

[0070] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A light-emitting layer of a perovskite white light-emitting diode, characterized in that: The light-emitting layer is composed of a molecular formula of FA 0.08 Cs 0.92 The perovskite nanocrystals of Pb(Br,Cl)3 and PCDTBT8 are composed in a mass ratio of 150 to 400:

1.

2. The light-emitting layer of the perovskite white light-emitting diode according to claim 1, characterized in that: The preparation method of the perovskite nanocrystal comprises: adding a cesium precursor solution and a formamidine precursor solution to a lead precursor solution, and reacting for 1 to 3 minutes; then adding a ligand solution to the reaction solution, and reacting for 2 to 4 minutes; then adding a toluene solution of ZnBr2 and tetraoctylammonium bromide to the reaction solution and continuing to react for 3 to 5 minutes to obtain a crude nanocrystal solution; purifying the crude nanocrystal solution, and then centrifuging to obtain a precipitate, dispersing the precipitate in cyclohexane, and centrifuging to obtain a supernatant to obtain a perovskite nanocrystal solution.

3. The light-emitting layer of the perovskite white light-emitting diode according to claim 2, characterized in that: The cesium precursor solution is an octanoic acid solution of cesium carbonate, the formamidine precursor solution is an octanoic acid solution of formamidine acetate, and the lead precursor solution is a toluene solution of lead bromide, lead chloride and tetraoctylammonium bromide.

4. The light-emitting layer of the perovskite white light-emitting diode according to claim 3, characterized in that: The purification includes primary purification and secondary purification; the solvent of the primary purification is ethyl acetate; the solvent of the secondary purification is a mixed solution of ethyl acetate and trimethoxyphenethylamine in a volume ratio of 500:

1.

5. A method for preparing a light-emitting layer of a perovskite white light-emitting diode, comprising the following steps: According to the mass ratio of perovskite nanocrystal to PCDTBT8 being 150 to 400:1, the cyclohexane solution of perovskite nanocrystal and the toluene solution of PCDTBT8 are evenly mixed to obtain a light-emitting layer solution; the light-emitting layer solution is spin-coated on the transport layer and annealed on a hot stage to obtain a light-emitting layer of a perovskite white light-emitting diode; the molecular formula of the perovskite nanocrystal is FA 0.08 Cs 0.92 Pb(Br,Cl)3.

6. The preparation method according to claim 5, characterized in that: In the cyclohexane solution of the perovskite nanocrystal, the content of the perovskite nanocrystal is 20-25 mg / ml; in the toluene solution of PCDTBT8, the content of PCDTBT8 is 0.5-1.5 mg / mL.

7. The preparation method according to claim 6, characterized in that: The mixing temperature is 20-30° C., and the mixing time is 0.5-2 h.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: adding toluene to a mixed solution of the cyclohexane solution of the perovskite nanocrystal and the toluene solution of PCDTBT8, so that the volume ratio of cyclohexane to toluene in the mixed solution is 7:

3.

9. The preparation method according to claim 8, characterized in that: The thickness of the light-emitting layer is 30-40 nm.

10. A single-light-emitting-layer perovskite white light-emitting diode, characterized in that: From bottom to top, it includes substrate and transparent conductive anode ITO, hole injection layer HIL, hole transport layer HTL, light emitting layer, electron transport layer, electrode modification layer and metal cathode; The light-emitting layer is the light-emitting layer according to any one of claims 1 to 4, or the light-emitting layer prepared by the preparation method according to any one of claims 5 to 9.

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