Preparation method and application of carbon dots and carbon dot / perovskite composite film

Abstract

The present invention discloses a preparation method and application of carbon dots and carbon dot / perovskite composite films. First, a new type of carbon dot material is prepared by improving the preparation method, and the carbon dot material is coupled into a perovskite precursor solution. The carbon dot material is then co-deposited on a conductive glass substrate by a solution processing method to form a self-assembled carbon dot / perovskite composite film. During the formation of the carbon dot / perovskite composite film, the carbon dots induce the nucleation and growth of the perovskite and form a spatial network structure, which is self-assembled at the perovskite grain boundaries to achieve efficient hole injection and interface passivation. Without the need for additional preparation of a hole injection layer or a hole transport layer, the preparation of a high-performance perovskite light-emitting diode is achieved. The method is simple to operate and simplifies the steps of traditional device preparation.

Description

Technical Field

[0001] The present invention relates to the field of display and lighting technology, and in particular to a method for preparing carbon dots and a carbon dot / perovskite composite film and applications thereof. Background Art

[0002] Metal halide perovskites offer high quantum yields, high color purity, tunable colors, solution processability, and low raw material costs. In recent years, metal halide perovskites, thanks to their excellent optoelectronic properties, have demonstrated tremendous potential as light-emitting layer materials in light-emitting diodes (LEDs), sparking widespread research interest in both research and industry. Currently, high-performance perovskite LEDs typically utilize a "sandwich" device structure similar to conventional QLEDs and OLEDs, where the light-emitting layer is surrounded by a hole-transport layer and an electron-transport layer, respectively. Currently, research on metal halide perovskites is primarily focused on improving materials and enhancing performance. To fabricate high-performance perovskite LEDs with multilayer thin-film structures, electrons and holes must be injected into the perovskite layer through both the electron-transport layer and the hole-transport layer for radiative recombination. This complex and challenging device fabrication process results in low device production efficiency, hindering future large-scale, low-cost industrial production. Therefore, finding simpler methods to fabricate high-performance perovskite LEDs is a pressing need, potentially reducing overall manufacturing costs and improving production efficiency. Summary of the Invention

[0003] To solve the problems existing in the prior art, the present invention provides a method for preparing carbon dots and carbon dot / perovskite composite films and their applications, which can simplify the device structure, eliminate the need for a hole transport layer, and produce perovskite LED devices with high efficiency, low starting voltage, simple process, and low cost.

[0004] The technical solutions of the present invention are as follows:

[0005] The present invention provides a method for preparing carbon dots. O-phenylenediamine, 1,8-naphthalene dicarboxylic anhydride and polyvinyl pyrrolidone are used as raw materials, and the carbon dots are prepared by reacting the raw materials under high temperature and high pressure conditions and then purifying the raw materials.

[0006] Preferably, o-phenylenediamine, 1,8-naphthalic anhydride and polyvinylpyrrolidone are dissolved in a solvent to obtain a mixed solution; the solution is transferred to a reactor and reacted under high temperature and high pressure; the reactor is naturally cooled to room temperature, and carbon dots are obtained by purification by column chromatography.

[0007] Preferably, the solvent is any one of deionized water, dimethyl sulfoxide, N,N-dimethylformamide, ethanol, or a mixed solvent.

[0008] Preferably, the high temperature and high pressure reaction time is 0.5-12 hours, and the reaction temperature is 150-250°C.

[0009] The present invention also provides a method for preparing a carbon dot / perovskite composite film, comprising the following steps:

[0010] (1) dispersing the carbon dots prepared by the method in an organic solvent to prepare a carbon dot solution;

[0011] (2) dissolving the carbon dot solution and the perovskite precursor in an organic solvent, stirring and dissolving them thoroughly;

[0012] (3) A solution containing carbon dots and a perovskite precursor is coated on a substrate by a spin coating method, and then annealed to obtain a carbon dot / perovskite composite film.

[0013] Preferably, the perovskite precursor is prepared from AX1, BX2 and MX3 in a molar ratio of a:b:c, a:b:c = (0-100): (0-100): (1-100), wherein A is a phenylethylamine cation, a butylamine cation or a thiopheneethylamine cation, B is a methylamine cation, a formamidinium cation or a cesium ion, M is a metallic lead element, X1, X2 and X3 are all halogen elements, and can be the same or different halogen elements at the same time.

[0014] Preferably, the organic solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone or N-methylpyrrolidone.

[0015] Preferably, the mass concentration of the carbon dot solution is 0.1-20 mg / mL, the mass solubility of the perovskite precursor is 0.1-0.5 M, and the carbon dot solution and the perovskite precursor are mixed in a volume ratio of 1:1-100.

[0016] The present invention also provides a light-emitting diode, comprising a conductive glass substrate, a carbon dot / perovskite composite film prepared by the above method, an electron transport layer, a cathode modification layer and a metal electrode, which are arranged in sequence from bottom to top;

[0017] The conductive glass substrate is any one of ITO, FTO, IZO or AZO conductive white glass substrates;

[0018] The electron transport layer is any one of a metal oxide electron transport material, an oxadiazole electron transport material or an imidazole electron transport material;

[0019] The cathode modification layer is any one of Ca, Mg, Cs, CsCO3 or LiF.

[0020] Preferably, the thickness of the carbon dot / perovskite composite film in the light-emitting diode is 5 to 1000 nm, the thickness of the electron transport layer is 1 to 200 nm, the thickness of the cathode modification layer is 0.5 to 50 nm, and the thickness of the metal electrode is 5 to 1000 nm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The preparation method of the carbon dot / perovskite composite film provided by the present invention provides a novel carbon dot material with excellent photoelectric properties. By using inexpensive and readily available o-phenylenediamine, 1,8-naphthalic anhydride, and polyvinylpyrrolidone as carbon sources, the prepared carbon dot material has a uniform size distribution and an optical band gap that well matches that of perovskite.

[0023] 2. The carbon dot material provided by the present invention can be well coupled with the perovskite precursor solution. During the solution processing, the carbon dots can promote the uniform nucleation and growth of perovskite, and self-assemble at the perovskite grain boundaries to form a unique spatial dendritic network structure, thereby achieving efficient hole injection and grain boundary passivation effects. In addition, without the need for additional hole transport materials, the perovskite PeLED achieves high external quantum efficiency and stable spectral emission; without the need for additional preparation of a hole injection layer or a hole transport layer, the preparation of high-performance perovskite light-emitting diodes is achieved. This method is simple to operate and simplifies the traditional device preparation process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a transmission microscope photograph of the carbon dots prepared in Example 1;

[0025] Figure 2 Statistical diagram of particle size distribution of carbon dots prepared in Example 1;

[0026] Figure 3 is the UV-visible absorption spectrum of the carbon dot solution prepared in Example 1;

[0027] Figure 4 is the steady-state fluorescence spectrum of the carbon dot solution prepared in Example 1;

[0028] Figure 5 Scanning electron microscope images of the pure perovskite film and the carbon dot / perovskite composite film in Example 4;

[0029] Figure 6 Graphs showing fluorescence spectra of the pure perovskite film and the carbon dot / perovskite composite film in Example 4;

[0030] Figure 7 This is a comparison chart of the quantum yields of the pure perovskite film and the carbon dot / perovskite composite film in Example 4;

[0031] Figure 8 Schematic diagram of the structure of the traditional perovskite device and the carbon dot / perovskite composite thin film device in Example 7;

[0032] Figure 9 The current density-voltage curves of traditional perovskite devices and carbon dot / perovskite composite thin film devices;

[0033] Figure 10 The brightness-voltage curves of traditional perovskite devices and carbon dot / perovskite composite thin film devices are shown;

[0034] Figure 11 The external quantum efficiency-voltage curves of traditional perovskite devices and carbon dot / perovskite composite thin film devices;

[0035] Figure 12 Electroluminescence spectra of traditional perovskite devices and carbon dot / perovskite composite thin film devices. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with preferred embodiments. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0037] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0038] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0039] Example 1

[0040] This embodiment provides a method for preparing carbon dots. O-phenylenediamine, 1,8-naphthalic anhydride, and polyvinylpyrrolidone are used as raw materials. 0.1 g of o-phenylenediamine, 0.1 g of 1,8-naphthalic anhydride, and 0.01 g of polyvinylpyrrolidone are dissolved in 10 mL of deionized water and N,N-dimethylformamide to obtain a mixed solution, wherein the volume ratio of deionized water to N,N-dimethylformamide is 1:1. The above solution is transferred to a reactor and reacted at a temperature of 200° C. for 6 hours. The reactor is naturally cooled to room temperature, and the carbon dots are purified by column chromatography.

[0041] like Figure 1 As shown in FIG. 1 , a transmission microscope image of carbon dots prepared according to Example 1 is shown. It can be seen that the carbon dots are spherical in shape and have a uniform size distribution. Figure 2The average particle size of carbon dots was found to be 3.2 nm by statistics; the UV-visible absorption spectrum (see attached Figure 3 ) It can be seen that the absorption edge of carbon dots is located near 362nm, and the optical band gap is deduced to be around 3.4eV. It is a wide-bandgap semiconductor material that does not absorb visible light and is expected to be used as a charge transport material for perovskite LEDs. Figure 4 It can be seen that the fluorescence peak of carbon dots is located at around 450nm, and the emission peak is relatively wide (>100nm), which is consistent with the luminescence characteristics of general fluorescent carbon dots.

[0042] Example 2

[0043] The difference between the carbon dot preparation method of Example 2 and Example 1 is that o-phenylenediamine, 1,8-naphthalic anhydride and polyvinylpyrrolidone are dissolved in deionized water and dimethyl sulfoxide to obtain a mixed solution, wherein the volume ratio of deionized water to dimethyl sulfoxide is 1:1; the mixed solution is transferred to a reactor, the reaction temperature is 250°C, and the reaction time is 0.5 h.

[0044] Example 3

[0045] The carbon dot preparation method of Example 3 differs from that of Example 1 in that o-phenylenediamine, 1,8-naphthalic anhydride and polyvinylpyrrolidone are dissolved in ethanol to obtain a mixed solution; the mixed solution is transferred to a reactor, the reaction temperature is 150° C., and the reaction time is 12 h.

[0046] Example 4

[0047] This embodiment provides a method for preparing a carbon dot / perovskite composite film, comprising the following steps:

[0048] (1) The carbon dots prepared in Example 1, Example 2, or Example 3 were dispersed in N,N-dimethylformamide to prepare a carbon dot solution with a mass concentration of 4.5 mg / mL;

[0049] (2) dissolving the carbon dot solution and a perovskite precursor with a molar concentration of 0.3 M in an organic solvent at a volume ratio of 1:100, stirring and dissolving the mixture thoroughly; wherein the perovskite precursor is prepared by phenylethylamine bromide (PEABr), cesium bromide (CsBr), CH(NH2)2Br (FABr) and lead bromide PbBr2 at a molar ratio of 0.4:1:0.2:1;

[0050] (3) A solution containing carbon dots and perovskite precursors was deposited on a glass substrate using a spin coating method. As the perovskite crystals precipitated, the carbon dots were “squeezed” to the grain boundaries and eventually remained in the film, forming a spatial network structure. Finally, a carbon dot / perovskite composite film was formed in situ with a thickness of about 50 nm.

[0051] The carbon dot / perovskite composite film prepared in Example 4 was compared with a conventional pure perovskite film, and the scanning electron microscope (SEM) at the same scale (such as Figure 5 ) photographed the surface morphology of the perovskite film and the carbon dot / perovskite composite film. From left to right, they are the conventional perovskite film and the carbon dot / perovskite composite film. It can be observed that there are some holes on the surface of the pure perovskite film. These holes will cause leakage current in the device and reduce device performance. In the carbon dot / perovskite composite film, the carbon dots exist at the perovskite grain boundaries. The carboxyl groups on the surface of the carbon dots have a strong passivation effect on the perovskite. The carbon dots distributed at the perovskite grain boundaries provide passivation for the entire perovskite film. The fluorescence spectrum provides strong evidence for this mechanism. Figure 6 It can be seen that the fluorescence of conventional perovskite films is relatively weak, with a corresponding emission peak at 515nm. In contrast, the fluorescence of carbon dot / perovskite composite films is significantly enhanced, and the emission peak remains at 515nm. Figure 7 ) compared the photoluminescence quantum yield of conventional perovskite films and carbon dot / perovskite composite films. The quantum yield of carbon dot / perovskite composite films increased from 66.42% of conventional perovskite films to 86.31%, which was also due to the passivation effect of luminescent carbon dots on perovskite.

[0052] Example 5

[0053] This embodiment provides a method for preparing a carbon dot / perovskite composite film, comprising the following steps:

[0054] (1) The carbon dots prepared in Example 1, Example 2, or Example 3 were dispersed in N-methylpyrrolidone to prepare a carbon dot solution with a mass concentration of 20 mg / mL;

[0055] (2) dissolving the carbon dot solution and a perovskite precursor with a molar concentration of 0.5 M in an organic solvent at a volume ratio of 1:50, stirring and dissolving the mixture thoroughly; wherein the perovskite precursor is prepared by butylamine bromide (PEABr), cesium chloride (CsCl), cesium bromide (CsBr), CH6BrN (MABr) and lead bromide (PbBr2) at a molar ratio of 0.35:0.3:0.7:0.2:1;

[0056] (3) A solution containing carbon dots and a perovskite precursor is coated on a substrate by a spin coating method, and then annealed to obtain a carbon dot / perovskite composite film.

[0057] Example 6

[0058] This embodiment provides a method for preparing a carbon dot / perovskite composite film, comprising the following steps:

[0059] (1) The carbon dots prepared in Example 1, Example 2, or Example 3 were dispersed in dimethyl sulfoxide to prepare a carbon dot solution with a mass concentration of 0.1 mg / mL;

[0060] (2) dissolving the carbon dot solution and a perovskite precursor with a molar concentration of 0.1 M in an organic solvent at a volume ratio of 1:1, stirring and dissolving them fully; wherein the perovskite precursor is prepared by thiopheneethylamine iodine (2-ThEAI), cesium iodide (CsI), CH(NH2)2I (FAI), and lead iodide (PbI2) at a molar ratio of 0.3:1:0.2:1;

[0061] (3) A solution containing carbon dots and a perovskite precursor is coated on a substrate by a spin coating method, and then annealed to obtain a carbon dot / perovskite composite film.

[0062] Example 7

[0063] This embodiment provides a light-emitting diode, which comprises, from bottom to top, an ITO conductive glass substrate anode, a carbon dot / perovskite composite thin film electroluminescent layer prepared according to embodiment 4, embodiment 5, or embodiment 6, a PO-T2T electron transport layer, a LiF cathode modification layer, and an Al cathode, wherein the carbon dot / perovskite composite thin film has a thickness of 5 to 1000 nm, the electron transport layer has a thickness of 1 to 200 nm, the cathode modification layer has a thickness of 0.5 to 50 nm, and the metal electrode has a thickness of 5 to 1000 nm.

[0064] The preparation method of the light-emitting diode is: spin coating a carbon dot / perovskite composite film on ITO conductive glass, and then forming a PO-T2T layer, a LiF layer and an Al cathode in sequence on the composite film by vacuum evaporation.

[0065] Figure 8 Schematic diagrams of two light-emitting diode device structures are shown; the left side shows a conventional perovskite LED device structure, which, from bottom to top, consists of an ITO transparent conductive glass anode, a pure perovskite thin film electroluminescent layer, a PO-T2T electron transport layer, a LiF cathode modification layer, and an Al metal electrode cathode; the right side shows the light-emitting diode provided in Example 7; Figure 9 The current density-voltage characteristic curves of LED devices based on pure perovskite and carbon dot / perovskite composite film as the light-emitting layer, respectively, show that the device based on carbon dot / perovskite composite film exhibits a higher current injection level, which is related to the ability of carbon dots to improve the hole injection characteristics of the device; Figure 10 The brightness-voltage characteristic curves of the two devices show that the device based on carbon dot / perovskite composite film has a lower starting voltage and higher brightness. The starting voltage is only 1.8V and the maximum brightness is 53858cd / m 2, not only better than the comparison device (starting voltage: 2V, maximum brightness 48278cd / m 2 ), and it also has the lowest starting voltage among the green perovskite LEDs reported in the world. In addition, the external quantum efficiency of the device has also increased from 4.7% to 16.2% (e.g. Figure 11 ), which is one of the highest values ​​reported so far for green perovskite LEDs without a hole transport layer; Figure 12 It shows that the electroluminescence spectra of the two device structures are basically consistent, which is consistent with the photoluminescence spectra;

[0066] In summary, the above results all indicate that the carbon dot / perovskite composite film prepared by the present invention can achieve excellent device performance without the need for a hole transport layer, and can match the performance of other conventional green light perovskite LEDs. This will greatly promote the preparation of high-performance perovskite LEDs, simplify the process steps, and reduce production costs.

[0067] In addition to the conductive glass substrate being ITO transparent conductive glass as recorded in the above embodiment, the conductive glass substrate can also be selected as FTO, IZO or AZO conductive white glass substrate; the electron transport layer can also be selected from other types of metal oxide electron transport materials, oxadiazole electron transport materials or imidazole electron transport materials; the cathode modification layer is Ca, Mg, Cs or CsCO3. In the various component structures of the light-emitting diode, the thickness of the carbon dot / perovskite composite film electron photoluminescent layer, electron transport layer, cathode modification layer and metal electrode can be selected in a wide range, among which the carbon dot / perovskite composite film electron photoluminescent layer is 5 to 1000 nm, the electron transport layer is 1 to 200 nm, the cathode modification layer is 0.5 to 50 nm, and the metal electrode is 5 to 1000 nm, all of which can achieve basically the same technical effect.

[0068] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing carbon dots, characterized in that: Taking o-phenylenediamine, 1,8-naphthalene dicarboxylic anhydride and polyvinyl pyrrolidone as raw materials, o-phenylenediamine, 1,8-naphthalene dicarboxylic anhydride and polyvinyl pyrrolidone are dissolved in a solvent to obtain a mixed solution; the above solution is transferred to a reactor, reacted under high temperature and high pressure conditions, and then the reactor is naturally cooled to room temperature. Carbon dots are purified by column chromatography.

2. The method for preparing carbon dots according to claim 1, wherein: The solvent is any one of deionized water, dimethyl sulfoxide, N,N-dimethylformamide, and ethanol, or a mixed solvent of multiple thereof.

3. The method for preparing carbon dots according to claim 1, wherein: The high temperature and high pressure reaction time is 0.5-12 hours, and the reaction temperature is 150-250°C.

4. A method for preparing a carbon dot / perovskite composite film, characterized in that: The following steps are involved: (1) dispersing the carbon dots prepared by the method according to any one of claims 1 to 3 in an organic solvent to prepare a carbon dot solution; (2) Dissolve the carbon dot solution and the perovskite precursor in an organic solvent, stir and dissolve them thoroughly; (3) A solution containing carbon dots and perovskite precursors is coated on a substrate by spin coating, and then annealed to obtain a carbon dot / perovskite composite film.

5. The method for preparing a carbon dot / perovskite composite film according to claim 4, wherein: The perovskite precursor is prepared from AX1, BX2 and MX3 in a molar ratio of a:b:c, where a:b:c = (0-100): (0-100): (1-100), wherein A is a phenylethylamine cation, a butylamine cation or a thiopheneethylamine cation, B is a methylamine cation, a formamidinium cation or a cesium ion, M is a metallic lead element, and X1, X2 and X3 are all halogen elements, and can be the same or different halogen elements at the same time.

6. The method for preparing a carbon dot / perovskite composite film according to claim 4, wherein: The organic solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone or N-methylpyrrolidone.

7. The method for preparing a carbon dot / perovskite composite film according to claim 4, wherein: The mass concentration of the carbon dot solution is 0.1-20 mg / mL, the molar concentration of the perovskite precursor is 0.1-0.5 M, and the carbon dot solution and the perovskite precursor are mixed in a volume ratio of 1:1-100.

8. A light emitting diode, characterized in that: The method comprises, arranged in order from bottom to top, a conductive glass substrate, a carbon dot / perovskite composite film prepared by the method according to claim 4, an electron transport layer, a cathode modification layer and a metal electrode; The conductive glass substrate is any one of ITO, FTO, IZO or AZO conductive white glass substrates; The electron transport layer is any one of a metal oxide electron transport material, an oxadiazole electron transport material or an imidazole electron transport material; The cathode modification layer is any one of Ca, Mg, Cs, Cs2CO3 or LiF.

9. The light emitting diode according to claim 8, characterized in that: In the light-emitting diode, the thickness of the carbon dot / perovskite composite film is 5-1000 nm, the thickness of the electron transport layer is 1-200 nm, the thickness of the cathode modification layer is 0.5-50 nm, and the thickness of the metal electrode is 5-1000 nm.

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