CN115440920A - Method for inducing crystallization of perovskite thin film by carbon dots and perovskite light-emitting diode - Google Patents
Method for inducing crystallization of perovskite thin film by carbon dots and perovskite light-emitting diode Download PDFInfo
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Abstract
The invention discloses a method for realizing perovskite room temperature crystallization and simultaneously improving the efficiency of a light-emitting diode by using carbon dots, and relates to the technical field of photoelectricity. The method for realizing the room-temperature crystallization of the perovskite thin film is that the carbon dot thin film containing alkali metal ions is used as an interface modification layer of the perovskite light-emitting diode and is used between a current carrier transmission layer and a perovskite light-emitting layer; the carbon dots serve as the centers of heterogeneous nuclei to enhance the crystallization of the perovskite, so that the perovskite light-emitting diode thin film is crystallized under the condition that the active layer is not annealed: the invention designs the cheap, simple and easy carbon dots with the surfaces rich in alkali metal ions, and uses the film of the carbon dots as the interface modification layer of the quasi-two-dimensional perovskite light-emitting diode, so that the perovskite film can realize good crystallization at room temperature without thermal annealing, and the invention has the functions of improving the performance of devices and simplifying the preparation process of the light-emitting diode.
Description
Technical Field
The invention relates to the field of photoelectric technology, in particular to a method for realizing room-temperature crystallization of a perovskite thin film by utilizing carbon point induction and a perovskite light-emitting diode.
Background
Perovskites are generally represented by having CaTiO 3 Crystal structure of the formula ABX 3 The material (a) of (b) is,wherein A and B are positive ions and X is negative ions. [ BX6 ] sharing corners in three-dimensional (3D) perovskites in the ideal cubic crystal structure of the perovskite] 4- The octahedron forms a cubic cage to hold the a cations. X of the halide perovskite being I - 、Br - And Cl - The halide anion of (a), the cation at position a is usually a monovalent cation, such as Cs + 、MA + (CH 3 NH 3 + )、FA + (NH 2 CH＝NH 2 + ) The cation at the B position is typically a divalent metal cation, such as Pb 2+ 、Sn 2+ . In recent years, metal Halide Perovskites (MHPs) have shown excellent performance, providing desirable performance for the next generation of efficient, low cost optoelectronic devices, including Light Emitting Diodes (LEDs), solar cells, and photodetectors.
Some key advantages of perovskite LEDs over traditional inorganic LEDs are low temperature fabrication, simple solution processing, and bandgap tunability. In the existing perovskite LED, the quasi-two-dimensional perovskite combines the better stability of the 2D perovskite with the excellent photoelectric properties (including high light quantum yield and carrier mobility) of the 3D perovskite, so that a non-radiative recombination path in a luminescent layer can be effectively eliminated, and the structure of the quasi-two-dimensional multiple quantum well enables the quasi-two-dimensional multiple quantum well to have higher exciton binding energy. However, the quasi-two-dimensional perovskite has small crystal grains, more crystal boundaries and poor film quality, and the thermal annealing process required in the film preparation process can cause nonuniform nucleation, which is not favorable for forming a smooth and uniform perovskite film. In addition, the process is time consuming and costly, and the perovskite organic component is volatile and is easily decomposed during the heating process. Therefore, there is a need for a method for ensuring the crystallinity of thin films without annealing room temperature crystallization in perovskite LEDs.
Disclosure of Invention
The invention aims to provide a method for realizing perovskite room-temperature crystallization by utilizing carbon dot induction and a perovskite light-emitting diode, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for realizing room-temperature crystallization of a perovskite thin film by utilizing carbon point induction comprises the following steps: synthesizing carbon dots containing alkali metal ions; the thin film of the carbon dots is used as an interface modification layer of the perovskite light-emitting diode and is used between the hole transport layer and the perovskite light-emitting layer; the carbon dots serve as the centers of heterogeneous nucleation to enhance the crystallization of perovskite, and the perovskite light-emitting diode thin film is crystallized under the condition that the active layer is not annealed.
On the basis of the technical scheme, the invention also provides the following optional technical scheme:
in one alternative: the preparation method of the carbon dots containing the alkali metal ions comprises the following steps: the method comprises the following steps: citric acid and urea are used as carbon sources, and are heated for 4-24h at 160 ℃ in N, N-dimethylformamide by a solvothermal method to synthesize carbon dots with surfaces rich in carboxyl; step two: washing the obtained carbon dots by using a saturated strong alkali solution to enable the surfaces of the carbon dots to be rich in alkali metal ions; and finally, washing away redundant alkali and salt by using water and ethanol, centrifuging, and freeze-drying to obtain the carbon dots.
In one alternative: the strong alkali solution is sodium hydroxide solution or potassium hydroxide solution.
The perovskite light-emitting diode is prepared by the method for realizing the crystallization of the perovskite thin film without annealing; the perovskite light-emitting diode is structurally characterized in that a cathode, a hole transport layer, an interface modification layer, a perovskite light-emitting layer, an electron transport layer, an electron injection layer and a metal anode are sequentially arranged from bottom to top; the cathode adopts ITO conductive glass;
the perovskite light-emitting diode comprises the following steps of:
step 1, cleaning and processing an ITO substrate: cleaning an ITO substrate with a cleaning agent, and then respectively carrying out ultrasonic cleaning for 15min with deionized water, acetone and isopropanol to obtain a clean ITO substrate, and storing the clean ITO substrate in clean isopropanol;
step 3, spin coating a hole transport layer: preparing a hole transport layer on the ITO substrate by using a solution spin coating method in a rotating speed range of 2000-6000r, and then carrying out thermal annealing;
step 5, spin coating a perovskite light emitting layer: transferring the annealed ITO substrate to a nitrogen-filled glove box, and spin-coating a perovskite precursor in the same way at a rotating speed of 3000-5000 r;
In one alternative: the hole transport layer adopts one of PEDOT, PSS, poly-TPD, TFB, TCTA and TAPC; the electron transmission layer adopts one of ZnO, TPBi and TmPyPb; the electron injection layer adopts one of LiF, PEI and PEIE; the metal electrode adopts aluminum or silver electrode
In one alternative: the interface modification layer between the hole transport layer and the perovskite luminescent layer is spin-coated on the hole transport layer by using carbon dot aqueous solution with the concentration range of 0.02-0.05 mg/ml.
In one alternative: the perovskite luminescent layer adopts quasi-two-dimensional perovskite prepared by a precursor; the precursors include lead halides, cesium halides, polyethylene oxides, and organic spacer cations.
In one alternative: the organic spacer cation is at least one cation selected from n-butyl ammonium halide, benzyl ammonium halide, phenethyl ammonium halide, phenylpropyl ammonium halide and phenylbutyl ammonium halide.
In one alternative: the precursor solvent is N, N '-dimethylformamide, dimethyl sulfoxide or a mixed solvent of the N, N' -dimethylformamide and the dimethyl sulfoxide in any proportion; the molar ratio of each component of the precursor is lead halide: cesium halide: organic spacer cation = 1.2; the concentration of polyoxyethylene was 6mg/mL; the concentration of precursor lead ions is 0.15-0.2M; the halide ions contained in the halide adopted by the precursor are any one or a mixture of two of chlorine, bromine and iodine; the precursor is heated at 60 deg.C in dark and stirred for 6 hr until dissolved.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, the film forming quality of the perovskite can be effectively improved by introducing the hydrophilic interface into the carbon points, the alkali metal ions can help to realize excellent crystallization, and the perovskite active layer can be induced to realize excellent crystallization at room temperature; meanwhile, the defects at the interface can be passivated, and non-radiative recombination is inhibited.
2. The carbon dots have low synthesis cost, and the surface of the carbon dots is easy to functionalize, so that the carbon dots can be endowed with abundant functional groups on the surface through simple treatment and have various different properties.
3. The manufacturing process of the quasi-two-dimensional perovskite light-emitting diode device is simple and easy to implement.
Drawings
FIG. 1 is a schematic diagram illustrating the interaction between perovskite and carbon dots in the present invention.
FIG. 2 shows the XRD analysis results of the perovskite thin films of example 1 and comparative example 1 of the present invention.
FIG. 3 is a normalized photoluminescence spectrum of the perovskite thin films of example 1 and comparative example 1 of the present invention.
FIG. 4 is a normalized electroluminescence spectrum of perovskite light emitting diodes in example 1 and comparative example 1 of the present invention.
Fig. 5 is a graph comparing the external quantum efficiency of the perovskite light emitting diode in example 1 of the present invention with that in comparative examples 1 and 2.
FIG. 6 is a graph comparing the brightness of perovskite light emitting diodes in example 1 of the present invention and comparative examples 1 and 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. The examples are given only for illustrating the present invention and are not intended to limit the scope of the present invention. Any obvious modifications or variations can be made to the present invention without departing from the spirit or scope of the present invention.
Example 1
In this example, the carbon dots are synthesized by weighing 3g of citric acid and 6g of urea as carbon sources, heating the carbon sources in 40mL of n, n' -dimethylformamide at 160 ℃ for 6 hours by a solvothermal method, and obtaining brown solution as carbon dots with carboxyl groups on the surface; then, mixing saturated potassium hydroxide solution with ethanol, cleaning the obtained carbon points to enable the surfaces of the carbon points to be rich in potassium ions, and centrifuging for 10min at the rotating speed of 8000 r; washing the obtained precipitate with water and ethanol twice, washing off excessive alkali and salt, centrifuging at 16000r for 10min, and lyophilizing to obtain carbon dots with surface rich in potassium ions.
The perovskite light-emitting diode is manufactured by adopting a method of spin coating and evaporation layer by layer, and the structure of the perovskite light-emitting diode is sequentially provided with a cathode, a hole transport layer, an interface modification layer, a light-emitting layer, an electron transport layer, an electron injection layer and a metal electrode from bottom to top.
The specific basic manufacturing process comprises the following steps:
(1) Cleaning and processing an ITO substrate: cleaning a purchased ITO glass substrate with a cleaning agent, and then respectively carrying out ultrasonic cleaning for 15min with deionized water, acetone and isopropanol to obtain a clean substrate, storing the clean substrate in clean isopropanol, and then directly using the clean substrate for LED manufacturing;
(2) Before manufacturing a device, an ITO is dried by a nitrogen gun, and the dried ITO substrate is treated on the surface of the ITO by an ultraviolet ozone cleaning machine, so that the surface hydrophilicity is increased;
(3) And (3) spin coating PEDOT: PSS layer: commercially available PEDOT: the PSS aqueous solution was first filtered through a 0.45 μm aqueous filter, after which PEDOT: PSS film, then thermal annealing at 150 ℃ for 15min, the thickness of the obtained film is 40nm;
(4) Spin coating a carbon dot interface modification layer: after the substrate is cooled, a layer of carbon dot solution with the concentration of 0.04mg/ml is coated in a spinning mode, and thermal annealing is carried out for 10min at the temperature of 100 ℃ to obtain a layer of extremely thin carbon dot film;
(5) Spin coating a perovskite light emitting layer: transferring the cooled ITO substrate to a glove box filled with nitrogen, and spin-coating a perovskite precursor with lead ion concentration of 0.15M in the glove box to obtain a light-emitting layer with the thickness of 35 nm;
(6) Putting the spin-coated ITO into a vacuum evaporation instrument, and keeping the vacuum degree to be 5 \1093 -4 And (3) evaporating an electron transport layer TPBi (40 nm), an electron injection layer LiF (1.5 nm) and a metal electrode Al (120 nm) layer by layer at Pa, and finishing the preparation of the device.
The luminescent layer adopts precursor solution to prepare quasi-two-dimensional perovskite by spin coating, and the precursor comprises lead bromide, cesium bromide, polyethylene oxide and organic spacer cation which is n-butyl ammonium bromide. The precursor solvent was 1.5mL of dimethyl sulfoxide. The molar ratio of each component of the precursor is lead bromide: cesium bromide: organic spacer cation = 1.2; the concentration of polyoxyethylene was 6mg/mL; the precursor lead ion concentration was 0.15M. The prepared precursor needs to be heated at 60 ℃ in the dark and stirred for 6 hours until dissolved.
The devices PL and EL prepared according to the examples have the luminous peak position of about 510nm, the starting voltage of 2.9V, the external quantum efficiency of the light-emitting diode of 15.3 percent and the maximum brightness of 52060cd/cm 2 。
Comparative example 1
This comparative example compares the performance difference between the annealed perovskite light emitting diode without the interface modification layer and the light emitting diode described in example 1.
In the comparative example, carbon points are not used as an interface modification layer, and the quasi-two-dimensional perovskite light-emitting diode is directly manufactured by using a traditional thermal annealing method.
The perovskite light-emitting diode is manufactured by adopting a method of spin coating and evaporation layer by layer, and the structure of the perovskite light-emitting diode is sequentially provided with a cathode, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a metal electrode from bottom to top.
The specific basic manufacturing process comprises the following steps:
cleaning and processing an ITO substrate: cleaning a purchased ITO glass substrate with a cleaning agent, and then respectively carrying out ultrasonic cleaning for 15min with deionized water, acetone and isopropanol to obtain a clean substrate, storing the clean substrate in clean isopropanol, and then directly using the clean substrate for LED manufacturing;
b. before manufacturing a device, an ITO is dried by a nitrogen gun, and the dried ITO substrate is treated on the surface of the ITO by an ultraviolet ozone cleaning machine, so that the surface hydrophilicity is increased;
c. and (3) spin coating PEDOT: PSS layer: commercially available PEDOT: the PSS aqueous solution was first filtered through a 0.45 μm aqueous filter, after which PEDOT: PSS film, then thermal annealing at 150 ℃ for 15min, the thickness of the obtained film is 40nm;
d. spin coating a perovskite light-emitting layer: transferring the cooled ITO substrate to a glove box filled with nitrogen, spin-coating a perovskite precursor with lead ion concentration of 0.15M in the glove box, and carrying out thermal annealing at 80 ℃ for 5min to obtain a light-emitting layer with the thickness of 35 nm;
putting the cooled ITO into a vacuum evaporation instrument, and keeping the vacuum degree to be 5 \1093 -4 And (3) evaporating an electron transport layer TPBi (40 nm), an electron injection layer LiF (1.5 nm) and a metal electrode Al (120 nm) layer by layer at Pa, and finishing the preparation of the device. The luminescent layer is prepared into quasi-two-dimensional perovskite by perovskite precursor solution, and the precursor comprises lead bromide, cesium bromide, polyethylene oxide and organic spacer cation n-butyl ammonium bromide. The precursor solvent was 1.5mL of dimethyl sulfoxide. The molar ratio of each component of the precursor is lead bromide: cesium bromide: organic spacer cation = 1.2; the concentration of polyoxyethylene was 6mg/mL; the precursor lead ion concentration was 0.15M. The prepared precursor needs to be heated at 60 ℃ in the dark and stirred for 6 hours until dissolved.
The devices PL and EL prepared by the comparative example have the emission peak position of 512nm, the turn-on voltage of 3.1V, the external quantum efficiency of the light-emitting diode of 13.9 percent and the highest brightness of 68500cd/cm 2 。
Comparative example 2
This comparative example compares primarily the performance differences between perovskite light emitting diodes without interface modification and without annealing and the light emitting diodes described in example 1.
In the comparative example, carbon points are not used as interface modification layers, and the perovskite thin film is not subjected to thermal annealing treatment and is directly used for manufacturing the quasi-two-dimensional perovskite light-emitting diode.
The perovskite light-emitting diode is manufactured by adopting a method of spin coating and evaporation layer by layer, and the structure of the perovskite light-emitting diode is sequentially provided with a cathode, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a metal electrode from bottom to top.
The specific basic manufacturing process comprises the following steps:
cleaning and processing an ITO substrate: cleaning a purchased ITO glass substrate with a cleaning agent, then respectively carrying out ultrasonic cleaning for 15min with deionized water, acetone and isopropanol, storing the obtained clean substrate in clean isopropanol, and then directly using the clean substrate for manufacturing an LED;
b. before manufacturing a device, an ITO (indium tin oxide) is dried by a nitrogen gun, and the dried ITO substrate is treated on the surface of the ITO by an ultraviolet ozone cleaning machine to increase the surface hydrophilicity;
c. and (3) spin coating PEDOT: PSS layer: commercially available PEDOT: the PSS aqueous solution was first filtered through a 0.45 μm aqueous filter, after which PEDOT: a PSS film, followed by thermal annealing at 150 ℃ for 15min, the resulting film having a thickness of 40nm;
d. spin coating a perovskite light emitting layer: transferring the cooled ITO substrate to a glove box filled with nitrogen, and spin-coating a perovskite precursor with lead ion concentration of 0.15M in the glove box to obtain a light-emitting layer with the thickness of 35 nm;
putting the ITO subjected to spin coating into a vacuum evaporation instrument, and enabling the vacuum degree to reach 5 \1093 -4 And (3) evaporating an electron transport layer TPBi (40 nm), an electron injection layer LiF (1.5 nm) and a metal electrode Al (120 nm) layer by layer at Pa, and finishing the preparation of the device.
The luminescent layer is prepared into quasi-two-dimensional perovskite through perovskite precursor solution, and the precursor comprises lead bromide, cesium bromide, polyethylene oxide and organic spacer cation which is n-butyl ammonium bromide. The precursor solvent was 1.5mL of dimethyl sulfoxide. The molar ratio of each component of the precursor is lead bromide: cesium bromide: organic spacer cation = 1.2; the concentration of polyoxyethylene was 6mg/mL; the precursor lead ion concentration was 0.15M. The prepared precursor needs to be heated at 60 ℃ in the dark and stirred for 6 hours until dissolved.
The device prepared by the comparative example has the turn-on voltage of 3.5V, the external quantum efficiency of the LED is only 1.31 percent, and the maximum brightness is 20548cd/cm 2 。
Experimental test analysis:
the comparison of the device performance and the luminescence in the embodiment 1 and the comparison example 1 is shown in the attached drawings of the specification, and experiments prove that in the light-emitting diode with the carbon point as the interface modification layer, the perovskite active layer can be induced at room temperature to realize high-quality crystallization, and the crystallization quality is equivalent to that of the perovskite active layer subjected to annealing treatment on the carbon-point-free interface layer; both the photoluminescence and electroluminescence of the film have 1-2nm blue shift, which shows that the defects in the perovskite are effectively passivated by alkali metal ions in carbon points; the starting voltage of the device is reduced, which shows that the carrier injection potential barrier is reduced, and the external quantum efficiency of the device is improved to a certain extent. Comparing the device performance of example 1 with that of comparative example 2, we found that it is difficult to prepare a high-performance light-emitting device without annealing the perovskite active layer when the carbon dot interface layer is not introduced. The experimental results prove that the carbon dots containing the alkali metal ions as the interface modification layer can realize high-quality perovskite crystallization without annealing processing of the active layer, simplify the preparation process of the device, reduce the turn-on voltage of the device and improve the external quantum efficiency of the device.
The invention is not the best known technology.
The above description is only for the specific embodiments of the present disclosure, but the scope of the present disclosure is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present disclosure, and all the changes or substitutions should be covered within the scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.
Claims (9)
1. A method for inducing perovskite thin film to crystallize at room temperature by carbon points is characterized by comprising the following steps: synthesizing carbon dots containing alkali metal ions; the thin film of the carbon dots is used as an interface modification layer of the perovskite light-emitting diode and is used between the hole transport layer and the perovskite light-emitting layer; the carbon dots serve as the centers of heterogeneous nucleation to enhance the crystallization of the perovskite, and the perovskite light emitting diode thin film is crystallized under the condition that the active layer is not annealed.
2. The method for room temperature crystallization of a carbon dot-induced perovskite thin film according to claim 1, wherein the method for preparing the carbon dot containing the alkali metal ion comprises the steps of: the method comprises the following steps: citric acid and urea are used as carbon sources, and are heated for 4-24h at 160 ℃ in N, N-dimethylformamide by a solvothermal method to synthesize carbon points with rich carboxyl on the surface; step two: washing the obtained carbon dots by using a saturated strong alkali solution to enable the surfaces of the carbon dots to be rich in alkali metal ions; and finally, washing away redundant alkali and salt by using water and ethanol, centrifuging, and freeze-drying to obtain the carbon dots.
3. The method for room temperature crystallization of carbon dot-induced perovskite thin film according to claim 2, wherein the strong alkaline solution is sodium hydroxide solution or potassium hydroxide solution.
4. A perovskite light emitting diode, which is prepared by the method for realizing the crystallization of a perovskite thin film without annealing according to any one of claims 1 to 3; the perovskite light emitting diode structurally comprises ITO conductive glass, a hole transport layer, an interface modification layer, a perovskite light emitting layer, an electron transport layer, an electron injection layer and a metal electrode.
5. The perovskite light-emitting diode according to claim 4, wherein the hole transport layer is one of PEDOT PSS, poly-TPD, TFB, TCTA, TAPC; the electron transport layer adopts one of ZnO, TPBi and TmPyPb; the electron injection layer adopts one of LiF, PEI and PEIE; the metal electrode adopts an aluminum or silver electrode.
6. The perovskite light-emitting diode of claim 4, wherein the interface modification layer between the hole transport layer and the perovskite light-emitting layer is spin coated on the hole transport layer using an aqueous solution of carbon dots at a concentration in the range of 0.02-0.05 mg/ml.
7. The perovskite light-emitting diode according to claim 4, wherein the perovskite light-emitting layer is a quasi-two-dimensional perovskite made of precursors; the precursors include lead halides, cesium halides, polyethylene oxides, and organic spacer cations.
8. The perovskite light-emitting diode of claim 7, wherein the organic spacer cation is at least one cation selected from the group consisting of n-butyl amine halides, benzyl amine halides, phenethyl amine halides, phenylpropyl amine halides, and phenylbutyl amine halides.
9. The perovskite light-emitting diode of claim 7, wherein the precursor solvent is N, N' -dimethylformamide, dimethyl sulfoxide or a mixed solvent of the two in any proportion; the molar ratio of each component of the precursor is lead halide: cesium halide: organic spacer cation = 1.2; the concentration of polyoxyethylene was 6mg/mL; the concentration of precursor lead ions is 0.15-0.2M; the halide ions contained in the halide adopted by the precursor are any one or a mixture of two of chlorine, bromine and iodine; the precursor which is prepared and finished needs to be heated at 60 ℃ in the dark and stirred for 6 hours until being dissolved.
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