A method for testing shallow-level defect distribution in perovskite thin films based on time-resolved fluorescence spectroscopy

Abstract

The present application relates to a kind of perovskite film shallow level defect distribution test methods based on time-resolved fluorescence spectrum, the recombination rate equation of charge carrier is combined with genetic algorithm and statistical method, the time-resolved fluorescence spectrum signal of film is fitted, to realize the direct measurement of potential well density value and potential well depth value.The method helps to successfully determine the potential well distribution of different samples.This measurement method is important for optimizing material performance and improving device efficiency.

Description

Technical Field

[0001] This invention belongs to the field of organic polymer photovoltaic devices or organic semiconductor thin-film solar cells, and specifically relates to a test method for shallow energy level defect distribution of perovskite thin films based on time-resolved fluorescence spectroscopy. Background Technology

[0002] Time-resolved photoluminescence (TRPL), as a powerful optical testing tool, offers wide applications for studying the carrier dynamics of various materials. In semiconductor research, TRPL helps scientists gain deeper insights into carrier lifetime, diffusion processes, and recombination mechanisms, thereby revealing the optoelectronic properties of materials. In perovskite material research, TRPL is a commonly used tool for evaluating its quality and performance. By measuring the photoluminescence lifetime and fluorescence dynamics of perovskite materials, information about important parameters such as carrier lifetime, recombination rate, and surface potential well density can be obtained. This information is crucial for the performance of perovskite optoelectronic devices; therefore, TRPL provides strong support for the optimization and performance improvement of perovskite materials. The traditional TRPL data analysis method is the double exponential fitting method, which uses the fitted fluorescence lifetime to determine the potential well density.

[0003] However, two problems exist: one is a matter of principle, and the other is a matter of accuracy. Regarding the principle, the two fluorescence lifetimes and the carrier decay rates associated with different recombination pathways do not correspond one-to-one; they are coupled. Furthermore, the untrapping process is a significant factor. When electrons are trapped in a potential well state, the untrapping process can allow them to re-jump back into the conduction band, thus participating in the radiative recombination process. This means that even in the presence of a potential well state, the untrapping process may prevent carriers from participating in non-radiative recombination, thereby affecting the fluorescence lifetime value. This complexity indicates that the fluorescence lifetime value alone cannot directly and accurately indicate the magnitude of the potential well density. In addition, regarding the accuracy issue, the parameter adjustment space of the double exponential fit lacks a standardized method for selecting the most reliable parameter set. This means that in the same curve fitting, different parameter choices may lead to different interpretations and results. This lack of standardization reduces the reliability of the double exponential fit because it is impossible to determine which set of parameters is the most reliable and accurate.

[0004] Therefore, it is necessary to re-examine the TRPL data processing program to ensure that it can accurately perform its function of quantifying defect parameters. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a method for testing the potential well distribution (potential well density and potential well depth) of perovskite thin films based on time-resolved fluorescence spectroscopy. This method can conveniently, simply, and non-destructively measure the potential well distribution in perovskite thin films, and can obtain more accurate information compared to unmodified processing methods.

[0006] The technical solution of the present invention is as follows:

[0007] A method for testing the potential well distribution of perovskite thin films based on time-resolved fluorescence spectroscopy, characterized by comprising the following steps:

[0008] S1. Select perovskite as the sample to be tested and place it on the sample stage of the time-resolved fluorescence spectroscopy detection system.

[0009] S2. Using a time-resolved fluorescence spectroscopy detection system to detect Iexc at different power levels i Lasers of different powers are used to irradiate the test samples, generating fluorescence. A time-correlated single-photon counter is used to collect the different fluorescence generated by the test samples under different laser powers. The corresponding fluorescence intensity-time graph I is determined based on the time difference between the pulse excitation event and the photon reception event. i (t);

[0010] S3. Based on the carrier recombination and transition model, fit the fluorescence intensity-time graph I. i (t), and use a genetic algorithm to optimize the parameter selection process to obtain a set of parameters set1. Repeat this step until n+1 sets of parameters are obtained, i.e., {set1, set2, set3, ... set...} n+1};

[0011] S4. Extract the potential well density {trap density1, trap density2, trap density3, ..., trap density} from the n+1 sets of parameters. n+1 The potential well density is counted in each interval to obtain the potential well distribution of the perovskite thin film, i.e., the most probable value N of the potential well density. t ;

[0012] S5. Extract the potential well depth from the n+1 sets of parameters to obtain the most probable value of the potential well depth ΔE.

[0013] Furthermore, in step S2, the time-resolved fluorescence spectroscopy detection system is used to detect different power Iexc i Lasers of different powers are used to irradiate the test samples, generating fluorescence. A time-correlated single-photon counter is used to collect the different fluorescence generated by the test samples under different laser powers. The corresponding fluorescence intensity-time graph I is determined based on the time difference between the pulse excitation event and the photon reception event. i(t), specifically including:

[0014] S2.1 Adjust the pulse frequency in the light source module of the time fluorescence spectroscopy detection system so that the periodic pulse passes through the attenuator and generates a laser with a power of Iexc1, which irradiates the sample to be tested.

[0015] S2.2 The sample to be tested generates fluorescence, which is collected by a time-dependent single-photon counter. The corresponding fluorescence intensity-time graph I1(t) is determined based on the time difference between the pulse excitation event and the photon reception event.

[0016] S2.3 Adjust the attenuator and repeat step S2.1 to generate a laser with a power of Iexc2, which is then used to irradiate the sample under test.

[0017] S2.4 Repeat step S2.2 to determine the corresponding fluorescence intensity-time graph I2(t);

[0018] S2.5 Repeat steps S2.1-S2.2 until the corresponding fluorescence intensity-time plot I is determined. i (t).

[0019] The carrier recombination and transition model used is:

[0020]

[0021] Where B represents the radiative recombination rate, N t σ represents the potential well density. n,p The trapping cross section for electrons and holes, v n,p This represents the thermal velocity of electrons and holes. Furthermore, when the Fermi level falls within the potential well level, the electron concentration is n. * =N c exp[(E t -E c [) / kT], hole concentration is p * =N v exp[(E v -E t ) / kT], where N c Let N be the effective density of states function in the conduction band. v E is the effective density of states function in the valence band. c E represents the conduction band energy level. v E represents the valence band energy level. t This represents the potential well level. n represents the electron concentration, p represents the hole concentration, and f represents the concentration of potential wells occupied by electrons.

[0022] Furthermore, the attenuators corresponding to Iexc1, Iexc2, and Iexc3 are OD0, OD1, and OD2, respectively, which means no attenuation, 90% attenuation, and 99% attenuation.

[0023] Furthermore, the parameter sets used for simultaneously fitting I1(t), I2(t), and I3(t) are all identical except for the excitation light intensity.

[0024] Furthermore, due to the randomness of each simulation initialization and the randomness of mutations and crossovers during each iteration of the same simulation, the results of each simulation will differ. However, given enough repetitions and parameter combinations, these values ​​will converge within a specific range.

[0025] Furthermore, to obtain the statistical distribution of a specific parameter, the maximum and minimum values ​​in the potential well density dataset are used as the endpoints of the horizontal axis, and the dataset is divided into several intervals. Next, the number of data points within each interval is calculated, thus plotting the statistical distribution of the potential well density.

[0026] Furthermore, the most probable value of the potential well density is the peak value of the statistical distribution of the potential well density.

[0027] A method for testing the potential well distribution (potential well density and potential well depth) of perovskite thin films based on time-resolved fluorescence spectroscopy, characterized in that the preparation of the sample to be tested includes the following steps:

[0028] The ITO glass substrate was ultrasonically cleaned using diluted glass cleaner; then, after being cleaned with deionized water, it was ultrasonically cleaned a second time using acetone and isopropanol; finally, after being dried with a nitrogen gun, the ITO glass substrate was placed in an ultraviolet ozone cleaner for a third cleaning process.

[0029] Dissolve PTAA powder in CB. Prepare a MAPbI3 precursor solution by dissolving MAI and PbI2 in 2-ME. Alternatively, dissolve FABr and PbBr2 powder in a mixed solution of DMF and DMSO to obtain a FAPbBr3 precursor solution. Dilute the precursor solution before spin coating or blade coating.

[0030] Additives such as L-α-PC, MACl, and DMSO or AHP are added to the precursor solution;

[0031] MAPbI3 or FAPbBr3 thin films were prepared by blade coating or spin coating.

[0032] The substrate is annealed using a thermal annealing method.

[0033] Furthermore, the heat annealing method employs one or more of the following: constant temperature hot table heating, oven heating, far-infrared heating, hot air heating, or microwave heating.

[0034] Furthermore, the annealing temperature for spin coating is 110℃, and the annealing temperature for blade coating is 150℃, with an annealing time of 15 minutes.

[0035] The beneficial effects of this invention are as follows:

[0036] Compared to other methods that require attached electrodes, this method is a non-destructive technique. The sample is only photoexcited to generate a fluorescence signal without any physical or chemical damage. This allows the sample to remain intact during the measurement process, facilitating subsequent analysis or reuse. Compared to the previous TRPL treatment method, this method no longer indirectly determines the size of the potential well density through fluorescence lifetime. Instead, it allows for direct and quantitative determination of the trap density and depth, and reduces the influence of the carrier capture-decapitation process on the determination of the potential well state.

[0037] This invention provides a convenient, simple, and non-destructive method for measuring the potential well distribution in perovskite films, yielding more accurate information compared to unmodified processing methods. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the genetic algorithm of the present invention;

[0039] Figure 2 This is a schematic diagram illustrating the statistical distribution of potential well density obtained by analyzing perovskite thin films according to the present invention;

[0040] Figure 3 This is a schematic diagram illustrating the statistical distribution of potential well depth obtained by analyzing perovskite thin films according to the present invention. Detailed Implementation

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] Example 1: An ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A 2.0 M MAPbI3 precursor solution was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before blade coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. The PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 10 minutes. Subsequently, the precursor solution was scraped onto the PTAA-coated ITO glass substrate with gaps of 300 μm. Finally, it was annealed in air at 150 °C for 15 minutes. Under standard test conditions, the N of the film was measured. t = 7.5 × 10 16 cm -3 ,ΔE=0.23 eV.

[0043] Example 2: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A MAPbI3 precursor solution with a concentration of 2.0 M was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. An AHP solution was prepared by dissolving AHP (20 mg / ml) in 2-ME and added as an additional additive (4% v / v) to the precursor solutions. PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 10 minutes. Subsequently, a precursor solution was blade-coated onto the PTAA-coated ITO glass substrate at a gap of 300 μm. Finally, the substrate was annealed in air at 150°C for 15 minutes. Under standard test conditions, the nitrogen content of the film was measured. t = 3.0 × 10 16 cm -3,ΔE=0.17eV.

[0044] Example 3: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A MAPbI3 precursor solution with a concentration of 2.0 M was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. An AHP solution was prepared by dissolving AHP (20 mg / ml) in 2-ME and added as an additional additive (4% v / v) to the precursor solutions. PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 8 minutes. Subsequently, a precursor solution was blade-coated onto the PTAA-coated ITO glass substrate at a gap of 300 μm. Finally, the substrate was annealed in air at 150 °C for 15 minutes. Under standard test conditions, the nitrogen content of the film was measured. t = 3.0 × 10 16 cm -3 ,ΔE=0.19 eV.

[0045] Example 4: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A 2.0 M MAPbI3 precursor solution was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before blade coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. The PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 12 minutes. Subsequently, the precursor solution was scraped onto the PTAA-coated ITO glass substrate with gaps of 300 μm. Finally, it was annealed in air at 150 °C for 15 minutes. Under standard test conditions, the N of the film was measured. t= 1.5×10 16 cm -3 ,ΔE=0.29 eV.

[0046] Example 5: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A 2.0 M MAPbI3 precursor solution was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before blade coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. The PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 15 minutes. Subsequently, the precursor solution was scraped onto the PTAA-coated ITO glass substrate with gaps of 300 μm. Finally, it was annealed in air at 150 °C for 15 minutes. Under standard test conditions, the N of the film was measured. t = 7.0 × 10 16 cm -3 ,ΔE=0.19 eV.

[0047] Example 6: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. PTAA powder was dissolved in CB at a concentration of 6 mg / ml. A 2.0 M MAPbI3 precursor solution was prepared by dissolving MAI and PbI2 in 2-ME. These precursor solutions were diluted to 1.1 M before blade coating. Additives such as L-α-PC (0.4 mg / ml), MACl (0.2 mg / ml), and DMSO (2.8% v / v) were added to the precursor solutions. The PTAA solution was coated onto the substrate using a blade coating method at a speed of 30 mm / s and a coating gap of 250 μm, followed by annealing for 10 minutes. Subsequently, the precursor solution was scraped onto the PTAA-coated ITO glass substrate with gaps of 300 μm. Finally, it was annealed in air at 150 °C for 15 minutes. Under standard test conditions, the N of the film was measured. t = 5.0 × 10 16cm -3 ,ΔE=0.11 eV.

[0048] Example 7: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. FABr and PbBr2 powders were dissolved in a mixed solution of DMF and DMSO to obtain a 1.4 M FAPbBr3 precursor solution. 60 μL of DMF was pipetted onto the substrate (1000 rpm, 10 s); then 96 μL of the precursor solution was pipetted onto the substrate (4000 rpm, 30 s). At the 15th second of spin coating, 135 μL of CB as an antisolvent was rapidly pipetted onto the film. After spin coating, the film was annealed at 110 °C for 15 minutes on a hot plate. Under standard test conditions: the N of the thin film was measured. t = 5.0 × 10 16 cm -3 ,ΔE=0.17 eV.

[0049] Example 8: The ITO glass substrate was ultrasonically cleaned using a diluted glass cleaner for 15 minutes. Subsequently, the substrate was rinsed with deionized water, followed by ultrasonic cleaning with acetone and isopropanol, each step lasting 15 minutes. The substrate was dried using a nitrogen gun. The ITO substrate was then treated in a UV ozone cleaner for 10 minutes. FABr and PbBr2 powders were dissolved in a mixed solution of DMF and DMSO to obtain a 1.4 M FAPbBr3 precursor solution. PTAA solution was coated onto the substrate using a blade coating method at a speed of 20 mm / s and a coating gap of 250 μm, followed by annealing for 10 minutes. Subsequently, the precursor solution was blade-coated onto the PTAA-coated ITO glass substrate at a gap of 300 μm. Finally, annealing was performed in air at 150 °C for 15 minutes. Under standard test conditions: the N of the film was measured. t = 1.5×10 17 cm -3 ,ΔE=0.18 eV.

[0050] The embodiments of the present invention are preferred embodiments, but their specific implementation is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations. As long as they do not depart from the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for testing shallow level defect distribution of perovskite thin film based on time-resolved fluorescence spectrum, characterized in that, The method comprises the following steps: S1, selecting a perovskite as a sample to be tested and placing the sample on a sample stage of a time-resolved fluorescence spectrum detection system; S2, using a time-resolved fluorescence spectrum detection system, different power Iexc i laser lights are respectively irradiated on the sample to be measured to generate fluorescence, different fluorescence generated by the sample to be measured under different laser powers is collected by using a time-dependent single photon counter, and the corresponding fluorescence intensity-time graph I i (t) is determined according to the time difference between the pulse excitation event and the photon receiving event. S3. According to the carrier recombination and transition model, the fluorescence intensity-time graph I is fitted i (t), and the parameter selection process is optimized by using a genetic algorithm to obtain a set of parameters set1. The step is repeated until n+1 sets of parameters are obtained, i.e. {set1, set2, set3, … set n+1}; S4, extracting trap density {trap density1, trap density2, trap density3, ……trap density n+1} from the n+1 groups of parameters, and counting the number of trap densities extracted in each interval to obtain the perovskite film trap distribution, i.e. the most probable value N of trap density t ; S5, extracting a potential well depth from the n+1 groups of parameters to obtain a most probable value ΔE of the potential well depth.

2. The method for testing shallow level defect distribution of perovskite thin film according to claim 1, characterized in that, The step S2, using a time-resolved fluorescence spectrum detection system to make different power Iexc i laser respectively irradiate on the sample to be measured to produce fluorescence, using a time-correlated single photon counter to collect different fluorescence produced by the sample to be measured under different laser power, and determining the corresponding fluorescence intensity-time graph I i (t) according to the time difference between the pulse excitation event and the photon receiving event. S2.1, adjusting a pulse frequency in a light source board of the time-resolved fluorescence spectrum detection system, so that a periodic pulse passes through an attenuating sheet and generates laser light with a power Iexc1, which irradiates on the sample to be tested; S2.2, the sample to be tested generates fluorescence, which is collected by a time-correlated single photon counter, and a corresponding fluorescence intensity-time graph I1(t) is determined according to a time difference between a pulse excitation event and a photon receiving event; S2.3, adjusting the attenuating sheet and repeating step S2.1 to generate laser light with a power Iexc2, which finally irradiates on the sample to be tested; S2.4, repeating step S2.2 to determine a corresponding fluorescence intensity-time graph I2(t); S2.5 Repeating steps S2.1-S2.2 until a corresponding fluorescence intensity-time profile I is determined i (t).

3. The method for testing shallow level defect distribution of perovskite thin film according to claim 2, characterized in that, When i=3, the attenuating sheets corresponding to the powers Iexc1, Iexc2 and Iexc3 are OD0, OD1 and OD2, i.e. no attenuation, 90% attenuation and 99% attenuation. 4.The method for testing shallow level defect distribution of perovskite thin film according to claim 1, characterized in that, The maximum value and the minimum value in the potential well density data set are used as end points of the horizontal axis, and are divided into several intervals; the number of data points in each interval is calculated, so as to draw a statistical distribution graph of the potential well density.

5. The method for testing shallow level defect distribution of perovskite thin film according to claim 1, characterized in that, The most probable value of the potential well density is a peak value of the statistical distribution of the potential well density.

6. The method for testing shallow level defect distribution of perovskite thin film according to claim 1, characterized in that, The preparation of the sample to be tested comprises the following steps: S1, ultrasonic cleaning ITO glass substrates by using diluted glass detergent; then, after cleaning the ITO glass substrates with deionized water, performing secondary ultrasonic cleaning by using acetone and isopropyl alcohol; after blowing the ITO glass substrates dry by using a nitrogen gun, performing three times of cleaning treatment in an ultraviolet ozone cleaning machine; S2, dissolving PTAA powder in CB, dissolving MAI and PbI2 in 2-ME to prepare a MAPbI3 precursor solution; or dissolving FABr and PbBr2 powder in a mixed solution of DMF and DMSO to obtain a FAPbBr3 precursor solution; before scraping or spin coating, diluting the precursor solution; S3, adding additives L-α-PC, MACl and DMSO or AHP to the precursor solution; S4, preparing a MAPbI3 or FAPbBr3 thin film by using a scraping method or a spin coating method; S5, performing heat annealing treatment on the ITO glass substrates.

7. The method for testing perovskite film shallow level defect distribution based on time-resolved fluorescence spectrum according to claim 6, characterized in that, The heat annealing treatment comprises one or more of constant temperature hot table heating, oven heating, far infrared heating, hot air heating or microwave heating. 8.The method for testing perovskite film shallow level defect distribution based on time-resolved fluorescence spectrum according to claim 6, characterized in that, The annealing temperature of the spin coating method is 110 DEG C, and the annealing temperature of the scraping method is 150 DEG C, and the annealing time is 15 minutes.

Images