Monitoring Method and System for Carrier Transport in Two-Dimensional Perovskite Thin Films with Multiple Quantum Wells

Abstract

This invention discloses a method and system for monitoring carrier transport in a two-dimensional perovskite film with multiple quantum wells (MFUs). It relates to the field of carrier transport monitoring technology. The method analyzes the transient absorption spectra of the front and back sides of the MFUs two-dimensional perovskite film to determine the phase distribution. Based on the phase distribution, the optimal pump light wavelength and power are determined. Using the optimal pump light wavelength and power, a transient absorption microscopy imaging system is employed to probe the front and back sides of the MFUs two-dimensional perovskite film. Based on the spatial distribution information sets of the carriers on the front and back sides, the influence of the phase distribution on carrier transport is determined. This allows for direct monitoring of the impact of the phase distribution on the carrier transport process in the MFUs two-dimensional perovskite film, enabling monitoring of carrier transport in the MFUs two-dimensional perovskite film from a spatiotemporal perspective. This facilitates subsequent optimization of device performance based on the MFUs two-dimensional perovskite film.

Description

Technical Field

[0001] This invention relates to the field of carrier transport monitoring technology, and in particular to a method and system for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells. Background Technology

[0002] Recently, two-dimensional perovskite materials have shown great promise in the field of photovoltaic devices. In particular, the hydrophobic organic cations significantly improve moisture resistance, providing a potential solution to the environmental stability issues of perovskite solar cells. However, it has also been found that due to the insertion of organic cations, two-dimensional perovskite films are actually composed of multiple quantum well perovskite phases, meaning that the number of two-dimensional perovskite inorganic layers (n) between the organic cation spacer layers in each phase is different. The band arrangement between different quantum well phases and their distribution in the film affect the carrier transport properties, which has a crucial impact on the application of two-dimensional perovskite films: the diffusion rate and distance of carriers significantly affect their efficient migration to the carrier transport layer, directly determining the device efficiency.

[0003] In fact, carrier transport often occurs on the same timescale as the carrier transfer process within the sample. Most current research focuses on carrier dynamics in the time domain, with less research on the spatial dynamics of carrier transport processes at the nanometer to micrometer scale within the same timescale. In particular, the influence of phase distribution in multi-quantum-well two-dimensional perovskite films on carrier transport processes remains unclear, which is crucial for optimizing the performance of devices based on two-dimensional perovskite films. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for monitoring carrier transport in multi-quantum-well two-dimensional perovskite thin films. This method can monitor the influence of phase distribution on carrier transport in multi-quantum-well two-dimensional perovskite thin films, which is beneficial for optimizing the performance of devices based on two-dimensional perovskite thin films.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells, comprising:

[0007] Obtain a first transient absorption spectrum set of the thin film; the first transient absorption spectrum set includes the transient absorption spectrum of the front side of the thin film and the transient absorption spectrum of the back side of the thin film; the thin film is a two-dimensional perovskite thin film with multiple quantum wells;

[0008] The phase distribution of the thin film is determined by analyzing the first transient absorption spectrum set.

[0009] Obtain the second transient absorption spectrum set of the thin film under each of the different parameter combinations; analyze all the second transient absorption spectrum sets based on the phase distribution to determine the optimal parameter combination; the parameter combination includes the pump light wavelength and the pump light power; the second transient absorption spectrum set includes the transient absorption spectrum of the front side of the thin film and the transient absorption spectrum of the back side of the thin film;

[0010] Under the optimal parameter combination, the carrier spatial distribution information sets of the front and back sides of the thin film are obtained by using a transient absorption microscopy imaging system to detect the front and back sides of the thin film. Based on the carrier spatial distribution information sets of the front and back sides of the thin film, the monitoring results of carrier transport are determined. The carrier spatial distribution information set includes the photogenerated carrier density distribution under different delay times. The monitoring results are the results of the influence of phase distribution on carrier transport.

[0011] In some embodiments, analyzing the first transient absorption spectrum set to determine the phase distribution of the thin film specifically includes:

[0012] The content of each quantum well perovskite phase in the front of the film is obtained by integrating the ground state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the front of the film.

[0013] The content of each quantum well perovskite phase in the reverse side of the film is obtained by integrating the ground state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the reverse side of the film.

[0014] The phase distribution of the thin film is determined based on the content of each quantum well perovskite phase in the front side and the content of each quantum well perovskite phase in the back side of the thin film. The phase distribution includes a higher proportion of large n phases in the front side of the thin film and a higher proportion of small n phases in the back side of the thin film. Large n phases are quantum well perovskite phases with n greater than or equal to a preset value, and small n phases are quantum well perovskite phases with n less than a preset value, where n is the number of two-dimensional perovskite inorganic layers.

[0015] In some embodiments, before obtaining the second transient absorption spectrum set of the thin film under each of the different parameter combinations, the method further includes: selecting a preset wavelength for the pump light wavelength and selecting multiple values ​​for the pump light power to obtain multiple different parameter combinations.

[0016] In some embodiments, the optimal parameter combination is determined by analyzing all the second transient absorption spectrum sets based on the phase distribution, specifically including:

[0017] For each of the second transient absorption spectrum sets, the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 in the front side of the film are determined based on the transient absorption spectrum of the front side of the film, and the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 in the back side of the film are determined based on the transient absorption spectrum of the back side of the film; the ground-state bleaching peak dynamics are the curves showing the change of ground-state bleaching intensity with time delay.

[0018] Based on the phase distribution, by comparing the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 on the front side of the film and the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 on the back side of the film corresponding to all the second transient absorption spectrum sets, the pump power that can reflect the different carrier transfer processes caused by the phase distribution differences is determined, and the optimal parameter combination is obtained.

[0019] In some embodiments, the monitoring results of carrier transport are determined based on the carrier spatial distribution information set on the front side of the thin film and the carrier spatial distribution information set on the back side of the thin film, specifically including:

[0020] By fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the front side of the thin film using a two-dimensional Gaussian function, the variance of the carrier Gaussian distribution at each delay time in the front side of the thin film is obtained.

[0021] By fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the back side of the thin film using a two-dimensional Gaussian function, the variance of the carrier Gaussian distribution at each delay time in the back side of the thin film is obtained.

[0022] The carrier diffusion coefficient and carrier diffusion length of the front side of the thin film are calculated based on the variance of the Gaussian distribution of carriers at each delay time in the front side of the thin film. The carrier diffusion coefficient and carrier diffusion length of the back side of the thin film are calculated based on the variance of the Gaussian distribution of carriers at each delay time in the back side of the thin film.

[0023] The monitoring results of carrier transport are determined by measuring the carrier diffusion coefficient and carrier diffusion length on the front and back sides of the thin film.

[0024] A computer system includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method for monitoring carrier transport in a multi-quantum-well two-dimensional perovskite thin film.

[0025] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0026] This invention provides a method and system for monitoring carrier transport in two-dimensional perovskite films with multiple quantum wells. The transient absorption spectra of the front and back sides of the film are analyzed to determine the phase distribution. Based on the phase distribution, the optimal pump wavelength and power are determined. Using the optimal pump wavelength and power, a transient absorption microscopy system is employed to probe the front and back sides of the film. Based on the spatial distribution information sets of the carriers on the front and back sides, the influence of the phase distribution on carrier transport is determined. This allows for direct monitoring of the impact of the phase distribution on the carrier transport process in the two-dimensional perovskite film with multiple quantum wells, enabling spatiotemporal monitoring of carrier transport in the film. This facilitates subsequent optimization of device performance based on the two-dimensional perovskite film with multiple quantum wells. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the monitoring method provided in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the transient absorption spectrum and phase distribution of the (PEA)2MAPb2I7 two-dimensional perovskite thin film provided in Embodiment 1 of the present invention; wherein, Figure 2 a) in the spectrum represents the transient absorption spectrum under reverse excitation; Figure 2 b) in the figure represents the transient absorption spectrum under positive excitation; Figure 2 c) represents the relative content of different quantum well perovskite phases;

[0030] Figure 3 This is a schematic diagram illustrating the power dependence of the ground-state bleaching peak dynamics of the quantum well perovskite phase of the (PEA)2MAPb2I7 two-dimensional perovskite thin film with n=3 provided in Embodiment 1 of the present invention; wherein, Figure 3 In the figure, a) represents a pump light power of 1.5 μJ / cm. 2 A schematic diagram comparing the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 under reverse excitation and forward excitation. Figure 3 b) in the figure represents a pump light power of 5 μJ / cm. 2 A schematic diagram comparing the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 under reverse excitation and forward excitation.

[0031] Figure 4This is a schematic diagram of the transient absorption microscopy imaging results of the (PEA)2MAPb2I7 two-dimensional perovskite thin film provided in Embodiment 1 of the present invention; wherein, Figure 4 a) in the figure shows the relationship between the variance of the Gaussian distribution of the front-excited downloader and the delay time; Figure 4 b) in the figure shows the relationship between the variance of the Gaussian distribution of the reverse-excited carrier and the delay time. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide a method and system for monitoring carrier transport in multi-quantum-well two-dimensional perovskite thin films. This method can monitor the influence of phase distribution on carrier transport in multi-quantum-well two-dimensional perovskite thin films, which is beneficial for optimizing the performance of devices based on two-dimensional perovskite thin films.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1:

[0036] This embodiment provides a method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells, such as... Figure 1 As shown, it includes:

[0037] S1: Obtain the first transient absorption spectrum set of the thin film; the first transient absorption spectrum set includes the transient absorption spectrum of the front side of the thin film and the transient absorption spectrum of the back side of the thin film; the thin film is a two-dimensional perovskite thin film with multiple quantum wells.

[0038] Before S1, in this embodiment, a two-dimensional perovskite film with multiple quantum wells can be prepared. Specifically, any existing preparation method can be used, such as using a one-step spin coating method to prepare a (PEA)2MAPb2I7 two-dimensional perovskite film.

[0039] In this embodiment, a femtosecond transient absorption spectroscopy system is used to test the front and back sides of a multi-quantum-well two-dimensional perovskite thin film, obtaining the transient absorption spectra of the front side and the transient absorption spectra of the back side of the film, which together form the first transient absorption spectrum set of the film.

[0040] S2: Analyze the first transient absorption spectrum set to determine the phase distribution of the thin film.

[0041] The analysis of the first transient absorption spectrum set to determine the phase distribution of the thin film may include: integrating the ground-state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the front side of the thin film to obtain the content of each quantum well perovskite phase in the front side of the thin film; integrating the ground-state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the back side of the thin film to obtain the content of each quantum well perovskite phase in the back side of the thin film; determining the phase distribution of the thin film based on the content of each quantum well perovskite phase in the front side and the content of each quantum well perovskite phase in the back side of the thin film, wherein the phase distribution includes a higher proportion of large n phases on the front side of the thin film and a higher proportion of small n phases on the back side of the thin film, where large n phases are quantum well perovskite phases with n greater than or equal to a preset value, and small n phases are quantum well perovskite phases with n less than a preset value, where n is the number of two-dimensional perovskite inorganic layers, and different n values ​​represent different quantum well perovskite phases. In this embodiment, the preset value may be 4.

[0042] Specifically, taking the prepared (PEA)2MAPb2I7 two-dimensional perovskite thin film as an example, with a pump light wavelength of 480 nm and an excitation flux (i.e., pump light power) of 5 μJ / cm, 2 Under certain conditions, the front and back sides of the (PEA)2MAPb2I7 two-dimensional perovskite film were tested using a femtosecond transient absorption spectroscopy system, and the transient absorption spectra of the front and back sides of the film were obtained.

[0043] like Figure 2 As shown in a), this is the transient absorption spectrum of the reverse side of the (PEA)2MAPb2I7 two-dimensional perovskite film. The transient absorption spectrum is a graph showing the change in the absorption spectrum ΔA before and after sample excitation as a function of delay time and wavelength. Each quantum well perovskite phase is determined through the transient absorption spectrum. For each quantum well perovskite phase, a fixed delay time is first determined, and the ground-state bleaching signal at that fixed delay time is obtained. Figure 2 In section a), draw a horizontal line. The vertical axis of this line is equal to the fixed delay time, and the range of the horizontal axis corresponds to the wavelength range of the quantum well perovskite phase. By selecting data points on this line where ΔA is negative, the ground-state bleaching signal of the quantum well perovskite phase can be obtained. Integrating the ground-state bleaching signal corresponding to the quantum well perovskite phase yields the content of the quantum well perovskite phase. Based on the above process, the content of each quantum well perovskite phase in the reverse side of the film can be determined.

[0044] like Figure 2As shown in b), this is the transient absorption spectrum of the front side of the (PEA)2MAPb2I7 two-dimensional perovskite film. The transient absorption spectrum is a graph showing the change in absorption spectrum ΔA before and after sample excitation as a function of delay time and wavelength. Each quantum well perovskite phase is determined through the transient absorption spectrum. For each quantum well perovskite phase, a fixed delay time is first determined, and the ground-state bleaching signal at that fixed delay time is obtained. Figure 2 In step b), draw a horizontal line with its ordinate equal to the fixed delay time. The range of the horizontal axis corresponds to the wavelength range of the quantum well perovskite phase. By selecting data points on this line where ΔA is negative, the ground-state bleaching signal of the quantum well perovskite phase can be obtained. Integrating the ground-state bleaching signal corresponding to the quantum well perovskite phase yields the content of that quantum well perovskite phase. Based on the above process, the content of each quantum well perovskite phase in the front side of the film can be determined.

[0045] In calculating the content, the fixed delay time can be selected as 0 picoseconds. This is equivalent to integrating the ground state bleaching signal of each quantum well perovskite phase at the initial moment to calculate the content of each quantum well perovskite phase. The obtained content is the content at the initial moment.

[0046] The content ratio of each quantum well perovskite phase in the front side of the film is calculated based on the content of each quantum well perovskite phase in the back side of the film. The phase distribution of the film is determined based on the content ratios of each quantum well perovskite phase in the front and back sides, thus obtaining the phase distribution law in the (PEA)₂MAPb₂I₇ two-dimensional perovskite film. Figure 2 As shown in c), this represents the content ratio of each quantum well perovskite phase in the front and back of the film. (Observation) Figure 2 As shown in c), the phase distribution pattern in the (PEA)2MAPb2I7 two-dimensional perovskite film is as follows: the large n phase (n≥4) accounts for more of the proportion on the front side of the film, while the small n phase (n=2 and n=3) accounts for more of the proportion on the back side of the film.

[0047] S3: Obtain the second transient absorption spectrum set of the thin film under each parameter combination in different parameter combinations; analyze all the second transient absorption spectrum sets based on the phase distribution to determine the optimal parameter combination; the parameter combination includes pump light wavelength and pump light power; the second transient absorption spectrum set includes the transient absorption spectrum of the front side of the thin film and the transient absorption spectrum of the back side of the thin film.

[0048] Before obtaining the second transient absorption spectrum set of the thin film under each parameter combination in different parameter combinations, the monitoring method of this embodiment further includes: selecting a preset wavelength (which can be 480nm) for the pump light wavelength, selecting multiple values ​​for the pump light power, and combining them to obtain multiple different parameter combinations. That is, in the different parameter combinations of this embodiment, only the pump light power is a variable value.

[0049] After determining different parameter combinations, for each parameter combination, the front and back sides of the multi-quantum-well two-dimensional perovskite thin film can be tested using a femtosecond transient absorption spectroscopy system to obtain the transient absorption spectra of the front side and the transient absorption spectra of the back side of the film, forming the second transient absorption spectrum set of the film, so as to obtain the second transient absorption spectrum set of the film under each parameter combination.

[0050] As the value of n increases, the band gap (energy difference between the conduction band and the valence band) of perovskite gradually decreases. In particular, there is a larger energy difference between the conduction bands of each quantum well phase, which leads to a greater driving force for the transfer of electrons in the conduction band from the small n phase to the large n phase after photoexcitation. Conversely, the energy difference between the valence bands is smaller, which leads to a smaller driving force for the transfer of holes in the valence band from the small n phase to the large n phase after photoexcitation. Analyzing all second transient absorption spectrum sets based on phase distribution and band arrangement among quantum well perovskite phases to determine the optimal parameter combination can include: for each second transient absorption spectrum set, determining the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the front side of the film based on the transient absorption spectrum of the film's front side, and determining the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the back side of the film based on the transient absorption spectrum of the film's back side. The ground-state bleaching peak dynamics are the curves showing the change in ground-state bleaching intensity with time delay. Based on phase distribution, comparing the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the front side of the film and the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the back side of the film corresponding to all second transient absorption spectrum sets, determining the pump power that reflects the different carrier transfer processes caused by the differences in phase distribution, and obtaining the optimal parameter combination.

[0051] Specifically, taking the prepared (PEA)2MAPb2I7 two-dimensional perovskite thin film as an example, the excitation flux (i.e., pump power) at a pump light wavelength of 480 nm is 1.5 μJ / cm. 2 and 5μJ / cm 2 Under certain conditions, the front and back sides of the (PEA)2MAPb2I7 two-dimensional perovskite film were tested using a femtosecond transient absorption spectroscopy system to obtain the transient absorption spectra of the front side and the back side of the film under different pump light powers.

[0052] The dynamics of the ground-state bleaching peak corresponding to the n=3 quantum well perovskite were determined by transient absorption spectroscopy. First, a fixed wavelength was determined, and the curve of the ground-state bleaching intensity changing with time at that fixed wavelength was obtained. Figure 2 a) or Figure 2 By drawing a vertical line in section b) with its horizontal coordinate equal to a fixed wavelength, the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase can be obtained. Following the above process, the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the front and back sides of the film under different pump light powers can be determined. The fixed wavelength can be the wavelength corresponding to the peak value of the n=3 ground-state bleaching signal.

[0053] Based on the above process, the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on both the front and back sides of the film can be extracted by changing the pump light power during the transient absorption spectroscopy test. Combining the phase distribution law obtained in S2 and the band arrangement between the quantum well perovskite phases, the influence of the (PEA)₂MAPb₂I₇ two-dimensional perovskite film phase distribution on carrier transfer is determined, and its influence on the carrier transport process is inferred. In the ground-state bleaching peak dynamics, the initial ultrafast decay represents the transfer of electrons to the large n phase.

[0054] like Figure 3 As shown in a), the pump light power is 1.5 μJ / cm. 2 A comparative schematic diagram showing the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase in the reverse side of the film and the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase in the front side of the film, as shown in the figure. Figure 3 As shown in b), the pump light power is 5 μJ / cm. 2 A comparative schematic diagram of the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the reverse side of the thin film and the ground-state bleaching peak dynamics of the n=3 quantum well perovskite phase on the front side of the thin film is presented. By comparing the power-dependent transient absorption spectra of the front and back sides of the thin film, the influence of different phase distributions on the carrier transfer process is investigated. It is found that with the increase of excitation flux, the rate and amplitude of ultrafast decay from the small n phase to the large n phase on both the front and back sides are significantly suppressed, indicating that with the increase of excitation flux, the transfer of electrons from the small n phase to the large n phase gradually approaches saturation. Especially at 5 μJ / cm 2 At this point, the ultrafast decay of anti-excitation was significantly suppressed, while the ultrafast decay of front-excitation remained similar to that at low excitation flux. This indicates that due to the lower proportion of the large n phase on the anti-excitation side, the transfer of electrons from the small n phase to the large n phase was more severely suppressed. In other words, at an excitation flux of 5 μJ / cm², the ultrafast decay of anti-excitation was significantly suppressed. 2At this time, some electrons in the reverse n=3 phase cannot transfer to the larger n phase, meaning some electrons remain in the n=3 phase, while electrons in the forward n=3 phase can transfer completely to the larger n phase. This difference in phase distribution leads to different carrier transfer processes, affecting the distribution of carriers in different quantum wells, and thus affecting the carrier transport process. Therefore, this embodiment selects 5 μJ / cm². 2 The optimal pump power is achieved by using a preset pump wavelength (e.g., 480 nm) and a pump power of 5 μJ / cm². 2 .

[0055] S4: Under the optimal parameter combination, obtain the carrier spatial distribution information set of the front side of the thin film and the carrier spatial distribution information set of the back side of the thin film obtained by detecting the front and back sides of the thin film using a transient absorption microscopy imaging system. Determine the monitoring result of carrier transport based on the carrier spatial distribution information set of the front side and the back side of the thin film; the carrier spatial distribution information set includes the photogenerated carrier density distribution under different delay times; the monitoring result is the result of the influence of phase distribution on carrier transport.

[0056] The determination of carrier transport monitoring results based on the carrier spatial distribution information sets on the front and back sides of the thin film can include: fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the front side of the thin film using a two-dimensional Gaussian function to obtain the variance of the carrier Gaussian distribution at each delay time on the front side of the thin film; fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the back side of the thin film using a two-dimensional Gaussian function to obtain the variance of the carrier Gaussian distribution at each delay time on the back side of the thin film; calculating the carrier diffusion coefficient and carrier diffusion length on the front side of the thin film based on the variance of the carrier Gaussian distribution at each delay time on the front side of the thin film, and calculating the carrier diffusion coefficient and carrier diffusion length on the back side of the thin film based on the variance of the carrier Gaussian distribution at each delay time on the back side of the thin film; and determining the carrier transport monitoring results using the carrier diffusion coefficient and carrier diffusion length on both the front and back sides of the thin film.

[0057] Specifically, taking the prepared (PEA)2MAPb2I7 two-dimensional perovskite film as an example, because at 5 μJ / cm 2 At a pump light power of 480 nm, the differences in carrier transport in the thin film due to different phase distributions can be more clearly observed. Therefore, at a pump light wavelength of 480 nm and a pump light power of 5 μJ / cm², the differences in carrier transport in the thin film due to different phase distributions can be more clearly observed. 2Under the condition that the peak wavelength of the ground state bleaching signal of the quantum well perovskite phase with a detection wavelength of n=3 corresponds to the wavelength, the front and back sides of the (PEA)2MAPb2I7 two-dimensional perovskite thin film are detected using a transient absorption microscopy imaging system to obtain the carrier spatial distribution information set of the front side of the film and the carrier spatial distribution information set of the back side of the film.

[0058] The process of probing the front and back sides of the thin film using a transient absorption microscopy system includes: first, exciting the thin film with a fixed pump light to generate an initial distribution of photogenerated carriers, i.e., obtaining the photogenerated carrier density distribution at zero delay time. Then, using a delay platform, the probe light has a certain delay time relative to the pump light. With this fixed delay time, a two-dimensional galvanometer system is used to scan the probe light relative to the pump light, capturing the differential signal to obtain the photogenerated carrier density information at different positions at a given delay time, i.e., obtaining the photogenerated carrier density distribution at a specific delay time. By selecting an appropriate delay time, a series of photogenerated carrier density distributions at different delay times can be obtained. Based on this process, a spatial distribution information set of carriers on the front and back sides of the thin film can be obtained, including the photogenerated carrier density distribution at different delay times.

[0059] The transient absorption imaging results were fitted using a two-dimensional Gaussian function, specifically by fitting the photogenerated carrier density distribution at the delay time. After fitting, the total number of carriers at the initial time was determined. Where N is the fitting coefficient, and (x0, y0) are the coordinates of the Gaussian peak at the initial time. Let be the variance of the Gaussian distribution along the x-direction at the initial time. The variance of the Gaussian distribution along the y-direction at the initial time is given by the total number of charge carriers at a delay time t. Among them, (x t y t ( ) represents the coordinates of the Gaussian peak at time t. Let be the variance of the Gaussian distribution along the x-direction at time t. Let be the variance of the Gaussian distribution along the y-direction at time t. The variance of the carrier Gaussian distribution is defined as the average of the variances of the Gaussian distributions along the x-direction and the y-direction, i.e. Where, σ r,0 Let σ be the variance of the Gaussian distribution of charge carriers at the initial time. r,t Let be the variance of the Gaussian distribution of charge carriers at time t. Since the variances of the Gaussian distributions along the x and y directions have already been determined through fitting a two-dimensional Gaussian function, the variance of the Gaussian distribution of charge carriers can be calculated. Based on the above process, the variances of the Gaussian distribution of charge carriers at each delay time on the front side of the film and the variances of the Gaussian distribution of charge carriers at each delay time on the back side of the film can be determined.

[0060] The total number of charge carriers, as a function of time and space, can be described by the following differential equation: Where n(r,t) is the total number of charge carriers, r is the position coordinate, D is the carrier diffusion coefficient, and τ is the carrier lifetime, then the diffusion coefficient D is... When t = τ, the carrier diffusion distance Based on the above process, the carrier diffusion coefficient and carrier diffusion length on the front and back sides of the thin film can be determined. By using the carrier diffusion coefficients and carrier diffusion lengths on both sides, the influence of phase distribution on carrier transport can be derived.

[0061] like Figure 4 As shown in a), it is the curve of the variance of the Gaussian distribution of carriers on the front side of the thin film as a function of the pump-probe delay time, as follows. Figure 4 As shown in b), the variance of the Gaussian distribution of charge carriers on the reverse side of the thin film varies with the pump-probe delay time. It can be seen that during front-side excitation, electrons in the n=3 phase can be fully transferred to the large n phase. Therefore, the carrier diffusion measured in the n=3 quantum well perovskite phase is hole diffusion. However, during back-side excitation, carrier transport exhibits two distinct stages: fast diffusion occurs in the first 1 nanosecond, followed by slow diffusion after 1 nanosecond. The slow diffusion coefficient is consistent with the diffusion coefficient of the n=3 phase during front-side excitation, indicating hole diffusion, while the fast diffusion coefficient is attributed to the presence of n=3 phase electrons on a timescale of hundreds of picoseconds. Due to the insufficient content of the large n phase on the reverse side of the thin film, the transfer of electrons from the n=3 phase to the large n phase is suppressed, and some electrons remain in the n=3 phase, leading to faster carrier diffusion and a longer transport distance.

[0062] Current research only utilizes transient absorption spectroscopy to analyze carrier transfer processes in multi-quantum-well two-dimensional perovskite films, focusing solely on time-domain carrier dynamics. It fails to comprehensively analyze the impact of phase distribution on carrier transport from a spatiotemporal perspective. Transient absorption microscopy, however, possesses both temporal and spatial resolution. By combining the phase distribution obtained from transient absorption spectroscopy with appropriate pump light wavelengths and power, it is possible to directly monitor the influence of phase distribution on carrier transport in multi-quantum-well two-dimensional perovskite films. This is crucial for optimizing the performance of devices based on two-dimensional perovskite films. For example, separated electrons and holes, faster carrier diffusion coefficients (i.e., diffusion rates), and longer carrier diffusion lengths facilitate carrier extraction and utilization in solar cells, improving device performance. Therefore, by combining power-dependent femtosecond transient absorption spectroscopy with transient absorption microscopy, the influence of phase distribution on carrier transport in multi-quantum-well two-dimensional perovskite films can be monitored, providing guidance for optimizing device performance.

[0063] Example 2:

[0064] This embodiment provides a computer system, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program to implement the steps of the monitoring method for carrier transport in a multi-quantum-well two-dimensional perovskite thin film as described in Embodiment 1.

[0065] Each embodiment in this specification focuses on the differences from other embodiments. For the same or similar parts between the embodiments, please refer to each other.

[0066] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells, characterized in that, include: Obtain the first transient absorption spectrum set of the thin film; The first transient absorption spectrum set includes the transient absorption spectrum of the front side of the film and the transient absorption spectrum of the back side of the film; The thin film is a two-dimensional perovskite thin film with multiple quantum wells; The phase distribution of the thin film is determined by analyzing the first transient absorption spectrum set. Obtain the second transient absorption spectrum set of the thin film under each of the different parameter combinations; analyze all the second transient absorption spectrum sets based on the phase distribution to determine the optimal parameter combination; the parameter combination includes the pump light wavelength and the pump light power; the second transient absorption spectrum set includes the transient absorption spectrum of the front side of the thin film and the transient absorption spectrum of the back side of the thin film; Under the optimal parameter combination, the carrier spatial distribution information set of the front side of the thin film and the carrier spatial distribution information set of the back side of the thin film are obtained by using a transient absorption microscopy imaging system to detect the front and back sides of the thin film. Based on the carrier spatial distribution information set of the front side of the thin film and the carrier spatial distribution information set of the back side of the thin film, the monitoring results of carrier transport are determined. The carrier spatial distribution information set includes the photogenerated carrier density distribution at different delay times; the monitoring results are the results of the influence of phase distribution on carrier transport.

2. The method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells according to claim 1, characterized in that, Analyzing the first transient absorption spectrum set to determine the phase distribution of the thin film specifically includes: The content of each quantum well perovskite phase in the front of the film is obtained by integrating the ground state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the front of the film. The content of each quantum well perovskite phase in the reverse side of the film is obtained by integrating the ground state bleaching signal corresponding to each quantum well perovskite in the transient absorption spectrum of the reverse side of the film. The phase distribution of the thin film is determined based on the content of each quantum well perovskite phase in the front side and the content of each quantum well perovskite phase in the back side of the thin film. The phase distribution includes a higher proportion of large n phases in the front side of the thin film and a higher proportion of small n phases in the back side of the thin film. Large n phases are quantum well perovskite phases with n greater than or equal to a preset value, and small n phases are quantum well perovskite phases with n less than a preset value, where n is the number of two-dimensional perovskite inorganic layers.

3. The method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells according to claim 1, characterized in that, Before obtaining the second transient absorption spectrum set of the thin film under each of the different parameter combinations, the method further includes: selecting a preset wavelength for the pump light wavelength and selecting multiple values ​​for the pump light power to obtain multiple different parameter combinations.

4. The method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells according to claim 3, characterized in that, Based on the phase distribution, all the second transient absorption spectra are analyzed to determine the optimal parameter combination, specifically including: For each of the second transient absorption spectrum sets, the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 in the front side of the film are determined based on the transient absorption spectrum of the front side of the film, and the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 in the back side of the film are determined based on the transient absorption spectrum of the back side of the film; the ground-state bleaching peak dynamics are the curves showing the change of ground-state bleaching intensity with time delay. Based on the phase distribution, by comparing the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 on the front side of the film and the ground-state bleaching peak dynamics of the quantum well perovskite phase with n=3 on the back side of the film corresponding to all the second transient absorption spectrum sets, the pump power that can reflect the different carrier transfer processes caused by the phase distribution differences is determined, and the optimal parameter combination is obtained.

5. The method for monitoring carrier transport in a two-dimensional perovskite thin film with multiple quantum wells according to claim 1, characterized in that, The monitoring results of carrier transport are determined based on the carrier spatial distribution information sets on the front and back sides of the thin film, specifically including: By fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the front side of the thin film using a two-dimensional Gaussian function, the variance of the carrier Gaussian distribution at each delay time in the front side of the thin film is obtained. By fitting the photogenerated carrier density distribution at each delay time in the carrier spatial distribution information set on the back side of the thin film using a two-dimensional Gaussian function, the variance of the carrier Gaussian distribution at each delay time in the back side of the thin film is obtained. The carrier diffusion coefficient and carrier diffusion length of the front side of the thin film are calculated based on the variance of the Gaussian distribution of carriers at each delay time in the front side of the thin film. The carrier diffusion coefficient and carrier diffusion length of the back side of the thin film are calculated based on the variance of the Gaussian distribution of carriers at each delay time in the back side of the thin film. The monitoring results of carrier transport are determined by measuring the carrier diffusion coefficient and carrier diffusion length on the front and back sides of the thin film.

6. A computer system, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the steps of a method for monitoring carrier transport in a multi-quantum-well two-dimensional perovskite thin film as described in any one of claims 1-5.

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