CN115663569B - Method of using laser irradiation to enhance random laser emission characteristics of perovskite microcrystals - Google Patents

Abstract

The invention provides a method for using laser irradiation to enhance the random laser emission characteristics of perovskite microcrystals, which includes the following steps: S1. Fix the perovskite film on a precision three-dimensional moving platform; S2. Use femtosecond laser pulses to The surface of the titanium film is scanned to induce compressive stress in the perovskite film to balance the residual tensile strain present inside the perovskite film, as well as to induce crystal melting and grain cluster edges in the perovskite film. The secondary crystallization effect reduces the distance between grain clusters in the perovskite film. The present invention can improve the surface properties of perovskite films without any other treatment other than femtosecond laser, including: residual strain change, increase in grain clusters, reduction in grain cluster spacing, and passivation of surface recombination centers. , effectively reducing the random laser oscillation threshold of the perovskite film and increasing the laser emission intensity. This method is expected to promote the application of perovskite materials in the fields of lasers, light-emitting diodes and other light-emitting devices.

Description

Method of using laser irradiation to enhance random laser emission characteristics of perovskite microcrystals

Technical field

The invention relates to the field of laser processing technology, and in particular to a method that utilizes femtosecond laser irradiation to cure surface defects and bulk defects of a perovskite film, and enhances the perovskite by increasing the size of grain clusters and reducing the distance between grain clusters. Methods for random laser emission characteristics of microcrystals.

Background technique

Miniaturized high-performance laser light sources have always been popular devices in the field of lighting. Thanks to its miniaturization characteristics, there is great development prospect in integrating it into various optoelectronic systems, such as photoelectric sensing and high-resolution imaging. As a very promising optical gain medium, perovskite materials rely on their high absorption coefficient, large gain coefficient, high defect tolerance, long carrier lifetime, easy integration into different substrates using solution processing, and throughout the Broad-band tunability in the visible spectrum has attracted great attention from domestic and foreign researchers in recent years in the manufacture of micro-laser sources.

In the past few years, people have conducted extensive research on the random laser emission characteristics of perovskite materials, which can be roughly divided into three categories: 1. In-plane crystal plate structure lasers using the whispering gallery effect; 2. Using nanowires Fabry-Perot cavity lasers realized with microelectrode structures; 3. Vertical cavity surface-emitting lasers (VCSELs) realized using distributed feedback Bragg (DFB) gratings. However, these extremely small-sized microcavities and VCSEL devices require expensive and complex fabrication equipment, as well as limited control over perovskite crystal growth and its lasing.

In order to take full advantage of the convenient preparation of perovskite materials, while simplifying the preparation process and reducing preparation costs, the development of polycrystalline films with randomly arranged grains has become the preferred form of light-emitting devices. At present, relevant researchers have used spin coating methods to prepare perovskite lasers. The perovskite microcrystalline structure causes multiple scattering of laser light, resulting in higher optical gain and emission output, and its characteristics are similar to ordinary lasers. Usually, the spatial confinement of light in perovskites is achieved by utilizing the strong scattering effect produced by multiple light cycles at the material grain boundaries. This phenomenon helps achieve laser inversion conditions and provides sufficient light amplification.

However, various surface defects and bulk defects generated during the formation of perovskite films act as nonradiative recombination centers and hinder the filling of carriers in the excited state. In addition, if the bonding between grain clusters in the perovskite film is not tight enough, the larger grain cluster spacing will lead to significant out-of-plane scattering loss, thus increasing the emission threshold of random laser. In order to develop efficient light-emitting and optoelectronic devices, effective advanced technologies need to be developed to suppress the above-mentioned common problems. In order to reduce the defect density on the material surface, researchers have widely adopted surface engineering treatment technologies, such as using various additives to passivate the film surface. However, this method requires precise control of the amount and addition sequence of additives, complicated operations, and excessive additives are difficult to remove. In order to achieve batch modification of body defects, people use high-energy ultraviolet, near-infrared and solar light to cure body defects. However, this method takes a long time to operate, and excessive light intensity may cause permanent damage to the material. Therefore, the industry is currently in urgent need of a simple, fast, and efficient method to regulate the surface passivation and crystal structure of perovskite films to reduce the body defect density.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a method of using laser irradiation to enhance the random laser emission characteristics of perovskite microcrystals to precisely control the surface structure of polycrystalline films through femtosecond laser irradiation. Inducing crystal melting and secondary crystallization makes the perovskite grain clusters more closely arranged, and the in-plane multiple scattering at the grain cluster interface is increased, thereby reducing the out-of-plane scattering of random laser oscillation in the perovskite film. Loss, improving the random laser emission intensity of the material.

In order to achieve the above objects, the present invention adopts the following specific technical solutions:

The method provided by the present invention for using laser irradiation to enhance the random laser emission characteristics of perovskite microcrystals includes the following steps:

S1. Fix the perovskite film on a precision three-dimensional moving platform;

S2. Use femtosecond laser pulses to scan the surface of the perovskite film to induce compressive stress in the perovskite film to balance the residual tensile strain existing inside the perovskite film and induce stress in the perovskite film. Produce crystal melting and secondary crystallization effects at the edges of grain clusters, reducing the distance between grain clusters in the perovskite film.

Preferably, the width of the femtosecond laser pulse is less than 10 ^-13 s, the center wavelength is 800nm, and the laser flux is 10mJ/cm ² -120mJ/cm ² .

Preferably, the femtosecond laser pulse completely releases the residual tensile strain in the perovskite film and induces additional compressive stress inside the perovskite film. The pressure amplitude value of the additional compressive stress is -12.4± 1.1MPa.

Preferably, the random laser oscillation threshold of the perovskite film is reduced from 11.54 μJ/cm ² to 0.92 μJ/cm ² .

Preferably, the random laser luminescence efficiency of the perovskite film is increased from eta ~ 150 to eta ~ 2398.

Preferably, the grain cluster spacing of the perovskite film is reduced by 20 nm.

Preferably, the perovskite film is a MAPbBr _{polycrystalline} film.

Preferably, after step S2, the following steps are also included:

S3. Use blue femtosecond laser pulses with a pulse width less than 10 ^-13 s and a central wavelength of 400 nm to irradiate the perovskite film to excite the perovskite film to generate random laser light.

The present invention can achieve the following technical effects:

(1) The compressive stress induced by irradiating the perovskite film with femtosecond laser pulses is used to balance the residual tensile strain generated in the perovskite film during the spin coating process. When the flux of the femtosecond laser pulse is from 10mJ/ ^cm to 120mJ/ ^cm , compressive stresses of different strengths can be obtained.

(2) Femtosecond laser pulse irradiation treatment with a luminous flux of 10mJ/ ^cm2 is used to induce a compressive stress of -12.4±1.1MPa, thereby passivating the non-radiative recombination center of the perovskite film body.

(3) Passivation of the nonradiative recombination center delays the lifetime of excited carriers in the perovskite film by ∼371.35% and is conducive to higher photoluminescence rates.

(4) The surface of MAPbBr ₃ film treated with femtosecond laser pulse irradiation shows enhanced random laser emission behavior, such as lower laser threshold and higher luminous efficiency. The random laser generation threshold of the material is reduced from 11.54 μJ/cm ² to 0.92 μJ/cm ² , and the luminous efficiency is significantly increased from eta ~ 150 to eta ~ 2398.

(5) After femtosecond laser pulse irradiation treatment, the distance between grain clusters of the perovskite film is reduced by 20nm, which reduces the out-of-plane scattering loss during random laser emission in the perovskite film, thereby helping to improve randomness. The output intensity of the laser.

Description of the drawings

Figure 1 is a flow chart of a method for enhancing the random laser emission characteristics of perovskite microcrystals by using laser irradiation provided by the present invention.

Figure 2a is a scanning electron microscope image of the surface of a MAPbBr ₃ film without femtosecond laser pulse irradiation, which particularly shows a significantly larger spacing between adjacent grain clusters.

Figure 2b is a scanning electron microscope image of the surface of a MAPbBr ₃ film treated with femtosecond laser pulse irradiation, which particularly shows that the spacing between grain clusters is reduced by 20 nm.

Figure 3a is a map of random laser emission sites on the surface of a MAPbBr ₃ film that has not been irradiated with femtosecond laser pulses.

Figure 3b is a diagram of random laser emission sites with enhanced intensity on the surface of the MAPbBr ₃ film treated with femtosecond laser pulse irradiation.

Figure 4a shows the residual stress measurement using the d~sin2(ψ) method on the surface of MAPbBr ₃ films without and after femtosecond laser pulse irradiation treatment, where the positive slope and negative slope represent tensile stress and compressive stress respectively.

Figure 4b shows the residual stress value of each sample extracted from Figure 4a. The sample without laser irradiation shows tensile stress, while the tensile stress of the sample after femtosecond laser irradiation continues to decrease and eventually transforms into of compressive stress.

Figure 5a shows the steady-state photoluminescence measurement of the MAPbBr ₃ film surface without and after femtosecond laser pulse irradiation treatment. The sample surface after laser irradiation treatment shows enhanced photoluminescence behavior.

Figure 5b shows time-resolved photoluminescence measurements corresponding to the surface of the MAPbBr ₃ film without and after femtosecond laser pulse irradiation treatment.

Figure 5c shows the average lifetime (τ _avg ) of carriers in the material extracted from Figure 5b, which shows that femtosecond laser pulse treatment extends the lifetime of carriers, where the irradiation flux is 10mJ/cm ² . The lower sample surface shows an increase of ~371.35%.

Figure 6a shows the output spectral bandwidth of the MAPbBr ₃ film when it is greater than the random laser threshold without and after femtosecond laser irradiation treatment.

Figure 6b shows the change in luminescence intensity of the MAPbBr ₃ film without and after femtosecond laser irradiation treatment, where the position of sudden intensity increase represents the emission threshold of the random laser.

Detailed ways

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are designated with the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, its detailed description will not be repeated.

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and do not constitute limitations of the present invention.

Perovskite materials undergo large tensile strains during annealing and subsequent cooling, which is mainly attributed to the different thermal expansion coefficients of the film and the underlying substrate material. These strains can lead to the formation of defects on the surface and body of the material, further causing non-radiative recombination of carriers. Femtosecond laser irradiation can induce compressive strains within the material to balance residual tensile strains in the film. The femtosecond laser flux range is from 10mJ/ ^cm2 to 120mJ/ ^cm2 , which is used to balance the different tensile strains remaining inside the film. The total residual stress can be calculated from the XRD test results. The research results found that the tensile stress (expressed by a positive slope) inside the sample gradually decreased after femtosecond laser treatment and converted into compressive stress (expressed by a negative slope). This proves that there is basically a linear relationship between the residual stress change inside the perovskite film and the femtosecond laser flux. When the femtosecond laser flux is 10mJ/ ^cm2 , the tensile stress of 18.6±1.9MPa existing in the processed sample is completely released, and an additional lower compressive stress of -12.4±1.1MPa is introduced. When the femtosecond laser flux is 120mJ/ ^cm2 , it further increases to -38.0±4MPa. After the additional compressive stress induced by the femtosecond laser, the measured steady-state photofluorescence intensity is significantly enhanced. Time-resolved photoluminescence measurements from the sample surface confirmed that the excited carrier lifetime of the material was significantly extended by ∼371.35% after femtosecond laser irradiation treatment. This is attributed to the healing of nonradiative composite defects by femtosecond laser-induced compressive stress and strain.

The room temperature fluorescence characteristics test results of MAPbBr ₃ film samples show that when the excitation light flux is lower than the luminescence threshold, the fluorescence center spectrum is 533nm and the line width is ~29nm. When the excitation light flux reaches the random laser emission threshold, the fluorescence center spectrum is 549nm, and the linewidth decreases sharply to ~3.0nm. At the same time, the high excitation flux significantly enhances the luminescence peak intensity. The random laser intensity output by the sample treated by femtosecond laser irradiation is significantly higher than that of the untreated sample. At the random laser energy threshold, there is a clear transition between the decrease in spectral linewidth and the increase in output intensity. Compared with the untreated MAPbBr ₃ film sample, the random laser emission threshold of the sample after femtosecond laser treatment was significantly reduced from 11.54 μJ/cm ² to 0.92 μJ/cm ² . Through linear fitting, the growth rate of the random laser output intensity relative to the irradiation treatment luminous flux can be obtained, which is called the luminous efficiency (η) here. After femtosecond laser treatment, the η value of the sample increased significantly, and the sample treated under 10mJ/cm ² light flux conditions had the best performance, and its corresponding eta value was ~2398, almost the same as the untreated sample (η ~150) 15 times. This shows that femtosecond laser irradiation treatment is an effective method to achieve high-brightness random laser emission.

As shown in Figure 1, the method provided by the present invention for enhancing the random laser emission characteristics of perovskite microcrystals by using femtosecond laser irradiation treatment includes the following steps:

S1. Fix the perovskite film on a precision three-dimensional moving platform.

The perovskite film is driven by a precision three-dimensional moving platform to scan the perovskite film with femtosecond laser.

S2. Use femtosecond laser pulses to scan the surface of the perovskite film to induce compressive stress in the perovskite film to balance the residual tensile strain existing inside the perovskite film and induce stress in the perovskite film. Produce crystal melting and secondary crystallization effects at the edges of grain clusters, reducing the distance between grain clusters in the perovskite film.

On the surface of the perovskite film, a near-infrared femtosecond laser beam with a light flux of 10mJ/ ^cm2 to 120mJ/ ^cm2 is irradiated to induce a recrystallization process around the grain boundaries, thereby inducing a certain amount of The degree of compressive stress weakens and offsets the residual tensile strain generated during film spin coating. At the same time, because the femtosecond laser irradiation process induces crystal melting and secondary crystallization effects at the edges of grain clusters, the spacing between grain clusters in the material is reduced by 20 nm, reducing the risk of random laser oscillation in the perovskite film. Out-of-plane scattering loss.

In step S2, the residual tensile stress in the sample after femtosecond laser irradiation is completely released, and an additional compressive stress with a pressure amplitude of -12.4±1.1MPa is induced. In addition, by passivating the non-radiative recombination center of the body, the photoluminescence effect of the perovskite film is also improved, and compared with the case without femtosecond laser treatment, the average lifetime of carriers in the perovskite film is improved is extended, which provides a suitable inversion condition for the material to emit light.

Use a blue femtosecond laser pulse with a central wavelength of 400nm and a pulse width of less than 10 ^-13 s as a pump source to excite the perovskite film treated by infrared femtosecond laser irradiation. When the pump light energy is appropriate, Random laser generation of the material was observed.

After femtosecond laser irradiation treatment, the reduction of non-radiative recombination centers in the material and the reduction of the spacing between grain clusters reduce the laser generation threshold of the perovskite film by more than one order of magnitude, that is, from 11.54 μJ/cm ² to 0.92μJ/cm ² . In addition, the luminous efficiency of the perovskite film also increased from eta ~ 150 to eta ~ 2398, which shows that femtosecond laser irradiation treatment can significantly increase the random laser emission intensity of the material.

Example 1

This Example 1 provides a method of using femtosecond laser irradiation treatment to enhance the random laser emission characteristics of perovskite crystallites for precise surface treatment and crystal structure modification of MAPbBr ₃ polycrystalline films, which specifically includes the following step.

S1. Fix the MAPbBr ₃ polycrystalline film on a precision three-dimensional moving platform.

The platform movement accuracy is ±3μm, and the movement process is controlled by a computer program.

S2. Use near-infrared femtosecond laser to irradiate the MAPbBr ₃ polycrystalline film to change its crystal structure characteristics.

The irradiation light source adopts a sapphire femtosecond laser pulser with a central wavelength of 800nm, a pulse width of 40fs, and a repetition frequency of 1kHz. The incident light flux was adjusted to 10mJ/cm ² . A spherical lens with a focal length of 200 mm is used to focus to form a focused spot with a diameter of 250 μm, and the surface of the MAPbBr ₃ polycrystalline film is scanned. The moving speed of the precision three-dimensional mobile platform is 1mm/s. After femtosecond laser irradiation treatment, Figure 2b shows that the spacing between grain clusters of the MAPbBr ₃ polycrystalline film is reduced by about 20 nm. Compared with Figure 2a, the spacing between adjacent grain clusters is significantly reduced.

Experimental results show that under femtosecond laser pumping conditions with a central wavelength of 400 nm, the random laser emission intensity of the perovskite film sample (see Figure 3a) has been significantly improved after femtosecond laser treatment, as shown in Figure 3b.

Example 2

This embodiment 2 provides a method of using femtosecond laser irradiation treatment to enhance the random laser emission characteristics of perovskite microcrystals.

Referring to the preparation method of Example 1, by introducing the compressive stress generated by femtosecond laser treatment, the residual tensile stress during the formation of the perovskite film is released, as shown in Figures 4a and 4b. Different from Example 1, the perovskite film was irradiated using femtosecond laser pulses with a luminous flux of 20 mJ/ ^cm , and the steady-state photoluminescence performance of the material surface was enhanced, as shown in Figure 5a. At the same time, as shown in Figure 5b and Figure 5c, the average lifetime of excited carriers inside the material increases by ~371.35%.

Example 3

This Example 3 provides a method for enhancing the random laser luminescence characteristics of perovskite microcrystals by using femtosecond laser irradiation treatment. Referring to the preparation method of Example 1, under the action of pump light with a central wavelength of 400 nm, perovskite crystallites The random laser characteristics (including laser threshold and luminous efficiency) of the mineral film are enhanced when the luminous flux is 10mJ/ ^cm2 . As shown in Figure 6a and Figure 6b. After femtosecond laser irradiation treatment, the random laser emission threshold of the perovskite film decreased from 11.54 μJ/cm ² to 0.92 μJ/cm ² . At the same time, the luminous efficiency increases from eta = ~150 to eta = ~2398.

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "an example," "specific examples," or "some examples" or the like means that specific features are described in connection with the embodiment or example. , structures, materials or features are included in at least one embodiment or example of the invention. In this specification, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine different embodiments or examples and features of different embodiments or examples described in this specification unless they are inconsistent with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above-mentioned embodiments are illustrative and should not be construed as limitations of the present invention. Those of ordinary skill in the art can make modifications to the above-mentioned embodiments within the scope of the present invention. The embodiments are subject to changes, modifications, substitutions and variations.

The above specific embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (5)

1. A method of using laser irradiation to enhance the random laser emission characteristics of perovskite crystallites, which is characterized by comprising the following steps: S1. Fix the perovskite film on a precision three-dimensional moving platform. The perovskite film is a MAPbBr ₃ polycrystalline film; S2. Use femtosecond laser pulses to scan the surface of the perovskite film to induce compressive stress in the perovskite film to balance the residual tensile strain existing inside the perovskite film, and in The perovskite film induces crystal melting and secondary crystallization effects at the edges of grain clusters to reduce the spacing between grain clusters in the perovskite film; wherein the width of the femtosecond laser pulse is less than 10 ^{- 13} s, the center wavelength is 800nm, and the laser flux is 10mJ/cm ² -120mJ/cm ² ; the femtosecond laser pulse completely releases the residual tensile strain in the perovskite film and induces the The perovskite film generates additional compressive stress inside, and the pressure amplitude of the additional compressive stress is -12.4±1.1MPa. 2. The method of utilizing laser irradiation to enhance random laser emission characteristics of perovskite crystallites as claimed in claim 1, characterized in that the random laser oscillation threshold of the perovskite film is reduced from 11.54 μJ/ ^cm to 0.92 μJ/cm ² . 3. The method of utilizing laser irradiation to enhance the random laser emission characteristics of perovskite microcrystals as claimed in claim 1, characterized in that the random laser luminescence efficiency of the perovskite film is increased from eta to 150 to eta to 2398. . 4. The method of using laser irradiation to enhance the random laser emission characteristics of perovskite microcrystals according to claim 1, characterized in that the grain cluster spacing of the perovskite film is reduced by 20 nm. 5. The method of utilizing laser irradiation to enhance random laser emission characteristics of perovskite microcrystals as claimed in claim 1, characterized in that, after step S2, it also includes the following steps: S3. Use blue femtosecond laser pulses with a pulse width less than 10 ^-13 s and a central wavelength of 400 nm to irradiate the perovskite film to excite the perovskite film to generate random laser light.