Near-infrared perovskite laser and preparation method thereof

Abstract

The invention provides a near-infrared perovskite laser and a preparation method thereof. The near-infrared perovskite laser includes: a substrate; the perovskite gain dielectric layer is arranged on the substrate, a microcrystalline structure is formed on the perovskite gain dielectric layer, and the microcrystalline structure is a resonant cavity of the perovskite gain dielectric layer. The near-infrared perovskite laser provided by the invention can realize lasing under optical pumping at room temperature without adopting an additional resonant cavity, so that the device structure is greatly simplified, and the integration of the laser is improved; by regulating and controlling the components and the preparation process, the regulation of the lasing peak can be realized, the regulation precision is high, and the use requirements of multiple wavelengths can be met; a full-solution method can be adopted for preparation, the process is simple, and the cost is low.

Description

Technical Field

[0001] The invention relates to the field of perovskite lasers, and in particular to a near-infrared perovskite laser and a preparation method thereof. Background Art

[0002] Metal halide perovskite materials have the advantages of high fluorescence quantum efficiency, high light absorption coefficient, long carrier diffusion distance, adjustable band gap and solution preparation, showing great development potential in the field of optoelectronic devices. The efficiency of solar cells based on metal halide perovskite materials has exceeded 26%, which is comparable to traditional silicon solar cells and has become a leader in new solar cells. Perovskite light-emitting diodes (LEDs) have also developed rapidly in recent years. The external quantum efficiency of red and green devices has exceeded 25%, and the external quantum efficiency of blue LEDs has also exceeded 18%, showing great application potential in the future lighting and full-color display fields. In contrast, the development of perovskite lasers is relatively slow. Current research on perovskite lasers is mainly concentrated in the visible light range, especially the green light band, and there are few reports in the near-infrared band, especially the 860-910nm wavelength range.

[0003] Near-infrared solid-state lasers have important applications in laser communications, optical storage, optical information processing, etc. At present, near-infrared solid-state lasers are mainly based on III-V semiconductor materials, which usually require metal-organic chemical vapor deposition, molecular beam epitaxy and other methods to prepare, which are costly and difficult to make the lasing peak continuously adjustable. Therefore, it is urgent to develop near-infrared lasers that can be prepared by solution method, among which the development of wavelength-adjustable near-infrared perovskite lasers is of great significance. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a near-infrared perovskite laser and a preparation method thereof. The near-infrared perovskite laser can be prepared by a solution method, does not require an external resonant cavity, has a simple process, and has an adjustable wavelength.

[0005] On the one hand, an embodiment of the present invention provides a near-infrared perovskite laser, comprising: a substrate; a perovskite gain medium layer disposed on the substrate, a microcrystalline structure formed on the perovskite gain medium layer, and the microcrystalline structure is a resonant cavity of the perovskite gain medium layer.

[0006] In some embodiments, the microcrystalline structure includes a plurality of microcrystalline units, the plurality of microcrystalline units are separated from each other, and the shape of the microcrystalline units includes a leaf shape or a star shape.

[0007] In some embodiments, the excitation wavelength of the near-infrared perovskite laser is related to the composition of the perovskite gain medium layer.

[0008] In some embodiments, the composition of the perovskite gain medium layer includes A' y A1-y SnI3, the excitation wavelength of the near-infrared perovskite laser is related to the material of A', the material of A and the value of y in the components of the perovskite gain medium layer, where A' and A are two different organic cations, the size of A' is larger than A, and the value range of y is 0~1.

[0009] In some embodiments, the material A' in the composition of the perovskite gain medium layer includes phenylethylamine (PEA + ), p-fluorophenylethylamine (pF-PEA + )、m-Fluorophenylethylamine(mF-PEA + )、1-naphthylmethylamine(NMA + ) or butylamine (BA + The material A in the components of the perovskite gain medium layer includes methylamine (MA + ) or formamidine (FA + ); the value range of y is 0~0.6.

[0010] In some embodiments, the excitation wavelength of the near-infrared perovskite laser is in the range of 860 nm to 910 nm.

[0011] In some embodiments, the substrate includes a rigid substrate or a flexible substrate.

[0012] In some embodiments, the near-infrared perovskite laser further includes: an isolation layer disposed on the perovskite gain medium layer and covering the microcrystalline structure.

[0013] In some embodiments, the refractive index of the isolation layer ranges from 1.4 to 1.6.

[0014] On the other hand, an embodiment of the present invention also provides a method for preparing a near-infrared perovskite laser, comprising: spin coating a perovskite solution on a pretreated substrate, and then performing a thermal annealing treatment to form a perovskite gain medium layer with a microcrystalline structure, wherein the microcrystalline structure is a resonant cavity of the perovskite gain medium layer.

[0015] The near-infrared perovskite laser and the preparation method thereof provided by the embodiments of the present invention have at least the following beneficial effects:

[0016] (1) The near-infrared perovskite laser of the embodiment of the present invention uses the microcrystalline structure of the perovskite gain medium layer as a resonant cavity, and can achieve lasing under optical pumping at room temperature without using an external resonant cavity, which greatly simplifies the device structure and improves the integrability of the laser;

[0017] (2) The perovskite laser of the embodiment of the present invention can achieve adjustable lasing peak in the 860-910 nm band through the regulation of components and preparation process, and the adjustment accuracy is high, which can meet the use requirements of multiple wavelengths;

[0018] (3) The near-infrared perovskite laser of the embodiment of the present invention can be prepared by a full solution method, avoiding the need for conventional near-infrared semiconductor lasers to use complex metal-organic chemical vapor deposition, molecular beam epitaxy and other methods, which can significantly reduce costs and process complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0020] Figure 1 Schematically showing the structure of a near-infrared perovskite laser according to some embodiments of the present invention;

[0021] Figure 2 Schematically showing the structure of a near-infrared perovskite laser according to some embodiments of the present invention;

[0022] Figure 3 A flow chart schematically shows a method for preparing a near-infrared perovskite laser according to some embodiments of the present invention;

[0023] Figure 4 Schematically shows an emission spectrum diagram of a near-infrared perovskite laser according to an embodiment of the present invention;

[0024] Figure 5 Schematically shows an X-ray diffraction diagram of a perovskite gain medium (y=0.2) of a near-infrared perovskite laser according to an embodiment of the present invention;

[0025] Figure 6 A scanning electron microscopic image of a perovskite gain medium (y=0.2) of a near-infrared perovskite laser according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0026] The following examples are listed and described in detail with the accompanying drawings, but the examples provided are not intended to limit the scope of the present invention. In addition, the drawings are for illustration purposes only and are not drawn to their original size. For ease of understanding, the same elements will be described with the same symbols in the following description.

[0027] The terms "include", "including", "have", etc. used in this document are open terms, which means "including but not limited to".

[0028] In addition, the directional terms mentioned herein, such as "above", "below", etc., are only used to refer to the directions of the drawings and are not used to limit the present invention. Therefore, it should be understood that "above" can be used interchangeably with "below", and when an element such as a layer or film is placed "on" another element, the element can be placed directly on the other element, or there can be an intermediate element. On the other hand, when an element is said to be placed "directly" on another element, there is no intermediate element between the two.

[0029] In order to realize a low-cost, external cavity-free, wavelength-tunable near-infrared laser, the present invention proposes a wavelength-tunable near-infrared perovskite laser and a preparation method thereof. This laser can be prepared by a full solution method, does not require an external resonant cavity, and the excitation wavelength can cover the 860-910 nm near-infrared band, and the wavelength is adjustable.

[0030] See also Figure 1 , Figure 1 The structure of a near-infrared perovskite laser 100 according to some embodiments of the present invention is schematically shown. The near-infrared perovskite laser 100 may include a substrate 110 and a perovskite gain medium layer 120 .

[0031] In some embodiments, the substrate 110 may be a rigid substrate. For example, it may be a quartz wafer or a silicon wafer. In some embodiments, the substrate 110 may be a flexible substrate. For example, it may be a substrate made of polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyimide (PI). The flexible thin film laser prepared on the flexible substrate has great application potential in manufacturing various sensors in water or biological solutions.

[0032] A perovskite gain medium layer 120 is disposed on the substrate 110, and a microcrystalline structure 121 is formed on the perovskite gain medium layer 120. In this article, microcrystals refer to micron-sized crystals, which can be grown by controlling process parameters when preparing the perovskite gain medium layer 120. The microcrystalline structure 121 can serve as a resonant cavity of the perovskite gain medium layer 120. In other words, the perovskite gain medium layer 120 can simultaneously serve as a gain medium and a resonant cavity of the near-infrared perovskite laser 100. In this way, the near-infrared perovskite laser 100 can achieve lasing under optical pumping at room temperature without the use of an external resonant cavity, which greatly simplifies the device structure and improves the integrability of the laser.

[0033] It should be noted that Figure 1The region of the microcrystalline structure 121 shown in the figure is only an example and is not used to limit the position of the microcrystalline structure 121. In fact, the microcrystalline structure 121 can be formed on the entire perovskite gain medium layer 120. In other words, the perovskite gain medium layer 120 has a microcrystalline morphology, and the microcrystalline morphology can be grown when the perovskite gain medium layer 120 is prepared.

[0034] Please continue reading Figure 1 , Figure 1 A partially enlarged top view of the microcrystalline structure 121 is shown (located at Figure 1 inside the dotted circle), which is equivalent to Figure 1 A view looking down from above.

[0035] exist Figure 1 In the partially enlarged top view in the figure, the microcrystalline structure 121 may include a plurality of microcrystalline units 121a, 121b, and these microcrystalline units 121a, 121b are separated from each other. Separated from each other means that there is a certain interval between each microcrystalline unit. The shape of the microcrystalline units 121a, 121b can be a leaf-like shape (such as microcrystalline unit 121a), or a star-like shape such as a cross, a five-pointed star, or a hexagon (microcrystalline unit 121b). The shape of the microcrystalline unit refers to the surface morphology of the microcrystal seen under an optical microscope or a scanning electron microscope. Understandably, Figure 1 The number, size and shape of the microcrystalline units shown are only examples and are not intended to limit the number, size and shape of the microcrystalline units. Microcrystalline structures of different sizes and morphologies can provide different gain effects.

[0036] Perovskite generally refers to a class of compounds with a general formula of ABX3, where A usually refers to a monovalent cation, B refers to a divalent metal cation, and X refers to a halogen anion. In the embodiment of the present invention, the excitation wavelength of the near-infrared perovskite laser 100 can be changed by changing the composition of the perovskite gain medium layer 120, that is, by changing the composition and proportion of A, B, and X in the traditional ABX3 structure to achieve different emission wavelengths.

[0037] In some embodiments, the composition of the perovskite gain medium layer 120 in the near-infrared perovskite laser 100 may be A' y A 1-y SnI3, where A' and A are two different organic cations, the size of A' is larger than A, and the value range of y is 0~1. A' y A 1-y A' in SnI3 y A 1-y Corresponding to A, A' in the traditional ABX3 structure y A 1-y Sn (tin) in SnI3 corresponds to B, A' in the traditional ABX3 structurey A 1-y I (iodine) in SnI3 corresponds to X in the traditional ABX3 structure. In some embodiments, A' y A 1-y The materials of A' in SnI3 include but are not limited to phenylethylamine (PEA + ), p-fluorophenylethylamine (pF-PEA + )、m-Fluorophenylethylamine(mF-PEA + )、1-naphthylmethylamine(NMA + ) or butylamine (BA + ); A' y A 1-y The materials A in SnI3 include methylamine (MA + ) or formamidine (FA + ); the value range of y can be further set to 0~0.6, where y can be equal to 0 or 0.6. For example, A' y A 1-y SnI3 can be ASnI3 (y=0), A' 0.2 A 0.8 SnI3(y=0.2)、A' 0.6 A 0.4 SnI3 (y=0.6), etc. In this embodiment, by changing A' y A 1-y The material of A', the material of A and the value of y in SnI3 can adjust the band gap of the perovskite, thereby realizing the regulation of the excitation wavelength of the near-infrared perovskite laser 100. Specifically, the excitation wavelength of the near-infrared perovskite laser 100 can be regulated between 860 nm and 910 nm, with an adjustment accuracy of less than 5 nm, and the quality factor of the laser is greater than 1000.

[0038] As an example, A' y A 1-y A' in SnI3 can be PEA + , A can be FA + , y can be 0.2, then the component of the perovskite gain medium layer 120 can be PEA 0.2 FA 0.8 SnI3, 20% PEA + and 80% of FA + That is, the organic cation A in the traditional ABX3 structure is equivalent to PEA 0.2 FA 0.8 20% PEA in SnI3 + and 80% of FA + .PEA +The introduction of cations of equal size can reduce the perovskite from a three-dimensional (3D) structure to a mixture of two-dimensional (2D) and three-dimensional perovskite phases, forming a quasi-two-dimensional structure. The presence of the 2D phase on the surface of the perovskite particles acts as a barrier, effectively blocking the entry of oxygen and water molecules, preventing the discharge of decomposition products, and improving the long-term stability of the perovskite film. y A 1-y The use of Sn (tin) as metal B in SnI3 in the traditional ABX3 structure can narrow the band gap of metal halide perovskite materials, red-shift the emission peak, achieve luminescence in the near-infrared region, and obtain perovskite lasers in the near-infrared band above 860 nm, which is difficult to achieve using conventional lead (Pb)-based metal halide perovskite materials.

[0039] See also Figure 2 , Figure 2 The structure of a near-infrared perovskite laser 200 according to some embodiments of the present invention is schematically shown. Figure 1 and Figure 2 The same number is used for the same components. The main difference between the near-infrared perovskite laser 200 and the near-infrared perovskite laser 100 is that an isolation layer 130 is provided on the perovskite gain medium layer 120, and the isolation layer 130 covers the microcrystalline structure ( Figure 2 not shown).

[0040] In an aerobic environment, A' y A 1-y Sn in SnI3 2+ Very easily oxidized to Sn 4+ , leaving the unnecessary Sn 2+ Vacancies become non-radiative recombination centers, quench radiation, and cause great attenuation of the luminescence performance of perovskite films and devices. The isolation layer 130 can isolate the perovskite layer from water, oxygen, and the external solvent atmosphere, significantly improving the stability of the Sn-based perovskite film. In some embodiments, the refractive index range of the isolation layer 130 is 1.4 to 1.6, which can make the transmittance of the 800 nm-1000 nm band greater than 97%. As an example, the isolation layer 130 can be polymethyl methacrylate or NOA UV curing glue, which has a high transmittance, can be prepared by a solution method, has a simple process, does not require high-temperature treatment, and will not damage the perovskite layer.

[0041] See also Figure 3 , Figure 3 The flowchart of the method for preparing a near-infrared perovskite laser according to some embodiments of the present invention is schematically shown. The method for preparing a near-infrared perovskite laser may include operation S310.

[0042] In operation S310 , after spin coating the perovskite solution on the pre-treated substrate 110 , a thermal annealing process is performed to form a perovskite gain medium layer 120 with a microcrystalline structure 121 . The microcrystalline structure 121 is a resonant cavity of the perovskite gain medium layer 120 .

[0043] Specifically, the substrate 110 may be a quartz wafer, a silicon wafer, polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or polyimide (PI). The pretreatment may be a cleaning treatment. For example, the substrate 110 may be treated with ultraviolet ozone for 10-30 minutes, and the grease and organic matter on the surface of the substrate 110 may be oxidized and removed by ultraviolet light and ozone to achieve a cleaning effect; at the same time, the hydrophilicity and hydrophobicity of the surface of the substrate 110 may be changed to facilitate spin coating of the solution. The perovskite solution has A' y A 1-y SnI3 component. The meanings and materials of A' and A have been explained in the previous text and will not be repeated here. The solvent of the perovskite solution can be a mixed solution of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), and the concentration of the perovskite solution is 0.2~1 M. The annealing temperature of the thermal annealing treatment can be 60~80 degrees Celsius, and the annealing time is 5~15 min. The above-mentioned polar solvent can be removed by thermal annealing and drying treatment. In the process of solvent removal, the perovskite material is supersaturated, causing nucleation and crystal growth to form a perovskite gain medium layer 120 with a microcrystalline structure 121.

[0044] It should be emphasized that the method for preparing the near-infrared perovskite laser provided by the embodiment of the present invention does not need to drip an anti-solvent on the substrate during the spin coating of the perovskite solution. In the conventional preparation of perovskite thin films, chlorobenzene, toluene and other solvents are usually dripped on the substrate as anti-solvents during the spin coating of the perovskite precursor solution. However, the present invention does not use an anti-solvent, which can slow down the nucleation and growth process of the perovskite, so that it forms a discrete microcrystalline structure. This specific crystal morphology can enable the near-infrared perovskite laser provided by the embodiment of the present invention to achieve lasing without an external resonant cavity.

[0045] In some embodiments, by implementing the preparation method provided in operation S310, a Figure 1 The near-infrared perovskite laser 100 shown in FIG. 1 is a near-infrared perovskite laser 100. In some embodiments, the isolation layer 130 may be further prepared based on operation S310 to obtain Figure 2 A near-infrared perovskite laser 200 is shown.

[0046] Specifically, the isolation layer solution may be spin-coated on the perovskite gain medium layer 120 and dried to obtain the isolation layer 130 .

[0047] For example, a chlorobenzene solution of polymethyl methacrylate or an isolation layer solution such as NOA UV curing glue can be spin-coated on the perovskite gain medium 120 prepared in operation S310, and then dried to form an isolation layer 130 to obtain a near-infrared perovskite laser 200. The drying temperature is 40 to 80 degrees Celsius and the time is 3 to 10 minutes. The refractive index of the isolation layer 130 is 1.4-1.6, and the transmittance in the 800 nm-1000 nm band is greater than 97%.

[0048] Example

[0049] (1) Prepare perovskite precursor solution

[0050] Prepare 1 mL of PEA y FA 1-y SnI3 perovskite solution, the solvent is 800 μL DMF + 200 μL DMSO, the concentration is 0.8 M. The molar ratio of PEAI, FAI, SnI2, SnF2 is 0:1:1:0.075 (y=0) or 0.1:0.9:1:0.075 (y=0.1) or 0.15:0.85:1:0.075 (y=0.15) or 0.2:0.8:1:0.075 (y=0.2) or 0.3:0.7:1:0.075 (y=0.3) or 0.4:0.6:1:0.075 (y=0.4), stirred and dissolved to obtain a perovskite precursor solution.

[0051] (2) Preparation of perovskite lasers

[0052] The quartz substrate 110 was ultrasonically cleaned with detergent water, deionized water, acetone and isopropanol solution for 20 minutes in sequence, and then dried with nitrogen gas, and then placed in a UV ozone cleaning machine for 15 minutes.

[0053] The substrate 110 is moved into a glove box and the perovskite precursor solution is spin-coated at a rotation speed of 1000 rpm for 10 s + 5000 rpm for 30 s. The sample is then placed on a hot stage and annealed at 70 degrees Celsius for 10 minutes to form a perovskite gain medium layer 120 having a microcrystalline structure 121, and the perovskite laser 100 can be obtained.

[0054] After annealing, a chlorobenzene solution of polymethyl methacrylate (with a concentration of 20 mg / mL) is spin-coated, followed by drying at 40 degrees Celsius for 3 minutes to form an isolation layer 130 , and then the preparation of the perovskite laser 200 can be completed.

[0055] See also Figure 4 , Figure 4 The emission spectrum of the near-infrared perovskite laser according to an embodiment of the present invention is schematically shown.

[0056] Figure 4The horizontal axis represents wavelength in nm, and the vertical axis represents normalized intensity in au. It can be seen that by using the near-infrared perovskite laser provided by the embodiment of the present invention, a series of lasing peaks are obtained in the wavelength range of 860-910 nm, and the peak position can be adjusted in this range with an adjustment accuracy of less than 5 nm. The half-width of the lasing peak can be obtained from the lasing spectrum, and the quality factor of the laser can be calculated. The maximum quality factor of the near-infrared perovskite laser is 1251. Please refer to Figure 5 , Figure 5 The X-ray diffraction pattern (XRD) of the perovskite gain medium (y=0.2) of the near-infrared perovskite laser according to an embodiment of the present invention is schematically shown.

[0057] Figure 5 The horizontal axis represents the angle (degree), the unit is degree, and the vertical axis represents the intensity (intensity), the unit is au. y A 1-y The y of SnI3 is 0.2. It can be seen that the perovskite gain medium has good crystallinity when the near-infrared perovskite laser provided by the embodiment of the present invention is used.

[0058] See also Figure 6 , Figure 6 A scanning electron microscopic image (SEM) of a perovskite gain medium (y=0.2) of a near-infrared perovskite laser according to an embodiment of the present invention is schematically shown.

[0059] A' in perovskite gain media y A 1-y The y of SnI3 is 0.2. It can be seen that the perovskite gain medium forms a large number of leaf-shaped or star-shaped microcrystals. These microcrystals spontaneously form a resonant cavity without the need for an external resonant cavity, and microcrystal regions of different sizes and morphologies can provide different gain effects.

[0060] At this point, a near-infrared perovskite laser and its preparation method have been introduced. According to multiple embodiments, the near-infrared perovskite laser of the present invention can be prepared by a full solution method, avoiding the need for conventional near-infrared semiconductor lasers to use complex metal-organic chemical vapor deposition, molecular beam epitaxy and other methods, which can significantly reduce costs and process complexity; through the regulation of components and preparation processes, the lasing peak can be adjusted in the 860-910 nm band with high adjustment accuracy, which can meet the use requirements of multiple wavelengths; the perovskite laser prepared by the present invention does not require an external resonant cavity, and can achieve lasing under optical pumping at room temperature, which greatly simplifies the device structure and improves the integrability of the laser.

[0061] In summary, although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. A person skilled in the art to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the attached claims.

Claims

1. A near-infrared perovskite laser, characterized in that: include: substrate; A perovskite gain medium layer is disposed on the substrate, a microcrystalline structure is formed on the perovskite gain medium layer, and the microcrystalline structure is a resonant cavity of the perovskite gain medium layer.

2. The near-infrared perovskite laser according to claim 1, characterized in that: The microcrystalline structure includes a plurality of microcrystalline units, the plurality of microcrystalline units are separated from each other, and the shape of the microcrystalline unit includes a leaf shape or a star shape.

3. The near-infrared perovskite laser according to claim 1, characterized in that: The excitation wavelength of the near-infrared perovskite laser is related to the composition of the perovskite gain medium layer.

4. The near-infrared perovskite laser according to claim 3, characterized in that: The components of the perovskite gain medium layer include A' y A 1-y SnI3, the excitation wavelength of the near-infrared perovskite laser is related to the material of A', the material of A and the value of y in the components of the perovskite gain medium layer, wherein A' and A are two different organic cations, the size of A' is larger than A, and the value range of y is 0~1.

5. The near-infrared perovskite laser according to claim 4, characterized in that: The material A' in the components of the perovskite gain medium layer includes phenylethylamine (PEA + ), p-fluorophenylethylamine (pF-PEA + )、m-Fluorophenylethylamine(mF-PEA + )、1-naphthylmethylamine(NMA + ) or butylamine (BA + ); The material A in the components of the perovskite gain medium layer includes methylamine (MA + ) or formamidine (FA + ); The value range of y is 0~0.

6.

6. The near-infrared perovskite laser according to claim 5, characterized in that: The excitation wavelength of the near-infrared perovskite laser is in the range of 860 nm to 910 nm.

7. The near-infrared perovskite laser according to claim 1, characterized in that: The substrate includes a rigid substrate or a flexible substrate.

8. The near-infrared perovskite laser according to claim 1, characterized in that: Also includes: The isolation layer is disposed on the perovskite gain medium layer and covers the microcrystalline structure.

9. The near-infrared perovskite laser according to claim 8, characterized in that: The refractive index of the isolation layer is in the range of 1.4 to 1.

6.

10. A method for preparing a near-infrared perovskite laser according to any one of claims 1 to 9, characterized in that: include: After the perovskite solution is spin-coated on the pretreated substrate, a thermal annealing treatment is performed to form a perovskite gain medium layer with a microcrystalline structure, wherein the microcrystalline structure is a resonant cavity of the perovskite gain medium layer.

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