Method for synthesizing perovskite thin film with continuous gradient band gap by using thermal evaporation

Abstract

The invention discloses a method for synthesizing a perovskite thin film with a continuous gradient band gap through thermal evaporation. The device comprises a thermal evaporation vacuum chamber, a substrate table, an evaporation source, a thermal evaporation vacuumizing module and a vacuum displacement module, the perovskite thin film with the band gap continuously and gradually changed is synthesized at a time under high vacuum by utilizing thermal evaporation equipment and a vacuum displacement motor, so that the proportion of Br and Cl is continuously increased, the proportion of Br and I is continuously reduced and the band gap is continuously narrowed from left to right on the whole evaporated thin film from one end to the other end.

Description

Technical Field

[0001] The invention belongs to the field of thermal evaporation, and in particular relates to a method for synthesizing a band gap continuous gradient perovskite film by thermal evaporation. Background Art

[0002] Bandgap gradient perovskite materials have played a huge role in improving the efficiency of stacked silicon solar cells, designing tunable light-emitting diodes, wide-spectrum detectors and other optoelectronic fields due to their advantages such as higher photoelectric conversion efficiency, wider spectral absorption range and flexible optical regulation capabilities.

[0003] The band gap gradient of perovskite materials is mainly achieved by adjusting the ratio of halogen elements. Therefore, it can be prepared by repeatedly mixing solutions of halogen elements with different concentrations. However, this preparation method is cumbersome and cannot synthesize perovskite materials with continuously gradient band gaps in one go.

[0004] In recent years, in order to achieve the one-time synthesis of perovskite materials with continuous gradient band gap, scientists have proposed solid-gas exchange method, solid-liquid exchange method, gradient scraping method and droplet self-diffusion method. The solid-gas exchange method is to place the pre-prepared perovskite film in another halide gas, and use the different degrees of ion exchange between gas and solid film at different temperatures to achieve gradient, so the gradient controllability is poor, and the applicable material range is narrow, and it is not universal. The solid-liquid exchange method is to immerse the pre-prepared perovskite film in a halide solution, and then slowly pull out the film, and use the length of solid-liquid ion exchange to prepare a gradient film. Compared with the previous method, the controllability of the preparation is increased, but due to the presence of solvents in the solution, the performance of subsequent optoelectronic devices is often reduced. The gradient scraping method is to prepare a gradient film by continuously changing the ratio of halogen elements during the scraping process. Similarly, the solvent in the solution will affect the subsequent optoelectronic devices. The droplet self-diffusion method uses the self-diffusion and mutual diffusion between perovskite precursor droplets to prepare a gradient film at the interface, so the prepared film size is small and the gradient range is narrow.

[0005] In summary, due to the limitations of experimental methods and instruments and equipment, the currently proposed synthesis methods have problems such as narrow application range, poor controllability, and limited gradient range, and they cannot meet the needs of uniformity and large-scale compatibility with industrial production. Summary of the invention

[0006] In order to solve the problems in the prior art, the present invention proposes a device for synthesizing a bandgap continuous gradient perovskite film by thermal evaporation, comprising a thermal evaporation vacuum chamber, a substrate stage, an evaporation source, a thermal evaporation vacuum module and a vacuum displacement module;

[0007] The thermal evaporation vacuum chamber is used to provide a vacuum environment; the substrate stage is arranged at the top of the thermal evaporation vacuum chamber, and the substrate stage is used to fix the substrate; the evaporation source is arranged at the bottom of the thermal evaporation vacuum chamber, and the evaporation source is used to hold the precursor material; the thermal evaporation vacuum module is used to evacuate the thermal evaporation vacuum chamber; the vacuum displacement module is arranged in the thermal evaporation vacuum chamber, and the vacuum displacement module is used to shield the deposition of the evaporation material during the thermal evaporation process;

[0008] The vacuum displacement module includes a shielding mask plate, a support rod and a vacuum displacement motor; the shielding mask plate is fixedly connected to one end of the support rod, and the other end of the support rod is fixed to the vacuum displacement motor; during the thermal evaporation process, the thickness of the evaporation material deposition is adjusted by moving the vacuum displacement motor.

[0009] The present invention also provides a method for synthesizing a bandgap continuous gradient perovskite film based on the above device, comprising the following steps:

[0010] 1) Fix the substrate on the substrate table, and place sufficient amounts of PbBr powder, CsI powder, and CsCl powder in three evaporation sources respectively;

[0011] 2) evacuating the thermal evaporation vacuum chamber by means of a thermal evaporation vacuum module;

[0012] 3) rotating the substrate stage at a constant speed, and uniformly depositing PbBr on the substrate by thermal evaporation;

[0013] 4) After the PbBr deposition is completed, the substrate stage is stopped from rotating; CsI or CsCl is deposited by thermal evaporation, and at the same time, the vacuum displacement motor is started to drive the shielding mask plate to move, so that the thickness of the deposited CsCl or CsI is continuously and gradually changed;

[0014] 5) resetting the vacuum displacement motor (10), rotating the substrate stage 180°, depositing the remaining precursor material by thermal evaporation, and simultaneously starting the vacuum displacement motor to drive the shielding mask plate to move, thereby achieving a continuous and gradual thickness change of the deposited last precursor material;

[0015] 6) After the deposition of CsCl and CsI is completed, the substrate is taken out, and the taken out substrate is subjected to high temperature annealing to obtain a band gap continuous gradient perovskite film.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention introduces a vacuum displacement motor into a thermal evaporation chamber for the first time, laying the foundation for industrial large-scale coating.

[0018] The present invention realizes the one-time synthesis of a perovskite material with a continuously gradient band gap under high vacuum, and the prepared film realizes a continuous change in the band gap through a gradual thickness change; in a high vacuum environment, the overall film quality is ensured to be higher, the evaporated film is more uniform, the roughness is further reduced, and the absence of a solution also avoids the dissolution of crystals; the present invention has a more precise control over the film thickness and can achieve precise control at the nanometer level.

[0019] The band gap gradient range of the film prepared by the method of the present invention is wider, and all the variable band gaps of the perovskite material can be realized. In addition, the method is applicable to a wide range of materials and is also applicable to other materials, and has high versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 It is a schematic diagram of a device for synthesizing a band gap continuously gradient perovskite by thermal evaporation according to the present invention.

[0021] Attached Figure 2 This is a detailed diagram of the evaporation of a method for synthesizing a band gap continuous gradient perovskite film by thermal evaporation according to the present invention.

[0022] Attached Figure 3 This is a fluorescence range diagram of a perovskite film with a continuous gradient band gap synthesized by thermal evaporation according to the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described and illustrated below in conjunction with specific embodiments. The embodiments are merely exemplary of the present disclosure and do not define the scope of limitation. The technical features of each embodiment of the present invention may be combined accordingly without conflicting with each other.

[0024] The present invention proposes a brand-new method, which uses thermal evaporation equipment and vacuum displacement motors to achieve the one-time synthesis of perovskite materials with continuously gradient band gaps under high vacuum. Compared with the solution method, the film thickness prepared by the evaporation process is precisely controllable, smoother and flatter, and because no solvents such as DMF, methanol, chlorobenzene, etc. are required, the dissolution of the prepared crystals in the solution is avoided. At the same time, the band gap gradient range of the film is wider, and all the variable band gaps of the perovskite material can be realized. The method is applicable to a wide range of materials and is also applicable to other materials, with high versatility.

[0025] The preparation of perovskite films by vacuum thermal evaporation includes single-source evaporation, dual-source layer evaporation and dual-source co-evaporation. The single-source evaporation method is to use one evaporation source to mix the evaporation materials at the same time. For example, when preparing the all-inorganic perovskite CsPbX3 (X is a halogen element Cl, Br, I) film, the precursor materials CsX and PbX2 are placed in one evaporation source, and the two materials are deposited on the substrate at the same time. After high-temperature annealing, a high-quality perovskite film is generated. However, for precursor materials with large differences in melting and boiling points, the proportion will be imbalanced after evaporation, and large defects will often occur. The dual-source layer evaporation method is to deposit the film step by step. First, CsX (or PbX2) from one evaporation source is evaporated on the substrate, and then PbX2 (or CsX) from another evaporation source is evaporated. The same high-temperature annealing generates a high-quality film. The dual-source co-evaporation method is to simultaneously deposit CsX and PbX2 from two evaporation sources, and prepare perovskite films through in-situ reactions during deposition. The films prepared by this method have the highest quality, and some materials do not even require subsequent annealing processes. However, it has high requirements for equipment, such as dual evaporation sources, dual film thickness detection devices, etc. It is also necessary to strictly control the material ratio of the two precursors reaching the substrate, which reduces the controllability of the experiment.

[0026] like Figure 1 As shown, the device of the present invention includes a thermal evaporation vacuum chamber 3, a substrate stage 1, an evaporation source, a thermal evaporation vacuum module) and a vacuum displacement module;

[0027] The thermal evaporation vacuum chamber 3 is used to provide a vacuum environment; the substrate stage 1 is arranged at the top inside the thermal evaporation vacuum chamber), and the substrate stage 1 is used to fix the substrate; the evaporation source is arranged at the bottom inside the thermal evaporation vacuum chamber 3, and the evaporation source is used to hold the precursor material; the thermal evaporation vacuum module 9 is used to evacuate the thermal evaporation vacuum chamber 3; the vacuum displacement module is arranged in the thermal evaporation vacuum chamber 3, and the vacuum displacement module is used to shield the deposition of the evaporation material during the thermal evaporation process;

[0028] The vacuum displacement module includes a shielding mask plate 6, a support rod 7 and a vacuum displacement motor 10; the shielding mask plate 6 is fixedly connected to one end of the support rod 7, and the other end of the support rod 7 is fixed on the vacuum displacement motor 10; during the thermal evaporation process, the thickness of the evaporation material deposition is adjusted by moving the vacuum displacement motor 10.

[0029] The present invention improves the dual-source layer evaporation method and realizes the one-time preparation of a perovskite film with a continuous gradient band gap by combining a vacuum displacement motor. Taking the preparation of the all-inorganic perovskite CsPbX3 film as an example, the precursor materials are selected as PbCl2, CsCl, PbBr2, CsBr, PbI2, and CsI. Through the layer evaporation method, PbCl2 is first evaporated, and then CsCl is evaporated. After subsequent high-temperature annealing, the material obtained is CsPbCl3. The same method can be used to prepare CsPbBr3 and CsPbCl3.

[0030] Furthermore, when PbBr2 is first evaporated and then CsI with different thicknesses is evaporated multiple times, the ratio of halogen elements Br and I changes, and the prepared multiple CsPbBr (x) I (3-x) The film has different band gaps, and using ultraviolet laser pumping can produce different fluorescence from green to red. Similarly, when PbBr2 is first evaporated, and then CsCl with different thicknesses is evaporated multiple times, CsPbBr (x) Cl (3-x) Fluorescence varies from green to blue.

[0031] Furthermore, after pre-evaporating the first layer of PbBr2, when evaporating the second layer of CsCl (or CsI), the deposition rate is kept unchanged, and the mask plate almost attached to the substrate is moved at a constant speed. The mask plate is pulled by a vacuum displacement motor, and the deposited CsCl (or CsI) will have a continuously gradual thickness, that is, after subsequent high-temperature annealing, the ratio of Br and Cl (or I) changes continuously along the direction of motor movement. Therefore, a perovskite film with a continuously gradual band gap is synthesized in one step, and the film can achieve continuously gradual fluorescence on a single wafer.

[0032] Taking inorganic perovskite CsPbX3 as an example, the specific situation during evaporation is as shown in the attached Figure 1 As shown, firstly, a sufficient amount of PbBr powder is placed in the No. 1 evaporation source, and a sufficient amount of CsI or CsCl powder is placed in the No. 2 evaporation source (there will be three evaporation boats to place the precursor materials respectively during the actual evaporation), and then the pressure in the thermal evaporation vacuum chamber reaches 5e-4pa through the thermal evaporation vacuum system, and then the evaporation source power is turned on and the substrate stage is set to rotate at a constant speed, and PbBr is evenly deposited on the placed substrate. Then stop the rotation of the substrate stage, set the vacuum displacement motor installed in the vacuum chamber to drive the shielding mask plate to move at a constant speed, and at the same time, deposit CsI or CsCl at a constant speed, and deposit a second layer of film with a gradient thickness, that is, the ratio of Br and I (or Cl) is gradient along the direction of motor movement, and then take out the film and anneal it at high temperature to obtain a high-quality band gap continuous gradient perovskite film.

[0033] Details of the evaporated film are as follows Figure 2 As shown in the figure, the first deposition was a PbBr film with uniform thickness, the second deposition was assisted by a vacuum displacement motor to deposit a CsCl film with varying thickness, and the third deposition was to change the direction of the vacuum displacement motor to deposit a CsI film with varying thickness. Therefore, the ratio of Br to I increases from left to right, while the ratio of Br to Cl decreases, and the band gap widens continuously from left to right. After high-temperature annealing to promote ion exchange, the film fluorescence is characterized as shown in the attached figure. Figure 3However, the continuous gradient range of fluorescence can only cover about 440-630nm. Figure 2 By vapor-depositing PbI2 on the far left of the thin film structure, CsBr in the middle, and PbCl2 on the far right, continuous fluorescence covering 418-704nm can be achieved. The dotted lines in the figure represent the fluorescence corresponding to CsPbCl3, CsPbBr3, and CsPbI3, and the solid lines represent the fluorescence collected every 20nm on the prepared band gap continuous gradient perovskite film.

[0034] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A device for synthesizing a bandgap continuous gradient perovskite film by thermal evaporation, characterized in that: It comprises a thermal evaporation vacuum chamber (3), a substrate stage (1), an evaporation source, a thermal evaporation vacuum module (9) and a vacuum displacement module; The thermal evaporation vacuum chamber (3) is used to provide a vacuum environment; the substrate stage (1) is arranged at the top of the thermal evaporation vacuum chamber (3), and the substrate stage (1) is used to fix the substrate; the evaporation source is arranged at the bottom of the thermal evaporation vacuum chamber (3), and the evaporation source is used to hold the precursor material; the thermal evaporation vacuum pumping module (9) is used to evacuate the thermal evaporation vacuum chamber (3); the vacuum displacement module is arranged in the thermal evaporation vacuum chamber (3), and the vacuum displacement module is used to shield the evaporation material when it is deposited during the thermal evaporation process; The vacuum displacement module comprises a shielding mask plate (6), a support rod (7) and a vacuum displacement motor (10); the shielding mask plate (6) is fixedly connected to one end of the support rod (7), and the other end of the support rod (7) is fixed to the vacuum displacement motor (10); during the thermal evaporation process, the thickness of the evaporation material deposition is adjusted by moving the vacuum displacement motor (10).

2. A method for synthesizing a bandgap continuously gradient perovskite film based on the device of claim 1, characterized in that: The following steps are involved: 1) Fixing a substrate on a substrate stage (1), placing sufficient amounts of PbBr powder, CsI powder and CsCl powder in three evaporation sources respectively; 2) evacuating the thermal evaporation vacuum chamber (3) by means of a thermal evaporation vacuum module (9); 3) rotating the substrate stage (1) at a constant speed, and uniformly depositing PbBr on the substrate by thermal evaporation; 4) After the PbBr deposition is completed, the rotation of the substrate stage (1) is stopped; one of CsI or CsCl is deposited by thermal evaporation, and at the same time, the vacuum displacement motor (10) is started to drive the shielding mask plate to move, so that the thickness of the deposited CsCl or CsI is continuously and gradually changed; 5) resetting the vacuum displacement motor (10) and rotating the substrate stage (1) by 180 degrees, depositing the remaining precursor material by thermal evaporation, and simultaneously starting the vacuum displacement motor (10) to drive the shielding mask plate to move, so that the thickness of the last material deposited is continuously and gradually changed; 6) After the deposition of CsCl and CsI is completed, the substrate is taken out, and the taken out substrate is subjected to high temperature annealing to obtain a band gap continuous gradient perovskite film.

3. The method for synthesizing a bandgap continuously gradient perovskite film according to claim 1, characterized in that: After the thermal evaporation vacuum chamber (3) is evacuated by the thermal evaporation vacuum module (9) in step 2), the vacuum degree in the thermal evaporation vacuum chamber (3) is better than 5e -4 pa.

4. The method for synthesizing a bandgap continuously graded perovskite film according to claim 1, characterized in that: After the evaporation, the thickness of CsI gradually increases on one side of the substrate surface, and the thickness of CsCl gradually increases on the other side.

5. The method for synthesizing a bandgap continuously graded perovskite film according to claim 4, characterized in that: The band gap after evaporation is continuously gradient. The ratio of Br and Cl on the surface of the perovskite film decreases continuously from one side to the middle, and the ratio of Br and I decreases continuously from the other side to the middle, so the band gap will continuously narrow from one side to the other.

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