A preparation method of pure-phase RP perovskite thin film

Abstract

The present invention relates to a method for preparing a pure-phase RP perovskite thin film. After preparing a mixed solution of lead halide and organic ammonium halide salt, a low-pressure assisted treatment is used to treat the perovskite thin film precursor thin film deposited on a substrate to form a well-crystallized intermediate-phase thin film, and then a pure-phase RP perovskite thin film is formed by heating. The present invention has low cost and is compatible with large-area thin film preparation. The obtained perovskite thin film can be used in various optoelectronic devices such as solar cells, photodetectors, light-emitting diodes, and X-ray detectors, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of novel semiconductor optoelectronics, and particularly relates to a method for converting two-dimensional perovskites with different n values into pure-phase Ruddlesden-Popper (RP) perovskites by combining solvent engineering and additive engineering with low-pressure assisted treatment. The perovskite thin films prepared by this method can be used in various optoelectronic devices such as solar cells, photodetectors, light-emitting diodes, and X-ray detectors. Background Art

[0002] With the development of technology, the problems of environmental deterioration and energy crisis are becoming increasingly serious, which puts forward new requirements for human energy utilization. The development of the optoelectronic field brings new hope to mankind. In recent years, three-dimensional perovskite materials have been widely studied due to their excellent optoelectronic properties such as high light absorption coefficient, adjustable bandgap, and high carrier mobility. However, the problem of poor stability limits its further development in the optoelectronic field. As a new type of optoelectronic material, two-dimensional perovskites have received extensive attention due to their good stability and excellent optoelectronic properties. Studying the structure and properties of two-dimensional perovskite materials is of great significance for the development of perovskite optoelectronic devices with high stability and high optoelectronic conversion efficiency.

[0003] Currently, the certified optoelectronic conversion efficiency of organic-inorganic hybrid perovskite optoelectronic devices has reached 25.7%, which can be comparable to the efficiency of single-crystalline silicon cells. However, due to the intrinsic instability of the perovskite structure, it is easy to degrade under the influence of external environments such as water, oxygen, temperature, and light, affecting the practical application of perovskite optoelectronic devices. Two-dimensional perovskites have attracted much attention due to their excellent optoelectronic properties and good stability. Based on two-dimensional perovskites, combining solvent engineering and additive engineering to design and manufacture many optoelectronic devices such as solar cells, photodetectors, and LEDs is an inevitable choice for the development of two-dimensional perovskite technology. Compared with three-dimensional perovskites, the layered structure of two-dimensional perovskites relaxes the size requirements for organic cations, allowing large organic cations to insert into the inorganic layer. Therefore, many cations are available for selection, and specific properties and functions can be obtained by designing the composition. Two-dimensional perovskites have the characteristics of solution processability, flexibility, wearability, and low-cost and easy preparation of two-dimensional materials, as well as the characteristics of high crystallinity, high carrier mobility, low exciton binding energy, high quantum efficiency, wide absorption spectrum, high light absorption coefficient, and low energy consumption loss of perovskite materials, making them widely used in the field of solar photovoltaic power generation.

[0004] In recent years, although many encouraging progress has been made in the field of two-dimensional perovskite optoelectronics, it still faces a huge challenge of difficult to generate pure-phase perovskites. The general structural formula of two-dimensional perovskites represented by the RP phase is A 2 B n- 1 Pbn I 3n+1 When preparing two-dimensional perovskite films by solution method, although each component is calculated according to the stoichiometric ratio at a determined n value, the poor thermodynamic stability of the perovskite phase with a larger n value makes it difficult to form a pure-phase perovskite, that is, the prepared two-dimensional perovskite contains phases with different n values. The distribution of each n value in the perovskite affects the transport and recombination of carriers, seriously affecting the performance of the device. Therefore, it is particularly important to propose a method for preparing pure RP-phase perovskite films. Summary of the Invention

[0005] The purpose of the present invention is to propose a method for preparing a pure RP-phase perovskite film in view of the problem that it is difficult to form a pure phase of two-dimensional RP-phase perovskite at present. After preparing a mixed solution of lead halide and organic ammonium halide salt, a low-pressure auxiliary device is used to process the perovskite film precursor film deposited on the substrate to form a well-crystallized intermediate-phase film, and then a pure-phase RP perovskite film is formed by heating. The present invention has low cost and is compatible with large-area film preparation. The obtained perovskite film can be used in various optoelectronic devices such as solar cells, photodetectors, light-emitting diodes, and X-ray detectors, and has broad application prospects.

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

[0007] A method for preparing a pure-phase RP perovskite film, the method comprising the following steps:

[0008] Step 1: Dissolve lead iodide PbI 2 , organic ammonium iodide AI and formamidinium iodide FAI into a solvent, and then add an additive to obtain an RP-phase perovskite precursor solution;

[0009] Among them, the molar ratio is - lead iodide: organic ammonium iodide: formamidinium iodide: additive = 1: 0.1-1: 0.05-0.5: 0.1-1; the concentration of Pb 2+ in the precursor solution is 0.05-2 mol / L;

[0010] The additive is a chloride or a fluoride;

[0011] Step 2: Use a spin-coating device to coat the precursor solution on the substrate to obtain a perovskite film;

[0012] Among them, 10-100 μl of the precursor solution is coated on every 1-10 cm 2 substrate;

[0013] The rotation speed of the spin-coating device is 1500-8000 rmp, the rotation time is 5-30 s, the ambient temperature is 1-50 °C, and the ambient relative humidity is 30-90%;

[0014] Step 3: Use a low-pressure auxiliary device to perform low-pressure treatment on the perovskite film deposited on the substrate, and then anneal it through a constant-temperature heating device to obtain the RP-phase perovskite A 2 (FA)Pb 2 I 7 , that is, a pure-phase RP perovskite film;

[0015] The structural general formula of the RP-phase perovskite is A 2 (FA)Pb 2 I 7 , where A is an organic cation, and FA + is the formamidinium cation.

[0016] Among them, the vacuum degree during the treatment of the low-pressure auxiliary device is 1-100 Pa, and the treatment time is 1-60 s.

[0017] The annealing temperature is 50-200 °C, and the annealing time is 1-60 min.

[0018] In the iodinated organic ammonium salt AI, A is an organic cation which is dimethylamine ion (DMA + ), ethylamine ion (EA + ), mercaptoethylamine ion (ESA + ), ethanolamine ion (EOA + ), propylamine ion (PA + ), isopropylamine ion (iPA + ), cyclopropylamine ion (CyPA + ), butylamine ion (BA + ), isobutylamine ion (iBA + ), tert-butylamine ion (t-BA + ), pentylamine ion (PentA + ), phenylamine ion (PhA + ), methoxyphenethylamine ion (2-MeOPEA + ), trifluoroethylamine ion (F 3 EA + ), trifluoromethylaniline ion (CF 3 PhA + ), trifluoromethylbenzylamine ion (CF 3 PMA + ), trifluoromethylphenethylamine (CF 3 PEA + ), pyridine methylamine ion (PyA + ), 3-dimethylamino-1-propylamine ion (3-Me2PDA + ), diethylamine ion (DEA + ), benzylamine ion (PMA+ )), phenethylamine ion (PEA + )), p - fluorophenethylamine ion (p - F - PEA + )), m - fluorophenethylamine ion (m - F - PEA + )), o - fluorophenethylamine ion (o - F - PEA + )), phenylpropylamine ion (PPA + )), phenylbutylamine ion (PhBA + )), 4 - tert - butylaniline ion (tBPA + )), 4 - tert - butylbenzylamine ion (tBBA + ) or more than one of them.

[0019] The chloride additive described in Step 1 is at least one of ammonium chloride, methylammonium chloride, formamidine hydrochloride, ethylammonium chloride, propylammonium chloride, butylammonium chloride, and the fluoride is at least one of ammonium fluoride, lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride.

[0020] The solvent described includes at least one of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N - methylpyrrolidone (NMP), and dimethylacetamide (DMAc).

[0021] The substrate described in Step 2 is fluorine - doped SnO 2 Conductive glass (FTO), indium tin oxide transparent conductive film glass (ITO), PET / ITO (PET is polyethylene terephthalate), PEN / ITO (PEN is polyethylene naphthalate), or metal sheet.

[0022] The pure - phase RP perovskite thin film can be used in various optoelectronic devices such as photovoltaic devices (including indoor photovoltaic devices and semitransparent photovoltaic devices), photodetectors (photovoltaic type and photoconductive type), light - emitting diodes, and X - ray detectors.

[0023] The substantial features of the present invention are as follows:

[0024] In the current technology, pure - phase A 2 (FA)Pb 2 I 7 has not been reported. Through the adjustment of the precursor solution components and the control of the preparation conditions, the present invention adds a fluoride or a chloride as an additive to the precursor solution, and chloride ions or fluoride ions can induce the formation of [PbX 6 4- (X is Cl or F), [PbX 6 4- ​​The formation of three-dimensional perovskite can be inhibited; controlling the preparation conditions can also suppress the formation of the three-dimensional phase. Combining low-pressure assistance with annealing-assisted solvent method enables the uniform evaporation of the solvent during the crystallization process, resulting in dense large-sized grains, obtaining a two-dimensional perovskite film with good phase distribution and high crystallinity, and finally preparing a pure-phase A 2 (FA)Pb 2 I 7 film.

[0025] The beneficial effects of the present invention are as follows

[0026] 1. The preparation method of a pure-phase RP perovskite film provided by the present invention is simple, feasible, and low-cost, and can be applied to the preparation of large-area films;

[0027] 2. The method of the present invention can transform perovskite containing phases with different n values into pure-phase Ruddlesden-Popper (RP) perovskite by controlling the components and solvents of the perovskite precursor solution and adjusting the preparation condition parameters, and has broad application prospects in photovoltaic devices, photodetectors, light-emitting diodes, X-ray detectors, etc.

[0028] 3. The pure-phase RP perovskite film prepared by the method of the present invention has good environmental stability. At room temperature, after 30 days (see Figure 5 ), its crystal structure remains unchanged. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the preparation process of the perovskite film in Example 1 of the present invention.

[0030] Figure 2 It is the X-ray diffraction pattern of the perovskite film in Example 1.

[0031] Figure 3 It is the SEM image of the perovskite film in Example 1.

[0032] Figure 4 It is the ultraviolet-visible light absorption spectrum of the perovskite film in Example 1.

[0033] Figure 5 It is the X-ray diffraction pattern of the perovskite film in the initial state and after being placed for 30 days prepared in Example 1

[0034] Figure 6 It is the X-ray diffraction pattern of the perovskite film in Comparative Example 1.

[0035] Figure 7 It is the ultraviolet-visible absorption spectrum of the perovskite film in Comparative Example 1.

[0036] Figure 8 It is the X-ray diffraction pattern of the perovskite film in Comparative Example 2. Detailed implementation mode

[0037] The present invention will be further described below in conjunction with embodiments.

[0038] The preparation process of the perovskite thin film of the present invention is as Figure 1 shown. After preparing a mixed precursor solution of lead halide and organic ammonium halide salt, it is spin-coated onto a substrate, and then a low-pressure auxiliary device is used to process the perovskite thin film precursor film deposited on the substrate to form a well-crystallized intermediate phase film, and then a pure-phase RP perovskite thin film is formed by heating.

[0039] Example 1.

[0040] Pure RP-phase perovskite (PEA) 2 FAPb 2 I 7 Preparation of thin film

[0041] The preparation process is as Figure 1 shown, and includes the following steps:

[0042] Step 1: Dissolve 0.4610 g (1.0 mmol) of PbI 2 , 0.2490 g (1.0 mmol) of PEAI (C 6 H 5 CH 2 CH 2 NH 3 I), 0.0860 g (0.5 mmol) of FAI (HC(NH 2 ) 2 I) into 1 ml of a mixed solution of DMF and NMP, and add 0.0236 g (0.35 mmol) of methylammonium chloride (MACl) as an additive, where the volume ratio of DMF:NMP is 9:1, to prepare a perovskite precursor solution with a concentration of 1 mol / L.

[0043] Step 2: Use a spin-coating device (KW-4A desktop spin coater) to deposit the precursor solution on an ITO substrate (with an area of 4 cm 2 ). Among them, the rotation speed of the spin-coating device is 4000 rpm, the rotation time is 10 s, the volume of the perovskite precursor for each spin-coating is 50 μl, and the temperature is controlled at 22 °C and the humidity is controlled at 60% during the spin-coating process.

[0044] Step 3: Use low-pressure auxiliary equipment (DL-10A quartz vacuum gauge and vacuum pump) to perform low-pressure treatment on the perovskite film deposited on the substrate, and then perform annealing through a constant-temperature heating device (heating stage) to obtain a pure-phase RP perovskite film. The vacuum degree during the low-pressure auxiliary equipment treatment is 10 Pa, the low-pressure treatment time is 60 s, the annealing temperature of the heating stage is 100 °C, and the annealing time is 15 min. Perform X-ray diffraction analysis, SEM surface morphology analysis, and absorption spectrum analysis on the obtained perovskite film respectively. The results of X-ray diffraction are as Figure 2 shown. It can be seen from the figure that diffraction peaks of two-dimensional perovskite appear near 4°, 8°, 12°, 16°, etc. of the prepared film, all corresponding to the (0k0) crystal plane, proving the successful preparation of the pure-phase (PEA) 2 FAPb 2 I 7 film. The results of SEM are as Figure 3 shown. It can be seen from the figure that the prepared film exhibits a layered characteristic, indicating again that we have prepared a layered pure-phase (PEA) 2 FAPb 2 I 7 film. The results of the absorption spectrum are as Figure 4 shown. It can be seen from the figure that the prepared film has only one obvious absorption edge and one exciton absorption peak, proving again that the film we prepared only contains (PEA) 2 FAPb 2 I 7 this one phase. Place the prepared sample in the air, and use an X-ray diffractometer to perform a stability test on the film after 30 days. The test results are as Figure 5 shown. It can be seen from the figure that when the film we prepared is placed in the air for more than 30 days, the results of its X-ray diffraction are still the same as those of the initially prepared film, proving that the film we prepared has good stability.

[0045] Example 2.

[0046] Preparation of pure RP-phase perovskite (PMA) 2 FAPb 2 I 7 film

[0047] Different from Example 1, the solutes in the perovskite precursor are 0.461 g (1.0 mmol) of PbI 2 , 0.233 g (1.0 mmol) of PMAI (C 7 H 8 IN), 0.0860 g (0.5 mmol) of FAI (HC(NH 2 ) 2I) Dissolve it in a 1 ml mixed solution of DMF and NMP (DMF:NMP = 9:1), and add 0.0236 g (0.35 mmol) of methylammonium chloride (MACl) as an additive.

[0048] Example 3.

[0049] Pure RP-phase perovskite (BA) 2 FAPb 2 I 7 Preparation of thin film

[0050] Different from Example 1, the solute in the perovskite precursor is 0.4610 g (1.0 mmol) of PbI 2 , 0.201 g (1.0 mmol) of BAI(CH 3 CH 2 CH 2 NH 3 I), 0.0860 g (0.5 mmol) of FAI(HC(NH 2 ) 2 I) is dissolved in a 1 ml mixed solution of DMF and NMP (DMF:NMP = 9:1), and 0.0236 g (0.35 mmol) of methylammonium chloride (MACl) is added as an additive.

[0051] Example 4.

[0052] Pure RP-phase perovskite (PA) 2 FAPb 2 I 7 Preparation of thin film

[0053] Different from Example 1, the solute in the perovskite precursor is 0.4610 g (1.0 mmol) of PbI 2 , 0.187 g (1.0 mmol) of PAI(CH 3 CH 2 CH 2 NH 3 I), 0.0860 g (0.5 mmol) of FAI(HC(NH 2 ) 2 I) is dissolved in a 1 ml mixed solution of DMF and NMP (DMF:NMP = 9:1), and 0.0268 g (0.4 mmol) of methylammonium chloride (MACl) is added as an additive.

[0054] Example 5.

[0055] Pure RP-phase perovskite (tBBA) 2 FAPb 2 I7 Preparation of thin film

[0056] Different from Example 1, the solute in the perovskite precursor is 0.4610 g (1.0 mmol) of PbI 2 , 0.276 g (1.0 mmol) of tBBAI (4-tert-butylbenzylamine iodide), 0.0860 g (0.5 mmol) of FAI (HC(NH 2 ) 2 I) is dissolved in 1 ml of a mixed solution of DMF and NMP (DMF:NMP = 9:1), and 0.0268 g (0.4 mmol) of methylammonium chloride (MACl) is added as an additive.

[0057] Example 6.

[0058] Pure RP-phase perovskite (iBA) 2 FAPb 2 I 7 Preparation of thin film

[0059] Different from Example 1, the solute in the perovskite precursor is 0.4610 g (1.0 mmol) of PbI 2 , 0.201 g (1.0 mmol) of iBAI (CH(CH 3 ) 2 CH 2 NH 3 I), 0.0860 g (0.5 mmol) of FAI (HC(NH 2 ) 2 I) is dissolved in 1 ml of a mixed solution of DMF and NMP (DMF:NMP = 9:1), and 0.0268 g (0.4 mmol) of methylammonium chloride (MACl) is added as an additive.

[0060] Comparative Example 1.

[0061] RP-phase perovskite (PEA) 2 FAPb 2 I 7 Preparation of thin film

[0062] Different from Example 1, the solute in the perovskite precursor is 0.461 g (1.0 mmol) of PbI 2 , 0.2490 g (1.0 mmol) of PEAI (C 6 H 5 CH 2 CH 2 NH 3 I), 0.0860 g (0.5 mmol) of FAI (HC(NH 2 )2 I) It is dissolved in a 1 ml mixed solution of DMF and NMP (DMF:NMP = 9:1), and no additives are added.

[0063] Comparative Example 2.

[0064] RP phase perovskite (PEA) 2 FAPb 2 I 7 Preparation of thin film

[0065] Different from Comparative Example 1, a spin coating device (KW-4A desktop spin coater) is used to deposit the precursor solution on the ITO substrate (with an area of 4 cm 2 ). Among them, the rotation speed of the spin coating device is 4000 rpm, the rotation time is 10 s, the volume of the perovskite precursor for each spin coating is 50 μl, the temperature is controlled at 22 °C during the spin coating process, and the humidity is controlled at 20%.

[0066] The XRD results of Comparative Example 1 are as Figure 6 shown. It can be seen from the figure that diffraction peaks of two-dimensional perovskite appear near 4°, 8°, 12°, 16°, etc. of the prepared thin film, all corresponding to the (0k0) crystal plane, but the diffraction peaks are wide. Diffraction peaks of one-dimensional perovskite appear near 5.5°, 11°, 16.5°, 22°, corresponding to the (00k) crystal plane, and a diffraction peak of three-dimensional perovskite appears near 14°. The XRD results indicate that the obtained perovskite thin film has small grains, poor crystallinity, and low phase purity; the results of the absorption spectrum are as Figure 7 shown. It can be seen from the figure that the prepared thin film contains multiple absorption peaks, corresponding to the multi-phase structure of the thin film, indicating that the phase purity of the prepared thin film is relatively low. The XRD results of Comparative Example 2 are as Figure 8 shown. It can be known from the figure that when the environmental relative humidity is relatively small, significant diffraction peaks of one-dimensional and three-dimensional perovskite appear. After increasing the environmental relative humidity, the intensity of the one-dimensional perovskite diffraction peak decreases, and the intensity of the two-dimensional diffraction peak increases, indicating that increasing the environmental humidity has the effect of inhibiting the formation of one-dimensional and three-dimensional perovskite phases and is beneficial to improving the phase purity of two-dimensional perovskite thin films.

[0067] It can be seen from this that the present invention adjusts the composition of the precursor solution and controls the preparation conditions, adjusts the solvent ratio to form a solvent compound with PbI 2 to slow down the crystallization rate of perovskite; MACl is added as an additive to the precursor solution, and chloride ions will compete with iodide ions for the coordination sites of Pb 2+ to induce the formation of [PbCl 6 4- [PbCl 6 4- ​​The formation of three-dimensional perovskite can be inhibited; controlling the preparation conditions to increase the relative humidity of the environment can also inhibit the formation of the three-dimensional perovskite phase and further improve the phase purity of the film; combining low-pressure assistance with annealing-assisted solvent method to control the annealing temperature and time can enable the uniform evaporation of the solvent during the crystallization process, generating dense large-sized grains, and finally a pure-phase A 2 (FA)Pb 2 I 7 film is prepared. The film added with MACl has good crystallinity and excellent stability at the same time. The pure-phase perovskite film obtained by the present invention can be widely applied to various optoelectronic devices such as photodetectors (photovoltaic type and photoconductive type), light-emitting diodes, and X-ray detectors, improving the stability and other optoelectronic properties of the devices.

[0068] In summary, the preparation method of a pure-phase RP perovskite film proposed by the present invention is not only simple and easy to implement, low in cost, and can be mass-produced; at the same time, high-quality and excellent-performance electronic devices are obtained. The pure-phase RP perovskite film can be used in various optoelectronic devices (including indoor photovoltaic devices and semi-transparent photovoltaic devices), photodetectors (photovoltaic type and photoconductive type), light-emitting diodes, and X-ray detectors, etc., providing an effective method for realizing the large-scale industrial production of high-performance perovskite optoelectronic devices.

[0069] Matters not covered by the present invention are well-known technologies.

Claims

1. A method for preparing a pure-phase RP perovskite thin film, characterized in that, the method comprises the following steps: Step 1: Dissolve lead iodide PbI 2 , organic ammonium iodide AI and formamidinium iodide FAI in a solvent, and then add an additive to obtain an RP-phase perovskite precursor solution; Among them, the molar ratio is lead iodide: organic ammonium iodide: formamidinium iodide: additive = 1: 0.1 to 1: 0.05 to 0.5: 0.1 to 1; the concentration of Pb 2+ in the precursor solution is 0.05 to 2 mol / L; the additive is methylammonium chloride; Step 2: Using a spin coating device, coat a precursor solution on a substrate to obtain a perovskite thin film; Among them, every 1 to 10 cm 2 The substrate is coated with 10 to 100 μl of the precursor solution; Step 3: Use a low-pressure auxiliary device to perform low-pressure treatment on the perovskite film deposited on the substrate, and then perform annealing through a constant-temperature heating device to obtain the RP-phase perovskite A 2 (FA)Pb 2 I 7 , that is, a pure-phase RP perovskite film; The general structural formula of the RP-phase perovskite is A 2 (FA)Pb 2 I 7 , where A is an organic cation and FA + is the formamidinium cation; wherein, the vacuum degree during the treatment of the low-pressure auxiliary device is 10 Pa, and the treatment time is 60 s; the annealing temperature is 100 °C, and the annealing time is 15 min; in the iodinated organic ammonium salt AI, A is one or more of dimethylamine ion, ethylamine ion, mercaptoethylamine ion, ethanolamine ion, propylamine ion, isopropylamine ion, cyclopropylamine ion, butylamine ion, isobutylamine ion, tert-butylamine ion, pentylamine ion, phenylamine ion, methoxyphenethylamine ion, trifluoroethylamine ion, trifluoromethylaniline ion, trifluoromethylbenzylamine ion, trifluoromethylphenethylamine, pyridinemethylamine ion, 3-dimethylamino-1-propylamine ion, diethylamine ion, benzylamine ion, phenethylamine ion, p-fluorophenethylamine ion, m-fluorophenethylamine ion, o-fluorophenethylamine ion, phenylpropylamine ion, phenylbutylamine ion, 4-tert-butylaniline ion, 4-tert-butylbenzylamine ion; the solvents are DMF and NMP; the volume ratio of DMF:NMP is 9:1; The substrate described in Step 2 is SnO doped with fluorine 2 Conductive glass, indium tin oxide transparent conductive film glass, PET / ITO, PEN / ITO or metal sheet; the rotation speed of the spin coating device is 1500~8000 rmp, the rotation time is 5~30 s, the ambient temperature is 20 °C, and the ambient relative humidity is 60%.

2. The application of the pure-phase RP perovskite thin film prepared by the method according to claim 1, characterized in that, it is used for photovoltaic devices, light-emitting diodes or X-ray detectors; the photovoltaic device is an indoor photovoltaic device or a semi-transparent photovoltaic device.

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