A prediction method for A-site ion doping modification in ABX3-type perovskites

Abstract

The present invention relates to a theoretical prediction method for the doping modification of A-site ions in ABX3-type perovskites. The method comprises: analyzing the stability of the crystal structure of a pure ABX3-type perovskite unit cell; designing the partial substitution ratio of the A-site cation; optimizing ABX3-type perovskites with different doping ratios and doping sites to obtain the lowest-energy doping site configuration; determining the stability of the lowest-energy configuration of the ABX3-type perovskite at each doping ratio; analyzing the effect of changes in unit cell parameters on the electronic structure after doping modification of the A-site cation in the ABX3-type perovskite; and calculating and analyzing the optical properties of perovskite materials with a specific doping composition and doping configuration to screen for materials with superior performance. The present invention can effectively predict the structure and performance of ABX3-type perovskites after A-site ion doping modification.

Description

Technical Field

[0001] The present invention relates to the field of solar cell materials, and in particular to a method for predicting A-site ion doping modification in ABX3-type perovskite. Background Art

[0002] As energy and environmental issues become increasingly urgent, the research and development of new high-efficiency, environmentally friendly and low-cost solar cell materials has been extremely active since the new century. + , CH(NH2)2 + , Cs + etc., B=Pb 2+ , Sn 2 + etc., X=Cl - ,Br-,I - These materials, known as organic-inorganic hybrid perovskites, have attracted considerable attention from photovoltaic researchers due to their high conversion rates, low manufacturing costs, and the ability to fabricate flexible structures. In recent years, organic-inorganic hybrid perovskites have emerged as the most promising photovoltaic materials due to their exceptional electrical and optical properties, including high light absorption coefficients, ideal band gaps, long carrier diffusion lengths, low trap densities, and small exciton binding energies.

[0003] Since the first use of perovskites as light absorbers in dye-sensitized solar cells in 2009, power conversion efficiency (PCE) has increased from 3.8% to 25.7%. In recent years, advanced performance has expanded their applications to light-emitting diodes, lasers, and sensors. ABX3-type perovskites generally have poor tolerance to heat and humidity, leading to degradation during manufacturing and device operation. This makes it difficult to provide superior stability and extended carrier lifetimes. All inorganic Cs-based perovskites are difficult to prepare into uniform polycrystalline thin films, resulting in low current efficiency. Their wide band gap further limits their applications. To simultaneously improve material stability and access a wider range of the solar spectrum, blending two or more monovalent cations shows great potential to combine the advantages of all ABX3-type perovskites into a single material. Summary of the Invention

[0004] The purpose of the present invention is to provide a prediction method for A-site ion doping modification in ABX3-type perovskite. Combined with first-principles density functional theory, the A-site cation-doped compounds are studied from the aspects of energy, thermodynamic stability, and photoelectric properties, the component-structure-property relationship is explored, the regulation rules of their comprehensive performance are summarized, and solar cell materials with application prospects are screened out.

[0005] To achieve the above object, the technical solution of the present invention is: a method for predicting the doping modification of A-site ions in ABX3-type perovskite, characterized by comprising the following steps:

[0006] Step S1: using a first-principles calculation method based on density functional theory to calculate the crystallographic structure parameters of a pure ABX3 perovskite unit cell, and analyzing the stability of its crystal structure based on a tolerance factor;

[0007] Step S2: Design a series of substitution ratios for partial substitution doping of the A-site cations, and then construct a supercell based on available computing resources (computing power), setting the substitution configuration according to the size of the doping ratio;

[0008] Step S3: Design different doping ratios of the same substituting cations. For each doping ratio, further design different doping substitution sites to explore whether the doped particles may exist in a near-neighbor aggregation or far from a uniform state. Perform first-principles total energy calculations for various doping configurations, and simultaneously obtain the ABX3 perovskite crystal structure (lattice constant, bond length, etc.) for various doping ratios. Compare the total energy values ​​of the system under various doping site configurations to obtain the doping site configuration with the lowest energy.

[0009] Step S4, calculating the tolerance factor of the lowest energy configuration of the ABX3 type perovskite at each doping ratio, and further determining its stability based on the tolerance factor and defect formation energy;

[0010] Step S5, calculating and analyzing the electronic structure of the lowest energy configuration of ABX3 type perovskite with various doping ratios, including energy band and band gap values, state density, effective mass and charge density, and analyzing the effect of changes in unit cell parameters on the electronic structure;

[0011] Step S6: using a first-principles calculation method based on density functional theory to calculate and analyze the optical properties of a certain doping component and doping configuration perovskite material, thereby obtaining the real and imaginary matrix of the dielectric function, as well as the light absorption spectrum, reflection spectrum, refraction spectrum, and extinction spectrum;

[0012] Step S7: Summarize and summarize the modification rules of the structure and performance of ABX3-type perovskite by A-site cation doping, and screen materials with excellent performance.

[0013] Compared with the existing technology, the present invention has the following beneficial effects: the present invention combines the first-principles density functional theory to study the A-site cation-doped ABX3-type perovskite from the aspects of energy, thermodynamic stability, photoelectric properties, etc., explores the component-structure-property relationship, and summarizes the regulation rules of its comprehensive performance, which is conducive to the further design and synthesis of more efficient organic-inorganic perovskite solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of the method of the present invention.

[0015] Figure 2 Schematic diagram of the crystal structure of a single-cell FAPbI3 and a 2×2×2 supercell FAPbI3 in one embodiment of the present invention; (a) is a single-cell FAPbI3; (b) is a 2×2×2 supercell FAPbI3.

[0016] Figure 3 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the optimized crystal structure of PbI3 (0.125≤x≤0.875) doped compound; X increases from left to right and from top to bottom.

[0017] Figure 4-11 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the energy band of PbI3 (0≤x≤0.875) doped compounds.

[0018] Figure 12-19 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the electronic density of states of PbI3 (0≤x≤0.875) doped compounds.

[0019] Figure 20 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the effective carrier mass of PbI3 (0≤x≤0.875) doped compounds.

[0020] Figure 21 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the valence band top charge density of PbI3 (0≤x≤0.875) doped compounds; X increases from left to right and from top to bottom.

[0021] Figure 22-25 In one embodiment of the present invention, FA 1-X Cs x Schematic diagram of the light absorption spectrum, refraction spectrum, reflection spectrum, and extinction spectrum of PbI3 (0≤x≤0.875) doped compounds. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the present invention is a prediction method for A-site ion doping modification in ABX3 type perovskite, comprising the following steps:

[0024] Step S1, analyzing the crystal structure of a pure ABX3 perovskite unit cell based on first-principles density functional theory, and analyzing the stability of the crystal structure based on a tolerance factor;

[0025] Step S2: designing the substitution ratio of the A-site cation partial substitution doping, and then expanding the ABX3 perovskite unit cell according to the doping ratio, and then designing the configuration and doping;

[0026] Step S3, respectively optimize the ABX3 type perovskites with different doping ratios and the same ratio but different doping sites, explore whether the doped particles may exist in a neighboring aggregation or far away from the uniform state (the purpose is to obtain the doping configuration with the lowest total energy of the system after substitutional doping), perform first-principles total energy calculations of various doping configurations, and obtain the ABX3 type perovskite crystal structure (lattice constant, bond length, etc.) of various doping ratios at the same time, compare the total energy values ​​of the system under various doping point configurations, and obtain the doping point configuration with the lowest energy.

[0027] Step S4, calculating the tolerance factor of the lowest energy configuration of the ABX3 type perovskite at each doping ratio, and further determining its stability based on the tolerance factor and the doping formation energy;

[0028] Step S5, calculating the electronic structure (energy band and band gap, density of states, effective mass, charge density) of ABX3 type perovskites with various doping ratios, and analyzing the influence of changes in unit cell parameters on the electronic structure after cation doping modification at the A site of ABX3 type perovskites;

[0029] Step S6: using a first-principles calculation method based on density functional theory to calculate and analyze the optical properties of a certain doping component and doping configuration perovskite material, thereby obtaining the real and imaginary matrix of the dielectric function, the light absorption spectrum, the reflection spectrum, the refraction spectrum, and the extinction spectrum;

[0030] Step S7: Summarize the modification patterns of the A-site cation doping modification on the structure and performance of the ABX3 perovskite. Select materials with superior performance. The present invention effectively predicts the structure and performance of ABX3 perovskites after A-site cation doping modification, thereby optimizing the design of ABX3 perovskite solar cell materials.

[0031] The following is a specific embodiment of the present invention.

[0032] In this example, the cubic phase FAPbI3(FA=CH(NH2)2 +), with an ideal 1.45 eV bandgap, moderate stability, and a long carrier lifetime, and a room temperature tolerance factor greater than 1, making it an ideal perovskite phase. However, the cubic phase FAPbI3 readily transforms into a non-perovskite hexagonal phase with a larger bandgap at room temperature. At this point, its tolerance factor exceeds 1, significantly reducing its application value. Most Cs-based perovskites struggle to form the ideal cubic perovskite phase at room temperature due to their small tolerance factors. Furthermore, their wide bandgap further limits their application in photovoltaic solar cells. Using smaller Cs cations to dope larger FA cations can improve material stability and capture a wider range of the solar spectrum, demonstrating significant potential for combining the advantages of different materials. Therefore, first-principles calculations are highly valuable for predicting the potential of A-site Cs cation-doped FAPbI3 for modification.

[0033] In this embodiment, step S1 is specifically as follows: the ABX3 type perovskite is a cubic phase FAPbI3 unit cell with a space group of Pm-3m, FA organic cations are located in the central interstitial position, Pb ions are located at the vertices of the cubic unit cell, and 6 halogen ions form a coordinated octahedron around the Pb ions. To ensure contrast with the doped compound, the FAPbI3 unit cell is expanded to 2×2×2, and the crystal structure is as follows: Figure 2 As shown, self-consistent calculations were performed in the form of DFT+D3 to optimize the crystal structure. The optimized lattice constants The volume is The tolerance factor t>1, it is unstable at room temperature and easily transforms into a wide-bandgap non-perovskite phase.

[0034] In this embodiment, the step S2 is specifically as follows: using inorganic Cs cations to dope FAPbI3, firstly expanding the FAPbI3 unit cell into 2×2×2 cells, and then doping to form FA 1-X Cs x PbI3 (0.125≤x≤0.875) doped compound, the structure of the system when the Cs:FA ratio during the doping process is 1:7, 1:3, 3:5, 1:1, 5:3, 3:1, 7:1.

[0035] In this embodiment, the step S3 is specifically as follows: during the optimization process, the structure of the system is optimized when the Cs:FA ratio is 1:7, 1:3, 3:5, 1:1, 5:3, 3:1, and 7:1. The latter ratio is based on the relative arrangement of organic molecules corresponding to the lowest energy of the former ratio. The ratio is further changed, various arrangement optimization structures are considered, and then the lowest energy organic molecular arrangement is obtained. A step-by-step optimization strategy is adopted to sequentially perform the optimization steps of ion optimization, unit cell optimization, and global optimization. The INCAR parameter ISIF is set to 2, 6, and 3 respectively. The optimized crystal structure is as follows Figure 3As shown in the figure, the Cs cation doping ratio gradually increases from left to right. The defect formation energy and tolerance factor are shown in Table 1. It can be seen that the tolerance factor decreases with increasing Cs cation doping ratio. The formation energy of all seven doping systems is less than 0, indicating that they are thermodynamically stable.

[0036] In this embodiment, the steps S3 and S4 are specifically as follows: 1-X The optimized structure of CsxPbI3(0.125≤x≤0.875) doped compound is as follows Figure 3 The lattice parameter changes and stability are shown in Table 1.

[0037] Table 1FA 1-X Lattice constant and stability of optimized CsxPbI3(0≤x≤0.875) doped compounds

[0038]

[0039]

[0040] In this embodiment, the step S5 is specifically as follows: when calculating the energy band, the Monkhorst-Pack method is used to automatically generate a calculation file (KPOINTS), wherein the K point path is Γ-ZURTZ|XU|YT|SR, FA 1-X Cs x The energy bands of PbI3 (0≤x≤0.875) doped compounds are as follows Figure 4-11 As shown in the figure, from top to bottom, the Cs cation doping ratio X increases successively. It can be seen from the figure that the doped compounds are all direct bandgap semiconductors, and the bottom of the conduction band and the top of the valence band are both located at the Γ high symmetry point. When the Cs doping ratio is 0≤x≤0.375, the bandgap increases from 1.43eV to 1.54eV, when 0.375≤x≤0.75, the bandgap decreases from 1.54eV to 1.38eV, and when 0.75≤x≤0.875, the bandgap increases from 1.38eV to 1.60eV. The electronic state density of the doped compound is shown in the figure. Figure 12-19 As shown, the corresponding relationship refers to Figure 4-11 It can be seen that the bottom of the conduction band is mainly contributed by the Pb-6p and I-5p orbitals, the top of the valence band is mainly contributed by the I-5p and Pb-6s orbitals, and the A-position cations basically do not contribute to the orbitals. The effective mass of the carriers of the doped compound is as follows Figure 20 As shown, the path is along the Γ-Y ​​direction. It can be seen from the figure that when the doping ratio x = 0.125, the effective mass of the hole is the lowest 0.172m0, when the doping ratio x = 0.375, the effective mass of the conduction band bottom is the lowest 0.43m0, and the charge density at the top of the valence band is as follows Figure 21As shown, the doping ratio of Cs cations increases from 0 to 0.875 from left to right. Figure 21 It can be seen that the charge density is mainly distributed around the Pb ions and I ions, especially around the I atoms in the horizontal direction, where a large amount of charge is distributed, and there is almost no charge distribution around the A-site ions.

[0041] Combining Table 1 and the energy band diagram, it can be seen that the Pb-I bond length gradually decreases with the increase of the Cs doping ratio. The reason is that the Cs ion radius is smaller than the FA ion radius, so doping will cause the unit cell to shrink and the Pb-I octahedron to distort, which in turn leads to a decrease in the Pb-I bond length. The distortion of the Pb-I octahedron will reduce the bond angle, thereby reducing orbital overlap. The reduction of the Pb-I bond length will increase orbital overlap, and the two compete with each other. The conduction band bottom is primarily composed of π antibonding orbitals formed by hybridization of the Pb-6p and I-5p orbitals. A decrease in the Pb-I bond length increases the overlap of the Pb-I antibonding orbitals, leading to an unstable increase in the conduction band bottom energy. Therefore, when 0.125 ≤ x ≤ 0.375, the band gap shows an increasing trend. When 0.375 ≤ x ≤ 0.75, the reduced bond angle caused by octahedral distortion has a greater impact on orbital overlap than the reduced Pb-I bond length. Consequently, the overlap of the Pb-6p and I-5p orbitals decreases, reducing the energy of the conduction band bottom and, consequently, the band gap. When x ≥ 0.75, due to excessive octahedral distortion, the doped compound gradually deviates from the perovskite phase, resulting in a sudden increase in the band gap. Observation of the charge density distribution at the top of the valence band reveals that the charge distribution perpendicular to the I ion increases with increasing Cs ion doping, indicating that Cs ion doping favors an increase in the charge distribution at the top of the valence band.

[0042] In this embodiment, step S6 specifically includes: modifying the INCAR optical calculation parameters from the output file obtained by static calculation to obtain the real and imaginary matrices of the dielectric function, extracting optical data using VASPKIT, and importing the extracted ABSORPTION.dat, REFRACTIVE.dat, REFLECTIVITY.dat, and EXTINCTION.dat files into Origin for plotting and integration to obtain the absorption spectrum, reflection spectrum, refraction spectrum, and extinction spectrum, as shown in Figure 2. Figure 22 As shown in the optical absorption spectrum, compared with pure phase FAPbI3, the doping of Cs cations will cause the absorption curve to red-shift and increase the absorption of visible light. The rest of the optical properties are shown in Figure 23-25 .

[0043] In this embodiment, the step S7 is specifically as follows: the doping of the FAPbI3A site cation by Cs cations will cause the unit cell to shrink, the bond length of the Pb-I bond to decrease, the Pb-I octahedron to distort, and the bond angle to decrease. When the doping ratio of the Cs cation is 0.125≤x≤0.375, the doping compound FA 1-X Csx The band gap of PbI3 shows an increasing trend. When the doping ratio of Cs cation is 0.375≤x≤0.75, the doped compound FA 1-X Cs x The band gap of PbI3 shows a decreasing trend. When the doping ratio of Cs cations x ≥ 0.75, the band gap will experience another sudden increase. The electron state density diagram shows that the bottom of the conduction band is mainly contributed by the Pb-6p and I-5p orbitals, and the top of the valence band is mainly contributed by the I-5p and Pb-6s orbitals. The A-site cations contribute very little, and the Cs cations belong to the A-site doping, so naturally they don’t contribute much to the energy band. The charge density diagram at the top of the valence band shows that Cs cation doping will significantly increase the charge distribution of I ions in the vertical direction, which is beneficial to the separation of photogenerated electron-hole pairs, accelerates charge transfer, and may have better photovoltaic performance. Analysis of the optical absorption spectrum shows that the doping of Cs cations will cause the absorption curve to generally red-shift, FA 0.875 Cs 0.125 The red shift of PbI3-doped compounds is the largest, with an absorption peak at around 470nm, and when the doping ratio of Cs cations is 0.125≤x≤0.375, the absorption curve gradually blue-shifts as x increases. 0.875 Cs 0.125 PbI3-doped compounds have the strongest light absorption ability and should be an excellent light-absorbing material.

[0044] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A method for predicting the doping modification of A-site ions in ABX3-type perovskites, characterized in that: The steps include: Step S1: using a first-principles calculation method based on density functional theory to calculate the crystallographic structure parameters of a pure ABX3 perovskite unit cell, and analyzing the stability of its crystal structure based on a tolerance factor; Step S2: designing a series of substitution ratios for partial substitution doping of the A-site cations, and then constructing a supercell based on available computing resources, setting the substitution configuration according to the size of the doping ratio; Step S3: Design different doping ratios of the same substituting cations. For each doping ratio, design different doping substitution sites, explore whether the doped particles exist in a near-neighbor aggregation or far from a uniform state, perform first-principles total energy calculations for various doping configurations, and simultaneously obtain ABX3-type perovskite crystal structures with various doping ratios. Compare the total energy values ​​of the system under various doping site configurations to obtain the doping site configuration with the lowest energy; Step S31: After the supercell is constructed, the number of cation sites at position A is N. A The number of cation sites substituted at position A in the supercell is N d When designing the cation doping substitution configuration at site A, one of the atoms is selected as a fixed substitution position, that is, as the reference origin. Using the combination method, the number M of doping substitution site configurations is obtained as: Optimize ions, optimize unit cells, and optimize the distribution of ABX3 perovskite substitution doping compounds; Step S32: according to the optimization result of the A-site cation doping compound, obtain the change of its lattice constant, compare the total energy value of the system under various doping site configurations, and obtain the doping site configuration with the lowest energy; Step S4, calculating the tolerance factor of the lowest energy configuration of the ABX3 type perovskite with each doping ratio, and determining its stability based on the tolerance factor and defect formation energy; To determine the stability of the doping compound, the tolerance factor and defect formation energy are used to determine its stability. The tolerance factor t is calculated as follows: Among them, r A is the radius of the A-site cation, r B is the radius of the B-site cation, r X is the radius of the C-site anion. To calculate the tolerance factor of the A-site cation-doped compound, the weighted average of the atomic ratios of different cations is introduced as the estimated effective cation size. Defect formation energy E f =E doped -E pure -∑ i n i μ i (Formula 3) Among them, E doped 、E pure They represent the formation energy of the doping compound and the ABX3 type perovskite prototype respectively. The third term on the right side of the equal sign represents the energy change caused by the change of composition. Based on the prototype FAPbI3, for the doping atom, n i >0; for the replaced atom, n i <0;μ i Represents the chemical potential energy of the corresponding atomic bulk state; Step S5, calculating and analyzing the electronic structure of the lowest energy configuration of ABX3 type perovskite with various doping ratios, including energy band and band gap values, state density, effective mass and charge density, and analyzing the effect of changes in unit cell parameters on the electronic structure; Step S6: Calculate and analyze the optical properties of a certain doping component and doping configuration perovskite material using a first-principles calculation method based on density functional theory to obtain the real and imaginary matrix of the dielectric function, as well as the light absorption spectrum, reflection spectrum, refraction spectrum, and extinction spectrum; Step S7: Summarize and summarize the modification rules of the structure and performance of ABX3-type perovskite by A-site cation doping, and screen materials with excellent performance.

2. The method for predicting A-site ion doping modification in ABX3 type perovskite according to claim 1, characterized in that: In step S1, the first-principles calculation method of density functional theory is adopted, and the VASP software package is used to perform PBE functional calculation to analyze the crystallographic structural stability of the ABX3 type perovskite unit cell.

3. The method for predicting A-site ion doping modification in ABX3 type perovskite according to claim 1, characterized in that: There are organic ions in the ABX3 type perovskite, and an empirical dispersion correction method DFT+D3 is introduced.

4. The method for predicting A-site ion doping modification in ABX3 type perovskite according to claim 1, characterized in that: Step S5 is specifically as follows: Step S51, calculating the electronic structure of the A-site cation-doped compound, including energy bands, band gap values, state density, partial-wave state density, partial charge density, and effective carrier mass, analyzing and determining the main electron orbital contributions to the conduction band bottom and valence band top, as well as the charge distribution at the valence band top; Step S52: analyzing the influence of the change in unit cell parameters on the electronic structure after partial doping of the A-site cations in the ABX3 type perovskite.

5. The method for predicting A-site ion doping modification in ABX3 type perovskite according to claim 1, characterized in that: Step S6 specifically comprises: using a first-principles calculation method based on density functional theory to calculate and analyze the optical properties of a certain doping component and doping configuration perovskite material to obtain light absorption spectrum, reflection spectrum, refraction spectrum and extinction spectrum; the calculation formulas are: Absorption coefficient α(λ): Refractive index n(λ): Reflection coefficient R(λ): Extinction coefficient κ(λ): ε1(λ) represents the real part of the dielectric function, ε2(λ) represents the imaginary part of the dielectric function, and λ is the wavelength.

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